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8122019 hspa_e_lp
httpslidepdfcomreaderfullhspaelp 130
HS-PDSCH High speed physical downlink shared channel
29
21 HS-PDSCH High speed physical downlink shared channel
This channel transports the physical downlink traffic to the UEs anduses a shared concept ie there can be several UEs receiving data on
the common used channel Fig 2-3 below outlines the structure of the
HS-PDSCH
J Spreading factor 16J Assignment of multiple channelization codes to one UE possible
Slot 0
Slot 1
Slot 2
Tslot
= 2560 chips
HS-DSCHtransport channelwith user data
1 subframe of 3 slots 2 ms
HS-PDSCHphysical channel
320 bits for QPSK 640 bits for 16QAM
Fig 2-3 HS-PDSCH structure
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The HS-PDSCH always uses a spreading factor of 16 Due to its shared
channel structure the WCDMA Rel-99 concept of a variable spreading
factor must be discontinued Multiple channelization code allocation is
possible to increase the throughput Using a spreading factor of 16 rep-
resents an optimization of the efficiency Recalling the effect of code
blocking in WCDMA with the CPICH and P-CCPCH always blockingthe codes CchSF0 it is clear that the definition of a constant spreading
factor of 16 represents a good compromise between reduced signaling
effort (ie if a spreading factor gt16 were used the higher layer proto-
cols would require more signaling overhead to indicate the amount of
multiple codes) and the total available physical resources (ie if a
spreading factor lt16 were used the code blocking effect would reduce
the remaining capacity within a cell) A side effect is that the spreading
factor itself is not signaled to the UE and only the number of codes iscontained in the control information The physical channel HS-PDSCH
carries a transport block that is delivered by the transport channel
HS-DSCH within a TTI of 2 ms This time is also constant and no flex-
ibility is allowed The flexible values on the HS-PDSCH are the modu-
lation scheme (QPSK or 16QAM) and the transport block size ie the
amount of data bits contained in one HS-DSCH transport block This
is set by the puncturing scheme and indicated as the redundancy ver-
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30
HSDPA operation overview and physical channels
sion Additionally the redundancy version can be changed meaning
the puncturing procedure can be executed in different ways If the UE
category allows HS-DSCH transport blocks can be scheduled to theUE continuously ie in every TTI Less complex UEs corresponding to
a lower UE category can only process data received in every second or
even every third TTI This is described by the so-called inter-TTI dis-
tance parameter see section 28 page 79 for further details An
inter-TTI distance of 1 corresponds to continuous HS-PDSCH trans-
mission (assuming data is available for transmission) An example of
the maximum amount of multiple channelization codes used for
HS-PDSCH is shown in Fig 2-4 Here all of the 15 possible channeliza-
tion codes for spreading factor 16 are assigned but as can be seen this
already occupies most of the available resources provided by the NodeB
SF = 1 SF = 2 SF = 4 SF = 8 SF = 16 SF = 32 SF = 64 SF = 128 SF = 256
20
21
4080
160320
640
12802561
161
81
41
42
43
10
641
1281
hellip
82
83
2560All possible HS-PDSCH codes
Possible HS-SCCH codes (example)
CPICH
P-CCPCHBlocked
2563
2562
1282
12832567
2566
2565
2564
321
642
12842569
643
128525611
25610
1286
128725615
25614
25613
25612
2568
6462
128124256249
6463
128125256251
256250
128126
128127256255
256254
256253
256252
2562483230
3231
162
163
164
165
166
167
168
16984
851610
1611
1612
161386
871614
1615
hellip
Fig 2-4 Example of HS-PDSCH code allocation maximum allocation
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HS-DSCH High speed downlink shared channel transport channel
31
Additional physical layer parameters applied by the HS-PDSCH are for
example the constellation rearrangement retransmission indication
and redundancy version see section 223 page 44 for further details
22 HS-DSCH High speed downlink shared channel
transport channel
In this book we would like to distinguish between different types of
channels such as the physical transport and logical channels A log-
ical channel is defined by what type of information is sent a physical
channel is defined by its physical characteristics and a transport chan-
nel describes how the information is formatted HSDPA defines a new
transport channel known as the HS-DSCH which provides a higher
data rate due to its larger transport block sizes and allows flexible chan-
nel coding compared to the existing transport channels in WCDMA
Rel-99 This means the HS-DSCH may use different redundancy ver-
sions with various ways of puncturing This section discusses somecharacteristics of the transport format used on this channel type The
total coding chain is outlined in Fig 2-5
Data arrives at the coding unit at amaximum rate of one transportblock per transmission time interval
CRC attachment to
each transport block
Bit scrambling
Code block segmentation
Channel codingTurbo coding rate 13
Physical layer hybridARQ functionality
Physical channel mapping
Constellationrearrangement for
16QAM
HS-DSCH interleaving
Physical channelsegmentation
PhCH 1 PhCH P
Fig 2-5 Coding chain of HS-DSCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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HSDPA operation overview and physical channels
The data arriving here is represented by a MAC-hs PDU a protocol
data unit coming from the MAC layer and representing a transport
block that is sent once every transmit time interval of 2 ms The firststep in the coding chain is the attachment of a cyclic redundancy check
(CRC) with a length of 24 bits to the transport block In HSDPA the
CRC is used for error detection and the ACK NACK feedback sent by
the UE is based on the CRC status The next step involving bit scram-
bling uses a bitwise XOR combination of the input bits with a pseudo-
random bit sequence to randomize the data and avoid long sequences
of constant bits that can prevent proper decoding This is a precon-
dition for the turbo coder performed two steps later To speed up the
channel coding process and for memory reasons the turbo coder has a
maximum limit of 5114 input bits If the transport block is larger than
5114 bits it will be split into several parallel coding segments and chan-
nel coding will be performed in a parallel architecture HSDPA uses
the turbo coding principle with a code rate of ⅓ ie for one input bit
the turbo coder generates three output bits Turbo coding generates
systematic bits representing the input along with two groups of par-ity bits [Ref 12] They are handled separately particularly in the sub-
sequent puncturing process The step physical layer HARQ functional-
ity represents several puncturing and buffering procedures It includes
a two-stage rate adaptation to the subsequent HS-PDSCH formats see
Fig 2-6 The redundancy version signaled on HS-SCCH controls this
process A first step separates the bits into systematic and parity bits a
first rate matching step constrains the bit sequence to the size of the virtual IR buffer which is needed for optional retransmissions and
a second rate matching step linked to the adaptive coding technique
punctures a certain number of bits The decision on how many bits to
puncture and what bits to puncture is indicated as the redundancy ver-
sion This involves the principles of chase combining and incremen-
tal redundancy as explained in section 222 page 41 The size of the
virtual IR buffer depends on the UE category
Systematicbits
Separation of bits1st rate matching
Turbocoderoutput
Parity bits 1
Parity bits 2
HS-PDSCH
Redundancy version
Virtual IR buffer
2nd rate
matching
Fig 2-6 Basic principle of HARQ functionality on HS-PDSCH
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HS-DSCH High speed downlink shared channel transport channel
33
After the HARQ functionality step the remaining bits are segmented
into parallel streams due to the fact that the physical layer in HSDPA can
use several channelization codes for the physical channel HS-PDSCHDepending on the physical layer status which involves how many chan-
nelization codes can be used for transmission this step divides the data
into parallel streams Another step for error protection is the avoidance
of bundled errors Here the data sent in parallel HS-PDSCH codes is
interleaved to provide an interleaving gain to the channel decoder If
the 16QAM modulation scheme is used the following step of constel-
lation mapping will set a mapping scheme for which bits are mapped to
which modulation symbol The various constellation mapping schemes
are shown in Fig 2-15 page 45 Finally the resulting modulation
symbols must be mapped onto the physical channel ie they are first
spread with a channelization code having spreading factor 16 then
they are scrambled by using the NodeB specific primary or secondary
scrambling code and finally they are mapped on the carrier frequency
221 Brief digression into channel coding
Since channel coding is a substantial feature of HSPA a short digres-
sion into general aspects of channel coding is included here to help the
reader understand the procedures used in HSPA It is not the inten-
tion of this book to discuss channel coding in detail Interested read-
ers can seek out relevant literature on this topic eg [Ref 9] [Ref 10][Ref 11] and [Ref 14] HSDPA channel coding comprises block cod-
ing with CRC for error detection turbo coding for error correction
and interleaving to mitigate error bursts Channel coding is performed
in this order at the data source and in the reverse order at the data
sink Fig 2-7 below provides an overview of channel coding and its
components
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HSDPA operation overview and physical channels
Error detection
addedJ Block codingJ CRC attachmentJ Parity bits
Redundancy added
for error correctionForward errorcorrection (FEC) by J Convolutional codingJ Turbo coding
Rate matching
J PuncturingJ Repetition
Inter-
leaving
Deinter-leaving
Error correctionConvolutionaldecodingJ
Turbo decoding
Error detectionJ CRC check J Parity check
Transmitting end
Receiving end
Fig 2-7 General channel coding components example
Error detection ndash Example with block coding
Generally known as outer loop error correction this step involves
attachment of some error detection mechanisms that are added onto
the data block by the transmitter to enable the receiver to detect errorsCommon examples are parity bit attachments or cyclic redundancy
checks using the block coding principle Block coding involves calcu-
lating a certain number of parity bits for a block of data bits and then
appending them to the data block At the data sink ie the receiving
end errors in the received code word can be detected with the aid of
these redundancy bits
HSDPA uses a type of block code known as a cyclic redundancy check
(CRC) The cyclic codes of this type are also known as (nk) codes
where n represents the number of code symbols (bits) and k the num-
ber of data symbols (bits) The number of check bits is therefore nk
In HSDPA there is only one length of cyclic redundancy check Every
transport block in the HS-DSCH is followed by a 24-bit CRC An exam-
ple of how this CRC-based block coding works is given below
These check bits and thus the code word are produced by a generating
polynomial A polynomial is used to represent a bit sequence as a code
word with the power of each term in the polynomial corresponding to
a bit position and the coefficient of each term to a bit (Dm) A data word
with k bits is therefore represented as follows
Dk ∙ x
k
+ Dkndash1 ∙ x
kndash1
+ hellip + D983089 ∙ x + D983088
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HS-DSCH High speed downlink shared channel transport channel
35
An example could be the simple bit pattern 1101 which would repre-
sented as polynomial 983160983091 + 983160 + 1 i e 1 ∙ x 983091 + 0 ∙ x 983090 + 1 ∙ x 1048625 + 1 ∙ x 1048624
To calculate the check bits the data word D(x ) is multiplied by x nndashk
and then divided by the generating polynomial G(x ) which is of degree
(nndashk) The remainder R(x ) is the check word comprising the check bits
R x mainder x D x
G x
n k
( ) Re ( )
( )=
sdot
minus
The code word C (x ) is now obtained by appending the check word to
the data word
C (x ) = x nndashk ∙ D(x ) + R(x )
The receiver knows the generating polynomial G(x ) and performs the
division C (x )G(x ) If there are no transmission errors the code word
C (x ) is divisible by G(x ) The probability is therefore high that anyerrors will be detected The maximum number of errors per code word
that can be detected is determined by the length of the check word
which in our case is the length of the CRC But what is not known is the
position of those errors and thus there is no way to correct them This
is the responsibility of the ldquoinnerrdquo error correction such as the attach-
ment of redundancy bits which enable the receiver to correct some bit
errors Note that block codes can also be used in general to correcterrors but this is not performed in HSPA because this would increase
the overall latency time
Error correction performed with forward error correction (FEC)
principle of convolutional coding
With forward error correction (FEC) redundant bits are inserted into
data packets (bursts) at the transmitting end to enable the receiving
end to implement a correction mechanism The assumption is that theerrors do not occur in a burst Here the principle of a convolutional
coder is used This type of coder ldquoremembersrdquo the last n bits sent and
adds each input bit to the stored n bits The words obtained at the out-
put are usually longer than one bit The code rate defines the ratio of
the input bits to the output bits for example a coder using a code rate
of frac12 generates for each input bit a code word of two output bits Error
correction is based on the fact that a previous state ie a word or a bit
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36
HSDPA operation overview and physical channels
sequence can only assume one of two succeeding states depending on
whether 0 or 1 was entered into the coder ie the decoder decides for
the metric providing the minimum error estimation If a word arrivesat the receiver in a state that cannot be reached from a state obtain-
able from one of the two input combinations a transmission error has
occurred and needs to be corrected This procedure is equivalent to
tracing a path through a trellis diagram which is familiar from cod-
ing theory
We would now like to discuss a brief example to demonstrate the func-
tionality of channel coding and the subsequent steps of puncturing
Please note that this example does not represent the real coders used
in HSDPA Consult the relevant literature for further details of cod-
ing theory [Ref 10] [Ref 11] and [Ref 14] as well as the specification
[TS 25212 Ref 21] which describes the coding applied in HSPA
The convolutional coder shown in Fig 2-8 consists of one input fol-
lowed by three registers in a shift configuration and finally two out-puts With each clock generation the content of each register is shifted
one register to the right as the last registerrsquos content is discarded and
a new input bit is inserted into the first register The outputs 1 and 2
are generated by an XOR operation between the linked register con-
tents In this manner we create a finite response filter and a certain
memory effect Letrsquos assume we want to transmit the following input bit
sequence 110110 01 Here the nomenclature 01 means that the lastbit of our contemplated sequence can be either 0 or 1 and we wish to
consider both alternatives The registers are initialized with all 0s and
typically some tail bits are attached to the code word which will ensure
this for the succeeding code word The table in Fig 2-8 shows the input
bit on the left side the register sequence content after each step and
outputs 1 and 2 on the right side The output sequence for the given
input will be 11 01 01 00 01 011100 Note the last two lines in the table
We do assume an either or ie there are two alternatives such thatalternative A means that after the sequence 110110 has been sent to the
coder the following bit will be logical 0 Alternative B means that after
the sequence 110110 the following bit will be a logical 1 So we present
an either or situation This will be used to explain the coding principle
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HS-DSCH High speed downlink shared channel transport channel
37
Example of convolutional coding
Input Regis-
ter 1
Regis-
ter 2
Regis-
ter 3
Out-
put 1
Out-
put 2
XOR operation
Register 3Register 2Register 1
+
Input
Output 1
Output 2
+ +
1 1 0 0 1 1
1 1 1 0 0 1
0 0 1 1 0 1
1 1 0 1 0 0
1 1 1 0 0 1
0 0 1 1 0 1
Alt A 0 0 0 1 1 1
Alt B 1 1 0 1 0 0
Fig 2-8 Simple example for convolutional coding
In Fig 2-9 that follows there is a trellis diagram representing in each
column the four possible output values of our channel coder 00 01 10
or 11 and in bold color there is the trellis path through this diagram
resulting from the input sequence Recalling our definition of the two
alternatives for the last bit of our example code word we can see that
the rightmost part of this trellis diagram shows the two possible steps
From state 01 we can only reach either state 00 or state 11 The twoother states 01 or 10 are not possible and with no input to the coder
shown in Fig 2-8 the output can reach these two states in this step For
example if the receiver detects a sequence such as 11 01 01 00 01 01 01
it knows there is an error at the last position 01 which had to be cor-
rected as either 00 or 11 because only these two alternatives are pos-
sible The error correction is performed by looking at the total trellis
path and selecting the maximum likelihood sequence estimation basedon the received data pattern In our short example we admit that we
stopped at this point of course Imagine that the input sequence of bits
continues The decoder would not know if it should proceed with the
pattern 00 or 11 so the decision will be to continue both ways The fol-
lowing step is then checked again and one of the assumed ways will dif-
fer more from the demodulated pattern than the other one This prin-
ciple is described in the Viterbi algorithm [Ref 15] Based on this algo-
rithm the stronger path will survive ie the decoder checks at eachstep which path of the examined ones in the trellis path exhibits the
smallest deviation from the demodulation sequence and thus this path
will be continued The paths exhibiting a higher deviation are discarded
to reduce the calculation expense The path through the trellis diagram
is called a ldquometricrdquo and the term ldquomaximum likelihood sequence esti-
mationrdquo (MLSE) represents the selection by the channel decoder of the
real possible metric which is the closest to the received data pattern As
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HSDPA operation overview and physical channels
an analogy If we do a crossword puzzle and find some characters in a
word the channel decoder would check in a primer or dictionary of the
language containing all possible character combinations that we callldquowordsrdquo and select the existing word that has the maximum likelihood
for the prevailing sequence of characters
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
Alternative B
Alternative A
Register 2
+ +
+
Output 1
Output 2
XOR operation
Trellis diagram above showsmetric for input sequence
110110 0
or 1
into a coder such as
1
1
0
1 10
0
1
Register 3Register 1
Fig 2-9 Metric in trellis diagram
Interleaving
Forward error correction based on convolutional coders has one disad-
vantage related to the impact of block errors If the transmission errors
are distributed they can be corrected as demonstrated in the trellis dia-gram example using the Viterbi algorithm but if many adjacent bits
are lost the decoder will have problems retrieving the right bit pattern
Interleaving means that the information to be transmitted is spread or
distributed over several bursts in such a way that contiguous informa-
tion is split up and transmitted in a time or block distributed mode
To avoid error bursts an attempt is made to spread the bit errors over
several code words This is achieved by interleaving several code wordsThis method is also called diagonal interleaving see Fig 2-10 Another
kind of interleaving is block interleaving as shown in Fig 2-11 Blocks
of code words are written row-by-row into a matrix and then read col-
umn-by-column With both methods consecutive bits of a code word
are never transmitted consecutively and conversely when the bits are
deinterleaved at the receive end error bursts are spread over several
code words
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HS-DSCH High speed downlink shared channel transport channel
39
As several code words are interleaved the decoder has to ldquowaitrdquo a cer-
tain time until all bits of a particular code word arrive This delay ie
the ldquomeasure for spreading over timerdquo is referred to as the ldquointerleav-ing depthrdquo The greater the interleaving depth the more code words are
available for spreading the error bursts and the greater the probability
that errored bits can be corrected but on the other hand this increases
the overall latency time
HSDPA uses the block diagonal interleaving principle for the HS-DSCH
only since as we should recall one goal is to have a short round-trip
time
Spreadinghellip
Interleaving
hellip
hellip
Fig 2-10 Diagonal interleaving
Write
Read
Interleaving-Matrix
Fig 2-11 Block interleaving
Puncturing
Having briefly described the principle of convolutional coding another
mechanism will be presented that is used to increase the throughputof user data and coordinate with the AMC mechanism described in
section 12 page 10 After adding redundancy the total bit stream is
now known as soft bits ie the sum including all of the raw data bits
at the input of the channel coder plus the added redundancy bits This
quantity must match the required transport block size demanded by
the transport layer and the process performed here is called rate match-
ing ie deleting some of the soft bits at the transmitting end in a pre-
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HSDPA operation overview and physical channels
defined manner or repeating or adding some stuffing bits In HSPA the
rate matching mechanism uses puncturing which provides higher data
throughput The signaled values TBS and RV tell the receiving convo-lutional coder how many and where bits have been punctured This
allows the decoder to insert blank positions which have to be filled later
by performing trellis decoding In other words we may consider the
punctured bits as bit losses created intentionally by the transmitter In
this manner the total amount of data bits can be increased for the sake
of lower redundancy In HSDPA this puncturing scheme will be very
flexible and the NodeB scheduler will set the puncturing rate adapted
to the prevailing RF conditions on the radio channel to obtain the high-
est possible data throughput under the existing conditions The disad-
vantage of adaptive coding is that we need signaling information so
that the transmitter has to inform the receiver about how many soft bits
have been punctured This is seen in Fig 2-26 page 55 in the form
of the redundancy version carried by the HS-SCCH control channel
Fig 2-12 below again depicts the principle of puncturing in HSDPAand clarifies some signaling parameters such as the transport block size
1 1 0 1 1 0 0
11 01 01 00 01 01 11
Transport block sizeInput bits into channel coder
Soft bitsOutput from channel encoder
Rate matchingPuncturing or repeating bits
11 01 01 00 01 01 11
1 01 0 00 0 01 1Coded composite transport bitsCan be several combined streams aftercoding + rate matching
Transport block size FEC
Fig 2-12 Puncturing based on coding example from Fig 2-8 page 37
The process of channel coding starts first with the transport block
size which is given by the size of the input data bit sequence added
by a cyclic redundancy checksum The next step is the channel cod-
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HS-DSCH High speed downlink shared channel transport channel
41
ing which is performed in HSPA by a so-called turbo coder The turbo
coder is a parallel concatenated convolutional coder that exhibits bet-
ter reliability compared to a single convolutional coder Discussingthe functionality of a turbo coder in all of its details would represent a
major digression from the intention of this book Accordingly we will
simply encourage the interested reader to consult the channel coding
literature for more details about turbo coders and their applications
[Ref 10] [Ref 12] Determined by the scheduler of the base station or
the redundancy version to be used the next step known as the redun-
dancy version will either puncture (the most likely) or repeat some of
the bits resulting from the channel coding process How many bits will
be punctured is defined by the coding rate In our example in Fig 2-12
we see that the input bit sequence has a length of 7 bits resulting in
14 soft bits after channel coding with our example coder providing a
coding rate of frac12 The scheduler decided to puncture 4 bits so that we
finally obtain 10 bits which have to be mapped on the physical chan-
nels Our overall coding rate is therefore given as ⁷frasl983089983088 In other words
some bits are protected with redundancy information while othersare not Note that the size of the coded composite transport channel
is determined by the physical layer parameters such as the number of
channelization codes used to convey the HS-PDSCH the modulation
scheme and the transmit time interval which is constant for HSDPA
but can be either 2 or 10 ms for HSUPA Thus its size does not need
to be signaled to the receiver and only the transport block size and the
redundancy versions will be contained in the HS-SCCH channel
222 Incremental redundancy and chase combining
for HS-DSCH
Until now we have presented some general characteristics of HSDPA
and HSUPA which we would now like to discuss in a combined pro-
cedure and then deduce two other principles The HARQ abbreviationcombines an automatic retransmission of erroneous data with a soft
combination at the receiving end A related question can now be how
the transmitter has to repeat the transport block should the retrans-
mission of data occur in an identical retransmission mode or should
some changes in coding parameters eg the manner of puncturing be
applied This question is also important for the implementation of the
rate matching step shown in Fig 2-12 The transmitter has to provide
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HSDPA operation overview and physical channels
a certain soft buffer ie a memory that stores the transmitted data for
the sake of possible retransmissions and deletes it after having received
a positive acknowledgment from the receiver Should the transmitternow store the coded composite transport data i e the data after coding
but also after puncturing This would restrict it to repeating the data in
an identical manner A better approach is to store the data after channel
coding and before puncturing Even if this requires more memory it
gives the flexibility to change the puncturing scheme and retransmit the
transport block in a different way Fig 2-13 and Fig 2-14 represent both
mechanisms that are used in HSDPA and HSUPA Identical retransmis-
sion is called chase combining and non-identical retransmission with
a different puncturing scheme is called incremental redundancy The
scheduler in the base station can decide which retransmission scheme
will be used We do not wish to delve into the details of channel coding
theory to discuss which mechanism is the better one ndash chase combin-
ing or incremental redundancy We will only mention that both mech-
anisms have their advantages and thus their applications Chase com-
bining has the advantage that the systematic bits representing the orig-inal data input into the channel coder are contained in the transmit-
ted sequence after puncturing Thus chase combined transport blocks
are ldquoself-decodablerdquo If we consider a situation where the original trans-
port block is lost completely and only the retransmitted block is pres-
ent at the receiver there is a chance to decode the data properly Mean-
while incremental redundancy seems to add more redundancy when
retransmitting but in a scenario where the first transmission contain-ing the systematic bits is lost completely and only the retransmission
is present the receiver will have no chance to decode the data without
having some of the systematic bits Accordingly incremental redun-
dancy is applied whenever sporadic bit errors occur due to a time vari-
ant channel and chase combining is selected whenever we have to deal
with complete transport block errors i e the time variance of the radio
link exhibits some bursted fading dips
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HS-DSCH High speed downlink shared channel transport channel
43
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Chase combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Transmitted bit
Punctured bit
Systematic bits
Parity 1
Parity 2
Systematic bits
Parity 1
Parity 2
Fig 2-13 Chase combining principle
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Incremental redundancy combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Systematic bits
Parity 1
Parity 2
Systematic bitsParity 1
Parity 2
Fig 2-14 Incremental redundancy
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HSDPA operation overview and physical channels
223 Constellation rearrangement
Due to the fact that HSDPA introduces a higher-order modulationscheme (16QAM) we can recognize some effects due to the physi-
cal layer influencing the susceptibility to noisy RF conditions One of
these effects can be explained by looking at the constellation diagram
in the 16QAM modulation scheme see section 12 page 10 As we
recall there is a total of 16 different constellation points given by the
modulation vector and represented by its phase and amplitude Con-
sidering the Euclidean distance which is the distance in this constella-
tion diagram between two neighboring points we can clearly see that
some points have more neighbors than others Especially the four con-
stellation points at the very four corners only have three direct neigh-
bors making them less susceptible to misdetection due to noise shift-
ing them in a certain direction On the other hand the four constella-
tion points representing the inner square of the constellation have eight
direct neighbors each and are therefore more likely to be incorrectly
detected The idea of constellation rearrangement is now to change themapping scheme applied in the original transmission when retrans-
mitting As we know the receiver will soft combine the retransmit-
ted data with the previously received information so we can achieve a
certain incremented redundancy and a certain protection mechanism
Note however that considering a sole transmission of a transport block
using a certain constellation arrangement will not show any more pos-
itive or negative results compared to other constellation arrangementsThe redundancy gain is only achieved by rearranging the constellation
mapping in a retransmitted transport block and performing soft com-
bining at the receiver Overall HSDPA defines four constellation rear-
rangement schemes which are indicated in the redundancy version
field of the HS-SCCH and are represented by the ldquobrdquo bit field ranging
from b = 0 to b = 3 All four constellation schemes are Gray encoded
ie the directly adjacent constellation symbols do not exhibit four com-
pletely different bits in order to reduce the impact of misdetection onbit errors
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High speed shared control channel (HS-SCCH)
45
Q
I
(ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1) (1 1ndash1ndash1)
(ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1) (1 1ndash1 1)
(ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1) (1ndash1ndash1 1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 0
Q
I
(ndash1 1 1 1) (ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1)
(ndash1 1 1ndash1) (ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1)
(ndash1ndash1 1ndash1) (ndash1ndash1ndash1ndash1) (1ndash1ndash1ndash1) (1ndash1 1ndash1)
(ndash1 1 1 1) (ndash1ndash1ndash1 1) (1ndash1ndash1 1) (1ndash1 1 1)
b = 2
Q
I
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (1ndash1 1 1) (ndash1ndash1 1 1)
(ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1) (ndash1 1 1 1)
(ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1) (ndash1 1 1ndash1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 1
Q
I
(1 1ndash1 1) (ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1)
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1)
(1ndash1ndash1ndash1) (ndash1ndash1ndash1ndash1) (ndash1ndash1 1ndash1) (1ndash1 1ndash1)
(1 1ndash1ndash1) (ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1)
b = 3
Fig 2-15 Constellation rearrangement in HSDPA
23 High speed shared control channel (HS-SCCH)
The HS-SCCH sends scheduling information to the UEs As seen before
the HS-PDSCH has a very flexible configuration for physical parame-
ters such as the coding rate number of code channels or retransmis-sions This high flexibility increases the complexity and engenders the
need for additional signaling information transferred on the HS-SCCH
Reception of user data in HSDPA is always a two-step procedure
First the receiver has to capture the scheduling control information
and afterwards based on the received control information it may start
demodulating and decoding the HS-PDSCH containing the user data
This two-step procedure is shown in Fig 2-16 below which lists what
kind of control information is sent to the UEs via the HS-SCCH Asshown in Fig 2-2 page 28 which describes the overall HSDPA chan-
nel structure there can be up to four HS-SCCHs assigned to one UE
But only one HS-SCCH would contain the scheduling information for
this UE within one TTI Thus the network can assign resources simul-
taneously to various UEs in the downlink direction
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HSDPA operation overview and physical channels
I would like to receive databut I dont know where myHS-PDSCH resources areand what they look like
HS-SCCH
Read the 1st HS-SCCH slotfor HS-DSCH channelizationcodes UE identity and
modulation scheme
Then the 2nd and 3rd HS-SCCHslots provide transport block sizeinformation hybrid ARQ process in-formation redundancy constellationversion new data indicator
HS-PDSCH
Fig 2-16 HS-SCCH control channel usage
Regarding the physical layer parameters we see in Fig 2-17 that the
HS-SCCH uses a channelization code with a spreading factor of 128
and it also uses the newly introduced transmit time interval of one sub-
frame which is equal to 2 ms It should be mentioned that the spread-ing factor of 128 requires double the capacity compared to similar con-
trol channels in WCDMA Release 99 reflecting the signaling overhead
needed to guarantee the huge flexibility introduced with HSDPA Addi-
tionally Fig 2-16 shows that the control information is sent consecu-
tively within one subframe The first slot within this subframe contains
the control information UE identity channelization code information
and modulation scheme identifier Slots 2 and 3 of the subframe con-tain the remaining control information Transport block size HARQ
process identifier redundancy version and new data indicator Conse-
quently the UE can self-decode slot 1 alone and slots 2 and 3 in a sec-
ond step even if they represent one logical unit This raw control infor-
mation is of course also channel coded using a turbo and on the phys-
ical layer the quantity of bits after the rate matching step is 40 bits con-
veyed in one slot corresponding to 666 micros [TS 25212 Ref 21] see also
Fig 2-28 page 56
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High speed shared control channel (HS-SCCH)
47
The HS-SCCH is a fixed rate (60 kbps SF = 128) downlinkphysical channel used to carry downlink signaling related toHS-DSCH transmission
Slot 0
Slot 1
Slot 2
Tslot
= 2560 chips
Data = 40 bits
1 subframe = 2 ms
Fig 2-17 Structure of High speed shared control channel HS-SCCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
We would like to return now to the time consecutive transmission of
control information There is a difference in the control information
in terms of its priority Some information is needed at the UE end
very urgently while other control information does not have such a
high priority But why This will be explained by looking at some tim-ing aspects defined for HSDPA If we consider the timing between
the shared data channel HS-PDSCH and the shared control chan-
nel HS-SCCH as shown in Fig 2-18 we see that the HS-PDSCH fol-
lows the HS-SCCH by exactly two slots or 5120 chips The HS-SCCH
is completely time-aligned with the general control channels CPICH
and P-CCPCH of the NodeB This is mandatory because it is a shared
channel Consider several UEs with different distances to the NodeBwanting to receive the HS-SCCH channel Thus it must have constant
timing that is known a priori The shared data channel HS-PDSCH is
now transmitted exactly 5120 chips after the first chip of the HS-SCCH
This leads to an overlapping slot thereby requiring multitasking recep-
tion at the UE end While the UE is still receiving the last slot of an
ongoing HS-SCCH subframe it may already start the reception of an
HS-PDSCH transport block The first slot in the HS-SCCH subframe
now contains information required by the physical layer to performdespreading and demodulation These values are the UE identity indi-
cating whether the UE will start demodulation of the HS-PDSCH or
not in case it is not scheduled the modulation scheme information
since the UE has to know how to interpret the received constellation
vector and whether it has to be considered as a QPSK or 16QAM con-
stellation point and finally the UE has to know which channelization
codes it has to apply to capture the HS-PDSCH transport block The
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HSDPA operation overview and physical channels
overall UE reaction time when being scheduled is now seen as 1 slot
or 2560 chips This tough requirement for the UEs is due to the objec-
tive to obtain overall a much shorter latency than legacy standards Theadditional control information such as the new data indicator redun-
dancy version and transport block size is not that urgent since it is
needed after demodulation but before channel decoding So first the
UE will sample the whole three slots of the HS-PDSCH and demodu-
late them into a bit stream which is finally handed over to the channel
decoder This principle is known as post-processing and is used typi-
cally in mobile communications technologies
J Start of HS-SCCH subframe 0 is aligned with startof P-CCPCH frames
J The HS-PDSCH starts
τ HS-PDSCH
(2times Tslot
= 5120 chips)
after the start of the HS-SCCH
UE identity etc
processing timeof receiver
HS-DSCH subframe
3 times Tslot= 7680 chips
3 times Tslot
= 7680 chips
τ HS-PDSCH
(2times Tslot
= 5120 chips)
HS-SCCH
HS-PDSCH
Fig 2-18 Timing relation between HS-SCCH and HS-PDSCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
Content of the HS-SCCH control channelThe control information contained in the HS-SCCH control chan-
nel has already been mentioned so we will now consider the values
in more detail We will begin with an overview of what kind of control
information is contained in the HS-SCCH channel before proceeding
with further details about the single control elements The following
control information is present in the HS-SCCH [TS 25212 Ref 21]
Channelization code set information (7 bits)
Modulation scheme information (1 bit) Transport block size information (6 bits)
Hybrid ARQ process information (3 bits)
Redundancy and constellation version (3 bits)
New data indicator (1 bit)
UE identity (16 bits) = H-RNTI
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High speed shared control channel (HS-SCCH)
49
Some of these parameters are more or less self-explanatory while oth-
ers require additional background information and closer examination
Modulation scheme information 1 bit
This single bit is used to inform the receiver whether the modulation
scheme QPSK or 16QAM is applied on the data channel HS-PDSCH
The interpretation of the bit x ms1 is as follows
ms1
x
if QPSK
otherwise
0
1
=
New data indicator 1 bit
The new data indicator bit field informs the receiving entity that the
prevailing PDU transmitted by the current HARQ process is either a
retransmission or contains new data This is done by setting the new
data bit to the value 0 for the first PDU on this particular HARQ process
and incrementing the value by 1 with every new data sent [TS 25321Ref 30] This leads to a toggled value In case the new data bit is not
incremented ie if it remains at its previous value it is an indicator for
retransmission
1st PDU of this
HARQ process
NDI = New data indicator
NDI = 0 NDI = 1
NACK
NDI = 1
ACK
NDI = 0
HS-SCCH HS-SCCH HS-SCCHHS-SCCH
ACK
Fig 2-19 New data indicator bit principle of incrementing value
Channelization code set information 7 bits
This field is used to indicate the number of channelization codes usedfor transmitting the transport block on the HS-PDSCH As was already
described the spreading factor applied on the HS-PDSCH is constant
with a value of 16 but the flexible values are the number of channeliza-
tion codes forming a cluster when using multiple codes and their posi-
tion in the code tree It is not allowed to distribute the code channels
over the code tree diagram For the sake of simplicity in signaling sev-
eral channelization codes form one cluster and these codes are con-
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HSDPA operation overview and physical channels
tiguous in the channelization code tree [TS 25213 Ref 22] Fig 2-20
illustrates the principle of indicating the channelization codes on the
HS-SCCH
SF = 16
Code ldquo0rdquo isreserved forcommonchannels
Code offset 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15P = 5O = 7
Code group indicatorx
ccs1 x
ccs2 x
ccs3 = min (Pminus 1 15 minusP)
Code offset indicatorx
ccs4 x
ccs5 x
ccs6 x
ccs7 = |Ominus 1minus P8 times15|
A cluster of codes
can be allocated to a UEC
ch16Ohellip C
ch16O + P minus 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1
2 2 2 2 2 2 2 2 2 2 2 2 2 2 14 14
1 2 3 4 5 6 7 8 9 10 11 12 13 14 2 1
3 3 3 3 3 3 3 3 3 3 3 3 3 13 13 13
1 2 3 4 5 6 7 8 9 10 11 12 13 3 2 1
4 4 4 4 4 4 4 4 4 4 4 4 12 12 12 121 2 3 4 5 6 7 8 9 10 11 12 4 3 2 1
5 5 5 5 5 5 5 5 5 5 5 11 11 11 11 11
1 2 3 4 5 6 7 8 9 10 11 5 4 3 2 1
6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10
1 2 3 4 5 6 7 8 9 10 6 5 4 3 2 1
7 7 7 7 7 7 7 7 7 9 9 9 9 9 9 9
1 2 3 4 5 6 7 8 9 7 6 5 4 3 2 1
8 8 8 8 8 8 8 8
8 7 6 5 4 3 2 1
0 (115)
1 (214)
2 (313)
3 (412)
4 (511)
5 (610)
6 (79)
7 (88) Redundant area
C l u s t e r c o d e i n d i c a t o r ( 3 b i t s )
Tree offset indicator (4 bits)
Signaled on HS-SCCH
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
PO
Decoding notation
Number ofmulti-codes
Offset fromleft right incode tree (SF = 16)
Fig 2-20 Channelization code set indicating the HS-PDSCH code cluster
The idea behind the code indication is a matrix with the rows repre-
senting the number of codes per cluster and the columns represent-
ing the position of that cluster the offset value in the code tree Recall-
ing that the maximum number of channelization codes per clusteris 15 and if the cluster size is 1 the offset values can also range from
1 to 15 the resulting matrix would have 15 rows and 15 columns Since
we know that four bits are needed to represent an integer from 1 to 15
we need a total of 4 + 4 = 8 bits for representation of the channeliza-
tion code set information It is a smart idea to save one bit The 15 times 15
matrix would contain much redundant information By way of analogy
like in a road map indicating distances between cities A table showing
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High speed shared control channel (HS-SCCH)
51
the distance from city A to city B the opposite distance from city B to
city A is redundant information The useful information has the form
of a triangle The idea is to cut the lower part rotate it and append itto the spare part of the upper table In this manner a table is obtained
with 7 rows and 15 columns and it is possible to indicate each position
in it with just 7 bits
1 5 r o w s 7
r o w s
Matrix reduction for channeli-
zation code set information
15 columns
Fig 2-21 Matrix size reduction for channelization code set information
The content of the channelization code set matrix can be described as
a value with two numbers The upper number is the number of mul-
ticodes forming one cluster and the lower number is the offset in the
channelization code tree Accordingly the example in Fig 2-20 can be
interpreted to mean the HS-SCCH sends the bits as row number 4 and
column number 6 in the matrix The content of this element are the
values 5 over 7 which have to be interpreted as a cluster size of 5 codesand an offset of 7
Transport block size information 6 bits
With a length of six bits the transport block size (TBS) informa-
tion informs the receiving UE entity about the data block size of the
transport block sent on the HS-PDSCH We should keep in mind the
link adaptation performed with the adaptive modulation and coding
scheme that was described in section 12 page 10 The ratio errorcorrection and user data are flexible while the physical layer param-
eters such as the spreading factor modulation scheme and number of
channelization codes determine the physical block size This physical
block consists of the user data ratio or transport block size and the for-
ward error correction or redundancy information As this ratio is flex-
ible the HS-SCCH will inform the receiving UE entity about the size
of the transport block Here too there is a strategy of bit reduction the
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HSDPA operation overview and physical channels
goal is to inform the receiver with as few bits as possible A non-effi-
cient approach would involve conversion of the decimal number repre-
senting the TBS into a binary sequence but the number of bits neededwould exceed the space available on the HS-SCCH Imagine that the
range of transport block sizes depends on the physical layer condi-
tions The ambient physical layer parameters modulation scheme and
number of channelization codes set a certain working point where the
remaining flexibility for a different TBS configuration can be obtained
by more or less puncturing resulting in a flexible ratio between for-
ward error correction and user data This will lead to a two-step proce-
dure when evaluating the transport block size First the receiver exam-
ines the information modulation scheme and number of channeliza-
tion codes scheduled via HS-SCCH which indicate the value k0 l as
shown in Fig 2-22 The 6-bit HS-SCCH control parameter transport
block size information will be the transport format resource indica-
tor (TFRI) named ki Let k t be the sum of the two values kt = ki + k0i
Both values kt and k0 i can be obtained from tables given by [TS 25321
Ref 30] The range for the TFRI is from 1 to 256 and the derived trans-port block size ranges from 137 bits to 27 952 bits The first table indi-
cates the value k 0 i based on the channelization code and the modula-
tion scheme
Combination i Modulation scheme Number of channelization codes k0 i
0
QPSK
1 1
1 2 40
2 3 633 4 79
4 5 92
5 6 102
Fig 2-22 Extract from TS 25321 table representing k0 i
The second table indicates the final transport block size based on kt
Index TB size Index TB size Index TB size1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
4 173 89 1456 174 6673
5 185 90 1483 175 6793
6 197 91 1509 176 6916
7 209 92 1537 177 7041
Fig 2-23 Extract from TS 25321 table representing kt
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High speed shared control channel (HS-SCCH)
53
J The transport block size used on HS-DSCH is not signaled explicitly on HS-SCCHJ Instead a transport block size index k
i is signaled to indicate the transport block size
First stepModulation scheme andnumber of channelizationcodes as signaled on HS-SCCHdetermine value k
0 i
Second step
Index kt = k
i + k
0i
determines HS-DSCH
transport block size
kt = k
i + k
0i
Table according to 3GPP TS 25321 extract from QPSK section
Table according to 3GPP TS 25321 254 entries in total
Combination i Modulation
scheme
Number of
channelization codes
k0 i
0
QPSK
1 1
1 2 40
2 3 63
3 4 79
4 hellip hellip
Index TB size Index TB size Index TB size
1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
helliphellip hellip hellip hellip hellip
Fig 2-24 Retrieval of transport block size information
Source Fig 2-22 to Fig 2-24 [TS 25321 Ref 30] reproduced by permission of 3GPP
Hybrid ARQ process information 3 bits
The concept behind the hybrid automatic repeat request (HARQ) was
introduced in section 13 page 14 One feature is the possibility of
multitasking ie having several HARQ processes activated at the same
time Fig 2-25 below shows the need to signal the process identity tothe receiver Remember that on the downlink there is a shared chan-
nel concept so the NodeB can flexibly decide which UE will be sched-
uled with a downlink transport block Up to eight HARQ processes
can be signaled via higher layers to one UE Note however that due to
the round-trip timing six HARQ processes must be active to achieve
the maximum throughput as shown in Fig 2-51 page 79 Compared
with HSUPA the HARQ processes on the downlink are asynchronous
so they have to be indicated but on the uplink they are synchronous sothey do not need to be signaled explicitly
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HSDPA operation overview and physical channels
Asynchronous DL minus Synchronous ULNumber of H-ARQ rocesses = 1 to 8 er UE
UL HS-DPCCH UE1
UE1 HARQ processes 1 to 4
3 4 1 42 11 1 32retrans
2
A N A A
A A
N A
UL HS-DPCCH UE2
HS-PDSCH
UE2 HARQ processes 1 to 2
Fig 2-25 HARQ process indication on HS-SCCH
Fig 2-25 shows a typical situation on the downlink (point-to-multi-
point) The NodeB sends data to several UEs sharing the HS-PDSCH
so therefore the HARQ process is asynchronous The time when a
transport block is retransmitted is not fixed For this reason the pro-
cess identifier is signaled on the HS-SCCH Based on the HARQ pro-
cess identity and the new data indicator bit the receiving entity knows
which part of the soft buffer memory has to be used in case of soft com-bining On the uplink the situation is slightly simpler The UE only
communicates with one NodeB so it is a point-to-point connection
Thus retransmission always occurs at a fixed time linked to the origi-
nal transmission
Redundancy and constellation version 3 bits
Adaptive modulation and coding involve flexible selection of modula-tion and coding schemes that are signaled to the receiving UE via the
parameters transport block size and modulation scheme information
Another concept used in HSDPA was previously discussed Chase com-
bining or incremental redundancy (see section 222 page 41) This
means that in case of retransmission the transmit entity can dynami-
cally select another puncturing scheme or keep the puncturing as it was
in the original transmission The applied puncturing scheme is signaled
as redundancy information to the receiver Additionally in case of the16QAM modulation scheme the transmitter can select another constel-
lation arrangement which is also signaled to the UE with the three bits
for the redundancy and constellation version see Fig 2-15 page 45
Depending on the modulation scheme (QPSK or 16QAM) there are
two different tables indicating the parameters ldquosrdquo ldquorrdquo and ldquobrdquo The
parameters ldquosrdquo and ldquorrdquo indicate which scheme is used for puncturing
ie if the puncturing mechanism prioritizes the systematic bits or not
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High speed shared control channel (HS-SCCH)
55
and which puncturing algorithm is used The parameter ldquobrdquo indicates
the constellation mapping version The receiver needs this information
to perform proper demodulation and decoding
Initial transmission
1st retransmission
2nd retransmission
3rd retransmission
r
0
0
1
1
2
2
3
xrv
(value)
s
0 1
1 0
2 1
3 0
4 1
5 0
6 1
7 0 3
s = 1 Systematic bits are prioritizeds = 0 Non-systematic bits are prioritized
r (range 0 to 3 for QPSK) influencesJ Input parameter for puncturing or (together with s) for repetition algorithm defined in TS 25212J Selection of parity bits
Redundancy version coding sequences are signaled on HS-SCCH egndash 0 2 5 6 One initial transmission + 3 retransmissions with different r and s parameters
Fig 2-26 Signaling of redundancy version parameters r and s QPSK case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
Initial transmission
2nd retransmission
1st retransmission
3rd retransmission
r (range 0 to 1 for 16QAM)influences input parameterfor puncturing or (togetherwith s) for repetitionalgorithm defined in
TS 25212 and thus selectionof parity bits
Redundancy version coding sequences are signaled on HS-SCCH egminus 6 4 0 5 Chase combining (no change in s and r parameters ie same redundancyversion) with four possible constellations
x rv (value) s r b
0 1 0 0
1 0 0 0
2 1 1 1
3 0 1 1
4 1 0 1
5 1 0 2
6 1 0 3
7 1 1 0
Definition of parameter s as for QPSK
b (range 0 to 3) describes constellationrearrangement to averagereliability of bits
Fig 2-27 Signaling of redundancy version parameters r s and b 16QAM case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
UE identity H-RNTI 16 bits
The HSDPA radio network transaction identifier (H-RNTI) unam-
biguously identifies the UE having an HS-PDSCH assignment within
a cell It is allocated to the UE via layer 3 signaling procedures at the
radio bearer setup if the radio bearer is an HSDPA connection This
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HSDPA operation overview and physical channels
value represents a temporary name of the UE used to address it when
scheduling data packets via HS-SCCH
HS-SCCH channel coding
The control information contained in the HS-SCCH is of course pro-
tected with channel coding mechanisms the whole coding chain is
described in Fig 2-28 Fig 2-18 page 48 presents the separation of
the control information into two code blocks which are sent consec-
utively mapped on slot 1 and slot 2 + 3 of one HS-SCCH subframe
This principle is also visible in the coding chain The first control block
consisting of channelization information modulation scheme and UE
identity is coded separately from the remaining control values to enable
the UE receiver to decode this first slot separately and prepare for pos-
sible HS-PDSCH reception The coding steps shown in Fig 2-28 such
as rate matching 1 and 2 are similar to the HS-PDSCH coding chain
and are further described in [TS 25212 Ref 21]
Channelcoding 1
R atematching 1
mux
Channelcoding 2
Ratematching 2
RVcoding
UE-specificCRC attachment
UE-specificmasking
Physical channelmapping
r s b
mux
Channelizationcode set
Modulationscheme
Transport block size information
HARQ processinformation
Redundancy andconstellation version
New data indicator
UE identity
UE identity
Fig 2-28 Channel coding for HS-SCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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High speed dedicated physical control channel (HS-DPCCH)
57
24 High speed dedicated physical control channel (HS-DPCCH)
In an active HSDPA connection the UE has to send acknowledgment ornon-acknowledgment reports (as described in section 13 page 14
where the HARQ process is described) as well as channel status infor-
mation to the network The reporting is performed on this physical
control channel HS-DPCCH
As ubiquitous in HSDPA the uplink is also configured into a subframe
structure of 2 ms corresponding to three slots The first slot of the sub-
frame carries the ACK NACK information the UE sends to the NodeB
while the following two slots ie slot 2 and 3 of the subframe convey
the CQI value the channel quality information to the NodeB
Subframe 0 Subframe i Subframe 4
Tslot
= 2560 chips J The spreading factor of theHS-DPCCH is 256 (10 bits peruplink slot)
J The HS-DPCCH can only existtogether with an UL DPCCH
(ded phys control channel)J The DPDCH (dedicated physical data channel) the DPCCH andthe HS-DPCCH are IQ codemultiplexed
HARQ-ACK CQI = Channel quality information
2 times Tslot
= 5120 chips
One radio frame Tf = 10 ms
One HS-DPCCH subframe 2 ms
Fig 2-29 HS-DPCCH configuration
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The slot format for HS-DPCCH describes a quantity of 30 bits per sub-frame resulting in a data rate of 15 kbps The spreading factor used for
the HS-DPCCH is constant and is always equal to 256 but the chan-
nelization code that is used as well as the mapping on either the I or
Q axis depends on several factors eg the co-existence of an HSDPA
connection with a circuit-switched connection meaning whether a
DPDCH established or not Fig 2-36 page 64 illustrates this IQ
mapping and Fig 2-35 page 63 shows the channelization code used
for HS-DPCCH
The HS-DPCCH builds a logical unit of one subframe but having the
independent control information HARQ-ACK and CQI included which
could be separately decoded at the NodeB Note that the slot carrying
the ACK NACK statement is active only when the UE has been sched-
uled by an HS-PDSCH subframe in the corresponding downlink sub-
frame previously Assuming the UE has not received a transport block
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HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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HSDPA operation overview and physical channels
sion Additionally the redundancy version can be changed meaning
the puncturing procedure can be executed in different ways If the UE
category allows HS-DSCH transport blocks can be scheduled to theUE continuously ie in every TTI Less complex UEs corresponding to
a lower UE category can only process data received in every second or
even every third TTI This is described by the so-called inter-TTI dis-
tance parameter see section 28 page 79 for further details An
inter-TTI distance of 1 corresponds to continuous HS-PDSCH trans-
mission (assuming data is available for transmission) An example of
the maximum amount of multiple channelization codes used for
HS-PDSCH is shown in Fig 2-4 Here all of the 15 possible channeliza-
tion codes for spreading factor 16 are assigned but as can be seen this
already occupies most of the available resources provided by the NodeB
SF = 1 SF = 2 SF = 4 SF = 8 SF = 16 SF = 32 SF = 64 SF = 128 SF = 256
20
21
4080
160320
640
12802561
161
81
41
42
43
10
641
1281
hellip
82
83
2560All possible HS-PDSCH codes
Possible HS-SCCH codes (example)
CPICH
P-CCPCHBlocked
2563
2562
1282
12832567
2566
2565
2564
321
642
12842569
643
128525611
25610
1286
128725615
25614
25613
25612
2568
6462
128124256249
6463
128125256251
256250
128126
128127256255
256254
256253
256252
2562483230
3231
162
163
164
165
166
167
168
16984
851610
1611
1612
161386
871614
1615
hellip
Fig 2-4 Example of HS-PDSCH code allocation maximum allocation
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HS-DSCH High speed downlink shared channel transport channel
31
Additional physical layer parameters applied by the HS-PDSCH are for
example the constellation rearrangement retransmission indication
and redundancy version see section 223 page 44 for further details
22 HS-DSCH High speed downlink shared channel
transport channel
In this book we would like to distinguish between different types of
channels such as the physical transport and logical channels A log-
ical channel is defined by what type of information is sent a physical
channel is defined by its physical characteristics and a transport chan-
nel describes how the information is formatted HSDPA defines a new
transport channel known as the HS-DSCH which provides a higher
data rate due to its larger transport block sizes and allows flexible chan-
nel coding compared to the existing transport channels in WCDMA
Rel-99 This means the HS-DSCH may use different redundancy ver-
sions with various ways of puncturing This section discusses somecharacteristics of the transport format used on this channel type The
total coding chain is outlined in Fig 2-5
Data arrives at the coding unit at amaximum rate of one transportblock per transmission time interval
CRC attachment to
each transport block
Bit scrambling
Code block segmentation
Channel codingTurbo coding rate 13
Physical layer hybridARQ functionality
Physical channel mapping
Constellationrearrangement for
16QAM
HS-DSCH interleaving
Physical channelsegmentation
PhCH 1 PhCH P
Fig 2-5 Coding chain of HS-DSCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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HSDPA operation overview and physical channels
The data arriving here is represented by a MAC-hs PDU a protocol
data unit coming from the MAC layer and representing a transport
block that is sent once every transmit time interval of 2 ms The firststep in the coding chain is the attachment of a cyclic redundancy check
(CRC) with a length of 24 bits to the transport block In HSDPA the
CRC is used for error detection and the ACK NACK feedback sent by
the UE is based on the CRC status The next step involving bit scram-
bling uses a bitwise XOR combination of the input bits with a pseudo-
random bit sequence to randomize the data and avoid long sequences
of constant bits that can prevent proper decoding This is a precon-
dition for the turbo coder performed two steps later To speed up the
channel coding process and for memory reasons the turbo coder has a
maximum limit of 5114 input bits If the transport block is larger than
5114 bits it will be split into several parallel coding segments and chan-
nel coding will be performed in a parallel architecture HSDPA uses
the turbo coding principle with a code rate of ⅓ ie for one input bit
the turbo coder generates three output bits Turbo coding generates
systematic bits representing the input along with two groups of par-ity bits [Ref 12] They are handled separately particularly in the sub-
sequent puncturing process The step physical layer HARQ functional-
ity represents several puncturing and buffering procedures It includes
a two-stage rate adaptation to the subsequent HS-PDSCH formats see
Fig 2-6 The redundancy version signaled on HS-SCCH controls this
process A first step separates the bits into systematic and parity bits a
first rate matching step constrains the bit sequence to the size of the virtual IR buffer which is needed for optional retransmissions and
a second rate matching step linked to the adaptive coding technique
punctures a certain number of bits The decision on how many bits to
puncture and what bits to puncture is indicated as the redundancy ver-
sion This involves the principles of chase combining and incremen-
tal redundancy as explained in section 222 page 41 The size of the
virtual IR buffer depends on the UE category
Systematicbits
Separation of bits1st rate matching
Turbocoderoutput
Parity bits 1
Parity bits 2
HS-PDSCH
Redundancy version
Virtual IR buffer
2nd rate
matching
Fig 2-6 Basic principle of HARQ functionality on HS-PDSCH
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HS-DSCH High speed downlink shared channel transport channel
33
After the HARQ functionality step the remaining bits are segmented
into parallel streams due to the fact that the physical layer in HSDPA can
use several channelization codes for the physical channel HS-PDSCHDepending on the physical layer status which involves how many chan-
nelization codes can be used for transmission this step divides the data
into parallel streams Another step for error protection is the avoidance
of bundled errors Here the data sent in parallel HS-PDSCH codes is
interleaved to provide an interleaving gain to the channel decoder If
the 16QAM modulation scheme is used the following step of constel-
lation mapping will set a mapping scheme for which bits are mapped to
which modulation symbol The various constellation mapping schemes
are shown in Fig 2-15 page 45 Finally the resulting modulation
symbols must be mapped onto the physical channel ie they are first
spread with a channelization code having spreading factor 16 then
they are scrambled by using the NodeB specific primary or secondary
scrambling code and finally they are mapped on the carrier frequency
221 Brief digression into channel coding
Since channel coding is a substantial feature of HSPA a short digres-
sion into general aspects of channel coding is included here to help the
reader understand the procedures used in HSPA It is not the inten-
tion of this book to discuss channel coding in detail Interested read-
ers can seek out relevant literature on this topic eg [Ref 9] [Ref 10][Ref 11] and [Ref 14] HSDPA channel coding comprises block cod-
ing with CRC for error detection turbo coding for error correction
and interleaving to mitigate error bursts Channel coding is performed
in this order at the data source and in the reverse order at the data
sink Fig 2-7 below provides an overview of channel coding and its
components
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HSDPA operation overview and physical channels
Error detection
addedJ Block codingJ CRC attachmentJ Parity bits
Redundancy added
for error correctionForward errorcorrection (FEC) by J Convolutional codingJ Turbo coding
Rate matching
J PuncturingJ Repetition
Inter-
leaving
Deinter-leaving
Error correctionConvolutionaldecodingJ
Turbo decoding
Error detectionJ CRC check J Parity check
Transmitting end
Receiving end
Fig 2-7 General channel coding components example
Error detection ndash Example with block coding
Generally known as outer loop error correction this step involves
attachment of some error detection mechanisms that are added onto
the data block by the transmitter to enable the receiver to detect errorsCommon examples are parity bit attachments or cyclic redundancy
checks using the block coding principle Block coding involves calcu-
lating a certain number of parity bits for a block of data bits and then
appending them to the data block At the data sink ie the receiving
end errors in the received code word can be detected with the aid of
these redundancy bits
HSDPA uses a type of block code known as a cyclic redundancy check
(CRC) The cyclic codes of this type are also known as (nk) codes
where n represents the number of code symbols (bits) and k the num-
ber of data symbols (bits) The number of check bits is therefore nk
In HSDPA there is only one length of cyclic redundancy check Every
transport block in the HS-DSCH is followed by a 24-bit CRC An exam-
ple of how this CRC-based block coding works is given below
These check bits and thus the code word are produced by a generating
polynomial A polynomial is used to represent a bit sequence as a code
word with the power of each term in the polynomial corresponding to
a bit position and the coefficient of each term to a bit (Dm) A data word
with k bits is therefore represented as follows
Dk ∙ x
k
+ Dkndash1 ∙ x
kndash1
+ hellip + D983089 ∙ x + D983088
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HS-DSCH High speed downlink shared channel transport channel
35
An example could be the simple bit pattern 1101 which would repre-
sented as polynomial 983160983091 + 983160 + 1 i e 1 ∙ x 983091 + 0 ∙ x 983090 + 1 ∙ x 1048625 + 1 ∙ x 1048624
To calculate the check bits the data word D(x ) is multiplied by x nndashk
and then divided by the generating polynomial G(x ) which is of degree
(nndashk) The remainder R(x ) is the check word comprising the check bits
R x mainder x D x
G x
n k
( ) Re ( )
( )=
sdot
minus
The code word C (x ) is now obtained by appending the check word to
the data word
C (x ) = x nndashk ∙ D(x ) + R(x )
The receiver knows the generating polynomial G(x ) and performs the
division C (x )G(x ) If there are no transmission errors the code word
C (x ) is divisible by G(x ) The probability is therefore high that anyerrors will be detected The maximum number of errors per code word
that can be detected is determined by the length of the check word
which in our case is the length of the CRC But what is not known is the
position of those errors and thus there is no way to correct them This
is the responsibility of the ldquoinnerrdquo error correction such as the attach-
ment of redundancy bits which enable the receiver to correct some bit
errors Note that block codes can also be used in general to correcterrors but this is not performed in HSPA because this would increase
the overall latency time
Error correction performed with forward error correction (FEC)
principle of convolutional coding
With forward error correction (FEC) redundant bits are inserted into
data packets (bursts) at the transmitting end to enable the receiving
end to implement a correction mechanism The assumption is that theerrors do not occur in a burst Here the principle of a convolutional
coder is used This type of coder ldquoremembersrdquo the last n bits sent and
adds each input bit to the stored n bits The words obtained at the out-
put are usually longer than one bit The code rate defines the ratio of
the input bits to the output bits for example a coder using a code rate
of frac12 generates for each input bit a code word of two output bits Error
correction is based on the fact that a previous state ie a word or a bit
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HSDPA operation overview and physical channels
sequence can only assume one of two succeeding states depending on
whether 0 or 1 was entered into the coder ie the decoder decides for
the metric providing the minimum error estimation If a word arrivesat the receiver in a state that cannot be reached from a state obtain-
able from one of the two input combinations a transmission error has
occurred and needs to be corrected This procedure is equivalent to
tracing a path through a trellis diagram which is familiar from cod-
ing theory
We would now like to discuss a brief example to demonstrate the func-
tionality of channel coding and the subsequent steps of puncturing
Please note that this example does not represent the real coders used
in HSDPA Consult the relevant literature for further details of cod-
ing theory [Ref 10] [Ref 11] and [Ref 14] as well as the specification
[TS 25212 Ref 21] which describes the coding applied in HSPA
The convolutional coder shown in Fig 2-8 consists of one input fol-
lowed by three registers in a shift configuration and finally two out-puts With each clock generation the content of each register is shifted
one register to the right as the last registerrsquos content is discarded and
a new input bit is inserted into the first register The outputs 1 and 2
are generated by an XOR operation between the linked register con-
tents In this manner we create a finite response filter and a certain
memory effect Letrsquos assume we want to transmit the following input bit
sequence 110110 01 Here the nomenclature 01 means that the lastbit of our contemplated sequence can be either 0 or 1 and we wish to
consider both alternatives The registers are initialized with all 0s and
typically some tail bits are attached to the code word which will ensure
this for the succeeding code word The table in Fig 2-8 shows the input
bit on the left side the register sequence content after each step and
outputs 1 and 2 on the right side The output sequence for the given
input will be 11 01 01 00 01 011100 Note the last two lines in the table
We do assume an either or ie there are two alternatives such thatalternative A means that after the sequence 110110 has been sent to the
coder the following bit will be logical 0 Alternative B means that after
the sequence 110110 the following bit will be a logical 1 So we present
an either or situation This will be used to explain the coding principle
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HS-DSCH High speed downlink shared channel transport channel
37
Example of convolutional coding
Input Regis-
ter 1
Regis-
ter 2
Regis-
ter 3
Out-
put 1
Out-
put 2
XOR operation
Register 3Register 2Register 1
+
Input
Output 1
Output 2
+ +
1 1 0 0 1 1
1 1 1 0 0 1
0 0 1 1 0 1
1 1 0 1 0 0
1 1 1 0 0 1
0 0 1 1 0 1
Alt A 0 0 0 1 1 1
Alt B 1 1 0 1 0 0
Fig 2-8 Simple example for convolutional coding
In Fig 2-9 that follows there is a trellis diagram representing in each
column the four possible output values of our channel coder 00 01 10
or 11 and in bold color there is the trellis path through this diagram
resulting from the input sequence Recalling our definition of the two
alternatives for the last bit of our example code word we can see that
the rightmost part of this trellis diagram shows the two possible steps
From state 01 we can only reach either state 00 or state 11 The twoother states 01 or 10 are not possible and with no input to the coder
shown in Fig 2-8 the output can reach these two states in this step For
example if the receiver detects a sequence such as 11 01 01 00 01 01 01
it knows there is an error at the last position 01 which had to be cor-
rected as either 00 or 11 because only these two alternatives are pos-
sible The error correction is performed by looking at the total trellis
path and selecting the maximum likelihood sequence estimation basedon the received data pattern In our short example we admit that we
stopped at this point of course Imagine that the input sequence of bits
continues The decoder would not know if it should proceed with the
pattern 00 or 11 so the decision will be to continue both ways The fol-
lowing step is then checked again and one of the assumed ways will dif-
fer more from the demodulated pattern than the other one This prin-
ciple is described in the Viterbi algorithm [Ref 15] Based on this algo-
rithm the stronger path will survive ie the decoder checks at eachstep which path of the examined ones in the trellis path exhibits the
smallest deviation from the demodulation sequence and thus this path
will be continued The paths exhibiting a higher deviation are discarded
to reduce the calculation expense The path through the trellis diagram
is called a ldquometricrdquo and the term ldquomaximum likelihood sequence esti-
mationrdquo (MLSE) represents the selection by the channel decoder of the
real possible metric which is the closest to the received data pattern As
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HSDPA operation overview and physical channels
an analogy If we do a crossword puzzle and find some characters in a
word the channel decoder would check in a primer or dictionary of the
language containing all possible character combinations that we callldquowordsrdquo and select the existing word that has the maximum likelihood
for the prevailing sequence of characters
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
Alternative B
Alternative A
Register 2
+ +
+
Output 1
Output 2
XOR operation
Trellis diagram above showsmetric for input sequence
110110 0
or 1
into a coder such as
1
1
0
1 10
0
1
Register 3Register 1
Fig 2-9 Metric in trellis diagram
Interleaving
Forward error correction based on convolutional coders has one disad-
vantage related to the impact of block errors If the transmission errors
are distributed they can be corrected as demonstrated in the trellis dia-gram example using the Viterbi algorithm but if many adjacent bits
are lost the decoder will have problems retrieving the right bit pattern
Interleaving means that the information to be transmitted is spread or
distributed over several bursts in such a way that contiguous informa-
tion is split up and transmitted in a time or block distributed mode
To avoid error bursts an attempt is made to spread the bit errors over
several code words This is achieved by interleaving several code wordsThis method is also called diagonal interleaving see Fig 2-10 Another
kind of interleaving is block interleaving as shown in Fig 2-11 Blocks
of code words are written row-by-row into a matrix and then read col-
umn-by-column With both methods consecutive bits of a code word
are never transmitted consecutively and conversely when the bits are
deinterleaved at the receive end error bursts are spread over several
code words
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HS-DSCH High speed downlink shared channel transport channel
39
As several code words are interleaved the decoder has to ldquowaitrdquo a cer-
tain time until all bits of a particular code word arrive This delay ie
the ldquomeasure for spreading over timerdquo is referred to as the ldquointerleav-ing depthrdquo The greater the interleaving depth the more code words are
available for spreading the error bursts and the greater the probability
that errored bits can be corrected but on the other hand this increases
the overall latency time
HSDPA uses the block diagonal interleaving principle for the HS-DSCH
only since as we should recall one goal is to have a short round-trip
time
Spreadinghellip
Interleaving
hellip
hellip
Fig 2-10 Diagonal interleaving
Write
Read
Interleaving-Matrix
Fig 2-11 Block interleaving
Puncturing
Having briefly described the principle of convolutional coding another
mechanism will be presented that is used to increase the throughputof user data and coordinate with the AMC mechanism described in
section 12 page 10 After adding redundancy the total bit stream is
now known as soft bits ie the sum including all of the raw data bits
at the input of the channel coder plus the added redundancy bits This
quantity must match the required transport block size demanded by
the transport layer and the process performed here is called rate match-
ing ie deleting some of the soft bits at the transmitting end in a pre-
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HSDPA operation overview and physical channels
defined manner or repeating or adding some stuffing bits In HSPA the
rate matching mechanism uses puncturing which provides higher data
throughput The signaled values TBS and RV tell the receiving convo-lutional coder how many and where bits have been punctured This
allows the decoder to insert blank positions which have to be filled later
by performing trellis decoding In other words we may consider the
punctured bits as bit losses created intentionally by the transmitter In
this manner the total amount of data bits can be increased for the sake
of lower redundancy In HSDPA this puncturing scheme will be very
flexible and the NodeB scheduler will set the puncturing rate adapted
to the prevailing RF conditions on the radio channel to obtain the high-
est possible data throughput under the existing conditions The disad-
vantage of adaptive coding is that we need signaling information so
that the transmitter has to inform the receiver about how many soft bits
have been punctured This is seen in Fig 2-26 page 55 in the form
of the redundancy version carried by the HS-SCCH control channel
Fig 2-12 below again depicts the principle of puncturing in HSDPAand clarifies some signaling parameters such as the transport block size
1 1 0 1 1 0 0
11 01 01 00 01 01 11
Transport block sizeInput bits into channel coder
Soft bitsOutput from channel encoder
Rate matchingPuncturing or repeating bits
11 01 01 00 01 01 11
1 01 0 00 0 01 1Coded composite transport bitsCan be several combined streams aftercoding + rate matching
Transport block size FEC
Fig 2-12 Puncturing based on coding example from Fig 2-8 page 37
The process of channel coding starts first with the transport block
size which is given by the size of the input data bit sequence added
by a cyclic redundancy checksum The next step is the channel cod-
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HS-DSCH High speed downlink shared channel transport channel
41
ing which is performed in HSPA by a so-called turbo coder The turbo
coder is a parallel concatenated convolutional coder that exhibits bet-
ter reliability compared to a single convolutional coder Discussingthe functionality of a turbo coder in all of its details would represent a
major digression from the intention of this book Accordingly we will
simply encourage the interested reader to consult the channel coding
literature for more details about turbo coders and their applications
[Ref 10] [Ref 12] Determined by the scheduler of the base station or
the redundancy version to be used the next step known as the redun-
dancy version will either puncture (the most likely) or repeat some of
the bits resulting from the channel coding process How many bits will
be punctured is defined by the coding rate In our example in Fig 2-12
we see that the input bit sequence has a length of 7 bits resulting in
14 soft bits after channel coding with our example coder providing a
coding rate of frac12 The scheduler decided to puncture 4 bits so that we
finally obtain 10 bits which have to be mapped on the physical chan-
nels Our overall coding rate is therefore given as ⁷frasl983089983088 In other words
some bits are protected with redundancy information while othersare not Note that the size of the coded composite transport channel
is determined by the physical layer parameters such as the number of
channelization codes used to convey the HS-PDSCH the modulation
scheme and the transmit time interval which is constant for HSDPA
but can be either 2 or 10 ms for HSUPA Thus its size does not need
to be signaled to the receiver and only the transport block size and the
redundancy versions will be contained in the HS-SCCH channel
222 Incremental redundancy and chase combining
for HS-DSCH
Until now we have presented some general characteristics of HSDPA
and HSUPA which we would now like to discuss in a combined pro-
cedure and then deduce two other principles The HARQ abbreviationcombines an automatic retransmission of erroneous data with a soft
combination at the receiving end A related question can now be how
the transmitter has to repeat the transport block should the retrans-
mission of data occur in an identical retransmission mode or should
some changes in coding parameters eg the manner of puncturing be
applied This question is also important for the implementation of the
rate matching step shown in Fig 2-12 The transmitter has to provide
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HSDPA operation overview and physical channels
a certain soft buffer ie a memory that stores the transmitted data for
the sake of possible retransmissions and deletes it after having received
a positive acknowledgment from the receiver Should the transmitternow store the coded composite transport data i e the data after coding
but also after puncturing This would restrict it to repeating the data in
an identical manner A better approach is to store the data after channel
coding and before puncturing Even if this requires more memory it
gives the flexibility to change the puncturing scheme and retransmit the
transport block in a different way Fig 2-13 and Fig 2-14 represent both
mechanisms that are used in HSDPA and HSUPA Identical retransmis-
sion is called chase combining and non-identical retransmission with
a different puncturing scheme is called incremental redundancy The
scheduler in the base station can decide which retransmission scheme
will be used We do not wish to delve into the details of channel coding
theory to discuss which mechanism is the better one ndash chase combin-
ing or incremental redundancy We will only mention that both mech-
anisms have their advantages and thus their applications Chase com-
bining has the advantage that the systematic bits representing the orig-inal data input into the channel coder are contained in the transmit-
ted sequence after puncturing Thus chase combined transport blocks
are ldquoself-decodablerdquo If we consider a situation where the original trans-
port block is lost completely and only the retransmitted block is pres-
ent at the receiver there is a chance to decode the data properly Mean-
while incremental redundancy seems to add more redundancy when
retransmitting but in a scenario where the first transmission contain-ing the systematic bits is lost completely and only the retransmission
is present the receiver will have no chance to decode the data without
having some of the systematic bits Accordingly incremental redun-
dancy is applied whenever sporadic bit errors occur due to a time vari-
ant channel and chase combining is selected whenever we have to deal
with complete transport block errors i e the time variance of the radio
link exhibits some bursted fading dips
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HS-DSCH High speed downlink shared channel transport channel
43
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Chase combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Transmitted bit
Punctured bit
Systematic bits
Parity 1
Parity 2
Systematic bits
Parity 1
Parity 2
Fig 2-13 Chase combining principle
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Incremental redundancy combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Systematic bits
Parity 1
Parity 2
Systematic bitsParity 1
Parity 2
Fig 2-14 Incremental redundancy
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HSDPA operation overview and physical channels
223 Constellation rearrangement
Due to the fact that HSDPA introduces a higher-order modulationscheme (16QAM) we can recognize some effects due to the physi-
cal layer influencing the susceptibility to noisy RF conditions One of
these effects can be explained by looking at the constellation diagram
in the 16QAM modulation scheme see section 12 page 10 As we
recall there is a total of 16 different constellation points given by the
modulation vector and represented by its phase and amplitude Con-
sidering the Euclidean distance which is the distance in this constella-
tion diagram between two neighboring points we can clearly see that
some points have more neighbors than others Especially the four con-
stellation points at the very four corners only have three direct neigh-
bors making them less susceptible to misdetection due to noise shift-
ing them in a certain direction On the other hand the four constella-
tion points representing the inner square of the constellation have eight
direct neighbors each and are therefore more likely to be incorrectly
detected The idea of constellation rearrangement is now to change themapping scheme applied in the original transmission when retrans-
mitting As we know the receiver will soft combine the retransmit-
ted data with the previously received information so we can achieve a
certain incremented redundancy and a certain protection mechanism
Note however that considering a sole transmission of a transport block
using a certain constellation arrangement will not show any more pos-
itive or negative results compared to other constellation arrangementsThe redundancy gain is only achieved by rearranging the constellation
mapping in a retransmitted transport block and performing soft com-
bining at the receiver Overall HSDPA defines four constellation rear-
rangement schemes which are indicated in the redundancy version
field of the HS-SCCH and are represented by the ldquobrdquo bit field ranging
from b = 0 to b = 3 All four constellation schemes are Gray encoded
ie the directly adjacent constellation symbols do not exhibit four com-
pletely different bits in order to reduce the impact of misdetection onbit errors
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High speed shared control channel (HS-SCCH)
45
Q
I
(ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1) (1 1ndash1ndash1)
(ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1) (1 1ndash1 1)
(ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1) (1ndash1ndash1 1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 0
Q
I
(ndash1 1 1 1) (ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1)
(ndash1 1 1ndash1) (ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1)
(ndash1ndash1 1ndash1) (ndash1ndash1ndash1ndash1) (1ndash1ndash1ndash1) (1ndash1 1ndash1)
(ndash1 1 1 1) (ndash1ndash1ndash1 1) (1ndash1ndash1 1) (1ndash1 1 1)
b = 2
Q
I
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (1ndash1 1 1) (ndash1ndash1 1 1)
(ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1) (ndash1 1 1 1)
(ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1) (ndash1 1 1ndash1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 1
Q
I
(1 1ndash1 1) (ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1)
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1)
(1ndash1ndash1ndash1) (ndash1ndash1ndash1ndash1) (ndash1ndash1 1ndash1) (1ndash1 1ndash1)
(1 1ndash1ndash1) (ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1)
b = 3
Fig 2-15 Constellation rearrangement in HSDPA
23 High speed shared control channel (HS-SCCH)
The HS-SCCH sends scheduling information to the UEs As seen before
the HS-PDSCH has a very flexible configuration for physical parame-
ters such as the coding rate number of code channels or retransmis-sions This high flexibility increases the complexity and engenders the
need for additional signaling information transferred on the HS-SCCH
Reception of user data in HSDPA is always a two-step procedure
First the receiver has to capture the scheduling control information
and afterwards based on the received control information it may start
demodulating and decoding the HS-PDSCH containing the user data
This two-step procedure is shown in Fig 2-16 below which lists what
kind of control information is sent to the UEs via the HS-SCCH Asshown in Fig 2-2 page 28 which describes the overall HSDPA chan-
nel structure there can be up to four HS-SCCHs assigned to one UE
But only one HS-SCCH would contain the scheduling information for
this UE within one TTI Thus the network can assign resources simul-
taneously to various UEs in the downlink direction
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HSDPA operation overview and physical channels
I would like to receive databut I dont know where myHS-PDSCH resources areand what they look like
HS-SCCH
Read the 1st HS-SCCH slotfor HS-DSCH channelizationcodes UE identity and
modulation scheme
Then the 2nd and 3rd HS-SCCHslots provide transport block sizeinformation hybrid ARQ process in-formation redundancy constellationversion new data indicator
HS-PDSCH
Fig 2-16 HS-SCCH control channel usage
Regarding the physical layer parameters we see in Fig 2-17 that the
HS-SCCH uses a channelization code with a spreading factor of 128
and it also uses the newly introduced transmit time interval of one sub-
frame which is equal to 2 ms It should be mentioned that the spread-ing factor of 128 requires double the capacity compared to similar con-
trol channels in WCDMA Release 99 reflecting the signaling overhead
needed to guarantee the huge flexibility introduced with HSDPA Addi-
tionally Fig 2-16 shows that the control information is sent consecu-
tively within one subframe The first slot within this subframe contains
the control information UE identity channelization code information
and modulation scheme identifier Slots 2 and 3 of the subframe con-tain the remaining control information Transport block size HARQ
process identifier redundancy version and new data indicator Conse-
quently the UE can self-decode slot 1 alone and slots 2 and 3 in a sec-
ond step even if they represent one logical unit This raw control infor-
mation is of course also channel coded using a turbo and on the phys-
ical layer the quantity of bits after the rate matching step is 40 bits con-
veyed in one slot corresponding to 666 micros [TS 25212 Ref 21] see also
Fig 2-28 page 56
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High speed shared control channel (HS-SCCH)
47
The HS-SCCH is a fixed rate (60 kbps SF = 128) downlinkphysical channel used to carry downlink signaling related toHS-DSCH transmission
Slot 0
Slot 1
Slot 2
Tslot
= 2560 chips
Data = 40 bits
1 subframe = 2 ms
Fig 2-17 Structure of High speed shared control channel HS-SCCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
We would like to return now to the time consecutive transmission of
control information There is a difference in the control information
in terms of its priority Some information is needed at the UE end
very urgently while other control information does not have such a
high priority But why This will be explained by looking at some tim-ing aspects defined for HSDPA If we consider the timing between
the shared data channel HS-PDSCH and the shared control chan-
nel HS-SCCH as shown in Fig 2-18 we see that the HS-PDSCH fol-
lows the HS-SCCH by exactly two slots or 5120 chips The HS-SCCH
is completely time-aligned with the general control channels CPICH
and P-CCPCH of the NodeB This is mandatory because it is a shared
channel Consider several UEs with different distances to the NodeBwanting to receive the HS-SCCH channel Thus it must have constant
timing that is known a priori The shared data channel HS-PDSCH is
now transmitted exactly 5120 chips after the first chip of the HS-SCCH
This leads to an overlapping slot thereby requiring multitasking recep-
tion at the UE end While the UE is still receiving the last slot of an
ongoing HS-SCCH subframe it may already start the reception of an
HS-PDSCH transport block The first slot in the HS-SCCH subframe
now contains information required by the physical layer to performdespreading and demodulation These values are the UE identity indi-
cating whether the UE will start demodulation of the HS-PDSCH or
not in case it is not scheduled the modulation scheme information
since the UE has to know how to interpret the received constellation
vector and whether it has to be considered as a QPSK or 16QAM con-
stellation point and finally the UE has to know which channelization
codes it has to apply to capture the HS-PDSCH transport block The
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HSDPA operation overview and physical channels
overall UE reaction time when being scheduled is now seen as 1 slot
or 2560 chips This tough requirement for the UEs is due to the objec-
tive to obtain overall a much shorter latency than legacy standards Theadditional control information such as the new data indicator redun-
dancy version and transport block size is not that urgent since it is
needed after demodulation but before channel decoding So first the
UE will sample the whole three slots of the HS-PDSCH and demodu-
late them into a bit stream which is finally handed over to the channel
decoder This principle is known as post-processing and is used typi-
cally in mobile communications technologies
J Start of HS-SCCH subframe 0 is aligned with startof P-CCPCH frames
J The HS-PDSCH starts
τ HS-PDSCH
(2times Tslot
= 5120 chips)
after the start of the HS-SCCH
UE identity etc
processing timeof receiver
HS-DSCH subframe
3 times Tslot= 7680 chips
3 times Tslot
= 7680 chips
τ HS-PDSCH
(2times Tslot
= 5120 chips)
HS-SCCH
HS-PDSCH
Fig 2-18 Timing relation between HS-SCCH and HS-PDSCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
Content of the HS-SCCH control channelThe control information contained in the HS-SCCH control chan-
nel has already been mentioned so we will now consider the values
in more detail We will begin with an overview of what kind of control
information is contained in the HS-SCCH channel before proceeding
with further details about the single control elements The following
control information is present in the HS-SCCH [TS 25212 Ref 21]
Channelization code set information (7 bits)
Modulation scheme information (1 bit) Transport block size information (6 bits)
Hybrid ARQ process information (3 bits)
Redundancy and constellation version (3 bits)
New data indicator (1 bit)
UE identity (16 bits) = H-RNTI
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High speed shared control channel (HS-SCCH)
49
Some of these parameters are more or less self-explanatory while oth-
ers require additional background information and closer examination
Modulation scheme information 1 bit
This single bit is used to inform the receiver whether the modulation
scheme QPSK or 16QAM is applied on the data channel HS-PDSCH
The interpretation of the bit x ms1 is as follows
ms1
x
if QPSK
otherwise
0
1
=
New data indicator 1 bit
The new data indicator bit field informs the receiving entity that the
prevailing PDU transmitted by the current HARQ process is either a
retransmission or contains new data This is done by setting the new
data bit to the value 0 for the first PDU on this particular HARQ process
and incrementing the value by 1 with every new data sent [TS 25321Ref 30] This leads to a toggled value In case the new data bit is not
incremented ie if it remains at its previous value it is an indicator for
retransmission
1st PDU of this
HARQ process
NDI = New data indicator
NDI = 0 NDI = 1
NACK
NDI = 1
ACK
NDI = 0
HS-SCCH HS-SCCH HS-SCCHHS-SCCH
ACK
Fig 2-19 New data indicator bit principle of incrementing value
Channelization code set information 7 bits
This field is used to indicate the number of channelization codes usedfor transmitting the transport block on the HS-PDSCH As was already
described the spreading factor applied on the HS-PDSCH is constant
with a value of 16 but the flexible values are the number of channeliza-
tion codes forming a cluster when using multiple codes and their posi-
tion in the code tree It is not allowed to distribute the code channels
over the code tree diagram For the sake of simplicity in signaling sev-
eral channelization codes form one cluster and these codes are con-
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HSDPA operation overview and physical channels
tiguous in the channelization code tree [TS 25213 Ref 22] Fig 2-20
illustrates the principle of indicating the channelization codes on the
HS-SCCH
SF = 16
Code ldquo0rdquo isreserved forcommonchannels
Code offset 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15P = 5O = 7
Code group indicatorx
ccs1 x
ccs2 x
ccs3 = min (Pminus 1 15 minusP)
Code offset indicatorx
ccs4 x
ccs5 x
ccs6 x
ccs7 = |Ominus 1minus P8 times15|
A cluster of codes
can be allocated to a UEC
ch16Ohellip C
ch16O + P minus 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1
2 2 2 2 2 2 2 2 2 2 2 2 2 2 14 14
1 2 3 4 5 6 7 8 9 10 11 12 13 14 2 1
3 3 3 3 3 3 3 3 3 3 3 3 3 13 13 13
1 2 3 4 5 6 7 8 9 10 11 12 13 3 2 1
4 4 4 4 4 4 4 4 4 4 4 4 12 12 12 121 2 3 4 5 6 7 8 9 10 11 12 4 3 2 1
5 5 5 5 5 5 5 5 5 5 5 11 11 11 11 11
1 2 3 4 5 6 7 8 9 10 11 5 4 3 2 1
6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10
1 2 3 4 5 6 7 8 9 10 6 5 4 3 2 1
7 7 7 7 7 7 7 7 7 9 9 9 9 9 9 9
1 2 3 4 5 6 7 8 9 7 6 5 4 3 2 1
8 8 8 8 8 8 8 8
8 7 6 5 4 3 2 1
0 (115)
1 (214)
2 (313)
3 (412)
4 (511)
5 (610)
6 (79)
7 (88) Redundant area
C l u s t e r c o d e i n d i c a t o r ( 3 b i t s )
Tree offset indicator (4 bits)
Signaled on HS-SCCH
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
PO
Decoding notation
Number ofmulti-codes
Offset fromleft right incode tree (SF = 16)
Fig 2-20 Channelization code set indicating the HS-PDSCH code cluster
The idea behind the code indication is a matrix with the rows repre-
senting the number of codes per cluster and the columns represent-
ing the position of that cluster the offset value in the code tree Recall-
ing that the maximum number of channelization codes per clusteris 15 and if the cluster size is 1 the offset values can also range from
1 to 15 the resulting matrix would have 15 rows and 15 columns Since
we know that four bits are needed to represent an integer from 1 to 15
we need a total of 4 + 4 = 8 bits for representation of the channeliza-
tion code set information It is a smart idea to save one bit The 15 times 15
matrix would contain much redundant information By way of analogy
like in a road map indicating distances between cities A table showing
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High speed shared control channel (HS-SCCH)
51
the distance from city A to city B the opposite distance from city B to
city A is redundant information The useful information has the form
of a triangle The idea is to cut the lower part rotate it and append itto the spare part of the upper table In this manner a table is obtained
with 7 rows and 15 columns and it is possible to indicate each position
in it with just 7 bits
1 5 r o w s 7
r o w s
Matrix reduction for channeli-
zation code set information
15 columns
Fig 2-21 Matrix size reduction for channelization code set information
The content of the channelization code set matrix can be described as
a value with two numbers The upper number is the number of mul-
ticodes forming one cluster and the lower number is the offset in the
channelization code tree Accordingly the example in Fig 2-20 can be
interpreted to mean the HS-SCCH sends the bits as row number 4 and
column number 6 in the matrix The content of this element are the
values 5 over 7 which have to be interpreted as a cluster size of 5 codesand an offset of 7
Transport block size information 6 bits
With a length of six bits the transport block size (TBS) informa-
tion informs the receiving UE entity about the data block size of the
transport block sent on the HS-PDSCH We should keep in mind the
link adaptation performed with the adaptive modulation and coding
scheme that was described in section 12 page 10 The ratio errorcorrection and user data are flexible while the physical layer param-
eters such as the spreading factor modulation scheme and number of
channelization codes determine the physical block size This physical
block consists of the user data ratio or transport block size and the for-
ward error correction or redundancy information As this ratio is flex-
ible the HS-SCCH will inform the receiving UE entity about the size
of the transport block Here too there is a strategy of bit reduction the
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HSDPA operation overview and physical channels
goal is to inform the receiver with as few bits as possible A non-effi-
cient approach would involve conversion of the decimal number repre-
senting the TBS into a binary sequence but the number of bits neededwould exceed the space available on the HS-SCCH Imagine that the
range of transport block sizes depends on the physical layer condi-
tions The ambient physical layer parameters modulation scheme and
number of channelization codes set a certain working point where the
remaining flexibility for a different TBS configuration can be obtained
by more or less puncturing resulting in a flexible ratio between for-
ward error correction and user data This will lead to a two-step proce-
dure when evaluating the transport block size First the receiver exam-
ines the information modulation scheme and number of channeliza-
tion codes scheduled via HS-SCCH which indicate the value k0 l as
shown in Fig 2-22 The 6-bit HS-SCCH control parameter transport
block size information will be the transport format resource indica-
tor (TFRI) named ki Let k t be the sum of the two values kt = ki + k0i
Both values kt and k0 i can be obtained from tables given by [TS 25321
Ref 30] The range for the TFRI is from 1 to 256 and the derived trans-port block size ranges from 137 bits to 27 952 bits The first table indi-
cates the value k 0 i based on the channelization code and the modula-
tion scheme
Combination i Modulation scheme Number of channelization codes k0 i
0
QPSK
1 1
1 2 40
2 3 633 4 79
4 5 92
5 6 102
Fig 2-22 Extract from TS 25321 table representing k0 i
The second table indicates the final transport block size based on kt
Index TB size Index TB size Index TB size1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
4 173 89 1456 174 6673
5 185 90 1483 175 6793
6 197 91 1509 176 6916
7 209 92 1537 177 7041
Fig 2-23 Extract from TS 25321 table representing kt
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High speed shared control channel (HS-SCCH)
53
J The transport block size used on HS-DSCH is not signaled explicitly on HS-SCCHJ Instead a transport block size index k
i is signaled to indicate the transport block size
First stepModulation scheme andnumber of channelizationcodes as signaled on HS-SCCHdetermine value k
0 i
Second step
Index kt = k
i + k
0i
determines HS-DSCH
transport block size
kt = k
i + k
0i
Table according to 3GPP TS 25321 extract from QPSK section
Table according to 3GPP TS 25321 254 entries in total
Combination i Modulation
scheme
Number of
channelization codes
k0 i
0
QPSK
1 1
1 2 40
2 3 63
3 4 79
4 hellip hellip
Index TB size Index TB size Index TB size
1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
helliphellip hellip hellip hellip hellip
Fig 2-24 Retrieval of transport block size information
Source Fig 2-22 to Fig 2-24 [TS 25321 Ref 30] reproduced by permission of 3GPP
Hybrid ARQ process information 3 bits
The concept behind the hybrid automatic repeat request (HARQ) was
introduced in section 13 page 14 One feature is the possibility of
multitasking ie having several HARQ processes activated at the same
time Fig 2-25 below shows the need to signal the process identity tothe receiver Remember that on the downlink there is a shared chan-
nel concept so the NodeB can flexibly decide which UE will be sched-
uled with a downlink transport block Up to eight HARQ processes
can be signaled via higher layers to one UE Note however that due to
the round-trip timing six HARQ processes must be active to achieve
the maximum throughput as shown in Fig 2-51 page 79 Compared
with HSUPA the HARQ processes on the downlink are asynchronous
so they have to be indicated but on the uplink they are synchronous sothey do not need to be signaled explicitly
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HSDPA operation overview and physical channels
Asynchronous DL minus Synchronous ULNumber of H-ARQ rocesses = 1 to 8 er UE
UL HS-DPCCH UE1
UE1 HARQ processes 1 to 4
3 4 1 42 11 1 32retrans
2
A N A A
A A
N A
UL HS-DPCCH UE2
HS-PDSCH
UE2 HARQ processes 1 to 2
Fig 2-25 HARQ process indication on HS-SCCH
Fig 2-25 shows a typical situation on the downlink (point-to-multi-
point) The NodeB sends data to several UEs sharing the HS-PDSCH
so therefore the HARQ process is asynchronous The time when a
transport block is retransmitted is not fixed For this reason the pro-
cess identifier is signaled on the HS-SCCH Based on the HARQ pro-
cess identity and the new data indicator bit the receiving entity knows
which part of the soft buffer memory has to be used in case of soft com-bining On the uplink the situation is slightly simpler The UE only
communicates with one NodeB so it is a point-to-point connection
Thus retransmission always occurs at a fixed time linked to the origi-
nal transmission
Redundancy and constellation version 3 bits
Adaptive modulation and coding involve flexible selection of modula-tion and coding schemes that are signaled to the receiving UE via the
parameters transport block size and modulation scheme information
Another concept used in HSDPA was previously discussed Chase com-
bining or incremental redundancy (see section 222 page 41) This
means that in case of retransmission the transmit entity can dynami-
cally select another puncturing scheme or keep the puncturing as it was
in the original transmission The applied puncturing scheme is signaled
as redundancy information to the receiver Additionally in case of the16QAM modulation scheme the transmitter can select another constel-
lation arrangement which is also signaled to the UE with the three bits
for the redundancy and constellation version see Fig 2-15 page 45
Depending on the modulation scheme (QPSK or 16QAM) there are
two different tables indicating the parameters ldquosrdquo ldquorrdquo and ldquobrdquo The
parameters ldquosrdquo and ldquorrdquo indicate which scheme is used for puncturing
ie if the puncturing mechanism prioritizes the systematic bits or not
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High speed shared control channel (HS-SCCH)
55
and which puncturing algorithm is used The parameter ldquobrdquo indicates
the constellation mapping version The receiver needs this information
to perform proper demodulation and decoding
Initial transmission
1st retransmission
2nd retransmission
3rd retransmission
r
0
0
1
1
2
2
3
xrv
(value)
s
0 1
1 0
2 1
3 0
4 1
5 0
6 1
7 0 3
s = 1 Systematic bits are prioritizeds = 0 Non-systematic bits are prioritized
r (range 0 to 3 for QPSK) influencesJ Input parameter for puncturing or (together with s) for repetition algorithm defined in TS 25212J Selection of parity bits
Redundancy version coding sequences are signaled on HS-SCCH egndash 0 2 5 6 One initial transmission + 3 retransmissions with different r and s parameters
Fig 2-26 Signaling of redundancy version parameters r and s QPSK case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
Initial transmission
2nd retransmission
1st retransmission
3rd retransmission
r (range 0 to 1 for 16QAM)influences input parameterfor puncturing or (togetherwith s) for repetitionalgorithm defined in
TS 25212 and thus selectionof parity bits
Redundancy version coding sequences are signaled on HS-SCCH egminus 6 4 0 5 Chase combining (no change in s and r parameters ie same redundancyversion) with four possible constellations
x rv (value) s r b
0 1 0 0
1 0 0 0
2 1 1 1
3 0 1 1
4 1 0 1
5 1 0 2
6 1 0 3
7 1 1 0
Definition of parameter s as for QPSK
b (range 0 to 3) describes constellationrearrangement to averagereliability of bits
Fig 2-27 Signaling of redundancy version parameters r s and b 16QAM case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
UE identity H-RNTI 16 bits
The HSDPA radio network transaction identifier (H-RNTI) unam-
biguously identifies the UE having an HS-PDSCH assignment within
a cell It is allocated to the UE via layer 3 signaling procedures at the
radio bearer setup if the radio bearer is an HSDPA connection This
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HSDPA operation overview and physical channels
value represents a temporary name of the UE used to address it when
scheduling data packets via HS-SCCH
HS-SCCH channel coding
The control information contained in the HS-SCCH is of course pro-
tected with channel coding mechanisms the whole coding chain is
described in Fig 2-28 Fig 2-18 page 48 presents the separation of
the control information into two code blocks which are sent consec-
utively mapped on slot 1 and slot 2 + 3 of one HS-SCCH subframe
This principle is also visible in the coding chain The first control block
consisting of channelization information modulation scheme and UE
identity is coded separately from the remaining control values to enable
the UE receiver to decode this first slot separately and prepare for pos-
sible HS-PDSCH reception The coding steps shown in Fig 2-28 such
as rate matching 1 and 2 are similar to the HS-PDSCH coding chain
and are further described in [TS 25212 Ref 21]
Channelcoding 1
R atematching 1
mux
Channelcoding 2
Ratematching 2
RVcoding
UE-specificCRC attachment
UE-specificmasking
Physical channelmapping
r s b
mux
Channelizationcode set
Modulationscheme
Transport block size information
HARQ processinformation
Redundancy andconstellation version
New data indicator
UE identity
UE identity
Fig 2-28 Channel coding for HS-SCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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High speed dedicated physical control channel (HS-DPCCH)
57
24 High speed dedicated physical control channel (HS-DPCCH)
In an active HSDPA connection the UE has to send acknowledgment ornon-acknowledgment reports (as described in section 13 page 14
where the HARQ process is described) as well as channel status infor-
mation to the network The reporting is performed on this physical
control channel HS-DPCCH
As ubiquitous in HSDPA the uplink is also configured into a subframe
structure of 2 ms corresponding to three slots The first slot of the sub-
frame carries the ACK NACK information the UE sends to the NodeB
while the following two slots ie slot 2 and 3 of the subframe convey
the CQI value the channel quality information to the NodeB
Subframe 0 Subframe i Subframe 4
Tslot
= 2560 chips J The spreading factor of theHS-DPCCH is 256 (10 bits peruplink slot)
J The HS-DPCCH can only existtogether with an UL DPCCH
(ded phys control channel)J The DPDCH (dedicated physical data channel) the DPCCH andthe HS-DPCCH are IQ codemultiplexed
HARQ-ACK CQI = Channel quality information
2 times Tslot
= 5120 chips
One radio frame Tf = 10 ms
One HS-DPCCH subframe 2 ms
Fig 2-29 HS-DPCCH configuration
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The slot format for HS-DPCCH describes a quantity of 30 bits per sub-frame resulting in a data rate of 15 kbps The spreading factor used for
the HS-DPCCH is constant and is always equal to 256 but the chan-
nelization code that is used as well as the mapping on either the I or
Q axis depends on several factors eg the co-existence of an HSDPA
connection with a circuit-switched connection meaning whether a
DPDCH established or not Fig 2-36 page 64 illustrates this IQ
mapping and Fig 2-35 page 63 shows the channelization code used
for HS-DPCCH
The HS-DPCCH builds a logical unit of one subframe but having the
independent control information HARQ-ACK and CQI included which
could be separately decoded at the NodeB Note that the slot carrying
the ACK NACK statement is active only when the UE has been sched-
uled by an HS-PDSCH subframe in the corresponding downlink sub-
frame previously Assuming the UE has not received a transport block
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HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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HS-DSCH High speed downlink shared channel transport channel
31
Additional physical layer parameters applied by the HS-PDSCH are for
example the constellation rearrangement retransmission indication
and redundancy version see section 223 page 44 for further details
22 HS-DSCH High speed downlink shared channel
transport channel
In this book we would like to distinguish between different types of
channels such as the physical transport and logical channels A log-
ical channel is defined by what type of information is sent a physical
channel is defined by its physical characteristics and a transport chan-
nel describes how the information is formatted HSDPA defines a new
transport channel known as the HS-DSCH which provides a higher
data rate due to its larger transport block sizes and allows flexible chan-
nel coding compared to the existing transport channels in WCDMA
Rel-99 This means the HS-DSCH may use different redundancy ver-
sions with various ways of puncturing This section discusses somecharacteristics of the transport format used on this channel type The
total coding chain is outlined in Fig 2-5
Data arrives at the coding unit at amaximum rate of one transportblock per transmission time interval
CRC attachment to
each transport block
Bit scrambling
Code block segmentation
Channel codingTurbo coding rate 13
Physical layer hybridARQ functionality
Physical channel mapping
Constellationrearrangement for
16QAM
HS-DSCH interleaving
Physical channelsegmentation
PhCH 1 PhCH P
Fig 2-5 Coding chain of HS-DSCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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HSDPA operation overview and physical channels
The data arriving here is represented by a MAC-hs PDU a protocol
data unit coming from the MAC layer and representing a transport
block that is sent once every transmit time interval of 2 ms The firststep in the coding chain is the attachment of a cyclic redundancy check
(CRC) with a length of 24 bits to the transport block In HSDPA the
CRC is used for error detection and the ACK NACK feedback sent by
the UE is based on the CRC status The next step involving bit scram-
bling uses a bitwise XOR combination of the input bits with a pseudo-
random bit sequence to randomize the data and avoid long sequences
of constant bits that can prevent proper decoding This is a precon-
dition for the turbo coder performed two steps later To speed up the
channel coding process and for memory reasons the turbo coder has a
maximum limit of 5114 input bits If the transport block is larger than
5114 bits it will be split into several parallel coding segments and chan-
nel coding will be performed in a parallel architecture HSDPA uses
the turbo coding principle with a code rate of ⅓ ie for one input bit
the turbo coder generates three output bits Turbo coding generates
systematic bits representing the input along with two groups of par-ity bits [Ref 12] They are handled separately particularly in the sub-
sequent puncturing process The step physical layer HARQ functional-
ity represents several puncturing and buffering procedures It includes
a two-stage rate adaptation to the subsequent HS-PDSCH formats see
Fig 2-6 The redundancy version signaled on HS-SCCH controls this
process A first step separates the bits into systematic and parity bits a
first rate matching step constrains the bit sequence to the size of the virtual IR buffer which is needed for optional retransmissions and
a second rate matching step linked to the adaptive coding technique
punctures a certain number of bits The decision on how many bits to
puncture and what bits to puncture is indicated as the redundancy ver-
sion This involves the principles of chase combining and incremen-
tal redundancy as explained in section 222 page 41 The size of the
virtual IR buffer depends on the UE category
Systematicbits
Separation of bits1st rate matching
Turbocoderoutput
Parity bits 1
Parity bits 2
HS-PDSCH
Redundancy version
Virtual IR buffer
2nd rate
matching
Fig 2-6 Basic principle of HARQ functionality on HS-PDSCH
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HS-DSCH High speed downlink shared channel transport channel
33
After the HARQ functionality step the remaining bits are segmented
into parallel streams due to the fact that the physical layer in HSDPA can
use several channelization codes for the physical channel HS-PDSCHDepending on the physical layer status which involves how many chan-
nelization codes can be used for transmission this step divides the data
into parallel streams Another step for error protection is the avoidance
of bundled errors Here the data sent in parallel HS-PDSCH codes is
interleaved to provide an interleaving gain to the channel decoder If
the 16QAM modulation scheme is used the following step of constel-
lation mapping will set a mapping scheme for which bits are mapped to
which modulation symbol The various constellation mapping schemes
are shown in Fig 2-15 page 45 Finally the resulting modulation
symbols must be mapped onto the physical channel ie they are first
spread with a channelization code having spreading factor 16 then
they are scrambled by using the NodeB specific primary or secondary
scrambling code and finally they are mapped on the carrier frequency
221 Brief digression into channel coding
Since channel coding is a substantial feature of HSPA a short digres-
sion into general aspects of channel coding is included here to help the
reader understand the procedures used in HSPA It is not the inten-
tion of this book to discuss channel coding in detail Interested read-
ers can seek out relevant literature on this topic eg [Ref 9] [Ref 10][Ref 11] and [Ref 14] HSDPA channel coding comprises block cod-
ing with CRC for error detection turbo coding for error correction
and interleaving to mitigate error bursts Channel coding is performed
in this order at the data source and in the reverse order at the data
sink Fig 2-7 below provides an overview of channel coding and its
components
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HSDPA operation overview and physical channels
Error detection
addedJ Block codingJ CRC attachmentJ Parity bits
Redundancy added
for error correctionForward errorcorrection (FEC) by J Convolutional codingJ Turbo coding
Rate matching
J PuncturingJ Repetition
Inter-
leaving
Deinter-leaving
Error correctionConvolutionaldecodingJ
Turbo decoding
Error detectionJ CRC check J Parity check
Transmitting end
Receiving end
Fig 2-7 General channel coding components example
Error detection ndash Example with block coding
Generally known as outer loop error correction this step involves
attachment of some error detection mechanisms that are added onto
the data block by the transmitter to enable the receiver to detect errorsCommon examples are parity bit attachments or cyclic redundancy
checks using the block coding principle Block coding involves calcu-
lating a certain number of parity bits for a block of data bits and then
appending them to the data block At the data sink ie the receiving
end errors in the received code word can be detected with the aid of
these redundancy bits
HSDPA uses a type of block code known as a cyclic redundancy check
(CRC) The cyclic codes of this type are also known as (nk) codes
where n represents the number of code symbols (bits) and k the num-
ber of data symbols (bits) The number of check bits is therefore nk
In HSDPA there is only one length of cyclic redundancy check Every
transport block in the HS-DSCH is followed by a 24-bit CRC An exam-
ple of how this CRC-based block coding works is given below
These check bits and thus the code word are produced by a generating
polynomial A polynomial is used to represent a bit sequence as a code
word with the power of each term in the polynomial corresponding to
a bit position and the coefficient of each term to a bit (Dm) A data word
with k bits is therefore represented as follows
Dk ∙ x
k
+ Dkndash1 ∙ x
kndash1
+ hellip + D983089 ∙ x + D983088
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HS-DSCH High speed downlink shared channel transport channel
35
An example could be the simple bit pattern 1101 which would repre-
sented as polynomial 983160983091 + 983160 + 1 i e 1 ∙ x 983091 + 0 ∙ x 983090 + 1 ∙ x 1048625 + 1 ∙ x 1048624
To calculate the check bits the data word D(x ) is multiplied by x nndashk
and then divided by the generating polynomial G(x ) which is of degree
(nndashk) The remainder R(x ) is the check word comprising the check bits
R x mainder x D x
G x
n k
( ) Re ( )
( )=
sdot
minus
The code word C (x ) is now obtained by appending the check word to
the data word
C (x ) = x nndashk ∙ D(x ) + R(x )
The receiver knows the generating polynomial G(x ) and performs the
division C (x )G(x ) If there are no transmission errors the code word
C (x ) is divisible by G(x ) The probability is therefore high that anyerrors will be detected The maximum number of errors per code word
that can be detected is determined by the length of the check word
which in our case is the length of the CRC But what is not known is the
position of those errors and thus there is no way to correct them This
is the responsibility of the ldquoinnerrdquo error correction such as the attach-
ment of redundancy bits which enable the receiver to correct some bit
errors Note that block codes can also be used in general to correcterrors but this is not performed in HSPA because this would increase
the overall latency time
Error correction performed with forward error correction (FEC)
principle of convolutional coding
With forward error correction (FEC) redundant bits are inserted into
data packets (bursts) at the transmitting end to enable the receiving
end to implement a correction mechanism The assumption is that theerrors do not occur in a burst Here the principle of a convolutional
coder is used This type of coder ldquoremembersrdquo the last n bits sent and
adds each input bit to the stored n bits The words obtained at the out-
put are usually longer than one bit The code rate defines the ratio of
the input bits to the output bits for example a coder using a code rate
of frac12 generates for each input bit a code word of two output bits Error
correction is based on the fact that a previous state ie a word or a bit
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HSDPA operation overview and physical channels
sequence can only assume one of two succeeding states depending on
whether 0 or 1 was entered into the coder ie the decoder decides for
the metric providing the minimum error estimation If a word arrivesat the receiver in a state that cannot be reached from a state obtain-
able from one of the two input combinations a transmission error has
occurred and needs to be corrected This procedure is equivalent to
tracing a path through a trellis diagram which is familiar from cod-
ing theory
We would now like to discuss a brief example to demonstrate the func-
tionality of channel coding and the subsequent steps of puncturing
Please note that this example does not represent the real coders used
in HSDPA Consult the relevant literature for further details of cod-
ing theory [Ref 10] [Ref 11] and [Ref 14] as well as the specification
[TS 25212 Ref 21] which describes the coding applied in HSPA
The convolutional coder shown in Fig 2-8 consists of one input fol-
lowed by three registers in a shift configuration and finally two out-puts With each clock generation the content of each register is shifted
one register to the right as the last registerrsquos content is discarded and
a new input bit is inserted into the first register The outputs 1 and 2
are generated by an XOR operation between the linked register con-
tents In this manner we create a finite response filter and a certain
memory effect Letrsquos assume we want to transmit the following input bit
sequence 110110 01 Here the nomenclature 01 means that the lastbit of our contemplated sequence can be either 0 or 1 and we wish to
consider both alternatives The registers are initialized with all 0s and
typically some tail bits are attached to the code word which will ensure
this for the succeeding code word The table in Fig 2-8 shows the input
bit on the left side the register sequence content after each step and
outputs 1 and 2 on the right side The output sequence for the given
input will be 11 01 01 00 01 011100 Note the last two lines in the table
We do assume an either or ie there are two alternatives such thatalternative A means that after the sequence 110110 has been sent to the
coder the following bit will be logical 0 Alternative B means that after
the sequence 110110 the following bit will be a logical 1 So we present
an either or situation This will be used to explain the coding principle
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HS-DSCH High speed downlink shared channel transport channel
37
Example of convolutional coding
Input Regis-
ter 1
Regis-
ter 2
Regis-
ter 3
Out-
put 1
Out-
put 2
XOR operation
Register 3Register 2Register 1
+
Input
Output 1
Output 2
+ +
1 1 0 0 1 1
1 1 1 0 0 1
0 0 1 1 0 1
1 1 0 1 0 0
1 1 1 0 0 1
0 0 1 1 0 1
Alt A 0 0 0 1 1 1
Alt B 1 1 0 1 0 0
Fig 2-8 Simple example for convolutional coding
In Fig 2-9 that follows there is a trellis diagram representing in each
column the four possible output values of our channel coder 00 01 10
or 11 and in bold color there is the trellis path through this diagram
resulting from the input sequence Recalling our definition of the two
alternatives for the last bit of our example code word we can see that
the rightmost part of this trellis diagram shows the two possible steps
From state 01 we can only reach either state 00 or state 11 The twoother states 01 or 10 are not possible and with no input to the coder
shown in Fig 2-8 the output can reach these two states in this step For
example if the receiver detects a sequence such as 11 01 01 00 01 01 01
it knows there is an error at the last position 01 which had to be cor-
rected as either 00 or 11 because only these two alternatives are pos-
sible The error correction is performed by looking at the total trellis
path and selecting the maximum likelihood sequence estimation basedon the received data pattern In our short example we admit that we
stopped at this point of course Imagine that the input sequence of bits
continues The decoder would not know if it should proceed with the
pattern 00 or 11 so the decision will be to continue both ways The fol-
lowing step is then checked again and one of the assumed ways will dif-
fer more from the demodulated pattern than the other one This prin-
ciple is described in the Viterbi algorithm [Ref 15] Based on this algo-
rithm the stronger path will survive ie the decoder checks at eachstep which path of the examined ones in the trellis path exhibits the
smallest deviation from the demodulation sequence and thus this path
will be continued The paths exhibiting a higher deviation are discarded
to reduce the calculation expense The path through the trellis diagram
is called a ldquometricrdquo and the term ldquomaximum likelihood sequence esti-
mationrdquo (MLSE) represents the selection by the channel decoder of the
real possible metric which is the closest to the received data pattern As
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HSDPA operation overview and physical channels
an analogy If we do a crossword puzzle and find some characters in a
word the channel decoder would check in a primer or dictionary of the
language containing all possible character combinations that we callldquowordsrdquo and select the existing word that has the maximum likelihood
for the prevailing sequence of characters
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
Alternative B
Alternative A
Register 2
+ +
+
Output 1
Output 2
XOR operation
Trellis diagram above showsmetric for input sequence
110110 0
or 1
into a coder such as
1
1
0
1 10
0
1
Register 3Register 1
Fig 2-9 Metric in trellis diagram
Interleaving
Forward error correction based on convolutional coders has one disad-
vantage related to the impact of block errors If the transmission errors
are distributed they can be corrected as demonstrated in the trellis dia-gram example using the Viterbi algorithm but if many adjacent bits
are lost the decoder will have problems retrieving the right bit pattern
Interleaving means that the information to be transmitted is spread or
distributed over several bursts in such a way that contiguous informa-
tion is split up and transmitted in a time or block distributed mode
To avoid error bursts an attempt is made to spread the bit errors over
several code words This is achieved by interleaving several code wordsThis method is also called diagonal interleaving see Fig 2-10 Another
kind of interleaving is block interleaving as shown in Fig 2-11 Blocks
of code words are written row-by-row into a matrix and then read col-
umn-by-column With both methods consecutive bits of a code word
are never transmitted consecutively and conversely when the bits are
deinterleaved at the receive end error bursts are spread over several
code words
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HS-DSCH High speed downlink shared channel transport channel
39
As several code words are interleaved the decoder has to ldquowaitrdquo a cer-
tain time until all bits of a particular code word arrive This delay ie
the ldquomeasure for spreading over timerdquo is referred to as the ldquointerleav-ing depthrdquo The greater the interleaving depth the more code words are
available for spreading the error bursts and the greater the probability
that errored bits can be corrected but on the other hand this increases
the overall latency time
HSDPA uses the block diagonal interleaving principle for the HS-DSCH
only since as we should recall one goal is to have a short round-trip
time
Spreadinghellip
Interleaving
hellip
hellip
Fig 2-10 Diagonal interleaving
Write
Read
Interleaving-Matrix
Fig 2-11 Block interleaving
Puncturing
Having briefly described the principle of convolutional coding another
mechanism will be presented that is used to increase the throughputof user data and coordinate with the AMC mechanism described in
section 12 page 10 After adding redundancy the total bit stream is
now known as soft bits ie the sum including all of the raw data bits
at the input of the channel coder plus the added redundancy bits This
quantity must match the required transport block size demanded by
the transport layer and the process performed here is called rate match-
ing ie deleting some of the soft bits at the transmitting end in a pre-
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HSDPA operation overview and physical channels
defined manner or repeating or adding some stuffing bits In HSPA the
rate matching mechanism uses puncturing which provides higher data
throughput The signaled values TBS and RV tell the receiving convo-lutional coder how many and where bits have been punctured This
allows the decoder to insert blank positions which have to be filled later
by performing trellis decoding In other words we may consider the
punctured bits as bit losses created intentionally by the transmitter In
this manner the total amount of data bits can be increased for the sake
of lower redundancy In HSDPA this puncturing scheme will be very
flexible and the NodeB scheduler will set the puncturing rate adapted
to the prevailing RF conditions on the radio channel to obtain the high-
est possible data throughput under the existing conditions The disad-
vantage of adaptive coding is that we need signaling information so
that the transmitter has to inform the receiver about how many soft bits
have been punctured This is seen in Fig 2-26 page 55 in the form
of the redundancy version carried by the HS-SCCH control channel
Fig 2-12 below again depicts the principle of puncturing in HSDPAand clarifies some signaling parameters such as the transport block size
1 1 0 1 1 0 0
11 01 01 00 01 01 11
Transport block sizeInput bits into channel coder
Soft bitsOutput from channel encoder
Rate matchingPuncturing or repeating bits
11 01 01 00 01 01 11
1 01 0 00 0 01 1Coded composite transport bitsCan be several combined streams aftercoding + rate matching
Transport block size FEC
Fig 2-12 Puncturing based on coding example from Fig 2-8 page 37
The process of channel coding starts first with the transport block
size which is given by the size of the input data bit sequence added
by a cyclic redundancy checksum The next step is the channel cod-
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HS-DSCH High speed downlink shared channel transport channel
41
ing which is performed in HSPA by a so-called turbo coder The turbo
coder is a parallel concatenated convolutional coder that exhibits bet-
ter reliability compared to a single convolutional coder Discussingthe functionality of a turbo coder in all of its details would represent a
major digression from the intention of this book Accordingly we will
simply encourage the interested reader to consult the channel coding
literature for more details about turbo coders and their applications
[Ref 10] [Ref 12] Determined by the scheduler of the base station or
the redundancy version to be used the next step known as the redun-
dancy version will either puncture (the most likely) or repeat some of
the bits resulting from the channel coding process How many bits will
be punctured is defined by the coding rate In our example in Fig 2-12
we see that the input bit sequence has a length of 7 bits resulting in
14 soft bits after channel coding with our example coder providing a
coding rate of frac12 The scheduler decided to puncture 4 bits so that we
finally obtain 10 bits which have to be mapped on the physical chan-
nels Our overall coding rate is therefore given as ⁷frasl983089983088 In other words
some bits are protected with redundancy information while othersare not Note that the size of the coded composite transport channel
is determined by the physical layer parameters such as the number of
channelization codes used to convey the HS-PDSCH the modulation
scheme and the transmit time interval which is constant for HSDPA
but can be either 2 or 10 ms for HSUPA Thus its size does not need
to be signaled to the receiver and only the transport block size and the
redundancy versions will be contained in the HS-SCCH channel
222 Incremental redundancy and chase combining
for HS-DSCH
Until now we have presented some general characteristics of HSDPA
and HSUPA which we would now like to discuss in a combined pro-
cedure and then deduce two other principles The HARQ abbreviationcombines an automatic retransmission of erroneous data with a soft
combination at the receiving end A related question can now be how
the transmitter has to repeat the transport block should the retrans-
mission of data occur in an identical retransmission mode or should
some changes in coding parameters eg the manner of puncturing be
applied This question is also important for the implementation of the
rate matching step shown in Fig 2-12 The transmitter has to provide
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HSDPA operation overview and physical channels
a certain soft buffer ie a memory that stores the transmitted data for
the sake of possible retransmissions and deletes it after having received
a positive acknowledgment from the receiver Should the transmitternow store the coded composite transport data i e the data after coding
but also after puncturing This would restrict it to repeating the data in
an identical manner A better approach is to store the data after channel
coding and before puncturing Even if this requires more memory it
gives the flexibility to change the puncturing scheme and retransmit the
transport block in a different way Fig 2-13 and Fig 2-14 represent both
mechanisms that are used in HSDPA and HSUPA Identical retransmis-
sion is called chase combining and non-identical retransmission with
a different puncturing scheme is called incremental redundancy The
scheduler in the base station can decide which retransmission scheme
will be used We do not wish to delve into the details of channel coding
theory to discuss which mechanism is the better one ndash chase combin-
ing or incremental redundancy We will only mention that both mech-
anisms have their advantages and thus their applications Chase com-
bining has the advantage that the systematic bits representing the orig-inal data input into the channel coder are contained in the transmit-
ted sequence after puncturing Thus chase combined transport blocks
are ldquoself-decodablerdquo If we consider a situation where the original trans-
port block is lost completely and only the retransmitted block is pres-
ent at the receiver there is a chance to decode the data properly Mean-
while incremental redundancy seems to add more redundancy when
retransmitting but in a scenario where the first transmission contain-ing the systematic bits is lost completely and only the retransmission
is present the receiver will have no chance to decode the data without
having some of the systematic bits Accordingly incremental redun-
dancy is applied whenever sporadic bit errors occur due to a time vari-
ant channel and chase combining is selected whenever we have to deal
with complete transport block errors i e the time variance of the radio
link exhibits some bursted fading dips
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HS-DSCH High speed downlink shared channel transport channel
43
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Chase combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Transmitted bit
Punctured bit
Systematic bits
Parity 1
Parity 2
Systematic bits
Parity 1
Parity 2
Fig 2-13 Chase combining principle
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Incremental redundancy combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Systematic bits
Parity 1
Parity 2
Systematic bitsParity 1
Parity 2
Fig 2-14 Incremental redundancy
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HSDPA operation overview and physical channels
223 Constellation rearrangement
Due to the fact that HSDPA introduces a higher-order modulationscheme (16QAM) we can recognize some effects due to the physi-
cal layer influencing the susceptibility to noisy RF conditions One of
these effects can be explained by looking at the constellation diagram
in the 16QAM modulation scheme see section 12 page 10 As we
recall there is a total of 16 different constellation points given by the
modulation vector and represented by its phase and amplitude Con-
sidering the Euclidean distance which is the distance in this constella-
tion diagram between two neighboring points we can clearly see that
some points have more neighbors than others Especially the four con-
stellation points at the very four corners only have three direct neigh-
bors making them less susceptible to misdetection due to noise shift-
ing them in a certain direction On the other hand the four constella-
tion points representing the inner square of the constellation have eight
direct neighbors each and are therefore more likely to be incorrectly
detected The idea of constellation rearrangement is now to change themapping scheme applied in the original transmission when retrans-
mitting As we know the receiver will soft combine the retransmit-
ted data with the previously received information so we can achieve a
certain incremented redundancy and a certain protection mechanism
Note however that considering a sole transmission of a transport block
using a certain constellation arrangement will not show any more pos-
itive or negative results compared to other constellation arrangementsThe redundancy gain is only achieved by rearranging the constellation
mapping in a retransmitted transport block and performing soft com-
bining at the receiver Overall HSDPA defines four constellation rear-
rangement schemes which are indicated in the redundancy version
field of the HS-SCCH and are represented by the ldquobrdquo bit field ranging
from b = 0 to b = 3 All four constellation schemes are Gray encoded
ie the directly adjacent constellation symbols do not exhibit four com-
pletely different bits in order to reduce the impact of misdetection onbit errors
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High speed shared control channel (HS-SCCH)
45
Q
I
(ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1) (1 1ndash1ndash1)
(ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1) (1 1ndash1 1)
(ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1) (1ndash1ndash1 1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 0
Q
I
(ndash1 1 1 1) (ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1)
(ndash1 1 1ndash1) (ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1)
(ndash1ndash1 1ndash1) (ndash1ndash1ndash1ndash1) (1ndash1ndash1ndash1) (1ndash1 1ndash1)
(ndash1 1 1 1) (ndash1ndash1ndash1 1) (1ndash1ndash1 1) (1ndash1 1 1)
b = 2
Q
I
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (1ndash1 1 1) (ndash1ndash1 1 1)
(ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1) (ndash1 1 1 1)
(ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1) (ndash1 1 1ndash1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 1
Q
I
(1 1ndash1 1) (ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1)
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1)
(1ndash1ndash1ndash1) (ndash1ndash1ndash1ndash1) (ndash1ndash1 1ndash1) (1ndash1 1ndash1)
(1 1ndash1ndash1) (ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1)
b = 3
Fig 2-15 Constellation rearrangement in HSDPA
23 High speed shared control channel (HS-SCCH)
The HS-SCCH sends scheduling information to the UEs As seen before
the HS-PDSCH has a very flexible configuration for physical parame-
ters such as the coding rate number of code channels or retransmis-sions This high flexibility increases the complexity and engenders the
need for additional signaling information transferred on the HS-SCCH
Reception of user data in HSDPA is always a two-step procedure
First the receiver has to capture the scheduling control information
and afterwards based on the received control information it may start
demodulating and decoding the HS-PDSCH containing the user data
This two-step procedure is shown in Fig 2-16 below which lists what
kind of control information is sent to the UEs via the HS-SCCH Asshown in Fig 2-2 page 28 which describes the overall HSDPA chan-
nel structure there can be up to four HS-SCCHs assigned to one UE
But only one HS-SCCH would contain the scheduling information for
this UE within one TTI Thus the network can assign resources simul-
taneously to various UEs in the downlink direction
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HSDPA operation overview and physical channels
I would like to receive databut I dont know where myHS-PDSCH resources areand what they look like
HS-SCCH
Read the 1st HS-SCCH slotfor HS-DSCH channelizationcodes UE identity and
modulation scheme
Then the 2nd and 3rd HS-SCCHslots provide transport block sizeinformation hybrid ARQ process in-formation redundancy constellationversion new data indicator
HS-PDSCH
Fig 2-16 HS-SCCH control channel usage
Regarding the physical layer parameters we see in Fig 2-17 that the
HS-SCCH uses a channelization code with a spreading factor of 128
and it also uses the newly introduced transmit time interval of one sub-
frame which is equal to 2 ms It should be mentioned that the spread-ing factor of 128 requires double the capacity compared to similar con-
trol channels in WCDMA Release 99 reflecting the signaling overhead
needed to guarantee the huge flexibility introduced with HSDPA Addi-
tionally Fig 2-16 shows that the control information is sent consecu-
tively within one subframe The first slot within this subframe contains
the control information UE identity channelization code information
and modulation scheme identifier Slots 2 and 3 of the subframe con-tain the remaining control information Transport block size HARQ
process identifier redundancy version and new data indicator Conse-
quently the UE can self-decode slot 1 alone and slots 2 and 3 in a sec-
ond step even if they represent one logical unit This raw control infor-
mation is of course also channel coded using a turbo and on the phys-
ical layer the quantity of bits after the rate matching step is 40 bits con-
veyed in one slot corresponding to 666 micros [TS 25212 Ref 21] see also
Fig 2-28 page 56
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High speed shared control channel (HS-SCCH)
47
The HS-SCCH is a fixed rate (60 kbps SF = 128) downlinkphysical channel used to carry downlink signaling related toHS-DSCH transmission
Slot 0
Slot 1
Slot 2
Tslot
= 2560 chips
Data = 40 bits
1 subframe = 2 ms
Fig 2-17 Structure of High speed shared control channel HS-SCCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
We would like to return now to the time consecutive transmission of
control information There is a difference in the control information
in terms of its priority Some information is needed at the UE end
very urgently while other control information does not have such a
high priority But why This will be explained by looking at some tim-ing aspects defined for HSDPA If we consider the timing between
the shared data channel HS-PDSCH and the shared control chan-
nel HS-SCCH as shown in Fig 2-18 we see that the HS-PDSCH fol-
lows the HS-SCCH by exactly two slots or 5120 chips The HS-SCCH
is completely time-aligned with the general control channels CPICH
and P-CCPCH of the NodeB This is mandatory because it is a shared
channel Consider several UEs with different distances to the NodeBwanting to receive the HS-SCCH channel Thus it must have constant
timing that is known a priori The shared data channel HS-PDSCH is
now transmitted exactly 5120 chips after the first chip of the HS-SCCH
This leads to an overlapping slot thereby requiring multitasking recep-
tion at the UE end While the UE is still receiving the last slot of an
ongoing HS-SCCH subframe it may already start the reception of an
HS-PDSCH transport block The first slot in the HS-SCCH subframe
now contains information required by the physical layer to performdespreading and demodulation These values are the UE identity indi-
cating whether the UE will start demodulation of the HS-PDSCH or
not in case it is not scheduled the modulation scheme information
since the UE has to know how to interpret the received constellation
vector and whether it has to be considered as a QPSK or 16QAM con-
stellation point and finally the UE has to know which channelization
codes it has to apply to capture the HS-PDSCH transport block The
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HSDPA operation overview and physical channels
overall UE reaction time when being scheduled is now seen as 1 slot
or 2560 chips This tough requirement for the UEs is due to the objec-
tive to obtain overall a much shorter latency than legacy standards Theadditional control information such as the new data indicator redun-
dancy version and transport block size is not that urgent since it is
needed after demodulation but before channel decoding So first the
UE will sample the whole three slots of the HS-PDSCH and demodu-
late them into a bit stream which is finally handed over to the channel
decoder This principle is known as post-processing and is used typi-
cally in mobile communications technologies
J Start of HS-SCCH subframe 0 is aligned with startof P-CCPCH frames
J The HS-PDSCH starts
τ HS-PDSCH
(2times Tslot
= 5120 chips)
after the start of the HS-SCCH
UE identity etc
processing timeof receiver
HS-DSCH subframe
3 times Tslot= 7680 chips
3 times Tslot
= 7680 chips
τ HS-PDSCH
(2times Tslot
= 5120 chips)
HS-SCCH
HS-PDSCH
Fig 2-18 Timing relation between HS-SCCH and HS-PDSCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
Content of the HS-SCCH control channelThe control information contained in the HS-SCCH control chan-
nel has already been mentioned so we will now consider the values
in more detail We will begin with an overview of what kind of control
information is contained in the HS-SCCH channel before proceeding
with further details about the single control elements The following
control information is present in the HS-SCCH [TS 25212 Ref 21]
Channelization code set information (7 bits)
Modulation scheme information (1 bit) Transport block size information (6 bits)
Hybrid ARQ process information (3 bits)
Redundancy and constellation version (3 bits)
New data indicator (1 bit)
UE identity (16 bits) = H-RNTI
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High speed shared control channel (HS-SCCH)
49
Some of these parameters are more or less self-explanatory while oth-
ers require additional background information and closer examination
Modulation scheme information 1 bit
This single bit is used to inform the receiver whether the modulation
scheme QPSK or 16QAM is applied on the data channel HS-PDSCH
The interpretation of the bit x ms1 is as follows
ms1
x
if QPSK
otherwise
0
1
=
New data indicator 1 bit
The new data indicator bit field informs the receiving entity that the
prevailing PDU transmitted by the current HARQ process is either a
retransmission or contains new data This is done by setting the new
data bit to the value 0 for the first PDU on this particular HARQ process
and incrementing the value by 1 with every new data sent [TS 25321Ref 30] This leads to a toggled value In case the new data bit is not
incremented ie if it remains at its previous value it is an indicator for
retransmission
1st PDU of this
HARQ process
NDI = New data indicator
NDI = 0 NDI = 1
NACK
NDI = 1
ACK
NDI = 0
HS-SCCH HS-SCCH HS-SCCHHS-SCCH
ACK
Fig 2-19 New data indicator bit principle of incrementing value
Channelization code set information 7 bits
This field is used to indicate the number of channelization codes usedfor transmitting the transport block on the HS-PDSCH As was already
described the spreading factor applied on the HS-PDSCH is constant
with a value of 16 but the flexible values are the number of channeliza-
tion codes forming a cluster when using multiple codes and their posi-
tion in the code tree It is not allowed to distribute the code channels
over the code tree diagram For the sake of simplicity in signaling sev-
eral channelization codes form one cluster and these codes are con-
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HSDPA operation overview and physical channels
tiguous in the channelization code tree [TS 25213 Ref 22] Fig 2-20
illustrates the principle of indicating the channelization codes on the
HS-SCCH
SF = 16
Code ldquo0rdquo isreserved forcommonchannels
Code offset 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15P = 5O = 7
Code group indicatorx
ccs1 x
ccs2 x
ccs3 = min (Pminus 1 15 minusP)
Code offset indicatorx
ccs4 x
ccs5 x
ccs6 x
ccs7 = |Ominus 1minus P8 times15|
A cluster of codes
can be allocated to a UEC
ch16Ohellip C
ch16O + P minus 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1
2 2 2 2 2 2 2 2 2 2 2 2 2 2 14 14
1 2 3 4 5 6 7 8 9 10 11 12 13 14 2 1
3 3 3 3 3 3 3 3 3 3 3 3 3 13 13 13
1 2 3 4 5 6 7 8 9 10 11 12 13 3 2 1
4 4 4 4 4 4 4 4 4 4 4 4 12 12 12 121 2 3 4 5 6 7 8 9 10 11 12 4 3 2 1
5 5 5 5 5 5 5 5 5 5 5 11 11 11 11 11
1 2 3 4 5 6 7 8 9 10 11 5 4 3 2 1
6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10
1 2 3 4 5 6 7 8 9 10 6 5 4 3 2 1
7 7 7 7 7 7 7 7 7 9 9 9 9 9 9 9
1 2 3 4 5 6 7 8 9 7 6 5 4 3 2 1
8 8 8 8 8 8 8 8
8 7 6 5 4 3 2 1
0 (115)
1 (214)
2 (313)
3 (412)
4 (511)
5 (610)
6 (79)
7 (88) Redundant area
C l u s t e r c o d e i n d i c a t o r ( 3 b i t s )
Tree offset indicator (4 bits)
Signaled on HS-SCCH
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
PO
Decoding notation
Number ofmulti-codes
Offset fromleft right incode tree (SF = 16)
Fig 2-20 Channelization code set indicating the HS-PDSCH code cluster
The idea behind the code indication is a matrix with the rows repre-
senting the number of codes per cluster and the columns represent-
ing the position of that cluster the offset value in the code tree Recall-
ing that the maximum number of channelization codes per clusteris 15 and if the cluster size is 1 the offset values can also range from
1 to 15 the resulting matrix would have 15 rows and 15 columns Since
we know that four bits are needed to represent an integer from 1 to 15
we need a total of 4 + 4 = 8 bits for representation of the channeliza-
tion code set information It is a smart idea to save one bit The 15 times 15
matrix would contain much redundant information By way of analogy
like in a road map indicating distances between cities A table showing
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High speed shared control channel (HS-SCCH)
51
the distance from city A to city B the opposite distance from city B to
city A is redundant information The useful information has the form
of a triangle The idea is to cut the lower part rotate it and append itto the spare part of the upper table In this manner a table is obtained
with 7 rows and 15 columns and it is possible to indicate each position
in it with just 7 bits
1 5 r o w s 7
r o w s
Matrix reduction for channeli-
zation code set information
15 columns
Fig 2-21 Matrix size reduction for channelization code set information
The content of the channelization code set matrix can be described as
a value with two numbers The upper number is the number of mul-
ticodes forming one cluster and the lower number is the offset in the
channelization code tree Accordingly the example in Fig 2-20 can be
interpreted to mean the HS-SCCH sends the bits as row number 4 and
column number 6 in the matrix The content of this element are the
values 5 over 7 which have to be interpreted as a cluster size of 5 codesand an offset of 7
Transport block size information 6 bits
With a length of six bits the transport block size (TBS) informa-
tion informs the receiving UE entity about the data block size of the
transport block sent on the HS-PDSCH We should keep in mind the
link adaptation performed with the adaptive modulation and coding
scheme that was described in section 12 page 10 The ratio errorcorrection and user data are flexible while the physical layer param-
eters such as the spreading factor modulation scheme and number of
channelization codes determine the physical block size This physical
block consists of the user data ratio or transport block size and the for-
ward error correction or redundancy information As this ratio is flex-
ible the HS-SCCH will inform the receiving UE entity about the size
of the transport block Here too there is a strategy of bit reduction the
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HSDPA operation overview and physical channels
goal is to inform the receiver with as few bits as possible A non-effi-
cient approach would involve conversion of the decimal number repre-
senting the TBS into a binary sequence but the number of bits neededwould exceed the space available on the HS-SCCH Imagine that the
range of transport block sizes depends on the physical layer condi-
tions The ambient physical layer parameters modulation scheme and
number of channelization codes set a certain working point where the
remaining flexibility for a different TBS configuration can be obtained
by more or less puncturing resulting in a flexible ratio between for-
ward error correction and user data This will lead to a two-step proce-
dure when evaluating the transport block size First the receiver exam-
ines the information modulation scheme and number of channeliza-
tion codes scheduled via HS-SCCH which indicate the value k0 l as
shown in Fig 2-22 The 6-bit HS-SCCH control parameter transport
block size information will be the transport format resource indica-
tor (TFRI) named ki Let k t be the sum of the two values kt = ki + k0i
Both values kt and k0 i can be obtained from tables given by [TS 25321
Ref 30] The range for the TFRI is from 1 to 256 and the derived trans-port block size ranges from 137 bits to 27 952 bits The first table indi-
cates the value k 0 i based on the channelization code and the modula-
tion scheme
Combination i Modulation scheme Number of channelization codes k0 i
0
QPSK
1 1
1 2 40
2 3 633 4 79
4 5 92
5 6 102
Fig 2-22 Extract from TS 25321 table representing k0 i
The second table indicates the final transport block size based on kt
Index TB size Index TB size Index TB size1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
4 173 89 1456 174 6673
5 185 90 1483 175 6793
6 197 91 1509 176 6916
7 209 92 1537 177 7041
Fig 2-23 Extract from TS 25321 table representing kt
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High speed shared control channel (HS-SCCH)
53
J The transport block size used on HS-DSCH is not signaled explicitly on HS-SCCHJ Instead a transport block size index k
i is signaled to indicate the transport block size
First stepModulation scheme andnumber of channelizationcodes as signaled on HS-SCCHdetermine value k
0 i
Second step
Index kt = k
i + k
0i
determines HS-DSCH
transport block size
kt = k
i + k
0i
Table according to 3GPP TS 25321 extract from QPSK section
Table according to 3GPP TS 25321 254 entries in total
Combination i Modulation
scheme
Number of
channelization codes
k0 i
0
QPSK
1 1
1 2 40
2 3 63
3 4 79
4 hellip hellip
Index TB size Index TB size Index TB size
1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
helliphellip hellip hellip hellip hellip
Fig 2-24 Retrieval of transport block size information
Source Fig 2-22 to Fig 2-24 [TS 25321 Ref 30] reproduced by permission of 3GPP
Hybrid ARQ process information 3 bits
The concept behind the hybrid automatic repeat request (HARQ) was
introduced in section 13 page 14 One feature is the possibility of
multitasking ie having several HARQ processes activated at the same
time Fig 2-25 below shows the need to signal the process identity tothe receiver Remember that on the downlink there is a shared chan-
nel concept so the NodeB can flexibly decide which UE will be sched-
uled with a downlink transport block Up to eight HARQ processes
can be signaled via higher layers to one UE Note however that due to
the round-trip timing six HARQ processes must be active to achieve
the maximum throughput as shown in Fig 2-51 page 79 Compared
with HSUPA the HARQ processes on the downlink are asynchronous
so they have to be indicated but on the uplink they are synchronous sothey do not need to be signaled explicitly
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HSDPA operation overview and physical channels
Asynchronous DL minus Synchronous ULNumber of H-ARQ rocesses = 1 to 8 er UE
UL HS-DPCCH UE1
UE1 HARQ processes 1 to 4
3 4 1 42 11 1 32retrans
2
A N A A
A A
N A
UL HS-DPCCH UE2
HS-PDSCH
UE2 HARQ processes 1 to 2
Fig 2-25 HARQ process indication on HS-SCCH
Fig 2-25 shows a typical situation on the downlink (point-to-multi-
point) The NodeB sends data to several UEs sharing the HS-PDSCH
so therefore the HARQ process is asynchronous The time when a
transport block is retransmitted is not fixed For this reason the pro-
cess identifier is signaled on the HS-SCCH Based on the HARQ pro-
cess identity and the new data indicator bit the receiving entity knows
which part of the soft buffer memory has to be used in case of soft com-bining On the uplink the situation is slightly simpler The UE only
communicates with one NodeB so it is a point-to-point connection
Thus retransmission always occurs at a fixed time linked to the origi-
nal transmission
Redundancy and constellation version 3 bits
Adaptive modulation and coding involve flexible selection of modula-tion and coding schemes that are signaled to the receiving UE via the
parameters transport block size and modulation scheme information
Another concept used in HSDPA was previously discussed Chase com-
bining or incremental redundancy (see section 222 page 41) This
means that in case of retransmission the transmit entity can dynami-
cally select another puncturing scheme or keep the puncturing as it was
in the original transmission The applied puncturing scheme is signaled
as redundancy information to the receiver Additionally in case of the16QAM modulation scheme the transmitter can select another constel-
lation arrangement which is also signaled to the UE with the three bits
for the redundancy and constellation version see Fig 2-15 page 45
Depending on the modulation scheme (QPSK or 16QAM) there are
two different tables indicating the parameters ldquosrdquo ldquorrdquo and ldquobrdquo The
parameters ldquosrdquo and ldquorrdquo indicate which scheme is used for puncturing
ie if the puncturing mechanism prioritizes the systematic bits or not
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High speed shared control channel (HS-SCCH)
55
and which puncturing algorithm is used The parameter ldquobrdquo indicates
the constellation mapping version The receiver needs this information
to perform proper demodulation and decoding
Initial transmission
1st retransmission
2nd retransmission
3rd retransmission
r
0
0
1
1
2
2
3
xrv
(value)
s
0 1
1 0
2 1
3 0
4 1
5 0
6 1
7 0 3
s = 1 Systematic bits are prioritizeds = 0 Non-systematic bits are prioritized
r (range 0 to 3 for QPSK) influencesJ Input parameter for puncturing or (together with s) for repetition algorithm defined in TS 25212J Selection of parity bits
Redundancy version coding sequences are signaled on HS-SCCH egndash 0 2 5 6 One initial transmission + 3 retransmissions with different r and s parameters
Fig 2-26 Signaling of redundancy version parameters r and s QPSK case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
Initial transmission
2nd retransmission
1st retransmission
3rd retransmission
r (range 0 to 1 for 16QAM)influences input parameterfor puncturing or (togetherwith s) for repetitionalgorithm defined in
TS 25212 and thus selectionof parity bits
Redundancy version coding sequences are signaled on HS-SCCH egminus 6 4 0 5 Chase combining (no change in s and r parameters ie same redundancyversion) with four possible constellations
x rv (value) s r b
0 1 0 0
1 0 0 0
2 1 1 1
3 0 1 1
4 1 0 1
5 1 0 2
6 1 0 3
7 1 1 0
Definition of parameter s as for QPSK
b (range 0 to 3) describes constellationrearrangement to averagereliability of bits
Fig 2-27 Signaling of redundancy version parameters r s and b 16QAM case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
UE identity H-RNTI 16 bits
The HSDPA radio network transaction identifier (H-RNTI) unam-
biguously identifies the UE having an HS-PDSCH assignment within
a cell It is allocated to the UE via layer 3 signaling procedures at the
radio bearer setup if the radio bearer is an HSDPA connection This
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HSDPA operation overview and physical channels
value represents a temporary name of the UE used to address it when
scheduling data packets via HS-SCCH
HS-SCCH channel coding
The control information contained in the HS-SCCH is of course pro-
tected with channel coding mechanisms the whole coding chain is
described in Fig 2-28 Fig 2-18 page 48 presents the separation of
the control information into two code blocks which are sent consec-
utively mapped on slot 1 and slot 2 + 3 of one HS-SCCH subframe
This principle is also visible in the coding chain The first control block
consisting of channelization information modulation scheme and UE
identity is coded separately from the remaining control values to enable
the UE receiver to decode this first slot separately and prepare for pos-
sible HS-PDSCH reception The coding steps shown in Fig 2-28 such
as rate matching 1 and 2 are similar to the HS-PDSCH coding chain
and are further described in [TS 25212 Ref 21]
Channelcoding 1
R atematching 1
mux
Channelcoding 2
Ratematching 2
RVcoding
UE-specificCRC attachment
UE-specificmasking
Physical channelmapping
r s b
mux
Channelizationcode set
Modulationscheme
Transport block size information
HARQ processinformation
Redundancy andconstellation version
New data indicator
UE identity
UE identity
Fig 2-28 Channel coding for HS-SCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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High speed dedicated physical control channel (HS-DPCCH)
57
24 High speed dedicated physical control channel (HS-DPCCH)
In an active HSDPA connection the UE has to send acknowledgment ornon-acknowledgment reports (as described in section 13 page 14
where the HARQ process is described) as well as channel status infor-
mation to the network The reporting is performed on this physical
control channel HS-DPCCH
As ubiquitous in HSDPA the uplink is also configured into a subframe
structure of 2 ms corresponding to three slots The first slot of the sub-
frame carries the ACK NACK information the UE sends to the NodeB
while the following two slots ie slot 2 and 3 of the subframe convey
the CQI value the channel quality information to the NodeB
Subframe 0 Subframe i Subframe 4
Tslot
= 2560 chips J The spreading factor of theHS-DPCCH is 256 (10 bits peruplink slot)
J The HS-DPCCH can only existtogether with an UL DPCCH
(ded phys control channel)J The DPDCH (dedicated physical data channel) the DPCCH andthe HS-DPCCH are IQ codemultiplexed
HARQ-ACK CQI = Channel quality information
2 times Tslot
= 5120 chips
One radio frame Tf = 10 ms
One HS-DPCCH subframe 2 ms
Fig 2-29 HS-DPCCH configuration
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The slot format for HS-DPCCH describes a quantity of 30 bits per sub-frame resulting in a data rate of 15 kbps The spreading factor used for
the HS-DPCCH is constant and is always equal to 256 but the chan-
nelization code that is used as well as the mapping on either the I or
Q axis depends on several factors eg the co-existence of an HSDPA
connection with a circuit-switched connection meaning whether a
DPDCH established or not Fig 2-36 page 64 illustrates this IQ
mapping and Fig 2-35 page 63 shows the channelization code used
for HS-DPCCH
The HS-DPCCH builds a logical unit of one subframe but having the
independent control information HARQ-ACK and CQI included which
could be separately decoded at the NodeB Note that the slot carrying
the ACK NACK statement is active only when the UE has been sched-
uled by an HS-PDSCH subframe in the corresponding downlink sub-
frame previously Assuming the UE has not received a transport block
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HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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HSDPA operation overview and physical channels
The data arriving here is represented by a MAC-hs PDU a protocol
data unit coming from the MAC layer and representing a transport
block that is sent once every transmit time interval of 2 ms The firststep in the coding chain is the attachment of a cyclic redundancy check
(CRC) with a length of 24 bits to the transport block In HSDPA the
CRC is used for error detection and the ACK NACK feedback sent by
the UE is based on the CRC status The next step involving bit scram-
bling uses a bitwise XOR combination of the input bits with a pseudo-
random bit sequence to randomize the data and avoid long sequences
of constant bits that can prevent proper decoding This is a precon-
dition for the turbo coder performed two steps later To speed up the
channel coding process and for memory reasons the turbo coder has a
maximum limit of 5114 input bits If the transport block is larger than
5114 bits it will be split into several parallel coding segments and chan-
nel coding will be performed in a parallel architecture HSDPA uses
the turbo coding principle with a code rate of ⅓ ie for one input bit
the turbo coder generates three output bits Turbo coding generates
systematic bits representing the input along with two groups of par-ity bits [Ref 12] They are handled separately particularly in the sub-
sequent puncturing process The step physical layer HARQ functional-
ity represents several puncturing and buffering procedures It includes
a two-stage rate adaptation to the subsequent HS-PDSCH formats see
Fig 2-6 The redundancy version signaled on HS-SCCH controls this
process A first step separates the bits into systematic and parity bits a
first rate matching step constrains the bit sequence to the size of the virtual IR buffer which is needed for optional retransmissions and
a second rate matching step linked to the adaptive coding technique
punctures a certain number of bits The decision on how many bits to
puncture and what bits to puncture is indicated as the redundancy ver-
sion This involves the principles of chase combining and incremen-
tal redundancy as explained in section 222 page 41 The size of the
virtual IR buffer depends on the UE category
Systematicbits
Separation of bits1st rate matching
Turbocoderoutput
Parity bits 1
Parity bits 2
HS-PDSCH
Redundancy version
Virtual IR buffer
2nd rate
matching
Fig 2-6 Basic principle of HARQ functionality on HS-PDSCH
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HS-DSCH High speed downlink shared channel transport channel
33
After the HARQ functionality step the remaining bits are segmented
into parallel streams due to the fact that the physical layer in HSDPA can
use several channelization codes for the physical channel HS-PDSCHDepending on the physical layer status which involves how many chan-
nelization codes can be used for transmission this step divides the data
into parallel streams Another step for error protection is the avoidance
of bundled errors Here the data sent in parallel HS-PDSCH codes is
interleaved to provide an interleaving gain to the channel decoder If
the 16QAM modulation scheme is used the following step of constel-
lation mapping will set a mapping scheme for which bits are mapped to
which modulation symbol The various constellation mapping schemes
are shown in Fig 2-15 page 45 Finally the resulting modulation
symbols must be mapped onto the physical channel ie they are first
spread with a channelization code having spreading factor 16 then
they are scrambled by using the NodeB specific primary or secondary
scrambling code and finally they are mapped on the carrier frequency
221 Brief digression into channel coding
Since channel coding is a substantial feature of HSPA a short digres-
sion into general aspects of channel coding is included here to help the
reader understand the procedures used in HSPA It is not the inten-
tion of this book to discuss channel coding in detail Interested read-
ers can seek out relevant literature on this topic eg [Ref 9] [Ref 10][Ref 11] and [Ref 14] HSDPA channel coding comprises block cod-
ing with CRC for error detection turbo coding for error correction
and interleaving to mitigate error bursts Channel coding is performed
in this order at the data source and in the reverse order at the data
sink Fig 2-7 below provides an overview of channel coding and its
components
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HSDPA operation overview and physical channels
Error detection
addedJ Block codingJ CRC attachmentJ Parity bits
Redundancy added
for error correctionForward errorcorrection (FEC) by J Convolutional codingJ Turbo coding
Rate matching
J PuncturingJ Repetition
Inter-
leaving
Deinter-leaving
Error correctionConvolutionaldecodingJ
Turbo decoding
Error detectionJ CRC check J Parity check
Transmitting end
Receiving end
Fig 2-7 General channel coding components example
Error detection ndash Example with block coding
Generally known as outer loop error correction this step involves
attachment of some error detection mechanisms that are added onto
the data block by the transmitter to enable the receiver to detect errorsCommon examples are parity bit attachments or cyclic redundancy
checks using the block coding principle Block coding involves calcu-
lating a certain number of parity bits for a block of data bits and then
appending them to the data block At the data sink ie the receiving
end errors in the received code word can be detected with the aid of
these redundancy bits
HSDPA uses a type of block code known as a cyclic redundancy check
(CRC) The cyclic codes of this type are also known as (nk) codes
where n represents the number of code symbols (bits) and k the num-
ber of data symbols (bits) The number of check bits is therefore nk
In HSDPA there is only one length of cyclic redundancy check Every
transport block in the HS-DSCH is followed by a 24-bit CRC An exam-
ple of how this CRC-based block coding works is given below
These check bits and thus the code word are produced by a generating
polynomial A polynomial is used to represent a bit sequence as a code
word with the power of each term in the polynomial corresponding to
a bit position and the coefficient of each term to a bit (Dm) A data word
with k bits is therefore represented as follows
Dk ∙ x
k
+ Dkndash1 ∙ x
kndash1
+ hellip + D983089 ∙ x + D983088
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HS-DSCH High speed downlink shared channel transport channel
35
An example could be the simple bit pattern 1101 which would repre-
sented as polynomial 983160983091 + 983160 + 1 i e 1 ∙ x 983091 + 0 ∙ x 983090 + 1 ∙ x 1048625 + 1 ∙ x 1048624
To calculate the check bits the data word D(x ) is multiplied by x nndashk
and then divided by the generating polynomial G(x ) which is of degree
(nndashk) The remainder R(x ) is the check word comprising the check bits
R x mainder x D x
G x
n k
( ) Re ( )
( )=
sdot
minus
The code word C (x ) is now obtained by appending the check word to
the data word
C (x ) = x nndashk ∙ D(x ) + R(x )
The receiver knows the generating polynomial G(x ) and performs the
division C (x )G(x ) If there are no transmission errors the code word
C (x ) is divisible by G(x ) The probability is therefore high that anyerrors will be detected The maximum number of errors per code word
that can be detected is determined by the length of the check word
which in our case is the length of the CRC But what is not known is the
position of those errors and thus there is no way to correct them This
is the responsibility of the ldquoinnerrdquo error correction such as the attach-
ment of redundancy bits which enable the receiver to correct some bit
errors Note that block codes can also be used in general to correcterrors but this is not performed in HSPA because this would increase
the overall latency time
Error correction performed with forward error correction (FEC)
principle of convolutional coding
With forward error correction (FEC) redundant bits are inserted into
data packets (bursts) at the transmitting end to enable the receiving
end to implement a correction mechanism The assumption is that theerrors do not occur in a burst Here the principle of a convolutional
coder is used This type of coder ldquoremembersrdquo the last n bits sent and
adds each input bit to the stored n bits The words obtained at the out-
put are usually longer than one bit The code rate defines the ratio of
the input bits to the output bits for example a coder using a code rate
of frac12 generates for each input bit a code word of two output bits Error
correction is based on the fact that a previous state ie a word or a bit
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HSDPA operation overview and physical channels
sequence can only assume one of two succeeding states depending on
whether 0 or 1 was entered into the coder ie the decoder decides for
the metric providing the minimum error estimation If a word arrivesat the receiver in a state that cannot be reached from a state obtain-
able from one of the two input combinations a transmission error has
occurred and needs to be corrected This procedure is equivalent to
tracing a path through a trellis diagram which is familiar from cod-
ing theory
We would now like to discuss a brief example to demonstrate the func-
tionality of channel coding and the subsequent steps of puncturing
Please note that this example does not represent the real coders used
in HSDPA Consult the relevant literature for further details of cod-
ing theory [Ref 10] [Ref 11] and [Ref 14] as well as the specification
[TS 25212 Ref 21] which describes the coding applied in HSPA
The convolutional coder shown in Fig 2-8 consists of one input fol-
lowed by three registers in a shift configuration and finally two out-puts With each clock generation the content of each register is shifted
one register to the right as the last registerrsquos content is discarded and
a new input bit is inserted into the first register The outputs 1 and 2
are generated by an XOR operation between the linked register con-
tents In this manner we create a finite response filter and a certain
memory effect Letrsquos assume we want to transmit the following input bit
sequence 110110 01 Here the nomenclature 01 means that the lastbit of our contemplated sequence can be either 0 or 1 and we wish to
consider both alternatives The registers are initialized with all 0s and
typically some tail bits are attached to the code word which will ensure
this for the succeeding code word The table in Fig 2-8 shows the input
bit on the left side the register sequence content after each step and
outputs 1 and 2 on the right side The output sequence for the given
input will be 11 01 01 00 01 011100 Note the last two lines in the table
We do assume an either or ie there are two alternatives such thatalternative A means that after the sequence 110110 has been sent to the
coder the following bit will be logical 0 Alternative B means that after
the sequence 110110 the following bit will be a logical 1 So we present
an either or situation This will be used to explain the coding principle
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HS-DSCH High speed downlink shared channel transport channel
37
Example of convolutional coding
Input Regis-
ter 1
Regis-
ter 2
Regis-
ter 3
Out-
put 1
Out-
put 2
XOR operation
Register 3Register 2Register 1
+
Input
Output 1
Output 2
+ +
1 1 0 0 1 1
1 1 1 0 0 1
0 0 1 1 0 1
1 1 0 1 0 0
1 1 1 0 0 1
0 0 1 1 0 1
Alt A 0 0 0 1 1 1
Alt B 1 1 0 1 0 0
Fig 2-8 Simple example for convolutional coding
In Fig 2-9 that follows there is a trellis diagram representing in each
column the four possible output values of our channel coder 00 01 10
or 11 and in bold color there is the trellis path through this diagram
resulting from the input sequence Recalling our definition of the two
alternatives for the last bit of our example code word we can see that
the rightmost part of this trellis diagram shows the two possible steps
From state 01 we can only reach either state 00 or state 11 The twoother states 01 or 10 are not possible and with no input to the coder
shown in Fig 2-8 the output can reach these two states in this step For
example if the receiver detects a sequence such as 11 01 01 00 01 01 01
it knows there is an error at the last position 01 which had to be cor-
rected as either 00 or 11 because only these two alternatives are pos-
sible The error correction is performed by looking at the total trellis
path and selecting the maximum likelihood sequence estimation basedon the received data pattern In our short example we admit that we
stopped at this point of course Imagine that the input sequence of bits
continues The decoder would not know if it should proceed with the
pattern 00 or 11 so the decision will be to continue both ways The fol-
lowing step is then checked again and one of the assumed ways will dif-
fer more from the demodulated pattern than the other one This prin-
ciple is described in the Viterbi algorithm [Ref 15] Based on this algo-
rithm the stronger path will survive ie the decoder checks at eachstep which path of the examined ones in the trellis path exhibits the
smallest deviation from the demodulation sequence and thus this path
will be continued The paths exhibiting a higher deviation are discarded
to reduce the calculation expense The path through the trellis diagram
is called a ldquometricrdquo and the term ldquomaximum likelihood sequence esti-
mationrdquo (MLSE) represents the selection by the channel decoder of the
real possible metric which is the closest to the received data pattern As
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HSDPA operation overview and physical channels
an analogy If we do a crossword puzzle and find some characters in a
word the channel decoder would check in a primer or dictionary of the
language containing all possible character combinations that we callldquowordsrdquo and select the existing word that has the maximum likelihood
for the prevailing sequence of characters
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
Alternative B
Alternative A
Register 2
+ +
+
Output 1
Output 2
XOR operation
Trellis diagram above showsmetric for input sequence
110110 0
or 1
into a coder such as
1
1
0
1 10
0
1
Register 3Register 1
Fig 2-9 Metric in trellis diagram
Interleaving
Forward error correction based on convolutional coders has one disad-
vantage related to the impact of block errors If the transmission errors
are distributed they can be corrected as demonstrated in the trellis dia-gram example using the Viterbi algorithm but if many adjacent bits
are lost the decoder will have problems retrieving the right bit pattern
Interleaving means that the information to be transmitted is spread or
distributed over several bursts in such a way that contiguous informa-
tion is split up and transmitted in a time or block distributed mode
To avoid error bursts an attempt is made to spread the bit errors over
several code words This is achieved by interleaving several code wordsThis method is also called diagonal interleaving see Fig 2-10 Another
kind of interleaving is block interleaving as shown in Fig 2-11 Blocks
of code words are written row-by-row into a matrix and then read col-
umn-by-column With both methods consecutive bits of a code word
are never transmitted consecutively and conversely when the bits are
deinterleaved at the receive end error bursts are spread over several
code words
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HS-DSCH High speed downlink shared channel transport channel
39
As several code words are interleaved the decoder has to ldquowaitrdquo a cer-
tain time until all bits of a particular code word arrive This delay ie
the ldquomeasure for spreading over timerdquo is referred to as the ldquointerleav-ing depthrdquo The greater the interleaving depth the more code words are
available for spreading the error bursts and the greater the probability
that errored bits can be corrected but on the other hand this increases
the overall latency time
HSDPA uses the block diagonal interleaving principle for the HS-DSCH
only since as we should recall one goal is to have a short round-trip
time
Spreadinghellip
Interleaving
hellip
hellip
Fig 2-10 Diagonal interleaving
Write
Read
Interleaving-Matrix
Fig 2-11 Block interleaving
Puncturing
Having briefly described the principle of convolutional coding another
mechanism will be presented that is used to increase the throughputof user data and coordinate with the AMC mechanism described in
section 12 page 10 After adding redundancy the total bit stream is
now known as soft bits ie the sum including all of the raw data bits
at the input of the channel coder plus the added redundancy bits This
quantity must match the required transport block size demanded by
the transport layer and the process performed here is called rate match-
ing ie deleting some of the soft bits at the transmitting end in a pre-
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HSDPA operation overview and physical channels
defined manner or repeating or adding some stuffing bits In HSPA the
rate matching mechanism uses puncturing which provides higher data
throughput The signaled values TBS and RV tell the receiving convo-lutional coder how many and where bits have been punctured This
allows the decoder to insert blank positions which have to be filled later
by performing trellis decoding In other words we may consider the
punctured bits as bit losses created intentionally by the transmitter In
this manner the total amount of data bits can be increased for the sake
of lower redundancy In HSDPA this puncturing scheme will be very
flexible and the NodeB scheduler will set the puncturing rate adapted
to the prevailing RF conditions on the radio channel to obtain the high-
est possible data throughput under the existing conditions The disad-
vantage of adaptive coding is that we need signaling information so
that the transmitter has to inform the receiver about how many soft bits
have been punctured This is seen in Fig 2-26 page 55 in the form
of the redundancy version carried by the HS-SCCH control channel
Fig 2-12 below again depicts the principle of puncturing in HSDPAand clarifies some signaling parameters such as the transport block size
1 1 0 1 1 0 0
11 01 01 00 01 01 11
Transport block sizeInput bits into channel coder
Soft bitsOutput from channel encoder
Rate matchingPuncturing or repeating bits
11 01 01 00 01 01 11
1 01 0 00 0 01 1Coded composite transport bitsCan be several combined streams aftercoding + rate matching
Transport block size FEC
Fig 2-12 Puncturing based on coding example from Fig 2-8 page 37
The process of channel coding starts first with the transport block
size which is given by the size of the input data bit sequence added
by a cyclic redundancy checksum The next step is the channel cod-
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HS-DSCH High speed downlink shared channel transport channel
41
ing which is performed in HSPA by a so-called turbo coder The turbo
coder is a parallel concatenated convolutional coder that exhibits bet-
ter reliability compared to a single convolutional coder Discussingthe functionality of a turbo coder in all of its details would represent a
major digression from the intention of this book Accordingly we will
simply encourage the interested reader to consult the channel coding
literature for more details about turbo coders and their applications
[Ref 10] [Ref 12] Determined by the scheduler of the base station or
the redundancy version to be used the next step known as the redun-
dancy version will either puncture (the most likely) or repeat some of
the bits resulting from the channel coding process How many bits will
be punctured is defined by the coding rate In our example in Fig 2-12
we see that the input bit sequence has a length of 7 bits resulting in
14 soft bits after channel coding with our example coder providing a
coding rate of frac12 The scheduler decided to puncture 4 bits so that we
finally obtain 10 bits which have to be mapped on the physical chan-
nels Our overall coding rate is therefore given as ⁷frasl983089983088 In other words
some bits are protected with redundancy information while othersare not Note that the size of the coded composite transport channel
is determined by the physical layer parameters such as the number of
channelization codes used to convey the HS-PDSCH the modulation
scheme and the transmit time interval which is constant for HSDPA
but can be either 2 or 10 ms for HSUPA Thus its size does not need
to be signaled to the receiver and only the transport block size and the
redundancy versions will be contained in the HS-SCCH channel
222 Incremental redundancy and chase combining
for HS-DSCH
Until now we have presented some general characteristics of HSDPA
and HSUPA which we would now like to discuss in a combined pro-
cedure and then deduce two other principles The HARQ abbreviationcombines an automatic retransmission of erroneous data with a soft
combination at the receiving end A related question can now be how
the transmitter has to repeat the transport block should the retrans-
mission of data occur in an identical retransmission mode or should
some changes in coding parameters eg the manner of puncturing be
applied This question is also important for the implementation of the
rate matching step shown in Fig 2-12 The transmitter has to provide
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HSDPA operation overview and physical channels
a certain soft buffer ie a memory that stores the transmitted data for
the sake of possible retransmissions and deletes it after having received
a positive acknowledgment from the receiver Should the transmitternow store the coded composite transport data i e the data after coding
but also after puncturing This would restrict it to repeating the data in
an identical manner A better approach is to store the data after channel
coding and before puncturing Even if this requires more memory it
gives the flexibility to change the puncturing scheme and retransmit the
transport block in a different way Fig 2-13 and Fig 2-14 represent both
mechanisms that are used in HSDPA and HSUPA Identical retransmis-
sion is called chase combining and non-identical retransmission with
a different puncturing scheme is called incremental redundancy The
scheduler in the base station can decide which retransmission scheme
will be used We do not wish to delve into the details of channel coding
theory to discuss which mechanism is the better one ndash chase combin-
ing or incremental redundancy We will only mention that both mech-
anisms have their advantages and thus their applications Chase com-
bining has the advantage that the systematic bits representing the orig-inal data input into the channel coder are contained in the transmit-
ted sequence after puncturing Thus chase combined transport blocks
are ldquoself-decodablerdquo If we consider a situation where the original trans-
port block is lost completely and only the retransmitted block is pres-
ent at the receiver there is a chance to decode the data properly Mean-
while incremental redundancy seems to add more redundancy when
retransmitting but in a scenario where the first transmission contain-ing the systematic bits is lost completely and only the retransmission
is present the receiver will have no chance to decode the data without
having some of the systematic bits Accordingly incremental redun-
dancy is applied whenever sporadic bit errors occur due to a time vari-
ant channel and chase combining is selected whenever we have to deal
with complete transport block errors i e the time variance of the radio
link exhibits some bursted fading dips
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HS-DSCH High speed downlink shared channel transport channel
43
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Chase combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Transmitted bit
Punctured bit
Systematic bits
Parity 1
Parity 2
Systematic bits
Parity 1
Parity 2
Fig 2-13 Chase combining principle
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Incremental redundancy combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Systematic bits
Parity 1
Parity 2
Systematic bitsParity 1
Parity 2
Fig 2-14 Incremental redundancy
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HSDPA operation overview and physical channels
223 Constellation rearrangement
Due to the fact that HSDPA introduces a higher-order modulationscheme (16QAM) we can recognize some effects due to the physi-
cal layer influencing the susceptibility to noisy RF conditions One of
these effects can be explained by looking at the constellation diagram
in the 16QAM modulation scheme see section 12 page 10 As we
recall there is a total of 16 different constellation points given by the
modulation vector and represented by its phase and amplitude Con-
sidering the Euclidean distance which is the distance in this constella-
tion diagram between two neighboring points we can clearly see that
some points have more neighbors than others Especially the four con-
stellation points at the very four corners only have three direct neigh-
bors making them less susceptible to misdetection due to noise shift-
ing them in a certain direction On the other hand the four constella-
tion points representing the inner square of the constellation have eight
direct neighbors each and are therefore more likely to be incorrectly
detected The idea of constellation rearrangement is now to change themapping scheme applied in the original transmission when retrans-
mitting As we know the receiver will soft combine the retransmit-
ted data with the previously received information so we can achieve a
certain incremented redundancy and a certain protection mechanism
Note however that considering a sole transmission of a transport block
using a certain constellation arrangement will not show any more pos-
itive or negative results compared to other constellation arrangementsThe redundancy gain is only achieved by rearranging the constellation
mapping in a retransmitted transport block and performing soft com-
bining at the receiver Overall HSDPA defines four constellation rear-
rangement schemes which are indicated in the redundancy version
field of the HS-SCCH and are represented by the ldquobrdquo bit field ranging
from b = 0 to b = 3 All four constellation schemes are Gray encoded
ie the directly adjacent constellation symbols do not exhibit four com-
pletely different bits in order to reduce the impact of misdetection onbit errors
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High speed shared control channel (HS-SCCH)
45
Q
I
(ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1) (1 1ndash1ndash1)
(ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1) (1 1ndash1 1)
(ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1) (1ndash1ndash1 1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 0
Q
I
(ndash1 1 1 1) (ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1)
(ndash1 1 1ndash1) (ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1)
(ndash1ndash1 1ndash1) (ndash1ndash1ndash1ndash1) (1ndash1ndash1ndash1) (1ndash1 1ndash1)
(ndash1 1 1 1) (ndash1ndash1ndash1 1) (1ndash1ndash1 1) (1ndash1 1 1)
b = 2
Q
I
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (1ndash1 1 1) (ndash1ndash1 1 1)
(ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1) (ndash1 1 1 1)
(ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1) (ndash1 1 1ndash1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 1
Q
I
(1 1ndash1 1) (ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1)
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1)
(1ndash1ndash1ndash1) (ndash1ndash1ndash1ndash1) (ndash1ndash1 1ndash1) (1ndash1 1ndash1)
(1 1ndash1ndash1) (ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1)
b = 3
Fig 2-15 Constellation rearrangement in HSDPA
23 High speed shared control channel (HS-SCCH)
The HS-SCCH sends scheduling information to the UEs As seen before
the HS-PDSCH has a very flexible configuration for physical parame-
ters such as the coding rate number of code channels or retransmis-sions This high flexibility increases the complexity and engenders the
need for additional signaling information transferred on the HS-SCCH
Reception of user data in HSDPA is always a two-step procedure
First the receiver has to capture the scheduling control information
and afterwards based on the received control information it may start
demodulating and decoding the HS-PDSCH containing the user data
This two-step procedure is shown in Fig 2-16 below which lists what
kind of control information is sent to the UEs via the HS-SCCH Asshown in Fig 2-2 page 28 which describes the overall HSDPA chan-
nel structure there can be up to four HS-SCCHs assigned to one UE
But only one HS-SCCH would contain the scheduling information for
this UE within one TTI Thus the network can assign resources simul-
taneously to various UEs in the downlink direction
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HSDPA operation overview and physical channels
I would like to receive databut I dont know where myHS-PDSCH resources areand what they look like
HS-SCCH
Read the 1st HS-SCCH slotfor HS-DSCH channelizationcodes UE identity and
modulation scheme
Then the 2nd and 3rd HS-SCCHslots provide transport block sizeinformation hybrid ARQ process in-formation redundancy constellationversion new data indicator
HS-PDSCH
Fig 2-16 HS-SCCH control channel usage
Regarding the physical layer parameters we see in Fig 2-17 that the
HS-SCCH uses a channelization code with a spreading factor of 128
and it also uses the newly introduced transmit time interval of one sub-
frame which is equal to 2 ms It should be mentioned that the spread-ing factor of 128 requires double the capacity compared to similar con-
trol channels in WCDMA Release 99 reflecting the signaling overhead
needed to guarantee the huge flexibility introduced with HSDPA Addi-
tionally Fig 2-16 shows that the control information is sent consecu-
tively within one subframe The first slot within this subframe contains
the control information UE identity channelization code information
and modulation scheme identifier Slots 2 and 3 of the subframe con-tain the remaining control information Transport block size HARQ
process identifier redundancy version and new data indicator Conse-
quently the UE can self-decode slot 1 alone and slots 2 and 3 in a sec-
ond step even if they represent one logical unit This raw control infor-
mation is of course also channel coded using a turbo and on the phys-
ical layer the quantity of bits after the rate matching step is 40 bits con-
veyed in one slot corresponding to 666 micros [TS 25212 Ref 21] see also
Fig 2-28 page 56
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High speed shared control channel (HS-SCCH)
47
The HS-SCCH is a fixed rate (60 kbps SF = 128) downlinkphysical channel used to carry downlink signaling related toHS-DSCH transmission
Slot 0
Slot 1
Slot 2
Tslot
= 2560 chips
Data = 40 bits
1 subframe = 2 ms
Fig 2-17 Structure of High speed shared control channel HS-SCCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
We would like to return now to the time consecutive transmission of
control information There is a difference in the control information
in terms of its priority Some information is needed at the UE end
very urgently while other control information does not have such a
high priority But why This will be explained by looking at some tim-ing aspects defined for HSDPA If we consider the timing between
the shared data channel HS-PDSCH and the shared control chan-
nel HS-SCCH as shown in Fig 2-18 we see that the HS-PDSCH fol-
lows the HS-SCCH by exactly two slots or 5120 chips The HS-SCCH
is completely time-aligned with the general control channels CPICH
and P-CCPCH of the NodeB This is mandatory because it is a shared
channel Consider several UEs with different distances to the NodeBwanting to receive the HS-SCCH channel Thus it must have constant
timing that is known a priori The shared data channel HS-PDSCH is
now transmitted exactly 5120 chips after the first chip of the HS-SCCH
This leads to an overlapping slot thereby requiring multitasking recep-
tion at the UE end While the UE is still receiving the last slot of an
ongoing HS-SCCH subframe it may already start the reception of an
HS-PDSCH transport block The first slot in the HS-SCCH subframe
now contains information required by the physical layer to performdespreading and demodulation These values are the UE identity indi-
cating whether the UE will start demodulation of the HS-PDSCH or
not in case it is not scheduled the modulation scheme information
since the UE has to know how to interpret the received constellation
vector and whether it has to be considered as a QPSK or 16QAM con-
stellation point and finally the UE has to know which channelization
codes it has to apply to capture the HS-PDSCH transport block The
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48
HSDPA operation overview and physical channels
overall UE reaction time when being scheduled is now seen as 1 slot
or 2560 chips This tough requirement for the UEs is due to the objec-
tive to obtain overall a much shorter latency than legacy standards Theadditional control information such as the new data indicator redun-
dancy version and transport block size is not that urgent since it is
needed after demodulation but before channel decoding So first the
UE will sample the whole three slots of the HS-PDSCH and demodu-
late them into a bit stream which is finally handed over to the channel
decoder This principle is known as post-processing and is used typi-
cally in mobile communications technologies
J Start of HS-SCCH subframe 0 is aligned with startof P-CCPCH frames
J The HS-PDSCH starts
τ HS-PDSCH
(2times Tslot
= 5120 chips)
after the start of the HS-SCCH
UE identity etc
processing timeof receiver
HS-DSCH subframe
3 times Tslot= 7680 chips
3 times Tslot
= 7680 chips
τ HS-PDSCH
(2times Tslot
= 5120 chips)
HS-SCCH
HS-PDSCH
Fig 2-18 Timing relation between HS-SCCH and HS-PDSCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
Content of the HS-SCCH control channelThe control information contained in the HS-SCCH control chan-
nel has already been mentioned so we will now consider the values
in more detail We will begin with an overview of what kind of control
information is contained in the HS-SCCH channel before proceeding
with further details about the single control elements The following
control information is present in the HS-SCCH [TS 25212 Ref 21]
Channelization code set information (7 bits)
Modulation scheme information (1 bit) Transport block size information (6 bits)
Hybrid ARQ process information (3 bits)
Redundancy and constellation version (3 bits)
New data indicator (1 bit)
UE identity (16 bits) = H-RNTI
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High speed shared control channel (HS-SCCH)
49
Some of these parameters are more or less self-explanatory while oth-
ers require additional background information and closer examination
Modulation scheme information 1 bit
This single bit is used to inform the receiver whether the modulation
scheme QPSK or 16QAM is applied on the data channel HS-PDSCH
The interpretation of the bit x ms1 is as follows
ms1
x
if QPSK
otherwise
0
1
=
New data indicator 1 bit
The new data indicator bit field informs the receiving entity that the
prevailing PDU transmitted by the current HARQ process is either a
retransmission or contains new data This is done by setting the new
data bit to the value 0 for the first PDU on this particular HARQ process
and incrementing the value by 1 with every new data sent [TS 25321Ref 30] This leads to a toggled value In case the new data bit is not
incremented ie if it remains at its previous value it is an indicator for
retransmission
1st PDU of this
HARQ process
NDI = New data indicator
NDI = 0 NDI = 1
NACK
NDI = 1
ACK
NDI = 0
HS-SCCH HS-SCCH HS-SCCHHS-SCCH
ACK
Fig 2-19 New data indicator bit principle of incrementing value
Channelization code set information 7 bits
This field is used to indicate the number of channelization codes usedfor transmitting the transport block on the HS-PDSCH As was already
described the spreading factor applied on the HS-PDSCH is constant
with a value of 16 but the flexible values are the number of channeliza-
tion codes forming a cluster when using multiple codes and their posi-
tion in the code tree It is not allowed to distribute the code channels
over the code tree diagram For the sake of simplicity in signaling sev-
eral channelization codes form one cluster and these codes are con-
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HSDPA operation overview and physical channels
tiguous in the channelization code tree [TS 25213 Ref 22] Fig 2-20
illustrates the principle of indicating the channelization codes on the
HS-SCCH
SF = 16
Code ldquo0rdquo isreserved forcommonchannels
Code offset 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15P = 5O = 7
Code group indicatorx
ccs1 x
ccs2 x
ccs3 = min (Pminus 1 15 minusP)
Code offset indicatorx
ccs4 x
ccs5 x
ccs6 x
ccs7 = |Ominus 1minus P8 times15|
A cluster of codes
can be allocated to a UEC
ch16Ohellip C
ch16O + P minus 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1
2 2 2 2 2 2 2 2 2 2 2 2 2 2 14 14
1 2 3 4 5 6 7 8 9 10 11 12 13 14 2 1
3 3 3 3 3 3 3 3 3 3 3 3 3 13 13 13
1 2 3 4 5 6 7 8 9 10 11 12 13 3 2 1
4 4 4 4 4 4 4 4 4 4 4 4 12 12 12 121 2 3 4 5 6 7 8 9 10 11 12 4 3 2 1
5 5 5 5 5 5 5 5 5 5 5 11 11 11 11 11
1 2 3 4 5 6 7 8 9 10 11 5 4 3 2 1
6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10
1 2 3 4 5 6 7 8 9 10 6 5 4 3 2 1
7 7 7 7 7 7 7 7 7 9 9 9 9 9 9 9
1 2 3 4 5 6 7 8 9 7 6 5 4 3 2 1
8 8 8 8 8 8 8 8
8 7 6 5 4 3 2 1
0 (115)
1 (214)
2 (313)
3 (412)
4 (511)
5 (610)
6 (79)
7 (88) Redundant area
C l u s t e r c o d e i n d i c a t o r ( 3 b i t s )
Tree offset indicator (4 bits)
Signaled on HS-SCCH
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
PO
Decoding notation
Number ofmulti-codes
Offset fromleft right incode tree (SF = 16)
Fig 2-20 Channelization code set indicating the HS-PDSCH code cluster
The idea behind the code indication is a matrix with the rows repre-
senting the number of codes per cluster and the columns represent-
ing the position of that cluster the offset value in the code tree Recall-
ing that the maximum number of channelization codes per clusteris 15 and if the cluster size is 1 the offset values can also range from
1 to 15 the resulting matrix would have 15 rows and 15 columns Since
we know that four bits are needed to represent an integer from 1 to 15
we need a total of 4 + 4 = 8 bits for representation of the channeliza-
tion code set information It is a smart idea to save one bit The 15 times 15
matrix would contain much redundant information By way of analogy
like in a road map indicating distances between cities A table showing
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High speed shared control channel (HS-SCCH)
51
the distance from city A to city B the opposite distance from city B to
city A is redundant information The useful information has the form
of a triangle The idea is to cut the lower part rotate it and append itto the spare part of the upper table In this manner a table is obtained
with 7 rows and 15 columns and it is possible to indicate each position
in it with just 7 bits
1 5 r o w s 7
r o w s
Matrix reduction for channeli-
zation code set information
15 columns
Fig 2-21 Matrix size reduction for channelization code set information
The content of the channelization code set matrix can be described as
a value with two numbers The upper number is the number of mul-
ticodes forming one cluster and the lower number is the offset in the
channelization code tree Accordingly the example in Fig 2-20 can be
interpreted to mean the HS-SCCH sends the bits as row number 4 and
column number 6 in the matrix The content of this element are the
values 5 over 7 which have to be interpreted as a cluster size of 5 codesand an offset of 7
Transport block size information 6 bits
With a length of six bits the transport block size (TBS) informa-
tion informs the receiving UE entity about the data block size of the
transport block sent on the HS-PDSCH We should keep in mind the
link adaptation performed with the adaptive modulation and coding
scheme that was described in section 12 page 10 The ratio errorcorrection and user data are flexible while the physical layer param-
eters such as the spreading factor modulation scheme and number of
channelization codes determine the physical block size This physical
block consists of the user data ratio or transport block size and the for-
ward error correction or redundancy information As this ratio is flex-
ible the HS-SCCH will inform the receiving UE entity about the size
of the transport block Here too there is a strategy of bit reduction the
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HSDPA operation overview and physical channels
goal is to inform the receiver with as few bits as possible A non-effi-
cient approach would involve conversion of the decimal number repre-
senting the TBS into a binary sequence but the number of bits neededwould exceed the space available on the HS-SCCH Imagine that the
range of transport block sizes depends on the physical layer condi-
tions The ambient physical layer parameters modulation scheme and
number of channelization codes set a certain working point where the
remaining flexibility for a different TBS configuration can be obtained
by more or less puncturing resulting in a flexible ratio between for-
ward error correction and user data This will lead to a two-step proce-
dure when evaluating the transport block size First the receiver exam-
ines the information modulation scheme and number of channeliza-
tion codes scheduled via HS-SCCH which indicate the value k0 l as
shown in Fig 2-22 The 6-bit HS-SCCH control parameter transport
block size information will be the transport format resource indica-
tor (TFRI) named ki Let k t be the sum of the two values kt = ki + k0i
Both values kt and k0 i can be obtained from tables given by [TS 25321
Ref 30] The range for the TFRI is from 1 to 256 and the derived trans-port block size ranges from 137 bits to 27 952 bits The first table indi-
cates the value k 0 i based on the channelization code and the modula-
tion scheme
Combination i Modulation scheme Number of channelization codes k0 i
0
QPSK
1 1
1 2 40
2 3 633 4 79
4 5 92
5 6 102
Fig 2-22 Extract from TS 25321 table representing k0 i
The second table indicates the final transport block size based on kt
Index TB size Index TB size Index TB size1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
4 173 89 1456 174 6673
5 185 90 1483 175 6793
6 197 91 1509 176 6916
7 209 92 1537 177 7041
Fig 2-23 Extract from TS 25321 table representing kt
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High speed shared control channel (HS-SCCH)
53
J The transport block size used on HS-DSCH is not signaled explicitly on HS-SCCHJ Instead a transport block size index k
i is signaled to indicate the transport block size
First stepModulation scheme andnumber of channelizationcodes as signaled on HS-SCCHdetermine value k
0 i
Second step
Index kt = k
i + k
0i
determines HS-DSCH
transport block size
kt = k
i + k
0i
Table according to 3GPP TS 25321 extract from QPSK section
Table according to 3GPP TS 25321 254 entries in total
Combination i Modulation
scheme
Number of
channelization codes
k0 i
0
QPSK
1 1
1 2 40
2 3 63
3 4 79
4 hellip hellip
Index TB size Index TB size Index TB size
1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
helliphellip hellip hellip hellip hellip
Fig 2-24 Retrieval of transport block size information
Source Fig 2-22 to Fig 2-24 [TS 25321 Ref 30] reproduced by permission of 3GPP
Hybrid ARQ process information 3 bits
The concept behind the hybrid automatic repeat request (HARQ) was
introduced in section 13 page 14 One feature is the possibility of
multitasking ie having several HARQ processes activated at the same
time Fig 2-25 below shows the need to signal the process identity tothe receiver Remember that on the downlink there is a shared chan-
nel concept so the NodeB can flexibly decide which UE will be sched-
uled with a downlink transport block Up to eight HARQ processes
can be signaled via higher layers to one UE Note however that due to
the round-trip timing six HARQ processes must be active to achieve
the maximum throughput as shown in Fig 2-51 page 79 Compared
with HSUPA the HARQ processes on the downlink are asynchronous
so they have to be indicated but on the uplink they are synchronous sothey do not need to be signaled explicitly
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HSDPA operation overview and physical channels
Asynchronous DL minus Synchronous ULNumber of H-ARQ rocesses = 1 to 8 er UE
UL HS-DPCCH UE1
UE1 HARQ processes 1 to 4
3 4 1 42 11 1 32retrans
2
A N A A
A A
N A
UL HS-DPCCH UE2
HS-PDSCH
UE2 HARQ processes 1 to 2
Fig 2-25 HARQ process indication on HS-SCCH
Fig 2-25 shows a typical situation on the downlink (point-to-multi-
point) The NodeB sends data to several UEs sharing the HS-PDSCH
so therefore the HARQ process is asynchronous The time when a
transport block is retransmitted is not fixed For this reason the pro-
cess identifier is signaled on the HS-SCCH Based on the HARQ pro-
cess identity and the new data indicator bit the receiving entity knows
which part of the soft buffer memory has to be used in case of soft com-bining On the uplink the situation is slightly simpler The UE only
communicates with one NodeB so it is a point-to-point connection
Thus retransmission always occurs at a fixed time linked to the origi-
nal transmission
Redundancy and constellation version 3 bits
Adaptive modulation and coding involve flexible selection of modula-tion and coding schemes that are signaled to the receiving UE via the
parameters transport block size and modulation scheme information
Another concept used in HSDPA was previously discussed Chase com-
bining or incremental redundancy (see section 222 page 41) This
means that in case of retransmission the transmit entity can dynami-
cally select another puncturing scheme or keep the puncturing as it was
in the original transmission The applied puncturing scheme is signaled
as redundancy information to the receiver Additionally in case of the16QAM modulation scheme the transmitter can select another constel-
lation arrangement which is also signaled to the UE with the three bits
for the redundancy and constellation version see Fig 2-15 page 45
Depending on the modulation scheme (QPSK or 16QAM) there are
two different tables indicating the parameters ldquosrdquo ldquorrdquo and ldquobrdquo The
parameters ldquosrdquo and ldquorrdquo indicate which scheme is used for puncturing
ie if the puncturing mechanism prioritizes the systematic bits or not
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High speed shared control channel (HS-SCCH)
55
and which puncturing algorithm is used The parameter ldquobrdquo indicates
the constellation mapping version The receiver needs this information
to perform proper demodulation and decoding
Initial transmission
1st retransmission
2nd retransmission
3rd retransmission
r
0
0
1
1
2
2
3
xrv
(value)
s
0 1
1 0
2 1
3 0
4 1
5 0
6 1
7 0 3
s = 1 Systematic bits are prioritizeds = 0 Non-systematic bits are prioritized
r (range 0 to 3 for QPSK) influencesJ Input parameter for puncturing or (together with s) for repetition algorithm defined in TS 25212J Selection of parity bits
Redundancy version coding sequences are signaled on HS-SCCH egndash 0 2 5 6 One initial transmission + 3 retransmissions with different r and s parameters
Fig 2-26 Signaling of redundancy version parameters r and s QPSK case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
Initial transmission
2nd retransmission
1st retransmission
3rd retransmission
r (range 0 to 1 for 16QAM)influences input parameterfor puncturing or (togetherwith s) for repetitionalgorithm defined in
TS 25212 and thus selectionof parity bits
Redundancy version coding sequences are signaled on HS-SCCH egminus 6 4 0 5 Chase combining (no change in s and r parameters ie same redundancyversion) with four possible constellations
x rv (value) s r b
0 1 0 0
1 0 0 0
2 1 1 1
3 0 1 1
4 1 0 1
5 1 0 2
6 1 0 3
7 1 1 0
Definition of parameter s as for QPSK
b (range 0 to 3) describes constellationrearrangement to averagereliability of bits
Fig 2-27 Signaling of redundancy version parameters r s and b 16QAM case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
UE identity H-RNTI 16 bits
The HSDPA radio network transaction identifier (H-RNTI) unam-
biguously identifies the UE having an HS-PDSCH assignment within
a cell It is allocated to the UE via layer 3 signaling procedures at the
radio bearer setup if the radio bearer is an HSDPA connection This
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HSDPA operation overview and physical channels
value represents a temporary name of the UE used to address it when
scheduling data packets via HS-SCCH
HS-SCCH channel coding
The control information contained in the HS-SCCH is of course pro-
tected with channel coding mechanisms the whole coding chain is
described in Fig 2-28 Fig 2-18 page 48 presents the separation of
the control information into two code blocks which are sent consec-
utively mapped on slot 1 and slot 2 + 3 of one HS-SCCH subframe
This principle is also visible in the coding chain The first control block
consisting of channelization information modulation scheme and UE
identity is coded separately from the remaining control values to enable
the UE receiver to decode this first slot separately and prepare for pos-
sible HS-PDSCH reception The coding steps shown in Fig 2-28 such
as rate matching 1 and 2 are similar to the HS-PDSCH coding chain
and are further described in [TS 25212 Ref 21]
Channelcoding 1
R atematching 1
mux
Channelcoding 2
Ratematching 2
RVcoding
UE-specificCRC attachment
UE-specificmasking
Physical channelmapping
r s b
mux
Channelizationcode set
Modulationscheme
Transport block size information
HARQ processinformation
Redundancy andconstellation version
New data indicator
UE identity
UE identity
Fig 2-28 Channel coding for HS-SCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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High speed dedicated physical control channel (HS-DPCCH)
57
24 High speed dedicated physical control channel (HS-DPCCH)
In an active HSDPA connection the UE has to send acknowledgment ornon-acknowledgment reports (as described in section 13 page 14
where the HARQ process is described) as well as channel status infor-
mation to the network The reporting is performed on this physical
control channel HS-DPCCH
As ubiquitous in HSDPA the uplink is also configured into a subframe
structure of 2 ms corresponding to three slots The first slot of the sub-
frame carries the ACK NACK information the UE sends to the NodeB
while the following two slots ie slot 2 and 3 of the subframe convey
the CQI value the channel quality information to the NodeB
Subframe 0 Subframe i Subframe 4
Tslot
= 2560 chips J The spreading factor of theHS-DPCCH is 256 (10 bits peruplink slot)
J The HS-DPCCH can only existtogether with an UL DPCCH
(ded phys control channel)J The DPDCH (dedicated physical data channel) the DPCCH andthe HS-DPCCH are IQ codemultiplexed
HARQ-ACK CQI = Channel quality information
2 times Tslot
= 5120 chips
One radio frame Tf = 10 ms
One HS-DPCCH subframe 2 ms
Fig 2-29 HS-DPCCH configuration
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The slot format for HS-DPCCH describes a quantity of 30 bits per sub-frame resulting in a data rate of 15 kbps The spreading factor used for
the HS-DPCCH is constant and is always equal to 256 but the chan-
nelization code that is used as well as the mapping on either the I or
Q axis depends on several factors eg the co-existence of an HSDPA
connection with a circuit-switched connection meaning whether a
DPDCH established or not Fig 2-36 page 64 illustrates this IQ
mapping and Fig 2-35 page 63 shows the channelization code used
for HS-DPCCH
The HS-DPCCH builds a logical unit of one subframe but having the
independent control information HARQ-ACK and CQI included which
could be separately decoded at the NodeB Note that the slot carrying
the ACK NACK statement is active only when the UE has been sched-
uled by an HS-PDSCH subframe in the corresponding downlink sub-
frame previously Assuming the UE has not received a transport block
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HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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HS-DSCH High speed downlink shared channel transport channel
33
After the HARQ functionality step the remaining bits are segmented
into parallel streams due to the fact that the physical layer in HSDPA can
use several channelization codes for the physical channel HS-PDSCHDepending on the physical layer status which involves how many chan-
nelization codes can be used for transmission this step divides the data
into parallel streams Another step for error protection is the avoidance
of bundled errors Here the data sent in parallel HS-PDSCH codes is
interleaved to provide an interleaving gain to the channel decoder If
the 16QAM modulation scheme is used the following step of constel-
lation mapping will set a mapping scheme for which bits are mapped to
which modulation symbol The various constellation mapping schemes
are shown in Fig 2-15 page 45 Finally the resulting modulation
symbols must be mapped onto the physical channel ie they are first
spread with a channelization code having spreading factor 16 then
they are scrambled by using the NodeB specific primary or secondary
scrambling code and finally they are mapped on the carrier frequency
221 Brief digression into channel coding
Since channel coding is a substantial feature of HSPA a short digres-
sion into general aspects of channel coding is included here to help the
reader understand the procedures used in HSPA It is not the inten-
tion of this book to discuss channel coding in detail Interested read-
ers can seek out relevant literature on this topic eg [Ref 9] [Ref 10][Ref 11] and [Ref 14] HSDPA channel coding comprises block cod-
ing with CRC for error detection turbo coding for error correction
and interleaving to mitigate error bursts Channel coding is performed
in this order at the data source and in the reverse order at the data
sink Fig 2-7 below provides an overview of channel coding and its
components
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HSDPA operation overview and physical channels
Error detection
addedJ Block codingJ CRC attachmentJ Parity bits
Redundancy added
for error correctionForward errorcorrection (FEC) by J Convolutional codingJ Turbo coding
Rate matching
J PuncturingJ Repetition
Inter-
leaving
Deinter-leaving
Error correctionConvolutionaldecodingJ
Turbo decoding
Error detectionJ CRC check J Parity check
Transmitting end
Receiving end
Fig 2-7 General channel coding components example
Error detection ndash Example with block coding
Generally known as outer loop error correction this step involves
attachment of some error detection mechanisms that are added onto
the data block by the transmitter to enable the receiver to detect errorsCommon examples are parity bit attachments or cyclic redundancy
checks using the block coding principle Block coding involves calcu-
lating a certain number of parity bits for a block of data bits and then
appending them to the data block At the data sink ie the receiving
end errors in the received code word can be detected with the aid of
these redundancy bits
HSDPA uses a type of block code known as a cyclic redundancy check
(CRC) The cyclic codes of this type are also known as (nk) codes
where n represents the number of code symbols (bits) and k the num-
ber of data symbols (bits) The number of check bits is therefore nk
In HSDPA there is only one length of cyclic redundancy check Every
transport block in the HS-DSCH is followed by a 24-bit CRC An exam-
ple of how this CRC-based block coding works is given below
These check bits and thus the code word are produced by a generating
polynomial A polynomial is used to represent a bit sequence as a code
word with the power of each term in the polynomial corresponding to
a bit position and the coefficient of each term to a bit (Dm) A data word
with k bits is therefore represented as follows
Dk ∙ x
k
+ Dkndash1 ∙ x
kndash1
+ hellip + D983089 ∙ x + D983088
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HS-DSCH High speed downlink shared channel transport channel
35
An example could be the simple bit pattern 1101 which would repre-
sented as polynomial 983160983091 + 983160 + 1 i e 1 ∙ x 983091 + 0 ∙ x 983090 + 1 ∙ x 1048625 + 1 ∙ x 1048624
To calculate the check bits the data word D(x ) is multiplied by x nndashk
and then divided by the generating polynomial G(x ) which is of degree
(nndashk) The remainder R(x ) is the check word comprising the check bits
R x mainder x D x
G x
n k
( ) Re ( )
( )=
sdot
minus
The code word C (x ) is now obtained by appending the check word to
the data word
C (x ) = x nndashk ∙ D(x ) + R(x )
The receiver knows the generating polynomial G(x ) and performs the
division C (x )G(x ) If there are no transmission errors the code word
C (x ) is divisible by G(x ) The probability is therefore high that anyerrors will be detected The maximum number of errors per code word
that can be detected is determined by the length of the check word
which in our case is the length of the CRC But what is not known is the
position of those errors and thus there is no way to correct them This
is the responsibility of the ldquoinnerrdquo error correction such as the attach-
ment of redundancy bits which enable the receiver to correct some bit
errors Note that block codes can also be used in general to correcterrors but this is not performed in HSPA because this would increase
the overall latency time
Error correction performed with forward error correction (FEC)
principle of convolutional coding
With forward error correction (FEC) redundant bits are inserted into
data packets (bursts) at the transmitting end to enable the receiving
end to implement a correction mechanism The assumption is that theerrors do not occur in a burst Here the principle of a convolutional
coder is used This type of coder ldquoremembersrdquo the last n bits sent and
adds each input bit to the stored n bits The words obtained at the out-
put are usually longer than one bit The code rate defines the ratio of
the input bits to the output bits for example a coder using a code rate
of frac12 generates for each input bit a code word of two output bits Error
correction is based on the fact that a previous state ie a word or a bit
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HSDPA operation overview and physical channels
sequence can only assume one of two succeeding states depending on
whether 0 or 1 was entered into the coder ie the decoder decides for
the metric providing the minimum error estimation If a word arrivesat the receiver in a state that cannot be reached from a state obtain-
able from one of the two input combinations a transmission error has
occurred and needs to be corrected This procedure is equivalent to
tracing a path through a trellis diagram which is familiar from cod-
ing theory
We would now like to discuss a brief example to demonstrate the func-
tionality of channel coding and the subsequent steps of puncturing
Please note that this example does not represent the real coders used
in HSDPA Consult the relevant literature for further details of cod-
ing theory [Ref 10] [Ref 11] and [Ref 14] as well as the specification
[TS 25212 Ref 21] which describes the coding applied in HSPA
The convolutional coder shown in Fig 2-8 consists of one input fol-
lowed by three registers in a shift configuration and finally two out-puts With each clock generation the content of each register is shifted
one register to the right as the last registerrsquos content is discarded and
a new input bit is inserted into the first register The outputs 1 and 2
are generated by an XOR operation between the linked register con-
tents In this manner we create a finite response filter and a certain
memory effect Letrsquos assume we want to transmit the following input bit
sequence 110110 01 Here the nomenclature 01 means that the lastbit of our contemplated sequence can be either 0 or 1 and we wish to
consider both alternatives The registers are initialized with all 0s and
typically some tail bits are attached to the code word which will ensure
this for the succeeding code word The table in Fig 2-8 shows the input
bit on the left side the register sequence content after each step and
outputs 1 and 2 on the right side The output sequence for the given
input will be 11 01 01 00 01 011100 Note the last two lines in the table
We do assume an either or ie there are two alternatives such thatalternative A means that after the sequence 110110 has been sent to the
coder the following bit will be logical 0 Alternative B means that after
the sequence 110110 the following bit will be a logical 1 So we present
an either or situation This will be used to explain the coding principle
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HS-DSCH High speed downlink shared channel transport channel
37
Example of convolutional coding
Input Regis-
ter 1
Regis-
ter 2
Regis-
ter 3
Out-
put 1
Out-
put 2
XOR operation
Register 3Register 2Register 1
+
Input
Output 1
Output 2
+ +
1 1 0 0 1 1
1 1 1 0 0 1
0 0 1 1 0 1
1 1 0 1 0 0
1 1 1 0 0 1
0 0 1 1 0 1
Alt A 0 0 0 1 1 1
Alt B 1 1 0 1 0 0
Fig 2-8 Simple example for convolutional coding
In Fig 2-9 that follows there is a trellis diagram representing in each
column the four possible output values of our channel coder 00 01 10
or 11 and in bold color there is the trellis path through this diagram
resulting from the input sequence Recalling our definition of the two
alternatives for the last bit of our example code word we can see that
the rightmost part of this trellis diagram shows the two possible steps
From state 01 we can only reach either state 00 or state 11 The twoother states 01 or 10 are not possible and with no input to the coder
shown in Fig 2-8 the output can reach these two states in this step For
example if the receiver detects a sequence such as 11 01 01 00 01 01 01
it knows there is an error at the last position 01 which had to be cor-
rected as either 00 or 11 because only these two alternatives are pos-
sible The error correction is performed by looking at the total trellis
path and selecting the maximum likelihood sequence estimation basedon the received data pattern In our short example we admit that we
stopped at this point of course Imagine that the input sequence of bits
continues The decoder would not know if it should proceed with the
pattern 00 or 11 so the decision will be to continue both ways The fol-
lowing step is then checked again and one of the assumed ways will dif-
fer more from the demodulated pattern than the other one This prin-
ciple is described in the Viterbi algorithm [Ref 15] Based on this algo-
rithm the stronger path will survive ie the decoder checks at eachstep which path of the examined ones in the trellis path exhibits the
smallest deviation from the demodulation sequence and thus this path
will be continued The paths exhibiting a higher deviation are discarded
to reduce the calculation expense The path through the trellis diagram
is called a ldquometricrdquo and the term ldquomaximum likelihood sequence esti-
mationrdquo (MLSE) represents the selection by the channel decoder of the
real possible metric which is the closest to the received data pattern As
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HSDPA operation overview and physical channels
an analogy If we do a crossword puzzle and find some characters in a
word the channel decoder would check in a primer or dictionary of the
language containing all possible character combinations that we callldquowordsrdquo and select the existing word that has the maximum likelihood
for the prevailing sequence of characters
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
Alternative B
Alternative A
Register 2
+ +
+
Output 1
Output 2
XOR operation
Trellis diagram above showsmetric for input sequence
110110 0
or 1
into a coder such as
1
1
0
1 10
0
1
Register 3Register 1
Fig 2-9 Metric in trellis diagram
Interleaving
Forward error correction based on convolutional coders has one disad-
vantage related to the impact of block errors If the transmission errors
are distributed they can be corrected as demonstrated in the trellis dia-gram example using the Viterbi algorithm but if many adjacent bits
are lost the decoder will have problems retrieving the right bit pattern
Interleaving means that the information to be transmitted is spread or
distributed over several bursts in such a way that contiguous informa-
tion is split up and transmitted in a time or block distributed mode
To avoid error bursts an attempt is made to spread the bit errors over
several code words This is achieved by interleaving several code wordsThis method is also called diagonal interleaving see Fig 2-10 Another
kind of interleaving is block interleaving as shown in Fig 2-11 Blocks
of code words are written row-by-row into a matrix and then read col-
umn-by-column With both methods consecutive bits of a code word
are never transmitted consecutively and conversely when the bits are
deinterleaved at the receive end error bursts are spread over several
code words
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HS-DSCH High speed downlink shared channel transport channel
39
As several code words are interleaved the decoder has to ldquowaitrdquo a cer-
tain time until all bits of a particular code word arrive This delay ie
the ldquomeasure for spreading over timerdquo is referred to as the ldquointerleav-ing depthrdquo The greater the interleaving depth the more code words are
available for spreading the error bursts and the greater the probability
that errored bits can be corrected but on the other hand this increases
the overall latency time
HSDPA uses the block diagonal interleaving principle for the HS-DSCH
only since as we should recall one goal is to have a short round-trip
time
Spreadinghellip
Interleaving
hellip
hellip
Fig 2-10 Diagonal interleaving
Write
Read
Interleaving-Matrix
Fig 2-11 Block interleaving
Puncturing
Having briefly described the principle of convolutional coding another
mechanism will be presented that is used to increase the throughputof user data and coordinate with the AMC mechanism described in
section 12 page 10 After adding redundancy the total bit stream is
now known as soft bits ie the sum including all of the raw data bits
at the input of the channel coder plus the added redundancy bits This
quantity must match the required transport block size demanded by
the transport layer and the process performed here is called rate match-
ing ie deleting some of the soft bits at the transmitting end in a pre-
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HSDPA operation overview and physical channels
defined manner or repeating or adding some stuffing bits In HSPA the
rate matching mechanism uses puncturing which provides higher data
throughput The signaled values TBS and RV tell the receiving convo-lutional coder how many and where bits have been punctured This
allows the decoder to insert blank positions which have to be filled later
by performing trellis decoding In other words we may consider the
punctured bits as bit losses created intentionally by the transmitter In
this manner the total amount of data bits can be increased for the sake
of lower redundancy In HSDPA this puncturing scheme will be very
flexible and the NodeB scheduler will set the puncturing rate adapted
to the prevailing RF conditions on the radio channel to obtain the high-
est possible data throughput under the existing conditions The disad-
vantage of adaptive coding is that we need signaling information so
that the transmitter has to inform the receiver about how many soft bits
have been punctured This is seen in Fig 2-26 page 55 in the form
of the redundancy version carried by the HS-SCCH control channel
Fig 2-12 below again depicts the principle of puncturing in HSDPAand clarifies some signaling parameters such as the transport block size
1 1 0 1 1 0 0
11 01 01 00 01 01 11
Transport block sizeInput bits into channel coder
Soft bitsOutput from channel encoder
Rate matchingPuncturing or repeating bits
11 01 01 00 01 01 11
1 01 0 00 0 01 1Coded composite transport bitsCan be several combined streams aftercoding + rate matching
Transport block size FEC
Fig 2-12 Puncturing based on coding example from Fig 2-8 page 37
The process of channel coding starts first with the transport block
size which is given by the size of the input data bit sequence added
by a cyclic redundancy checksum The next step is the channel cod-
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HS-DSCH High speed downlink shared channel transport channel
41
ing which is performed in HSPA by a so-called turbo coder The turbo
coder is a parallel concatenated convolutional coder that exhibits bet-
ter reliability compared to a single convolutional coder Discussingthe functionality of a turbo coder in all of its details would represent a
major digression from the intention of this book Accordingly we will
simply encourage the interested reader to consult the channel coding
literature for more details about turbo coders and their applications
[Ref 10] [Ref 12] Determined by the scheduler of the base station or
the redundancy version to be used the next step known as the redun-
dancy version will either puncture (the most likely) or repeat some of
the bits resulting from the channel coding process How many bits will
be punctured is defined by the coding rate In our example in Fig 2-12
we see that the input bit sequence has a length of 7 bits resulting in
14 soft bits after channel coding with our example coder providing a
coding rate of frac12 The scheduler decided to puncture 4 bits so that we
finally obtain 10 bits which have to be mapped on the physical chan-
nels Our overall coding rate is therefore given as ⁷frasl983089983088 In other words
some bits are protected with redundancy information while othersare not Note that the size of the coded composite transport channel
is determined by the physical layer parameters such as the number of
channelization codes used to convey the HS-PDSCH the modulation
scheme and the transmit time interval which is constant for HSDPA
but can be either 2 or 10 ms for HSUPA Thus its size does not need
to be signaled to the receiver and only the transport block size and the
redundancy versions will be contained in the HS-SCCH channel
222 Incremental redundancy and chase combining
for HS-DSCH
Until now we have presented some general characteristics of HSDPA
and HSUPA which we would now like to discuss in a combined pro-
cedure and then deduce two other principles The HARQ abbreviationcombines an automatic retransmission of erroneous data with a soft
combination at the receiving end A related question can now be how
the transmitter has to repeat the transport block should the retrans-
mission of data occur in an identical retransmission mode or should
some changes in coding parameters eg the manner of puncturing be
applied This question is also important for the implementation of the
rate matching step shown in Fig 2-12 The transmitter has to provide
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HSDPA operation overview and physical channels
a certain soft buffer ie a memory that stores the transmitted data for
the sake of possible retransmissions and deletes it after having received
a positive acknowledgment from the receiver Should the transmitternow store the coded composite transport data i e the data after coding
but also after puncturing This would restrict it to repeating the data in
an identical manner A better approach is to store the data after channel
coding and before puncturing Even if this requires more memory it
gives the flexibility to change the puncturing scheme and retransmit the
transport block in a different way Fig 2-13 and Fig 2-14 represent both
mechanisms that are used in HSDPA and HSUPA Identical retransmis-
sion is called chase combining and non-identical retransmission with
a different puncturing scheme is called incremental redundancy The
scheduler in the base station can decide which retransmission scheme
will be used We do not wish to delve into the details of channel coding
theory to discuss which mechanism is the better one ndash chase combin-
ing or incremental redundancy We will only mention that both mech-
anisms have their advantages and thus their applications Chase com-
bining has the advantage that the systematic bits representing the orig-inal data input into the channel coder are contained in the transmit-
ted sequence after puncturing Thus chase combined transport blocks
are ldquoself-decodablerdquo If we consider a situation where the original trans-
port block is lost completely and only the retransmitted block is pres-
ent at the receiver there is a chance to decode the data properly Mean-
while incremental redundancy seems to add more redundancy when
retransmitting but in a scenario where the first transmission contain-ing the systematic bits is lost completely and only the retransmission
is present the receiver will have no chance to decode the data without
having some of the systematic bits Accordingly incremental redun-
dancy is applied whenever sporadic bit errors occur due to a time vari-
ant channel and chase combining is selected whenever we have to deal
with complete transport block errors i e the time variance of the radio
link exhibits some bursted fading dips
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HS-DSCH High speed downlink shared channel transport channel
43
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Chase combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Transmitted bit
Punctured bit
Systematic bits
Parity 1
Parity 2
Systematic bits
Parity 1
Parity 2
Fig 2-13 Chase combining principle
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Incremental redundancy combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Systematic bits
Parity 1
Parity 2
Systematic bitsParity 1
Parity 2
Fig 2-14 Incremental redundancy
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HSDPA operation overview and physical channels
223 Constellation rearrangement
Due to the fact that HSDPA introduces a higher-order modulationscheme (16QAM) we can recognize some effects due to the physi-
cal layer influencing the susceptibility to noisy RF conditions One of
these effects can be explained by looking at the constellation diagram
in the 16QAM modulation scheme see section 12 page 10 As we
recall there is a total of 16 different constellation points given by the
modulation vector and represented by its phase and amplitude Con-
sidering the Euclidean distance which is the distance in this constella-
tion diagram between two neighboring points we can clearly see that
some points have more neighbors than others Especially the four con-
stellation points at the very four corners only have three direct neigh-
bors making them less susceptible to misdetection due to noise shift-
ing them in a certain direction On the other hand the four constella-
tion points representing the inner square of the constellation have eight
direct neighbors each and are therefore more likely to be incorrectly
detected The idea of constellation rearrangement is now to change themapping scheme applied in the original transmission when retrans-
mitting As we know the receiver will soft combine the retransmit-
ted data with the previously received information so we can achieve a
certain incremented redundancy and a certain protection mechanism
Note however that considering a sole transmission of a transport block
using a certain constellation arrangement will not show any more pos-
itive or negative results compared to other constellation arrangementsThe redundancy gain is only achieved by rearranging the constellation
mapping in a retransmitted transport block and performing soft com-
bining at the receiver Overall HSDPA defines four constellation rear-
rangement schemes which are indicated in the redundancy version
field of the HS-SCCH and are represented by the ldquobrdquo bit field ranging
from b = 0 to b = 3 All four constellation schemes are Gray encoded
ie the directly adjacent constellation symbols do not exhibit four com-
pletely different bits in order to reduce the impact of misdetection onbit errors
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High speed shared control channel (HS-SCCH)
45
Q
I
(ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1) (1 1ndash1ndash1)
(ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1) (1 1ndash1 1)
(ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1) (1ndash1ndash1 1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 0
Q
I
(ndash1 1 1 1) (ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1)
(ndash1 1 1ndash1) (ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1)
(ndash1ndash1 1ndash1) (ndash1ndash1ndash1ndash1) (1ndash1ndash1ndash1) (1ndash1 1ndash1)
(ndash1 1 1 1) (ndash1ndash1ndash1 1) (1ndash1ndash1 1) (1ndash1 1 1)
b = 2
Q
I
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (1ndash1 1 1) (ndash1ndash1 1 1)
(ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1) (ndash1 1 1 1)
(ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1) (ndash1 1 1ndash1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 1
Q
I
(1 1ndash1 1) (ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1)
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1)
(1ndash1ndash1ndash1) (ndash1ndash1ndash1ndash1) (ndash1ndash1 1ndash1) (1ndash1 1ndash1)
(1 1ndash1ndash1) (ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1)
b = 3
Fig 2-15 Constellation rearrangement in HSDPA
23 High speed shared control channel (HS-SCCH)
The HS-SCCH sends scheduling information to the UEs As seen before
the HS-PDSCH has a very flexible configuration for physical parame-
ters such as the coding rate number of code channels or retransmis-sions This high flexibility increases the complexity and engenders the
need for additional signaling information transferred on the HS-SCCH
Reception of user data in HSDPA is always a two-step procedure
First the receiver has to capture the scheduling control information
and afterwards based on the received control information it may start
demodulating and decoding the HS-PDSCH containing the user data
This two-step procedure is shown in Fig 2-16 below which lists what
kind of control information is sent to the UEs via the HS-SCCH Asshown in Fig 2-2 page 28 which describes the overall HSDPA chan-
nel structure there can be up to four HS-SCCHs assigned to one UE
But only one HS-SCCH would contain the scheduling information for
this UE within one TTI Thus the network can assign resources simul-
taneously to various UEs in the downlink direction
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HSDPA operation overview and physical channels
I would like to receive databut I dont know where myHS-PDSCH resources areand what they look like
HS-SCCH
Read the 1st HS-SCCH slotfor HS-DSCH channelizationcodes UE identity and
modulation scheme
Then the 2nd and 3rd HS-SCCHslots provide transport block sizeinformation hybrid ARQ process in-formation redundancy constellationversion new data indicator
HS-PDSCH
Fig 2-16 HS-SCCH control channel usage
Regarding the physical layer parameters we see in Fig 2-17 that the
HS-SCCH uses a channelization code with a spreading factor of 128
and it also uses the newly introduced transmit time interval of one sub-
frame which is equal to 2 ms It should be mentioned that the spread-ing factor of 128 requires double the capacity compared to similar con-
trol channels in WCDMA Release 99 reflecting the signaling overhead
needed to guarantee the huge flexibility introduced with HSDPA Addi-
tionally Fig 2-16 shows that the control information is sent consecu-
tively within one subframe The first slot within this subframe contains
the control information UE identity channelization code information
and modulation scheme identifier Slots 2 and 3 of the subframe con-tain the remaining control information Transport block size HARQ
process identifier redundancy version and new data indicator Conse-
quently the UE can self-decode slot 1 alone and slots 2 and 3 in a sec-
ond step even if they represent one logical unit This raw control infor-
mation is of course also channel coded using a turbo and on the phys-
ical layer the quantity of bits after the rate matching step is 40 bits con-
veyed in one slot corresponding to 666 micros [TS 25212 Ref 21] see also
Fig 2-28 page 56
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High speed shared control channel (HS-SCCH)
47
The HS-SCCH is a fixed rate (60 kbps SF = 128) downlinkphysical channel used to carry downlink signaling related toHS-DSCH transmission
Slot 0
Slot 1
Slot 2
Tslot
= 2560 chips
Data = 40 bits
1 subframe = 2 ms
Fig 2-17 Structure of High speed shared control channel HS-SCCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
We would like to return now to the time consecutive transmission of
control information There is a difference in the control information
in terms of its priority Some information is needed at the UE end
very urgently while other control information does not have such a
high priority But why This will be explained by looking at some tim-ing aspects defined for HSDPA If we consider the timing between
the shared data channel HS-PDSCH and the shared control chan-
nel HS-SCCH as shown in Fig 2-18 we see that the HS-PDSCH fol-
lows the HS-SCCH by exactly two slots or 5120 chips The HS-SCCH
is completely time-aligned with the general control channels CPICH
and P-CCPCH of the NodeB This is mandatory because it is a shared
channel Consider several UEs with different distances to the NodeBwanting to receive the HS-SCCH channel Thus it must have constant
timing that is known a priori The shared data channel HS-PDSCH is
now transmitted exactly 5120 chips after the first chip of the HS-SCCH
This leads to an overlapping slot thereby requiring multitasking recep-
tion at the UE end While the UE is still receiving the last slot of an
ongoing HS-SCCH subframe it may already start the reception of an
HS-PDSCH transport block The first slot in the HS-SCCH subframe
now contains information required by the physical layer to performdespreading and demodulation These values are the UE identity indi-
cating whether the UE will start demodulation of the HS-PDSCH or
not in case it is not scheduled the modulation scheme information
since the UE has to know how to interpret the received constellation
vector and whether it has to be considered as a QPSK or 16QAM con-
stellation point and finally the UE has to know which channelization
codes it has to apply to capture the HS-PDSCH transport block The
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HSDPA operation overview and physical channels
overall UE reaction time when being scheduled is now seen as 1 slot
or 2560 chips This tough requirement for the UEs is due to the objec-
tive to obtain overall a much shorter latency than legacy standards Theadditional control information such as the new data indicator redun-
dancy version and transport block size is not that urgent since it is
needed after demodulation but before channel decoding So first the
UE will sample the whole three slots of the HS-PDSCH and demodu-
late them into a bit stream which is finally handed over to the channel
decoder This principle is known as post-processing and is used typi-
cally in mobile communications technologies
J Start of HS-SCCH subframe 0 is aligned with startof P-CCPCH frames
J The HS-PDSCH starts
τ HS-PDSCH
(2times Tslot
= 5120 chips)
after the start of the HS-SCCH
UE identity etc
processing timeof receiver
HS-DSCH subframe
3 times Tslot= 7680 chips
3 times Tslot
= 7680 chips
τ HS-PDSCH
(2times Tslot
= 5120 chips)
HS-SCCH
HS-PDSCH
Fig 2-18 Timing relation between HS-SCCH and HS-PDSCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
Content of the HS-SCCH control channelThe control information contained in the HS-SCCH control chan-
nel has already been mentioned so we will now consider the values
in more detail We will begin with an overview of what kind of control
information is contained in the HS-SCCH channel before proceeding
with further details about the single control elements The following
control information is present in the HS-SCCH [TS 25212 Ref 21]
Channelization code set information (7 bits)
Modulation scheme information (1 bit) Transport block size information (6 bits)
Hybrid ARQ process information (3 bits)
Redundancy and constellation version (3 bits)
New data indicator (1 bit)
UE identity (16 bits) = H-RNTI
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High speed shared control channel (HS-SCCH)
49
Some of these parameters are more or less self-explanatory while oth-
ers require additional background information and closer examination
Modulation scheme information 1 bit
This single bit is used to inform the receiver whether the modulation
scheme QPSK or 16QAM is applied on the data channel HS-PDSCH
The interpretation of the bit x ms1 is as follows
ms1
x
if QPSK
otherwise
0
1
=
New data indicator 1 bit
The new data indicator bit field informs the receiving entity that the
prevailing PDU transmitted by the current HARQ process is either a
retransmission or contains new data This is done by setting the new
data bit to the value 0 for the first PDU on this particular HARQ process
and incrementing the value by 1 with every new data sent [TS 25321Ref 30] This leads to a toggled value In case the new data bit is not
incremented ie if it remains at its previous value it is an indicator for
retransmission
1st PDU of this
HARQ process
NDI = New data indicator
NDI = 0 NDI = 1
NACK
NDI = 1
ACK
NDI = 0
HS-SCCH HS-SCCH HS-SCCHHS-SCCH
ACK
Fig 2-19 New data indicator bit principle of incrementing value
Channelization code set information 7 bits
This field is used to indicate the number of channelization codes usedfor transmitting the transport block on the HS-PDSCH As was already
described the spreading factor applied on the HS-PDSCH is constant
with a value of 16 but the flexible values are the number of channeliza-
tion codes forming a cluster when using multiple codes and their posi-
tion in the code tree It is not allowed to distribute the code channels
over the code tree diagram For the sake of simplicity in signaling sev-
eral channelization codes form one cluster and these codes are con-
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HSDPA operation overview and physical channels
tiguous in the channelization code tree [TS 25213 Ref 22] Fig 2-20
illustrates the principle of indicating the channelization codes on the
HS-SCCH
SF = 16
Code ldquo0rdquo isreserved forcommonchannels
Code offset 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15P = 5O = 7
Code group indicatorx
ccs1 x
ccs2 x
ccs3 = min (Pminus 1 15 minusP)
Code offset indicatorx
ccs4 x
ccs5 x
ccs6 x
ccs7 = |Ominus 1minus P8 times15|
A cluster of codes
can be allocated to a UEC
ch16Ohellip C
ch16O + P minus 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1
2 2 2 2 2 2 2 2 2 2 2 2 2 2 14 14
1 2 3 4 5 6 7 8 9 10 11 12 13 14 2 1
3 3 3 3 3 3 3 3 3 3 3 3 3 13 13 13
1 2 3 4 5 6 7 8 9 10 11 12 13 3 2 1
4 4 4 4 4 4 4 4 4 4 4 4 12 12 12 121 2 3 4 5 6 7 8 9 10 11 12 4 3 2 1
5 5 5 5 5 5 5 5 5 5 5 11 11 11 11 11
1 2 3 4 5 6 7 8 9 10 11 5 4 3 2 1
6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10
1 2 3 4 5 6 7 8 9 10 6 5 4 3 2 1
7 7 7 7 7 7 7 7 7 9 9 9 9 9 9 9
1 2 3 4 5 6 7 8 9 7 6 5 4 3 2 1
8 8 8 8 8 8 8 8
8 7 6 5 4 3 2 1
0 (115)
1 (214)
2 (313)
3 (412)
4 (511)
5 (610)
6 (79)
7 (88) Redundant area
C l u s t e r c o d e i n d i c a t o r ( 3 b i t s )
Tree offset indicator (4 bits)
Signaled on HS-SCCH
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
PO
Decoding notation
Number ofmulti-codes
Offset fromleft right incode tree (SF = 16)
Fig 2-20 Channelization code set indicating the HS-PDSCH code cluster
The idea behind the code indication is a matrix with the rows repre-
senting the number of codes per cluster and the columns represent-
ing the position of that cluster the offset value in the code tree Recall-
ing that the maximum number of channelization codes per clusteris 15 and if the cluster size is 1 the offset values can also range from
1 to 15 the resulting matrix would have 15 rows and 15 columns Since
we know that four bits are needed to represent an integer from 1 to 15
we need a total of 4 + 4 = 8 bits for representation of the channeliza-
tion code set information It is a smart idea to save one bit The 15 times 15
matrix would contain much redundant information By way of analogy
like in a road map indicating distances between cities A table showing
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High speed shared control channel (HS-SCCH)
51
the distance from city A to city B the opposite distance from city B to
city A is redundant information The useful information has the form
of a triangle The idea is to cut the lower part rotate it and append itto the spare part of the upper table In this manner a table is obtained
with 7 rows and 15 columns and it is possible to indicate each position
in it with just 7 bits
1 5 r o w s 7
r o w s
Matrix reduction for channeli-
zation code set information
15 columns
Fig 2-21 Matrix size reduction for channelization code set information
The content of the channelization code set matrix can be described as
a value with two numbers The upper number is the number of mul-
ticodes forming one cluster and the lower number is the offset in the
channelization code tree Accordingly the example in Fig 2-20 can be
interpreted to mean the HS-SCCH sends the bits as row number 4 and
column number 6 in the matrix The content of this element are the
values 5 over 7 which have to be interpreted as a cluster size of 5 codesand an offset of 7
Transport block size information 6 bits
With a length of six bits the transport block size (TBS) informa-
tion informs the receiving UE entity about the data block size of the
transport block sent on the HS-PDSCH We should keep in mind the
link adaptation performed with the adaptive modulation and coding
scheme that was described in section 12 page 10 The ratio errorcorrection and user data are flexible while the physical layer param-
eters such as the spreading factor modulation scheme and number of
channelization codes determine the physical block size This physical
block consists of the user data ratio or transport block size and the for-
ward error correction or redundancy information As this ratio is flex-
ible the HS-SCCH will inform the receiving UE entity about the size
of the transport block Here too there is a strategy of bit reduction the
8122019 hspa_e_lp
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HSDPA operation overview and physical channels
goal is to inform the receiver with as few bits as possible A non-effi-
cient approach would involve conversion of the decimal number repre-
senting the TBS into a binary sequence but the number of bits neededwould exceed the space available on the HS-SCCH Imagine that the
range of transport block sizes depends on the physical layer condi-
tions The ambient physical layer parameters modulation scheme and
number of channelization codes set a certain working point where the
remaining flexibility for a different TBS configuration can be obtained
by more or less puncturing resulting in a flexible ratio between for-
ward error correction and user data This will lead to a two-step proce-
dure when evaluating the transport block size First the receiver exam-
ines the information modulation scheme and number of channeliza-
tion codes scheduled via HS-SCCH which indicate the value k0 l as
shown in Fig 2-22 The 6-bit HS-SCCH control parameter transport
block size information will be the transport format resource indica-
tor (TFRI) named ki Let k t be the sum of the two values kt = ki + k0i
Both values kt and k0 i can be obtained from tables given by [TS 25321
Ref 30] The range for the TFRI is from 1 to 256 and the derived trans-port block size ranges from 137 bits to 27 952 bits The first table indi-
cates the value k 0 i based on the channelization code and the modula-
tion scheme
Combination i Modulation scheme Number of channelization codes k0 i
0
QPSK
1 1
1 2 40
2 3 633 4 79
4 5 92
5 6 102
Fig 2-22 Extract from TS 25321 table representing k0 i
The second table indicates the final transport block size based on kt
Index TB size Index TB size Index TB size1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
4 173 89 1456 174 6673
5 185 90 1483 175 6793
6 197 91 1509 176 6916
7 209 92 1537 177 7041
Fig 2-23 Extract from TS 25321 table representing kt
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High speed shared control channel (HS-SCCH)
53
J The transport block size used on HS-DSCH is not signaled explicitly on HS-SCCHJ Instead a transport block size index k
i is signaled to indicate the transport block size
First stepModulation scheme andnumber of channelizationcodes as signaled on HS-SCCHdetermine value k
0 i
Second step
Index kt = k
i + k
0i
determines HS-DSCH
transport block size
kt = k
i + k
0i
Table according to 3GPP TS 25321 extract from QPSK section
Table according to 3GPP TS 25321 254 entries in total
Combination i Modulation
scheme
Number of
channelization codes
k0 i
0
QPSK
1 1
1 2 40
2 3 63
3 4 79
4 hellip hellip
Index TB size Index TB size Index TB size
1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
helliphellip hellip hellip hellip hellip
Fig 2-24 Retrieval of transport block size information
Source Fig 2-22 to Fig 2-24 [TS 25321 Ref 30] reproduced by permission of 3GPP
Hybrid ARQ process information 3 bits
The concept behind the hybrid automatic repeat request (HARQ) was
introduced in section 13 page 14 One feature is the possibility of
multitasking ie having several HARQ processes activated at the same
time Fig 2-25 below shows the need to signal the process identity tothe receiver Remember that on the downlink there is a shared chan-
nel concept so the NodeB can flexibly decide which UE will be sched-
uled with a downlink transport block Up to eight HARQ processes
can be signaled via higher layers to one UE Note however that due to
the round-trip timing six HARQ processes must be active to achieve
the maximum throughput as shown in Fig 2-51 page 79 Compared
with HSUPA the HARQ processes on the downlink are asynchronous
so they have to be indicated but on the uplink they are synchronous sothey do not need to be signaled explicitly
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HSDPA operation overview and physical channels
Asynchronous DL minus Synchronous ULNumber of H-ARQ rocesses = 1 to 8 er UE
UL HS-DPCCH UE1
UE1 HARQ processes 1 to 4
3 4 1 42 11 1 32retrans
2
A N A A
A A
N A
UL HS-DPCCH UE2
HS-PDSCH
UE2 HARQ processes 1 to 2
Fig 2-25 HARQ process indication on HS-SCCH
Fig 2-25 shows a typical situation on the downlink (point-to-multi-
point) The NodeB sends data to several UEs sharing the HS-PDSCH
so therefore the HARQ process is asynchronous The time when a
transport block is retransmitted is not fixed For this reason the pro-
cess identifier is signaled on the HS-SCCH Based on the HARQ pro-
cess identity and the new data indicator bit the receiving entity knows
which part of the soft buffer memory has to be used in case of soft com-bining On the uplink the situation is slightly simpler The UE only
communicates with one NodeB so it is a point-to-point connection
Thus retransmission always occurs at a fixed time linked to the origi-
nal transmission
Redundancy and constellation version 3 bits
Adaptive modulation and coding involve flexible selection of modula-tion and coding schemes that are signaled to the receiving UE via the
parameters transport block size and modulation scheme information
Another concept used in HSDPA was previously discussed Chase com-
bining or incremental redundancy (see section 222 page 41) This
means that in case of retransmission the transmit entity can dynami-
cally select another puncturing scheme or keep the puncturing as it was
in the original transmission The applied puncturing scheme is signaled
as redundancy information to the receiver Additionally in case of the16QAM modulation scheme the transmitter can select another constel-
lation arrangement which is also signaled to the UE with the three bits
for the redundancy and constellation version see Fig 2-15 page 45
Depending on the modulation scheme (QPSK or 16QAM) there are
two different tables indicating the parameters ldquosrdquo ldquorrdquo and ldquobrdquo The
parameters ldquosrdquo and ldquorrdquo indicate which scheme is used for puncturing
ie if the puncturing mechanism prioritizes the systematic bits or not
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High speed shared control channel (HS-SCCH)
55
and which puncturing algorithm is used The parameter ldquobrdquo indicates
the constellation mapping version The receiver needs this information
to perform proper demodulation and decoding
Initial transmission
1st retransmission
2nd retransmission
3rd retransmission
r
0
0
1
1
2
2
3
xrv
(value)
s
0 1
1 0
2 1
3 0
4 1
5 0
6 1
7 0 3
s = 1 Systematic bits are prioritizeds = 0 Non-systematic bits are prioritized
r (range 0 to 3 for QPSK) influencesJ Input parameter for puncturing or (together with s) for repetition algorithm defined in TS 25212J Selection of parity bits
Redundancy version coding sequences are signaled on HS-SCCH egndash 0 2 5 6 One initial transmission + 3 retransmissions with different r and s parameters
Fig 2-26 Signaling of redundancy version parameters r and s QPSK case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
Initial transmission
2nd retransmission
1st retransmission
3rd retransmission
r (range 0 to 1 for 16QAM)influences input parameterfor puncturing or (togetherwith s) for repetitionalgorithm defined in
TS 25212 and thus selectionof parity bits
Redundancy version coding sequences are signaled on HS-SCCH egminus 6 4 0 5 Chase combining (no change in s and r parameters ie same redundancyversion) with four possible constellations
x rv (value) s r b
0 1 0 0
1 0 0 0
2 1 1 1
3 0 1 1
4 1 0 1
5 1 0 2
6 1 0 3
7 1 1 0
Definition of parameter s as for QPSK
b (range 0 to 3) describes constellationrearrangement to averagereliability of bits
Fig 2-27 Signaling of redundancy version parameters r s and b 16QAM case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
UE identity H-RNTI 16 bits
The HSDPA radio network transaction identifier (H-RNTI) unam-
biguously identifies the UE having an HS-PDSCH assignment within
a cell It is allocated to the UE via layer 3 signaling procedures at the
radio bearer setup if the radio bearer is an HSDPA connection This
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HSDPA operation overview and physical channels
value represents a temporary name of the UE used to address it when
scheduling data packets via HS-SCCH
HS-SCCH channel coding
The control information contained in the HS-SCCH is of course pro-
tected with channel coding mechanisms the whole coding chain is
described in Fig 2-28 Fig 2-18 page 48 presents the separation of
the control information into two code blocks which are sent consec-
utively mapped on slot 1 and slot 2 + 3 of one HS-SCCH subframe
This principle is also visible in the coding chain The first control block
consisting of channelization information modulation scheme and UE
identity is coded separately from the remaining control values to enable
the UE receiver to decode this first slot separately and prepare for pos-
sible HS-PDSCH reception The coding steps shown in Fig 2-28 such
as rate matching 1 and 2 are similar to the HS-PDSCH coding chain
and are further described in [TS 25212 Ref 21]
Channelcoding 1
R atematching 1
mux
Channelcoding 2
Ratematching 2
RVcoding
UE-specificCRC attachment
UE-specificmasking
Physical channelmapping
r s b
mux
Channelizationcode set
Modulationscheme
Transport block size information
HARQ processinformation
Redundancy andconstellation version
New data indicator
UE identity
UE identity
Fig 2-28 Channel coding for HS-SCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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High speed dedicated physical control channel (HS-DPCCH)
57
24 High speed dedicated physical control channel (HS-DPCCH)
In an active HSDPA connection the UE has to send acknowledgment ornon-acknowledgment reports (as described in section 13 page 14
where the HARQ process is described) as well as channel status infor-
mation to the network The reporting is performed on this physical
control channel HS-DPCCH
As ubiquitous in HSDPA the uplink is also configured into a subframe
structure of 2 ms corresponding to three slots The first slot of the sub-
frame carries the ACK NACK information the UE sends to the NodeB
while the following two slots ie slot 2 and 3 of the subframe convey
the CQI value the channel quality information to the NodeB
Subframe 0 Subframe i Subframe 4
Tslot
= 2560 chips J The spreading factor of theHS-DPCCH is 256 (10 bits peruplink slot)
J The HS-DPCCH can only existtogether with an UL DPCCH
(ded phys control channel)J The DPDCH (dedicated physical data channel) the DPCCH andthe HS-DPCCH are IQ codemultiplexed
HARQ-ACK CQI = Channel quality information
2 times Tslot
= 5120 chips
One radio frame Tf = 10 ms
One HS-DPCCH subframe 2 ms
Fig 2-29 HS-DPCCH configuration
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The slot format for HS-DPCCH describes a quantity of 30 bits per sub-frame resulting in a data rate of 15 kbps The spreading factor used for
the HS-DPCCH is constant and is always equal to 256 but the chan-
nelization code that is used as well as the mapping on either the I or
Q axis depends on several factors eg the co-existence of an HSDPA
connection with a circuit-switched connection meaning whether a
DPDCH established or not Fig 2-36 page 64 illustrates this IQ
mapping and Fig 2-35 page 63 shows the channelization code used
for HS-DPCCH
The HS-DPCCH builds a logical unit of one subframe but having the
independent control information HARQ-ACK and CQI included which
could be separately decoded at the NodeB Note that the slot carrying
the ACK NACK statement is active only when the UE has been sched-
uled by an HS-PDSCH subframe in the corresponding downlink sub-
frame previously Assuming the UE has not received a transport block
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HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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HSDPA operation overview and physical channels
Error detection
addedJ Block codingJ CRC attachmentJ Parity bits
Redundancy added
for error correctionForward errorcorrection (FEC) by J Convolutional codingJ Turbo coding
Rate matching
J PuncturingJ Repetition
Inter-
leaving
Deinter-leaving
Error correctionConvolutionaldecodingJ
Turbo decoding
Error detectionJ CRC check J Parity check
Transmitting end
Receiving end
Fig 2-7 General channel coding components example
Error detection ndash Example with block coding
Generally known as outer loop error correction this step involves
attachment of some error detection mechanisms that are added onto
the data block by the transmitter to enable the receiver to detect errorsCommon examples are parity bit attachments or cyclic redundancy
checks using the block coding principle Block coding involves calcu-
lating a certain number of parity bits for a block of data bits and then
appending them to the data block At the data sink ie the receiving
end errors in the received code word can be detected with the aid of
these redundancy bits
HSDPA uses a type of block code known as a cyclic redundancy check
(CRC) The cyclic codes of this type are also known as (nk) codes
where n represents the number of code symbols (bits) and k the num-
ber of data symbols (bits) The number of check bits is therefore nk
In HSDPA there is only one length of cyclic redundancy check Every
transport block in the HS-DSCH is followed by a 24-bit CRC An exam-
ple of how this CRC-based block coding works is given below
These check bits and thus the code word are produced by a generating
polynomial A polynomial is used to represent a bit sequence as a code
word with the power of each term in the polynomial corresponding to
a bit position and the coefficient of each term to a bit (Dm) A data word
with k bits is therefore represented as follows
Dk ∙ x
k
+ Dkndash1 ∙ x
kndash1
+ hellip + D983089 ∙ x + D983088
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HS-DSCH High speed downlink shared channel transport channel
35
An example could be the simple bit pattern 1101 which would repre-
sented as polynomial 983160983091 + 983160 + 1 i e 1 ∙ x 983091 + 0 ∙ x 983090 + 1 ∙ x 1048625 + 1 ∙ x 1048624
To calculate the check bits the data word D(x ) is multiplied by x nndashk
and then divided by the generating polynomial G(x ) which is of degree
(nndashk) The remainder R(x ) is the check word comprising the check bits
R x mainder x D x
G x
n k
( ) Re ( )
( )=
sdot
minus
The code word C (x ) is now obtained by appending the check word to
the data word
C (x ) = x nndashk ∙ D(x ) + R(x )
The receiver knows the generating polynomial G(x ) and performs the
division C (x )G(x ) If there are no transmission errors the code word
C (x ) is divisible by G(x ) The probability is therefore high that anyerrors will be detected The maximum number of errors per code word
that can be detected is determined by the length of the check word
which in our case is the length of the CRC But what is not known is the
position of those errors and thus there is no way to correct them This
is the responsibility of the ldquoinnerrdquo error correction such as the attach-
ment of redundancy bits which enable the receiver to correct some bit
errors Note that block codes can also be used in general to correcterrors but this is not performed in HSPA because this would increase
the overall latency time
Error correction performed with forward error correction (FEC)
principle of convolutional coding
With forward error correction (FEC) redundant bits are inserted into
data packets (bursts) at the transmitting end to enable the receiving
end to implement a correction mechanism The assumption is that theerrors do not occur in a burst Here the principle of a convolutional
coder is used This type of coder ldquoremembersrdquo the last n bits sent and
adds each input bit to the stored n bits The words obtained at the out-
put are usually longer than one bit The code rate defines the ratio of
the input bits to the output bits for example a coder using a code rate
of frac12 generates for each input bit a code word of two output bits Error
correction is based on the fact that a previous state ie a word or a bit
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HSDPA operation overview and physical channels
sequence can only assume one of two succeeding states depending on
whether 0 or 1 was entered into the coder ie the decoder decides for
the metric providing the minimum error estimation If a word arrivesat the receiver in a state that cannot be reached from a state obtain-
able from one of the two input combinations a transmission error has
occurred and needs to be corrected This procedure is equivalent to
tracing a path through a trellis diagram which is familiar from cod-
ing theory
We would now like to discuss a brief example to demonstrate the func-
tionality of channel coding and the subsequent steps of puncturing
Please note that this example does not represent the real coders used
in HSDPA Consult the relevant literature for further details of cod-
ing theory [Ref 10] [Ref 11] and [Ref 14] as well as the specification
[TS 25212 Ref 21] which describes the coding applied in HSPA
The convolutional coder shown in Fig 2-8 consists of one input fol-
lowed by three registers in a shift configuration and finally two out-puts With each clock generation the content of each register is shifted
one register to the right as the last registerrsquos content is discarded and
a new input bit is inserted into the first register The outputs 1 and 2
are generated by an XOR operation between the linked register con-
tents In this manner we create a finite response filter and a certain
memory effect Letrsquos assume we want to transmit the following input bit
sequence 110110 01 Here the nomenclature 01 means that the lastbit of our contemplated sequence can be either 0 or 1 and we wish to
consider both alternatives The registers are initialized with all 0s and
typically some tail bits are attached to the code word which will ensure
this for the succeeding code word The table in Fig 2-8 shows the input
bit on the left side the register sequence content after each step and
outputs 1 and 2 on the right side The output sequence for the given
input will be 11 01 01 00 01 011100 Note the last two lines in the table
We do assume an either or ie there are two alternatives such thatalternative A means that after the sequence 110110 has been sent to the
coder the following bit will be logical 0 Alternative B means that after
the sequence 110110 the following bit will be a logical 1 So we present
an either or situation This will be used to explain the coding principle
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HS-DSCH High speed downlink shared channel transport channel
37
Example of convolutional coding
Input Regis-
ter 1
Regis-
ter 2
Regis-
ter 3
Out-
put 1
Out-
put 2
XOR operation
Register 3Register 2Register 1
+
Input
Output 1
Output 2
+ +
1 1 0 0 1 1
1 1 1 0 0 1
0 0 1 1 0 1
1 1 0 1 0 0
1 1 1 0 0 1
0 0 1 1 0 1
Alt A 0 0 0 1 1 1
Alt B 1 1 0 1 0 0
Fig 2-8 Simple example for convolutional coding
In Fig 2-9 that follows there is a trellis diagram representing in each
column the four possible output values of our channel coder 00 01 10
or 11 and in bold color there is the trellis path through this diagram
resulting from the input sequence Recalling our definition of the two
alternatives for the last bit of our example code word we can see that
the rightmost part of this trellis diagram shows the two possible steps
From state 01 we can only reach either state 00 or state 11 The twoother states 01 or 10 are not possible and with no input to the coder
shown in Fig 2-8 the output can reach these two states in this step For
example if the receiver detects a sequence such as 11 01 01 00 01 01 01
it knows there is an error at the last position 01 which had to be cor-
rected as either 00 or 11 because only these two alternatives are pos-
sible The error correction is performed by looking at the total trellis
path and selecting the maximum likelihood sequence estimation basedon the received data pattern In our short example we admit that we
stopped at this point of course Imagine that the input sequence of bits
continues The decoder would not know if it should proceed with the
pattern 00 or 11 so the decision will be to continue both ways The fol-
lowing step is then checked again and one of the assumed ways will dif-
fer more from the demodulated pattern than the other one This prin-
ciple is described in the Viterbi algorithm [Ref 15] Based on this algo-
rithm the stronger path will survive ie the decoder checks at eachstep which path of the examined ones in the trellis path exhibits the
smallest deviation from the demodulation sequence and thus this path
will be continued The paths exhibiting a higher deviation are discarded
to reduce the calculation expense The path through the trellis diagram
is called a ldquometricrdquo and the term ldquomaximum likelihood sequence esti-
mationrdquo (MLSE) represents the selection by the channel decoder of the
real possible metric which is the closest to the received data pattern As
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HSDPA operation overview and physical channels
an analogy If we do a crossword puzzle and find some characters in a
word the channel decoder would check in a primer or dictionary of the
language containing all possible character combinations that we callldquowordsrdquo and select the existing word that has the maximum likelihood
for the prevailing sequence of characters
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
Alternative B
Alternative A
Register 2
+ +
+
Output 1
Output 2
XOR operation
Trellis diagram above showsmetric for input sequence
110110 0
or 1
into a coder such as
1
1
0
1 10
0
1
Register 3Register 1
Fig 2-9 Metric in trellis diagram
Interleaving
Forward error correction based on convolutional coders has one disad-
vantage related to the impact of block errors If the transmission errors
are distributed they can be corrected as demonstrated in the trellis dia-gram example using the Viterbi algorithm but if many adjacent bits
are lost the decoder will have problems retrieving the right bit pattern
Interleaving means that the information to be transmitted is spread or
distributed over several bursts in such a way that contiguous informa-
tion is split up and transmitted in a time or block distributed mode
To avoid error bursts an attempt is made to spread the bit errors over
several code words This is achieved by interleaving several code wordsThis method is also called diagonal interleaving see Fig 2-10 Another
kind of interleaving is block interleaving as shown in Fig 2-11 Blocks
of code words are written row-by-row into a matrix and then read col-
umn-by-column With both methods consecutive bits of a code word
are never transmitted consecutively and conversely when the bits are
deinterleaved at the receive end error bursts are spread over several
code words
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HS-DSCH High speed downlink shared channel transport channel
39
As several code words are interleaved the decoder has to ldquowaitrdquo a cer-
tain time until all bits of a particular code word arrive This delay ie
the ldquomeasure for spreading over timerdquo is referred to as the ldquointerleav-ing depthrdquo The greater the interleaving depth the more code words are
available for spreading the error bursts and the greater the probability
that errored bits can be corrected but on the other hand this increases
the overall latency time
HSDPA uses the block diagonal interleaving principle for the HS-DSCH
only since as we should recall one goal is to have a short round-trip
time
Spreadinghellip
Interleaving
hellip
hellip
Fig 2-10 Diagonal interleaving
Write
Read
Interleaving-Matrix
Fig 2-11 Block interleaving
Puncturing
Having briefly described the principle of convolutional coding another
mechanism will be presented that is used to increase the throughputof user data and coordinate with the AMC mechanism described in
section 12 page 10 After adding redundancy the total bit stream is
now known as soft bits ie the sum including all of the raw data bits
at the input of the channel coder plus the added redundancy bits This
quantity must match the required transport block size demanded by
the transport layer and the process performed here is called rate match-
ing ie deleting some of the soft bits at the transmitting end in a pre-
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HSDPA operation overview and physical channels
defined manner or repeating or adding some stuffing bits In HSPA the
rate matching mechanism uses puncturing which provides higher data
throughput The signaled values TBS and RV tell the receiving convo-lutional coder how many and where bits have been punctured This
allows the decoder to insert blank positions which have to be filled later
by performing trellis decoding In other words we may consider the
punctured bits as bit losses created intentionally by the transmitter In
this manner the total amount of data bits can be increased for the sake
of lower redundancy In HSDPA this puncturing scheme will be very
flexible and the NodeB scheduler will set the puncturing rate adapted
to the prevailing RF conditions on the radio channel to obtain the high-
est possible data throughput under the existing conditions The disad-
vantage of adaptive coding is that we need signaling information so
that the transmitter has to inform the receiver about how many soft bits
have been punctured This is seen in Fig 2-26 page 55 in the form
of the redundancy version carried by the HS-SCCH control channel
Fig 2-12 below again depicts the principle of puncturing in HSDPAand clarifies some signaling parameters such as the transport block size
1 1 0 1 1 0 0
11 01 01 00 01 01 11
Transport block sizeInput bits into channel coder
Soft bitsOutput from channel encoder
Rate matchingPuncturing or repeating bits
11 01 01 00 01 01 11
1 01 0 00 0 01 1Coded composite transport bitsCan be several combined streams aftercoding + rate matching
Transport block size FEC
Fig 2-12 Puncturing based on coding example from Fig 2-8 page 37
The process of channel coding starts first with the transport block
size which is given by the size of the input data bit sequence added
by a cyclic redundancy checksum The next step is the channel cod-
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HS-DSCH High speed downlink shared channel transport channel
41
ing which is performed in HSPA by a so-called turbo coder The turbo
coder is a parallel concatenated convolutional coder that exhibits bet-
ter reliability compared to a single convolutional coder Discussingthe functionality of a turbo coder in all of its details would represent a
major digression from the intention of this book Accordingly we will
simply encourage the interested reader to consult the channel coding
literature for more details about turbo coders and their applications
[Ref 10] [Ref 12] Determined by the scheduler of the base station or
the redundancy version to be used the next step known as the redun-
dancy version will either puncture (the most likely) or repeat some of
the bits resulting from the channel coding process How many bits will
be punctured is defined by the coding rate In our example in Fig 2-12
we see that the input bit sequence has a length of 7 bits resulting in
14 soft bits after channel coding with our example coder providing a
coding rate of frac12 The scheduler decided to puncture 4 bits so that we
finally obtain 10 bits which have to be mapped on the physical chan-
nels Our overall coding rate is therefore given as ⁷frasl983089983088 In other words
some bits are protected with redundancy information while othersare not Note that the size of the coded composite transport channel
is determined by the physical layer parameters such as the number of
channelization codes used to convey the HS-PDSCH the modulation
scheme and the transmit time interval which is constant for HSDPA
but can be either 2 or 10 ms for HSUPA Thus its size does not need
to be signaled to the receiver and only the transport block size and the
redundancy versions will be contained in the HS-SCCH channel
222 Incremental redundancy and chase combining
for HS-DSCH
Until now we have presented some general characteristics of HSDPA
and HSUPA which we would now like to discuss in a combined pro-
cedure and then deduce two other principles The HARQ abbreviationcombines an automatic retransmission of erroneous data with a soft
combination at the receiving end A related question can now be how
the transmitter has to repeat the transport block should the retrans-
mission of data occur in an identical retransmission mode or should
some changes in coding parameters eg the manner of puncturing be
applied This question is also important for the implementation of the
rate matching step shown in Fig 2-12 The transmitter has to provide
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HSDPA operation overview and physical channels
a certain soft buffer ie a memory that stores the transmitted data for
the sake of possible retransmissions and deletes it after having received
a positive acknowledgment from the receiver Should the transmitternow store the coded composite transport data i e the data after coding
but also after puncturing This would restrict it to repeating the data in
an identical manner A better approach is to store the data after channel
coding and before puncturing Even if this requires more memory it
gives the flexibility to change the puncturing scheme and retransmit the
transport block in a different way Fig 2-13 and Fig 2-14 represent both
mechanisms that are used in HSDPA and HSUPA Identical retransmis-
sion is called chase combining and non-identical retransmission with
a different puncturing scheme is called incremental redundancy The
scheduler in the base station can decide which retransmission scheme
will be used We do not wish to delve into the details of channel coding
theory to discuss which mechanism is the better one ndash chase combin-
ing or incremental redundancy We will only mention that both mech-
anisms have their advantages and thus their applications Chase com-
bining has the advantage that the systematic bits representing the orig-inal data input into the channel coder are contained in the transmit-
ted sequence after puncturing Thus chase combined transport blocks
are ldquoself-decodablerdquo If we consider a situation where the original trans-
port block is lost completely and only the retransmitted block is pres-
ent at the receiver there is a chance to decode the data properly Mean-
while incremental redundancy seems to add more redundancy when
retransmitting but in a scenario where the first transmission contain-ing the systematic bits is lost completely and only the retransmission
is present the receiver will have no chance to decode the data without
having some of the systematic bits Accordingly incremental redun-
dancy is applied whenever sporadic bit errors occur due to a time vari-
ant channel and chase combining is selected whenever we have to deal
with complete transport block errors i e the time variance of the radio
link exhibits some bursted fading dips
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HS-DSCH High speed downlink shared channel transport channel
43
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Chase combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Transmitted bit
Punctured bit
Systematic bits
Parity 1
Parity 2
Systematic bits
Parity 1
Parity 2
Fig 2-13 Chase combining principle
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Incremental redundancy combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Systematic bits
Parity 1
Parity 2
Systematic bitsParity 1
Parity 2
Fig 2-14 Incremental redundancy
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HSDPA operation overview and physical channels
223 Constellation rearrangement
Due to the fact that HSDPA introduces a higher-order modulationscheme (16QAM) we can recognize some effects due to the physi-
cal layer influencing the susceptibility to noisy RF conditions One of
these effects can be explained by looking at the constellation diagram
in the 16QAM modulation scheme see section 12 page 10 As we
recall there is a total of 16 different constellation points given by the
modulation vector and represented by its phase and amplitude Con-
sidering the Euclidean distance which is the distance in this constella-
tion diagram between two neighboring points we can clearly see that
some points have more neighbors than others Especially the four con-
stellation points at the very four corners only have three direct neigh-
bors making them less susceptible to misdetection due to noise shift-
ing them in a certain direction On the other hand the four constella-
tion points representing the inner square of the constellation have eight
direct neighbors each and are therefore more likely to be incorrectly
detected The idea of constellation rearrangement is now to change themapping scheme applied in the original transmission when retrans-
mitting As we know the receiver will soft combine the retransmit-
ted data with the previously received information so we can achieve a
certain incremented redundancy and a certain protection mechanism
Note however that considering a sole transmission of a transport block
using a certain constellation arrangement will not show any more pos-
itive or negative results compared to other constellation arrangementsThe redundancy gain is only achieved by rearranging the constellation
mapping in a retransmitted transport block and performing soft com-
bining at the receiver Overall HSDPA defines four constellation rear-
rangement schemes which are indicated in the redundancy version
field of the HS-SCCH and are represented by the ldquobrdquo bit field ranging
from b = 0 to b = 3 All four constellation schemes are Gray encoded
ie the directly adjacent constellation symbols do not exhibit four com-
pletely different bits in order to reduce the impact of misdetection onbit errors
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High speed shared control channel (HS-SCCH)
45
Q
I
(ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1) (1 1ndash1ndash1)
(ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1) (1 1ndash1 1)
(ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1) (1ndash1ndash1 1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 0
Q
I
(ndash1 1 1 1) (ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1)
(ndash1 1 1ndash1) (ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1)
(ndash1ndash1 1ndash1) (ndash1ndash1ndash1ndash1) (1ndash1ndash1ndash1) (1ndash1 1ndash1)
(ndash1 1 1 1) (ndash1ndash1ndash1 1) (1ndash1ndash1 1) (1ndash1 1 1)
b = 2
Q
I
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (1ndash1 1 1) (ndash1ndash1 1 1)
(ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1) (ndash1 1 1 1)
(ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1) (ndash1 1 1ndash1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 1
Q
I
(1 1ndash1 1) (ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1)
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1)
(1ndash1ndash1ndash1) (ndash1ndash1ndash1ndash1) (ndash1ndash1 1ndash1) (1ndash1 1ndash1)
(1 1ndash1ndash1) (ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1)
b = 3
Fig 2-15 Constellation rearrangement in HSDPA
23 High speed shared control channel (HS-SCCH)
The HS-SCCH sends scheduling information to the UEs As seen before
the HS-PDSCH has a very flexible configuration for physical parame-
ters such as the coding rate number of code channels or retransmis-sions This high flexibility increases the complexity and engenders the
need for additional signaling information transferred on the HS-SCCH
Reception of user data in HSDPA is always a two-step procedure
First the receiver has to capture the scheduling control information
and afterwards based on the received control information it may start
demodulating and decoding the HS-PDSCH containing the user data
This two-step procedure is shown in Fig 2-16 below which lists what
kind of control information is sent to the UEs via the HS-SCCH Asshown in Fig 2-2 page 28 which describes the overall HSDPA chan-
nel structure there can be up to four HS-SCCHs assigned to one UE
But only one HS-SCCH would contain the scheduling information for
this UE within one TTI Thus the network can assign resources simul-
taneously to various UEs in the downlink direction
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HSDPA operation overview and physical channels
I would like to receive databut I dont know where myHS-PDSCH resources areand what they look like
HS-SCCH
Read the 1st HS-SCCH slotfor HS-DSCH channelizationcodes UE identity and
modulation scheme
Then the 2nd and 3rd HS-SCCHslots provide transport block sizeinformation hybrid ARQ process in-formation redundancy constellationversion new data indicator
HS-PDSCH
Fig 2-16 HS-SCCH control channel usage
Regarding the physical layer parameters we see in Fig 2-17 that the
HS-SCCH uses a channelization code with a spreading factor of 128
and it also uses the newly introduced transmit time interval of one sub-
frame which is equal to 2 ms It should be mentioned that the spread-ing factor of 128 requires double the capacity compared to similar con-
trol channels in WCDMA Release 99 reflecting the signaling overhead
needed to guarantee the huge flexibility introduced with HSDPA Addi-
tionally Fig 2-16 shows that the control information is sent consecu-
tively within one subframe The first slot within this subframe contains
the control information UE identity channelization code information
and modulation scheme identifier Slots 2 and 3 of the subframe con-tain the remaining control information Transport block size HARQ
process identifier redundancy version and new data indicator Conse-
quently the UE can self-decode slot 1 alone and slots 2 and 3 in a sec-
ond step even if they represent one logical unit This raw control infor-
mation is of course also channel coded using a turbo and on the phys-
ical layer the quantity of bits after the rate matching step is 40 bits con-
veyed in one slot corresponding to 666 micros [TS 25212 Ref 21] see also
Fig 2-28 page 56
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High speed shared control channel (HS-SCCH)
47
The HS-SCCH is a fixed rate (60 kbps SF = 128) downlinkphysical channel used to carry downlink signaling related toHS-DSCH transmission
Slot 0
Slot 1
Slot 2
Tslot
= 2560 chips
Data = 40 bits
1 subframe = 2 ms
Fig 2-17 Structure of High speed shared control channel HS-SCCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
We would like to return now to the time consecutive transmission of
control information There is a difference in the control information
in terms of its priority Some information is needed at the UE end
very urgently while other control information does not have such a
high priority But why This will be explained by looking at some tim-ing aspects defined for HSDPA If we consider the timing between
the shared data channel HS-PDSCH and the shared control chan-
nel HS-SCCH as shown in Fig 2-18 we see that the HS-PDSCH fol-
lows the HS-SCCH by exactly two slots or 5120 chips The HS-SCCH
is completely time-aligned with the general control channels CPICH
and P-CCPCH of the NodeB This is mandatory because it is a shared
channel Consider several UEs with different distances to the NodeBwanting to receive the HS-SCCH channel Thus it must have constant
timing that is known a priori The shared data channel HS-PDSCH is
now transmitted exactly 5120 chips after the first chip of the HS-SCCH
This leads to an overlapping slot thereby requiring multitasking recep-
tion at the UE end While the UE is still receiving the last slot of an
ongoing HS-SCCH subframe it may already start the reception of an
HS-PDSCH transport block The first slot in the HS-SCCH subframe
now contains information required by the physical layer to performdespreading and demodulation These values are the UE identity indi-
cating whether the UE will start demodulation of the HS-PDSCH or
not in case it is not scheduled the modulation scheme information
since the UE has to know how to interpret the received constellation
vector and whether it has to be considered as a QPSK or 16QAM con-
stellation point and finally the UE has to know which channelization
codes it has to apply to capture the HS-PDSCH transport block The
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HSDPA operation overview and physical channels
overall UE reaction time when being scheduled is now seen as 1 slot
or 2560 chips This tough requirement for the UEs is due to the objec-
tive to obtain overall a much shorter latency than legacy standards Theadditional control information such as the new data indicator redun-
dancy version and transport block size is not that urgent since it is
needed after demodulation but before channel decoding So first the
UE will sample the whole three slots of the HS-PDSCH and demodu-
late them into a bit stream which is finally handed over to the channel
decoder This principle is known as post-processing and is used typi-
cally in mobile communications technologies
J Start of HS-SCCH subframe 0 is aligned with startof P-CCPCH frames
J The HS-PDSCH starts
τ HS-PDSCH
(2times Tslot
= 5120 chips)
after the start of the HS-SCCH
UE identity etc
processing timeof receiver
HS-DSCH subframe
3 times Tslot= 7680 chips
3 times Tslot
= 7680 chips
τ HS-PDSCH
(2times Tslot
= 5120 chips)
HS-SCCH
HS-PDSCH
Fig 2-18 Timing relation between HS-SCCH and HS-PDSCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
Content of the HS-SCCH control channelThe control information contained in the HS-SCCH control chan-
nel has already been mentioned so we will now consider the values
in more detail We will begin with an overview of what kind of control
information is contained in the HS-SCCH channel before proceeding
with further details about the single control elements The following
control information is present in the HS-SCCH [TS 25212 Ref 21]
Channelization code set information (7 bits)
Modulation scheme information (1 bit) Transport block size information (6 bits)
Hybrid ARQ process information (3 bits)
Redundancy and constellation version (3 bits)
New data indicator (1 bit)
UE identity (16 bits) = H-RNTI
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High speed shared control channel (HS-SCCH)
49
Some of these parameters are more or less self-explanatory while oth-
ers require additional background information and closer examination
Modulation scheme information 1 bit
This single bit is used to inform the receiver whether the modulation
scheme QPSK or 16QAM is applied on the data channel HS-PDSCH
The interpretation of the bit x ms1 is as follows
ms1
x
if QPSK
otherwise
0
1
=
New data indicator 1 bit
The new data indicator bit field informs the receiving entity that the
prevailing PDU transmitted by the current HARQ process is either a
retransmission or contains new data This is done by setting the new
data bit to the value 0 for the first PDU on this particular HARQ process
and incrementing the value by 1 with every new data sent [TS 25321Ref 30] This leads to a toggled value In case the new data bit is not
incremented ie if it remains at its previous value it is an indicator for
retransmission
1st PDU of this
HARQ process
NDI = New data indicator
NDI = 0 NDI = 1
NACK
NDI = 1
ACK
NDI = 0
HS-SCCH HS-SCCH HS-SCCHHS-SCCH
ACK
Fig 2-19 New data indicator bit principle of incrementing value
Channelization code set information 7 bits
This field is used to indicate the number of channelization codes usedfor transmitting the transport block on the HS-PDSCH As was already
described the spreading factor applied on the HS-PDSCH is constant
with a value of 16 but the flexible values are the number of channeliza-
tion codes forming a cluster when using multiple codes and their posi-
tion in the code tree It is not allowed to distribute the code channels
over the code tree diagram For the sake of simplicity in signaling sev-
eral channelization codes form one cluster and these codes are con-
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HSDPA operation overview and physical channels
tiguous in the channelization code tree [TS 25213 Ref 22] Fig 2-20
illustrates the principle of indicating the channelization codes on the
HS-SCCH
SF = 16
Code ldquo0rdquo isreserved forcommonchannels
Code offset 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15P = 5O = 7
Code group indicatorx
ccs1 x
ccs2 x
ccs3 = min (Pminus 1 15 minusP)
Code offset indicatorx
ccs4 x
ccs5 x
ccs6 x
ccs7 = |Ominus 1minus P8 times15|
A cluster of codes
can be allocated to a UEC
ch16Ohellip C
ch16O + P minus 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1
2 2 2 2 2 2 2 2 2 2 2 2 2 2 14 14
1 2 3 4 5 6 7 8 9 10 11 12 13 14 2 1
3 3 3 3 3 3 3 3 3 3 3 3 3 13 13 13
1 2 3 4 5 6 7 8 9 10 11 12 13 3 2 1
4 4 4 4 4 4 4 4 4 4 4 4 12 12 12 121 2 3 4 5 6 7 8 9 10 11 12 4 3 2 1
5 5 5 5 5 5 5 5 5 5 5 11 11 11 11 11
1 2 3 4 5 6 7 8 9 10 11 5 4 3 2 1
6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10
1 2 3 4 5 6 7 8 9 10 6 5 4 3 2 1
7 7 7 7 7 7 7 7 7 9 9 9 9 9 9 9
1 2 3 4 5 6 7 8 9 7 6 5 4 3 2 1
8 8 8 8 8 8 8 8
8 7 6 5 4 3 2 1
0 (115)
1 (214)
2 (313)
3 (412)
4 (511)
5 (610)
6 (79)
7 (88) Redundant area
C l u s t e r c o d e i n d i c a t o r ( 3 b i t s )
Tree offset indicator (4 bits)
Signaled on HS-SCCH
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
PO
Decoding notation
Number ofmulti-codes
Offset fromleft right incode tree (SF = 16)
Fig 2-20 Channelization code set indicating the HS-PDSCH code cluster
The idea behind the code indication is a matrix with the rows repre-
senting the number of codes per cluster and the columns represent-
ing the position of that cluster the offset value in the code tree Recall-
ing that the maximum number of channelization codes per clusteris 15 and if the cluster size is 1 the offset values can also range from
1 to 15 the resulting matrix would have 15 rows and 15 columns Since
we know that four bits are needed to represent an integer from 1 to 15
we need a total of 4 + 4 = 8 bits for representation of the channeliza-
tion code set information It is a smart idea to save one bit The 15 times 15
matrix would contain much redundant information By way of analogy
like in a road map indicating distances between cities A table showing
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High speed shared control channel (HS-SCCH)
51
the distance from city A to city B the opposite distance from city B to
city A is redundant information The useful information has the form
of a triangle The idea is to cut the lower part rotate it and append itto the spare part of the upper table In this manner a table is obtained
with 7 rows and 15 columns and it is possible to indicate each position
in it with just 7 bits
1 5 r o w s 7
r o w s
Matrix reduction for channeli-
zation code set information
15 columns
Fig 2-21 Matrix size reduction for channelization code set information
The content of the channelization code set matrix can be described as
a value with two numbers The upper number is the number of mul-
ticodes forming one cluster and the lower number is the offset in the
channelization code tree Accordingly the example in Fig 2-20 can be
interpreted to mean the HS-SCCH sends the bits as row number 4 and
column number 6 in the matrix The content of this element are the
values 5 over 7 which have to be interpreted as a cluster size of 5 codesand an offset of 7
Transport block size information 6 bits
With a length of six bits the transport block size (TBS) informa-
tion informs the receiving UE entity about the data block size of the
transport block sent on the HS-PDSCH We should keep in mind the
link adaptation performed with the adaptive modulation and coding
scheme that was described in section 12 page 10 The ratio errorcorrection and user data are flexible while the physical layer param-
eters such as the spreading factor modulation scheme and number of
channelization codes determine the physical block size This physical
block consists of the user data ratio or transport block size and the for-
ward error correction or redundancy information As this ratio is flex-
ible the HS-SCCH will inform the receiving UE entity about the size
of the transport block Here too there is a strategy of bit reduction the
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HSDPA operation overview and physical channels
goal is to inform the receiver with as few bits as possible A non-effi-
cient approach would involve conversion of the decimal number repre-
senting the TBS into a binary sequence but the number of bits neededwould exceed the space available on the HS-SCCH Imagine that the
range of transport block sizes depends on the physical layer condi-
tions The ambient physical layer parameters modulation scheme and
number of channelization codes set a certain working point where the
remaining flexibility for a different TBS configuration can be obtained
by more or less puncturing resulting in a flexible ratio between for-
ward error correction and user data This will lead to a two-step proce-
dure when evaluating the transport block size First the receiver exam-
ines the information modulation scheme and number of channeliza-
tion codes scheduled via HS-SCCH which indicate the value k0 l as
shown in Fig 2-22 The 6-bit HS-SCCH control parameter transport
block size information will be the transport format resource indica-
tor (TFRI) named ki Let k t be the sum of the two values kt = ki + k0i
Both values kt and k0 i can be obtained from tables given by [TS 25321
Ref 30] The range for the TFRI is from 1 to 256 and the derived trans-port block size ranges from 137 bits to 27 952 bits The first table indi-
cates the value k 0 i based on the channelization code and the modula-
tion scheme
Combination i Modulation scheme Number of channelization codes k0 i
0
QPSK
1 1
1 2 40
2 3 633 4 79
4 5 92
5 6 102
Fig 2-22 Extract from TS 25321 table representing k0 i
The second table indicates the final transport block size based on kt
Index TB size Index TB size Index TB size1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
4 173 89 1456 174 6673
5 185 90 1483 175 6793
6 197 91 1509 176 6916
7 209 92 1537 177 7041
Fig 2-23 Extract from TS 25321 table representing kt
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High speed shared control channel (HS-SCCH)
53
J The transport block size used on HS-DSCH is not signaled explicitly on HS-SCCHJ Instead a transport block size index k
i is signaled to indicate the transport block size
First stepModulation scheme andnumber of channelizationcodes as signaled on HS-SCCHdetermine value k
0 i
Second step
Index kt = k
i + k
0i
determines HS-DSCH
transport block size
kt = k
i + k
0i
Table according to 3GPP TS 25321 extract from QPSK section
Table according to 3GPP TS 25321 254 entries in total
Combination i Modulation
scheme
Number of
channelization codes
k0 i
0
QPSK
1 1
1 2 40
2 3 63
3 4 79
4 hellip hellip
Index TB size Index TB size Index TB size
1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
helliphellip hellip hellip hellip hellip
Fig 2-24 Retrieval of transport block size information
Source Fig 2-22 to Fig 2-24 [TS 25321 Ref 30] reproduced by permission of 3GPP
Hybrid ARQ process information 3 bits
The concept behind the hybrid automatic repeat request (HARQ) was
introduced in section 13 page 14 One feature is the possibility of
multitasking ie having several HARQ processes activated at the same
time Fig 2-25 below shows the need to signal the process identity tothe receiver Remember that on the downlink there is a shared chan-
nel concept so the NodeB can flexibly decide which UE will be sched-
uled with a downlink transport block Up to eight HARQ processes
can be signaled via higher layers to one UE Note however that due to
the round-trip timing six HARQ processes must be active to achieve
the maximum throughput as shown in Fig 2-51 page 79 Compared
with HSUPA the HARQ processes on the downlink are asynchronous
so they have to be indicated but on the uplink they are synchronous sothey do not need to be signaled explicitly
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HSDPA operation overview and physical channels
Asynchronous DL minus Synchronous ULNumber of H-ARQ rocesses = 1 to 8 er UE
UL HS-DPCCH UE1
UE1 HARQ processes 1 to 4
3 4 1 42 11 1 32retrans
2
A N A A
A A
N A
UL HS-DPCCH UE2
HS-PDSCH
UE2 HARQ processes 1 to 2
Fig 2-25 HARQ process indication on HS-SCCH
Fig 2-25 shows a typical situation on the downlink (point-to-multi-
point) The NodeB sends data to several UEs sharing the HS-PDSCH
so therefore the HARQ process is asynchronous The time when a
transport block is retransmitted is not fixed For this reason the pro-
cess identifier is signaled on the HS-SCCH Based on the HARQ pro-
cess identity and the new data indicator bit the receiving entity knows
which part of the soft buffer memory has to be used in case of soft com-bining On the uplink the situation is slightly simpler The UE only
communicates with one NodeB so it is a point-to-point connection
Thus retransmission always occurs at a fixed time linked to the origi-
nal transmission
Redundancy and constellation version 3 bits
Adaptive modulation and coding involve flexible selection of modula-tion and coding schemes that are signaled to the receiving UE via the
parameters transport block size and modulation scheme information
Another concept used in HSDPA was previously discussed Chase com-
bining or incremental redundancy (see section 222 page 41) This
means that in case of retransmission the transmit entity can dynami-
cally select another puncturing scheme or keep the puncturing as it was
in the original transmission The applied puncturing scheme is signaled
as redundancy information to the receiver Additionally in case of the16QAM modulation scheme the transmitter can select another constel-
lation arrangement which is also signaled to the UE with the three bits
for the redundancy and constellation version see Fig 2-15 page 45
Depending on the modulation scheme (QPSK or 16QAM) there are
two different tables indicating the parameters ldquosrdquo ldquorrdquo and ldquobrdquo The
parameters ldquosrdquo and ldquorrdquo indicate which scheme is used for puncturing
ie if the puncturing mechanism prioritizes the systematic bits or not
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High speed shared control channel (HS-SCCH)
55
and which puncturing algorithm is used The parameter ldquobrdquo indicates
the constellation mapping version The receiver needs this information
to perform proper demodulation and decoding
Initial transmission
1st retransmission
2nd retransmission
3rd retransmission
r
0
0
1
1
2
2
3
xrv
(value)
s
0 1
1 0
2 1
3 0
4 1
5 0
6 1
7 0 3
s = 1 Systematic bits are prioritizeds = 0 Non-systematic bits are prioritized
r (range 0 to 3 for QPSK) influencesJ Input parameter for puncturing or (together with s) for repetition algorithm defined in TS 25212J Selection of parity bits
Redundancy version coding sequences are signaled on HS-SCCH egndash 0 2 5 6 One initial transmission + 3 retransmissions with different r and s parameters
Fig 2-26 Signaling of redundancy version parameters r and s QPSK case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
Initial transmission
2nd retransmission
1st retransmission
3rd retransmission
r (range 0 to 1 for 16QAM)influences input parameterfor puncturing or (togetherwith s) for repetitionalgorithm defined in
TS 25212 and thus selectionof parity bits
Redundancy version coding sequences are signaled on HS-SCCH egminus 6 4 0 5 Chase combining (no change in s and r parameters ie same redundancyversion) with four possible constellations
x rv (value) s r b
0 1 0 0
1 0 0 0
2 1 1 1
3 0 1 1
4 1 0 1
5 1 0 2
6 1 0 3
7 1 1 0
Definition of parameter s as for QPSK
b (range 0 to 3) describes constellationrearrangement to averagereliability of bits
Fig 2-27 Signaling of redundancy version parameters r s and b 16QAM case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
UE identity H-RNTI 16 bits
The HSDPA radio network transaction identifier (H-RNTI) unam-
biguously identifies the UE having an HS-PDSCH assignment within
a cell It is allocated to the UE via layer 3 signaling procedures at the
radio bearer setup if the radio bearer is an HSDPA connection This
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HSDPA operation overview and physical channels
value represents a temporary name of the UE used to address it when
scheduling data packets via HS-SCCH
HS-SCCH channel coding
The control information contained in the HS-SCCH is of course pro-
tected with channel coding mechanisms the whole coding chain is
described in Fig 2-28 Fig 2-18 page 48 presents the separation of
the control information into two code blocks which are sent consec-
utively mapped on slot 1 and slot 2 + 3 of one HS-SCCH subframe
This principle is also visible in the coding chain The first control block
consisting of channelization information modulation scheme and UE
identity is coded separately from the remaining control values to enable
the UE receiver to decode this first slot separately and prepare for pos-
sible HS-PDSCH reception The coding steps shown in Fig 2-28 such
as rate matching 1 and 2 are similar to the HS-PDSCH coding chain
and are further described in [TS 25212 Ref 21]
Channelcoding 1
R atematching 1
mux
Channelcoding 2
Ratematching 2
RVcoding
UE-specificCRC attachment
UE-specificmasking
Physical channelmapping
r s b
mux
Channelizationcode set
Modulationscheme
Transport block size information
HARQ processinformation
Redundancy andconstellation version
New data indicator
UE identity
UE identity
Fig 2-28 Channel coding for HS-SCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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High speed dedicated physical control channel (HS-DPCCH)
57
24 High speed dedicated physical control channel (HS-DPCCH)
In an active HSDPA connection the UE has to send acknowledgment ornon-acknowledgment reports (as described in section 13 page 14
where the HARQ process is described) as well as channel status infor-
mation to the network The reporting is performed on this physical
control channel HS-DPCCH
As ubiquitous in HSDPA the uplink is also configured into a subframe
structure of 2 ms corresponding to three slots The first slot of the sub-
frame carries the ACK NACK information the UE sends to the NodeB
while the following two slots ie slot 2 and 3 of the subframe convey
the CQI value the channel quality information to the NodeB
Subframe 0 Subframe i Subframe 4
Tslot
= 2560 chips J The spreading factor of theHS-DPCCH is 256 (10 bits peruplink slot)
J The HS-DPCCH can only existtogether with an UL DPCCH
(ded phys control channel)J The DPDCH (dedicated physical data channel) the DPCCH andthe HS-DPCCH are IQ codemultiplexed
HARQ-ACK CQI = Channel quality information
2 times Tslot
= 5120 chips
One radio frame Tf = 10 ms
One HS-DPCCH subframe 2 ms
Fig 2-29 HS-DPCCH configuration
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The slot format for HS-DPCCH describes a quantity of 30 bits per sub-frame resulting in a data rate of 15 kbps The spreading factor used for
the HS-DPCCH is constant and is always equal to 256 but the chan-
nelization code that is used as well as the mapping on either the I or
Q axis depends on several factors eg the co-existence of an HSDPA
connection with a circuit-switched connection meaning whether a
DPDCH established or not Fig 2-36 page 64 illustrates this IQ
mapping and Fig 2-35 page 63 shows the channelization code used
for HS-DPCCH
The HS-DPCCH builds a logical unit of one subframe but having the
independent control information HARQ-ACK and CQI included which
could be separately decoded at the NodeB Note that the slot carrying
the ACK NACK statement is active only when the UE has been sched-
uled by an HS-PDSCH subframe in the corresponding downlink sub-
frame previously Assuming the UE has not received a transport block
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HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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HS-DSCH High speed downlink shared channel transport channel
35
An example could be the simple bit pattern 1101 which would repre-
sented as polynomial 983160983091 + 983160 + 1 i e 1 ∙ x 983091 + 0 ∙ x 983090 + 1 ∙ x 1048625 + 1 ∙ x 1048624
To calculate the check bits the data word D(x ) is multiplied by x nndashk
and then divided by the generating polynomial G(x ) which is of degree
(nndashk) The remainder R(x ) is the check word comprising the check bits
R x mainder x D x
G x
n k
( ) Re ( )
( )=
sdot
minus
The code word C (x ) is now obtained by appending the check word to
the data word
C (x ) = x nndashk ∙ D(x ) + R(x )
The receiver knows the generating polynomial G(x ) and performs the
division C (x )G(x ) If there are no transmission errors the code word
C (x ) is divisible by G(x ) The probability is therefore high that anyerrors will be detected The maximum number of errors per code word
that can be detected is determined by the length of the check word
which in our case is the length of the CRC But what is not known is the
position of those errors and thus there is no way to correct them This
is the responsibility of the ldquoinnerrdquo error correction such as the attach-
ment of redundancy bits which enable the receiver to correct some bit
errors Note that block codes can also be used in general to correcterrors but this is not performed in HSPA because this would increase
the overall latency time
Error correction performed with forward error correction (FEC)
principle of convolutional coding
With forward error correction (FEC) redundant bits are inserted into
data packets (bursts) at the transmitting end to enable the receiving
end to implement a correction mechanism The assumption is that theerrors do not occur in a burst Here the principle of a convolutional
coder is used This type of coder ldquoremembersrdquo the last n bits sent and
adds each input bit to the stored n bits The words obtained at the out-
put are usually longer than one bit The code rate defines the ratio of
the input bits to the output bits for example a coder using a code rate
of frac12 generates for each input bit a code word of two output bits Error
correction is based on the fact that a previous state ie a word or a bit
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HSDPA operation overview and physical channels
sequence can only assume one of two succeeding states depending on
whether 0 or 1 was entered into the coder ie the decoder decides for
the metric providing the minimum error estimation If a word arrivesat the receiver in a state that cannot be reached from a state obtain-
able from one of the two input combinations a transmission error has
occurred and needs to be corrected This procedure is equivalent to
tracing a path through a trellis diagram which is familiar from cod-
ing theory
We would now like to discuss a brief example to demonstrate the func-
tionality of channel coding and the subsequent steps of puncturing
Please note that this example does not represent the real coders used
in HSDPA Consult the relevant literature for further details of cod-
ing theory [Ref 10] [Ref 11] and [Ref 14] as well as the specification
[TS 25212 Ref 21] which describes the coding applied in HSPA
The convolutional coder shown in Fig 2-8 consists of one input fol-
lowed by three registers in a shift configuration and finally two out-puts With each clock generation the content of each register is shifted
one register to the right as the last registerrsquos content is discarded and
a new input bit is inserted into the first register The outputs 1 and 2
are generated by an XOR operation between the linked register con-
tents In this manner we create a finite response filter and a certain
memory effect Letrsquos assume we want to transmit the following input bit
sequence 110110 01 Here the nomenclature 01 means that the lastbit of our contemplated sequence can be either 0 or 1 and we wish to
consider both alternatives The registers are initialized with all 0s and
typically some tail bits are attached to the code word which will ensure
this for the succeeding code word The table in Fig 2-8 shows the input
bit on the left side the register sequence content after each step and
outputs 1 and 2 on the right side The output sequence for the given
input will be 11 01 01 00 01 011100 Note the last two lines in the table
We do assume an either or ie there are two alternatives such thatalternative A means that after the sequence 110110 has been sent to the
coder the following bit will be logical 0 Alternative B means that after
the sequence 110110 the following bit will be a logical 1 So we present
an either or situation This will be used to explain the coding principle
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HS-DSCH High speed downlink shared channel transport channel
37
Example of convolutional coding
Input Regis-
ter 1
Regis-
ter 2
Regis-
ter 3
Out-
put 1
Out-
put 2
XOR operation
Register 3Register 2Register 1
+
Input
Output 1
Output 2
+ +
1 1 0 0 1 1
1 1 1 0 0 1
0 0 1 1 0 1
1 1 0 1 0 0
1 1 1 0 0 1
0 0 1 1 0 1
Alt A 0 0 0 1 1 1
Alt B 1 1 0 1 0 0
Fig 2-8 Simple example for convolutional coding
In Fig 2-9 that follows there is a trellis diagram representing in each
column the four possible output values of our channel coder 00 01 10
or 11 and in bold color there is the trellis path through this diagram
resulting from the input sequence Recalling our definition of the two
alternatives for the last bit of our example code word we can see that
the rightmost part of this trellis diagram shows the two possible steps
From state 01 we can only reach either state 00 or state 11 The twoother states 01 or 10 are not possible and with no input to the coder
shown in Fig 2-8 the output can reach these two states in this step For
example if the receiver detects a sequence such as 11 01 01 00 01 01 01
it knows there is an error at the last position 01 which had to be cor-
rected as either 00 or 11 because only these two alternatives are pos-
sible The error correction is performed by looking at the total trellis
path and selecting the maximum likelihood sequence estimation basedon the received data pattern In our short example we admit that we
stopped at this point of course Imagine that the input sequence of bits
continues The decoder would not know if it should proceed with the
pattern 00 or 11 so the decision will be to continue both ways The fol-
lowing step is then checked again and one of the assumed ways will dif-
fer more from the demodulated pattern than the other one This prin-
ciple is described in the Viterbi algorithm [Ref 15] Based on this algo-
rithm the stronger path will survive ie the decoder checks at eachstep which path of the examined ones in the trellis path exhibits the
smallest deviation from the demodulation sequence and thus this path
will be continued The paths exhibiting a higher deviation are discarded
to reduce the calculation expense The path through the trellis diagram
is called a ldquometricrdquo and the term ldquomaximum likelihood sequence esti-
mationrdquo (MLSE) represents the selection by the channel decoder of the
real possible metric which is the closest to the received data pattern As
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HSDPA operation overview and physical channels
an analogy If we do a crossword puzzle and find some characters in a
word the channel decoder would check in a primer or dictionary of the
language containing all possible character combinations that we callldquowordsrdquo and select the existing word that has the maximum likelihood
for the prevailing sequence of characters
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
Alternative B
Alternative A
Register 2
+ +
+
Output 1
Output 2
XOR operation
Trellis diagram above showsmetric for input sequence
110110 0
or 1
into a coder such as
1
1
0
1 10
0
1
Register 3Register 1
Fig 2-9 Metric in trellis diagram
Interleaving
Forward error correction based on convolutional coders has one disad-
vantage related to the impact of block errors If the transmission errors
are distributed they can be corrected as demonstrated in the trellis dia-gram example using the Viterbi algorithm but if many adjacent bits
are lost the decoder will have problems retrieving the right bit pattern
Interleaving means that the information to be transmitted is spread or
distributed over several bursts in such a way that contiguous informa-
tion is split up and transmitted in a time or block distributed mode
To avoid error bursts an attempt is made to spread the bit errors over
several code words This is achieved by interleaving several code wordsThis method is also called diagonal interleaving see Fig 2-10 Another
kind of interleaving is block interleaving as shown in Fig 2-11 Blocks
of code words are written row-by-row into a matrix and then read col-
umn-by-column With both methods consecutive bits of a code word
are never transmitted consecutively and conversely when the bits are
deinterleaved at the receive end error bursts are spread over several
code words
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HS-DSCH High speed downlink shared channel transport channel
39
As several code words are interleaved the decoder has to ldquowaitrdquo a cer-
tain time until all bits of a particular code word arrive This delay ie
the ldquomeasure for spreading over timerdquo is referred to as the ldquointerleav-ing depthrdquo The greater the interleaving depth the more code words are
available for spreading the error bursts and the greater the probability
that errored bits can be corrected but on the other hand this increases
the overall latency time
HSDPA uses the block diagonal interleaving principle for the HS-DSCH
only since as we should recall one goal is to have a short round-trip
time
Spreadinghellip
Interleaving
hellip
hellip
Fig 2-10 Diagonal interleaving
Write
Read
Interleaving-Matrix
Fig 2-11 Block interleaving
Puncturing
Having briefly described the principle of convolutional coding another
mechanism will be presented that is used to increase the throughputof user data and coordinate with the AMC mechanism described in
section 12 page 10 After adding redundancy the total bit stream is
now known as soft bits ie the sum including all of the raw data bits
at the input of the channel coder plus the added redundancy bits This
quantity must match the required transport block size demanded by
the transport layer and the process performed here is called rate match-
ing ie deleting some of the soft bits at the transmitting end in a pre-
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HSDPA operation overview and physical channels
defined manner or repeating or adding some stuffing bits In HSPA the
rate matching mechanism uses puncturing which provides higher data
throughput The signaled values TBS and RV tell the receiving convo-lutional coder how many and where bits have been punctured This
allows the decoder to insert blank positions which have to be filled later
by performing trellis decoding In other words we may consider the
punctured bits as bit losses created intentionally by the transmitter In
this manner the total amount of data bits can be increased for the sake
of lower redundancy In HSDPA this puncturing scheme will be very
flexible and the NodeB scheduler will set the puncturing rate adapted
to the prevailing RF conditions on the radio channel to obtain the high-
est possible data throughput under the existing conditions The disad-
vantage of adaptive coding is that we need signaling information so
that the transmitter has to inform the receiver about how many soft bits
have been punctured This is seen in Fig 2-26 page 55 in the form
of the redundancy version carried by the HS-SCCH control channel
Fig 2-12 below again depicts the principle of puncturing in HSDPAand clarifies some signaling parameters such as the transport block size
1 1 0 1 1 0 0
11 01 01 00 01 01 11
Transport block sizeInput bits into channel coder
Soft bitsOutput from channel encoder
Rate matchingPuncturing or repeating bits
11 01 01 00 01 01 11
1 01 0 00 0 01 1Coded composite transport bitsCan be several combined streams aftercoding + rate matching
Transport block size FEC
Fig 2-12 Puncturing based on coding example from Fig 2-8 page 37
The process of channel coding starts first with the transport block
size which is given by the size of the input data bit sequence added
by a cyclic redundancy checksum The next step is the channel cod-
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HS-DSCH High speed downlink shared channel transport channel
41
ing which is performed in HSPA by a so-called turbo coder The turbo
coder is a parallel concatenated convolutional coder that exhibits bet-
ter reliability compared to a single convolutional coder Discussingthe functionality of a turbo coder in all of its details would represent a
major digression from the intention of this book Accordingly we will
simply encourage the interested reader to consult the channel coding
literature for more details about turbo coders and their applications
[Ref 10] [Ref 12] Determined by the scheduler of the base station or
the redundancy version to be used the next step known as the redun-
dancy version will either puncture (the most likely) or repeat some of
the bits resulting from the channel coding process How many bits will
be punctured is defined by the coding rate In our example in Fig 2-12
we see that the input bit sequence has a length of 7 bits resulting in
14 soft bits after channel coding with our example coder providing a
coding rate of frac12 The scheduler decided to puncture 4 bits so that we
finally obtain 10 bits which have to be mapped on the physical chan-
nels Our overall coding rate is therefore given as ⁷frasl983089983088 In other words
some bits are protected with redundancy information while othersare not Note that the size of the coded composite transport channel
is determined by the physical layer parameters such as the number of
channelization codes used to convey the HS-PDSCH the modulation
scheme and the transmit time interval which is constant for HSDPA
but can be either 2 or 10 ms for HSUPA Thus its size does not need
to be signaled to the receiver and only the transport block size and the
redundancy versions will be contained in the HS-SCCH channel
222 Incremental redundancy and chase combining
for HS-DSCH
Until now we have presented some general characteristics of HSDPA
and HSUPA which we would now like to discuss in a combined pro-
cedure and then deduce two other principles The HARQ abbreviationcombines an automatic retransmission of erroneous data with a soft
combination at the receiving end A related question can now be how
the transmitter has to repeat the transport block should the retrans-
mission of data occur in an identical retransmission mode or should
some changes in coding parameters eg the manner of puncturing be
applied This question is also important for the implementation of the
rate matching step shown in Fig 2-12 The transmitter has to provide
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HSDPA operation overview and physical channels
a certain soft buffer ie a memory that stores the transmitted data for
the sake of possible retransmissions and deletes it after having received
a positive acknowledgment from the receiver Should the transmitternow store the coded composite transport data i e the data after coding
but also after puncturing This would restrict it to repeating the data in
an identical manner A better approach is to store the data after channel
coding and before puncturing Even if this requires more memory it
gives the flexibility to change the puncturing scheme and retransmit the
transport block in a different way Fig 2-13 and Fig 2-14 represent both
mechanisms that are used in HSDPA and HSUPA Identical retransmis-
sion is called chase combining and non-identical retransmission with
a different puncturing scheme is called incremental redundancy The
scheduler in the base station can decide which retransmission scheme
will be used We do not wish to delve into the details of channel coding
theory to discuss which mechanism is the better one ndash chase combin-
ing or incremental redundancy We will only mention that both mech-
anisms have their advantages and thus their applications Chase com-
bining has the advantage that the systematic bits representing the orig-inal data input into the channel coder are contained in the transmit-
ted sequence after puncturing Thus chase combined transport blocks
are ldquoself-decodablerdquo If we consider a situation where the original trans-
port block is lost completely and only the retransmitted block is pres-
ent at the receiver there is a chance to decode the data properly Mean-
while incremental redundancy seems to add more redundancy when
retransmitting but in a scenario where the first transmission contain-ing the systematic bits is lost completely and only the retransmission
is present the receiver will have no chance to decode the data without
having some of the systematic bits Accordingly incremental redun-
dancy is applied whenever sporadic bit errors occur due to a time vari-
ant channel and chase combining is selected whenever we have to deal
with complete transport block errors i e the time variance of the radio
link exhibits some bursted fading dips
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HS-DSCH High speed downlink shared channel transport channel
43
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Chase combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Transmitted bit
Punctured bit
Systematic bits
Parity 1
Parity 2
Systematic bits
Parity 1
Parity 2
Fig 2-13 Chase combining principle
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Incremental redundancy combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Systematic bits
Parity 1
Parity 2
Systematic bitsParity 1
Parity 2
Fig 2-14 Incremental redundancy
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HSDPA operation overview and physical channels
223 Constellation rearrangement
Due to the fact that HSDPA introduces a higher-order modulationscheme (16QAM) we can recognize some effects due to the physi-
cal layer influencing the susceptibility to noisy RF conditions One of
these effects can be explained by looking at the constellation diagram
in the 16QAM modulation scheme see section 12 page 10 As we
recall there is a total of 16 different constellation points given by the
modulation vector and represented by its phase and amplitude Con-
sidering the Euclidean distance which is the distance in this constella-
tion diagram between two neighboring points we can clearly see that
some points have more neighbors than others Especially the four con-
stellation points at the very four corners only have three direct neigh-
bors making them less susceptible to misdetection due to noise shift-
ing them in a certain direction On the other hand the four constella-
tion points representing the inner square of the constellation have eight
direct neighbors each and are therefore more likely to be incorrectly
detected The idea of constellation rearrangement is now to change themapping scheme applied in the original transmission when retrans-
mitting As we know the receiver will soft combine the retransmit-
ted data with the previously received information so we can achieve a
certain incremented redundancy and a certain protection mechanism
Note however that considering a sole transmission of a transport block
using a certain constellation arrangement will not show any more pos-
itive or negative results compared to other constellation arrangementsThe redundancy gain is only achieved by rearranging the constellation
mapping in a retransmitted transport block and performing soft com-
bining at the receiver Overall HSDPA defines four constellation rear-
rangement schemes which are indicated in the redundancy version
field of the HS-SCCH and are represented by the ldquobrdquo bit field ranging
from b = 0 to b = 3 All four constellation schemes are Gray encoded
ie the directly adjacent constellation symbols do not exhibit four com-
pletely different bits in order to reduce the impact of misdetection onbit errors
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High speed shared control channel (HS-SCCH)
45
Q
I
(ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1) (1 1ndash1ndash1)
(ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1) (1 1ndash1 1)
(ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1) (1ndash1ndash1 1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 0
Q
I
(ndash1 1 1 1) (ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1)
(ndash1 1 1ndash1) (ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1)
(ndash1ndash1 1ndash1) (ndash1ndash1ndash1ndash1) (1ndash1ndash1ndash1) (1ndash1 1ndash1)
(ndash1 1 1 1) (ndash1ndash1ndash1 1) (1ndash1ndash1 1) (1ndash1 1 1)
b = 2
Q
I
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (1ndash1 1 1) (ndash1ndash1 1 1)
(ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1) (ndash1 1 1 1)
(ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1) (ndash1 1 1ndash1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 1
Q
I
(1 1ndash1 1) (ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1)
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1)
(1ndash1ndash1ndash1) (ndash1ndash1ndash1ndash1) (ndash1ndash1 1ndash1) (1ndash1 1ndash1)
(1 1ndash1ndash1) (ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1)
b = 3
Fig 2-15 Constellation rearrangement in HSDPA
23 High speed shared control channel (HS-SCCH)
The HS-SCCH sends scheduling information to the UEs As seen before
the HS-PDSCH has a very flexible configuration for physical parame-
ters such as the coding rate number of code channels or retransmis-sions This high flexibility increases the complexity and engenders the
need for additional signaling information transferred on the HS-SCCH
Reception of user data in HSDPA is always a two-step procedure
First the receiver has to capture the scheduling control information
and afterwards based on the received control information it may start
demodulating and decoding the HS-PDSCH containing the user data
This two-step procedure is shown in Fig 2-16 below which lists what
kind of control information is sent to the UEs via the HS-SCCH Asshown in Fig 2-2 page 28 which describes the overall HSDPA chan-
nel structure there can be up to four HS-SCCHs assigned to one UE
But only one HS-SCCH would contain the scheduling information for
this UE within one TTI Thus the network can assign resources simul-
taneously to various UEs in the downlink direction
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HSDPA operation overview and physical channels
I would like to receive databut I dont know where myHS-PDSCH resources areand what they look like
HS-SCCH
Read the 1st HS-SCCH slotfor HS-DSCH channelizationcodes UE identity and
modulation scheme
Then the 2nd and 3rd HS-SCCHslots provide transport block sizeinformation hybrid ARQ process in-formation redundancy constellationversion new data indicator
HS-PDSCH
Fig 2-16 HS-SCCH control channel usage
Regarding the physical layer parameters we see in Fig 2-17 that the
HS-SCCH uses a channelization code with a spreading factor of 128
and it also uses the newly introduced transmit time interval of one sub-
frame which is equal to 2 ms It should be mentioned that the spread-ing factor of 128 requires double the capacity compared to similar con-
trol channels in WCDMA Release 99 reflecting the signaling overhead
needed to guarantee the huge flexibility introduced with HSDPA Addi-
tionally Fig 2-16 shows that the control information is sent consecu-
tively within one subframe The first slot within this subframe contains
the control information UE identity channelization code information
and modulation scheme identifier Slots 2 and 3 of the subframe con-tain the remaining control information Transport block size HARQ
process identifier redundancy version and new data indicator Conse-
quently the UE can self-decode slot 1 alone and slots 2 and 3 in a sec-
ond step even if they represent one logical unit This raw control infor-
mation is of course also channel coded using a turbo and on the phys-
ical layer the quantity of bits after the rate matching step is 40 bits con-
veyed in one slot corresponding to 666 micros [TS 25212 Ref 21] see also
Fig 2-28 page 56
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High speed shared control channel (HS-SCCH)
47
The HS-SCCH is a fixed rate (60 kbps SF = 128) downlinkphysical channel used to carry downlink signaling related toHS-DSCH transmission
Slot 0
Slot 1
Slot 2
Tslot
= 2560 chips
Data = 40 bits
1 subframe = 2 ms
Fig 2-17 Structure of High speed shared control channel HS-SCCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
We would like to return now to the time consecutive transmission of
control information There is a difference in the control information
in terms of its priority Some information is needed at the UE end
very urgently while other control information does not have such a
high priority But why This will be explained by looking at some tim-ing aspects defined for HSDPA If we consider the timing between
the shared data channel HS-PDSCH and the shared control chan-
nel HS-SCCH as shown in Fig 2-18 we see that the HS-PDSCH fol-
lows the HS-SCCH by exactly two slots or 5120 chips The HS-SCCH
is completely time-aligned with the general control channels CPICH
and P-CCPCH of the NodeB This is mandatory because it is a shared
channel Consider several UEs with different distances to the NodeBwanting to receive the HS-SCCH channel Thus it must have constant
timing that is known a priori The shared data channel HS-PDSCH is
now transmitted exactly 5120 chips after the first chip of the HS-SCCH
This leads to an overlapping slot thereby requiring multitasking recep-
tion at the UE end While the UE is still receiving the last slot of an
ongoing HS-SCCH subframe it may already start the reception of an
HS-PDSCH transport block The first slot in the HS-SCCH subframe
now contains information required by the physical layer to performdespreading and demodulation These values are the UE identity indi-
cating whether the UE will start demodulation of the HS-PDSCH or
not in case it is not scheduled the modulation scheme information
since the UE has to know how to interpret the received constellation
vector and whether it has to be considered as a QPSK or 16QAM con-
stellation point and finally the UE has to know which channelization
codes it has to apply to capture the HS-PDSCH transport block The
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HSDPA operation overview and physical channels
overall UE reaction time when being scheduled is now seen as 1 slot
or 2560 chips This tough requirement for the UEs is due to the objec-
tive to obtain overall a much shorter latency than legacy standards Theadditional control information such as the new data indicator redun-
dancy version and transport block size is not that urgent since it is
needed after demodulation but before channel decoding So first the
UE will sample the whole three slots of the HS-PDSCH and demodu-
late them into a bit stream which is finally handed over to the channel
decoder This principle is known as post-processing and is used typi-
cally in mobile communications technologies
J Start of HS-SCCH subframe 0 is aligned with startof P-CCPCH frames
J The HS-PDSCH starts
τ HS-PDSCH
(2times Tslot
= 5120 chips)
after the start of the HS-SCCH
UE identity etc
processing timeof receiver
HS-DSCH subframe
3 times Tslot= 7680 chips
3 times Tslot
= 7680 chips
τ HS-PDSCH
(2times Tslot
= 5120 chips)
HS-SCCH
HS-PDSCH
Fig 2-18 Timing relation between HS-SCCH and HS-PDSCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
Content of the HS-SCCH control channelThe control information contained in the HS-SCCH control chan-
nel has already been mentioned so we will now consider the values
in more detail We will begin with an overview of what kind of control
information is contained in the HS-SCCH channel before proceeding
with further details about the single control elements The following
control information is present in the HS-SCCH [TS 25212 Ref 21]
Channelization code set information (7 bits)
Modulation scheme information (1 bit) Transport block size information (6 bits)
Hybrid ARQ process information (3 bits)
Redundancy and constellation version (3 bits)
New data indicator (1 bit)
UE identity (16 bits) = H-RNTI
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High speed shared control channel (HS-SCCH)
49
Some of these parameters are more or less self-explanatory while oth-
ers require additional background information and closer examination
Modulation scheme information 1 bit
This single bit is used to inform the receiver whether the modulation
scheme QPSK or 16QAM is applied on the data channel HS-PDSCH
The interpretation of the bit x ms1 is as follows
ms1
x
if QPSK
otherwise
0
1
=
New data indicator 1 bit
The new data indicator bit field informs the receiving entity that the
prevailing PDU transmitted by the current HARQ process is either a
retransmission or contains new data This is done by setting the new
data bit to the value 0 for the first PDU on this particular HARQ process
and incrementing the value by 1 with every new data sent [TS 25321Ref 30] This leads to a toggled value In case the new data bit is not
incremented ie if it remains at its previous value it is an indicator for
retransmission
1st PDU of this
HARQ process
NDI = New data indicator
NDI = 0 NDI = 1
NACK
NDI = 1
ACK
NDI = 0
HS-SCCH HS-SCCH HS-SCCHHS-SCCH
ACK
Fig 2-19 New data indicator bit principle of incrementing value
Channelization code set information 7 bits
This field is used to indicate the number of channelization codes usedfor transmitting the transport block on the HS-PDSCH As was already
described the spreading factor applied on the HS-PDSCH is constant
with a value of 16 but the flexible values are the number of channeliza-
tion codes forming a cluster when using multiple codes and their posi-
tion in the code tree It is not allowed to distribute the code channels
over the code tree diagram For the sake of simplicity in signaling sev-
eral channelization codes form one cluster and these codes are con-
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HSDPA operation overview and physical channels
tiguous in the channelization code tree [TS 25213 Ref 22] Fig 2-20
illustrates the principle of indicating the channelization codes on the
HS-SCCH
SF = 16
Code ldquo0rdquo isreserved forcommonchannels
Code offset 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15P = 5O = 7
Code group indicatorx
ccs1 x
ccs2 x
ccs3 = min (Pminus 1 15 minusP)
Code offset indicatorx
ccs4 x
ccs5 x
ccs6 x
ccs7 = |Ominus 1minus P8 times15|
A cluster of codes
can be allocated to a UEC
ch16Ohellip C
ch16O + P minus 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1
2 2 2 2 2 2 2 2 2 2 2 2 2 2 14 14
1 2 3 4 5 6 7 8 9 10 11 12 13 14 2 1
3 3 3 3 3 3 3 3 3 3 3 3 3 13 13 13
1 2 3 4 5 6 7 8 9 10 11 12 13 3 2 1
4 4 4 4 4 4 4 4 4 4 4 4 12 12 12 121 2 3 4 5 6 7 8 9 10 11 12 4 3 2 1
5 5 5 5 5 5 5 5 5 5 5 11 11 11 11 11
1 2 3 4 5 6 7 8 9 10 11 5 4 3 2 1
6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10
1 2 3 4 5 6 7 8 9 10 6 5 4 3 2 1
7 7 7 7 7 7 7 7 7 9 9 9 9 9 9 9
1 2 3 4 5 6 7 8 9 7 6 5 4 3 2 1
8 8 8 8 8 8 8 8
8 7 6 5 4 3 2 1
0 (115)
1 (214)
2 (313)
3 (412)
4 (511)
5 (610)
6 (79)
7 (88) Redundant area
C l u s t e r c o d e i n d i c a t o r ( 3 b i t s )
Tree offset indicator (4 bits)
Signaled on HS-SCCH
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
PO
Decoding notation
Number ofmulti-codes
Offset fromleft right incode tree (SF = 16)
Fig 2-20 Channelization code set indicating the HS-PDSCH code cluster
The idea behind the code indication is a matrix with the rows repre-
senting the number of codes per cluster and the columns represent-
ing the position of that cluster the offset value in the code tree Recall-
ing that the maximum number of channelization codes per clusteris 15 and if the cluster size is 1 the offset values can also range from
1 to 15 the resulting matrix would have 15 rows and 15 columns Since
we know that four bits are needed to represent an integer from 1 to 15
we need a total of 4 + 4 = 8 bits for representation of the channeliza-
tion code set information It is a smart idea to save one bit The 15 times 15
matrix would contain much redundant information By way of analogy
like in a road map indicating distances between cities A table showing
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High speed shared control channel (HS-SCCH)
51
the distance from city A to city B the opposite distance from city B to
city A is redundant information The useful information has the form
of a triangle The idea is to cut the lower part rotate it and append itto the spare part of the upper table In this manner a table is obtained
with 7 rows and 15 columns and it is possible to indicate each position
in it with just 7 bits
1 5 r o w s 7
r o w s
Matrix reduction for channeli-
zation code set information
15 columns
Fig 2-21 Matrix size reduction for channelization code set information
The content of the channelization code set matrix can be described as
a value with two numbers The upper number is the number of mul-
ticodes forming one cluster and the lower number is the offset in the
channelization code tree Accordingly the example in Fig 2-20 can be
interpreted to mean the HS-SCCH sends the bits as row number 4 and
column number 6 in the matrix The content of this element are the
values 5 over 7 which have to be interpreted as a cluster size of 5 codesand an offset of 7
Transport block size information 6 bits
With a length of six bits the transport block size (TBS) informa-
tion informs the receiving UE entity about the data block size of the
transport block sent on the HS-PDSCH We should keep in mind the
link adaptation performed with the adaptive modulation and coding
scheme that was described in section 12 page 10 The ratio errorcorrection and user data are flexible while the physical layer param-
eters such as the spreading factor modulation scheme and number of
channelization codes determine the physical block size This physical
block consists of the user data ratio or transport block size and the for-
ward error correction or redundancy information As this ratio is flex-
ible the HS-SCCH will inform the receiving UE entity about the size
of the transport block Here too there is a strategy of bit reduction the
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HSDPA operation overview and physical channels
goal is to inform the receiver with as few bits as possible A non-effi-
cient approach would involve conversion of the decimal number repre-
senting the TBS into a binary sequence but the number of bits neededwould exceed the space available on the HS-SCCH Imagine that the
range of transport block sizes depends on the physical layer condi-
tions The ambient physical layer parameters modulation scheme and
number of channelization codes set a certain working point where the
remaining flexibility for a different TBS configuration can be obtained
by more or less puncturing resulting in a flexible ratio between for-
ward error correction and user data This will lead to a two-step proce-
dure when evaluating the transport block size First the receiver exam-
ines the information modulation scheme and number of channeliza-
tion codes scheduled via HS-SCCH which indicate the value k0 l as
shown in Fig 2-22 The 6-bit HS-SCCH control parameter transport
block size information will be the transport format resource indica-
tor (TFRI) named ki Let k t be the sum of the two values kt = ki + k0i
Both values kt and k0 i can be obtained from tables given by [TS 25321
Ref 30] The range for the TFRI is from 1 to 256 and the derived trans-port block size ranges from 137 bits to 27 952 bits The first table indi-
cates the value k 0 i based on the channelization code and the modula-
tion scheme
Combination i Modulation scheme Number of channelization codes k0 i
0
QPSK
1 1
1 2 40
2 3 633 4 79
4 5 92
5 6 102
Fig 2-22 Extract from TS 25321 table representing k0 i
The second table indicates the final transport block size based on kt
Index TB size Index TB size Index TB size1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
4 173 89 1456 174 6673
5 185 90 1483 175 6793
6 197 91 1509 176 6916
7 209 92 1537 177 7041
Fig 2-23 Extract from TS 25321 table representing kt
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High speed shared control channel (HS-SCCH)
53
J The transport block size used on HS-DSCH is not signaled explicitly on HS-SCCHJ Instead a transport block size index k
i is signaled to indicate the transport block size
First stepModulation scheme andnumber of channelizationcodes as signaled on HS-SCCHdetermine value k
0 i
Second step
Index kt = k
i + k
0i
determines HS-DSCH
transport block size
kt = k
i + k
0i
Table according to 3GPP TS 25321 extract from QPSK section
Table according to 3GPP TS 25321 254 entries in total
Combination i Modulation
scheme
Number of
channelization codes
k0 i
0
QPSK
1 1
1 2 40
2 3 63
3 4 79
4 hellip hellip
Index TB size Index TB size Index TB size
1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
helliphellip hellip hellip hellip hellip
Fig 2-24 Retrieval of transport block size information
Source Fig 2-22 to Fig 2-24 [TS 25321 Ref 30] reproduced by permission of 3GPP
Hybrid ARQ process information 3 bits
The concept behind the hybrid automatic repeat request (HARQ) was
introduced in section 13 page 14 One feature is the possibility of
multitasking ie having several HARQ processes activated at the same
time Fig 2-25 below shows the need to signal the process identity tothe receiver Remember that on the downlink there is a shared chan-
nel concept so the NodeB can flexibly decide which UE will be sched-
uled with a downlink transport block Up to eight HARQ processes
can be signaled via higher layers to one UE Note however that due to
the round-trip timing six HARQ processes must be active to achieve
the maximum throughput as shown in Fig 2-51 page 79 Compared
with HSUPA the HARQ processes on the downlink are asynchronous
so they have to be indicated but on the uplink they are synchronous sothey do not need to be signaled explicitly
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HSDPA operation overview and physical channels
Asynchronous DL minus Synchronous ULNumber of H-ARQ rocesses = 1 to 8 er UE
UL HS-DPCCH UE1
UE1 HARQ processes 1 to 4
3 4 1 42 11 1 32retrans
2
A N A A
A A
N A
UL HS-DPCCH UE2
HS-PDSCH
UE2 HARQ processes 1 to 2
Fig 2-25 HARQ process indication on HS-SCCH
Fig 2-25 shows a typical situation on the downlink (point-to-multi-
point) The NodeB sends data to several UEs sharing the HS-PDSCH
so therefore the HARQ process is asynchronous The time when a
transport block is retransmitted is not fixed For this reason the pro-
cess identifier is signaled on the HS-SCCH Based on the HARQ pro-
cess identity and the new data indicator bit the receiving entity knows
which part of the soft buffer memory has to be used in case of soft com-bining On the uplink the situation is slightly simpler The UE only
communicates with one NodeB so it is a point-to-point connection
Thus retransmission always occurs at a fixed time linked to the origi-
nal transmission
Redundancy and constellation version 3 bits
Adaptive modulation and coding involve flexible selection of modula-tion and coding schemes that are signaled to the receiving UE via the
parameters transport block size and modulation scheme information
Another concept used in HSDPA was previously discussed Chase com-
bining or incremental redundancy (see section 222 page 41) This
means that in case of retransmission the transmit entity can dynami-
cally select another puncturing scheme or keep the puncturing as it was
in the original transmission The applied puncturing scheme is signaled
as redundancy information to the receiver Additionally in case of the16QAM modulation scheme the transmitter can select another constel-
lation arrangement which is also signaled to the UE with the three bits
for the redundancy and constellation version see Fig 2-15 page 45
Depending on the modulation scheme (QPSK or 16QAM) there are
two different tables indicating the parameters ldquosrdquo ldquorrdquo and ldquobrdquo The
parameters ldquosrdquo and ldquorrdquo indicate which scheme is used for puncturing
ie if the puncturing mechanism prioritizes the systematic bits or not
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High speed shared control channel (HS-SCCH)
55
and which puncturing algorithm is used The parameter ldquobrdquo indicates
the constellation mapping version The receiver needs this information
to perform proper demodulation and decoding
Initial transmission
1st retransmission
2nd retransmission
3rd retransmission
r
0
0
1
1
2
2
3
xrv
(value)
s
0 1
1 0
2 1
3 0
4 1
5 0
6 1
7 0 3
s = 1 Systematic bits are prioritizeds = 0 Non-systematic bits are prioritized
r (range 0 to 3 for QPSK) influencesJ Input parameter for puncturing or (together with s) for repetition algorithm defined in TS 25212J Selection of parity bits
Redundancy version coding sequences are signaled on HS-SCCH egndash 0 2 5 6 One initial transmission + 3 retransmissions with different r and s parameters
Fig 2-26 Signaling of redundancy version parameters r and s QPSK case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
Initial transmission
2nd retransmission
1st retransmission
3rd retransmission
r (range 0 to 1 for 16QAM)influences input parameterfor puncturing or (togetherwith s) for repetitionalgorithm defined in
TS 25212 and thus selectionof parity bits
Redundancy version coding sequences are signaled on HS-SCCH egminus 6 4 0 5 Chase combining (no change in s and r parameters ie same redundancyversion) with four possible constellations
x rv (value) s r b
0 1 0 0
1 0 0 0
2 1 1 1
3 0 1 1
4 1 0 1
5 1 0 2
6 1 0 3
7 1 1 0
Definition of parameter s as for QPSK
b (range 0 to 3) describes constellationrearrangement to averagereliability of bits
Fig 2-27 Signaling of redundancy version parameters r s and b 16QAM case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
UE identity H-RNTI 16 bits
The HSDPA radio network transaction identifier (H-RNTI) unam-
biguously identifies the UE having an HS-PDSCH assignment within
a cell It is allocated to the UE via layer 3 signaling procedures at the
radio bearer setup if the radio bearer is an HSDPA connection This
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HSDPA operation overview and physical channels
value represents a temporary name of the UE used to address it when
scheduling data packets via HS-SCCH
HS-SCCH channel coding
The control information contained in the HS-SCCH is of course pro-
tected with channel coding mechanisms the whole coding chain is
described in Fig 2-28 Fig 2-18 page 48 presents the separation of
the control information into two code blocks which are sent consec-
utively mapped on slot 1 and slot 2 + 3 of one HS-SCCH subframe
This principle is also visible in the coding chain The first control block
consisting of channelization information modulation scheme and UE
identity is coded separately from the remaining control values to enable
the UE receiver to decode this first slot separately and prepare for pos-
sible HS-PDSCH reception The coding steps shown in Fig 2-28 such
as rate matching 1 and 2 are similar to the HS-PDSCH coding chain
and are further described in [TS 25212 Ref 21]
Channelcoding 1
R atematching 1
mux
Channelcoding 2
Ratematching 2
RVcoding
UE-specificCRC attachment
UE-specificmasking
Physical channelmapping
r s b
mux
Channelizationcode set
Modulationscheme
Transport block size information
HARQ processinformation
Redundancy andconstellation version
New data indicator
UE identity
UE identity
Fig 2-28 Channel coding for HS-SCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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High speed dedicated physical control channel (HS-DPCCH)
57
24 High speed dedicated physical control channel (HS-DPCCH)
In an active HSDPA connection the UE has to send acknowledgment ornon-acknowledgment reports (as described in section 13 page 14
where the HARQ process is described) as well as channel status infor-
mation to the network The reporting is performed on this physical
control channel HS-DPCCH
As ubiquitous in HSDPA the uplink is also configured into a subframe
structure of 2 ms corresponding to three slots The first slot of the sub-
frame carries the ACK NACK information the UE sends to the NodeB
while the following two slots ie slot 2 and 3 of the subframe convey
the CQI value the channel quality information to the NodeB
Subframe 0 Subframe i Subframe 4
Tslot
= 2560 chips J The spreading factor of theHS-DPCCH is 256 (10 bits peruplink slot)
J The HS-DPCCH can only existtogether with an UL DPCCH
(ded phys control channel)J The DPDCH (dedicated physical data channel) the DPCCH andthe HS-DPCCH are IQ codemultiplexed
HARQ-ACK CQI = Channel quality information
2 times Tslot
= 5120 chips
One radio frame Tf = 10 ms
One HS-DPCCH subframe 2 ms
Fig 2-29 HS-DPCCH configuration
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The slot format for HS-DPCCH describes a quantity of 30 bits per sub-frame resulting in a data rate of 15 kbps The spreading factor used for
the HS-DPCCH is constant and is always equal to 256 but the chan-
nelization code that is used as well as the mapping on either the I or
Q axis depends on several factors eg the co-existence of an HSDPA
connection with a circuit-switched connection meaning whether a
DPDCH established or not Fig 2-36 page 64 illustrates this IQ
mapping and Fig 2-35 page 63 shows the channelization code used
for HS-DPCCH
The HS-DPCCH builds a logical unit of one subframe but having the
independent control information HARQ-ACK and CQI included which
could be separately decoded at the NodeB Note that the slot carrying
the ACK NACK statement is active only when the UE has been sched-
uled by an HS-PDSCH subframe in the corresponding downlink sub-
frame previously Assuming the UE has not received a transport block
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HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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HSDPA operation overview and physical channels
sequence can only assume one of two succeeding states depending on
whether 0 or 1 was entered into the coder ie the decoder decides for
the metric providing the minimum error estimation If a word arrivesat the receiver in a state that cannot be reached from a state obtain-
able from one of the two input combinations a transmission error has
occurred and needs to be corrected This procedure is equivalent to
tracing a path through a trellis diagram which is familiar from cod-
ing theory
We would now like to discuss a brief example to demonstrate the func-
tionality of channel coding and the subsequent steps of puncturing
Please note that this example does not represent the real coders used
in HSDPA Consult the relevant literature for further details of cod-
ing theory [Ref 10] [Ref 11] and [Ref 14] as well as the specification
[TS 25212 Ref 21] which describes the coding applied in HSPA
The convolutional coder shown in Fig 2-8 consists of one input fol-
lowed by three registers in a shift configuration and finally two out-puts With each clock generation the content of each register is shifted
one register to the right as the last registerrsquos content is discarded and
a new input bit is inserted into the first register The outputs 1 and 2
are generated by an XOR operation between the linked register con-
tents In this manner we create a finite response filter and a certain
memory effect Letrsquos assume we want to transmit the following input bit
sequence 110110 01 Here the nomenclature 01 means that the lastbit of our contemplated sequence can be either 0 or 1 and we wish to
consider both alternatives The registers are initialized with all 0s and
typically some tail bits are attached to the code word which will ensure
this for the succeeding code word The table in Fig 2-8 shows the input
bit on the left side the register sequence content after each step and
outputs 1 and 2 on the right side The output sequence for the given
input will be 11 01 01 00 01 011100 Note the last two lines in the table
We do assume an either or ie there are two alternatives such thatalternative A means that after the sequence 110110 has been sent to the
coder the following bit will be logical 0 Alternative B means that after
the sequence 110110 the following bit will be a logical 1 So we present
an either or situation This will be used to explain the coding principle
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HS-DSCH High speed downlink shared channel transport channel
37
Example of convolutional coding
Input Regis-
ter 1
Regis-
ter 2
Regis-
ter 3
Out-
put 1
Out-
put 2
XOR operation
Register 3Register 2Register 1
+
Input
Output 1
Output 2
+ +
1 1 0 0 1 1
1 1 1 0 0 1
0 0 1 1 0 1
1 1 0 1 0 0
1 1 1 0 0 1
0 0 1 1 0 1
Alt A 0 0 0 1 1 1
Alt B 1 1 0 1 0 0
Fig 2-8 Simple example for convolutional coding
In Fig 2-9 that follows there is a trellis diagram representing in each
column the four possible output values of our channel coder 00 01 10
or 11 and in bold color there is the trellis path through this diagram
resulting from the input sequence Recalling our definition of the two
alternatives for the last bit of our example code word we can see that
the rightmost part of this trellis diagram shows the two possible steps
From state 01 we can only reach either state 00 or state 11 The twoother states 01 or 10 are not possible and with no input to the coder
shown in Fig 2-8 the output can reach these two states in this step For
example if the receiver detects a sequence such as 11 01 01 00 01 01 01
it knows there is an error at the last position 01 which had to be cor-
rected as either 00 or 11 because only these two alternatives are pos-
sible The error correction is performed by looking at the total trellis
path and selecting the maximum likelihood sequence estimation basedon the received data pattern In our short example we admit that we
stopped at this point of course Imagine that the input sequence of bits
continues The decoder would not know if it should proceed with the
pattern 00 or 11 so the decision will be to continue both ways The fol-
lowing step is then checked again and one of the assumed ways will dif-
fer more from the demodulated pattern than the other one This prin-
ciple is described in the Viterbi algorithm [Ref 15] Based on this algo-
rithm the stronger path will survive ie the decoder checks at eachstep which path of the examined ones in the trellis path exhibits the
smallest deviation from the demodulation sequence and thus this path
will be continued The paths exhibiting a higher deviation are discarded
to reduce the calculation expense The path through the trellis diagram
is called a ldquometricrdquo and the term ldquomaximum likelihood sequence esti-
mationrdquo (MLSE) represents the selection by the channel decoder of the
real possible metric which is the closest to the received data pattern As
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HSDPA operation overview and physical channels
an analogy If we do a crossword puzzle and find some characters in a
word the channel decoder would check in a primer or dictionary of the
language containing all possible character combinations that we callldquowordsrdquo and select the existing word that has the maximum likelihood
for the prevailing sequence of characters
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
Alternative B
Alternative A
Register 2
+ +
+
Output 1
Output 2
XOR operation
Trellis diagram above showsmetric for input sequence
110110 0
or 1
into a coder such as
1
1
0
1 10
0
1
Register 3Register 1
Fig 2-9 Metric in trellis diagram
Interleaving
Forward error correction based on convolutional coders has one disad-
vantage related to the impact of block errors If the transmission errors
are distributed they can be corrected as demonstrated in the trellis dia-gram example using the Viterbi algorithm but if many adjacent bits
are lost the decoder will have problems retrieving the right bit pattern
Interleaving means that the information to be transmitted is spread or
distributed over several bursts in such a way that contiguous informa-
tion is split up and transmitted in a time or block distributed mode
To avoid error bursts an attempt is made to spread the bit errors over
several code words This is achieved by interleaving several code wordsThis method is also called diagonal interleaving see Fig 2-10 Another
kind of interleaving is block interleaving as shown in Fig 2-11 Blocks
of code words are written row-by-row into a matrix and then read col-
umn-by-column With both methods consecutive bits of a code word
are never transmitted consecutively and conversely when the bits are
deinterleaved at the receive end error bursts are spread over several
code words
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HS-DSCH High speed downlink shared channel transport channel
39
As several code words are interleaved the decoder has to ldquowaitrdquo a cer-
tain time until all bits of a particular code word arrive This delay ie
the ldquomeasure for spreading over timerdquo is referred to as the ldquointerleav-ing depthrdquo The greater the interleaving depth the more code words are
available for spreading the error bursts and the greater the probability
that errored bits can be corrected but on the other hand this increases
the overall latency time
HSDPA uses the block diagonal interleaving principle for the HS-DSCH
only since as we should recall one goal is to have a short round-trip
time
Spreadinghellip
Interleaving
hellip
hellip
Fig 2-10 Diagonal interleaving
Write
Read
Interleaving-Matrix
Fig 2-11 Block interleaving
Puncturing
Having briefly described the principle of convolutional coding another
mechanism will be presented that is used to increase the throughputof user data and coordinate with the AMC mechanism described in
section 12 page 10 After adding redundancy the total bit stream is
now known as soft bits ie the sum including all of the raw data bits
at the input of the channel coder plus the added redundancy bits This
quantity must match the required transport block size demanded by
the transport layer and the process performed here is called rate match-
ing ie deleting some of the soft bits at the transmitting end in a pre-
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HSDPA operation overview and physical channels
defined manner or repeating or adding some stuffing bits In HSPA the
rate matching mechanism uses puncturing which provides higher data
throughput The signaled values TBS and RV tell the receiving convo-lutional coder how many and where bits have been punctured This
allows the decoder to insert blank positions which have to be filled later
by performing trellis decoding In other words we may consider the
punctured bits as bit losses created intentionally by the transmitter In
this manner the total amount of data bits can be increased for the sake
of lower redundancy In HSDPA this puncturing scheme will be very
flexible and the NodeB scheduler will set the puncturing rate adapted
to the prevailing RF conditions on the radio channel to obtain the high-
est possible data throughput under the existing conditions The disad-
vantage of adaptive coding is that we need signaling information so
that the transmitter has to inform the receiver about how many soft bits
have been punctured This is seen in Fig 2-26 page 55 in the form
of the redundancy version carried by the HS-SCCH control channel
Fig 2-12 below again depicts the principle of puncturing in HSDPAand clarifies some signaling parameters such as the transport block size
1 1 0 1 1 0 0
11 01 01 00 01 01 11
Transport block sizeInput bits into channel coder
Soft bitsOutput from channel encoder
Rate matchingPuncturing or repeating bits
11 01 01 00 01 01 11
1 01 0 00 0 01 1Coded composite transport bitsCan be several combined streams aftercoding + rate matching
Transport block size FEC
Fig 2-12 Puncturing based on coding example from Fig 2-8 page 37
The process of channel coding starts first with the transport block
size which is given by the size of the input data bit sequence added
by a cyclic redundancy checksum The next step is the channel cod-
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HS-DSCH High speed downlink shared channel transport channel
41
ing which is performed in HSPA by a so-called turbo coder The turbo
coder is a parallel concatenated convolutional coder that exhibits bet-
ter reliability compared to a single convolutional coder Discussingthe functionality of a turbo coder in all of its details would represent a
major digression from the intention of this book Accordingly we will
simply encourage the interested reader to consult the channel coding
literature for more details about turbo coders and their applications
[Ref 10] [Ref 12] Determined by the scheduler of the base station or
the redundancy version to be used the next step known as the redun-
dancy version will either puncture (the most likely) or repeat some of
the bits resulting from the channel coding process How many bits will
be punctured is defined by the coding rate In our example in Fig 2-12
we see that the input bit sequence has a length of 7 bits resulting in
14 soft bits after channel coding with our example coder providing a
coding rate of frac12 The scheduler decided to puncture 4 bits so that we
finally obtain 10 bits which have to be mapped on the physical chan-
nels Our overall coding rate is therefore given as ⁷frasl983089983088 In other words
some bits are protected with redundancy information while othersare not Note that the size of the coded composite transport channel
is determined by the physical layer parameters such as the number of
channelization codes used to convey the HS-PDSCH the modulation
scheme and the transmit time interval which is constant for HSDPA
but can be either 2 or 10 ms for HSUPA Thus its size does not need
to be signaled to the receiver and only the transport block size and the
redundancy versions will be contained in the HS-SCCH channel
222 Incremental redundancy and chase combining
for HS-DSCH
Until now we have presented some general characteristics of HSDPA
and HSUPA which we would now like to discuss in a combined pro-
cedure and then deduce two other principles The HARQ abbreviationcombines an automatic retransmission of erroneous data with a soft
combination at the receiving end A related question can now be how
the transmitter has to repeat the transport block should the retrans-
mission of data occur in an identical retransmission mode or should
some changes in coding parameters eg the manner of puncturing be
applied This question is also important for the implementation of the
rate matching step shown in Fig 2-12 The transmitter has to provide
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HSDPA operation overview and physical channels
a certain soft buffer ie a memory that stores the transmitted data for
the sake of possible retransmissions and deletes it after having received
a positive acknowledgment from the receiver Should the transmitternow store the coded composite transport data i e the data after coding
but also after puncturing This would restrict it to repeating the data in
an identical manner A better approach is to store the data after channel
coding and before puncturing Even if this requires more memory it
gives the flexibility to change the puncturing scheme and retransmit the
transport block in a different way Fig 2-13 and Fig 2-14 represent both
mechanisms that are used in HSDPA and HSUPA Identical retransmis-
sion is called chase combining and non-identical retransmission with
a different puncturing scheme is called incremental redundancy The
scheduler in the base station can decide which retransmission scheme
will be used We do not wish to delve into the details of channel coding
theory to discuss which mechanism is the better one ndash chase combin-
ing or incremental redundancy We will only mention that both mech-
anisms have their advantages and thus their applications Chase com-
bining has the advantage that the systematic bits representing the orig-inal data input into the channel coder are contained in the transmit-
ted sequence after puncturing Thus chase combined transport blocks
are ldquoself-decodablerdquo If we consider a situation where the original trans-
port block is lost completely and only the retransmitted block is pres-
ent at the receiver there is a chance to decode the data properly Mean-
while incremental redundancy seems to add more redundancy when
retransmitting but in a scenario where the first transmission contain-ing the systematic bits is lost completely and only the retransmission
is present the receiver will have no chance to decode the data without
having some of the systematic bits Accordingly incremental redun-
dancy is applied whenever sporadic bit errors occur due to a time vari-
ant channel and chase combining is selected whenever we have to deal
with complete transport block errors i e the time variance of the radio
link exhibits some bursted fading dips
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HS-DSCH High speed downlink shared channel transport channel
43
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Chase combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Transmitted bit
Punctured bit
Systematic bits
Parity 1
Parity 2
Systematic bits
Parity 1
Parity 2
Fig 2-13 Chase combining principle
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Incremental redundancy combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Systematic bits
Parity 1
Parity 2
Systematic bitsParity 1
Parity 2
Fig 2-14 Incremental redundancy
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HSDPA operation overview and physical channels
223 Constellation rearrangement
Due to the fact that HSDPA introduces a higher-order modulationscheme (16QAM) we can recognize some effects due to the physi-
cal layer influencing the susceptibility to noisy RF conditions One of
these effects can be explained by looking at the constellation diagram
in the 16QAM modulation scheme see section 12 page 10 As we
recall there is a total of 16 different constellation points given by the
modulation vector and represented by its phase and amplitude Con-
sidering the Euclidean distance which is the distance in this constella-
tion diagram between two neighboring points we can clearly see that
some points have more neighbors than others Especially the four con-
stellation points at the very four corners only have three direct neigh-
bors making them less susceptible to misdetection due to noise shift-
ing them in a certain direction On the other hand the four constella-
tion points representing the inner square of the constellation have eight
direct neighbors each and are therefore more likely to be incorrectly
detected The idea of constellation rearrangement is now to change themapping scheme applied in the original transmission when retrans-
mitting As we know the receiver will soft combine the retransmit-
ted data with the previously received information so we can achieve a
certain incremented redundancy and a certain protection mechanism
Note however that considering a sole transmission of a transport block
using a certain constellation arrangement will not show any more pos-
itive or negative results compared to other constellation arrangementsThe redundancy gain is only achieved by rearranging the constellation
mapping in a retransmitted transport block and performing soft com-
bining at the receiver Overall HSDPA defines four constellation rear-
rangement schemes which are indicated in the redundancy version
field of the HS-SCCH and are represented by the ldquobrdquo bit field ranging
from b = 0 to b = 3 All four constellation schemes are Gray encoded
ie the directly adjacent constellation symbols do not exhibit four com-
pletely different bits in order to reduce the impact of misdetection onbit errors
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High speed shared control channel (HS-SCCH)
45
Q
I
(ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1) (1 1ndash1ndash1)
(ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1) (1 1ndash1 1)
(ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1) (1ndash1ndash1 1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 0
Q
I
(ndash1 1 1 1) (ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1)
(ndash1 1 1ndash1) (ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1)
(ndash1ndash1 1ndash1) (ndash1ndash1ndash1ndash1) (1ndash1ndash1ndash1) (1ndash1 1ndash1)
(ndash1 1 1 1) (ndash1ndash1ndash1 1) (1ndash1ndash1 1) (1ndash1 1 1)
b = 2
Q
I
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (1ndash1 1 1) (ndash1ndash1 1 1)
(ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1) (ndash1 1 1 1)
(ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1) (ndash1 1 1ndash1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 1
Q
I
(1 1ndash1 1) (ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1)
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1)
(1ndash1ndash1ndash1) (ndash1ndash1ndash1ndash1) (ndash1ndash1 1ndash1) (1ndash1 1ndash1)
(1 1ndash1ndash1) (ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1)
b = 3
Fig 2-15 Constellation rearrangement in HSDPA
23 High speed shared control channel (HS-SCCH)
The HS-SCCH sends scheduling information to the UEs As seen before
the HS-PDSCH has a very flexible configuration for physical parame-
ters such as the coding rate number of code channels or retransmis-sions This high flexibility increases the complexity and engenders the
need for additional signaling information transferred on the HS-SCCH
Reception of user data in HSDPA is always a two-step procedure
First the receiver has to capture the scheduling control information
and afterwards based on the received control information it may start
demodulating and decoding the HS-PDSCH containing the user data
This two-step procedure is shown in Fig 2-16 below which lists what
kind of control information is sent to the UEs via the HS-SCCH Asshown in Fig 2-2 page 28 which describes the overall HSDPA chan-
nel structure there can be up to four HS-SCCHs assigned to one UE
But only one HS-SCCH would contain the scheduling information for
this UE within one TTI Thus the network can assign resources simul-
taneously to various UEs in the downlink direction
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HSDPA operation overview and physical channels
I would like to receive databut I dont know where myHS-PDSCH resources areand what they look like
HS-SCCH
Read the 1st HS-SCCH slotfor HS-DSCH channelizationcodes UE identity and
modulation scheme
Then the 2nd and 3rd HS-SCCHslots provide transport block sizeinformation hybrid ARQ process in-formation redundancy constellationversion new data indicator
HS-PDSCH
Fig 2-16 HS-SCCH control channel usage
Regarding the physical layer parameters we see in Fig 2-17 that the
HS-SCCH uses a channelization code with a spreading factor of 128
and it also uses the newly introduced transmit time interval of one sub-
frame which is equal to 2 ms It should be mentioned that the spread-ing factor of 128 requires double the capacity compared to similar con-
trol channels in WCDMA Release 99 reflecting the signaling overhead
needed to guarantee the huge flexibility introduced with HSDPA Addi-
tionally Fig 2-16 shows that the control information is sent consecu-
tively within one subframe The first slot within this subframe contains
the control information UE identity channelization code information
and modulation scheme identifier Slots 2 and 3 of the subframe con-tain the remaining control information Transport block size HARQ
process identifier redundancy version and new data indicator Conse-
quently the UE can self-decode slot 1 alone and slots 2 and 3 in a sec-
ond step even if they represent one logical unit This raw control infor-
mation is of course also channel coded using a turbo and on the phys-
ical layer the quantity of bits after the rate matching step is 40 bits con-
veyed in one slot corresponding to 666 micros [TS 25212 Ref 21] see also
Fig 2-28 page 56
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High speed shared control channel (HS-SCCH)
47
The HS-SCCH is a fixed rate (60 kbps SF = 128) downlinkphysical channel used to carry downlink signaling related toHS-DSCH transmission
Slot 0
Slot 1
Slot 2
Tslot
= 2560 chips
Data = 40 bits
1 subframe = 2 ms
Fig 2-17 Structure of High speed shared control channel HS-SCCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
We would like to return now to the time consecutive transmission of
control information There is a difference in the control information
in terms of its priority Some information is needed at the UE end
very urgently while other control information does not have such a
high priority But why This will be explained by looking at some tim-ing aspects defined for HSDPA If we consider the timing between
the shared data channel HS-PDSCH and the shared control chan-
nel HS-SCCH as shown in Fig 2-18 we see that the HS-PDSCH fol-
lows the HS-SCCH by exactly two slots or 5120 chips The HS-SCCH
is completely time-aligned with the general control channels CPICH
and P-CCPCH of the NodeB This is mandatory because it is a shared
channel Consider several UEs with different distances to the NodeBwanting to receive the HS-SCCH channel Thus it must have constant
timing that is known a priori The shared data channel HS-PDSCH is
now transmitted exactly 5120 chips after the first chip of the HS-SCCH
This leads to an overlapping slot thereby requiring multitasking recep-
tion at the UE end While the UE is still receiving the last slot of an
ongoing HS-SCCH subframe it may already start the reception of an
HS-PDSCH transport block The first slot in the HS-SCCH subframe
now contains information required by the physical layer to performdespreading and demodulation These values are the UE identity indi-
cating whether the UE will start demodulation of the HS-PDSCH or
not in case it is not scheduled the modulation scheme information
since the UE has to know how to interpret the received constellation
vector and whether it has to be considered as a QPSK or 16QAM con-
stellation point and finally the UE has to know which channelization
codes it has to apply to capture the HS-PDSCH transport block The
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HSDPA operation overview and physical channels
overall UE reaction time when being scheduled is now seen as 1 slot
or 2560 chips This tough requirement for the UEs is due to the objec-
tive to obtain overall a much shorter latency than legacy standards Theadditional control information such as the new data indicator redun-
dancy version and transport block size is not that urgent since it is
needed after demodulation but before channel decoding So first the
UE will sample the whole three slots of the HS-PDSCH and demodu-
late them into a bit stream which is finally handed over to the channel
decoder This principle is known as post-processing and is used typi-
cally in mobile communications technologies
J Start of HS-SCCH subframe 0 is aligned with startof P-CCPCH frames
J The HS-PDSCH starts
τ HS-PDSCH
(2times Tslot
= 5120 chips)
after the start of the HS-SCCH
UE identity etc
processing timeof receiver
HS-DSCH subframe
3 times Tslot= 7680 chips
3 times Tslot
= 7680 chips
τ HS-PDSCH
(2times Tslot
= 5120 chips)
HS-SCCH
HS-PDSCH
Fig 2-18 Timing relation between HS-SCCH and HS-PDSCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
Content of the HS-SCCH control channelThe control information contained in the HS-SCCH control chan-
nel has already been mentioned so we will now consider the values
in more detail We will begin with an overview of what kind of control
information is contained in the HS-SCCH channel before proceeding
with further details about the single control elements The following
control information is present in the HS-SCCH [TS 25212 Ref 21]
Channelization code set information (7 bits)
Modulation scheme information (1 bit) Transport block size information (6 bits)
Hybrid ARQ process information (3 bits)
Redundancy and constellation version (3 bits)
New data indicator (1 bit)
UE identity (16 bits) = H-RNTI
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High speed shared control channel (HS-SCCH)
49
Some of these parameters are more or less self-explanatory while oth-
ers require additional background information and closer examination
Modulation scheme information 1 bit
This single bit is used to inform the receiver whether the modulation
scheme QPSK or 16QAM is applied on the data channel HS-PDSCH
The interpretation of the bit x ms1 is as follows
ms1
x
if QPSK
otherwise
0
1
=
New data indicator 1 bit
The new data indicator bit field informs the receiving entity that the
prevailing PDU transmitted by the current HARQ process is either a
retransmission or contains new data This is done by setting the new
data bit to the value 0 for the first PDU on this particular HARQ process
and incrementing the value by 1 with every new data sent [TS 25321Ref 30] This leads to a toggled value In case the new data bit is not
incremented ie if it remains at its previous value it is an indicator for
retransmission
1st PDU of this
HARQ process
NDI = New data indicator
NDI = 0 NDI = 1
NACK
NDI = 1
ACK
NDI = 0
HS-SCCH HS-SCCH HS-SCCHHS-SCCH
ACK
Fig 2-19 New data indicator bit principle of incrementing value
Channelization code set information 7 bits
This field is used to indicate the number of channelization codes usedfor transmitting the transport block on the HS-PDSCH As was already
described the spreading factor applied on the HS-PDSCH is constant
with a value of 16 but the flexible values are the number of channeliza-
tion codes forming a cluster when using multiple codes and their posi-
tion in the code tree It is not allowed to distribute the code channels
over the code tree diagram For the sake of simplicity in signaling sev-
eral channelization codes form one cluster and these codes are con-
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HSDPA operation overview and physical channels
tiguous in the channelization code tree [TS 25213 Ref 22] Fig 2-20
illustrates the principle of indicating the channelization codes on the
HS-SCCH
SF = 16
Code ldquo0rdquo isreserved forcommonchannels
Code offset 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15P = 5O = 7
Code group indicatorx
ccs1 x
ccs2 x
ccs3 = min (Pminus 1 15 minusP)
Code offset indicatorx
ccs4 x
ccs5 x
ccs6 x
ccs7 = |Ominus 1minus P8 times15|
A cluster of codes
can be allocated to a UEC
ch16Ohellip C
ch16O + P minus 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1
2 2 2 2 2 2 2 2 2 2 2 2 2 2 14 14
1 2 3 4 5 6 7 8 9 10 11 12 13 14 2 1
3 3 3 3 3 3 3 3 3 3 3 3 3 13 13 13
1 2 3 4 5 6 7 8 9 10 11 12 13 3 2 1
4 4 4 4 4 4 4 4 4 4 4 4 12 12 12 121 2 3 4 5 6 7 8 9 10 11 12 4 3 2 1
5 5 5 5 5 5 5 5 5 5 5 11 11 11 11 11
1 2 3 4 5 6 7 8 9 10 11 5 4 3 2 1
6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10
1 2 3 4 5 6 7 8 9 10 6 5 4 3 2 1
7 7 7 7 7 7 7 7 7 9 9 9 9 9 9 9
1 2 3 4 5 6 7 8 9 7 6 5 4 3 2 1
8 8 8 8 8 8 8 8
8 7 6 5 4 3 2 1
0 (115)
1 (214)
2 (313)
3 (412)
4 (511)
5 (610)
6 (79)
7 (88) Redundant area
C l u s t e r c o d e i n d i c a t o r ( 3 b i t s )
Tree offset indicator (4 bits)
Signaled on HS-SCCH
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
PO
Decoding notation
Number ofmulti-codes
Offset fromleft right incode tree (SF = 16)
Fig 2-20 Channelization code set indicating the HS-PDSCH code cluster
The idea behind the code indication is a matrix with the rows repre-
senting the number of codes per cluster and the columns represent-
ing the position of that cluster the offset value in the code tree Recall-
ing that the maximum number of channelization codes per clusteris 15 and if the cluster size is 1 the offset values can also range from
1 to 15 the resulting matrix would have 15 rows and 15 columns Since
we know that four bits are needed to represent an integer from 1 to 15
we need a total of 4 + 4 = 8 bits for representation of the channeliza-
tion code set information It is a smart idea to save one bit The 15 times 15
matrix would contain much redundant information By way of analogy
like in a road map indicating distances between cities A table showing
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High speed shared control channel (HS-SCCH)
51
the distance from city A to city B the opposite distance from city B to
city A is redundant information The useful information has the form
of a triangle The idea is to cut the lower part rotate it and append itto the spare part of the upper table In this manner a table is obtained
with 7 rows and 15 columns and it is possible to indicate each position
in it with just 7 bits
1 5 r o w s 7
r o w s
Matrix reduction for channeli-
zation code set information
15 columns
Fig 2-21 Matrix size reduction for channelization code set information
The content of the channelization code set matrix can be described as
a value with two numbers The upper number is the number of mul-
ticodes forming one cluster and the lower number is the offset in the
channelization code tree Accordingly the example in Fig 2-20 can be
interpreted to mean the HS-SCCH sends the bits as row number 4 and
column number 6 in the matrix The content of this element are the
values 5 over 7 which have to be interpreted as a cluster size of 5 codesand an offset of 7
Transport block size information 6 bits
With a length of six bits the transport block size (TBS) informa-
tion informs the receiving UE entity about the data block size of the
transport block sent on the HS-PDSCH We should keep in mind the
link adaptation performed with the adaptive modulation and coding
scheme that was described in section 12 page 10 The ratio errorcorrection and user data are flexible while the physical layer param-
eters such as the spreading factor modulation scheme and number of
channelization codes determine the physical block size This physical
block consists of the user data ratio or transport block size and the for-
ward error correction or redundancy information As this ratio is flex-
ible the HS-SCCH will inform the receiving UE entity about the size
of the transport block Here too there is a strategy of bit reduction the
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52
HSDPA operation overview and physical channels
goal is to inform the receiver with as few bits as possible A non-effi-
cient approach would involve conversion of the decimal number repre-
senting the TBS into a binary sequence but the number of bits neededwould exceed the space available on the HS-SCCH Imagine that the
range of transport block sizes depends on the physical layer condi-
tions The ambient physical layer parameters modulation scheme and
number of channelization codes set a certain working point where the
remaining flexibility for a different TBS configuration can be obtained
by more or less puncturing resulting in a flexible ratio between for-
ward error correction and user data This will lead to a two-step proce-
dure when evaluating the transport block size First the receiver exam-
ines the information modulation scheme and number of channeliza-
tion codes scheduled via HS-SCCH which indicate the value k0 l as
shown in Fig 2-22 The 6-bit HS-SCCH control parameter transport
block size information will be the transport format resource indica-
tor (TFRI) named ki Let k t be the sum of the two values kt = ki + k0i
Both values kt and k0 i can be obtained from tables given by [TS 25321
Ref 30] The range for the TFRI is from 1 to 256 and the derived trans-port block size ranges from 137 bits to 27 952 bits The first table indi-
cates the value k 0 i based on the channelization code and the modula-
tion scheme
Combination i Modulation scheme Number of channelization codes k0 i
0
QPSK
1 1
1 2 40
2 3 633 4 79
4 5 92
5 6 102
Fig 2-22 Extract from TS 25321 table representing k0 i
The second table indicates the final transport block size based on kt
Index TB size Index TB size Index TB size1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
4 173 89 1456 174 6673
5 185 90 1483 175 6793
6 197 91 1509 176 6916
7 209 92 1537 177 7041
Fig 2-23 Extract from TS 25321 table representing kt
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High speed shared control channel (HS-SCCH)
53
J The transport block size used on HS-DSCH is not signaled explicitly on HS-SCCHJ Instead a transport block size index k
i is signaled to indicate the transport block size
First stepModulation scheme andnumber of channelizationcodes as signaled on HS-SCCHdetermine value k
0 i
Second step
Index kt = k
i + k
0i
determines HS-DSCH
transport block size
kt = k
i + k
0i
Table according to 3GPP TS 25321 extract from QPSK section
Table according to 3GPP TS 25321 254 entries in total
Combination i Modulation
scheme
Number of
channelization codes
k0 i
0
QPSK
1 1
1 2 40
2 3 63
3 4 79
4 hellip hellip
Index TB size Index TB size Index TB size
1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
helliphellip hellip hellip hellip hellip
Fig 2-24 Retrieval of transport block size information
Source Fig 2-22 to Fig 2-24 [TS 25321 Ref 30] reproduced by permission of 3GPP
Hybrid ARQ process information 3 bits
The concept behind the hybrid automatic repeat request (HARQ) was
introduced in section 13 page 14 One feature is the possibility of
multitasking ie having several HARQ processes activated at the same
time Fig 2-25 below shows the need to signal the process identity tothe receiver Remember that on the downlink there is a shared chan-
nel concept so the NodeB can flexibly decide which UE will be sched-
uled with a downlink transport block Up to eight HARQ processes
can be signaled via higher layers to one UE Note however that due to
the round-trip timing six HARQ processes must be active to achieve
the maximum throughput as shown in Fig 2-51 page 79 Compared
with HSUPA the HARQ processes on the downlink are asynchronous
so they have to be indicated but on the uplink they are synchronous sothey do not need to be signaled explicitly
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HSDPA operation overview and physical channels
Asynchronous DL minus Synchronous ULNumber of H-ARQ rocesses = 1 to 8 er UE
UL HS-DPCCH UE1
UE1 HARQ processes 1 to 4
3 4 1 42 11 1 32retrans
2
A N A A
A A
N A
UL HS-DPCCH UE2
HS-PDSCH
UE2 HARQ processes 1 to 2
Fig 2-25 HARQ process indication on HS-SCCH
Fig 2-25 shows a typical situation on the downlink (point-to-multi-
point) The NodeB sends data to several UEs sharing the HS-PDSCH
so therefore the HARQ process is asynchronous The time when a
transport block is retransmitted is not fixed For this reason the pro-
cess identifier is signaled on the HS-SCCH Based on the HARQ pro-
cess identity and the new data indicator bit the receiving entity knows
which part of the soft buffer memory has to be used in case of soft com-bining On the uplink the situation is slightly simpler The UE only
communicates with one NodeB so it is a point-to-point connection
Thus retransmission always occurs at a fixed time linked to the origi-
nal transmission
Redundancy and constellation version 3 bits
Adaptive modulation and coding involve flexible selection of modula-tion and coding schemes that are signaled to the receiving UE via the
parameters transport block size and modulation scheme information
Another concept used in HSDPA was previously discussed Chase com-
bining or incremental redundancy (see section 222 page 41) This
means that in case of retransmission the transmit entity can dynami-
cally select another puncturing scheme or keep the puncturing as it was
in the original transmission The applied puncturing scheme is signaled
as redundancy information to the receiver Additionally in case of the16QAM modulation scheme the transmitter can select another constel-
lation arrangement which is also signaled to the UE with the three bits
for the redundancy and constellation version see Fig 2-15 page 45
Depending on the modulation scheme (QPSK or 16QAM) there are
two different tables indicating the parameters ldquosrdquo ldquorrdquo and ldquobrdquo The
parameters ldquosrdquo and ldquorrdquo indicate which scheme is used for puncturing
ie if the puncturing mechanism prioritizes the systematic bits or not
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High speed shared control channel (HS-SCCH)
55
and which puncturing algorithm is used The parameter ldquobrdquo indicates
the constellation mapping version The receiver needs this information
to perform proper demodulation and decoding
Initial transmission
1st retransmission
2nd retransmission
3rd retransmission
r
0
0
1
1
2
2
3
xrv
(value)
s
0 1
1 0
2 1
3 0
4 1
5 0
6 1
7 0 3
s = 1 Systematic bits are prioritizeds = 0 Non-systematic bits are prioritized
r (range 0 to 3 for QPSK) influencesJ Input parameter for puncturing or (together with s) for repetition algorithm defined in TS 25212J Selection of parity bits
Redundancy version coding sequences are signaled on HS-SCCH egndash 0 2 5 6 One initial transmission + 3 retransmissions with different r and s parameters
Fig 2-26 Signaling of redundancy version parameters r and s QPSK case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
Initial transmission
2nd retransmission
1st retransmission
3rd retransmission
r (range 0 to 1 for 16QAM)influences input parameterfor puncturing or (togetherwith s) for repetitionalgorithm defined in
TS 25212 and thus selectionof parity bits
Redundancy version coding sequences are signaled on HS-SCCH egminus 6 4 0 5 Chase combining (no change in s and r parameters ie same redundancyversion) with four possible constellations
x rv (value) s r b
0 1 0 0
1 0 0 0
2 1 1 1
3 0 1 1
4 1 0 1
5 1 0 2
6 1 0 3
7 1 1 0
Definition of parameter s as for QPSK
b (range 0 to 3) describes constellationrearrangement to averagereliability of bits
Fig 2-27 Signaling of redundancy version parameters r s and b 16QAM case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
UE identity H-RNTI 16 bits
The HSDPA radio network transaction identifier (H-RNTI) unam-
biguously identifies the UE having an HS-PDSCH assignment within
a cell It is allocated to the UE via layer 3 signaling procedures at the
radio bearer setup if the radio bearer is an HSDPA connection This
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HSDPA operation overview and physical channels
value represents a temporary name of the UE used to address it when
scheduling data packets via HS-SCCH
HS-SCCH channel coding
The control information contained in the HS-SCCH is of course pro-
tected with channel coding mechanisms the whole coding chain is
described in Fig 2-28 Fig 2-18 page 48 presents the separation of
the control information into two code blocks which are sent consec-
utively mapped on slot 1 and slot 2 + 3 of one HS-SCCH subframe
This principle is also visible in the coding chain The first control block
consisting of channelization information modulation scheme and UE
identity is coded separately from the remaining control values to enable
the UE receiver to decode this first slot separately and prepare for pos-
sible HS-PDSCH reception The coding steps shown in Fig 2-28 such
as rate matching 1 and 2 are similar to the HS-PDSCH coding chain
and are further described in [TS 25212 Ref 21]
Channelcoding 1
R atematching 1
mux
Channelcoding 2
Ratematching 2
RVcoding
UE-specificCRC attachment
UE-specificmasking
Physical channelmapping
r s b
mux
Channelizationcode set
Modulationscheme
Transport block size information
HARQ processinformation
Redundancy andconstellation version
New data indicator
UE identity
UE identity
Fig 2-28 Channel coding for HS-SCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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High speed dedicated physical control channel (HS-DPCCH)
57
24 High speed dedicated physical control channel (HS-DPCCH)
In an active HSDPA connection the UE has to send acknowledgment ornon-acknowledgment reports (as described in section 13 page 14
where the HARQ process is described) as well as channel status infor-
mation to the network The reporting is performed on this physical
control channel HS-DPCCH
As ubiquitous in HSDPA the uplink is also configured into a subframe
structure of 2 ms corresponding to three slots The first slot of the sub-
frame carries the ACK NACK information the UE sends to the NodeB
while the following two slots ie slot 2 and 3 of the subframe convey
the CQI value the channel quality information to the NodeB
Subframe 0 Subframe i Subframe 4
Tslot
= 2560 chips J The spreading factor of theHS-DPCCH is 256 (10 bits peruplink slot)
J The HS-DPCCH can only existtogether with an UL DPCCH
(ded phys control channel)J The DPDCH (dedicated physical data channel) the DPCCH andthe HS-DPCCH are IQ codemultiplexed
HARQ-ACK CQI = Channel quality information
2 times Tslot
= 5120 chips
One radio frame Tf = 10 ms
One HS-DPCCH subframe 2 ms
Fig 2-29 HS-DPCCH configuration
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The slot format for HS-DPCCH describes a quantity of 30 bits per sub-frame resulting in a data rate of 15 kbps The spreading factor used for
the HS-DPCCH is constant and is always equal to 256 but the chan-
nelization code that is used as well as the mapping on either the I or
Q axis depends on several factors eg the co-existence of an HSDPA
connection with a circuit-switched connection meaning whether a
DPDCH established or not Fig 2-36 page 64 illustrates this IQ
mapping and Fig 2-35 page 63 shows the channelization code used
for HS-DPCCH
The HS-DPCCH builds a logical unit of one subframe but having the
independent control information HARQ-ACK and CQI included which
could be separately decoded at the NodeB Note that the slot carrying
the ACK NACK statement is active only when the UE has been sched-
uled by an HS-PDSCH subframe in the corresponding downlink sub-
frame previously Assuming the UE has not received a transport block
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HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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HS-DSCH High speed downlink shared channel transport channel
37
Example of convolutional coding
Input Regis-
ter 1
Regis-
ter 2
Regis-
ter 3
Out-
put 1
Out-
put 2
XOR operation
Register 3Register 2Register 1
+
Input
Output 1
Output 2
+ +
1 1 0 0 1 1
1 1 1 0 0 1
0 0 1 1 0 1
1 1 0 1 0 0
1 1 1 0 0 1
0 0 1 1 0 1
Alt A 0 0 0 1 1 1
Alt B 1 1 0 1 0 0
Fig 2-8 Simple example for convolutional coding
In Fig 2-9 that follows there is a trellis diagram representing in each
column the four possible output values of our channel coder 00 01 10
or 11 and in bold color there is the trellis path through this diagram
resulting from the input sequence Recalling our definition of the two
alternatives for the last bit of our example code word we can see that
the rightmost part of this trellis diagram shows the two possible steps
From state 01 we can only reach either state 00 or state 11 The twoother states 01 or 10 are not possible and with no input to the coder
shown in Fig 2-8 the output can reach these two states in this step For
example if the receiver detects a sequence such as 11 01 01 00 01 01 01
it knows there is an error at the last position 01 which had to be cor-
rected as either 00 or 11 because only these two alternatives are pos-
sible The error correction is performed by looking at the total trellis
path and selecting the maximum likelihood sequence estimation basedon the received data pattern In our short example we admit that we
stopped at this point of course Imagine that the input sequence of bits
continues The decoder would not know if it should proceed with the
pattern 00 or 11 so the decision will be to continue both ways The fol-
lowing step is then checked again and one of the assumed ways will dif-
fer more from the demodulated pattern than the other one This prin-
ciple is described in the Viterbi algorithm [Ref 15] Based on this algo-
rithm the stronger path will survive ie the decoder checks at eachstep which path of the examined ones in the trellis path exhibits the
smallest deviation from the demodulation sequence and thus this path
will be continued The paths exhibiting a higher deviation are discarded
to reduce the calculation expense The path through the trellis diagram
is called a ldquometricrdquo and the term ldquomaximum likelihood sequence esti-
mationrdquo (MLSE) represents the selection by the channel decoder of the
real possible metric which is the closest to the received data pattern As
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HSDPA operation overview and physical channels
an analogy If we do a crossword puzzle and find some characters in a
word the channel decoder would check in a primer or dictionary of the
language containing all possible character combinations that we callldquowordsrdquo and select the existing word that has the maximum likelihood
for the prevailing sequence of characters
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
Alternative B
Alternative A
Register 2
+ +
+
Output 1
Output 2
XOR operation
Trellis diagram above showsmetric for input sequence
110110 0
or 1
into a coder such as
1
1
0
1 10
0
1
Register 3Register 1
Fig 2-9 Metric in trellis diagram
Interleaving
Forward error correction based on convolutional coders has one disad-
vantage related to the impact of block errors If the transmission errors
are distributed they can be corrected as demonstrated in the trellis dia-gram example using the Viterbi algorithm but if many adjacent bits
are lost the decoder will have problems retrieving the right bit pattern
Interleaving means that the information to be transmitted is spread or
distributed over several bursts in such a way that contiguous informa-
tion is split up and transmitted in a time or block distributed mode
To avoid error bursts an attempt is made to spread the bit errors over
several code words This is achieved by interleaving several code wordsThis method is also called diagonal interleaving see Fig 2-10 Another
kind of interleaving is block interleaving as shown in Fig 2-11 Blocks
of code words are written row-by-row into a matrix and then read col-
umn-by-column With both methods consecutive bits of a code word
are never transmitted consecutively and conversely when the bits are
deinterleaved at the receive end error bursts are spread over several
code words
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HS-DSCH High speed downlink shared channel transport channel
39
As several code words are interleaved the decoder has to ldquowaitrdquo a cer-
tain time until all bits of a particular code word arrive This delay ie
the ldquomeasure for spreading over timerdquo is referred to as the ldquointerleav-ing depthrdquo The greater the interleaving depth the more code words are
available for spreading the error bursts and the greater the probability
that errored bits can be corrected but on the other hand this increases
the overall latency time
HSDPA uses the block diagonal interleaving principle for the HS-DSCH
only since as we should recall one goal is to have a short round-trip
time
Spreadinghellip
Interleaving
hellip
hellip
Fig 2-10 Diagonal interleaving
Write
Read
Interleaving-Matrix
Fig 2-11 Block interleaving
Puncturing
Having briefly described the principle of convolutional coding another
mechanism will be presented that is used to increase the throughputof user data and coordinate with the AMC mechanism described in
section 12 page 10 After adding redundancy the total bit stream is
now known as soft bits ie the sum including all of the raw data bits
at the input of the channel coder plus the added redundancy bits This
quantity must match the required transport block size demanded by
the transport layer and the process performed here is called rate match-
ing ie deleting some of the soft bits at the transmitting end in a pre-
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HSDPA operation overview and physical channels
defined manner or repeating or adding some stuffing bits In HSPA the
rate matching mechanism uses puncturing which provides higher data
throughput The signaled values TBS and RV tell the receiving convo-lutional coder how many and where bits have been punctured This
allows the decoder to insert blank positions which have to be filled later
by performing trellis decoding In other words we may consider the
punctured bits as bit losses created intentionally by the transmitter In
this manner the total amount of data bits can be increased for the sake
of lower redundancy In HSDPA this puncturing scheme will be very
flexible and the NodeB scheduler will set the puncturing rate adapted
to the prevailing RF conditions on the radio channel to obtain the high-
est possible data throughput under the existing conditions The disad-
vantage of adaptive coding is that we need signaling information so
that the transmitter has to inform the receiver about how many soft bits
have been punctured This is seen in Fig 2-26 page 55 in the form
of the redundancy version carried by the HS-SCCH control channel
Fig 2-12 below again depicts the principle of puncturing in HSDPAand clarifies some signaling parameters such as the transport block size
1 1 0 1 1 0 0
11 01 01 00 01 01 11
Transport block sizeInput bits into channel coder
Soft bitsOutput from channel encoder
Rate matchingPuncturing or repeating bits
11 01 01 00 01 01 11
1 01 0 00 0 01 1Coded composite transport bitsCan be several combined streams aftercoding + rate matching
Transport block size FEC
Fig 2-12 Puncturing based on coding example from Fig 2-8 page 37
The process of channel coding starts first with the transport block
size which is given by the size of the input data bit sequence added
by a cyclic redundancy checksum The next step is the channel cod-
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HS-DSCH High speed downlink shared channel transport channel
41
ing which is performed in HSPA by a so-called turbo coder The turbo
coder is a parallel concatenated convolutional coder that exhibits bet-
ter reliability compared to a single convolutional coder Discussingthe functionality of a turbo coder in all of its details would represent a
major digression from the intention of this book Accordingly we will
simply encourage the interested reader to consult the channel coding
literature for more details about turbo coders and their applications
[Ref 10] [Ref 12] Determined by the scheduler of the base station or
the redundancy version to be used the next step known as the redun-
dancy version will either puncture (the most likely) or repeat some of
the bits resulting from the channel coding process How many bits will
be punctured is defined by the coding rate In our example in Fig 2-12
we see that the input bit sequence has a length of 7 bits resulting in
14 soft bits after channel coding with our example coder providing a
coding rate of frac12 The scheduler decided to puncture 4 bits so that we
finally obtain 10 bits which have to be mapped on the physical chan-
nels Our overall coding rate is therefore given as ⁷frasl983089983088 In other words
some bits are protected with redundancy information while othersare not Note that the size of the coded composite transport channel
is determined by the physical layer parameters such as the number of
channelization codes used to convey the HS-PDSCH the modulation
scheme and the transmit time interval which is constant for HSDPA
but can be either 2 or 10 ms for HSUPA Thus its size does not need
to be signaled to the receiver and only the transport block size and the
redundancy versions will be contained in the HS-SCCH channel
222 Incremental redundancy and chase combining
for HS-DSCH
Until now we have presented some general characteristics of HSDPA
and HSUPA which we would now like to discuss in a combined pro-
cedure and then deduce two other principles The HARQ abbreviationcombines an automatic retransmission of erroneous data with a soft
combination at the receiving end A related question can now be how
the transmitter has to repeat the transport block should the retrans-
mission of data occur in an identical retransmission mode or should
some changes in coding parameters eg the manner of puncturing be
applied This question is also important for the implementation of the
rate matching step shown in Fig 2-12 The transmitter has to provide
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HSDPA operation overview and physical channels
a certain soft buffer ie a memory that stores the transmitted data for
the sake of possible retransmissions and deletes it after having received
a positive acknowledgment from the receiver Should the transmitternow store the coded composite transport data i e the data after coding
but also after puncturing This would restrict it to repeating the data in
an identical manner A better approach is to store the data after channel
coding and before puncturing Even if this requires more memory it
gives the flexibility to change the puncturing scheme and retransmit the
transport block in a different way Fig 2-13 and Fig 2-14 represent both
mechanisms that are used in HSDPA and HSUPA Identical retransmis-
sion is called chase combining and non-identical retransmission with
a different puncturing scheme is called incremental redundancy The
scheduler in the base station can decide which retransmission scheme
will be used We do not wish to delve into the details of channel coding
theory to discuss which mechanism is the better one ndash chase combin-
ing or incremental redundancy We will only mention that both mech-
anisms have their advantages and thus their applications Chase com-
bining has the advantage that the systematic bits representing the orig-inal data input into the channel coder are contained in the transmit-
ted sequence after puncturing Thus chase combined transport blocks
are ldquoself-decodablerdquo If we consider a situation where the original trans-
port block is lost completely and only the retransmitted block is pres-
ent at the receiver there is a chance to decode the data properly Mean-
while incremental redundancy seems to add more redundancy when
retransmitting but in a scenario where the first transmission contain-ing the systematic bits is lost completely and only the retransmission
is present the receiver will have no chance to decode the data without
having some of the systematic bits Accordingly incremental redun-
dancy is applied whenever sporadic bit errors occur due to a time vari-
ant channel and chase combining is selected whenever we have to deal
with complete transport block errors i e the time variance of the radio
link exhibits some bursted fading dips
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HS-DSCH High speed downlink shared channel transport channel
43
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Chase combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Transmitted bit
Punctured bit
Systematic bits
Parity 1
Parity 2
Systematic bits
Parity 1
Parity 2
Fig 2-13 Chase combining principle
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Incremental redundancy combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Systematic bits
Parity 1
Parity 2
Systematic bitsParity 1
Parity 2
Fig 2-14 Incremental redundancy
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HSDPA operation overview and physical channels
223 Constellation rearrangement
Due to the fact that HSDPA introduces a higher-order modulationscheme (16QAM) we can recognize some effects due to the physi-
cal layer influencing the susceptibility to noisy RF conditions One of
these effects can be explained by looking at the constellation diagram
in the 16QAM modulation scheme see section 12 page 10 As we
recall there is a total of 16 different constellation points given by the
modulation vector and represented by its phase and amplitude Con-
sidering the Euclidean distance which is the distance in this constella-
tion diagram between two neighboring points we can clearly see that
some points have more neighbors than others Especially the four con-
stellation points at the very four corners only have three direct neigh-
bors making them less susceptible to misdetection due to noise shift-
ing them in a certain direction On the other hand the four constella-
tion points representing the inner square of the constellation have eight
direct neighbors each and are therefore more likely to be incorrectly
detected The idea of constellation rearrangement is now to change themapping scheme applied in the original transmission when retrans-
mitting As we know the receiver will soft combine the retransmit-
ted data with the previously received information so we can achieve a
certain incremented redundancy and a certain protection mechanism
Note however that considering a sole transmission of a transport block
using a certain constellation arrangement will not show any more pos-
itive or negative results compared to other constellation arrangementsThe redundancy gain is only achieved by rearranging the constellation
mapping in a retransmitted transport block and performing soft com-
bining at the receiver Overall HSDPA defines four constellation rear-
rangement schemes which are indicated in the redundancy version
field of the HS-SCCH and are represented by the ldquobrdquo bit field ranging
from b = 0 to b = 3 All four constellation schemes are Gray encoded
ie the directly adjacent constellation symbols do not exhibit four com-
pletely different bits in order to reduce the impact of misdetection onbit errors
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High speed shared control channel (HS-SCCH)
45
Q
I
(ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1) (1 1ndash1ndash1)
(ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1) (1 1ndash1 1)
(ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1) (1ndash1ndash1 1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 0
Q
I
(ndash1 1 1 1) (ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1)
(ndash1 1 1ndash1) (ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1)
(ndash1ndash1 1ndash1) (ndash1ndash1ndash1ndash1) (1ndash1ndash1ndash1) (1ndash1 1ndash1)
(ndash1 1 1 1) (ndash1ndash1ndash1 1) (1ndash1ndash1 1) (1ndash1 1 1)
b = 2
Q
I
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (1ndash1 1 1) (ndash1ndash1 1 1)
(ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1) (ndash1 1 1 1)
(ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1) (ndash1 1 1ndash1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 1
Q
I
(1 1ndash1 1) (ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1)
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1)
(1ndash1ndash1ndash1) (ndash1ndash1ndash1ndash1) (ndash1ndash1 1ndash1) (1ndash1 1ndash1)
(1 1ndash1ndash1) (ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1)
b = 3
Fig 2-15 Constellation rearrangement in HSDPA
23 High speed shared control channel (HS-SCCH)
The HS-SCCH sends scheduling information to the UEs As seen before
the HS-PDSCH has a very flexible configuration for physical parame-
ters such as the coding rate number of code channels or retransmis-sions This high flexibility increases the complexity and engenders the
need for additional signaling information transferred on the HS-SCCH
Reception of user data in HSDPA is always a two-step procedure
First the receiver has to capture the scheduling control information
and afterwards based on the received control information it may start
demodulating and decoding the HS-PDSCH containing the user data
This two-step procedure is shown in Fig 2-16 below which lists what
kind of control information is sent to the UEs via the HS-SCCH Asshown in Fig 2-2 page 28 which describes the overall HSDPA chan-
nel structure there can be up to four HS-SCCHs assigned to one UE
But only one HS-SCCH would contain the scheduling information for
this UE within one TTI Thus the network can assign resources simul-
taneously to various UEs in the downlink direction
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HSDPA operation overview and physical channels
I would like to receive databut I dont know where myHS-PDSCH resources areand what they look like
HS-SCCH
Read the 1st HS-SCCH slotfor HS-DSCH channelizationcodes UE identity and
modulation scheme
Then the 2nd and 3rd HS-SCCHslots provide transport block sizeinformation hybrid ARQ process in-formation redundancy constellationversion new data indicator
HS-PDSCH
Fig 2-16 HS-SCCH control channel usage
Regarding the physical layer parameters we see in Fig 2-17 that the
HS-SCCH uses a channelization code with a spreading factor of 128
and it also uses the newly introduced transmit time interval of one sub-
frame which is equal to 2 ms It should be mentioned that the spread-ing factor of 128 requires double the capacity compared to similar con-
trol channels in WCDMA Release 99 reflecting the signaling overhead
needed to guarantee the huge flexibility introduced with HSDPA Addi-
tionally Fig 2-16 shows that the control information is sent consecu-
tively within one subframe The first slot within this subframe contains
the control information UE identity channelization code information
and modulation scheme identifier Slots 2 and 3 of the subframe con-tain the remaining control information Transport block size HARQ
process identifier redundancy version and new data indicator Conse-
quently the UE can self-decode slot 1 alone and slots 2 and 3 in a sec-
ond step even if they represent one logical unit This raw control infor-
mation is of course also channel coded using a turbo and on the phys-
ical layer the quantity of bits after the rate matching step is 40 bits con-
veyed in one slot corresponding to 666 micros [TS 25212 Ref 21] see also
Fig 2-28 page 56
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High speed shared control channel (HS-SCCH)
47
The HS-SCCH is a fixed rate (60 kbps SF = 128) downlinkphysical channel used to carry downlink signaling related toHS-DSCH transmission
Slot 0
Slot 1
Slot 2
Tslot
= 2560 chips
Data = 40 bits
1 subframe = 2 ms
Fig 2-17 Structure of High speed shared control channel HS-SCCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
We would like to return now to the time consecutive transmission of
control information There is a difference in the control information
in terms of its priority Some information is needed at the UE end
very urgently while other control information does not have such a
high priority But why This will be explained by looking at some tim-ing aspects defined for HSDPA If we consider the timing between
the shared data channel HS-PDSCH and the shared control chan-
nel HS-SCCH as shown in Fig 2-18 we see that the HS-PDSCH fol-
lows the HS-SCCH by exactly two slots or 5120 chips The HS-SCCH
is completely time-aligned with the general control channels CPICH
and P-CCPCH of the NodeB This is mandatory because it is a shared
channel Consider several UEs with different distances to the NodeBwanting to receive the HS-SCCH channel Thus it must have constant
timing that is known a priori The shared data channel HS-PDSCH is
now transmitted exactly 5120 chips after the first chip of the HS-SCCH
This leads to an overlapping slot thereby requiring multitasking recep-
tion at the UE end While the UE is still receiving the last slot of an
ongoing HS-SCCH subframe it may already start the reception of an
HS-PDSCH transport block The first slot in the HS-SCCH subframe
now contains information required by the physical layer to performdespreading and demodulation These values are the UE identity indi-
cating whether the UE will start demodulation of the HS-PDSCH or
not in case it is not scheduled the modulation scheme information
since the UE has to know how to interpret the received constellation
vector and whether it has to be considered as a QPSK or 16QAM con-
stellation point and finally the UE has to know which channelization
codes it has to apply to capture the HS-PDSCH transport block The
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HSDPA operation overview and physical channels
overall UE reaction time when being scheduled is now seen as 1 slot
or 2560 chips This tough requirement for the UEs is due to the objec-
tive to obtain overall a much shorter latency than legacy standards Theadditional control information such as the new data indicator redun-
dancy version and transport block size is not that urgent since it is
needed after demodulation but before channel decoding So first the
UE will sample the whole three slots of the HS-PDSCH and demodu-
late them into a bit stream which is finally handed over to the channel
decoder This principle is known as post-processing and is used typi-
cally in mobile communications technologies
J Start of HS-SCCH subframe 0 is aligned with startof P-CCPCH frames
J The HS-PDSCH starts
τ HS-PDSCH
(2times Tslot
= 5120 chips)
after the start of the HS-SCCH
UE identity etc
processing timeof receiver
HS-DSCH subframe
3 times Tslot= 7680 chips
3 times Tslot
= 7680 chips
τ HS-PDSCH
(2times Tslot
= 5120 chips)
HS-SCCH
HS-PDSCH
Fig 2-18 Timing relation between HS-SCCH and HS-PDSCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
Content of the HS-SCCH control channelThe control information contained in the HS-SCCH control chan-
nel has already been mentioned so we will now consider the values
in more detail We will begin with an overview of what kind of control
information is contained in the HS-SCCH channel before proceeding
with further details about the single control elements The following
control information is present in the HS-SCCH [TS 25212 Ref 21]
Channelization code set information (7 bits)
Modulation scheme information (1 bit) Transport block size information (6 bits)
Hybrid ARQ process information (3 bits)
Redundancy and constellation version (3 bits)
New data indicator (1 bit)
UE identity (16 bits) = H-RNTI
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High speed shared control channel (HS-SCCH)
49
Some of these parameters are more or less self-explanatory while oth-
ers require additional background information and closer examination
Modulation scheme information 1 bit
This single bit is used to inform the receiver whether the modulation
scheme QPSK or 16QAM is applied on the data channel HS-PDSCH
The interpretation of the bit x ms1 is as follows
ms1
x
if QPSK
otherwise
0
1
=
New data indicator 1 bit
The new data indicator bit field informs the receiving entity that the
prevailing PDU transmitted by the current HARQ process is either a
retransmission or contains new data This is done by setting the new
data bit to the value 0 for the first PDU on this particular HARQ process
and incrementing the value by 1 with every new data sent [TS 25321Ref 30] This leads to a toggled value In case the new data bit is not
incremented ie if it remains at its previous value it is an indicator for
retransmission
1st PDU of this
HARQ process
NDI = New data indicator
NDI = 0 NDI = 1
NACK
NDI = 1
ACK
NDI = 0
HS-SCCH HS-SCCH HS-SCCHHS-SCCH
ACK
Fig 2-19 New data indicator bit principle of incrementing value
Channelization code set information 7 bits
This field is used to indicate the number of channelization codes usedfor transmitting the transport block on the HS-PDSCH As was already
described the spreading factor applied on the HS-PDSCH is constant
with a value of 16 but the flexible values are the number of channeliza-
tion codes forming a cluster when using multiple codes and their posi-
tion in the code tree It is not allowed to distribute the code channels
over the code tree diagram For the sake of simplicity in signaling sev-
eral channelization codes form one cluster and these codes are con-
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HSDPA operation overview and physical channels
tiguous in the channelization code tree [TS 25213 Ref 22] Fig 2-20
illustrates the principle of indicating the channelization codes on the
HS-SCCH
SF = 16
Code ldquo0rdquo isreserved forcommonchannels
Code offset 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15P = 5O = 7
Code group indicatorx
ccs1 x
ccs2 x
ccs3 = min (Pminus 1 15 minusP)
Code offset indicatorx
ccs4 x
ccs5 x
ccs6 x
ccs7 = |Ominus 1minus P8 times15|
A cluster of codes
can be allocated to a UEC
ch16Ohellip C
ch16O + P minus 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1
2 2 2 2 2 2 2 2 2 2 2 2 2 2 14 14
1 2 3 4 5 6 7 8 9 10 11 12 13 14 2 1
3 3 3 3 3 3 3 3 3 3 3 3 3 13 13 13
1 2 3 4 5 6 7 8 9 10 11 12 13 3 2 1
4 4 4 4 4 4 4 4 4 4 4 4 12 12 12 121 2 3 4 5 6 7 8 9 10 11 12 4 3 2 1
5 5 5 5 5 5 5 5 5 5 5 11 11 11 11 11
1 2 3 4 5 6 7 8 9 10 11 5 4 3 2 1
6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10
1 2 3 4 5 6 7 8 9 10 6 5 4 3 2 1
7 7 7 7 7 7 7 7 7 9 9 9 9 9 9 9
1 2 3 4 5 6 7 8 9 7 6 5 4 3 2 1
8 8 8 8 8 8 8 8
8 7 6 5 4 3 2 1
0 (115)
1 (214)
2 (313)
3 (412)
4 (511)
5 (610)
6 (79)
7 (88) Redundant area
C l u s t e r c o d e i n d i c a t o r ( 3 b i t s )
Tree offset indicator (4 bits)
Signaled on HS-SCCH
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
PO
Decoding notation
Number ofmulti-codes
Offset fromleft right incode tree (SF = 16)
Fig 2-20 Channelization code set indicating the HS-PDSCH code cluster
The idea behind the code indication is a matrix with the rows repre-
senting the number of codes per cluster and the columns represent-
ing the position of that cluster the offset value in the code tree Recall-
ing that the maximum number of channelization codes per clusteris 15 and if the cluster size is 1 the offset values can also range from
1 to 15 the resulting matrix would have 15 rows and 15 columns Since
we know that four bits are needed to represent an integer from 1 to 15
we need a total of 4 + 4 = 8 bits for representation of the channeliza-
tion code set information It is a smart idea to save one bit The 15 times 15
matrix would contain much redundant information By way of analogy
like in a road map indicating distances between cities A table showing
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High speed shared control channel (HS-SCCH)
51
the distance from city A to city B the opposite distance from city B to
city A is redundant information The useful information has the form
of a triangle The idea is to cut the lower part rotate it and append itto the spare part of the upper table In this manner a table is obtained
with 7 rows and 15 columns and it is possible to indicate each position
in it with just 7 bits
1 5 r o w s 7
r o w s
Matrix reduction for channeli-
zation code set information
15 columns
Fig 2-21 Matrix size reduction for channelization code set information
The content of the channelization code set matrix can be described as
a value with two numbers The upper number is the number of mul-
ticodes forming one cluster and the lower number is the offset in the
channelization code tree Accordingly the example in Fig 2-20 can be
interpreted to mean the HS-SCCH sends the bits as row number 4 and
column number 6 in the matrix The content of this element are the
values 5 over 7 which have to be interpreted as a cluster size of 5 codesand an offset of 7
Transport block size information 6 bits
With a length of six bits the transport block size (TBS) informa-
tion informs the receiving UE entity about the data block size of the
transport block sent on the HS-PDSCH We should keep in mind the
link adaptation performed with the adaptive modulation and coding
scheme that was described in section 12 page 10 The ratio errorcorrection and user data are flexible while the physical layer param-
eters such as the spreading factor modulation scheme and number of
channelization codes determine the physical block size This physical
block consists of the user data ratio or transport block size and the for-
ward error correction or redundancy information As this ratio is flex-
ible the HS-SCCH will inform the receiving UE entity about the size
of the transport block Here too there is a strategy of bit reduction the
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HSDPA operation overview and physical channels
goal is to inform the receiver with as few bits as possible A non-effi-
cient approach would involve conversion of the decimal number repre-
senting the TBS into a binary sequence but the number of bits neededwould exceed the space available on the HS-SCCH Imagine that the
range of transport block sizes depends on the physical layer condi-
tions The ambient physical layer parameters modulation scheme and
number of channelization codes set a certain working point where the
remaining flexibility for a different TBS configuration can be obtained
by more or less puncturing resulting in a flexible ratio between for-
ward error correction and user data This will lead to a two-step proce-
dure when evaluating the transport block size First the receiver exam-
ines the information modulation scheme and number of channeliza-
tion codes scheduled via HS-SCCH which indicate the value k0 l as
shown in Fig 2-22 The 6-bit HS-SCCH control parameter transport
block size information will be the transport format resource indica-
tor (TFRI) named ki Let k t be the sum of the two values kt = ki + k0i
Both values kt and k0 i can be obtained from tables given by [TS 25321
Ref 30] The range for the TFRI is from 1 to 256 and the derived trans-port block size ranges from 137 bits to 27 952 bits The first table indi-
cates the value k 0 i based on the channelization code and the modula-
tion scheme
Combination i Modulation scheme Number of channelization codes k0 i
0
QPSK
1 1
1 2 40
2 3 633 4 79
4 5 92
5 6 102
Fig 2-22 Extract from TS 25321 table representing k0 i
The second table indicates the final transport block size based on kt
Index TB size Index TB size Index TB size1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
4 173 89 1456 174 6673
5 185 90 1483 175 6793
6 197 91 1509 176 6916
7 209 92 1537 177 7041
Fig 2-23 Extract from TS 25321 table representing kt
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High speed shared control channel (HS-SCCH)
53
J The transport block size used on HS-DSCH is not signaled explicitly on HS-SCCHJ Instead a transport block size index k
i is signaled to indicate the transport block size
First stepModulation scheme andnumber of channelizationcodes as signaled on HS-SCCHdetermine value k
0 i
Second step
Index kt = k
i + k
0i
determines HS-DSCH
transport block size
kt = k
i + k
0i
Table according to 3GPP TS 25321 extract from QPSK section
Table according to 3GPP TS 25321 254 entries in total
Combination i Modulation
scheme
Number of
channelization codes
k0 i
0
QPSK
1 1
1 2 40
2 3 63
3 4 79
4 hellip hellip
Index TB size Index TB size Index TB size
1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
helliphellip hellip hellip hellip hellip
Fig 2-24 Retrieval of transport block size information
Source Fig 2-22 to Fig 2-24 [TS 25321 Ref 30] reproduced by permission of 3GPP
Hybrid ARQ process information 3 bits
The concept behind the hybrid automatic repeat request (HARQ) was
introduced in section 13 page 14 One feature is the possibility of
multitasking ie having several HARQ processes activated at the same
time Fig 2-25 below shows the need to signal the process identity tothe receiver Remember that on the downlink there is a shared chan-
nel concept so the NodeB can flexibly decide which UE will be sched-
uled with a downlink transport block Up to eight HARQ processes
can be signaled via higher layers to one UE Note however that due to
the round-trip timing six HARQ processes must be active to achieve
the maximum throughput as shown in Fig 2-51 page 79 Compared
with HSUPA the HARQ processes on the downlink are asynchronous
so they have to be indicated but on the uplink they are synchronous sothey do not need to be signaled explicitly
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HSDPA operation overview and physical channels
Asynchronous DL minus Synchronous ULNumber of H-ARQ rocesses = 1 to 8 er UE
UL HS-DPCCH UE1
UE1 HARQ processes 1 to 4
3 4 1 42 11 1 32retrans
2
A N A A
A A
N A
UL HS-DPCCH UE2
HS-PDSCH
UE2 HARQ processes 1 to 2
Fig 2-25 HARQ process indication on HS-SCCH
Fig 2-25 shows a typical situation on the downlink (point-to-multi-
point) The NodeB sends data to several UEs sharing the HS-PDSCH
so therefore the HARQ process is asynchronous The time when a
transport block is retransmitted is not fixed For this reason the pro-
cess identifier is signaled on the HS-SCCH Based on the HARQ pro-
cess identity and the new data indicator bit the receiving entity knows
which part of the soft buffer memory has to be used in case of soft com-bining On the uplink the situation is slightly simpler The UE only
communicates with one NodeB so it is a point-to-point connection
Thus retransmission always occurs at a fixed time linked to the origi-
nal transmission
Redundancy and constellation version 3 bits
Adaptive modulation and coding involve flexible selection of modula-tion and coding schemes that are signaled to the receiving UE via the
parameters transport block size and modulation scheme information
Another concept used in HSDPA was previously discussed Chase com-
bining or incremental redundancy (see section 222 page 41) This
means that in case of retransmission the transmit entity can dynami-
cally select another puncturing scheme or keep the puncturing as it was
in the original transmission The applied puncturing scheme is signaled
as redundancy information to the receiver Additionally in case of the16QAM modulation scheme the transmitter can select another constel-
lation arrangement which is also signaled to the UE with the three bits
for the redundancy and constellation version see Fig 2-15 page 45
Depending on the modulation scheme (QPSK or 16QAM) there are
two different tables indicating the parameters ldquosrdquo ldquorrdquo and ldquobrdquo The
parameters ldquosrdquo and ldquorrdquo indicate which scheme is used for puncturing
ie if the puncturing mechanism prioritizes the systematic bits or not
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High speed shared control channel (HS-SCCH)
55
and which puncturing algorithm is used The parameter ldquobrdquo indicates
the constellation mapping version The receiver needs this information
to perform proper demodulation and decoding
Initial transmission
1st retransmission
2nd retransmission
3rd retransmission
r
0
0
1
1
2
2
3
xrv
(value)
s
0 1
1 0
2 1
3 0
4 1
5 0
6 1
7 0 3
s = 1 Systematic bits are prioritizeds = 0 Non-systematic bits are prioritized
r (range 0 to 3 for QPSK) influencesJ Input parameter for puncturing or (together with s) for repetition algorithm defined in TS 25212J Selection of parity bits
Redundancy version coding sequences are signaled on HS-SCCH egndash 0 2 5 6 One initial transmission + 3 retransmissions with different r and s parameters
Fig 2-26 Signaling of redundancy version parameters r and s QPSK case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
Initial transmission
2nd retransmission
1st retransmission
3rd retransmission
r (range 0 to 1 for 16QAM)influences input parameterfor puncturing or (togetherwith s) for repetitionalgorithm defined in
TS 25212 and thus selectionof parity bits
Redundancy version coding sequences are signaled on HS-SCCH egminus 6 4 0 5 Chase combining (no change in s and r parameters ie same redundancyversion) with four possible constellations
x rv (value) s r b
0 1 0 0
1 0 0 0
2 1 1 1
3 0 1 1
4 1 0 1
5 1 0 2
6 1 0 3
7 1 1 0
Definition of parameter s as for QPSK
b (range 0 to 3) describes constellationrearrangement to averagereliability of bits
Fig 2-27 Signaling of redundancy version parameters r s and b 16QAM case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
UE identity H-RNTI 16 bits
The HSDPA radio network transaction identifier (H-RNTI) unam-
biguously identifies the UE having an HS-PDSCH assignment within
a cell It is allocated to the UE via layer 3 signaling procedures at the
radio bearer setup if the radio bearer is an HSDPA connection This
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HSDPA operation overview and physical channels
value represents a temporary name of the UE used to address it when
scheduling data packets via HS-SCCH
HS-SCCH channel coding
The control information contained in the HS-SCCH is of course pro-
tected with channel coding mechanisms the whole coding chain is
described in Fig 2-28 Fig 2-18 page 48 presents the separation of
the control information into two code blocks which are sent consec-
utively mapped on slot 1 and slot 2 + 3 of one HS-SCCH subframe
This principle is also visible in the coding chain The first control block
consisting of channelization information modulation scheme and UE
identity is coded separately from the remaining control values to enable
the UE receiver to decode this first slot separately and prepare for pos-
sible HS-PDSCH reception The coding steps shown in Fig 2-28 such
as rate matching 1 and 2 are similar to the HS-PDSCH coding chain
and are further described in [TS 25212 Ref 21]
Channelcoding 1
R atematching 1
mux
Channelcoding 2
Ratematching 2
RVcoding
UE-specificCRC attachment
UE-specificmasking
Physical channelmapping
r s b
mux
Channelizationcode set
Modulationscheme
Transport block size information
HARQ processinformation
Redundancy andconstellation version
New data indicator
UE identity
UE identity
Fig 2-28 Channel coding for HS-SCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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High speed dedicated physical control channel (HS-DPCCH)
57
24 High speed dedicated physical control channel (HS-DPCCH)
In an active HSDPA connection the UE has to send acknowledgment ornon-acknowledgment reports (as described in section 13 page 14
where the HARQ process is described) as well as channel status infor-
mation to the network The reporting is performed on this physical
control channel HS-DPCCH
As ubiquitous in HSDPA the uplink is also configured into a subframe
structure of 2 ms corresponding to three slots The first slot of the sub-
frame carries the ACK NACK information the UE sends to the NodeB
while the following two slots ie slot 2 and 3 of the subframe convey
the CQI value the channel quality information to the NodeB
Subframe 0 Subframe i Subframe 4
Tslot
= 2560 chips J The spreading factor of theHS-DPCCH is 256 (10 bits peruplink slot)
J The HS-DPCCH can only existtogether with an UL DPCCH
(ded phys control channel)J The DPDCH (dedicated physical data channel) the DPCCH andthe HS-DPCCH are IQ codemultiplexed
HARQ-ACK CQI = Channel quality information
2 times Tslot
= 5120 chips
One radio frame Tf = 10 ms
One HS-DPCCH subframe 2 ms
Fig 2-29 HS-DPCCH configuration
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The slot format for HS-DPCCH describes a quantity of 30 bits per sub-frame resulting in a data rate of 15 kbps The spreading factor used for
the HS-DPCCH is constant and is always equal to 256 but the chan-
nelization code that is used as well as the mapping on either the I or
Q axis depends on several factors eg the co-existence of an HSDPA
connection with a circuit-switched connection meaning whether a
DPDCH established or not Fig 2-36 page 64 illustrates this IQ
mapping and Fig 2-35 page 63 shows the channelization code used
for HS-DPCCH
The HS-DPCCH builds a logical unit of one subframe but having the
independent control information HARQ-ACK and CQI included which
could be separately decoded at the NodeB Note that the slot carrying
the ACK NACK statement is active only when the UE has been sched-
uled by an HS-PDSCH subframe in the corresponding downlink sub-
frame previously Assuming the UE has not received a transport block
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HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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HSDPA operation overview and physical channels
an analogy If we do a crossword puzzle and find some characters in a
word the channel decoder would check in a primer or dictionary of the
language containing all possible character combinations that we callldquowordsrdquo and select the existing word that has the maximum likelihood
for the prevailing sequence of characters
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
00
01
10
11
Alternative B
Alternative A
Register 2
+ +
+
Output 1
Output 2
XOR operation
Trellis diagram above showsmetric for input sequence
110110 0
or 1
into a coder such as
1
1
0
1 10
0
1
Register 3Register 1
Fig 2-9 Metric in trellis diagram
Interleaving
Forward error correction based on convolutional coders has one disad-
vantage related to the impact of block errors If the transmission errors
are distributed they can be corrected as demonstrated in the trellis dia-gram example using the Viterbi algorithm but if many adjacent bits
are lost the decoder will have problems retrieving the right bit pattern
Interleaving means that the information to be transmitted is spread or
distributed over several bursts in such a way that contiguous informa-
tion is split up and transmitted in a time or block distributed mode
To avoid error bursts an attempt is made to spread the bit errors over
several code words This is achieved by interleaving several code wordsThis method is also called diagonal interleaving see Fig 2-10 Another
kind of interleaving is block interleaving as shown in Fig 2-11 Blocks
of code words are written row-by-row into a matrix and then read col-
umn-by-column With both methods consecutive bits of a code word
are never transmitted consecutively and conversely when the bits are
deinterleaved at the receive end error bursts are spread over several
code words
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HS-DSCH High speed downlink shared channel transport channel
39
As several code words are interleaved the decoder has to ldquowaitrdquo a cer-
tain time until all bits of a particular code word arrive This delay ie
the ldquomeasure for spreading over timerdquo is referred to as the ldquointerleav-ing depthrdquo The greater the interleaving depth the more code words are
available for spreading the error bursts and the greater the probability
that errored bits can be corrected but on the other hand this increases
the overall latency time
HSDPA uses the block diagonal interleaving principle for the HS-DSCH
only since as we should recall one goal is to have a short round-trip
time
Spreadinghellip
Interleaving
hellip
hellip
Fig 2-10 Diagonal interleaving
Write
Read
Interleaving-Matrix
Fig 2-11 Block interleaving
Puncturing
Having briefly described the principle of convolutional coding another
mechanism will be presented that is used to increase the throughputof user data and coordinate with the AMC mechanism described in
section 12 page 10 After adding redundancy the total bit stream is
now known as soft bits ie the sum including all of the raw data bits
at the input of the channel coder plus the added redundancy bits This
quantity must match the required transport block size demanded by
the transport layer and the process performed here is called rate match-
ing ie deleting some of the soft bits at the transmitting end in a pre-
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HSDPA operation overview and physical channels
defined manner or repeating or adding some stuffing bits In HSPA the
rate matching mechanism uses puncturing which provides higher data
throughput The signaled values TBS and RV tell the receiving convo-lutional coder how many and where bits have been punctured This
allows the decoder to insert blank positions which have to be filled later
by performing trellis decoding In other words we may consider the
punctured bits as bit losses created intentionally by the transmitter In
this manner the total amount of data bits can be increased for the sake
of lower redundancy In HSDPA this puncturing scheme will be very
flexible and the NodeB scheduler will set the puncturing rate adapted
to the prevailing RF conditions on the radio channel to obtain the high-
est possible data throughput under the existing conditions The disad-
vantage of adaptive coding is that we need signaling information so
that the transmitter has to inform the receiver about how many soft bits
have been punctured This is seen in Fig 2-26 page 55 in the form
of the redundancy version carried by the HS-SCCH control channel
Fig 2-12 below again depicts the principle of puncturing in HSDPAand clarifies some signaling parameters such as the transport block size
1 1 0 1 1 0 0
11 01 01 00 01 01 11
Transport block sizeInput bits into channel coder
Soft bitsOutput from channel encoder
Rate matchingPuncturing or repeating bits
11 01 01 00 01 01 11
1 01 0 00 0 01 1Coded composite transport bitsCan be several combined streams aftercoding + rate matching
Transport block size FEC
Fig 2-12 Puncturing based on coding example from Fig 2-8 page 37
The process of channel coding starts first with the transport block
size which is given by the size of the input data bit sequence added
by a cyclic redundancy checksum The next step is the channel cod-
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HS-DSCH High speed downlink shared channel transport channel
41
ing which is performed in HSPA by a so-called turbo coder The turbo
coder is a parallel concatenated convolutional coder that exhibits bet-
ter reliability compared to a single convolutional coder Discussingthe functionality of a turbo coder in all of its details would represent a
major digression from the intention of this book Accordingly we will
simply encourage the interested reader to consult the channel coding
literature for more details about turbo coders and their applications
[Ref 10] [Ref 12] Determined by the scheduler of the base station or
the redundancy version to be used the next step known as the redun-
dancy version will either puncture (the most likely) or repeat some of
the bits resulting from the channel coding process How many bits will
be punctured is defined by the coding rate In our example in Fig 2-12
we see that the input bit sequence has a length of 7 bits resulting in
14 soft bits after channel coding with our example coder providing a
coding rate of frac12 The scheduler decided to puncture 4 bits so that we
finally obtain 10 bits which have to be mapped on the physical chan-
nels Our overall coding rate is therefore given as ⁷frasl983089983088 In other words
some bits are protected with redundancy information while othersare not Note that the size of the coded composite transport channel
is determined by the physical layer parameters such as the number of
channelization codes used to convey the HS-PDSCH the modulation
scheme and the transmit time interval which is constant for HSDPA
but can be either 2 or 10 ms for HSUPA Thus its size does not need
to be signaled to the receiver and only the transport block size and the
redundancy versions will be contained in the HS-SCCH channel
222 Incremental redundancy and chase combining
for HS-DSCH
Until now we have presented some general characteristics of HSDPA
and HSUPA which we would now like to discuss in a combined pro-
cedure and then deduce two other principles The HARQ abbreviationcombines an automatic retransmission of erroneous data with a soft
combination at the receiving end A related question can now be how
the transmitter has to repeat the transport block should the retrans-
mission of data occur in an identical retransmission mode or should
some changes in coding parameters eg the manner of puncturing be
applied This question is also important for the implementation of the
rate matching step shown in Fig 2-12 The transmitter has to provide
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HSDPA operation overview and physical channels
a certain soft buffer ie a memory that stores the transmitted data for
the sake of possible retransmissions and deletes it after having received
a positive acknowledgment from the receiver Should the transmitternow store the coded composite transport data i e the data after coding
but also after puncturing This would restrict it to repeating the data in
an identical manner A better approach is to store the data after channel
coding and before puncturing Even if this requires more memory it
gives the flexibility to change the puncturing scheme and retransmit the
transport block in a different way Fig 2-13 and Fig 2-14 represent both
mechanisms that are used in HSDPA and HSUPA Identical retransmis-
sion is called chase combining and non-identical retransmission with
a different puncturing scheme is called incremental redundancy The
scheduler in the base station can decide which retransmission scheme
will be used We do not wish to delve into the details of channel coding
theory to discuss which mechanism is the better one ndash chase combin-
ing or incremental redundancy We will only mention that both mech-
anisms have their advantages and thus their applications Chase com-
bining has the advantage that the systematic bits representing the orig-inal data input into the channel coder are contained in the transmit-
ted sequence after puncturing Thus chase combined transport blocks
are ldquoself-decodablerdquo If we consider a situation where the original trans-
port block is lost completely and only the retransmitted block is pres-
ent at the receiver there is a chance to decode the data properly Mean-
while incremental redundancy seems to add more redundancy when
retransmitting but in a scenario where the first transmission contain-ing the systematic bits is lost completely and only the retransmission
is present the receiver will have no chance to decode the data without
having some of the systematic bits Accordingly incremental redun-
dancy is applied whenever sporadic bit errors occur due to a time vari-
ant channel and chase combining is selected whenever we have to deal
with complete transport block errors i e the time variance of the radio
link exhibits some bursted fading dips
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HS-DSCH High speed downlink shared channel transport channel
43
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Chase combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Transmitted bit
Punctured bit
Systematic bits
Parity 1
Parity 2
Systematic bits
Parity 1
Parity 2
Fig 2-13 Chase combining principle
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Incremental redundancy combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Systematic bits
Parity 1
Parity 2
Systematic bitsParity 1
Parity 2
Fig 2-14 Incremental redundancy
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HSDPA operation overview and physical channels
223 Constellation rearrangement
Due to the fact that HSDPA introduces a higher-order modulationscheme (16QAM) we can recognize some effects due to the physi-
cal layer influencing the susceptibility to noisy RF conditions One of
these effects can be explained by looking at the constellation diagram
in the 16QAM modulation scheme see section 12 page 10 As we
recall there is a total of 16 different constellation points given by the
modulation vector and represented by its phase and amplitude Con-
sidering the Euclidean distance which is the distance in this constella-
tion diagram between two neighboring points we can clearly see that
some points have more neighbors than others Especially the four con-
stellation points at the very four corners only have three direct neigh-
bors making them less susceptible to misdetection due to noise shift-
ing them in a certain direction On the other hand the four constella-
tion points representing the inner square of the constellation have eight
direct neighbors each and are therefore more likely to be incorrectly
detected The idea of constellation rearrangement is now to change themapping scheme applied in the original transmission when retrans-
mitting As we know the receiver will soft combine the retransmit-
ted data with the previously received information so we can achieve a
certain incremented redundancy and a certain protection mechanism
Note however that considering a sole transmission of a transport block
using a certain constellation arrangement will not show any more pos-
itive or negative results compared to other constellation arrangementsThe redundancy gain is only achieved by rearranging the constellation
mapping in a retransmitted transport block and performing soft com-
bining at the receiver Overall HSDPA defines four constellation rear-
rangement schemes which are indicated in the redundancy version
field of the HS-SCCH and are represented by the ldquobrdquo bit field ranging
from b = 0 to b = 3 All four constellation schemes are Gray encoded
ie the directly adjacent constellation symbols do not exhibit four com-
pletely different bits in order to reduce the impact of misdetection onbit errors
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High speed shared control channel (HS-SCCH)
45
Q
I
(ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1) (1 1ndash1ndash1)
(ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1) (1 1ndash1 1)
(ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1) (1ndash1ndash1 1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 0
Q
I
(ndash1 1 1 1) (ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1)
(ndash1 1 1ndash1) (ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1)
(ndash1ndash1 1ndash1) (ndash1ndash1ndash1ndash1) (1ndash1ndash1ndash1) (1ndash1 1ndash1)
(ndash1 1 1 1) (ndash1ndash1ndash1 1) (1ndash1ndash1 1) (1ndash1 1 1)
b = 2
Q
I
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (1ndash1 1 1) (ndash1ndash1 1 1)
(ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1) (ndash1 1 1 1)
(ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1) (ndash1 1 1ndash1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 1
Q
I
(1 1ndash1 1) (ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1)
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1)
(1ndash1ndash1ndash1) (ndash1ndash1ndash1ndash1) (ndash1ndash1 1ndash1) (1ndash1 1ndash1)
(1 1ndash1ndash1) (ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1)
b = 3
Fig 2-15 Constellation rearrangement in HSDPA
23 High speed shared control channel (HS-SCCH)
The HS-SCCH sends scheduling information to the UEs As seen before
the HS-PDSCH has a very flexible configuration for physical parame-
ters such as the coding rate number of code channels or retransmis-sions This high flexibility increases the complexity and engenders the
need for additional signaling information transferred on the HS-SCCH
Reception of user data in HSDPA is always a two-step procedure
First the receiver has to capture the scheduling control information
and afterwards based on the received control information it may start
demodulating and decoding the HS-PDSCH containing the user data
This two-step procedure is shown in Fig 2-16 below which lists what
kind of control information is sent to the UEs via the HS-SCCH Asshown in Fig 2-2 page 28 which describes the overall HSDPA chan-
nel structure there can be up to four HS-SCCHs assigned to one UE
But only one HS-SCCH would contain the scheduling information for
this UE within one TTI Thus the network can assign resources simul-
taneously to various UEs in the downlink direction
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HSDPA operation overview and physical channels
I would like to receive databut I dont know where myHS-PDSCH resources areand what they look like
HS-SCCH
Read the 1st HS-SCCH slotfor HS-DSCH channelizationcodes UE identity and
modulation scheme
Then the 2nd and 3rd HS-SCCHslots provide transport block sizeinformation hybrid ARQ process in-formation redundancy constellationversion new data indicator
HS-PDSCH
Fig 2-16 HS-SCCH control channel usage
Regarding the physical layer parameters we see in Fig 2-17 that the
HS-SCCH uses a channelization code with a spreading factor of 128
and it also uses the newly introduced transmit time interval of one sub-
frame which is equal to 2 ms It should be mentioned that the spread-ing factor of 128 requires double the capacity compared to similar con-
trol channels in WCDMA Release 99 reflecting the signaling overhead
needed to guarantee the huge flexibility introduced with HSDPA Addi-
tionally Fig 2-16 shows that the control information is sent consecu-
tively within one subframe The first slot within this subframe contains
the control information UE identity channelization code information
and modulation scheme identifier Slots 2 and 3 of the subframe con-tain the remaining control information Transport block size HARQ
process identifier redundancy version and new data indicator Conse-
quently the UE can self-decode slot 1 alone and slots 2 and 3 in a sec-
ond step even if they represent one logical unit This raw control infor-
mation is of course also channel coded using a turbo and on the phys-
ical layer the quantity of bits after the rate matching step is 40 bits con-
veyed in one slot corresponding to 666 micros [TS 25212 Ref 21] see also
Fig 2-28 page 56
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High speed shared control channel (HS-SCCH)
47
The HS-SCCH is a fixed rate (60 kbps SF = 128) downlinkphysical channel used to carry downlink signaling related toHS-DSCH transmission
Slot 0
Slot 1
Slot 2
Tslot
= 2560 chips
Data = 40 bits
1 subframe = 2 ms
Fig 2-17 Structure of High speed shared control channel HS-SCCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
We would like to return now to the time consecutive transmission of
control information There is a difference in the control information
in terms of its priority Some information is needed at the UE end
very urgently while other control information does not have such a
high priority But why This will be explained by looking at some tim-ing aspects defined for HSDPA If we consider the timing between
the shared data channel HS-PDSCH and the shared control chan-
nel HS-SCCH as shown in Fig 2-18 we see that the HS-PDSCH fol-
lows the HS-SCCH by exactly two slots or 5120 chips The HS-SCCH
is completely time-aligned with the general control channels CPICH
and P-CCPCH of the NodeB This is mandatory because it is a shared
channel Consider several UEs with different distances to the NodeBwanting to receive the HS-SCCH channel Thus it must have constant
timing that is known a priori The shared data channel HS-PDSCH is
now transmitted exactly 5120 chips after the first chip of the HS-SCCH
This leads to an overlapping slot thereby requiring multitasking recep-
tion at the UE end While the UE is still receiving the last slot of an
ongoing HS-SCCH subframe it may already start the reception of an
HS-PDSCH transport block The first slot in the HS-SCCH subframe
now contains information required by the physical layer to performdespreading and demodulation These values are the UE identity indi-
cating whether the UE will start demodulation of the HS-PDSCH or
not in case it is not scheduled the modulation scheme information
since the UE has to know how to interpret the received constellation
vector and whether it has to be considered as a QPSK or 16QAM con-
stellation point and finally the UE has to know which channelization
codes it has to apply to capture the HS-PDSCH transport block The
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HSDPA operation overview and physical channels
overall UE reaction time when being scheduled is now seen as 1 slot
or 2560 chips This tough requirement for the UEs is due to the objec-
tive to obtain overall a much shorter latency than legacy standards Theadditional control information such as the new data indicator redun-
dancy version and transport block size is not that urgent since it is
needed after demodulation but before channel decoding So first the
UE will sample the whole three slots of the HS-PDSCH and demodu-
late them into a bit stream which is finally handed over to the channel
decoder This principle is known as post-processing and is used typi-
cally in mobile communications technologies
J Start of HS-SCCH subframe 0 is aligned with startof P-CCPCH frames
J The HS-PDSCH starts
τ HS-PDSCH
(2times Tslot
= 5120 chips)
after the start of the HS-SCCH
UE identity etc
processing timeof receiver
HS-DSCH subframe
3 times Tslot= 7680 chips
3 times Tslot
= 7680 chips
τ HS-PDSCH
(2times Tslot
= 5120 chips)
HS-SCCH
HS-PDSCH
Fig 2-18 Timing relation between HS-SCCH and HS-PDSCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
Content of the HS-SCCH control channelThe control information contained in the HS-SCCH control chan-
nel has already been mentioned so we will now consider the values
in more detail We will begin with an overview of what kind of control
information is contained in the HS-SCCH channel before proceeding
with further details about the single control elements The following
control information is present in the HS-SCCH [TS 25212 Ref 21]
Channelization code set information (7 bits)
Modulation scheme information (1 bit) Transport block size information (6 bits)
Hybrid ARQ process information (3 bits)
Redundancy and constellation version (3 bits)
New data indicator (1 bit)
UE identity (16 bits) = H-RNTI
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High speed shared control channel (HS-SCCH)
49
Some of these parameters are more or less self-explanatory while oth-
ers require additional background information and closer examination
Modulation scheme information 1 bit
This single bit is used to inform the receiver whether the modulation
scheme QPSK or 16QAM is applied on the data channel HS-PDSCH
The interpretation of the bit x ms1 is as follows
ms1
x
if QPSK
otherwise
0
1
=
New data indicator 1 bit
The new data indicator bit field informs the receiving entity that the
prevailing PDU transmitted by the current HARQ process is either a
retransmission or contains new data This is done by setting the new
data bit to the value 0 for the first PDU on this particular HARQ process
and incrementing the value by 1 with every new data sent [TS 25321Ref 30] This leads to a toggled value In case the new data bit is not
incremented ie if it remains at its previous value it is an indicator for
retransmission
1st PDU of this
HARQ process
NDI = New data indicator
NDI = 0 NDI = 1
NACK
NDI = 1
ACK
NDI = 0
HS-SCCH HS-SCCH HS-SCCHHS-SCCH
ACK
Fig 2-19 New data indicator bit principle of incrementing value
Channelization code set information 7 bits
This field is used to indicate the number of channelization codes usedfor transmitting the transport block on the HS-PDSCH As was already
described the spreading factor applied on the HS-PDSCH is constant
with a value of 16 but the flexible values are the number of channeliza-
tion codes forming a cluster when using multiple codes and their posi-
tion in the code tree It is not allowed to distribute the code channels
over the code tree diagram For the sake of simplicity in signaling sev-
eral channelization codes form one cluster and these codes are con-
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HSDPA operation overview and physical channels
tiguous in the channelization code tree [TS 25213 Ref 22] Fig 2-20
illustrates the principle of indicating the channelization codes on the
HS-SCCH
SF = 16
Code ldquo0rdquo isreserved forcommonchannels
Code offset 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15P = 5O = 7
Code group indicatorx
ccs1 x
ccs2 x
ccs3 = min (Pminus 1 15 minusP)
Code offset indicatorx
ccs4 x
ccs5 x
ccs6 x
ccs7 = |Ominus 1minus P8 times15|
A cluster of codes
can be allocated to a UEC
ch16Ohellip C
ch16O + P minus 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1
2 2 2 2 2 2 2 2 2 2 2 2 2 2 14 14
1 2 3 4 5 6 7 8 9 10 11 12 13 14 2 1
3 3 3 3 3 3 3 3 3 3 3 3 3 13 13 13
1 2 3 4 5 6 7 8 9 10 11 12 13 3 2 1
4 4 4 4 4 4 4 4 4 4 4 4 12 12 12 121 2 3 4 5 6 7 8 9 10 11 12 4 3 2 1
5 5 5 5 5 5 5 5 5 5 5 11 11 11 11 11
1 2 3 4 5 6 7 8 9 10 11 5 4 3 2 1
6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10
1 2 3 4 5 6 7 8 9 10 6 5 4 3 2 1
7 7 7 7 7 7 7 7 7 9 9 9 9 9 9 9
1 2 3 4 5 6 7 8 9 7 6 5 4 3 2 1
8 8 8 8 8 8 8 8
8 7 6 5 4 3 2 1
0 (115)
1 (214)
2 (313)
3 (412)
4 (511)
5 (610)
6 (79)
7 (88) Redundant area
C l u s t e r c o d e i n d i c a t o r ( 3 b i t s )
Tree offset indicator (4 bits)
Signaled on HS-SCCH
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
PO
Decoding notation
Number ofmulti-codes
Offset fromleft right incode tree (SF = 16)
Fig 2-20 Channelization code set indicating the HS-PDSCH code cluster
The idea behind the code indication is a matrix with the rows repre-
senting the number of codes per cluster and the columns represent-
ing the position of that cluster the offset value in the code tree Recall-
ing that the maximum number of channelization codes per clusteris 15 and if the cluster size is 1 the offset values can also range from
1 to 15 the resulting matrix would have 15 rows and 15 columns Since
we know that four bits are needed to represent an integer from 1 to 15
we need a total of 4 + 4 = 8 bits for representation of the channeliza-
tion code set information It is a smart idea to save one bit The 15 times 15
matrix would contain much redundant information By way of analogy
like in a road map indicating distances between cities A table showing
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High speed shared control channel (HS-SCCH)
51
the distance from city A to city B the opposite distance from city B to
city A is redundant information The useful information has the form
of a triangle The idea is to cut the lower part rotate it and append itto the spare part of the upper table In this manner a table is obtained
with 7 rows and 15 columns and it is possible to indicate each position
in it with just 7 bits
1 5 r o w s 7
r o w s
Matrix reduction for channeli-
zation code set information
15 columns
Fig 2-21 Matrix size reduction for channelization code set information
The content of the channelization code set matrix can be described as
a value with two numbers The upper number is the number of mul-
ticodes forming one cluster and the lower number is the offset in the
channelization code tree Accordingly the example in Fig 2-20 can be
interpreted to mean the HS-SCCH sends the bits as row number 4 and
column number 6 in the matrix The content of this element are the
values 5 over 7 which have to be interpreted as a cluster size of 5 codesand an offset of 7
Transport block size information 6 bits
With a length of six bits the transport block size (TBS) informa-
tion informs the receiving UE entity about the data block size of the
transport block sent on the HS-PDSCH We should keep in mind the
link adaptation performed with the adaptive modulation and coding
scheme that was described in section 12 page 10 The ratio errorcorrection and user data are flexible while the physical layer param-
eters such as the spreading factor modulation scheme and number of
channelization codes determine the physical block size This physical
block consists of the user data ratio or transport block size and the for-
ward error correction or redundancy information As this ratio is flex-
ible the HS-SCCH will inform the receiving UE entity about the size
of the transport block Here too there is a strategy of bit reduction the
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HSDPA operation overview and physical channels
goal is to inform the receiver with as few bits as possible A non-effi-
cient approach would involve conversion of the decimal number repre-
senting the TBS into a binary sequence but the number of bits neededwould exceed the space available on the HS-SCCH Imagine that the
range of transport block sizes depends on the physical layer condi-
tions The ambient physical layer parameters modulation scheme and
number of channelization codes set a certain working point where the
remaining flexibility for a different TBS configuration can be obtained
by more or less puncturing resulting in a flexible ratio between for-
ward error correction and user data This will lead to a two-step proce-
dure when evaluating the transport block size First the receiver exam-
ines the information modulation scheme and number of channeliza-
tion codes scheduled via HS-SCCH which indicate the value k0 l as
shown in Fig 2-22 The 6-bit HS-SCCH control parameter transport
block size information will be the transport format resource indica-
tor (TFRI) named ki Let k t be the sum of the two values kt = ki + k0i
Both values kt and k0 i can be obtained from tables given by [TS 25321
Ref 30] The range for the TFRI is from 1 to 256 and the derived trans-port block size ranges from 137 bits to 27 952 bits The first table indi-
cates the value k 0 i based on the channelization code and the modula-
tion scheme
Combination i Modulation scheme Number of channelization codes k0 i
0
QPSK
1 1
1 2 40
2 3 633 4 79
4 5 92
5 6 102
Fig 2-22 Extract from TS 25321 table representing k0 i
The second table indicates the final transport block size based on kt
Index TB size Index TB size Index TB size1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
4 173 89 1456 174 6673
5 185 90 1483 175 6793
6 197 91 1509 176 6916
7 209 92 1537 177 7041
Fig 2-23 Extract from TS 25321 table representing kt
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High speed shared control channel (HS-SCCH)
53
J The transport block size used on HS-DSCH is not signaled explicitly on HS-SCCHJ Instead a transport block size index k
i is signaled to indicate the transport block size
First stepModulation scheme andnumber of channelizationcodes as signaled on HS-SCCHdetermine value k
0 i
Second step
Index kt = k
i + k
0i
determines HS-DSCH
transport block size
kt = k
i + k
0i
Table according to 3GPP TS 25321 extract from QPSK section
Table according to 3GPP TS 25321 254 entries in total
Combination i Modulation
scheme
Number of
channelization codes
k0 i
0
QPSK
1 1
1 2 40
2 3 63
3 4 79
4 hellip hellip
Index TB size Index TB size Index TB size
1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
helliphellip hellip hellip hellip hellip
Fig 2-24 Retrieval of transport block size information
Source Fig 2-22 to Fig 2-24 [TS 25321 Ref 30] reproduced by permission of 3GPP
Hybrid ARQ process information 3 bits
The concept behind the hybrid automatic repeat request (HARQ) was
introduced in section 13 page 14 One feature is the possibility of
multitasking ie having several HARQ processes activated at the same
time Fig 2-25 below shows the need to signal the process identity tothe receiver Remember that on the downlink there is a shared chan-
nel concept so the NodeB can flexibly decide which UE will be sched-
uled with a downlink transport block Up to eight HARQ processes
can be signaled via higher layers to one UE Note however that due to
the round-trip timing six HARQ processes must be active to achieve
the maximum throughput as shown in Fig 2-51 page 79 Compared
with HSUPA the HARQ processes on the downlink are asynchronous
so they have to be indicated but on the uplink they are synchronous sothey do not need to be signaled explicitly
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HSDPA operation overview and physical channels
Asynchronous DL minus Synchronous ULNumber of H-ARQ rocesses = 1 to 8 er UE
UL HS-DPCCH UE1
UE1 HARQ processes 1 to 4
3 4 1 42 11 1 32retrans
2
A N A A
A A
N A
UL HS-DPCCH UE2
HS-PDSCH
UE2 HARQ processes 1 to 2
Fig 2-25 HARQ process indication on HS-SCCH
Fig 2-25 shows a typical situation on the downlink (point-to-multi-
point) The NodeB sends data to several UEs sharing the HS-PDSCH
so therefore the HARQ process is asynchronous The time when a
transport block is retransmitted is not fixed For this reason the pro-
cess identifier is signaled on the HS-SCCH Based on the HARQ pro-
cess identity and the new data indicator bit the receiving entity knows
which part of the soft buffer memory has to be used in case of soft com-bining On the uplink the situation is slightly simpler The UE only
communicates with one NodeB so it is a point-to-point connection
Thus retransmission always occurs at a fixed time linked to the origi-
nal transmission
Redundancy and constellation version 3 bits
Adaptive modulation and coding involve flexible selection of modula-tion and coding schemes that are signaled to the receiving UE via the
parameters transport block size and modulation scheme information
Another concept used in HSDPA was previously discussed Chase com-
bining or incremental redundancy (see section 222 page 41) This
means that in case of retransmission the transmit entity can dynami-
cally select another puncturing scheme or keep the puncturing as it was
in the original transmission The applied puncturing scheme is signaled
as redundancy information to the receiver Additionally in case of the16QAM modulation scheme the transmitter can select another constel-
lation arrangement which is also signaled to the UE with the three bits
for the redundancy and constellation version see Fig 2-15 page 45
Depending on the modulation scheme (QPSK or 16QAM) there are
two different tables indicating the parameters ldquosrdquo ldquorrdquo and ldquobrdquo The
parameters ldquosrdquo and ldquorrdquo indicate which scheme is used for puncturing
ie if the puncturing mechanism prioritizes the systematic bits or not
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High speed shared control channel (HS-SCCH)
55
and which puncturing algorithm is used The parameter ldquobrdquo indicates
the constellation mapping version The receiver needs this information
to perform proper demodulation and decoding
Initial transmission
1st retransmission
2nd retransmission
3rd retransmission
r
0
0
1
1
2
2
3
xrv
(value)
s
0 1
1 0
2 1
3 0
4 1
5 0
6 1
7 0 3
s = 1 Systematic bits are prioritizeds = 0 Non-systematic bits are prioritized
r (range 0 to 3 for QPSK) influencesJ Input parameter for puncturing or (together with s) for repetition algorithm defined in TS 25212J Selection of parity bits
Redundancy version coding sequences are signaled on HS-SCCH egndash 0 2 5 6 One initial transmission + 3 retransmissions with different r and s parameters
Fig 2-26 Signaling of redundancy version parameters r and s QPSK case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
Initial transmission
2nd retransmission
1st retransmission
3rd retransmission
r (range 0 to 1 for 16QAM)influences input parameterfor puncturing or (togetherwith s) for repetitionalgorithm defined in
TS 25212 and thus selectionof parity bits
Redundancy version coding sequences are signaled on HS-SCCH egminus 6 4 0 5 Chase combining (no change in s and r parameters ie same redundancyversion) with four possible constellations
x rv (value) s r b
0 1 0 0
1 0 0 0
2 1 1 1
3 0 1 1
4 1 0 1
5 1 0 2
6 1 0 3
7 1 1 0
Definition of parameter s as for QPSK
b (range 0 to 3) describes constellationrearrangement to averagereliability of bits
Fig 2-27 Signaling of redundancy version parameters r s and b 16QAM case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
UE identity H-RNTI 16 bits
The HSDPA radio network transaction identifier (H-RNTI) unam-
biguously identifies the UE having an HS-PDSCH assignment within
a cell It is allocated to the UE via layer 3 signaling procedures at the
radio bearer setup if the radio bearer is an HSDPA connection This
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HSDPA operation overview and physical channels
value represents a temporary name of the UE used to address it when
scheduling data packets via HS-SCCH
HS-SCCH channel coding
The control information contained in the HS-SCCH is of course pro-
tected with channel coding mechanisms the whole coding chain is
described in Fig 2-28 Fig 2-18 page 48 presents the separation of
the control information into two code blocks which are sent consec-
utively mapped on slot 1 and slot 2 + 3 of one HS-SCCH subframe
This principle is also visible in the coding chain The first control block
consisting of channelization information modulation scheme and UE
identity is coded separately from the remaining control values to enable
the UE receiver to decode this first slot separately and prepare for pos-
sible HS-PDSCH reception The coding steps shown in Fig 2-28 such
as rate matching 1 and 2 are similar to the HS-PDSCH coding chain
and are further described in [TS 25212 Ref 21]
Channelcoding 1
R atematching 1
mux
Channelcoding 2
Ratematching 2
RVcoding
UE-specificCRC attachment
UE-specificmasking
Physical channelmapping
r s b
mux
Channelizationcode set
Modulationscheme
Transport block size information
HARQ processinformation
Redundancy andconstellation version
New data indicator
UE identity
UE identity
Fig 2-28 Channel coding for HS-SCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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High speed dedicated physical control channel (HS-DPCCH)
57
24 High speed dedicated physical control channel (HS-DPCCH)
In an active HSDPA connection the UE has to send acknowledgment ornon-acknowledgment reports (as described in section 13 page 14
where the HARQ process is described) as well as channel status infor-
mation to the network The reporting is performed on this physical
control channel HS-DPCCH
As ubiquitous in HSDPA the uplink is also configured into a subframe
structure of 2 ms corresponding to three slots The first slot of the sub-
frame carries the ACK NACK information the UE sends to the NodeB
while the following two slots ie slot 2 and 3 of the subframe convey
the CQI value the channel quality information to the NodeB
Subframe 0 Subframe i Subframe 4
Tslot
= 2560 chips J The spreading factor of theHS-DPCCH is 256 (10 bits peruplink slot)
J The HS-DPCCH can only existtogether with an UL DPCCH
(ded phys control channel)J The DPDCH (dedicated physical data channel) the DPCCH andthe HS-DPCCH are IQ codemultiplexed
HARQ-ACK CQI = Channel quality information
2 times Tslot
= 5120 chips
One radio frame Tf = 10 ms
One HS-DPCCH subframe 2 ms
Fig 2-29 HS-DPCCH configuration
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The slot format for HS-DPCCH describes a quantity of 30 bits per sub-frame resulting in a data rate of 15 kbps The spreading factor used for
the HS-DPCCH is constant and is always equal to 256 but the chan-
nelization code that is used as well as the mapping on either the I or
Q axis depends on several factors eg the co-existence of an HSDPA
connection with a circuit-switched connection meaning whether a
DPDCH established or not Fig 2-36 page 64 illustrates this IQ
mapping and Fig 2-35 page 63 shows the channelization code used
for HS-DPCCH
The HS-DPCCH builds a logical unit of one subframe but having the
independent control information HARQ-ACK and CQI included which
could be separately decoded at the NodeB Note that the slot carrying
the ACK NACK statement is active only when the UE has been sched-
uled by an HS-PDSCH subframe in the corresponding downlink sub-
frame previously Assuming the UE has not received a transport block
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HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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HS-DSCH High speed downlink shared channel transport channel
39
As several code words are interleaved the decoder has to ldquowaitrdquo a cer-
tain time until all bits of a particular code word arrive This delay ie
the ldquomeasure for spreading over timerdquo is referred to as the ldquointerleav-ing depthrdquo The greater the interleaving depth the more code words are
available for spreading the error bursts and the greater the probability
that errored bits can be corrected but on the other hand this increases
the overall latency time
HSDPA uses the block diagonal interleaving principle for the HS-DSCH
only since as we should recall one goal is to have a short round-trip
time
Spreadinghellip
Interleaving
hellip
hellip
Fig 2-10 Diagonal interleaving
Write
Read
Interleaving-Matrix
Fig 2-11 Block interleaving
Puncturing
Having briefly described the principle of convolutional coding another
mechanism will be presented that is used to increase the throughputof user data and coordinate with the AMC mechanism described in
section 12 page 10 After adding redundancy the total bit stream is
now known as soft bits ie the sum including all of the raw data bits
at the input of the channel coder plus the added redundancy bits This
quantity must match the required transport block size demanded by
the transport layer and the process performed here is called rate match-
ing ie deleting some of the soft bits at the transmitting end in a pre-
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HSDPA operation overview and physical channels
defined manner or repeating or adding some stuffing bits In HSPA the
rate matching mechanism uses puncturing which provides higher data
throughput The signaled values TBS and RV tell the receiving convo-lutional coder how many and where bits have been punctured This
allows the decoder to insert blank positions which have to be filled later
by performing trellis decoding In other words we may consider the
punctured bits as bit losses created intentionally by the transmitter In
this manner the total amount of data bits can be increased for the sake
of lower redundancy In HSDPA this puncturing scheme will be very
flexible and the NodeB scheduler will set the puncturing rate adapted
to the prevailing RF conditions on the radio channel to obtain the high-
est possible data throughput under the existing conditions The disad-
vantage of adaptive coding is that we need signaling information so
that the transmitter has to inform the receiver about how many soft bits
have been punctured This is seen in Fig 2-26 page 55 in the form
of the redundancy version carried by the HS-SCCH control channel
Fig 2-12 below again depicts the principle of puncturing in HSDPAand clarifies some signaling parameters such as the transport block size
1 1 0 1 1 0 0
11 01 01 00 01 01 11
Transport block sizeInput bits into channel coder
Soft bitsOutput from channel encoder
Rate matchingPuncturing or repeating bits
11 01 01 00 01 01 11
1 01 0 00 0 01 1Coded composite transport bitsCan be several combined streams aftercoding + rate matching
Transport block size FEC
Fig 2-12 Puncturing based on coding example from Fig 2-8 page 37
The process of channel coding starts first with the transport block
size which is given by the size of the input data bit sequence added
by a cyclic redundancy checksum The next step is the channel cod-
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HS-DSCH High speed downlink shared channel transport channel
41
ing which is performed in HSPA by a so-called turbo coder The turbo
coder is a parallel concatenated convolutional coder that exhibits bet-
ter reliability compared to a single convolutional coder Discussingthe functionality of a turbo coder in all of its details would represent a
major digression from the intention of this book Accordingly we will
simply encourage the interested reader to consult the channel coding
literature for more details about turbo coders and their applications
[Ref 10] [Ref 12] Determined by the scheduler of the base station or
the redundancy version to be used the next step known as the redun-
dancy version will either puncture (the most likely) or repeat some of
the bits resulting from the channel coding process How many bits will
be punctured is defined by the coding rate In our example in Fig 2-12
we see that the input bit sequence has a length of 7 bits resulting in
14 soft bits after channel coding with our example coder providing a
coding rate of frac12 The scheduler decided to puncture 4 bits so that we
finally obtain 10 bits which have to be mapped on the physical chan-
nels Our overall coding rate is therefore given as ⁷frasl983089983088 In other words
some bits are protected with redundancy information while othersare not Note that the size of the coded composite transport channel
is determined by the physical layer parameters such as the number of
channelization codes used to convey the HS-PDSCH the modulation
scheme and the transmit time interval which is constant for HSDPA
but can be either 2 or 10 ms for HSUPA Thus its size does not need
to be signaled to the receiver and only the transport block size and the
redundancy versions will be contained in the HS-SCCH channel
222 Incremental redundancy and chase combining
for HS-DSCH
Until now we have presented some general characteristics of HSDPA
and HSUPA which we would now like to discuss in a combined pro-
cedure and then deduce two other principles The HARQ abbreviationcombines an automatic retransmission of erroneous data with a soft
combination at the receiving end A related question can now be how
the transmitter has to repeat the transport block should the retrans-
mission of data occur in an identical retransmission mode or should
some changes in coding parameters eg the manner of puncturing be
applied This question is also important for the implementation of the
rate matching step shown in Fig 2-12 The transmitter has to provide
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42
HSDPA operation overview and physical channels
a certain soft buffer ie a memory that stores the transmitted data for
the sake of possible retransmissions and deletes it after having received
a positive acknowledgment from the receiver Should the transmitternow store the coded composite transport data i e the data after coding
but also after puncturing This would restrict it to repeating the data in
an identical manner A better approach is to store the data after channel
coding and before puncturing Even if this requires more memory it
gives the flexibility to change the puncturing scheme and retransmit the
transport block in a different way Fig 2-13 and Fig 2-14 represent both
mechanisms that are used in HSDPA and HSUPA Identical retransmis-
sion is called chase combining and non-identical retransmission with
a different puncturing scheme is called incremental redundancy The
scheduler in the base station can decide which retransmission scheme
will be used We do not wish to delve into the details of channel coding
theory to discuss which mechanism is the better one ndash chase combin-
ing or incremental redundancy We will only mention that both mech-
anisms have their advantages and thus their applications Chase com-
bining has the advantage that the systematic bits representing the orig-inal data input into the channel coder are contained in the transmit-
ted sequence after puncturing Thus chase combined transport blocks
are ldquoself-decodablerdquo If we consider a situation where the original trans-
port block is lost completely and only the retransmitted block is pres-
ent at the receiver there is a chance to decode the data properly Mean-
while incremental redundancy seems to add more redundancy when
retransmitting but in a scenario where the first transmission contain-ing the systematic bits is lost completely and only the retransmission
is present the receiver will have no chance to decode the data without
having some of the systematic bits Accordingly incremental redun-
dancy is applied whenever sporadic bit errors occur due to a time vari-
ant channel and chase combining is selected whenever we have to deal
with complete transport block errors i e the time variance of the radio
link exhibits some bursted fading dips
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HS-DSCH High speed downlink shared channel transport channel
43
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Chase combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Transmitted bit
Punctured bit
Systematic bits
Parity 1
Parity 2
Systematic bits
Parity 1
Parity 2
Fig 2-13 Chase combining principle
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Incremental redundancy combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Systematic bits
Parity 1
Parity 2
Systematic bitsParity 1
Parity 2
Fig 2-14 Incremental redundancy
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HSDPA operation overview and physical channels
223 Constellation rearrangement
Due to the fact that HSDPA introduces a higher-order modulationscheme (16QAM) we can recognize some effects due to the physi-
cal layer influencing the susceptibility to noisy RF conditions One of
these effects can be explained by looking at the constellation diagram
in the 16QAM modulation scheme see section 12 page 10 As we
recall there is a total of 16 different constellation points given by the
modulation vector and represented by its phase and amplitude Con-
sidering the Euclidean distance which is the distance in this constella-
tion diagram between two neighboring points we can clearly see that
some points have more neighbors than others Especially the four con-
stellation points at the very four corners only have three direct neigh-
bors making them less susceptible to misdetection due to noise shift-
ing them in a certain direction On the other hand the four constella-
tion points representing the inner square of the constellation have eight
direct neighbors each and are therefore more likely to be incorrectly
detected The idea of constellation rearrangement is now to change themapping scheme applied in the original transmission when retrans-
mitting As we know the receiver will soft combine the retransmit-
ted data with the previously received information so we can achieve a
certain incremented redundancy and a certain protection mechanism
Note however that considering a sole transmission of a transport block
using a certain constellation arrangement will not show any more pos-
itive or negative results compared to other constellation arrangementsThe redundancy gain is only achieved by rearranging the constellation
mapping in a retransmitted transport block and performing soft com-
bining at the receiver Overall HSDPA defines four constellation rear-
rangement schemes which are indicated in the redundancy version
field of the HS-SCCH and are represented by the ldquobrdquo bit field ranging
from b = 0 to b = 3 All four constellation schemes are Gray encoded
ie the directly adjacent constellation symbols do not exhibit four com-
pletely different bits in order to reduce the impact of misdetection onbit errors
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High speed shared control channel (HS-SCCH)
45
Q
I
(ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1) (1 1ndash1ndash1)
(ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1) (1 1ndash1 1)
(ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1) (1ndash1ndash1 1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 0
Q
I
(ndash1 1 1 1) (ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1)
(ndash1 1 1ndash1) (ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1)
(ndash1ndash1 1ndash1) (ndash1ndash1ndash1ndash1) (1ndash1ndash1ndash1) (1ndash1 1ndash1)
(ndash1 1 1 1) (ndash1ndash1ndash1 1) (1ndash1ndash1 1) (1ndash1 1 1)
b = 2
Q
I
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (1ndash1 1 1) (ndash1ndash1 1 1)
(ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1) (ndash1 1 1 1)
(ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1) (ndash1 1 1ndash1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 1
Q
I
(1 1ndash1 1) (ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1)
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1)
(1ndash1ndash1ndash1) (ndash1ndash1ndash1ndash1) (ndash1ndash1 1ndash1) (1ndash1 1ndash1)
(1 1ndash1ndash1) (ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1)
b = 3
Fig 2-15 Constellation rearrangement in HSDPA
23 High speed shared control channel (HS-SCCH)
The HS-SCCH sends scheduling information to the UEs As seen before
the HS-PDSCH has a very flexible configuration for physical parame-
ters such as the coding rate number of code channels or retransmis-sions This high flexibility increases the complexity and engenders the
need for additional signaling information transferred on the HS-SCCH
Reception of user data in HSDPA is always a two-step procedure
First the receiver has to capture the scheduling control information
and afterwards based on the received control information it may start
demodulating and decoding the HS-PDSCH containing the user data
This two-step procedure is shown in Fig 2-16 below which lists what
kind of control information is sent to the UEs via the HS-SCCH Asshown in Fig 2-2 page 28 which describes the overall HSDPA chan-
nel structure there can be up to four HS-SCCHs assigned to one UE
But only one HS-SCCH would contain the scheduling information for
this UE within one TTI Thus the network can assign resources simul-
taneously to various UEs in the downlink direction
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HSDPA operation overview and physical channels
I would like to receive databut I dont know where myHS-PDSCH resources areand what they look like
HS-SCCH
Read the 1st HS-SCCH slotfor HS-DSCH channelizationcodes UE identity and
modulation scheme
Then the 2nd and 3rd HS-SCCHslots provide transport block sizeinformation hybrid ARQ process in-formation redundancy constellationversion new data indicator
HS-PDSCH
Fig 2-16 HS-SCCH control channel usage
Regarding the physical layer parameters we see in Fig 2-17 that the
HS-SCCH uses a channelization code with a spreading factor of 128
and it also uses the newly introduced transmit time interval of one sub-
frame which is equal to 2 ms It should be mentioned that the spread-ing factor of 128 requires double the capacity compared to similar con-
trol channels in WCDMA Release 99 reflecting the signaling overhead
needed to guarantee the huge flexibility introduced with HSDPA Addi-
tionally Fig 2-16 shows that the control information is sent consecu-
tively within one subframe The first slot within this subframe contains
the control information UE identity channelization code information
and modulation scheme identifier Slots 2 and 3 of the subframe con-tain the remaining control information Transport block size HARQ
process identifier redundancy version and new data indicator Conse-
quently the UE can self-decode slot 1 alone and slots 2 and 3 in a sec-
ond step even if they represent one logical unit This raw control infor-
mation is of course also channel coded using a turbo and on the phys-
ical layer the quantity of bits after the rate matching step is 40 bits con-
veyed in one slot corresponding to 666 micros [TS 25212 Ref 21] see also
Fig 2-28 page 56
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High speed shared control channel (HS-SCCH)
47
The HS-SCCH is a fixed rate (60 kbps SF = 128) downlinkphysical channel used to carry downlink signaling related toHS-DSCH transmission
Slot 0
Slot 1
Slot 2
Tslot
= 2560 chips
Data = 40 bits
1 subframe = 2 ms
Fig 2-17 Structure of High speed shared control channel HS-SCCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
We would like to return now to the time consecutive transmission of
control information There is a difference in the control information
in terms of its priority Some information is needed at the UE end
very urgently while other control information does not have such a
high priority But why This will be explained by looking at some tim-ing aspects defined for HSDPA If we consider the timing between
the shared data channel HS-PDSCH and the shared control chan-
nel HS-SCCH as shown in Fig 2-18 we see that the HS-PDSCH fol-
lows the HS-SCCH by exactly two slots or 5120 chips The HS-SCCH
is completely time-aligned with the general control channels CPICH
and P-CCPCH of the NodeB This is mandatory because it is a shared
channel Consider several UEs with different distances to the NodeBwanting to receive the HS-SCCH channel Thus it must have constant
timing that is known a priori The shared data channel HS-PDSCH is
now transmitted exactly 5120 chips after the first chip of the HS-SCCH
This leads to an overlapping slot thereby requiring multitasking recep-
tion at the UE end While the UE is still receiving the last slot of an
ongoing HS-SCCH subframe it may already start the reception of an
HS-PDSCH transport block The first slot in the HS-SCCH subframe
now contains information required by the physical layer to performdespreading and demodulation These values are the UE identity indi-
cating whether the UE will start demodulation of the HS-PDSCH or
not in case it is not scheduled the modulation scheme information
since the UE has to know how to interpret the received constellation
vector and whether it has to be considered as a QPSK or 16QAM con-
stellation point and finally the UE has to know which channelization
codes it has to apply to capture the HS-PDSCH transport block The
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HSDPA operation overview and physical channels
overall UE reaction time when being scheduled is now seen as 1 slot
or 2560 chips This tough requirement for the UEs is due to the objec-
tive to obtain overall a much shorter latency than legacy standards Theadditional control information such as the new data indicator redun-
dancy version and transport block size is not that urgent since it is
needed after demodulation but before channel decoding So first the
UE will sample the whole three slots of the HS-PDSCH and demodu-
late them into a bit stream which is finally handed over to the channel
decoder This principle is known as post-processing and is used typi-
cally in mobile communications technologies
J Start of HS-SCCH subframe 0 is aligned with startof P-CCPCH frames
J The HS-PDSCH starts
τ HS-PDSCH
(2times Tslot
= 5120 chips)
after the start of the HS-SCCH
UE identity etc
processing timeof receiver
HS-DSCH subframe
3 times Tslot= 7680 chips
3 times Tslot
= 7680 chips
τ HS-PDSCH
(2times Tslot
= 5120 chips)
HS-SCCH
HS-PDSCH
Fig 2-18 Timing relation between HS-SCCH and HS-PDSCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
Content of the HS-SCCH control channelThe control information contained in the HS-SCCH control chan-
nel has already been mentioned so we will now consider the values
in more detail We will begin with an overview of what kind of control
information is contained in the HS-SCCH channel before proceeding
with further details about the single control elements The following
control information is present in the HS-SCCH [TS 25212 Ref 21]
Channelization code set information (7 bits)
Modulation scheme information (1 bit) Transport block size information (6 bits)
Hybrid ARQ process information (3 bits)
Redundancy and constellation version (3 bits)
New data indicator (1 bit)
UE identity (16 bits) = H-RNTI
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High speed shared control channel (HS-SCCH)
49
Some of these parameters are more or less self-explanatory while oth-
ers require additional background information and closer examination
Modulation scheme information 1 bit
This single bit is used to inform the receiver whether the modulation
scheme QPSK or 16QAM is applied on the data channel HS-PDSCH
The interpretation of the bit x ms1 is as follows
ms1
x
if QPSK
otherwise
0
1
=
New data indicator 1 bit
The new data indicator bit field informs the receiving entity that the
prevailing PDU transmitted by the current HARQ process is either a
retransmission or contains new data This is done by setting the new
data bit to the value 0 for the first PDU on this particular HARQ process
and incrementing the value by 1 with every new data sent [TS 25321Ref 30] This leads to a toggled value In case the new data bit is not
incremented ie if it remains at its previous value it is an indicator for
retransmission
1st PDU of this
HARQ process
NDI = New data indicator
NDI = 0 NDI = 1
NACK
NDI = 1
ACK
NDI = 0
HS-SCCH HS-SCCH HS-SCCHHS-SCCH
ACK
Fig 2-19 New data indicator bit principle of incrementing value
Channelization code set information 7 bits
This field is used to indicate the number of channelization codes usedfor transmitting the transport block on the HS-PDSCH As was already
described the spreading factor applied on the HS-PDSCH is constant
with a value of 16 but the flexible values are the number of channeliza-
tion codes forming a cluster when using multiple codes and their posi-
tion in the code tree It is not allowed to distribute the code channels
over the code tree diagram For the sake of simplicity in signaling sev-
eral channelization codes form one cluster and these codes are con-
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HSDPA operation overview and physical channels
tiguous in the channelization code tree [TS 25213 Ref 22] Fig 2-20
illustrates the principle of indicating the channelization codes on the
HS-SCCH
SF = 16
Code ldquo0rdquo isreserved forcommonchannels
Code offset 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15P = 5O = 7
Code group indicatorx
ccs1 x
ccs2 x
ccs3 = min (Pminus 1 15 minusP)
Code offset indicatorx
ccs4 x
ccs5 x
ccs6 x
ccs7 = |Ominus 1minus P8 times15|
A cluster of codes
can be allocated to a UEC
ch16Ohellip C
ch16O + P minus 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1
2 2 2 2 2 2 2 2 2 2 2 2 2 2 14 14
1 2 3 4 5 6 7 8 9 10 11 12 13 14 2 1
3 3 3 3 3 3 3 3 3 3 3 3 3 13 13 13
1 2 3 4 5 6 7 8 9 10 11 12 13 3 2 1
4 4 4 4 4 4 4 4 4 4 4 4 12 12 12 121 2 3 4 5 6 7 8 9 10 11 12 4 3 2 1
5 5 5 5 5 5 5 5 5 5 5 11 11 11 11 11
1 2 3 4 5 6 7 8 9 10 11 5 4 3 2 1
6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10
1 2 3 4 5 6 7 8 9 10 6 5 4 3 2 1
7 7 7 7 7 7 7 7 7 9 9 9 9 9 9 9
1 2 3 4 5 6 7 8 9 7 6 5 4 3 2 1
8 8 8 8 8 8 8 8
8 7 6 5 4 3 2 1
0 (115)
1 (214)
2 (313)
3 (412)
4 (511)
5 (610)
6 (79)
7 (88) Redundant area
C l u s t e r c o d e i n d i c a t o r ( 3 b i t s )
Tree offset indicator (4 bits)
Signaled on HS-SCCH
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
PO
Decoding notation
Number ofmulti-codes
Offset fromleft right incode tree (SF = 16)
Fig 2-20 Channelization code set indicating the HS-PDSCH code cluster
The idea behind the code indication is a matrix with the rows repre-
senting the number of codes per cluster and the columns represent-
ing the position of that cluster the offset value in the code tree Recall-
ing that the maximum number of channelization codes per clusteris 15 and if the cluster size is 1 the offset values can also range from
1 to 15 the resulting matrix would have 15 rows and 15 columns Since
we know that four bits are needed to represent an integer from 1 to 15
we need a total of 4 + 4 = 8 bits for representation of the channeliza-
tion code set information It is a smart idea to save one bit The 15 times 15
matrix would contain much redundant information By way of analogy
like in a road map indicating distances between cities A table showing
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High speed shared control channel (HS-SCCH)
51
the distance from city A to city B the opposite distance from city B to
city A is redundant information The useful information has the form
of a triangle The idea is to cut the lower part rotate it and append itto the spare part of the upper table In this manner a table is obtained
with 7 rows and 15 columns and it is possible to indicate each position
in it with just 7 bits
1 5 r o w s 7
r o w s
Matrix reduction for channeli-
zation code set information
15 columns
Fig 2-21 Matrix size reduction for channelization code set information
The content of the channelization code set matrix can be described as
a value with two numbers The upper number is the number of mul-
ticodes forming one cluster and the lower number is the offset in the
channelization code tree Accordingly the example in Fig 2-20 can be
interpreted to mean the HS-SCCH sends the bits as row number 4 and
column number 6 in the matrix The content of this element are the
values 5 over 7 which have to be interpreted as a cluster size of 5 codesand an offset of 7
Transport block size information 6 bits
With a length of six bits the transport block size (TBS) informa-
tion informs the receiving UE entity about the data block size of the
transport block sent on the HS-PDSCH We should keep in mind the
link adaptation performed with the adaptive modulation and coding
scheme that was described in section 12 page 10 The ratio errorcorrection and user data are flexible while the physical layer param-
eters such as the spreading factor modulation scheme and number of
channelization codes determine the physical block size This physical
block consists of the user data ratio or transport block size and the for-
ward error correction or redundancy information As this ratio is flex-
ible the HS-SCCH will inform the receiving UE entity about the size
of the transport block Here too there is a strategy of bit reduction the
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HSDPA operation overview and physical channels
goal is to inform the receiver with as few bits as possible A non-effi-
cient approach would involve conversion of the decimal number repre-
senting the TBS into a binary sequence but the number of bits neededwould exceed the space available on the HS-SCCH Imagine that the
range of transport block sizes depends on the physical layer condi-
tions The ambient physical layer parameters modulation scheme and
number of channelization codes set a certain working point where the
remaining flexibility for a different TBS configuration can be obtained
by more or less puncturing resulting in a flexible ratio between for-
ward error correction and user data This will lead to a two-step proce-
dure when evaluating the transport block size First the receiver exam-
ines the information modulation scheme and number of channeliza-
tion codes scheduled via HS-SCCH which indicate the value k0 l as
shown in Fig 2-22 The 6-bit HS-SCCH control parameter transport
block size information will be the transport format resource indica-
tor (TFRI) named ki Let k t be the sum of the two values kt = ki + k0i
Both values kt and k0 i can be obtained from tables given by [TS 25321
Ref 30] The range for the TFRI is from 1 to 256 and the derived trans-port block size ranges from 137 bits to 27 952 bits The first table indi-
cates the value k 0 i based on the channelization code and the modula-
tion scheme
Combination i Modulation scheme Number of channelization codes k0 i
0
QPSK
1 1
1 2 40
2 3 633 4 79
4 5 92
5 6 102
Fig 2-22 Extract from TS 25321 table representing k0 i
The second table indicates the final transport block size based on kt
Index TB size Index TB size Index TB size1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
4 173 89 1456 174 6673
5 185 90 1483 175 6793
6 197 91 1509 176 6916
7 209 92 1537 177 7041
Fig 2-23 Extract from TS 25321 table representing kt
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High speed shared control channel (HS-SCCH)
53
J The transport block size used on HS-DSCH is not signaled explicitly on HS-SCCHJ Instead a transport block size index k
i is signaled to indicate the transport block size
First stepModulation scheme andnumber of channelizationcodes as signaled on HS-SCCHdetermine value k
0 i
Second step
Index kt = k
i + k
0i
determines HS-DSCH
transport block size
kt = k
i + k
0i
Table according to 3GPP TS 25321 extract from QPSK section
Table according to 3GPP TS 25321 254 entries in total
Combination i Modulation
scheme
Number of
channelization codes
k0 i
0
QPSK
1 1
1 2 40
2 3 63
3 4 79
4 hellip hellip
Index TB size Index TB size Index TB size
1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
helliphellip hellip hellip hellip hellip
Fig 2-24 Retrieval of transport block size information
Source Fig 2-22 to Fig 2-24 [TS 25321 Ref 30] reproduced by permission of 3GPP
Hybrid ARQ process information 3 bits
The concept behind the hybrid automatic repeat request (HARQ) was
introduced in section 13 page 14 One feature is the possibility of
multitasking ie having several HARQ processes activated at the same
time Fig 2-25 below shows the need to signal the process identity tothe receiver Remember that on the downlink there is a shared chan-
nel concept so the NodeB can flexibly decide which UE will be sched-
uled with a downlink transport block Up to eight HARQ processes
can be signaled via higher layers to one UE Note however that due to
the round-trip timing six HARQ processes must be active to achieve
the maximum throughput as shown in Fig 2-51 page 79 Compared
with HSUPA the HARQ processes on the downlink are asynchronous
so they have to be indicated but on the uplink they are synchronous sothey do not need to be signaled explicitly
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HSDPA operation overview and physical channels
Asynchronous DL minus Synchronous ULNumber of H-ARQ rocesses = 1 to 8 er UE
UL HS-DPCCH UE1
UE1 HARQ processes 1 to 4
3 4 1 42 11 1 32retrans
2
A N A A
A A
N A
UL HS-DPCCH UE2
HS-PDSCH
UE2 HARQ processes 1 to 2
Fig 2-25 HARQ process indication on HS-SCCH
Fig 2-25 shows a typical situation on the downlink (point-to-multi-
point) The NodeB sends data to several UEs sharing the HS-PDSCH
so therefore the HARQ process is asynchronous The time when a
transport block is retransmitted is not fixed For this reason the pro-
cess identifier is signaled on the HS-SCCH Based on the HARQ pro-
cess identity and the new data indicator bit the receiving entity knows
which part of the soft buffer memory has to be used in case of soft com-bining On the uplink the situation is slightly simpler The UE only
communicates with one NodeB so it is a point-to-point connection
Thus retransmission always occurs at a fixed time linked to the origi-
nal transmission
Redundancy and constellation version 3 bits
Adaptive modulation and coding involve flexible selection of modula-tion and coding schemes that are signaled to the receiving UE via the
parameters transport block size and modulation scheme information
Another concept used in HSDPA was previously discussed Chase com-
bining or incremental redundancy (see section 222 page 41) This
means that in case of retransmission the transmit entity can dynami-
cally select another puncturing scheme or keep the puncturing as it was
in the original transmission The applied puncturing scheme is signaled
as redundancy information to the receiver Additionally in case of the16QAM modulation scheme the transmitter can select another constel-
lation arrangement which is also signaled to the UE with the three bits
for the redundancy and constellation version see Fig 2-15 page 45
Depending on the modulation scheme (QPSK or 16QAM) there are
two different tables indicating the parameters ldquosrdquo ldquorrdquo and ldquobrdquo The
parameters ldquosrdquo and ldquorrdquo indicate which scheme is used for puncturing
ie if the puncturing mechanism prioritizes the systematic bits or not
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High speed shared control channel (HS-SCCH)
55
and which puncturing algorithm is used The parameter ldquobrdquo indicates
the constellation mapping version The receiver needs this information
to perform proper demodulation and decoding
Initial transmission
1st retransmission
2nd retransmission
3rd retransmission
r
0
0
1
1
2
2
3
xrv
(value)
s
0 1
1 0
2 1
3 0
4 1
5 0
6 1
7 0 3
s = 1 Systematic bits are prioritizeds = 0 Non-systematic bits are prioritized
r (range 0 to 3 for QPSK) influencesJ Input parameter for puncturing or (together with s) for repetition algorithm defined in TS 25212J Selection of parity bits
Redundancy version coding sequences are signaled on HS-SCCH egndash 0 2 5 6 One initial transmission + 3 retransmissions with different r and s parameters
Fig 2-26 Signaling of redundancy version parameters r and s QPSK case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
Initial transmission
2nd retransmission
1st retransmission
3rd retransmission
r (range 0 to 1 for 16QAM)influences input parameterfor puncturing or (togetherwith s) for repetitionalgorithm defined in
TS 25212 and thus selectionof parity bits
Redundancy version coding sequences are signaled on HS-SCCH egminus 6 4 0 5 Chase combining (no change in s and r parameters ie same redundancyversion) with four possible constellations
x rv (value) s r b
0 1 0 0
1 0 0 0
2 1 1 1
3 0 1 1
4 1 0 1
5 1 0 2
6 1 0 3
7 1 1 0
Definition of parameter s as for QPSK
b (range 0 to 3) describes constellationrearrangement to averagereliability of bits
Fig 2-27 Signaling of redundancy version parameters r s and b 16QAM case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
UE identity H-RNTI 16 bits
The HSDPA radio network transaction identifier (H-RNTI) unam-
biguously identifies the UE having an HS-PDSCH assignment within
a cell It is allocated to the UE via layer 3 signaling procedures at the
radio bearer setup if the radio bearer is an HSDPA connection This
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HSDPA operation overview and physical channels
value represents a temporary name of the UE used to address it when
scheduling data packets via HS-SCCH
HS-SCCH channel coding
The control information contained in the HS-SCCH is of course pro-
tected with channel coding mechanisms the whole coding chain is
described in Fig 2-28 Fig 2-18 page 48 presents the separation of
the control information into two code blocks which are sent consec-
utively mapped on slot 1 and slot 2 + 3 of one HS-SCCH subframe
This principle is also visible in the coding chain The first control block
consisting of channelization information modulation scheme and UE
identity is coded separately from the remaining control values to enable
the UE receiver to decode this first slot separately and prepare for pos-
sible HS-PDSCH reception The coding steps shown in Fig 2-28 such
as rate matching 1 and 2 are similar to the HS-PDSCH coding chain
and are further described in [TS 25212 Ref 21]
Channelcoding 1
R atematching 1
mux
Channelcoding 2
Ratematching 2
RVcoding
UE-specificCRC attachment
UE-specificmasking
Physical channelmapping
r s b
mux
Channelizationcode set
Modulationscheme
Transport block size information
HARQ processinformation
Redundancy andconstellation version
New data indicator
UE identity
UE identity
Fig 2-28 Channel coding for HS-SCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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High speed dedicated physical control channel (HS-DPCCH)
57
24 High speed dedicated physical control channel (HS-DPCCH)
In an active HSDPA connection the UE has to send acknowledgment ornon-acknowledgment reports (as described in section 13 page 14
where the HARQ process is described) as well as channel status infor-
mation to the network The reporting is performed on this physical
control channel HS-DPCCH
As ubiquitous in HSDPA the uplink is also configured into a subframe
structure of 2 ms corresponding to three slots The first slot of the sub-
frame carries the ACK NACK information the UE sends to the NodeB
while the following two slots ie slot 2 and 3 of the subframe convey
the CQI value the channel quality information to the NodeB
Subframe 0 Subframe i Subframe 4
Tslot
= 2560 chips J The spreading factor of theHS-DPCCH is 256 (10 bits peruplink slot)
J The HS-DPCCH can only existtogether with an UL DPCCH
(ded phys control channel)J The DPDCH (dedicated physical data channel) the DPCCH andthe HS-DPCCH are IQ codemultiplexed
HARQ-ACK CQI = Channel quality information
2 times Tslot
= 5120 chips
One radio frame Tf = 10 ms
One HS-DPCCH subframe 2 ms
Fig 2-29 HS-DPCCH configuration
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The slot format for HS-DPCCH describes a quantity of 30 bits per sub-frame resulting in a data rate of 15 kbps The spreading factor used for
the HS-DPCCH is constant and is always equal to 256 but the chan-
nelization code that is used as well as the mapping on either the I or
Q axis depends on several factors eg the co-existence of an HSDPA
connection with a circuit-switched connection meaning whether a
DPDCH established or not Fig 2-36 page 64 illustrates this IQ
mapping and Fig 2-35 page 63 shows the channelization code used
for HS-DPCCH
The HS-DPCCH builds a logical unit of one subframe but having the
independent control information HARQ-ACK and CQI included which
could be separately decoded at the NodeB Note that the slot carrying
the ACK NACK statement is active only when the UE has been sched-
uled by an HS-PDSCH subframe in the corresponding downlink sub-
frame previously Assuming the UE has not received a transport block
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HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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HSDPA operation overview and physical channels
defined manner or repeating or adding some stuffing bits In HSPA the
rate matching mechanism uses puncturing which provides higher data
throughput The signaled values TBS and RV tell the receiving convo-lutional coder how many and where bits have been punctured This
allows the decoder to insert blank positions which have to be filled later
by performing trellis decoding In other words we may consider the
punctured bits as bit losses created intentionally by the transmitter In
this manner the total amount of data bits can be increased for the sake
of lower redundancy In HSDPA this puncturing scheme will be very
flexible and the NodeB scheduler will set the puncturing rate adapted
to the prevailing RF conditions on the radio channel to obtain the high-
est possible data throughput under the existing conditions The disad-
vantage of adaptive coding is that we need signaling information so
that the transmitter has to inform the receiver about how many soft bits
have been punctured This is seen in Fig 2-26 page 55 in the form
of the redundancy version carried by the HS-SCCH control channel
Fig 2-12 below again depicts the principle of puncturing in HSDPAand clarifies some signaling parameters such as the transport block size
1 1 0 1 1 0 0
11 01 01 00 01 01 11
Transport block sizeInput bits into channel coder
Soft bitsOutput from channel encoder
Rate matchingPuncturing or repeating bits
11 01 01 00 01 01 11
1 01 0 00 0 01 1Coded composite transport bitsCan be several combined streams aftercoding + rate matching
Transport block size FEC
Fig 2-12 Puncturing based on coding example from Fig 2-8 page 37
The process of channel coding starts first with the transport block
size which is given by the size of the input data bit sequence added
by a cyclic redundancy checksum The next step is the channel cod-
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HS-DSCH High speed downlink shared channel transport channel
41
ing which is performed in HSPA by a so-called turbo coder The turbo
coder is a parallel concatenated convolutional coder that exhibits bet-
ter reliability compared to a single convolutional coder Discussingthe functionality of a turbo coder in all of its details would represent a
major digression from the intention of this book Accordingly we will
simply encourage the interested reader to consult the channel coding
literature for more details about turbo coders and their applications
[Ref 10] [Ref 12] Determined by the scheduler of the base station or
the redundancy version to be used the next step known as the redun-
dancy version will either puncture (the most likely) or repeat some of
the bits resulting from the channel coding process How many bits will
be punctured is defined by the coding rate In our example in Fig 2-12
we see that the input bit sequence has a length of 7 bits resulting in
14 soft bits after channel coding with our example coder providing a
coding rate of frac12 The scheduler decided to puncture 4 bits so that we
finally obtain 10 bits which have to be mapped on the physical chan-
nels Our overall coding rate is therefore given as ⁷frasl983089983088 In other words
some bits are protected with redundancy information while othersare not Note that the size of the coded composite transport channel
is determined by the physical layer parameters such as the number of
channelization codes used to convey the HS-PDSCH the modulation
scheme and the transmit time interval which is constant for HSDPA
but can be either 2 or 10 ms for HSUPA Thus its size does not need
to be signaled to the receiver and only the transport block size and the
redundancy versions will be contained in the HS-SCCH channel
222 Incremental redundancy and chase combining
for HS-DSCH
Until now we have presented some general characteristics of HSDPA
and HSUPA which we would now like to discuss in a combined pro-
cedure and then deduce two other principles The HARQ abbreviationcombines an automatic retransmission of erroneous data with a soft
combination at the receiving end A related question can now be how
the transmitter has to repeat the transport block should the retrans-
mission of data occur in an identical retransmission mode or should
some changes in coding parameters eg the manner of puncturing be
applied This question is also important for the implementation of the
rate matching step shown in Fig 2-12 The transmitter has to provide
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42
HSDPA operation overview and physical channels
a certain soft buffer ie a memory that stores the transmitted data for
the sake of possible retransmissions and deletes it after having received
a positive acknowledgment from the receiver Should the transmitternow store the coded composite transport data i e the data after coding
but also after puncturing This would restrict it to repeating the data in
an identical manner A better approach is to store the data after channel
coding and before puncturing Even if this requires more memory it
gives the flexibility to change the puncturing scheme and retransmit the
transport block in a different way Fig 2-13 and Fig 2-14 represent both
mechanisms that are used in HSDPA and HSUPA Identical retransmis-
sion is called chase combining and non-identical retransmission with
a different puncturing scheme is called incremental redundancy The
scheduler in the base station can decide which retransmission scheme
will be used We do not wish to delve into the details of channel coding
theory to discuss which mechanism is the better one ndash chase combin-
ing or incremental redundancy We will only mention that both mech-
anisms have their advantages and thus their applications Chase com-
bining has the advantage that the systematic bits representing the orig-inal data input into the channel coder are contained in the transmit-
ted sequence after puncturing Thus chase combined transport blocks
are ldquoself-decodablerdquo If we consider a situation where the original trans-
port block is lost completely and only the retransmitted block is pres-
ent at the receiver there is a chance to decode the data properly Mean-
while incremental redundancy seems to add more redundancy when
retransmitting but in a scenario where the first transmission contain-ing the systematic bits is lost completely and only the retransmission
is present the receiver will have no chance to decode the data without
having some of the systematic bits Accordingly incremental redun-
dancy is applied whenever sporadic bit errors occur due to a time vari-
ant channel and chase combining is selected whenever we have to deal
with complete transport block errors i e the time variance of the radio
link exhibits some bursted fading dips
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HS-DSCH High speed downlink shared channel transport channel
43
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Chase combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Transmitted bit
Punctured bit
Systematic bits
Parity 1
Parity 2
Systematic bits
Parity 1
Parity 2
Fig 2-13 Chase combining principle
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Incremental redundancy combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Systematic bits
Parity 1
Parity 2
Systematic bitsParity 1
Parity 2
Fig 2-14 Incremental redundancy
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HSDPA operation overview and physical channels
223 Constellation rearrangement
Due to the fact that HSDPA introduces a higher-order modulationscheme (16QAM) we can recognize some effects due to the physi-
cal layer influencing the susceptibility to noisy RF conditions One of
these effects can be explained by looking at the constellation diagram
in the 16QAM modulation scheme see section 12 page 10 As we
recall there is a total of 16 different constellation points given by the
modulation vector and represented by its phase and amplitude Con-
sidering the Euclidean distance which is the distance in this constella-
tion diagram between two neighboring points we can clearly see that
some points have more neighbors than others Especially the four con-
stellation points at the very four corners only have three direct neigh-
bors making them less susceptible to misdetection due to noise shift-
ing them in a certain direction On the other hand the four constella-
tion points representing the inner square of the constellation have eight
direct neighbors each and are therefore more likely to be incorrectly
detected The idea of constellation rearrangement is now to change themapping scheme applied in the original transmission when retrans-
mitting As we know the receiver will soft combine the retransmit-
ted data with the previously received information so we can achieve a
certain incremented redundancy and a certain protection mechanism
Note however that considering a sole transmission of a transport block
using a certain constellation arrangement will not show any more pos-
itive or negative results compared to other constellation arrangementsThe redundancy gain is only achieved by rearranging the constellation
mapping in a retransmitted transport block and performing soft com-
bining at the receiver Overall HSDPA defines four constellation rear-
rangement schemes which are indicated in the redundancy version
field of the HS-SCCH and are represented by the ldquobrdquo bit field ranging
from b = 0 to b = 3 All four constellation schemes are Gray encoded
ie the directly adjacent constellation symbols do not exhibit four com-
pletely different bits in order to reduce the impact of misdetection onbit errors
8122019 hspa_e_lp
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High speed shared control channel (HS-SCCH)
45
Q
I
(ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1) (1 1ndash1ndash1)
(ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1) (1 1ndash1 1)
(ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1) (1ndash1ndash1 1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 0
Q
I
(ndash1 1 1 1) (ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1)
(ndash1 1 1ndash1) (ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1)
(ndash1ndash1 1ndash1) (ndash1ndash1ndash1ndash1) (1ndash1ndash1ndash1) (1ndash1 1ndash1)
(ndash1 1 1 1) (ndash1ndash1ndash1 1) (1ndash1ndash1 1) (1ndash1 1 1)
b = 2
Q
I
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (1ndash1 1 1) (ndash1ndash1 1 1)
(ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1) (ndash1 1 1 1)
(ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1) (ndash1 1 1ndash1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 1
Q
I
(1 1ndash1 1) (ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1)
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1)
(1ndash1ndash1ndash1) (ndash1ndash1ndash1ndash1) (ndash1ndash1 1ndash1) (1ndash1 1ndash1)
(1 1ndash1ndash1) (ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1)
b = 3
Fig 2-15 Constellation rearrangement in HSDPA
23 High speed shared control channel (HS-SCCH)
The HS-SCCH sends scheduling information to the UEs As seen before
the HS-PDSCH has a very flexible configuration for physical parame-
ters such as the coding rate number of code channels or retransmis-sions This high flexibility increases the complexity and engenders the
need for additional signaling information transferred on the HS-SCCH
Reception of user data in HSDPA is always a two-step procedure
First the receiver has to capture the scheduling control information
and afterwards based on the received control information it may start
demodulating and decoding the HS-PDSCH containing the user data
This two-step procedure is shown in Fig 2-16 below which lists what
kind of control information is sent to the UEs via the HS-SCCH Asshown in Fig 2-2 page 28 which describes the overall HSDPA chan-
nel structure there can be up to four HS-SCCHs assigned to one UE
But only one HS-SCCH would contain the scheduling information for
this UE within one TTI Thus the network can assign resources simul-
taneously to various UEs in the downlink direction
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HSDPA operation overview and physical channels
I would like to receive databut I dont know where myHS-PDSCH resources areand what they look like
HS-SCCH
Read the 1st HS-SCCH slotfor HS-DSCH channelizationcodes UE identity and
modulation scheme
Then the 2nd and 3rd HS-SCCHslots provide transport block sizeinformation hybrid ARQ process in-formation redundancy constellationversion new data indicator
HS-PDSCH
Fig 2-16 HS-SCCH control channel usage
Regarding the physical layer parameters we see in Fig 2-17 that the
HS-SCCH uses a channelization code with a spreading factor of 128
and it also uses the newly introduced transmit time interval of one sub-
frame which is equal to 2 ms It should be mentioned that the spread-ing factor of 128 requires double the capacity compared to similar con-
trol channels in WCDMA Release 99 reflecting the signaling overhead
needed to guarantee the huge flexibility introduced with HSDPA Addi-
tionally Fig 2-16 shows that the control information is sent consecu-
tively within one subframe The first slot within this subframe contains
the control information UE identity channelization code information
and modulation scheme identifier Slots 2 and 3 of the subframe con-tain the remaining control information Transport block size HARQ
process identifier redundancy version and new data indicator Conse-
quently the UE can self-decode slot 1 alone and slots 2 and 3 in a sec-
ond step even if they represent one logical unit This raw control infor-
mation is of course also channel coded using a turbo and on the phys-
ical layer the quantity of bits after the rate matching step is 40 bits con-
veyed in one slot corresponding to 666 micros [TS 25212 Ref 21] see also
Fig 2-28 page 56
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High speed shared control channel (HS-SCCH)
47
The HS-SCCH is a fixed rate (60 kbps SF = 128) downlinkphysical channel used to carry downlink signaling related toHS-DSCH transmission
Slot 0
Slot 1
Slot 2
Tslot
= 2560 chips
Data = 40 bits
1 subframe = 2 ms
Fig 2-17 Structure of High speed shared control channel HS-SCCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
We would like to return now to the time consecutive transmission of
control information There is a difference in the control information
in terms of its priority Some information is needed at the UE end
very urgently while other control information does not have such a
high priority But why This will be explained by looking at some tim-ing aspects defined for HSDPA If we consider the timing between
the shared data channel HS-PDSCH and the shared control chan-
nel HS-SCCH as shown in Fig 2-18 we see that the HS-PDSCH fol-
lows the HS-SCCH by exactly two slots or 5120 chips The HS-SCCH
is completely time-aligned with the general control channels CPICH
and P-CCPCH of the NodeB This is mandatory because it is a shared
channel Consider several UEs with different distances to the NodeBwanting to receive the HS-SCCH channel Thus it must have constant
timing that is known a priori The shared data channel HS-PDSCH is
now transmitted exactly 5120 chips after the first chip of the HS-SCCH
This leads to an overlapping slot thereby requiring multitasking recep-
tion at the UE end While the UE is still receiving the last slot of an
ongoing HS-SCCH subframe it may already start the reception of an
HS-PDSCH transport block The first slot in the HS-SCCH subframe
now contains information required by the physical layer to performdespreading and demodulation These values are the UE identity indi-
cating whether the UE will start demodulation of the HS-PDSCH or
not in case it is not scheduled the modulation scheme information
since the UE has to know how to interpret the received constellation
vector and whether it has to be considered as a QPSK or 16QAM con-
stellation point and finally the UE has to know which channelization
codes it has to apply to capture the HS-PDSCH transport block The
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48
HSDPA operation overview and physical channels
overall UE reaction time when being scheduled is now seen as 1 slot
or 2560 chips This tough requirement for the UEs is due to the objec-
tive to obtain overall a much shorter latency than legacy standards Theadditional control information such as the new data indicator redun-
dancy version and transport block size is not that urgent since it is
needed after demodulation but before channel decoding So first the
UE will sample the whole three slots of the HS-PDSCH and demodu-
late them into a bit stream which is finally handed over to the channel
decoder This principle is known as post-processing and is used typi-
cally in mobile communications technologies
J Start of HS-SCCH subframe 0 is aligned with startof P-CCPCH frames
J The HS-PDSCH starts
τ HS-PDSCH
(2times Tslot
= 5120 chips)
after the start of the HS-SCCH
UE identity etc
processing timeof receiver
HS-DSCH subframe
3 times Tslot= 7680 chips
3 times Tslot
= 7680 chips
τ HS-PDSCH
(2times Tslot
= 5120 chips)
HS-SCCH
HS-PDSCH
Fig 2-18 Timing relation between HS-SCCH and HS-PDSCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
Content of the HS-SCCH control channelThe control information contained in the HS-SCCH control chan-
nel has already been mentioned so we will now consider the values
in more detail We will begin with an overview of what kind of control
information is contained in the HS-SCCH channel before proceeding
with further details about the single control elements The following
control information is present in the HS-SCCH [TS 25212 Ref 21]
Channelization code set information (7 bits)
Modulation scheme information (1 bit) Transport block size information (6 bits)
Hybrid ARQ process information (3 bits)
Redundancy and constellation version (3 bits)
New data indicator (1 bit)
UE identity (16 bits) = H-RNTI
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High speed shared control channel (HS-SCCH)
49
Some of these parameters are more or less self-explanatory while oth-
ers require additional background information and closer examination
Modulation scheme information 1 bit
This single bit is used to inform the receiver whether the modulation
scheme QPSK or 16QAM is applied on the data channel HS-PDSCH
The interpretation of the bit x ms1 is as follows
ms1
x
if QPSK
otherwise
0
1
=
New data indicator 1 bit
The new data indicator bit field informs the receiving entity that the
prevailing PDU transmitted by the current HARQ process is either a
retransmission or contains new data This is done by setting the new
data bit to the value 0 for the first PDU on this particular HARQ process
and incrementing the value by 1 with every new data sent [TS 25321Ref 30] This leads to a toggled value In case the new data bit is not
incremented ie if it remains at its previous value it is an indicator for
retransmission
1st PDU of this
HARQ process
NDI = New data indicator
NDI = 0 NDI = 1
NACK
NDI = 1
ACK
NDI = 0
HS-SCCH HS-SCCH HS-SCCHHS-SCCH
ACK
Fig 2-19 New data indicator bit principle of incrementing value
Channelization code set information 7 bits
This field is used to indicate the number of channelization codes usedfor transmitting the transport block on the HS-PDSCH As was already
described the spreading factor applied on the HS-PDSCH is constant
with a value of 16 but the flexible values are the number of channeliza-
tion codes forming a cluster when using multiple codes and their posi-
tion in the code tree It is not allowed to distribute the code channels
over the code tree diagram For the sake of simplicity in signaling sev-
eral channelization codes form one cluster and these codes are con-
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HSDPA operation overview and physical channels
tiguous in the channelization code tree [TS 25213 Ref 22] Fig 2-20
illustrates the principle of indicating the channelization codes on the
HS-SCCH
SF = 16
Code ldquo0rdquo isreserved forcommonchannels
Code offset 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15P = 5O = 7
Code group indicatorx
ccs1 x
ccs2 x
ccs3 = min (Pminus 1 15 minusP)
Code offset indicatorx
ccs4 x
ccs5 x
ccs6 x
ccs7 = |Ominus 1minus P8 times15|
A cluster of codes
can be allocated to a UEC
ch16Ohellip C
ch16O + P minus 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1
2 2 2 2 2 2 2 2 2 2 2 2 2 2 14 14
1 2 3 4 5 6 7 8 9 10 11 12 13 14 2 1
3 3 3 3 3 3 3 3 3 3 3 3 3 13 13 13
1 2 3 4 5 6 7 8 9 10 11 12 13 3 2 1
4 4 4 4 4 4 4 4 4 4 4 4 12 12 12 121 2 3 4 5 6 7 8 9 10 11 12 4 3 2 1
5 5 5 5 5 5 5 5 5 5 5 11 11 11 11 11
1 2 3 4 5 6 7 8 9 10 11 5 4 3 2 1
6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10
1 2 3 4 5 6 7 8 9 10 6 5 4 3 2 1
7 7 7 7 7 7 7 7 7 9 9 9 9 9 9 9
1 2 3 4 5 6 7 8 9 7 6 5 4 3 2 1
8 8 8 8 8 8 8 8
8 7 6 5 4 3 2 1
0 (115)
1 (214)
2 (313)
3 (412)
4 (511)
5 (610)
6 (79)
7 (88) Redundant area
C l u s t e r c o d e i n d i c a t o r ( 3 b i t s )
Tree offset indicator (4 bits)
Signaled on HS-SCCH
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
PO
Decoding notation
Number ofmulti-codes
Offset fromleft right incode tree (SF = 16)
Fig 2-20 Channelization code set indicating the HS-PDSCH code cluster
The idea behind the code indication is a matrix with the rows repre-
senting the number of codes per cluster and the columns represent-
ing the position of that cluster the offset value in the code tree Recall-
ing that the maximum number of channelization codes per clusteris 15 and if the cluster size is 1 the offset values can also range from
1 to 15 the resulting matrix would have 15 rows and 15 columns Since
we know that four bits are needed to represent an integer from 1 to 15
we need a total of 4 + 4 = 8 bits for representation of the channeliza-
tion code set information It is a smart idea to save one bit The 15 times 15
matrix would contain much redundant information By way of analogy
like in a road map indicating distances between cities A table showing
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High speed shared control channel (HS-SCCH)
51
the distance from city A to city B the opposite distance from city B to
city A is redundant information The useful information has the form
of a triangle The idea is to cut the lower part rotate it and append itto the spare part of the upper table In this manner a table is obtained
with 7 rows and 15 columns and it is possible to indicate each position
in it with just 7 bits
1 5 r o w s 7
r o w s
Matrix reduction for channeli-
zation code set information
15 columns
Fig 2-21 Matrix size reduction for channelization code set information
The content of the channelization code set matrix can be described as
a value with two numbers The upper number is the number of mul-
ticodes forming one cluster and the lower number is the offset in the
channelization code tree Accordingly the example in Fig 2-20 can be
interpreted to mean the HS-SCCH sends the bits as row number 4 and
column number 6 in the matrix The content of this element are the
values 5 over 7 which have to be interpreted as a cluster size of 5 codesand an offset of 7
Transport block size information 6 bits
With a length of six bits the transport block size (TBS) informa-
tion informs the receiving UE entity about the data block size of the
transport block sent on the HS-PDSCH We should keep in mind the
link adaptation performed with the adaptive modulation and coding
scheme that was described in section 12 page 10 The ratio errorcorrection and user data are flexible while the physical layer param-
eters such as the spreading factor modulation scheme and number of
channelization codes determine the physical block size This physical
block consists of the user data ratio or transport block size and the for-
ward error correction or redundancy information As this ratio is flex-
ible the HS-SCCH will inform the receiving UE entity about the size
of the transport block Here too there is a strategy of bit reduction the
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HSDPA operation overview and physical channels
goal is to inform the receiver with as few bits as possible A non-effi-
cient approach would involve conversion of the decimal number repre-
senting the TBS into a binary sequence but the number of bits neededwould exceed the space available on the HS-SCCH Imagine that the
range of transport block sizes depends on the physical layer condi-
tions The ambient physical layer parameters modulation scheme and
number of channelization codes set a certain working point where the
remaining flexibility for a different TBS configuration can be obtained
by more or less puncturing resulting in a flexible ratio between for-
ward error correction and user data This will lead to a two-step proce-
dure when evaluating the transport block size First the receiver exam-
ines the information modulation scheme and number of channeliza-
tion codes scheduled via HS-SCCH which indicate the value k0 l as
shown in Fig 2-22 The 6-bit HS-SCCH control parameter transport
block size information will be the transport format resource indica-
tor (TFRI) named ki Let k t be the sum of the two values kt = ki + k0i
Both values kt and k0 i can be obtained from tables given by [TS 25321
Ref 30] The range for the TFRI is from 1 to 256 and the derived trans-port block size ranges from 137 bits to 27 952 bits The first table indi-
cates the value k 0 i based on the channelization code and the modula-
tion scheme
Combination i Modulation scheme Number of channelization codes k0 i
0
QPSK
1 1
1 2 40
2 3 633 4 79
4 5 92
5 6 102
Fig 2-22 Extract from TS 25321 table representing k0 i
The second table indicates the final transport block size based on kt
Index TB size Index TB size Index TB size1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
4 173 89 1456 174 6673
5 185 90 1483 175 6793
6 197 91 1509 176 6916
7 209 92 1537 177 7041
Fig 2-23 Extract from TS 25321 table representing kt
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High speed shared control channel (HS-SCCH)
53
J The transport block size used on HS-DSCH is not signaled explicitly on HS-SCCHJ Instead a transport block size index k
i is signaled to indicate the transport block size
First stepModulation scheme andnumber of channelizationcodes as signaled on HS-SCCHdetermine value k
0 i
Second step
Index kt = k
i + k
0i
determines HS-DSCH
transport block size
kt = k
i + k
0i
Table according to 3GPP TS 25321 extract from QPSK section
Table according to 3GPP TS 25321 254 entries in total
Combination i Modulation
scheme
Number of
channelization codes
k0 i
0
QPSK
1 1
1 2 40
2 3 63
3 4 79
4 hellip hellip
Index TB size Index TB size Index TB size
1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
helliphellip hellip hellip hellip hellip
Fig 2-24 Retrieval of transport block size information
Source Fig 2-22 to Fig 2-24 [TS 25321 Ref 30] reproduced by permission of 3GPP
Hybrid ARQ process information 3 bits
The concept behind the hybrid automatic repeat request (HARQ) was
introduced in section 13 page 14 One feature is the possibility of
multitasking ie having several HARQ processes activated at the same
time Fig 2-25 below shows the need to signal the process identity tothe receiver Remember that on the downlink there is a shared chan-
nel concept so the NodeB can flexibly decide which UE will be sched-
uled with a downlink transport block Up to eight HARQ processes
can be signaled via higher layers to one UE Note however that due to
the round-trip timing six HARQ processes must be active to achieve
the maximum throughput as shown in Fig 2-51 page 79 Compared
with HSUPA the HARQ processes on the downlink are asynchronous
so they have to be indicated but on the uplink they are synchronous sothey do not need to be signaled explicitly
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HSDPA operation overview and physical channels
Asynchronous DL minus Synchronous ULNumber of H-ARQ rocesses = 1 to 8 er UE
UL HS-DPCCH UE1
UE1 HARQ processes 1 to 4
3 4 1 42 11 1 32retrans
2
A N A A
A A
N A
UL HS-DPCCH UE2
HS-PDSCH
UE2 HARQ processes 1 to 2
Fig 2-25 HARQ process indication on HS-SCCH
Fig 2-25 shows a typical situation on the downlink (point-to-multi-
point) The NodeB sends data to several UEs sharing the HS-PDSCH
so therefore the HARQ process is asynchronous The time when a
transport block is retransmitted is not fixed For this reason the pro-
cess identifier is signaled on the HS-SCCH Based on the HARQ pro-
cess identity and the new data indicator bit the receiving entity knows
which part of the soft buffer memory has to be used in case of soft com-bining On the uplink the situation is slightly simpler The UE only
communicates with one NodeB so it is a point-to-point connection
Thus retransmission always occurs at a fixed time linked to the origi-
nal transmission
Redundancy and constellation version 3 bits
Adaptive modulation and coding involve flexible selection of modula-tion and coding schemes that are signaled to the receiving UE via the
parameters transport block size and modulation scheme information
Another concept used in HSDPA was previously discussed Chase com-
bining or incremental redundancy (see section 222 page 41) This
means that in case of retransmission the transmit entity can dynami-
cally select another puncturing scheme or keep the puncturing as it was
in the original transmission The applied puncturing scheme is signaled
as redundancy information to the receiver Additionally in case of the16QAM modulation scheme the transmitter can select another constel-
lation arrangement which is also signaled to the UE with the three bits
for the redundancy and constellation version see Fig 2-15 page 45
Depending on the modulation scheme (QPSK or 16QAM) there are
two different tables indicating the parameters ldquosrdquo ldquorrdquo and ldquobrdquo The
parameters ldquosrdquo and ldquorrdquo indicate which scheme is used for puncturing
ie if the puncturing mechanism prioritizes the systematic bits or not
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High speed shared control channel (HS-SCCH)
55
and which puncturing algorithm is used The parameter ldquobrdquo indicates
the constellation mapping version The receiver needs this information
to perform proper demodulation and decoding
Initial transmission
1st retransmission
2nd retransmission
3rd retransmission
r
0
0
1
1
2
2
3
xrv
(value)
s
0 1
1 0
2 1
3 0
4 1
5 0
6 1
7 0 3
s = 1 Systematic bits are prioritizeds = 0 Non-systematic bits are prioritized
r (range 0 to 3 for QPSK) influencesJ Input parameter for puncturing or (together with s) for repetition algorithm defined in TS 25212J Selection of parity bits
Redundancy version coding sequences are signaled on HS-SCCH egndash 0 2 5 6 One initial transmission + 3 retransmissions with different r and s parameters
Fig 2-26 Signaling of redundancy version parameters r and s QPSK case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
Initial transmission
2nd retransmission
1st retransmission
3rd retransmission
r (range 0 to 1 for 16QAM)influences input parameterfor puncturing or (togetherwith s) for repetitionalgorithm defined in
TS 25212 and thus selectionof parity bits
Redundancy version coding sequences are signaled on HS-SCCH egminus 6 4 0 5 Chase combining (no change in s and r parameters ie same redundancyversion) with four possible constellations
x rv (value) s r b
0 1 0 0
1 0 0 0
2 1 1 1
3 0 1 1
4 1 0 1
5 1 0 2
6 1 0 3
7 1 1 0
Definition of parameter s as for QPSK
b (range 0 to 3) describes constellationrearrangement to averagereliability of bits
Fig 2-27 Signaling of redundancy version parameters r s and b 16QAM case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
UE identity H-RNTI 16 bits
The HSDPA radio network transaction identifier (H-RNTI) unam-
biguously identifies the UE having an HS-PDSCH assignment within
a cell It is allocated to the UE via layer 3 signaling procedures at the
radio bearer setup if the radio bearer is an HSDPA connection This
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HSDPA operation overview and physical channels
value represents a temporary name of the UE used to address it when
scheduling data packets via HS-SCCH
HS-SCCH channel coding
The control information contained in the HS-SCCH is of course pro-
tected with channel coding mechanisms the whole coding chain is
described in Fig 2-28 Fig 2-18 page 48 presents the separation of
the control information into two code blocks which are sent consec-
utively mapped on slot 1 and slot 2 + 3 of one HS-SCCH subframe
This principle is also visible in the coding chain The first control block
consisting of channelization information modulation scheme and UE
identity is coded separately from the remaining control values to enable
the UE receiver to decode this first slot separately and prepare for pos-
sible HS-PDSCH reception The coding steps shown in Fig 2-28 such
as rate matching 1 and 2 are similar to the HS-PDSCH coding chain
and are further described in [TS 25212 Ref 21]
Channelcoding 1
R atematching 1
mux
Channelcoding 2
Ratematching 2
RVcoding
UE-specificCRC attachment
UE-specificmasking
Physical channelmapping
r s b
mux
Channelizationcode set
Modulationscheme
Transport block size information
HARQ processinformation
Redundancy andconstellation version
New data indicator
UE identity
UE identity
Fig 2-28 Channel coding for HS-SCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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High speed dedicated physical control channel (HS-DPCCH)
57
24 High speed dedicated physical control channel (HS-DPCCH)
In an active HSDPA connection the UE has to send acknowledgment ornon-acknowledgment reports (as described in section 13 page 14
where the HARQ process is described) as well as channel status infor-
mation to the network The reporting is performed on this physical
control channel HS-DPCCH
As ubiquitous in HSDPA the uplink is also configured into a subframe
structure of 2 ms corresponding to three slots The first slot of the sub-
frame carries the ACK NACK information the UE sends to the NodeB
while the following two slots ie slot 2 and 3 of the subframe convey
the CQI value the channel quality information to the NodeB
Subframe 0 Subframe i Subframe 4
Tslot
= 2560 chips J The spreading factor of theHS-DPCCH is 256 (10 bits peruplink slot)
J The HS-DPCCH can only existtogether with an UL DPCCH
(ded phys control channel)J The DPDCH (dedicated physical data channel) the DPCCH andthe HS-DPCCH are IQ codemultiplexed
HARQ-ACK CQI = Channel quality information
2 times Tslot
= 5120 chips
One radio frame Tf = 10 ms
One HS-DPCCH subframe 2 ms
Fig 2-29 HS-DPCCH configuration
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The slot format for HS-DPCCH describes a quantity of 30 bits per sub-frame resulting in a data rate of 15 kbps The spreading factor used for
the HS-DPCCH is constant and is always equal to 256 but the chan-
nelization code that is used as well as the mapping on either the I or
Q axis depends on several factors eg the co-existence of an HSDPA
connection with a circuit-switched connection meaning whether a
DPDCH established or not Fig 2-36 page 64 illustrates this IQ
mapping and Fig 2-35 page 63 shows the channelization code used
for HS-DPCCH
The HS-DPCCH builds a logical unit of one subframe but having the
independent control information HARQ-ACK and CQI included which
could be separately decoded at the NodeB Note that the slot carrying
the ACK NACK statement is active only when the UE has been sched-
uled by an HS-PDSCH subframe in the corresponding downlink sub-
frame previously Assuming the UE has not received a transport block
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HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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HS-DSCH High speed downlink shared channel transport channel
41
ing which is performed in HSPA by a so-called turbo coder The turbo
coder is a parallel concatenated convolutional coder that exhibits bet-
ter reliability compared to a single convolutional coder Discussingthe functionality of a turbo coder in all of its details would represent a
major digression from the intention of this book Accordingly we will
simply encourage the interested reader to consult the channel coding
literature for more details about turbo coders and their applications
[Ref 10] [Ref 12] Determined by the scheduler of the base station or
the redundancy version to be used the next step known as the redun-
dancy version will either puncture (the most likely) or repeat some of
the bits resulting from the channel coding process How many bits will
be punctured is defined by the coding rate In our example in Fig 2-12
we see that the input bit sequence has a length of 7 bits resulting in
14 soft bits after channel coding with our example coder providing a
coding rate of frac12 The scheduler decided to puncture 4 bits so that we
finally obtain 10 bits which have to be mapped on the physical chan-
nels Our overall coding rate is therefore given as ⁷frasl983089983088 In other words
some bits are protected with redundancy information while othersare not Note that the size of the coded composite transport channel
is determined by the physical layer parameters such as the number of
channelization codes used to convey the HS-PDSCH the modulation
scheme and the transmit time interval which is constant for HSDPA
but can be either 2 or 10 ms for HSUPA Thus its size does not need
to be signaled to the receiver and only the transport block size and the
redundancy versions will be contained in the HS-SCCH channel
222 Incremental redundancy and chase combining
for HS-DSCH
Until now we have presented some general characteristics of HSDPA
and HSUPA which we would now like to discuss in a combined pro-
cedure and then deduce two other principles The HARQ abbreviationcombines an automatic retransmission of erroneous data with a soft
combination at the receiving end A related question can now be how
the transmitter has to repeat the transport block should the retrans-
mission of data occur in an identical retransmission mode or should
some changes in coding parameters eg the manner of puncturing be
applied This question is also important for the implementation of the
rate matching step shown in Fig 2-12 The transmitter has to provide
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HSDPA operation overview and physical channels
a certain soft buffer ie a memory that stores the transmitted data for
the sake of possible retransmissions and deletes it after having received
a positive acknowledgment from the receiver Should the transmitternow store the coded composite transport data i e the data after coding
but also after puncturing This would restrict it to repeating the data in
an identical manner A better approach is to store the data after channel
coding and before puncturing Even if this requires more memory it
gives the flexibility to change the puncturing scheme and retransmit the
transport block in a different way Fig 2-13 and Fig 2-14 represent both
mechanisms that are used in HSDPA and HSUPA Identical retransmis-
sion is called chase combining and non-identical retransmission with
a different puncturing scheme is called incremental redundancy The
scheduler in the base station can decide which retransmission scheme
will be used We do not wish to delve into the details of channel coding
theory to discuss which mechanism is the better one ndash chase combin-
ing or incremental redundancy We will only mention that both mech-
anisms have their advantages and thus their applications Chase com-
bining has the advantage that the systematic bits representing the orig-inal data input into the channel coder are contained in the transmit-
ted sequence after puncturing Thus chase combined transport blocks
are ldquoself-decodablerdquo If we consider a situation where the original trans-
port block is lost completely and only the retransmitted block is pres-
ent at the receiver there is a chance to decode the data properly Mean-
while incremental redundancy seems to add more redundancy when
retransmitting but in a scenario where the first transmission contain-ing the systematic bits is lost completely and only the retransmission
is present the receiver will have no chance to decode the data without
having some of the systematic bits Accordingly incremental redun-
dancy is applied whenever sporadic bit errors occur due to a time vari-
ant channel and chase combining is selected whenever we have to deal
with complete transport block errors i e the time variance of the radio
link exhibits some bursted fading dips
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HS-DSCH High speed downlink shared channel transport channel
43
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Chase combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Transmitted bit
Punctured bit
Systematic bits
Parity 1
Parity 2
Systematic bits
Parity 1
Parity 2
Fig 2-13 Chase combining principle
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Incremental redundancy combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Systematic bits
Parity 1
Parity 2
Systematic bitsParity 1
Parity 2
Fig 2-14 Incremental redundancy
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HSDPA operation overview and physical channels
223 Constellation rearrangement
Due to the fact that HSDPA introduces a higher-order modulationscheme (16QAM) we can recognize some effects due to the physi-
cal layer influencing the susceptibility to noisy RF conditions One of
these effects can be explained by looking at the constellation diagram
in the 16QAM modulation scheme see section 12 page 10 As we
recall there is a total of 16 different constellation points given by the
modulation vector and represented by its phase and amplitude Con-
sidering the Euclidean distance which is the distance in this constella-
tion diagram between two neighboring points we can clearly see that
some points have more neighbors than others Especially the four con-
stellation points at the very four corners only have three direct neigh-
bors making them less susceptible to misdetection due to noise shift-
ing them in a certain direction On the other hand the four constella-
tion points representing the inner square of the constellation have eight
direct neighbors each and are therefore more likely to be incorrectly
detected The idea of constellation rearrangement is now to change themapping scheme applied in the original transmission when retrans-
mitting As we know the receiver will soft combine the retransmit-
ted data with the previously received information so we can achieve a
certain incremented redundancy and a certain protection mechanism
Note however that considering a sole transmission of a transport block
using a certain constellation arrangement will not show any more pos-
itive or negative results compared to other constellation arrangementsThe redundancy gain is only achieved by rearranging the constellation
mapping in a retransmitted transport block and performing soft com-
bining at the receiver Overall HSDPA defines four constellation rear-
rangement schemes which are indicated in the redundancy version
field of the HS-SCCH and are represented by the ldquobrdquo bit field ranging
from b = 0 to b = 3 All four constellation schemes are Gray encoded
ie the directly adjacent constellation symbols do not exhibit four com-
pletely different bits in order to reduce the impact of misdetection onbit errors
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High speed shared control channel (HS-SCCH)
45
Q
I
(ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1) (1 1ndash1ndash1)
(ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1) (1 1ndash1 1)
(ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1) (1ndash1ndash1 1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 0
Q
I
(ndash1 1 1 1) (ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1)
(ndash1 1 1ndash1) (ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1)
(ndash1ndash1 1ndash1) (ndash1ndash1ndash1ndash1) (1ndash1ndash1ndash1) (1ndash1 1ndash1)
(ndash1 1 1 1) (ndash1ndash1ndash1 1) (1ndash1ndash1 1) (1ndash1 1 1)
b = 2
Q
I
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (1ndash1 1 1) (ndash1ndash1 1 1)
(ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1) (ndash1 1 1 1)
(ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1) (ndash1 1 1ndash1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 1
Q
I
(1 1ndash1 1) (ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1)
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1)
(1ndash1ndash1ndash1) (ndash1ndash1ndash1ndash1) (ndash1ndash1 1ndash1) (1ndash1 1ndash1)
(1 1ndash1ndash1) (ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1)
b = 3
Fig 2-15 Constellation rearrangement in HSDPA
23 High speed shared control channel (HS-SCCH)
The HS-SCCH sends scheduling information to the UEs As seen before
the HS-PDSCH has a very flexible configuration for physical parame-
ters such as the coding rate number of code channels or retransmis-sions This high flexibility increases the complexity and engenders the
need for additional signaling information transferred on the HS-SCCH
Reception of user data in HSDPA is always a two-step procedure
First the receiver has to capture the scheduling control information
and afterwards based on the received control information it may start
demodulating and decoding the HS-PDSCH containing the user data
This two-step procedure is shown in Fig 2-16 below which lists what
kind of control information is sent to the UEs via the HS-SCCH Asshown in Fig 2-2 page 28 which describes the overall HSDPA chan-
nel structure there can be up to four HS-SCCHs assigned to one UE
But only one HS-SCCH would contain the scheduling information for
this UE within one TTI Thus the network can assign resources simul-
taneously to various UEs in the downlink direction
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HSDPA operation overview and physical channels
I would like to receive databut I dont know where myHS-PDSCH resources areand what they look like
HS-SCCH
Read the 1st HS-SCCH slotfor HS-DSCH channelizationcodes UE identity and
modulation scheme
Then the 2nd and 3rd HS-SCCHslots provide transport block sizeinformation hybrid ARQ process in-formation redundancy constellationversion new data indicator
HS-PDSCH
Fig 2-16 HS-SCCH control channel usage
Regarding the physical layer parameters we see in Fig 2-17 that the
HS-SCCH uses a channelization code with a spreading factor of 128
and it also uses the newly introduced transmit time interval of one sub-
frame which is equal to 2 ms It should be mentioned that the spread-ing factor of 128 requires double the capacity compared to similar con-
trol channels in WCDMA Release 99 reflecting the signaling overhead
needed to guarantee the huge flexibility introduced with HSDPA Addi-
tionally Fig 2-16 shows that the control information is sent consecu-
tively within one subframe The first slot within this subframe contains
the control information UE identity channelization code information
and modulation scheme identifier Slots 2 and 3 of the subframe con-tain the remaining control information Transport block size HARQ
process identifier redundancy version and new data indicator Conse-
quently the UE can self-decode slot 1 alone and slots 2 and 3 in a sec-
ond step even if they represent one logical unit This raw control infor-
mation is of course also channel coded using a turbo and on the phys-
ical layer the quantity of bits after the rate matching step is 40 bits con-
veyed in one slot corresponding to 666 micros [TS 25212 Ref 21] see also
Fig 2-28 page 56
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High speed shared control channel (HS-SCCH)
47
The HS-SCCH is a fixed rate (60 kbps SF = 128) downlinkphysical channel used to carry downlink signaling related toHS-DSCH transmission
Slot 0
Slot 1
Slot 2
Tslot
= 2560 chips
Data = 40 bits
1 subframe = 2 ms
Fig 2-17 Structure of High speed shared control channel HS-SCCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
We would like to return now to the time consecutive transmission of
control information There is a difference in the control information
in terms of its priority Some information is needed at the UE end
very urgently while other control information does not have such a
high priority But why This will be explained by looking at some tim-ing aspects defined for HSDPA If we consider the timing between
the shared data channel HS-PDSCH and the shared control chan-
nel HS-SCCH as shown in Fig 2-18 we see that the HS-PDSCH fol-
lows the HS-SCCH by exactly two slots or 5120 chips The HS-SCCH
is completely time-aligned with the general control channels CPICH
and P-CCPCH of the NodeB This is mandatory because it is a shared
channel Consider several UEs with different distances to the NodeBwanting to receive the HS-SCCH channel Thus it must have constant
timing that is known a priori The shared data channel HS-PDSCH is
now transmitted exactly 5120 chips after the first chip of the HS-SCCH
This leads to an overlapping slot thereby requiring multitasking recep-
tion at the UE end While the UE is still receiving the last slot of an
ongoing HS-SCCH subframe it may already start the reception of an
HS-PDSCH transport block The first slot in the HS-SCCH subframe
now contains information required by the physical layer to performdespreading and demodulation These values are the UE identity indi-
cating whether the UE will start demodulation of the HS-PDSCH or
not in case it is not scheduled the modulation scheme information
since the UE has to know how to interpret the received constellation
vector and whether it has to be considered as a QPSK or 16QAM con-
stellation point and finally the UE has to know which channelization
codes it has to apply to capture the HS-PDSCH transport block The
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HSDPA operation overview and physical channels
overall UE reaction time when being scheduled is now seen as 1 slot
or 2560 chips This tough requirement for the UEs is due to the objec-
tive to obtain overall a much shorter latency than legacy standards Theadditional control information such as the new data indicator redun-
dancy version and transport block size is not that urgent since it is
needed after demodulation but before channel decoding So first the
UE will sample the whole three slots of the HS-PDSCH and demodu-
late them into a bit stream which is finally handed over to the channel
decoder This principle is known as post-processing and is used typi-
cally in mobile communications technologies
J Start of HS-SCCH subframe 0 is aligned with startof P-CCPCH frames
J The HS-PDSCH starts
τ HS-PDSCH
(2times Tslot
= 5120 chips)
after the start of the HS-SCCH
UE identity etc
processing timeof receiver
HS-DSCH subframe
3 times Tslot= 7680 chips
3 times Tslot
= 7680 chips
τ HS-PDSCH
(2times Tslot
= 5120 chips)
HS-SCCH
HS-PDSCH
Fig 2-18 Timing relation between HS-SCCH and HS-PDSCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
Content of the HS-SCCH control channelThe control information contained in the HS-SCCH control chan-
nel has already been mentioned so we will now consider the values
in more detail We will begin with an overview of what kind of control
information is contained in the HS-SCCH channel before proceeding
with further details about the single control elements The following
control information is present in the HS-SCCH [TS 25212 Ref 21]
Channelization code set information (7 bits)
Modulation scheme information (1 bit) Transport block size information (6 bits)
Hybrid ARQ process information (3 bits)
Redundancy and constellation version (3 bits)
New data indicator (1 bit)
UE identity (16 bits) = H-RNTI
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High speed shared control channel (HS-SCCH)
49
Some of these parameters are more or less self-explanatory while oth-
ers require additional background information and closer examination
Modulation scheme information 1 bit
This single bit is used to inform the receiver whether the modulation
scheme QPSK or 16QAM is applied on the data channel HS-PDSCH
The interpretation of the bit x ms1 is as follows
ms1
x
if QPSK
otherwise
0
1
=
New data indicator 1 bit
The new data indicator bit field informs the receiving entity that the
prevailing PDU transmitted by the current HARQ process is either a
retransmission or contains new data This is done by setting the new
data bit to the value 0 for the first PDU on this particular HARQ process
and incrementing the value by 1 with every new data sent [TS 25321Ref 30] This leads to a toggled value In case the new data bit is not
incremented ie if it remains at its previous value it is an indicator for
retransmission
1st PDU of this
HARQ process
NDI = New data indicator
NDI = 0 NDI = 1
NACK
NDI = 1
ACK
NDI = 0
HS-SCCH HS-SCCH HS-SCCHHS-SCCH
ACK
Fig 2-19 New data indicator bit principle of incrementing value
Channelization code set information 7 bits
This field is used to indicate the number of channelization codes usedfor transmitting the transport block on the HS-PDSCH As was already
described the spreading factor applied on the HS-PDSCH is constant
with a value of 16 but the flexible values are the number of channeliza-
tion codes forming a cluster when using multiple codes and their posi-
tion in the code tree It is not allowed to distribute the code channels
over the code tree diagram For the sake of simplicity in signaling sev-
eral channelization codes form one cluster and these codes are con-
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HSDPA operation overview and physical channels
tiguous in the channelization code tree [TS 25213 Ref 22] Fig 2-20
illustrates the principle of indicating the channelization codes on the
HS-SCCH
SF = 16
Code ldquo0rdquo isreserved forcommonchannels
Code offset 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15P = 5O = 7
Code group indicatorx
ccs1 x
ccs2 x
ccs3 = min (Pminus 1 15 minusP)
Code offset indicatorx
ccs4 x
ccs5 x
ccs6 x
ccs7 = |Ominus 1minus P8 times15|
A cluster of codes
can be allocated to a UEC
ch16Ohellip C
ch16O + P minus 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1
2 2 2 2 2 2 2 2 2 2 2 2 2 2 14 14
1 2 3 4 5 6 7 8 9 10 11 12 13 14 2 1
3 3 3 3 3 3 3 3 3 3 3 3 3 13 13 13
1 2 3 4 5 6 7 8 9 10 11 12 13 3 2 1
4 4 4 4 4 4 4 4 4 4 4 4 12 12 12 121 2 3 4 5 6 7 8 9 10 11 12 4 3 2 1
5 5 5 5 5 5 5 5 5 5 5 11 11 11 11 11
1 2 3 4 5 6 7 8 9 10 11 5 4 3 2 1
6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10
1 2 3 4 5 6 7 8 9 10 6 5 4 3 2 1
7 7 7 7 7 7 7 7 7 9 9 9 9 9 9 9
1 2 3 4 5 6 7 8 9 7 6 5 4 3 2 1
8 8 8 8 8 8 8 8
8 7 6 5 4 3 2 1
0 (115)
1 (214)
2 (313)
3 (412)
4 (511)
5 (610)
6 (79)
7 (88) Redundant area
C l u s t e r c o d e i n d i c a t o r ( 3 b i t s )
Tree offset indicator (4 bits)
Signaled on HS-SCCH
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
PO
Decoding notation
Number ofmulti-codes
Offset fromleft right incode tree (SF = 16)
Fig 2-20 Channelization code set indicating the HS-PDSCH code cluster
The idea behind the code indication is a matrix with the rows repre-
senting the number of codes per cluster and the columns represent-
ing the position of that cluster the offset value in the code tree Recall-
ing that the maximum number of channelization codes per clusteris 15 and if the cluster size is 1 the offset values can also range from
1 to 15 the resulting matrix would have 15 rows and 15 columns Since
we know that four bits are needed to represent an integer from 1 to 15
we need a total of 4 + 4 = 8 bits for representation of the channeliza-
tion code set information It is a smart idea to save one bit The 15 times 15
matrix would contain much redundant information By way of analogy
like in a road map indicating distances between cities A table showing
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High speed shared control channel (HS-SCCH)
51
the distance from city A to city B the opposite distance from city B to
city A is redundant information The useful information has the form
of a triangle The idea is to cut the lower part rotate it and append itto the spare part of the upper table In this manner a table is obtained
with 7 rows and 15 columns and it is possible to indicate each position
in it with just 7 bits
1 5 r o w s 7
r o w s
Matrix reduction for channeli-
zation code set information
15 columns
Fig 2-21 Matrix size reduction for channelization code set information
The content of the channelization code set matrix can be described as
a value with two numbers The upper number is the number of mul-
ticodes forming one cluster and the lower number is the offset in the
channelization code tree Accordingly the example in Fig 2-20 can be
interpreted to mean the HS-SCCH sends the bits as row number 4 and
column number 6 in the matrix The content of this element are the
values 5 over 7 which have to be interpreted as a cluster size of 5 codesand an offset of 7
Transport block size information 6 bits
With a length of six bits the transport block size (TBS) informa-
tion informs the receiving UE entity about the data block size of the
transport block sent on the HS-PDSCH We should keep in mind the
link adaptation performed with the adaptive modulation and coding
scheme that was described in section 12 page 10 The ratio errorcorrection and user data are flexible while the physical layer param-
eters such as the spreading factor modulation scheme and number of
channelization codes determine the physical block size This physical
block consists of the user data ratio or transport block size and the for-
ward error correction or redundancy information As this ratio is flex-
ible the HS-SCCH will inform the receiving UE entity about the size
of the transport block Here too there is a strategy of bit reduction the
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HSDPA operation overview and physical channels
goal is to inform the receiver with as few bits as possible A non-effi-
cient approach would involve conversion of the decimal number repre-
senting the TBS into a binary sequence but the number of bits neededwould exceed the space available on the HS-SCCH Imagine that the
range of transport block sizes depends on the physical layer condi-
tions The ambient physical layer parameters modulation scheme and
number of channelization codes set a certain working point where the
remaining flexibility for a different TBS configuration can be obtained
by more or less puncturing resulting in a flexible ratio between for-
ward error correction and user data This will lead to a two-step proce-
dure when evaluating the transport block size First the receiver exam-
ines the information modulation scheme and number of channeliza-
tion codes scheduled via HS-SCCH which indicate the value k0 l as
shown in Fig 2-22 The 6-bit HS-SCCH control parameter transport
block size information will be the transport format resource indica-
tor (TFRI) named ki Let k t be the sum of the two values kt = ki + k0i
Both values kt and k0 i can be obtained from tables given by [TS 25321
Ref 30] The range for the TFRI is from 1 to 256 and the derived trans-port block size ranges from 137 bits to 27 952 bits The first table indi-
cates the value k 0 i based on the channelization code and the modula-
tion scheme
Combination i Modulation scheme Number of channelization codes k0 i
0
QPSK
1 1
1 2 40
2 3 633 4 79
4 5 92
5 6 102
Fig 2-22 Extract from TS 25321 table representing k0 i
The second table indicates the final transport block size based on kt
Index TB size Index TB size Index TB size1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
4 173 89 1456 174 6673
5 185 90 1483 175 6793
6 197 91 1509 176 6916
7 209 92 1537 177 7041
Fig 2-23 Extract from TS 25321 table representing kt
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High speed shared control channel (HS-SCCH)
53
J The transport block size used on HS-DSCH is not signaled explicitly on HS-SCCHJ Instead a transport block size index k
i is signaled to indicate the transport block size
First stepModulation scheme andnumber of channelizationcodes as signaled on HS-SCCHdetermine value k
0 i
Second step
Index kt = k
i + k
0i
determines HS-DSCH
transport block size
kt = k
i + k
0i
Table according to 3GPP TS 25321 extract from QPSK section
Table according to 3GPP TS 25321 254 entries in total
Combination i Modulation
scheme
Number of
channelization codes
k0 i
0
QPSK
1 1
1 2 40
2 3 63
3 4 79
4 hellip hellip
Index TB size Index TB size Index TB size
1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
helliphellip hellip hellip hellip hellip
Fig 2-24 Retrieval of transport block size information
Source Fig 2-22 to Fig 2-24 [TS 25321 Ref 30] reproduced by permission of 3GPP
Hybrid ARQ process information 3 bits
The concept behind the hybrid automatic repeat request (HARQ) was
introduced in section 13 page 14 One feature is the possibility of
multitasking ie having several HARQ processes activated at the same
time Fig 2-25 below shows the need to signal the process identity tothe receiver Remember that on the downlink there is a shared chan-
nel concept so the NodeB can flexibly decide which UE will be sched-
uled with a downlink transport block Up to eight HARQ processes
can be signaled via higher layers to one UE Note however that due to
the round-trip timing six HARQ processes must be active to achieve
the maximum throughput as shown in Fig 2-51 page 79 Compared
with HSUPA the HARQ processes on the downlink are asynchronous
so they have to be indicated but on the uplink they are synchronous sothey do not need to be signaled explicitly
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HSDPA operation overview and physical channels
Asynchronous DL minus Synchronous ULNumber of H-ARQ rocesses = 1 to 8 er UE
UL HS-DPCCH UE1
UE1 HARQ processes 1 to 4
3 4 1 42 11 1 32retrans
2
A N A A
A A
N A
UL HS-DPCCH UE2
HS-PDSCH
UE2 HARQ processes 1 to 2
Fig 2-25 HARQ process indication on HS-SCCH
Fig 2-25 shows a typical situation on the downlink (point-to-multi-
point) The NodeB sends data to several UEs sharing the HS-PDSCH
so therefore the HARQ process is asynchronous The time when a
transport block is retransmitted is not fixed For this reason the pro-
cess identifier is signaled on the HS-SCCH Based on the HARQ pro-
cess identity and the new data indicator bit the receiving entity knows
which part of the soft buffer memory has to be used in case of soft com-bining On the uplink the situation is slightly simpler The UE only
communicates with one NodeB so it is a point-to-point connection
Thus retransmission always occurs at a fixed time linked to the origi-
nal transmission
Redundancy and constellation version 3 bits
Adaptive modulation and coding involve flexible selection of modula-tion and coding schemes that are signaled to the receiving UE via the
parameters transport block size and modulation scheme information
Another concept used in HSDPA was previously discussed Chase com-
bining or incremental redundancy (see section 222 page 41) This
means that in case of retransmission the transmit entity can dynami-
cally select another puncturing scheme or keep the puncturing as it was
in the original transmission The applied puncturing scheme is signaled
as redundancy information to the receiver Additionally in case of the16QAM modulation scheme the transmitter can select another constel-
lation arrangement which is also signaled to the UE with the three bits
for the redundancy and constellation version see Fig 2-15 page 45
Depending on the modulation scheme (QPSK or 16QAM) there are
two different tables indicating the parameters ldquosrdquo ldquorrdquo and ldquobrdquo The
parameters ldquosrdquo and ldquorrdquo indicate which scheme is used for puncturing
ie if the puncturing mechanism prioritizes the systematic bits or not
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High speed shared control channel (HS-SCCH)
55
and which puncturing algorithm is used The parameter ldquobrdquo indicates
the constellation mapping version The receiver needs this information
to perform proper demodulation and decoding
Initial transmission
1st retransmission
2nd retransmission
3rd retransmission
r
0
0
1
1
2
2
3
xrv
(value)
s
0 1
1 0
2 1
3 0
4 1
5 0
6 1
7 0 3
s = 1 Systematic bits are prioritizeds = 0 Non-systematic bits are prioritized
r (range 0 to 3 for QPSK) influencesJ Input parameter for puncturing or (together with s) for repetition algorithm defined in TS 25212J Selection of parity bits
Redundancy version coding sequences are signaled on HS-SCCH egndash 0 2 5 6 One initial transmission + 3 retransmissions with different r and s parameters
Fig 2-26 Signaling of redundancy version parameters r and s QPSK case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
Initial transmission
2nd retransmission
1st retransmission
3rd retransmission
r (range 0 to 1 for 16QAM)influences input parameterfor puncturing or (togetherwith s) for repetitionalgorithm defined in
TS 25212 and thus selectionof parity bits
Redundancy version coding sequences are signaled on HS-SCCH egminus 6 4 0 5 Chase combining (no change in s and r parameters ie same redundancyversion) with four possible constellations
x rv (value) s r b
0 1 0 0
1 0 0 0
2 1 1 1
3 0 1 1
4 1 0 1
5 1 0 2
6 1 0 3
7 1 1 0
Definition of parameter s as for QPSK
b (range 0 to 3) describes constellationrearrangement to averagereliability of bits
Fig 2-27 Signaling of redundancy version parameters r s and b 16QAM case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
UE identity H-RNTI 16 bits
The HSDPA radio network transaction identifier (H-RNTI) unam-
biguously identifies the UE having an HS-PDSCH assignment within
a cell It is allocated to the UE via layer 3 signaling procedures at the
radio bearer setup if the radio bearer is an HSDPA connection This
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HSDPA operation overview and physical channels
value represents a temporary name of the UE used to address it when
scheduling data packets via HS-SCCH
HS-SCCH channel coding
The control information contained in the HS-SCCH is of course pro-
tected with channel coding mechanisms the whole coding chain is
described in Fig 2-28 Fig 2-18 page 48 presents the separation of
the control information into two code blocks which are sent consec-
utively mapped on slot 1 and slot 2 + 3 of one HS-SCCH subframe
This principle is also visible in the coding chain The first control block
consisting of channelization information modulation scheme and UE
identity is coded separately from the remaining control values to enable
the UE receiver to decode this first slot separately and prepare for pos-
sible HS-PDSCH reception The coding steps shown in Fig 2-28 such
as rate matching 1 and 2 are similar to the HS-PDSCH coding chain
and are further described in [TS 25212 Ref 21]
Channelcoding 1
R atematching 1
mux
Channelcoding 2
Ratematching 2
RVcoding
UE-specificCRC attachment
UE-specificmasking
Physical channelmapping
r s b
mux
Channelizationcode set
Modulationscheme
Transport block size information
HARQ processinformation
Redundancy andconstellation version
New data indicator
UE identity
UE identity
Fig 2-28 Channel coding for HS-SCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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High speed dedicated physical control channel (HS-DPCCH)
57
24 High speed dedicated physical control channel (HS-DPCCH)
In an active HSDPA connection the UE has to send acknowledgment ornon-acknowledgment reports (as described in section 13 page 14
where the HARQ process is described) as well as channel status infor-
mation to the network The reporting is performed on this physical
control channel HS-DPCCH
As ubiquitous in HSDPA the uplink is also configured into a subframe
structure of 2 ms corresponding to three slots The first slot of the sub-
frame carries the ACK NACK information the UE sends to the NodeB
while the following two slots ie slot 2 and 3 of the subframe convey
the CQI value the channel quality information to the NodeB
Subframe 0 Subframe i Subframe 4
Tslot
= 2560 chips J The spreading factor of theHS-DPCCH is 256 (10 bits peruplink slot)
J The HS-DPCCH can only existtogether with an UL DPCCH
(ded phys control channel)J The DPDCH (dedicated physical data channel) the DPCCH andthe HS-DPCCH are IQ codemultiplexed
HARQ-ACK CQI = Channel quality information
2 times Tslot
= 5120 chips
One radio frame Tf = 10 ms
One HS-DPCCH subframe 2 ms
Fig 2-29 HS-DPCCH configuration
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The slot format for HS-DPCCH describes a quantity of 30 bits per sub-frame resulting in a data rate of 15 kbps The spreading factor used for
the HS-DPCCH is constant and is always equal to 256 but the chan-
nelization code that is used as well as the mapping on either the I or
Q axis depends on several factors eg the co-existence of an HSDPA
connection with a circuit-switched connection meaning whether a
DPDCH established or not Fig 2-36 page 64 illustrates this IQ
mapping and Fig 2-35 page 63 shows the channelization code used
for HS-DPCCH
The HS-DPCCH builds a logical unit of one subframe but having the
independent control information HARQ-ACK and CQI included which
could be separately decoded at the NodeB Note that the slot carrying
the ACK NACK statement is active only when the UE has been sched-
uled by an HS-PDSCH subframe in the corresponding downlink sub-
frame previously Assuming the UE has not received a transport block
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HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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HSDPA operation overview and physical channels
a certain soft buffer ie a memory that stores the transmitted data for
the sake of possible retransmissions and deletes it after having received
a positive acknowledgment from the receiver Should the transmitternow store the coded composite transport data i e the data after coding
but also after puncturing This would restrict it to repeating the data in
an identical manner A better approach is to store the data after channel
coding and before puncturing Even if this requires more memory it
gives the flexibility to change the puncturing scheme and retransmit the
transport block in a different way Fig 2-13 and Fig 2-14 represent both
mechanisms that are used in HSDPA and HSUPA Identical retransmis-
sion is called chase combining and non-identical retransmission with
a different puncturing scheme is called incremental redundancy The
scheduler in the base station can decide which retransmission scheme
will be used We do not wish to delve into the details of channel coding
theory to discuss which mechanism is the better one ndash chase combin-
ing or incremental redundancy We will only mention that both mech-
anisms have their advantages and thus their applications Chase com-
bining has the advantage that the systematic bits representing the orig-inal data input into the channel coder are contained in the transmit-
ted sequence after puncturing Thus chase combined transport blocks
are ldquoself-decodablerdquo If we consider a situation where the original trans-
port block is lost completely and only the retransmitted block is pres-
ent at the receiver there is a chance to decode the data properly Mean-
while incremental redundancy seems to add more redundancy when
retransmitting but in a scenario where the first transmission contain-ing the systematic bits is lost completely and only the retransmission
is present the receiver will have no chance to decode the data without
having some of the systematic bits Accordingly incremental redun-
dancy is applied whenever sporadic bit errors occur due to a time vari-
ant channel and chase combining is selected whenever we have to deal
with complete transport block errors i e the time variance of the radio
link exhibits some bursted fading dips
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HS-DSCH High speed downlink shared channel transport channel
43
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Chase combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Transmitted bit
Punctured bit
Systematic bits
Parity 1
Parity 2
Systematic bits
Parity 1
Parity 2
Fig 2-13 Chase combining principle
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Incremental redundancy combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Systematic bits
Parity 1
Parity 2
Systematic bitsParity 1
Parity 2
Fig 2-14 Incremental redundancy
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HSDPA operation overview and physical channels
223 Constellation rearrangement
Due to the fact that HSDPA introduces a higher-order modulationscheme (16QAM) we can recognize some effects due to the physi-
cal layer influencing the susceptibility to noisy RF conditions One of
these effects can be explained by looking at the constellation diagram
in the 16QAM modulation scheme see section 12 page 10 As we
recall there is a total of 16 different constellation points given by the
modulation vector and represented by its phase and amplitude Con-
sidering the Euclidean distance which is the distance in this constella-
tion diagram between two neighboring points we can clearly see that
some points have more neighbors than others Especially the four con-
stellation points at the very four corners only have three direct neigh-
bors making them less susceptible to misdetection due to noise shift-
ing them in a certain direction On the other hand the four constella-
tion points representing the inner square of the constellation have eight
direct neighbors each and are therefore more likely to be incorrectly
detected The idea of constellation rearrangement is now to change themapping scheme applied in the original transmission when retrans-
mitting As we know the receiver will soft combine the retransmit-
ted data with the previously received information so we can achieve a
certain incremented redundancy and a certain protection mechanism
Note however that considering a sole transmission of a transport block
using a certain constellation arrangement will not show any more pos-
itive or negative results compared to other constellation arrangementsThe redundancy gain is only achieved by rearranging the constellation
mapping in a retransmitted transport block and performing soft com-
bining at the receiver Overall HSDPA defines four constellation rear-
rangement schemes which are indicated in the redundancy version
field of the HS-SCCH and are represented by the ldquobrdquo bit field ranging
from b = 0 to b = 3 All four constellation schemes are Gray encoded
ie the directly adjacent constellation symbols do not exhibit four com-
pletely different bits in order to reduce the impact of misdetection onbit errors
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High speed shared control channel (HS-SCCH)
45
Q
I
(ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1) (1 1ndash1ndash1)
(ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1) (1 1ndash1 1)
(ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1) (1ndash1ndash1 1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 0
Q
I
(ndash1 1 1 1) (ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1)
(ndash1 1 1ndash1) (ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1)
(ndash1ndash1 1ndash1) (ndash1ndash1ndash1ndash1) (1ndash1ndash1ndash1) (1ndash1 1ndash1)
(ndash1 1 1 1) (ndash1ndash1ndash1 1) (1ndash1ndash1 1) (1ndash1 1 1)
b = 2
Q
I
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (1ndash1 1 1) (ndash1ndash1 1 1)
(ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1) (ndash1 1 1 1)
(ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1) (ndash1 1 1ndash1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 1
Q
I
(1 1ndash1 1) (ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1)
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1)
(1ndash1ndash1ndash1) (ndash1ndash1ndash1ndash1) (ndash1ndash1 1ndash1) (1ndash1 1ndash1)
(1 1ndash1ndash1) (ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1)
b = 3
Fig 2-15 Constellation rearrangement in HSDPA
23 High speed shared control channel (HS-SCCH)
The HS-SCCH sends scheduling information to the UEs As seen before
the HS-PDSCH has a very flexible configuration for physical parame-
ters such as the coding rate number of code channels or retransmis-sions This high flexibility increases the complexity and engenders the
need for additional signaling information transferred on the HS-SCCH
Reception of user data in HSDPA is always a two-step procedure
First the receiver has to capture the scheduling control information
and afterwards based on the received control information it may start
demodulating and decoding the HS-PDSCH containing the user data
This two-step procedure is shown in Fig 2-16 below which lists what
kind of control information is sent to the UEs via the HS-SCCH Asshown in Fig 2-2 page 28 which describes the overall HSDPA chan-
nel structure there can be up to four HS-SCCHs assigned to one UE
But only one HS-SCCH would contain the scheduling information for
this UE within one TTI Thus the network can assign resources simul-
taneously to various UEs in the downlink direction
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HSDPA operation overview and physical channels
I would like to receive databut I dont know where myHS-PDSCH resources areand what they look like
HS-SCCH
Read the 1st HS-SCCH slotfor HS-DSCH channelizationcodes UE identity and
modulation scheme
Then the 2nd and 3rd HS-SCCHslots provide transport block sizeinformation hybrid ARQ process in-formation redundancy constellationversion new data indicator
HS-PDSCH
Fig 2-16 HS-SCCH control channel usage
Regarding the physical layer parameters we see in Fig 2-17 that the
HS-SCCH uses a channelization code with a spreading factor of 128
and it also uses the newly introduced transmit time interval of one sub-
frame which is equal to 2 ms It should be mentioned that the spread-ing factor of 128 requires double the capacity compared to similar con-
trol channels in WCDMA Release 99 reflecting the signaling overhead
needed to guarantee the huge flexibility introduced with HSDPA Addi-
tionally Fig 2-16 shows that the control information is sent consecu-
tively within one subframe The first slot within this subframe contains
the control information UE identity channelization code information
and modulation scheme identifier Slots 2 and 3 of the subframe con-tain the remaining control information Transport block size HARQ
process identifier redundancy version and new data indicator Conse-
quently the UE can self-decode slot 1 alone and slots 2 and 3 in a sec-
ond step even if they represent one logical unit This raw control infor-
mation is of course also channel coded using a turbo and on the phys-
ical layer the quantity of bits after the rate matching step is 40 bits con-
veyed in one slot corresponding to 666 micros [TS 25212 Ref 21] see also
Fig 2-28 page 56
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High speed shared control channel (HS-SCCH)
47
The HS-SCCH is a fixed rate (60 kbps SF = 128) downlinkphysical channel used to carry downlink signaling related toHS-DSCH transmission
Slot 0
Slot 1
Slot 2
Tslot
= 2560 chips
Data = 40 bits
1 subframe = 2 ms
Fig 2-17 Structure of High speed shared control channel HS-SCCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
We would like to return now to the time consecutive transmission of
control information There is a difference in the control information
in terms of its priority Some information is needed at the UE end
very urgently while other control information does not have such a
high priority But why This will be explained by looking at some tim-ing aspects defined for HSDPA If we consider the timing between
the shared data channel HS-PDSCH and the shared control chan-
nel HS-SCCH as shown in Fig 2-18 we see that the HS-PDSCH fol-
lows the HS-SCCH by exactly two slots or 5120 chips The HS-SCCH
is completely time-aligned with the general control channels CPICH
and P-CCPCH of the NodeB This is mandatory because it is a shared
channel Consider several UEs with different distances to the NodeBwanting to receive the HS-SCCH channel Thus it must have constant
timing that is known a priori The shared data channel HS-PDSCH is
now transmitted exactly 5120 chips after the first chip of the HS-SCCH
This leads to an overlapping slot thereby requiring multitasking recep-
tion at the UE end While the UE is still receiving the last slot of an
ongoing HS-SCCH subframe it may already start the reception of an
HS-PDSCH transport block The first slot in the HS-SCCH subframe
now contains information required by the physical layer to performdespreading and demodulation These values are the UE identity indi-
cating whether the UE will start demodulation of the HS-PDSCH or
not in case it is not scheduled the modulation scheme information
since the UE has to know how to interpret the received constellation
vector and whether it has to be considered as a QPSK or 16QAM con-
stellation point and finally the UE has to know which channelization
codes it has to apply to capture the HS-PDSCH transport block The
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48
HSDPA operation overview and physical channels
overall UE reaction time when being scheduled is now seen as 1 slot
or 2560 chips This tough requirement for the UEs is due to the objec-
tive to obtain overall a much shorter latency than legacy standards Theadditional control information such as the new data indicator redun-
dancy version and transport block size is not that urgent since it is
needed after demodulation but before channel decoding So first the
UE will sample the whole three slots of the HS-PDSCH and demodu-
late them into a bit stream which is finally handed over to the channel
decoder This principle is known as post-processing and is used typi-
cally in mobile communications technologies
J Start of HS-SCCH subframe 0 is aligned with startof P-CCPCH frames
J The HS-PDSCH starts
τ HS-PDSCH
(2times Tslot
= 5120 chips)
after the start of the HS-SCCH
UE identity etc
processing timeof receiver
HS-DSCH subframe
3 times Tslot= 7680 chips
3 times Tslot
= 7680 chips
τ HS-PDSCH
(2times Tslot
= 5120 chips)
HS-SCCH
HS-PDSCH
Fig 2-18 Timing relation between HS-SCCH and HS-PDSCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
Content of the HS-SCCH control channelThe control information contained in the HS-SCCH control chan-
nel has already been mentioned so we will now consider the values
in more detail We will begin with an overview of what kind of control
information is contained in the HS-SCCH channel before proceeding
with further details about the single control elements The following
control information is present in the HS-SCCH [TS 25212 Ref 21]
Channelization code set information (7 bits)
Modulation scheme information (1 bit) Transport block size information (6 bits)
Hybrid ARQ process information (3 bits)
Redundancy and constellation version (3 bits)
New data indicator (1 bit)
UE identity (16 bits) = H-RNTI
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High speed shared control channel (HS-SCCH)
49
Some of these parameters are more or less self-explanatory while oth-
ers require additional background information and closer examination
Modulation scheme information 1 bit
This single bit is used to inform the receiver whether the modulation
scheme QPSK or 16QAM is applied on the data channel HS-PDSCH
The interpretation of the bit x ms1 is as follows
ms1
x
if QPSK
otherwise
0
1
=
New data indicator 1 bit
The new data indicator bit field informs the receiving entity that the
prevailing PDU transmitted by the current HARQ process is either a
retransmission or contains new data This is done by setting the new
data bit to the value 0 for the first PDU on this particular HARQ process
and incrementing the value by 1 with every new data sent [TS 25321Ref 30] This leads to a toggled value In case the new data bit is not
incremented ie if it remains at its previous value it is an indicator for
retransmission
1st PDU of this
HARQ process
NDI = New data indicator
NDI = 0 NDI = 1
NACK
NDI = 1
ACK
NDI = 0
HS-SCCH HS-SCCH HS-SCCHHS-SCCH
ACK
Fig 2-19 New data indicator bit principle of incrementing value
Channelization code set information 7 bits
This field is used to indicate the number of channelization codes usedfor transmitting the transport block on the HS-PDSCH As was already
described the spreading factor applied on the HS-PDSCH is constant
with a value of 16 but the flexible values are the number of channeliza-
tion codes forming a cluster when using multiple codes and their posi-
tion in the code tree It is not allowed to distribute the code channels
over the code tree diagram For the sake of simplicity in signaling sev-
eral channelization codes form one cluster and these codes are con-
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HSDPA operation overview and physical channels
tiguous in the channelization code tree [TS 25213 Ref 22] Fig 2-20
illustrates the principle of indicating the channelization codes on the
HS-SCCH
SF = 16
Code ldquo0rdquo isreserved forcommonchannels
Code offset 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15P = 5O = 7
Code group indicatorx
ccs1 x
ccs2 x
ccs3 = min (Pminus 1 15 minusP)
Code offset indicatorx
ccs4 x
ccs5 x
ccs6 x
ccs7 = |Ominus 1minus P8 times15|
A cluster of codes
can be allocated to a UEC
ch16Ohellip C
ch16O + P minus 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1
2 2 2 2 2 2 2 2 2 2 2 2 2 2 14 14
1 2 3 4 5 6 7 8 9 10 11 12 13 14 2 1
3 3 3 3 3 3 3 3 3 3 3 3 3 13 13 13
1 2 3 4 5 6 7 8 9 10 11 12 13 3 2 1
4 4 4 4 4 4 4 4 4 4 4 4 12 12 12 121 2 3 4 5 6 7 8 9 10 11 12 4 3 2 1
5 5 5 5 5 5 5 5 5 5 5 11 11 11 11 11
1 2 3 4 5 6 7 8 9 10 11 5 4 3 2 1
6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10
1 2 3 4 5 6 7 8 9 10 6 5 4 3 2 1
7 7 7 7 7 7 7 7 7 9 9 9 9 9 9 9
1 2 3 4 5 6 7 8 9 7 6 5 4 3 2 1
8 8 8 8 8 8 8 8
8 7 6 5 4 3 2 1
0 (115)
1 (214)
2 (313)
3 (412)
4 (511)
5 (610)
6 (79)
7 (88) Redundant area
C l u s t e r c o d e i n d i c a t o r ( 3 b i t s )
Tree offset indicator (4 bits)
Signaled on HS-SCCH
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
PO
Decoding notation
Number ofmulti-codes
Offset fromleft right incode tree (SF = 16)
Fig 2-20 Channelization code set indicating the HS-PDSCH code cluster
The idea behind the code indication is a matrix with the rows repre-
senting the number of codes per cluster and the columns represent-
ing the position of that cluster the offset value in the code tree Recall-
ing that the maximum number of channelization codes per clusteris 15 and if the cluster size is 1 the offset values can also range from
1 to 15 the resulting matrix would have 15 rows and 15 columns Since
we know that four bits are needed to represent an integer from 1 to 15
we need a total of 4 + 4 = 8 bits for representation of the channeliza-
tion code set information It is a smart idea to save one bit The 15 times 15
matrix would contain much redundant information By way of analogy
like in a road map indicating distances between cities A table showing
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High speed shared control channel (HS-SCCH)
51
the distance from city A to city B the opposite distance from city B to
city A is redundant information The useful information has the form
of a triangle The idea is to cut the lower part rotate it and append itto the spare part of the upper table In this manner a table is obtained
with 7 rows and 15 columns and it is possible to indicate each position
in it with just 7 bits
1 5 r o w s 7
r o w s
Matrix reduction for channeli-
zation code set information
15 columns
Fig 2-21 Matrix size reduction for channelization code set information
The content of the channelization code set matrix can be described as
a value with two numbers The upper number is the number of mul-
ticodes forming one cluster and the lower number is the offset in the
channelization code tree Accordingly the example in Fig 2-20 can be
interpreted to mean the HS-SCCH sends the bits as row number 4 and
column number 6 in the matrix The content of this element are the
values 5 over 7 which have to be interpreted as a cluster size of 5 codesand an offset of 7
Transport block size information 6 bits
With a length of six bits the transport block size (TBS) informa-
tion informs the receiving UE entity about the data block size of the
transport block sent on the HS-PDSCH We should keep in mind the
link adaptation performed with the adaptive modulation and coding
scheme that was described in section 12 page 10 The ratio errorcorrection and user data are flexible while the physical layer param-
eters such as the spreading factor modulation scheme and number of
channelization codes determine the physical block size This physical
block consists of the user data ratio or transport block size and the for-
ward error correction or redundancy information As this ratio is flex-
ible the HS-SCCH will inform the receiving UE entity about the size
of the transport block Here too there is a strategy of bit reduction the
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HSDPA operation overview and physical channels
goal is to inform the receiver with as few bits as possible A non-effi-
cient approach would involve conversion of the decimal number repre-
senting the TBS into a binary sequence but the number of bits neededwould exceed the space available on the HS-SCCH Imagine that the
range of transport block sizes depends on the physical layer condi-
tions The ambient physical layer parameters modulation scheme and
number of channelization codes set a certain working point where the
remaining flexibility for a different TBS configuration can be obtained
by more or less puncturing resulting in a flexible ratio between for-
ward error correction and user data This will lead to a two-step proce-
dure when evaluating the transport block size First the receiver exam-
ines the information modulation scheme and number of channeliza-
tion codes scheduled via HS-SCCH which indicate the value k0 l as
shown in Fig 2-22 The 6-bit HS-SCCH control parameter transport
block size information will be the transport format resource indica-
tor (TFRI) named ki Let k t be the sum of the two values kt = ki + k0i
Both values kt and k0 i can be obtained from tables given by [TS 25321
Ref 30] The range for the TFRI is from 1 to 256 and the derived trans-port block size ranges from 137 bits to 27 952 bits The first table indi-
cates the value k 0 i based on the channelization code and the modula-
tion scheme
Combination i Modulation scheme Number of channelization codes k0 i
0
QPSK
1 1
1 2 40
2 3 633 4 79
4 5 92
5 6 102
Fig 2-22 Extract from TS 25321 table representing k0 i
The second table indicates the final transport block size based on kt
Index TB size Index TB size Index TB size1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
4 173 89 1456 174 6673
5 185 90 1483 175 6793
6 197 91 1509 176 6916
7 209 92 1537 177 7041
Fig 2-23 Extract from TS 25321 table representing kt
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High speed shared control channel (HS-SCCH)
53
J The transport block size used on HS-DSCH is not signaled explicitly on HS-SCCHJ Instead a transport block size index k
i is signaled to indicate the transport block size
First stepModulation scheme andnumber of channelizationcodes as signaled on HS-SCCHdetermine value k
0 i
Second step
Index kt = k
i + k
0i
determines HS-DSCH
transport block size
kt = k
i + k
0i
Table according to 3GPP TS 25321 extract from QPSK section
Table according to 3GPP TS 25321 254 entries in total
Combination i Modulation
scheme
Number of
channelization codes
k0 i
0
QPSK
1 1
1 2 40
2 3 63
3 4 79
4 hellip hellip
Index TB size Index TB size Index TB size
1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
helliphellip hellip hellip hellip hellip
Fig 2-24 Retrieval of transport block size information
Source Fig 2-22 to Fig 2-24 [TS 25321 Ref 30] reproduced by permission of 3GPP
Hybrid ARQ process information 3 bits
The concept behind the hybrid automatic repeat request (HARQ) was
introduced in section 13 page 14 One feature is the possibility of
multitasking ie having several HARQ processes activated at the same
time Fig 2-25 below shows the need to signal the process identity tothe receiver Remember that on the downlink there is a shared chan-
nel concept so the NodeB can flexibly decide which UE will be sched-
uled with a downlink transport block Up to eight HARQ processes
can be signaled via higher layers to one UE Note however that due to
the round-trip timing six HARQ processes must be active to achieve
the maximum throughput as shown in Fig 2-51 page 79 Compared
with HSUPA the HARQ processes on the downlink are asynchronous
so they have to be indicated but on the uplink they are synchronous sothey do not need to be signaled explicitly
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HSDPA operation overview and physical channels
Asynchronous DL minus Synchronous ULNumber of H-ARQ rocesses = 1 to 8 er UE
UL HS-DPCCH UE1
UE1 HARQ processes 1 to 4
3 4 1 42 11 1 32retrans
2
A N A A
A A
N A
UL HS-DPCCH UE2
HS-PDSCH
UE2 HARQ processes 1 to 2
Fig 2-25 HARQ process indication on HS-SCCH
Fig 2-25 shows a typical situation on the downlink (point-to-multi-
point) The NodeB sends data to several UEs sharing the HS-PDSCH
so therefore the HARQ process is asynchronous The time when a
transport block is retransmitted is not fixed For this reason the pro-
cess identifier is signaled on the HS-SCCH Based on the HARQ pro-
cess identity and the new data indicator bit the receiving entity knows
which part of the soft buffer memory has to be used in case of soft com-bining On the uplink the situation is slightly simpler The UE only
communicates with one NodeB so it is a point-to-point connection
Thus retransmission always occurs at a fixed time linked to the origi-
nal transmission
Redundancy and constellation version 3 bits
Adaptive modulation and coding involve flexible selection of modula-tion and coding schemes that are signaled to the receiving UE via the
parameters transport block size and modulation scheme information
Another concept used in HSDPA was previously discussed Chase com-
bining or incremental redundancy (see section 222 page 41) This
means that in case of retransmission the transmit entity can dynami-
cally select another puncturing scheme or keep the puncturing as it was
in the original transmission The applied puncturing scheme is signaled
as redundancy information to the receiver Additionally in case of the16QAM modulation scheme the transmitter can select another constel-
lation arrangement which is also signaled to the UE with the three bits
for the redundancy and constellation version see Fig 2-15 page 45
Depending on the modulation scheme (QPSK or 16QAM) there are
two different tables indicating the parameters ldquosrdquo ldquorrdquo and ldquobrdquo The
parameters ldquosrdquo and ldquorrdquo indicate which scheme is used for puncturing
ie if the puncturing mechanism prioritizes the systematic bits or not
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High speed shared control channel (HS-SCCH)
55
and which puncturing algorithm is used The parameter ldquobrdquo indicates
the constellation mapping version The receiver needs this information
to perform proper demodulation and decoding
Initial transmission
1st retransmission
2nd retransmission
3rd retransmission
r
0
0
1
1
2
2
3
xrv
(value)
s
0 1
1 0
2 1
3 0
4 1
5 0
6 1
7 0 3
s = 1 Systematic bits are prioritizeds = 0 Non-systematic bits are prioritized
r (range 0 to 3 for QPSK) influencesJ Input parameter for puncturing or (together with s) for repetition algorithm defined in TS 25212J Selection of parity bits
Redundancy version coding sequences are signaled on HS-SCCH egndash 0 2 5 6 One initial transmission + 3 retransmissions with different r and s parameters
Fig 2-26 Signaling of redundancy version parameters r and s QPSK case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
Initial transmission
2nd retransmission
1st retransmission
3rd retransmission
r (range 0 to 1 for 16QAM)influences input parameterfor puncturing or (togetherwith s) for repetitionalgorithm defined in
TS 25212 and thus selectionof parity bits
Redundancy version coding sequences are signaled on HS-SCCH egminus 6 4 0 5 Chase combining (no change in s and r parameters ie same redundancyversion) with four possible constellations
x rv (value) s r b
0 1 0 0
1 0 0 0
2 1 1 1
3 0 1 1
4 1 0 1
5 1 0 2
6 1 0 3
7 1 1 0
Definition of parameter s as for QPSK
b (range 0 to 3) describes constellationrearrangement to averagereliability of bits
Fig 2-27 Signaling of redundancy version parameters r s and b 16QAM case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
UE identity H-RNTI 16 bits
The HSDPA radio network transaction identifier (H-RNTI) unam-
biguously identifies the UE having an HS-PDSCH assignment within
a cell It is allocated to the UE via layer 3 signaling procedures at the
radio bearer setup if the radio bearer is an HSDPA connection This
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HSDPA operation overview and physical channels
value represents a temporary name of the UE used to address it when
scheduling data packets via HS-SCCH
HS-SCCH channel coding
The control information contained in the HS-SCCH is of course pro-
tected with channel coding mechanisms the whole coding chain is
described in Fig 2-28 Fig 2-18 page 48 presents the separation of
the control information into two code blocks which are sent consec-
utively mapped on slot 1 and slot 2 + 3 of one HS-SCCH subframe
This principle is also visible in the coding chain The first control block
consisting of channelization information modulation scheme and UE
identity is coded separately from the remaining control values to enable
the UE receiver to decode this first slot separately and prepare for pos-
sible HS-PDSCH reception The coding steps shown in Fig 2-28 such
as rate matching 1 and 2 are similar to the HS-PDSCH coding chain
and are further described in [TS 25212 Ref 21]
Channelcoding 1
R atematching 1
mux
Channelcoding 2
Ratematching 2
RVcoding
UE-specificCRC attachment
UE-specificmasking
Physical channelmapping
r s b
mux
Channelizationcode set
Modulationscheme
Transport block size information
HARQ processinformation
Redundancy andconstellation version
New data indicator
UE identity
UE identity
Fig 2-28 Channel coding for HS-SCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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High speed dedicated physical control channel (HS-DPCCH)
57
24 High speed dedicated physical control channel (HS-DPCCH)
In an active HSDPA connection the UE has to send acknowledgment ornon-acknowledgment reports (as described in section 13 page 14
where the HARQ process is described) as well as channel status infor-
mation to the network The reporting is performed on this physical
control channel HS-DPCCH
As ubiquitous in HSDPA the uplink is also configured into a subframe
structure of 2 ms corresponding to three slots The first slot of the sub-
frame carries the ACK NACK information the UE sends to the NodeB
while the following two slots ie slot 2 and 3 of the subframe convey
the CQI value the channel quality information to the NodeB
Subframe 0 Subframe i Subframe 4
Tslot
= 2560 chips J The spreading factor of theHS-DPCCH is 256 (10 bits peruplink slot)
J The HS-DPCCH can only existtogether with an UL DPCCH
(ded phys control channel)J The DPDCH (dedicated physical data channel) the DPCCH andthe HS-DPCCH are IQ codemultiplexed
HARQ-ACK CQI = Channel quality information
2 times Tslot
= 5120 chips
One radio frame Tf = 10 ms
One HS-DPCCH subframe 2 ms
Fig 2-29 HS-DPCCH configuration
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The slot format for HS-DPCCH describes a quantity of 30 bits per sub-frame resulting in a data rate of 15 kbps The spreading factor used for
the HS-DPCCH is constant and is always equal to 256 but the chan-
nelization code that is used as well as the mapping on either the I or
Q axis depends on several factors eg the co-existence of an HSDPA
connection with a circuit-switched connection meaning whether a
DPDCH established or not Fig 2-36 page 64 illustrates this IQ
mapping and Fig 2-35 page 63 shows the channelization code used
for HS-DPCCH
The HS-DPCCH builds a logical unit of one subframe but having the
independent control information HARQ-ACK and CQI included which
could be separately decoded at the NodeB Note that the slot carrying
the ACK NACK statement is active only when the UE has been sched-
uled by an HS-PDSCH subframe in the corresponding downlink sub-
frame previously Assuming the UE has not received a transport block
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HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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HS-DSCH High speed downlink shared channel transport channel
43
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Chase combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Transmitted bit
Punctured bit
Systematic bits
Parity 1
Parity 2
Systematic bits
Parity 1
Parity 2
Fig 2-13 Chase combining principle
Turbo encoder output (36 bits)
Rate matching to 16 bits (puncturing)
Incremental redundancy combining at receiver
Systematic bits
Parity 1
Parity 2
Original transmission Retransmission
Systematic bits
Parity 1
Parity 2
Systematic bitsParity 1
Parity 2
Fig 2-14 Incremental redundancy
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HSDPA operation overview and physical channels
223 Constellation rearrangement
Due to the fact that HSDPA introduces a higher-order modulationscheme (16QAM) we can recognize some effects due to the physi-
cal layer influencing the susceptibility to noisy RF conditions One of
these effects can be explained by looking at the constellation diagram
in the 16QAM modulation scheme see section 12 page 10 As we
recall there is a total of 16 different constellation points given by the
modulation vector and represented by its phase and amplitude Con-
sidering the Euclidean distance which is the distance in this constella-
tion diagram between two neighboring points we can clearly see that
some points have more neighbors than others Especially the four con-
stellation points at the very four corners only have three direct neigh-
bors making them less susceptible to misdetection due to noise shift-
ing them in a certain direction On the other hand the four constella-
tion points representing the inner square of the constellation have eight
direct neighbors each and are therefore more likely to be incorrectly
detected The idea of constellation rearrangement is now to change themapping scheme applied in the original transmission when retrans-
mitting As we know the receiver will soft combine the retransmit-
ted data with the previously received information so we can achieve a
certain incremented redundancy and a certain protection mechanism
Note however that considering a sole transmission of a transport block
using a certain constellation arrangement will not show any more pos-
itive or negative results compared to other constellation arrangementsThe redundancy gain is only achieved by rearranging the constellation
mapping in a retransmitted transport block and performing soft com-
bining at the receiver Overall HSDPA defines four constellation rear-
rangement schemes which are indicated in the redundancy version
field of the HS-SCCH and are represented by the ldquobrdquo bit field ranging
from b = 0 to b = 3 All four constellation schemes are Gray encoded
ie the directly adjacent constellation symbols do not exhibit four com-
pletely different bits in order to reduce the impact of misdetection onbit errors
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High speed shared control channel (HS-SCCH)
45
Q
I
(ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1) (1 1ndash1ndash1)
(ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1) (1 1ndash1 1)
(ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1) (1ndash1ndash1 1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 0
Q
I
(ndash1 1 1 1) (ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1)
(ndash1 1 1ndash1) (ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1)
(ndash1ndash1 1ndash1) (ndash1ndash1ndash1ndash1) (1ndash1ndash1ndash1) (1ndash1 1ndash1)
(ndash1 1 1 1) (ndash1ndash1ndash1 1) (1ndash1ndash1 1) (1ndash1 1 1)
b = 2
Q
I
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (1ndash1 1 1) (ndash1ndash1 1 1)
(ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1) (ndash1 1 1 1)
(ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1) (ndash1 1 1ndash1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 1
Q
I
(1 1ndash1 1) (ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1)
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1)
(1ndash1ndash1ndash1) (ndash1ndash1ndash1ndash1) (ndash1ndash1 1ndash1) (1ndash1 1ndash1)
(1 1ndash1ndash1) (ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1)
b = 3
Fig 2-15 Constellation rearrangement in HSDPA
23 High speed shared control channel (HS-SCCH)
The HS-SCCH sends scheduling information to the UEs As seen before
the HS-PDSCH has a very flexible configuration for physical parame-
ters such as the coding rate number of code channels or retransmis-sions This high flexibility increases the complexity and engenders the
need for additional signaling information transferred on the HS-SCCH
Reception of user data in HSDPA is always a two-step procedure
First the receiver has to capture the scheduling control information
and afterwards based on the received control information it may start
demodulating and decoding the HS-PDSCH containing the user data
This two-step procedure is shown in Fig 2-16 below which lists what
kind of control information is sent to the UEs via the HS-SCCH Asshown in Fig 2-2 page 28 which describes the overall HSDPA chan-
nel structure there can be up to four HS-SCCHs assigned to one UE
But only one HS-SCCH would contain the scheduling information for
this UE within one TTI Thus the network can assign resources simul-
taneously to various UEs in the downlink direction
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HSDPA operation overview and physical channels
I would like to receive databut I dont know where myHS-PDSCH resources areand what they look like
HS-SCCH
Read the 1st HS-SCCH slotfor HS-DSCH channelizationcodes UE identity and
modulation scheme
Then the 2nd and 3rd HS-SCCHslots provide transport block sizeinformation hybrid ARQ process in-formation redundancy constellationversion new data indicator
HS-PDSCH
Fig 2-16 HS-SCCH control channel usage
Regarding the physical layer parameters we see in Fig 2-17 that the
HS-SCCH uses a channelization code with a spreading factor of 128
and it also uses the newly introduced transmit time interval of one sub-
frame which is equal to 2 ms It should be mentioned that the spread-ing factor of 128 requires double the capacity compared to similar con-
trol channels in WCDMA Release 99 reflecting the signaling overhead
needed to guarantee the huge flexibility introduced with HSDPA Addi-
tionally Fig 2-16 shows that the control information is sent consecu-
tively within one subframe The first slot within this subframe contains
the control information UE identity channelization code information
and modulation scheme identifier Slots 2 and 3 of the subframe con-tain the remaining control information Transport block size HARQ
process identifier redundancy version and new data indicator Conse-
quently the UE can self-decode slot 1 alone and slots 2 and 3 in a sec-
ond step even if they represent one logical unit This raw control infor-
mation is of course also channel coded using a turbo and on the phys-
ical layer the quantity of bits after the rate matching step is 40 bits con-
veyed in one slot corresponding to 666 micros [TS 25212 Ref 21] see also
Fig 2-28 page 56
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High speed shared control channel (HS-SCCH)
47
The HS-SCCH is a fixed rate (60 kbps SF = 128) downlinkphysical channel used to carry downlink signaling related toHS-DSCH transmission
Slot 0
Slot 1
Slot 2
Tslot
= 2560 chips
Data = 40 bits
1 subframe = 2 ms
Fig 2-17 Structure of High speed shared control channel HS-SCCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
We would like to return now to the time consecutive transmission of
control information There is a difference in the control information
in terms of its priority Some information is needed at the UE end
very urgently while other control information does not have such a
high priority But why This will be explained by looking at some tim-ing aspects defined for HSDPA If we consider the timing between
the shared data channel HS-PDSCH and the shared control chan-
nel HS-SCCH as shown in Fig 2-18 we see that the HS-PDSCH fol-
lows the HS-SCCH by exactly two slots or 5120 chips The HS-SCCH
is completely time-aligned with the general control channels CPICH
and P-CCPCH of the NodeB This is mandatory because it is a shared
channel Consider several UEs with different distances to the NodeBwanting to receive the HS-SCCH channel Thus it must have constant
timing that is known a priori The shared data channel HS-PDSCH is
now transmitted exactly 5120 chips after the first chip of the HS-SCCH
This leads to an overlapping slot thereby requiring multitasking recep-
tion at the UE end While the UE is still receiving the last slot of an
ongoing HS-SCCH subframe it may already start the reception of an
HS-PDSCH transport block The first slot in the HS-SCCH subframe
now contains information required by the physical layer to performdespreading and demodulation These values are the UE identity indi-
cating whether the UE will start demodulation of the HS-PDSCH or
not in case it is not scheduled the modulation scheme information
since the UE has to know how to interpret the received constellation
vector and whether it has to be considered as a QPSK or 16QAM con-
stellation point and finally the UE has to know which channelization
codes it has to apply to capture the HS-PDSCH transport block The
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HSDPA operation overview and physical channels
overall UE reaction time when being scheduled is now seen as 1 slot
or 2560 chips This tough requirement for the UEs is due to the objec-
tive to obtain overall a much shorter latency than legacy standards Theadditional control information such as the new data indicator redun-
dancy version and transport block size is not that urgent since it is
needed after demodulation but before channel decoding So first the
UE will sample the whole three slots of the HS-PDSCH and demodu-
late them into a bit stream which is finally handed over to the channel
decoder This principle is known as post-processing and is used typi-
cally in mobile communications technologies
J Start of HS-SCCH subframe 0 is aligned with startof P-CCPCH frames
J The HS-PDSCH starts
τ HS-PDSCH
(2times Tslot
= 5120 chips)
after the start of the HS-SCCH
UE identity etc
processing timeof receiver
HS-DSCH subframe
3 times Tslot= 7680 chips
3 times Tslot
= 7680 chips
τ HS-PDSCH
(2times Tslot
= 5120 chips)
HS-SCCH
HS-PDSCH
Fig 2-18 Timing relation between HS-SCCH and HS-PDSCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
Content of the HS-SCCH control channelThe control information contained in the HS-SCCH control chan-
nel has already been mentioned so we will now consider the values
in more detail We will begin with an overview of what kind of control
information is contained in the HS-SCCH channel before proceeding
with further details about the single control elements The following
control information is present in the HS-SCCH [TS 25212 Ref 21]
Channelization code set information (7 bits)
Modulation scheme information (1 bit) Transport block size information (6 bits)
Hybrid ARQ process information (3 bits)
Redundancy and constellation version (3 bits)
New data indicator (1 bit)
UE identity (16 bits) = H-RNTI
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High speed shared control channel (HS-SCCH)
49
Some of these parameters are more or less self-explanatory while oth-
ers require additional background information and closer examination
Modulation scheme information 1 bit
This single bit is used to inform the receiver whether the modulation
scheme QPSK or 16QAM is applied on the data channel HS-PDSCH
The interpretation of the bit x ms1 is as follows
ms1
x
if QPSK
otherwise
0
1
=
New data indicator 1 bit
The new data indicator bit field informs the receiving entity that the
prevailing PDU transmitted by the current HARQ process is either a
retransmission or contains new data This is done by setting the new
data bit to the value 0 for the first PDU on this particular HARQ process
and incrementing the value by 1 with every new data sent [TS 25321Ref 30] This leads to a toggled value In case the new data bit is not
incremented ie if it remains at its previous value it is an indicator for
retransmission
1st PDU of this
HARQ process
NDI = New data indicator
NDI = 0 NDI = 1
NACK
NDI = 1
ACK
NDI = 0
HS-SCCH HS-SCCH HS-SCCHHS-SCCH
ACK
Fig 2-19 New data indicator bit principle of incrementing value
Channelization code set information 7 bits
This field is used to indicate the number of channelization codes usedfor transmitting the transport block on the HS-PDSCH As was already
described the spreading factor applied on the HS-PDSCH is constant
with a value of 16 but the flexible values are the number of channeliza-
tion codes forming a cluster when using multiple codes and their posi-
tion in the code tree It is not allowed to distribute the code channels
over the code tree diagram For the sake of simplicity in signaling sev-
eral channelization codes form one cluster and these codes are con-
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HSDPA operation overview and physical channels
tiguous in the channelization code tree [TS 25213 Ref 22] Fig 2-20
illustrates the principle of indicating the channelization codes on the
HS-SCCH
SF = 16
Code ldquo0rdquo isreserved forcommonchannels
Code offset 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15P = 5O = 7
Code group indicatorx
ccs1 x
ccs2 x
ccs3 = min (Pminus 1 15 minusP)
Code offset indicatorx
ccs4 x
ccs5 x
ccs6 x
ccs7 = |Ominus 1minus P8 times15|
A cluster of codes
can be allocated to a UEC
ch16Ohellip C
ch16O + P minus 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1
2 2 2 2 2 2 2 2 2 2 2 2 2 2 14 14
1 2 3 4 5 6 7 8 9 10 11 12 13 14 2 1
3 3 3 3 3 3 3 3 3 3 3 3 3 13 13 13
1 2 3 4 5 6 7 8 9 10 11 12 13 3 2 1
4 4 4 4 4 4 4 4 4 4 4 4 12 12 12 121 2 3 4 5 6 7 8 9 10 11 12 4 3 2 1
5 5 5 5 5 5 5 5 5 5 5 11 11 11 11 11
1 2 3 4 5 6 7 8 9 10 11 5 4 3 2 1
6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10
1 2 3 4 5 6 7 8 9 10 6 5 4 3 2 1
7 7 7 7 7 7 7 7 7 9 9 9 9 9 9 9
1 2 3 4 5 6 7 8 9 7 6 5 4 3 2 1
8 8 8 8 8 8 8 8
8 7 6 5 4 3 2 1
0 (115)
1 (214)
2 (313)
3 (412)
4 (511)
5 (610)
6 (79)
7 (88) Redundant area
C l u s t e r c o d e i n d i c a t o r ( 3 b i t s )
Tree offset indicator (4 bits)
Signaled on HS-SCCH
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
PO
Decoding notation
Number ofmulti-codes
Offset fromleft right incode tree (SF = 16)
Fig 2-20 Channelization code set indicating the HS-PDSCH code cluster
The idea behind the code indication is a matrix with the rows repre-
senting the number of codes per cluster and the columns represent-
ing the position of that cluster the offset value in the code tree Recall-
ing that the maximum number of channelization codes per clusteris 15 and if the cluster size is 1 the offset values can also range from
1 to 15 the resulting matrix would have 15 rows and 15 columns Since
we know that four bits are needed to represent an integer from 1 to 15
we need a total of 4 + 4 = 8 bits for representation of the channeliza-
tion code set information It is a smart idea to save one bit The 15 times 15
matrix would contain much redundant information By way of analogy
like in a road map indicating distances between cities A table showing
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High speed shared control channel (HS-SCCH)
51
the distance from city A to city B the opposite distance from city B to
city A is redundant information The useful information has the form
of a triangle The idea is to cut the lower part rotate it and append itto the spare part of the upper table In this manner a table is obtained
with 7 rows and 15 columns and it is possible to indicate each position
in it with just 7 bits
1 5 r o w s 7
r o w s
Matrix reduction for channeli-
zation code set information
15 columns
Fig 2-21 Matrix size reduction for channelization code set information
The content of the channelization code set matrix can be described as
a value with two numbers The upper number is the number of mul-
ticodes forming one cluster and the lower number is the offset in the
channelization code tree Accordingly the example in Fig 2-20 can be
interpreted to mean the HS-SCCH sends the bits as row number 4 and
column number 6 in the matrix The content of this element are the
values 5 over 7 which have to be interpreted as a cluster size of 5 codesand an offset of 7
Transport block size information 6 bits
With a length of six bits the transport block size (TBS) informa-
tion informs the receiving UE entity about the data block size of the
transport block sent on the HS-PDSCH We should keep in mind the
link adaptation performed with the adaptive modulation and coding
scheme that was described in section 12 page 10 The ratio errorcorrection and user data are flexible while the physical layer param-
eters such as the spreading factor modulation scheme and number of
channelization codes determine the physical block size This physical
block consists of the user data ratio or transport block size and the for-
ward error correction or redundancy information As this ratio is flex-
ible the HS-SCCH will inform the receiving UE entity about the size
of the transport block Here too there is a strategy of bit reduction the
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HSDPA operation overview and physical channels
goal is to inform the receiver with as few bits as possible A non-effi-
cient approach would involve conversion of the decimal number repre-
senting the TBS into a binary sequence but the number of bits neededwould exceed the space available on the HS-SCCH Imagine that the
range of transport block sizes depends on the physical layer condi-
tions The ambient physical layer parameters modulation scheme and
number of channelization codes set a certain working point where the
remaining flexibility for a different TBS configuration can be obtained
by more or less puncturing resulting in a flexible ratio between for-
ward error correction and user data This will lead to a two-step proce-
dure when evaluating the transport block size First the receiver exam-
ines the information modulation scheme and number of channeliza-
tion codes scheduled via HS-SCCH which indicate the value k0 l as
shown in Fig 2-22 The 6-bit HS-SCCH control parameter transport
block size information will be the transport format resource indica-
tor (TFRI) named ki Let k t be the sum of the two values kt = ki + k0i
Both values kt and k0 i can be obtained from tables given by [TS 25321
Ref 30] The range for the TFRI is from 1 to 256 and the derived trans-port block size ranges from 137 bits to 27 952 bits The first table indi-
cates the value k 0 i based on the channelization code and the modula-
tion scheme
Combination i Modulation scheme Number of channelization codes k0 i
0
QPSK
1 1
1 2 40
2 3 633 4 79
4 5 92
5 6 102
Fig 2-22 Extract from TS 25321 table representing k0 i
The second table indicates the final transport block size based on kt
Index TB size Index TB size Index TB size1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
4 173 89 1456 174 6673
5 185 90 1483 175 6793
6 197 91 1509 176 6916
7 209 92 1537 177 7041
Fig 2-23 Extract from TS 25321 table representing kt
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High speed shared control channel (HS-SCCH)
53
J The transport block size used on HS-DSCH is not signaled explicitly on HS-SCCHJ Instead a transport block size index k
i is signaled to indicate the transport block size
First stepModulation scheme andnumber of channelizationcodes as signaled on HS-SCCHdetermine value k
0 i
Second step
Index kt = k
i + k
0i
determines HS-DSCH
transport block size
kt = k
i + k
0i
Table according to 3GPP TS 25321 extract from QPSK section
Table according to 3GPP TS 25321 254 entries in total
Combination i Modulation
scheme
Number of
channelization codes
k0 i
0
QPSK
1 1
1 2 40
2 3 63
3 4 79
4 hellip hellip
Index TB size Index TB size Index TB size
1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
helliphellip hellip hellip hellip hellip
Fig 2-24 Retrieval of transport block size information
Source Fig 2-22 to Fig 2-24 [TS 25321 Ref 30] reproduced by permission of 3GPP
Hybrid ARQ process information 3 bits
The concept behind the hybrid automatic repeat request (HARQ) was
introduced in section 13 page 14 One feature is the possibility of
multitasking ie having several HARQ processes activated at the same
time Fig 2-25 below shows the need to signal the process identity tothe receiver Remember that on the downlink there is a shared chan-
nel concept so the NodeB can flexibly decide which UE will be sched-
uled with a downlink transport block Up to eight HARQ processes
can be signaled via higher layers to one UE Note however that due to
the round-trip timing six HARQ processes must be active to achieve
the maximum throughput as shown in Fig 2-51 page 79 Compared
with HSUPA the HARQ processes on the downlink are asynchronous
so they have to be indicated but on the uplink they are synchronous sothey do not need to be signaled explicitly
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HSDPA operation overview and physical channels
Asynchronous DL minus Synchronous ULNumber of H-ARQ rocesses = 1 to 8 er UE
UL HS-DPCCH UE1
UE1 HARQ processes 1 to 4
3 4 1 42 11 1 32retrans
2
A N A A
A A
N A
UL HS-DPCCH UE2
HS-PDSCH
UE2 HARQ processes 1 to 2
Fig 2-25 HARQ process indication on HS-SCCH
Fig 2-25 shows a typical situation on the downlink (point-to-multi-
point) The NodeB sends data to several UEs sharing the HS-PDSCH
so therefore the HARQ process is asynchronous The time when a
transport block is retransmitted is not fixed For this reason the pro-
cess identifier is signaled on the HS-SCCH Based on the HARQ pro-
cess identity and the new data indicator bit the receiving entity knows
which part of the soft buffer memory has to be used in case of soft com-bining On the uplink the situation is slightly simpler The UE only
communicates with one NodeB so it is a point-to-point connection
Thus retransmission always occurs at a fixed time linked to the origi-
nal transmission
Redundancy and constellation version 3 bits
Adaptive modulation and coding involve flexible selection of modula-tion and coding schemes that are signaled to the receiving UE via the
parameters transport block size and modulation scheme information
Another concept used in HSDPA was previously discussed Chase com-
bining or incremental redundancy (see section 222 page 41) This
means that in case of retransmission the transmit entity can dynami-
cally select another puncturing scheme or keep the puncturing as it was
in the original transmission The applied puncturing scheme is signaled
as redundancy information to the receiver Additionally in case of the16QAM modulation scheme the transmitter can select another constel-
lation arrangement which is also signaled to the UE with the three bits
for the redundancy and constellation version see Fig 2-15 page 45
Depending on the modulation scheme (QPSK or 16QAM) there are
two different tables indicating the parameters ldquosrdquo ldquorrdquo and ldquobrdquo The
parameters ldquosrdquo and ldquorrdquo indicate which scheme is used for puncturing
ie if the puncturing mechanism prioritizes the systematic bits or not
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High speed shared control channel (HS-SCCH)
55
and which puncturing algorithm is used The parameter ldquobrdquo indicates
the constellation mapping version The receiver needs this information
to perform proper demodulation and decoding
Initial transmission
1st retransmission
2nd retransmission
3rd retransmission
r
0
0
1
1
2
2
3
xrv
(value)
s
0 1
1 0
2 1
3 0
4 1
5 0
6 1
7 0 3
s = 1 Systematic bits are prioritizeds = 0 Non-systematic bits are prioritized
r (range 0 to 3 for QPSK) influencesJ Input parameter for puncturing or (together with s) for repetition algorithm defined in TS 25212J Selection of parity bits
Redundancy version coding sequences are signaled on HS-SCCH egndash 0 2 5 6 One initial transmission + 3 retransmissions with different r and s parameters
Fig 2-26 Signaling of redundancy version parameters r and s QPSK case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
Initial transmission
2nd retransmission
1st retransmission
3rd retransmission
r (range 0 to 1 for 16QAM)influences input parameterfor puncturing or (togetherwith s) for repetitionalgorithm defined in
TS 25212 and thus selectionof parity bits
Redundancy version coding sequences are signaled on HS-SCCH egminus 6 4 0 5 Chase combining (no change in s and r parameters ie same redundancyversion) with four possible constellations
x rv (value) s r b
0 1 0 0
1 0 0 0
2 1 1 1
3 0 1 1
4 1 0 1
5 1 0 2
6 1 0 3
7 1 1 0
Definition of parameter s as for QPSK
b (range 0 to 3) describes constellationrearrangement to averagereliability of bits
Fig 2-27 Signaling of redundancy version parameters r s and b 16QAM case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
UE identity H-RNTI 16 bits
The HSDPA radio network transaction identifier (H-RNTI) unam-
biguously identifies the UE having an HS-PDSCH assignment within
a cell It is allocated to the UE via layer 3 signaling procedures at the
radio bearer setup if the radio bearer is an HSDPA connection This
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HSDPA operation overview and physical channels
value represents a temporary name of the UE used to address it when
scheduling data packets via HS-SCCH
HS-SCCH channel coding
The control information contained in the HS-SCCH is of course pro-
tected with channel coding mechanisms the whole coding chain is
described in Fig 2-28 Fig 2-18 page 48 presents the separation of
the control information into two code blocks which are sent consec-
utively mapped on slot 1 and slot 2 + 3 of one HS-SCCH subframe
This principle is also visible in the coding chain The first control block
consisting of channelization information modulation scheme and UE
identity is coded separately from the remaining control values to enable
the UE receiver to decode this first slot separately and prepare for pos-
sible HS-PDSCH reception The coding steps shown in Fig 2-28 such
as rate matching 1 and 2 are similar to the HS-PDSCH coding chain
and are further described in [TS 25212 Ref 21]
Channelcoding 1
R atematching 1
mux
Channelcoding 2
Ratematching 2
RVcoding
UE-specificCRC attachment
UE-specificmasking
Physical channelmapping
r s b
mux
Channelizationcode set
Modulationscheme
Transport block size information
HARQ processinformation
Redundancy andconstellation version
New data indicator
UE identity
UE identity
Fig 2-28 Channel coding for HS-SCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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High speed dedicated physical control channel (HS-DPCCH)
57
24 High speed dedicated physical control channel (HS-DPCCH)
In an active HSDPA connection the UE has to send acknowledgment ornon-acknowledgment reports (as described in section 13 page 14
where the HARQ process is described) as well as channel status infor-
mation to the network The reporting is performed on this physical
control channel HS-DPCCH
As ubiquitous in HSDPA the uplink is also configured into a subframe
structure of 2 ms corresponding to three slots The first slot of the sub-
frame carries the ACK NACK information the UE sends to the NodeB
while the following two slots ie slot 2 and 3 of the subframe convey
the CQI value the channel quality information to the NodeB
Subframe 0 Subframe i Subframe 4
Tslot
= 2560 chips J The spreading factor of theHS-DPCCH is 256 (10 bits peruplink slot)
J The HS-DPCCH can only existtogether with an UL DPCCH
(ded phys control channel)J The DPDCH (dedicated physical data channel) the DPCCH andthe HS-DPCCH are IQ codemultiplexed
HARQ-ACK CQI = Channel quality information
2 times Tslot
= 5120 chips
One radio frame Tf = 10 ms
One HS-DPCCH subframe 2 ms
Fig 2-29 HS-DPCCH configuration
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The slot format for HS-DPCCH describes a quantity of 30 bits per sub-frame resulting in a data rate of 15 kbps The spreading factor used for
the HS-DPCCH is constant and is always equal to 256 but the chan-
nelization code that is used as well as the mapping on either the I or
Q axis depends on several factors eg the co-existence of an HSDPA
connection with a circuit-switched connection meaning whether a
DPDCH established or not Fig 2-36 page 64 illustrates this IQ
mapping and Fig 2-35 page 63 shows the channelization code used
for HS-DPCCH
The HS-DPCCH builds a logical unit of one subframe but having the
independent control information HARQ-ACK and CQI included which
could be separately decoded at the NodeB Note that the slot carrying
the ACK NACK statement is active only when the UE has been sched-
uled by an HS-PDSCH subframe in the corresponding downlink sub-
frame previously Assuming the UE has not received a transport block
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HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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HSDPA operation overview and physical channels
223 Constellation rearrangement
Due to the fact that HSDPA introduces a higher-order modulationscheme (16QAM) we can recognize some effects due to the physi-
cal layer influencing the susceptibility to noisy RF conditions One of
these effects can be explained by looking at the constellation diagram
in the 16QAM modulation scheme see section 12 page 10 As we
recall there is a total of 16 different constellation points given by the
modulation vector and represented by its phase and amplitude Con-
sidering the Euclidean distance which is the distance in this constella-
tion diagram between two neighboring points we can clearly see that
some points have more neighbors than others Especially the four con-
stellation points at the very four corners only have three direct neigh-
bors making them less susceptible to misdetection due to noise shift-
ing them in a certain direction On the other hand the four constella-
tion points representing the inner square of the constellation have eight
direct neighbors each and are therefore more likely to be incorrectly
detected The idea of constellation rearrangement is now to change themapping scheme applied in the original transmission when retrans-
mitting As we know the receiver will soft combine the retransmit-
ted data with the previously received information so we can achieve a
certain incremented redundancy and a certain protection mechanism
Note however that considering a sole transmission of a transport block
using a certain constellation arrangement will not show any more pos-
itive or negative results compared to other constellation arrangementsThe redundancy gain is only achieved by rearranging the constellation
mapping in a retransmitted transport block and performing soft com-
bining at the receiver Overall HSDPA defines four constellation rear-
rangement schemes which are indicated in the redundancy version
field of the HS-SCCH and are represented by the ldquobrdquo bit field ranging
from b = 0 to b = 3 All four constellation schemes are Gray encoded
ie the directly adjacent constellation symbols do not exhibit four com-
pletely different bits in order to reduce the impact of misdetection onbit errors
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High speed shared control channel (HS-SCCH)
45
Q
I
(ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1) (1 1ndash1ndash1)
(ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1) (1 1ndash1 1)
(ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1) (1ndash1ndash1 1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 0
Q
I
(ndash1 1 1 1) (ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1)
(ndash1 1 1ndash1) (ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1)
(ndash1ndash1 1ndash1) (ndash1ndash1ndash1ndash1) (1ndash1ndash1ndash1) (1ndash1 1ndash1)
(ndash1 1 1 1) (ndash1ndash1ndash1 1) (1ndash1ndash1 1) (1ndash1 1 1)
b = 2
Q
I
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (1ndash1 1 1) (ndash1ndash1 1 1)
(ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1) (ndash1 1 1 1)
(ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1) (ndash1 1 1ndash1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 1
Q
I
(1 1ndash1 1) (ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1)
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1)
(1ndash1ndash1ndash1) (ndash1ndash1ndash1ndash1) (ndash1ndash1 1ndash1) (1ndash1 1ndash1)
(1 1ndash1ndash1) (ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1)
b = 3
Fig 2-15 Constellation rearrangement in HSDPA
23 High speed shared control channel (HS-SCCH)
The HS-SCCH sends scheduling information to the UEs As seen before
the HS-PDSCH has a very flexible configuration for physical parame-
ters such as the coding rate number of code channels or retransmis-sions This high flexibility increases the complexity and engenders the
need for additional signaling information transferred on the HS-SCCH
Reception of user data in HSDPA is always a two-step procedure
First the receiver has to capture the scheduling control information
and afterwards based on the received control information it may start
demodulating and decoding the HS-PDSCH containing the user data
This two-step procedure is shown in Fig 2-16 below which lists what
kind of control information is sent to the UEs via the HS-SCCH Asshown in Fig 2-2 page 28 which describes the overall HSDPA chan-
nel structure there can be up to four HS-SCCHs assigned to one UE
But only one HS-SCCH would contain the scheduling information for
this UE within one TTI Thus the network can assign resources simul-
taneously to various UEs in the downlink direction
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HSDPA operation overview and physical channels
I would like to receive databut I dont know where myHS-PDSCH resources areand what they look like
HS-SCCH
Read the 1st HS-SCCH slotfor HS-DSCH channelizationcodes UE identity and
modulation scheme
Then the 2nd and 3rd HS-SCCHslots provide transport block sizeinformation hybrid ARQ process in-formation redundancy constellationversion new data indicator
HS-PDSCH
Fig 2-16 HS-SCCH control channel usage
Regarding the physical layer parameters we see in Fig 2-17 that the
HS-SCCH uses a channelization code with a spreading factor of 128
and it also uses the newly introduced transmit time interval of one sub-
frame which is equal to 2 ms It should be mentioned that the spread-ing factor of 128 requires double the capacity compared to similar con-
trol channels in WCDMA Release 99 reflecting the signaling overhead
needed to guarantee the huge flexibility introduced with HSDPA Addi-
tionally Fig 2-16 shows that the control information is sent consecu-
tively within one subframe The first slot within this subframe contains
the control information UE identity channelization code information
and modulation scheme identifier Slots 2 and 3 of the subframe con-tain the remaining control information Transport block size HARQ
process identifier redundancy version and new data indicator Conse-
quently the UE can self-decode slot 1 alone and slots 2 and 3 in a sec-
ond step even if they represent one logical unit This raw control infor-
mation is of course also channel coded using a turbo and on the phys-
ical layer the quantity of bits after the rate matching step is 40 bits con-
veyed in one slot corresponding to 666 micros [TS 25212 Ref 21] see also
Fig 2-28 page 56
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High speed shared control channel (HS-SCCH)
47
The HS-SCCH is a fixed rate (60 kbps SF = 128) downlinkphysical channel used to carry downlink signaling related toHS-DSCH transmission
Slot 0
Slot 1
Slot 2
Tslot
= 2560 chips
Data = 40 bits
1 subframe = 2 ms
Fig 2-17 Structure of High speed shared control channel HS-SCCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
We would like to return now to the time consecutive transmission of
control information There is a difference in the control information
in terms of its priority Some information is needed at the UE end
very urgently while other control information does not have such a
high priority But why This will be explained by looking at some tim-ing aspects defined for HSDPA If we consider the timing between
the shared data channel HS-PDSCH and the shared control chan-
nel HS-SCCH as shown in Fig 2-18 we see that the HS-PDSCH fol-
lows the HS-SCCH by exactly two slots or 5120 chips The HS-SCCH
is completely time-aligned with the general control channels CPICH
and P-CCPCH of the NodeB This is mandatory because it is a shared
channel Consider several UEs with different distances to the NodeBwanting to receive the HS-SCCH channel Thus it must have constant
timing that is known a priori The shared data channel HS-PDSCH is
now transmitted exactly 5120 chips after the first chip of the HS-SCCH
This leads to an overlapping slot thereby requiring multitasking recep-
tion at the UE end While the UE is still receiving the last slot of an
ongoing HS-SCCH subframe it may already start the reception of an
HS-PDSCH transport block The first slot in the HS-SCCH subframe
now contains information required by the physical layer to performdespreading and demodulation These values are the UE identity indi-
cating whether the UE will start demodulation of the HS-PDSCH or
not in case it is not scheduled the modulation scheme information
since the UE has to know how to interpret the received constellation
vector and whether it has to be considered as a QPSK or 16QAM con-
stellation point and finally the UE has to know which channelization
codes it has to apply to capture the HS-PDSCH transport block The
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HSDPA operation overview and physical channels
overall UE reaction time when being scheduled is now seen as 1 slot
or 2560 chips This tough requirement for the UEs is due to the objec-
tive to obtain overall a much shorter latency than legacy standards Theadditional control information such as the new data indicator redun-
dancy version and transport block size is not that urgent since it is
needed after demodulation but before channel decoding So first the
UE will sample the whole three slots of the HS-PDSCH and demodu-
late them into a bit stream which is finally handed over to the channel
decoder This principle is known as post-processing and is used typi-
cally in mobile communications technologies
J Start of HS-SCCH subframe 0 is aligned with startof P-CCPCH frames
J The HS-PDSCH starts
τ HS-PDSCH
(2times Tslot
= 5120 chips)
after the start of the HS-SCCH
UE identity etc
processing timeof receiver
HS-DSCH subframe
3 times Tslot= 7680 chips
3 times Tslot
= 7680 chips
τ HS-PDSCH
(2times Tslot
= 5120 chips)
HS-SCCH
HS-PDSCH
Fig 2-18 Timing relation between HS-SCCH and HS-PDSCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
Content of the HS-SCCH control channelThe control information contained in the HS-SCCH control chan-
nel has already been mentioned so we will now consider the values
in more detail We will begin with an overview of what kind of control
information is contained in the HS-SCCH channel before proceeding
with further details about the single control elements The following
control information is present in the HS-SCCH [TS 25212 Ref 21]
Channelization code set information (7 bits)
Modulation scheme information (1 bit) Transport block size information (6 bits)
Hybrid ARQ process information (3 bits)
Redundancy and constellation version (3 bits)
New data indicator (1 bit)
UE identity (16 bits) = H-RNTI
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High speed shared control channel (HS-SCCH)
49
Some of these parameters are more or less self-explanatory while oth-
ers require additional background information and closer examination
Modulation scheme information 1 bit
This single bit is used to inform the receiver whether the modulation
scheme QPSK or 16QAM is applied on the data channel HS-PDSCH
The interpretation of the bit x ms1 is as follows
ms1
x
if QPSK
otherwise
0
1
=
New data indicator 1 bit
The new data indicator bit field informs the receiving entity that the
prevailing PDU transmitted by the current HARQ process is either a
retransmission or contains new data This is done by setting the new
data bit to the value 0 for the first PDU on this particular HARQ process
and incrementing the value by 1 with every new data sent [TS 25321Ref 30] This leads to a toggled value In case the new data bit is not
incremented ie if it remains at its previous value it is an indicator for
retransmission
1st PDU of this
HARQ process
NDI = New data indicator
NDI = 0 NDI = 1
NACK
NDI = 1
ACK
NDI = 0
HS-SCCH HS-SCCH HS-SCCHHS-SCCH
ACK
Fig 2-19 New data indicator bit principle of incrementing value
Channelization code set information 7 bits
This field is used to indicate the number of channelization codes usedfor transmitting the transport block on the HS-PDSCH As was already
described the spreading factor applied on the HS-PDSCH is constant
with a value of 16 but the flexible values are the number of channeliza-
tion codes forming a cluster when using multiple codes and their posi-
tion in the code tree It is not allowed to distribute the code channels
over the code tree diagram For the sake of simplicity in signaling sev-
eral channelization codes form one cluster and these codes are con-
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HSDPA operation overview and physical channels
tiguous in the channelization code tree [TS 25213 Ref 22] Fig 2-20
illustrates the principle of indicating the channelization codes on the
HS-SCCH
SF = 16
Code ldquo0rdquo isreserved forcommonchannels
Code offset 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15P = 5O = 7
Code group indicatorx
ccs1 x
ccs2 x
ccs3 = min (Pminus 1 15 minusP)
Code offset indicatorx
ccs4 x
ccs5 x
ccs6 x
ccs7 = |Ominus 1minus P8 times15|
A cluster of codes
can be allocated to a UEC
ch16Ohellip C
ch16O + P minus 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1
2 2 2 2 2 2 2 2 2 2 2 2 2 2 14 14
1 2 3 4 5 6 7 8 9 10 11 12 13 14 2 1
3 3 3 3 3 3 3 3 3 3 3 3 3 13 13 13
1 2 3 4 5 6 7 8 9 10 11 12 13 3 2 1
4 4 4 4 4 4 4 4 4 4 4 4 12 12 12 121 2 3 4 5 6 7 8 9 10 11 12 4 3 2 1
5 5 5 5 5 5 5 5 5 5 5 11 11 11 11 11
1 2 3 4 5 6 7 8 9 10 11 5 4 3 2 1
6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10
1 2 3 4 5 6 7 8 9 10 6 5 4 3 2 1
7 7 7 7 7 7 7 7 7 9 9 9 9 9 9 9
1 2 3 4 5 6 7 8 9 7 6 5 4 3 2 1
8 8 8 8 8 8 8 8
8 7 6 5 4 3 2 1
0 (115)
1 (214)
2 (313)
3 (412)
4 (511)
5 (610)
6 (79)
7 (88) Redundant area
C l u s t e r c o d e i n d i c a t o r ( 3 b i t s )
Tree offset indicator (4 bits)
Signaled on HS-SCCH
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
PO
Decoding notation
Number ofmulti-codes
Offset fromleft right incode tree (SF = 16)
Fig 2-20 Channelization code set indicating the HS-PDSCH code cluster
The idea behind the code indication is a matrix with the rows repre-
senting the number of codes per cluster and the columns represent-
ing the position of that cluster the offset value in the code tree Recall-
ing that the maximum number of channelization codes per clusteris 15 and if the cluster size is 1 the offset values can also range from
1 to 15 the resulting matrix would have 15 rows and 15 columns Since
we know that four bits are needed to represent an integer from 1 to 15
we need a total of 4 + 4 = 8 bits for representation of the channeliza-
tion code set information It is a smart idea to save one bit The 15 times 15
matrix would contain much redundant information By way of analogy
like in a road map indicating distances between cities A table showing
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High speed shared control channel (HS-SCCH)
51
the distance from city A to city B the opposite distance from city B to
city A is redundant information The useful information has the form
of a triangle The idea is to cut the lower part rotate it and append itto the spare part of the upper table In this manner a table is obtained
with 7 rows and 15 columns and it is possible to indicate each position
in it with just 7 bits
1 5 r o w s 7
r o w s
Matrix reduction for channeli-
zation code set information
15 columns
Fig 2-21 Matrix size reduction for channelization code set information
The content of the channelization code set matrix can be described as
a value with two numbers The upper number is the number of mul-
ticodes forming one cluster and the lower number is the offset in the
channelization code tree Accordingly the example in Fig 2-20 can be
interpreted to mean the HS-SCCH sends the bits as row number 4 and
column number 6 in the matrix The content of this element are the
values 5 over 7 which have to be interpreted as a cluster size of 5 codesand an offset of 7
Transport block size information 6 bits
With a length of six bits the transport block size (TBS) informa-
tion informs the receiving UE entity about the data block size of the
transport block sent on the HS-PDSCH We should keep in mind the
link adaptation performed with the adaptive modulation and coding
scheme that was described in section 12 page 10 The ratio errorcorrection and user data are flexible while the physical layer param-
eters such as the spreading factor modulation scheme and number of
channelization codes determine the physical block size This physical
block consists of the user data ratio or transport block size and the for-
ward error correction or redundancy information As this ratio is flex-
ible the HS-SCCH will inform the receiving UE entity about the size
of the transport block Here too there is a strategy of bit reduction the
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HSDPA operation overview and physical channels
goal is to inform the receiver with as few bits as possible A non-effi-
cient approach would involve conversion of the decimal number repre-
senting the TBS into a binary sequence but the number of bits neededwould exceed the space available on the HS-SCCH Imagine that the
range of transport block sizes depends on the physical layer condi-
tions The ambient physical layer parameters modulation scheme and
number of channelization codes set a certain working point where the
remaining flexibility for a different TBS configuration can be obtained
by more or less puncturing resulting in a flexible ratio between for-
ward error correction and user data This will lead to a two-step proce-
dure when evaluating the transport block size First the receiver exam-
ines the information modulation scheme and number of channeliza-
tion codes scheduled via HS-SCCH which indicate the value k0 l as
shown in Fig 2-22 The 6-bit HS-SCCH control parameter transport
block size information will be the transport format resource indica-
tor (TFRI) named ki Let k t be the sum of the two values kt = ki + k0i
Both values kt and k0 i can be obtained from tables given by [TS 25321
Ref 30] The range for the TFRI is from 1 to 256 and the derived trans-port block size ranges from 137 bits to 27 952 bits The first table indi-
cates the value k 0 i based on the channelization code and the modula-
tion scheme
Combination i Modulation scheme Number of channelization codes k0 i
0
QPSK
1 1
1 2 40
2 3 633 4 79
4 5 92
5 6 102
Fig 2-22 Extract from TS 25321 table representing k0 i
The second table indicates the final transport block size based on kt
Index TB size Index TB size Index TB size1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
4 173 89 1456 174 6673
5 185 90 1483 175 6793
6 197 91 1509 176 6916
7 209 92 1537 177 7041
Fig 2-23 Extract from TS 25321 table representing kt
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High speed shared control channel (HS-SCCH)
53
J The transport block size used on HS-DSCH is not signaled explicitly on HS-SCCHJ Instead a transport block size index k
i is signaled to indicate the transport block size
First stepModulation scheme andnumber of channelizationcodes as signaled on HS-SCCHdetermine value k
0 i
Second step
Index kt = k
i + k
0i
determines HS-DSCH
transport block size
kt = k
i + k
0i
Table according to 3GPP TS 25321 extract from QPSK section
Table according to 3GPP TS 25321 254 entries in total
Combination i Modulation
scheme
Number of
channelization codes
k0 i
0
QPSK
1 1
1 2 40
2 3 63
3 4 79
4 hellip hellip
Index TB size Index TB size Index TB size
1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
helliphellip hellip hellip hellip hellip
Fig 2-24 Retrieval of transport block size information
Source Fig 2-22 to Fig 2-24 [TS 25321 Ref 30] reproduced by permission of 3GPP
Hybrid ARQ process information 3 bits
The concept behind the hybrid automatic repeat request (HARQ) was
introduced in section 13 page 14 One feature is the possibility of
multitasking ie having several HARQ processes activated at the same
time Fig 2-25 below shows the need to signal the process identity tothe receiver Remember that on the downlink there is a shared chan-
nel concept so the NodeB can flexibly decide which UE will be sched-
uled with a downlink transport block Up to eight HARQ processes
can be signaled via higher layers to one UE Note however that due to
the round-trip timing six HARQ processes must be active to achieve
the maximum throughput as shown in Fig 2-51 page 79 Compared
with HSUPA the HARQ processes on the downlink are asynchronous
so they have to be indicated but on the uplink they are synchronous sothey do not need to be signaled explicitly
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HSDPA operation overview and physical channels
Asynchronous DL minus Synchronous ULNumber of H-ARQ rocesses = 1 to 8 er UE
UL HS-DPCCH UE1
UE1 HARQ processes 1 to 4
3 4 1 42 11 1 32retrans
2
A N A A
A A
N A
UL HS-DPCCH UE2
HS-PDSCH
UE2 HARQ processes 1 to 2
Fig 2-25 HARQ process indication on HS-SCCH
Fig 2-25 shows a typical situation on the downlink (point-to-multi-
point) The NodeB sends data to several UEs sharing the HS-PDSCH
so therefore the HARQ process is asynchronous The time when a
transport block is retransmitted is not fixed For this reason the pro-
cess identifier is signaled on the HS-SCCH Based on the HARQ pro-
cess identity and the new data indicator bit the receiving entity knows
which part of the soft buffer memory has to be used in case of soft com-bining On the uplink the situation is slightly simpler The UE only
communicates with one NodeB so it is a point-to-point connection
Thus retransmission always occurs at a fixed time linked to the origi-
nal transmission
Redundancy and constellation version 3 bits
Adaptive modulation and coding involve flexible selection of modula-tion and coding schemes that are signaled to the receiving UE via the
parameters transport block size and modulation scheme information
Another concept used in HSDPA was previously discussed Chase com-
bining or incremental redundancy (see section 222 page 41) This
means that in case of retransmission the transmit entity can dynami-
cally select another puncturing scheme or keep the puncturing as it was
in the original transmission The applied puncturing scheme is signaled
as redundancy information to the receiver Additionally in case of the16QAM modulation scheme the transmitter can select another constel-
lation arrangement which is also signaled to the UE with the three bits
for the redundancy and constellation version see Fig 2-15 page 45
Depending on the modulation scheme (QPSK or 16QAM) there are
two different tables indicating the parameters ldquosrdquo ldquorrdquo and ldquobrdquo The
parameters ldquosrdquo and ldquorrdquo indicate which scheme is used for puncturing
ie if the puncturing mechanism prioritizes the systematic bits or not
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High speed shared control channel (HS-SCCH)
55
and which puncturing algorithm is used The parameter ldquobrdquo indicates
the constellation mapping version The receiver needs this information
to perform proper demodulation and decoding
Initial transmission
1st retransmission
2nd retransmission
3rd retransmission
r
0
0
1
1
2
2
3
xrv
(value)
s
0 1
1 0
2 1
3 0
4 1
5 0
6 1
7 0 3
s = 1 Systematic bits are prioritizeds = 0 Non-systematic bits are prioritized
r (range 0 to 3 for QPSK) influencesJ Input parameter for puncturing or (together with s) for repetition algorithm defined in TS 25212J Selection of parity bits
Redundancy version coding sequences are signaled on HS-SCCH egndash 0 2 5 6 One initial transmission + 3 retransmissions with different r and s parameters
Fig 2-26 Signaling of redundancy version parameters r and s QPSK case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
Initial transmission
2nd retransmission
1st retransmission
3rd retransmission
r (range 0 to 1 for 16QAM)influences input parameterfor puncturing or (togetherwith s) for repetitionalgorithm defined in
TS 25212 and thus selectionof parity bits
Redundancy version coding sequences are signaled on HS-SCCH egminus 6 4 0 5 Chase combining (no change in s and r parameters ie same redundancyversion) with four possible constellations
x rv (value) s r b
0 1 0 0
1 0 0 0
2 1 1 1
3 0 1 1
4 1 0 1
5 1 0 2
6 1 0 3
7 1 1 0
Definition of parameter s as for QPSK
b (range 0 to 3) describes constellationrearrangement to averagereliability of bits
Fig 2-27 Signaling of redundancy version parameters r s and b 16QAM case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
UE identity H-RNTI 16 bits
The HSDPA radio network transaction identifier (H-RNTI) unam-
biguously identifies the UE having an HS-PDSCH assignment within
a cell It is allocated to the UE via layer 3 signaling procedures at the
radio bearer setup if the radio bearer is an HSDPA connection This
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HSDPA operation overview and physical channels
value represents a temporary name of the UE used to address it when
scheduling data packets via HS-SCCH
HS-SCCH channel coding
The control information contained in the HS-SCCH is of course pro-
tected with channel coding mechanisms the whole coding chain is
described in Fig 2-28 Fig 2-18 page 48 presents the separation of
the control information into two code blocks which are sent consec-
utively mapped on slot 1 and slot 2 + 3 of one HS-SCCH subframe
This principle is also visible in the coding chain The first control block
consisting of channelization information modulation scheme and UE
identity is coded separately from the remaining control values to enable
the UE receiver to decode this first slot separately and prepare for pos-
sible HS-PDSCH reception The coding steps shown in Fig 2-28 such
as rate matching 1 and 2 are similar to the HS-PDSCH coding chain
and are further described in [TS 25212 Ref 21]
Channelcoding 1
R atematching 1
mux
Channelcoding 2
Ratematching 2
RVcoding
UE-specificCRC attachment
UE-specificmasking
Physical channelmapping
r s b
mux
Channelizationcode set
Modulationscheme
Transport block size information
HARQ processinformation
Redundancy andconstellation version
New data indicator
UE identity
UE identity
Fig 2-28 Channel coding for HS-SCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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High speed dedicated physical control channel (HS-DPCCH)
57
24 High speed dedicated physical control channel (HS-DPCCH)
In an active HSDPA connection the UE has to send acknowledgment ornon-acknowledgment reports (as described in section 13 page 14
where the HARQ process is described) as well as channel status infor-
mation to the network The reporting is performed on this physical
control channel HS-DPCCH
As ubiquitous in HSDPA the uplink is also configured into a subframe
structure of 2 ms corresponding to three slots The first slot of the sub-
frame carries the ACK NACK information the UE sends to the NodeB
while the following two slots ie slot 2 and 3 of the subframe convey
the CQI value the channel quality information to the NodeB
Subframe 0 Subframe i Subframe 4
Tslot
= 2560 chips J The spreading factor of theHS-DPCCH is 256 (10 bits peruplink slot)
J The HS-DPCCH can only existtogether with an UL DPCCH
(ded phys control channel)J The DPDCH (dedicated physical data channel) the DPCCH andthe HS-DPCCH are IQ codemultiplexed
HARQ-ACK CQI = Channel quality information
2 times Tslot
= 5120 chips
One radio frame Tf = 10 ms
One HS-DPCCH subframe 2 ms
Fig 2-29 HS-DPCCH configuration
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The slot format for HS-DPCCH describes a quantity of 30 bits per sub-frame resulting in a data rate of 15 kbps The spreading factor used for
the HS-DPCCH is constant and is always equal to 256 but the chan-
nelization code that is used as well as the mapping on either the I or
Q axis depends on several factors eg the co-existence of an HSDPA
connection with a circuit-switched connection meaning whether a
DPDCH established or not Fig 2-36 page 64 illustrates this IQ
mapping and Fig 2-35 page 63 shows the channelization code used
for HS-DPCCH
The HS-DPCCH builds a logical unit of one subframe but having the
independent control information HARQ-ACK and CQI included which
could be separately decoded at the NodeB Note that the slot carrying
the ACK NACK statement is active only when the UE has been sched-
uled by an HS-PDSCH subframe in the corresponding downlink sub-
frame previously Assuming the UE has not received a transport block
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HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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High speed shared control channel (HS-SCCH)
45
Q
I
(ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1) (1 1ndash1ndash1)
(ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1) (1 1ndash1 1)
(ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1) (1ndash1ndash1 1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 0
Q
I
(ndash1 1 1 1) (ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1)
(ndash1 1 1ndash1) (ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1)
(ndash1ndash1 1ndash1) (ndash1ndash1ndash1ndash1) (1ndash1ndash1ndash1) (1ndash1 1ndash1)
(ndash1 1 1 1) (ndash1ndash1ndash1 1) (1ndash1ndash1 1) (1ndash1 1 1)
b = 2
Q
I
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (1ndash1 1 1) (ndash1ndash1 1 1)
(ndash1 1ndash1 1) (1 1ndash1 1) (1 1 1 1) (ndash1 1 1 1)
(ndash1 1ndash1ndash1) (1 1ndash1ndash1) (1 1 1ndash1) (ndash1 1 1ndash1)
(ndash1ndash1ndash1ndash1)(ndash1ndash1 1ndash1) (1ndash1 1ndash1) (1ndash1ndash1ndash1)
b = 1
Q
I
(1 1ndash1 1) (ndash1 1ndash1 1) (ndash1 1 1 1) (1 1 1 1)
(1ndash1ndash1 1) (ndash1ndash1ndash1 1) (ndash1ndash1 1 1) (1ndash1 1 1)
(1ndash1ndash1ndash1) (ndash1ndash1ndash1ndash1) (ndash1ndash1 1ndash1) (1ndash1 1ndash1)
(1 1ndash1ndash1) (ndash1 1ndash1ndash1) (ndash1 1 1ndash1) (1 1 1ndash1)
b = 3
Fig 2-15 Constellation rearrangement in HSDPA
23 High speed shared control channel (HS-SCCH)
The HS-SCCH sends scheduling information to the UEs As seen before
the HS-PDSCH has a very flexible configuration for physical parame-
ters such as the coding rate number of code channels or retransmis-sions This high flexibility increases the complexity and engenders the
need for additional signaling information transferred on the HS-SCCH
Reception of user data in HSDPA is always a two-step procedure
First the receiver has to capture the scheduling control information
and afterwards based on the received control information it may start
demodulating and decoding the HS-PDSCH containing the user data
This two-step procedure is shown in Fig 2-16 below which lists what
kind of control information is sent to the UEs via the HS-SCCH Asshown in Fig 2-2 page 28 which describes the overall HSDPA chan-
nel structure there can be up to four HS-SCCHs assigned to one UE
But only one HS-SCCH would contain the scheduling information for
this UE within one TTI Thus the network can assign resources simul-
taneously to various UEs in the downlink direction
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HSDPA operation overview and physical channels
I would like to receive databut I dont know where myHS-PDSCH resources areand what they look like
HS-SCCH
Read the 1st HS-SCCH slotfor HS-DSCH channelizationcodes UE identity and
modulation scheme
Then the 2nd and 3rd HS-SCCHslots provide transport block sizeinformation hybrid ARQ process in-formation redundancy constellationversion new data indicator
HS-PDSCH
Fig 2-16 HS-SCCH control channel usage
Regarding the physical layer parameters we see in Fig 2-17 that the
HS-SCCH uses a channelization code with a spreading factor of 128
and it also uses the newly introduced transmit time interval of one sub-
frame which is equal to 2 ms It should be mentioned that the spread-ing factor of 128 requires double the capacity compared to similar con-
trol channels in WCDMA Release 99 reflecting the signaling overhead
needed to guarantee the huge flexibility introduced with HSDPA Addi-
tionally Fig 2-16 shows that the control information is sent consecu-
tively within one subframe The first slot within this subframe contains
the control information UE identity channelization code information
and modulation scheme identifier Slots 2 and 3 of the subframe con-tain the remaining control information Transport block size HARQ
process identifier redundancy version and new data indicator Conse-
quently the UE can self-decode slot 1 alone and slots 2 and 3 in a sec-
ond step even if they represent one logical unit This raw control infor-
mation is of course also channel coded using a turbo and on the phys-
ical layer the quantity of bits after the rate matching step is 40 bits con-
veyed in one slot corresponding to 666 micros [TS 25212 Ref 21] see also
Fig 2-28 page 56
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High speed shared control channel (HS-SCCH)
47
The HS-SCCH is a fixed rate (60 kbps SF = 128) downlinkphysical channel used to carry downlink signaling related toHS-DSCH transmission
Slot 0
Slot 1
Slot 2
Tslot
= 2560 chips
Data = 40 bits
1 subframe = 2 ms
Fig 2-17 Structure of High speed shared control channel HS-SCCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
We would like to return now to the time consecutive transmission of
control information There is a difference in the control information
in terms of its priority Some information is needed at the UE end
very urgently while other control information does not have such a
high priority But why This will be explained by looking at some tim-ing aspects defined for HSDPA If we consider the timing between
the shared data channel HS-PDSCH and the shared control chan-
nel HS-SCCH as shown in Fig 2-18 we see that the HS-PDSCH fol-
lows the HS-SCCH by exactly two slots or 5120 chips The HS-SCCH
is completely time-aligned with the general control channels CPICH
and P-CCPCH of the NodeB This is mandatory because it is a shared
channel Consider several UEs with different distances to the NodeBwanting to receive the HS-SCCH channel Thus it must have constant
timing that is known a priori The shared data channel HS-PDSCH is
now transmitted exactly 5120 chips after the first chip of the HS-SCCH
This leads to an overlapping slot thereby requiring multitasking recep-
tion at the UE end While the UE is still receiving the last slot of an
ongoing HS-SCCH subframe it may already start the reception of an
HS-PDSCH transport block The first slot in the HS-SCCH subframe
now contains information required by the physical layer to performdespreading and demodulation These values are the UE identity indi-
cating whether the UE will start demodulation of the HS-PDSCH or
not in case it is not scheduled the modulation scheme information
since the UE has to know how to interpret the received constellation
vector and whether it has to be considered as a QPSK or 16QAM con-
stellation point and finally the UE has to know which channelization
codes it has to apply to capture the HS-PDSCH transport block The
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HSDPA operation overview and physical channels
overall UE reaction time when being scheduled is now seen as 1 slot
or 2560 chips This tough requirement for the UEs is due to the objec-
tive to obtain overall a much shorter latency than legacy standards Theadditional control information such as the new data indicator redun-
dancy version and transport block size is not that urgent since it is
needed after demodulation but before channel decoding So first the
UE will sample the whole three slots of the HS-PDSCH and demodu-
late them into a bit stream which is finally handed over to the channel
decoder This principle is known as post-processing and is used typi-
cally in mobile communications technologies
J Start of HS-SCCH subframe 0 is aligned with startof P-CCPCH frames
J The HS-PDSCH starts
τ HS-PDSCH
(2times Tslot
= 5120 chips)
after the start of the HS-SCCH
UE identity etc
processing timeof receiver
HS-DSCH subframe
3 times Tslot= 7680 chips
3 times Tslot
= 7680 chips
τ HS-PDSCH
(2times Tslot
= 5120 chips)
HS-SCCH
HS-PDSCH
Fig 2-18 Timing relation between HS-SCCH and HS-PDSCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
Content of the HS-SCCH control channelThe control information contained in the HS-SCCH control chan-
nel has already been mentioned so we will now consider the values
in more detail We will begin with an overview of what kind of control
information is contained in the HS-SCCH channel before proceeding
with further details about the single control elements The following
control information is present in the HS-SCCH [TS 25212 Ref 21]
Channelization code set information (7 bits)
Modulation scheme information (1 bit) Transport block size information (6 bits)
Hybrid ARQ process information (3 bits)
Redundancy and constellation version (3 bits)
New data indicator (1 bit)
UE identity (16 bits) = H-RNTI
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High speed shared control channel (HS-SCCH)
49
Some of these parameters are more or less self-explanatory while oth-
ers require additional background information and closer examination
Modulation scheme information 1 bit
This single bit is used to inform the receiver whether the modulation
scheme QPSK or 16QAM is applied on the data channel HS-PDSCH
The interpretation of the bit x ms1 is as follows
ms1
x
if QPSK
otherwise
0
1
=
New data indicator 1 bit
The new data indicator bit field informs the receiving entity that the
prevailing PDU transmitted by the current HARQ process is either a
retransmission or contains new data This is done by setting the new
data bit to the value 0 for the first PDU on this particular HARQ process
and incrementing the value by 1 with every new data sent [TS 25321Ref 30] This leads to a toggled value In case the new data bit is not
incremented ie if it remains at its previous value it is an indicator for
retransmission
1st PDU of this
HARQ process
NDI = New data indicator
NDI = 0 NDI = 1
NACK
NDI = 1
ACK
NDI = 0
HS-SCCH HS-SCCH HS-SCCHHS-SCCH
ACK
Fig 2-19 New data indicator bit principle of incrementing value
Channelization code set information 7 bits
This field is used to indicate the number of channelization codes usedfor transmitting the transport block on the HS-PDSCH As was already
described the spreading factor applied on the HS-PDSCH is constant
with a value of 16 but the flexible values are the number of channeliza-
tion codes forming a cluster when using multiple codes and their posi-
tion in the code tree It is not allowed to distribute the code channels
over the code tree diagram For the sake of simplicity in signaling sev-
eral channelization codes form one cluster and these codes are con-
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HSDPA operation overview and physical channels
tiguous in the channelization code tree [TS 25213 Ref 22] Fig 2-20
illustrates the principle of indicating the channelization codes on the
HS-SCCH
SF = 16
Code ldquo0rdquo isreserved forcommonchannels
Code offset 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15P = 5O = 7
Code group indicatorx
ccs1 x
ccs2 x
ccs3 = min (Pminus 1 15 minusP)
Code offset indicatorx
ccs4 x
ccs5 x
ccs6 x
ccs7 = |Ominus 1minus P8 times15|
A cluster of codes
can be allocated to a UEC
ch16Ohellip C
ch16O + P minus 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1
2 2 2 2 2 2 2 2 2 2 2 2 2 2 14 14
1 2 3 4 5 6 7 8 9 10 11 12 13 14 2 1
3 3 3 3 3 3 3 3 3 3 3 3 3 13 13 13
1 2 3 4 5 6 7 8 9 10 11 12 13 3 2 1
4 4 4 4 4 4 4 4 4 4 4 4 12 12 12 121 2 3 4 5 6 7 8 9 10 11 12 4 3 2 1
5 5 5 5 5 5 5 5 5 5 5 11 11 11 11 11
1 2 3 4 5 6 7 8 9 10 11 5 4 3 2 1
6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10
1 2 3 4 5 6 7 8 9 10 6 5 4 3 2 1
7 7 7 7 7 7 7 7 7 9 9 9 9 9 9 9
1 2 3 4 5 6 7 8 9 7 6 5 4 3 2 1
8 8 8 8 8 8 8 8
8 7 6 5 4 3 2 1
0 (115)
1 (214)
2 (313)
3 (412)
4 (511)
5 (610)
6 (79)
7 (88) Redundant area
C l u s t e r c o d e i n d i c a t o r ( 3 b i t s )
Tree offset indicator (4 bits)
Signaled on HS-SCCH
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
PO
Decoding notation
Number ofmulti-codes
Offset fromleft right incode tree (SF = 16)
Fig 2-20 Channelization code set indicating the HS-PDSCH code cluster
The idea behind the code indication is a matrix with the rows repre-
senting the number of codes per cluster and the columns represent-
ing the position of that cluster the offset value in the code tree Recall-
ing that the maximum number of channelization codes per clusteris 15 and if the cluster size is 1 the offset values can also range from
1 to 15 the resulting matrix would have 15 rows and 15 columns Since
we know that four bits are needed to represent an integer from 1 to 15
we need a total of 4 + 4 = 8 bits for representation of the channeliza-
tion code set information It is a smart idea to save one bit The 15 times 15
matrix would contain much redundant information By way of analogy
like in a road map indicating distances between cities A table showing
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High speed shared control channel (HS-SCCH)
51
the distance from city A to city B the opposite distance from city B to
city A is redundant information The useful information has the form
of a triangle The idea is to cut the lower part rotate it and append itto the spare part of the upper table In this manner a table is obtained
with 7 rows and 15 columns and it is possible to indicate each position
in it with just 7 bits
1 5 r o w s 7
r o w s
Matrix reduction for channeli-
zation code set information
15 columns
Fig 2-21 Matrix size reduction for channelization code set information
The content of the channelization code set matrix can be described as
a value with two numbers The upper number is the number of mul-
ticodes forming one cluster and the lower number is the offset in the
channelization code tree Accordingly the example in Fig 2-20 can be
interpreted to mean the HS-SCCH sends the bits as row number 4 and
column number 6 in the matrix The content of this element are the
values 5 over 7 which have to be interpreted as a cluster size of 5 codesand an offset of 7
Transport block size information 6 bits
With a length of six bits the transport block size (TBS) informa-
tion informs the receiving UE entity about the data block size of the
transport block sent on the HS-PDSCH We should keep in mind the
link adaptation performed with the adaptive modulation and coding
scheme that was described in section 12 page 10 The ratio errorcorrection and user data are flexible while the physical layer param-
eters such as the spreading factor modulation scheme and number of
channelization codes determine the physical block size This physical
block consists of the user data ratio or transport block size and the for-
ward error correction or redundancy information As this ratio is flex-
ible the HS-SCCH will inform the receiving UE entity about the size
of the transport block Here too there is a strategy of bit reduction the
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HSDPA operation overview and physical channels
goal is to inform the receiver with as few bits as possible A non-effi-
cient approach would involve conversion of the decimal number repre-
senting the TBS into a binary sequence but the number of bits neededwould exceed the space available on the HS-SCCH Imagine that the
range of transport block sizes depends on the physical layer condi-
tions The ambient physical layer parameters modulation scheme and
number of channelization codes set a certain working point where the
remaining flexibility for a different TBS configuration can be obtained
by more or less puncturing resulting in a flexible ratio between for-
ward error correction and user data This will lead to a two-step proce-
dure when evaluating the transport block size First the receiver exam-
ines the information modulation scheme and number of channeliza-
tion codes scheduled via HS-SCCH which indicate the value k0 l as
shown in Fig 2-22 The 6-bit HS-SCCH control parameter transport
block size information will be the transport format resource indica-
tor (TFRI) named ki Let k t be the sum of the two values kt = ki + k0i
Both values kt and k0 i can be obtained from tables given by [TS 25321
Ref 30] The range for the TFRI is from 1 to 256 and the derived trans-port block size ranges from 137 bits to 27 952 bits The first table indi-
cates the value k 0 i based on the channelization code and the modula-
tion scheme
Combination i Modulation scheme Number of channelization codes k0 i
0
QPSK
1 1
1 2 40
2 3 633 4 79
4 5 92
5 6 102
Fig 2-22 Extract from TS 25321 table representing k0 i
The second table indicates the final transport block size based on kt
Index TB size Index TB size Index TB size1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
4 173 89 1456 174 6673
5 185 90 1483 175 6793
6 197 91 1509 176 6916
7 209 92 1537 177 7041
Fig 2-23 Extract from TS 25321 table representing kt
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High speed shared control channel (HS-SCCH)
53
J The transport block size used on HS-DSCH is not signaled explicitly on HS-SCCHJ Instead a transport block size index k
i is signaled to indicate the transport block size
First stepModulation scheme andnumber of channelizationcodes as signaled on HS-SCCHdetermine value k
0 i
Second step
Index kt = k
i + k
0i
determines HS-DSCH
transport block size
kt = k
i + k
0i
Table according to 3GPP TS 25321 extract from QPSK section
Table according to 3GPP TS 25321 254 entries in total
Combination i Modulation
scheme
Number of
channelization codes
k0 i
0
QPSK
1 1
1 2 40
2 3 63
3 4 79
4 hellip hellip
Index TB size Index TB size Index TB size
1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
helliphellip hellip hellip hellip hellip
Fig 2-24 Retrieval of transport block size information
Source Fig 2-22 to Fig 2-24 [TS 25321 Ref 30] reproduced by permission of 3GPP
Hybrid ARQ process information 3 bits
The concept behind the hybrid automatic repeat request (HARQ) was
introduced in section 13 page 14 One feature is the possibility of
multitasking ie having several HARQ processes activated at the same
time Fig 2-25 below shows the need to signal the process identity tothe receiver Remember that on the downlink there is a shared chan-
nel concept so the NodeB can flexibly decide which UE will be sched-
uled with a downlink transport block Up to eight HARQ processes
can be signaled via higher layers to one UE Note however that due to
the round-trip timing six HARQ processes must be active to achieve
the maximum throughput as shown in Fig 2-51 page 79 Compared
with HSUPA the HARQ processes on the downlink are asynchronous
so they have to be indicated but on the uplink they are synchronous sothey do not need to be signaled explicitly
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HSDPA operation overview and physical channels
Asynchronous DL minus Synchronous ULNumber of H-ARQ rocesses = 1 to 8 er UE
UL HS-DPCCH UE1
UE1 HARQ processes 1 to 4
3 4 1 42 11 1 32retrans
2
A N A A
A A
N A
UL HS-DPCCH UE2
HS-PDSCH
UE2 HARQ processes 1 to 2
Fig 2-25 HARQ process indication on HS-SCCH
Fig 2-25 shows a typical situation on the downlink (point-to-multi-
point) The NodeB sends data to several UEs sharing the HS-PDSCH
so therefore the HARQ process is asynchronous The time when a
transport block is retransmitted is not fixed For this reason the pro-
cess identifier is signaled on the HS-SCCH Based on the HARQ pro-
cess identity and the new data indicator bit the receiving entity knows
which part of the soft buffer memory has to be used in case of soft com-bining On the uplink the situation is slightly simpler The UE only
communicates with one NodeB so it is a point-to-point connection
Thus retransmission always occurs at a fixed time linked to the origi-
nal transmission
Redundancy and constellation version 3 bits
Adaptive modulation and coding involve flexible selection of modula-tion and coding schemes that are signaled to the receiving UE via the
parameters transport block size and modulation scheme information
Another concept used in HSDPA was previously discussed Chase com-
bining or incremental redundancy (see section 222 page 41) This
means that in case of retransmission the transmit entity can dynami-
cally select another puncturing scheme or keep the puncturing as it was
in the original transmission The applied puncturing scheme is signaled
as redundancy information to the receiver Additionally in case of the16QAM modulation scheme the transmitter can select another constel-
lation arrangement which is also signaled to the UE with the three bits
for the redundancy and constellation version see Fig 2-15 page 45
Depending on the modulation scheme (QPSK or 16QAM) there are
two different tables indicating the parameters ldquosrdquo ldquorrdquo and ldquobrdquo The
parameters ldquosrdquo and ldquorrdquo indicate which scheme is used for puncturing
ie if the puncturing mechanism prioritizes the systematic bits or not
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High speed shared control channel (HS-SCCH)
55
and which puncturing algorithm is used The parameter ldquobrdquo indicates
the constellation mapping version The receiver needs this information
to perform proper demodulation and decoding
Initial transmission
1st retransmission
2nd retransmission
3rd retransmission
r
0
0
1
1
2
2
3
xrv
(value)
s
0 1
1 0
2 1
3 0
4 1
5 0
6 1
7 0 3
s = 1 Systematic bits are prioritizeds = 0 Non-systematic bits are prioritized
r (range 0 to 3 for QPSK) influencesJ Input parameter for puncturing or (together with s) for repetition algorithm defined in TS 25212J Selection of parity bits
Redundancy version coding sequences are signaled on HS-SCCH egndash 0 2 5 6 One initial transmission + 3 retransmissions with different r and s parameters
Fig 2-26 Signaling of redundancy version parameters r and s QPSK case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
Initial transmission
2nd retransmission
1st retransmission
3rd retransmission
r (range 0 to 1 for 16QAM)influences input parameterfor puncturing or (togetherwith s) for repetitionalgorithm defined in
TS 25212 and thus selectionof parity bits
Redundancy version coding sequences are signaled on HS-SCCH egminus 6 4 0 5 Chase combining (no change in s and r parameters ie same redundancyversion) with four possible constellations
x rv (value) s r b
0 1 0 0
1 0 0 0
2 1 1 1
3 0 1 1
4 1 0 1
5 1 0 2
6 1 0 3
7 1 1 0
Definition of parameter s as for QPSK
b (range 0 to 3) describes constellationrearrangement to averagereliability of bits
Fig 2-27 Signaling of redundancy version parameters r s and b 16QAM case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
UE identity H-RNTI 16 bits
The HSDPA radio network transaction identifier (H-RNTI) unam-
biguously identifies the UE having an HS-PDSCH assignment within
a cell It is allocated to the UE via layer 3 signaling procedures at the
radio bearer setup if the radio bearer is an HSDPA connection This
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HSDPA operation overview and physical channels
value represents a temporary name of the UE used to address it when
scheduling data packets via HS-SCCH
HS-SCCH channel coding
The control information contained in the HS-SCCH is of course pro-
tected with channel coding mechanisms the whole coding chain is
described in Fig 2-28 Fig 2-18 page 48 presents the separation of
the control information into two code blocks which are sent consec-
utively mapped on slot 1 and slot 2 + 3 of one HS-SCCH subframe
This principle is also visible in the coding chain The first control block
consisting of channelization information modulation scheme and UE
identity is coded separately from the remaining control values to enable
the UE receiver to decode this first slot separately and prepare for pos-
sible HS-PDSCH reception The coding steps shown in Fig 2-28 such
as rate matching 1 and 2 are similar to the HS-PDSCH coding chain
and are further described in [TS 25212 Ref 21]
Channelcoding 1
R atematching 1
mux
Channelcoding 2
Ratematching 2
RVcoding
UE-specificCRC attachment
UE-specificmasking
Physical channelmapping
r s b
mux
Channelizationcode set
Modulationscheme
Transport block size information
HARQ processinformation
Redundancy andconstellation version
New data indicator
UE identity
UE identity
Fig 2-28 Channel coding for HS-SCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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High speed dedicated physical control channel (HS-DPCCH)
57
24 High speed dedicated physical control channel (HS-DPCCH)
In an active HSDPA connection the UE has to send acknowledgment ornon-acknowledgment reports (as described in section 13 page 14
where the HARQ process is described) as well as channel status infor-
mation to the network The reporting is performed on this physical
control channel HS-DPCCH
As ubiquitous in HSDPA the uplink is also configured into a subframe
structure of 2 ms corresponding to three slots The first slot of the sub-
frame carries the ACK NACK information the UE sends to the NodeB
while the following two slots ie slot 2 and 3 of the subframe convey
the CQI value the channel quality information to the NodeB
Subframe 0 Subframe i Subframe 4
Tslot
= 2560 chips J The spreading factor of theHS-DPCCH is 256 (10 bits peruplink slot)
J The HS-DPCCH can only existtogether with an UL DPCCH
(ded phys control channel)J The DPDCH (dedicated physical data channel) the DPCCH andthe HS-DPCCH are IQ codemultiplexed
HARQ-ACK CQI = Channel quality information
2 times Tslot
= 5120 chips
One radio frame Tf = 10 ms
One HS-DPCCH subframe 2 ms
Fig 2-29 HS-DPCCH configuration
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The slot format for HS-DPCCH describes a quantity of 30 bits per sub-frame resulting in a data rate of 15 kbps The spreading factor used for
the HS-DPCCH is constant and is always equal to 256 but the chan-
nelization code that is used as well as the mapping on either the I or
Q axis depends on several factors eg the co-existence of an HSDPA
connection with a circuit-switched connection meaning whether a
DPDCH established or not Fig 2-36 page 64 illustrates this IQ
mapping and Fig 2-35 page 63 shows the channelization code used
for HS-DPCCH
The HS-DPCCH builds a logical unit of one subframe but having the
independent control information HARQ-ACK and CQI included which
could be separately decoded at the NodeB Note that the slot carrying
the ACK NACK statement is active only when the UE has been sched-
uled by an HS-PDSCH subframe in the corresponding downlink sub-
frame previously Assuming the UE has not received a transport block
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HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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HSDPA operation overview and physical channels
I would like to receive databut I dont know where myHS-PDSCH resources areand what they look like
HS-SCCH
Read the 1st HS-SCCH slotfor HS-DSCH channelizationcodes UE identity and
modulation scheme
Then the 2nd and 3rd HS-SCCHslots provide transport block sizeinformation hybrid ARQ process in-formation redundancy constellationversion new data indicator
HS-PDSCH
Fig 2-16 HS-SCCH control channel usage
Regarding the physical layer parameters we see in Fig 2-17 that the
HS-SCCH uses a channelization code with a spreading factor of 128
and it also uses the newly introduced transmit time interval of one sub-
frame which is equal to 2 ms It should be mentioned that the spread-ing factor of 128 requires double the capacity compared to similar con-
trol channels in WCDMA Release 99 reflecting the signaling overhead
needed to guarantee the huge flexibility introduced with HSDPA Addi-
tionally Fig 2-16 shows that the control information is sent consecu-
tively within one subframe The first slot within this subframe contains
the control information UE identity channelization code information
and modulation scheme identifier Slots 2 and 3 of the subframe con-tain the remaining control information Transport block size HARQ
process identifier redundancy version and new data indicator Conse-
quently the UE can self-decode slot 1 alone and slots 2 and 3 in a sec-
ond step even if they represent one logical unit This raw control infor-
mation is of course also channel coded using a turbo and on the phys-
ical layer the quantity of bits after the rate matching step is 40 bits con-
veyed in one slot corresponding to 666 micros [TS 25212 Ref 21] see also
Fig 2-28 page 56
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High speed shared control channel (HS-SCCH)
47
The HS-SCCH is a fixed rate (60 kbps SF = 128) downlinkphysical channel used to carry downlink signaling related toHS-DSCH transmission
Slot 0
Slot 1
Slot 2
Tslot
= 2560 chips
Data = 40 bits
1 subframe = 2 ms
Fig 2-17 Structure of High speed shared control channel HS-SCCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
We would like to return now to the time consecutive transmission of
control information There is a difference in the control information
in terms of its priority Some information is needed at the UE end
very urgently while other control information does not have such a
high priority But why This will be explained by looking at some tim-ing aspects defined for HSDPA If we consider the timing between
the shared data channel HS-PDSCH and the shared control chan-
nel HS-SCCH as shown in Fig 2-18 we see that the HS-PDSCH fol-
lows the HS-SCCH by exactly two slots or 5120 chips The HS-SCCH
is completely time-aligned with the general control channels CPICH
and P-CCPCH of the NodeB This is mandatory because it is a shared
channel Consider several UEs with different distances to the NodeBwanting to receive the HS-SCCH channel Thus it must have constant
timing that is known a priori The shared data channel HS-PDSCH is
now transmitted exactly 5120 chips after the first chip of the HS-SCCH
This leads to an overlapping slot thereby requiring multitasking recep-
tion at the UE end While the UE is still receiving the last slot of an
ongoing HS-SCCH subframe it may already start the reception of an
HS-PDSCH transport block The first slot in the HS-SCCH subframe
now contains information required by the physical layer to performdespreading and demodulation These values are the UE identity indi-
cating whether the UE will start demodulation of the HS-PDSCH or
not in case it is not scheduled the modulation scheme information
since the UE has to know how to interpret the received constellation
vector and whether it has to be considered as a QPSK or 16QAM con-
stellation point and finally the UE has to know which channelization
codes it has to apply to capture the HS-PDSCH transport block The
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HSDPA operation overview and physical channels
overall UE reaction time when being scheduled is now seen as 1 slot
or 2560 chips This tough requirement for the UEs is due to the objec-
tive to obtain overall a much shorter latency than legacy standards Theadditional control information such as the new data indicator redun-
dancy version and transport block size is not that urgent since it is
needed after demodulation but before channel decoding So first the
UE will sample the whole three slots of the HS-PDSCH and demodu-
late them into a bit stream which is finally handed over to the channel
decoder This principle is known as post-processing and is used typi-
cally in mobile communications technologies
J Start of HS-SCCH subframe 0 is aligned with startof P-CCPCH frames
J The HS-PDSCH starts
τ HS-PDSCH
(2times Tslot
= 5120 chips)
after the start of the HS-SCCH
UE identity etc
processing timeof receiver
HS-DSCH subframe
3 times Tslot= 7680 chips
3 times Tslot
= 7680 chips
τ HS-PDSCH
(2times Tslot
= 5120 chips)
HS-SCCH
HS-PDSCH
Fig 2-18 Timing relation between HS-SCCH and HS-PDSCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
Content of the HS-SCCH control channelThe control information contained in the HS-SCCH control chan-
nel has already been mentioned so we will now consider the values
in more detail We will begin with an overview of what kind of control
information is contained in the HS-SCCH channel before proceeding
with further details about the single control elements The following
control information is present in the HS-SCCH [TS 25212 Ref 21]
Channelization code set information (7 bits)
Modulation scheme information (1 bit) Transport block size information (6 bits)
Hybrid ARQ process information (3 bits)
Redundancy and constellation version (3 bits)
New data indicator (1 bit)
UE identity (16 bits) = H-RNTI
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High speed shared control channel (HS-SCCH)
49
Some of these parameters are more or less self-explanatory while oth-
ers require additional background information and closer examination
Modulation scheme information 1 bit
This single bit is used to inform the receiver whether the modulation
scheme QPSK or 16QAM is applied on the data channel HS-PDSCH
The interpretation of the bit x ms1 is as follows
ms1
x
if QPSK
otherwise
0
1
=
New data indicator 1 bit
The new data indicator bit field informs the receiving entity that the
prevailing PDU transmitted by the current HARQ process is either a
retransmission or contains new data This is done by setting the new
data bit to the value 0 for the first PDU on this particular HARQ process
and incrementing the value by 1 with every new data sent [TS 25321Ref 30] This leads to a toggled value In case the new data bit is not
incremented ie if it remains at its previous value it is an indicator for
retransmission
1st PDU of this
HARQ process
NDI = New data indicator
NDI = 0 NDI = 1
NACK
NDI = 1
ACK
NDI = 0
HS-SCCH HS-SCCH HS-SCCHHS-SCCH
ACK
Fig 2-19 New data indicator bit principle of incrementing value
Channelization code set information 7 bits
This field is used to indicate the number of channelization codes usedfor transmitting the transport block on the HS-PDSCH As was already
described the spreading factor applied on the HS-PDSCH is constant
with a value of 16 but the flexible values are the number of channeliza-
tion codes forming a cluster when using multiple codes and their posi-
tion in the code tree It is not allowed to distribute the code channels
over the code tree diagram For the sake of simplicity in signaling sev-
eral channelization codes form one cluster and these codes are con-
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HSDPA operation overview and physical channels
tiguous in the channelization code tree [TS 25213 Ref 22] Fig 2-20
illustrates the principle of indicating the channelization codes on the
HS-SCCH
SF = 16
Code ldquo0rdquo isreserved forcommonchannels
Code offset 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15P = 5O = 7
Code group indicatorx
ccs1 x
ccs2 x
ccs3 = min (Pminus 1 15 minusP)
Code offset indicatorx
ccs4 x
ccs5 x
ccs6 x
ccs7 = |Ominus 1minus P8 times15|
A cluster of codes
can be allocated to a UEC
ch16Ohellip C
ch16O + P minus 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1
2 2 2 2 2 2 2 2 2 2 2 2 2 2 14 14
1 2 3 4 5 6 7 8 9 10 11 12 13 14 2 1
3 3 3 3 3 3 3 3 3 3 3 3 3 13 13 13
1 2 3 4 5 6 7 8 9 10 11 12 13 3 2 1
4 4 4 4 4 4 4 4 4 4 4 4 12 12 12 121 2 3 4 5 6 7 8 9 10 11 12 4 3 2 1
5 5 5 5 5 5 5 5 5 5 5 11 11 11 11 11
1 2 3 4 5 6 7 8 9 10 11 5 4 3 2 1
6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10
1 2 3 4 5 6 7 8 9 10 6 5 4 3 2 1
7 7 7 7 7 7 7 7 7 9 9 9 9 9 9 9
1 2 3 4 5 6 7 8 9 7 6 5 4 3 2 1
8 8 8 8 8 8 8 8
8 7 6 5 4 3 2 1
0 (115)
1 (214)
2 (313)
3 (412)
4 (511)
5 (610)
6 (79)
7 (88) Redundant area
C l u s t e r c o d e i n d i c a t o r ( 3 b i t s )
Tree offset indicator (4 bits)
Signaled on HS-SCCH
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
PO
Decoding notation
Number ofmulti-codes
Offset fromleft right incode tree (SF = 16)
Fig 2-20 Channelization code set indicating the HS-PDSCH code cluster
The idea behind the code indication is a matrix with the rows repre-
senting the number of codes per cluster and the columns represent-
ing the position of that cluster the offset value in the code tree Recall-
ing that the maximum number of channelization codes per clusteris 15 and if the cluster size is 1 the offset values can also range from
1 to 15 the resulting matrix would have 15 rows and 15 columns Since
we know that four bits are needed to represent an integer from 1 to 15
we need a total of 4 + 4 = 8 bits for representation of the channeliza-
tion code set information It is a smart idea to save one bit The 15 times 15
matrix would contain much redundant information By way of analogy
like in a road map indicating distances between cities A table showing
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High speed shared control channel (HS-SCCH)
51
the distance from city A to city B the opposite distance from city B to
city A is redundant information The useful information has the form
of a triangle The idea is to cut the lower part rotate it and append itto the spare part of the upper table In this manner a table is obtained
with 7 rows and 15 columns and it is possible to indicate each position
in it with just 7 bits
1 5 r o w s 7
r o w s
Matrix reduction for channeli-
zation code set information
15 columns
Fig 2-21 Matrix size reduction for channelization code set information
The content of the channelization code set matrix can be described as
a value with two numbers The upper number is the number of mul-
ticodes forming one cluster and the lower number is the offset in the
channelization code tree Accordingly the example in Fig 2-20 can be
interpreted to mean the HS-SCCH sends the bits as row number 4 and
column number 6 in the matrix The content of this element are the
values 5 over 7 which have to be interpreted as a cluster size of 5 codesand an offset of 7
Transport block size information 6 bits
With a length of six bits the transport block size (TBS) informa-
tion informs the receiving UE entity about the data block size of the
transport block sent on the HS-PDSCH We should keep in mind the
link adaptation performed with the adaptive modulation and coding
scheme that was described in section 12 page 10 The ratio errorcorrection and user data are flexible while the physical layer param-
eters such as the spreading factor modulation scheme and number of
channelization codes determine the physical block size This physical
block consists of the user data ratio or transport block size and the for-
ward error correction or redundancy information As this ratio is flex-
ible the HS-SCCH will inform the receiving UE entity about the size
of the transport block Here too there is a strategy of bit reduction the
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HSDPA operation overview and physical channels
goal is to inform the receiver with as few bits as possible A non-effi-
cient approach would involve conversion of the decimal number repre-
senting the TBS into a binary sequence but the number of bits neededwould exceed the space available on the HS-SCCH Imagine that the
range of transport block sizes depends on the physical layer condi-
tions The ambient physical layer parameters modulation scheme and
number of channelization codes set a certain working point where the
remaining flexibility for a different TBS configuration can be obtained
by more or less puncturing resulting in a flexible ratio between for-
ward error correction and user data This will lead to a two-step proce-
dure when evaluating the transport block size First the receiver exam-
ines the information modulation scheme and number of channeliza-
tion codes scheduled via HS-SCCH which indicate the value k0 l as
shown in Fig 2-22 The 6-bit HS-SCCH control parameter transport
block size information will be the transport format resource indica-
tor (TFRI) named ki Let k t be the sum of the two values kt = ki + k0i
Both values kt and k0 i can be obtained from tables given by [TS 25321
Ref 30] The range for the TFRI is from 1 to 256 and the derived trans-port block size ranges from 137 bits to 27 952 bits The first table indi-
cates the value k 0 i based on the channelization code and the modula-
tion scheme
Combination i Modulation scheme Number of channelization codes k0 i
0
QPSK
1 1
1 2 40
2 3 633 4 79
4 5 92
5 6 102
Fig 2-22 Extract from TS 25321 table representing k0 i
The second table indicates the final transport block size based on kt
Index TB size Index TB size Index TB size1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
4 173 89 1456 174 6673
5 185 90 1483 175 6793
6 197 91 1509 176 6916
7 209 92 1537 177 7041
Fig 2-23 Extract from TS 25321 table representing kt
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High speed shared control channel (HS-SCCH)
53
J The transport block size used on HS-DSCH is not signaled explicitly on HS-SCCHJ Instead a transport block size index k
i is signaled to indicate the transport block size
First stepModulation scheme andnumber of channelizationcodes as signaled on HS-SCCHdetermine value k
0 i
Second step
Index kt = k
i + k
0i
determines HS-DSCH
transport block size
kt = k
i + k
0i
Table according to 3GPP TS 25321 extract from QPSK section
Table according to 3GPP TS 25321 254 entries in total
Combination i Modulation
scheme
Number of
channelization codes
k0 i
0
QPSK
1 1
1 2 40
2 3 63
3 4 79
4 hellip hellip
Index TB size Index TB size Index TB size
1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
helliphellip hellip hellip hellip hellip
Fig 2-24 Retrieval of transport block size information
Source Fig 2-22 to Fig 2-24 [TS 25321 Ref 30] reproduced by permission of 3GPP
Hybrid ARQ process information 3 bits
The concept behind the hybrid automatic repeat request (HARQ) was
introduced in section 13 page 14 One feature is the possibility of
multitasking ie having several HARQ processes activated at the same
time Fig 2-25 below shows the need to signal the process identity tothe receiver Remember that on the downlink there is a shared chan-
nel concept so the NodeB can flexibly decide which UE will be sched-
uled with a downlink transport block Up to eight HARQ processes
can be signaled via higher layers to one UE Note however that due to
the round-trip timing six HARQ processes must be active to achieve
the maximum throughput as shown in Fig 2-51 page 79 Compared
with HSUPA the HARQ processes on the downlink are asynchronous
so they have to be indicated but on the uplink they are synchronous sothey do not need to be signaled explicitly
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HSDPA operation overview and physical channels
Asynchronous DL minus Synchronous ULNumber of H-ARQ rocesses = 1 to 8 er UE
UL HS-DPCCH UE1
UE1 HARQ processes 1 to 4
3 4 1 42 11 1 32retrans
2
A N A A
A A
N A
UL HS-DPCCH UE2
HS-PDSCH
UE2 HARQ processes 1 to 2
Fig 2-25 HARQ process indication on HS-SCCH
Fig 2-25 shows a typical situation on the downlink (point-to-multi-
point) The NodeB sends data to several UEs sharing the HS-PDSCH
so therefore the HARQ process is asynchronous The time when a
transport block is retransmitted is not fixed For this reason the pro-
cess identifier is signaled on the HS-SCCH Based on the HARQ pro-
cess identity and the new data indicator bit the receiving entity knows
which part of the soft buffer memory has to be used in case of soft com-bining On the uplink the situation is slightly simpler The UE only
communicates with one NodeB so it is a point-to-point connection
Thus retransmission always occurs at a fixed time linked to the origi-
nal transmission
Redundancy and constellation version 3 bits
Adaptive modulation and coding involve flexible selection of modula-tion and coding schemes that are signaled to the receiving UE via the
parameters transport block size and modulation scheme information
Another concept used in HSDPA was previously discussed Chase com-
bining or incremental redundancy (see section 222 page 41) This
means that in case of retransmission the transmit entity can dynami-
cally select another puncturing scheme or keep the puncturing as it was
in the original transmission The applied puncturing scheme is signaled
as redundancy information to the receiver Additionally in case of the16QAM modulation scheme the transmitter can select another constel-
lation arrangement which is also signaled to the UE with the three bits
for the redundancy and constellation version see Fig 2-15 page 45
Depending on the modulation scheme (QPSK or 16QAM) there are
two different tables indicating the parameters ldquosrdquo ldquorrdquo and ldquobrdquo The
parameters ldquosrdquo and ldquorrdquo indicate which scheme is used for puncturing
ie if the puncturing mechanism prioritizes the systematic bits or not
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High speed shared control channel (HS-SCCH)
55
and which puncturing algorithm is used The parameter ldquobrdquo indicates
the constellation mapping version The receiver needs this information
to perform proper demodulation and decoding
Initial transmission
1st retransmission
2nd retransmission
3rd retransmission
r
0
0
1
1
2
2
3
xrv
(value)
s
0 1
1 0
2 1
3 0
4 1
5 0
6 1
7 0 3
s = 1 Systematic bits are prioritizeds = 0 Non-systematic bits are prioritized
r (range 0 to 3 for QPSK) influencesJ Input parameter for puncturing or (together with s) for repetition algorithm defined in TS 25212J Selection of parity bits
Redundancy version coding sequences are signaled on HS-SCCH egndash 0 2 5 6 One initial transmission + 3 retransmissions with different r and s parameters
Fig 2-26 Signaling of redundancy version parameters r and s QPSK case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
Initial transmission
2nd retransmission
1st retransmission
3rd retransmission
r (range 0 to 1 for 16QAM)influences input parameterfor puncturing or (togetherwith s) for repetitionalgorithm defined in
TS 25212 and thus selectionof parity bits
Redundancy version coding sequences are signaled on HS-SCCH egminus 6 4 0 5 Chase combining (no change in s and r parameters ie same redundancyversion) with four possible constellations
x rv (value) s r b
0 1 0 0
1 0 0 0
2 1 1 1
3 0 1 1
4 1 0 1
5 1 0 2
6 1 0 3
7 1 1 0
Definition of parameter s as for QPSK
b (range 0 to 3) describes constellationrearrangement to averagereliability of bits
Fig 2-27 Signaling of redundancy version parameters r s and b 16QAM case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
UE identity H-RNTI 16 bits
The HSDPA radio network transaction identifier (H-RNTI) unam-
biguously identifies the UE having an HS-PDSCH assignment within
a cell It is allocated to the UE via layer 3 signaling procedures at the
radio bearer setup if the radio bearer is an HSDPA connection This
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HSDPA operation overview and physical channels
value represents a temporary name of the UE used to address it when
scheduling data packets via HS-SCCH
HS-SCCH channel coding
The control information contained in the HS-SCCH is of course pro-
tected with channel coding mechanisms the whole coding chain is
described in Fig 2-28 Fig 2-18 page 48 presents the separation of
the control information into two code blocks which are sent consec-
utively mapped on slot 1 and slot 2 + 3 of one HS-SCCH subframe
This principle is also visible in the coding chain The first control block
consisting of channelization information modulation scheme and UE
identity is coded separately from the remaining control values to enable
the UE receiver to decode this first slot separately and prepare for pos-
sible HS-PDSCH reception The coding steps shown in Fig 2-28 such
as rate matching 1 and 2 are similar to the HS-PDSCH coding chain
and are further described in [TS 25212 Ref 21]
Channelcoding 1
R atematching 1
mux
Channelcoding 2
Ratematching 2
RVcoding
UE-specificCRC attachment
UE-specificmasking
Physical channelmapping
r s b
mux
Channelizationcode set
Modulationscheme
Transport block size information
HARQ processinformation
Redundancy andconstellation version
New data indicator
UE identity
UE identity
Fig 2-28 Channel coding for HS-SCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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High speed dedicated physical control channel (HS-DPCCH)
57
24 High speed dedicated physical control channel (HS-DPCCH)
In an active HSDPA connection the UE has to send acknowledgment ornon-acknowledgment reports (as described in section 13 page 14
where the HARQ process is described) as well as channel status infor-
mation to the network The reporting is performed on this physical
control channel HS-DPCCH
As ubiquitous in HSDPA the uplink is also configured into a subframe
structure of 2 ms corresponding to three slots The first slot of the sub-
frame carries the ACK NACK information the UE sends to the NodeB
while the following two slots ie slot 2 and 3 of the subframe convey
the CQI value the channel quality information to the NodeB
Subframe 0 Subframe i Subframe 4
Tslot
= 2560 chips J The spreading factor of theHS-DPCCH is 256 (10 bits peruplink slot)
J The HS-DPCCH can only existtogether with an UL DPCCH
(ded phys control channel)J The DPDCH (dedicated physical data channel) the DPCCH andthe HS-DPCCH are IQ codemultiplexed
HARQ-ACK CQI = Channel quality information
2 times Tslot
= 5120 chips
One radio frame Tf = 10 ms
One HS-DPCCH subframe 2 ms
Fig 2-29 HS-DPCCH configuration
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The slot format for HS-DPCCH describes a quantity of 30 bits per sub-frame resulting in a data rate of 15 kbps The spreading factor used for
the HS-DPCCH is constant and is always equal to 256 but the chan-
nelization code that is used as well as the mapping on either the I or
Q axis depends on several factors eg the co-existence of an HSDPA
connection with a circuit-switched connection meaning whether a
DPDCH established or not Fig 2-36 page 64 illustrates this IQ
mapping and Fig 2-35 page 63 shows the channelization code used
for HS-DPCCH
The HS-DPCCH builds a logical unit of one subframe but having the
independent control information HARQ-ACK and CQI included which
could be separately decoded at the NodeB Note that the slot carrying
the ACK NACK statement is active only when the UE has been sched-
uled by an HS-PDSCH subframe in the corresponding downlink sub-
frame previously Assuming the UE has not received a transport block
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HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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High speed shared control channel (HS-SCCH)
47
The HS-SCCH is a fixed rate (60 kbps SF = 128) downlinkphysical channel used to carry downlink signaling related toHS-DSCH transmission
Slot 0
Slot 1
Slot 2
Tslot
= 2560 chips
Data = 40 bits
1 subframe = 2 ms
Fig 2-17 Structure of High speed shared control channel HS-SCCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
We would like to return now to the time consecutive transmission of
control information There is a difference in the control information
in terms of its priority Some information is needed at the UE end
very urgently while other control information does not have such a
high priority But why This will be explained by looking at some tim-ing aspects defined for HSDPA If we consider the timing between
the shared data channel HS-PDSCH and the shared control chan-
nel HS-SCCH as shown in Fig 2-18 we see that the HS-PDSCH fol-
lows the HS-SCCH by exactly two slots or 5120 chips The HS-SCCH
is completely time-aligned with the general control channels CPICH
and P-CCPCH of the NodeB This is mandatory because it is a shared
channel Consider several UEs with different distances to the NodeBwanting to receive the HS-SCCH channel Thus it must have constant
timing that is known a priori The shared data channel HS-PDSCH is
now transmitted exactly 5120 chips after the first chip of the HS-SCCH
This leads to an overlapping slot thereby requiring multitasking recep-
tion at the UE end While the UE is still receiving the last slot of an
ongoing HS-SCCH subframe it may already start the reception of an
HS-PDSCH transport block The first slot in the HS-SCCH subframe
now contains information required by the physical layer to performdespreading and demodulation These values are the UE identity indi-
cating whether the UE will start demodulation of the HS-PDSCH or
not in case it is not scheduled the modulation scheme information
since the UE has to know how to interpret the received constellation
vector and whether it has to be considered as a QPSK or 16QAM con-
stellation point and finally the UE has to know which channelization
codes it has to apply to capture the HS-PDSCH transport block The
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48
HSDPA operation overview and physical channels
overall UE reaction time when being scheduled is now seen as 1 slot
or 2560 chips This tough requirement for the UEs is due to the objec-
tive to obtain overall a much shorter latency than legacy standards Theadditional control information such as the new data indicator redun-
dancy version and transport block size is not that urgent since it is
needed after demodulation but before channel decoding So first the
UE will sample the whole three slots of the HS-PDSCH and demodu-
late them into a bit stream which is finally handed over to the channel
decoder This principle is known as post-processing and is used typi-
cally in mobile communications technologies
J Start of HS-SCCH subframe 0 is aligned with startof P-CCPCH frames
J The HS-PDSCH starts
τ HS-PDSCH
(2times Tslot
= 5120 chips)
after the start of the HS-SCCH
UE identity etc
processing timeof receiver
HS-DSCH subframe
3 times Tslot= 7680 chips
3 times Tslot
= 7680 chips
τ HS-PDSCH
(2times Tslot
= 5120 chips)
HS-SCCH
HS-PDSCH
Fig 2-18 Timing relation between HS-SCCH and HS-PDSCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
Content of the HS-SCCH control channelThe control information contained in the HS-SCCH control chan-
nel has already been mentioned so we will now consider the values
in more detail We will begin with an overview of what kind of control
information is contained in the HS-SCCH channel before proceeding
with further details about the single control elements The following
control information is present in the HS-SCCH [TS 25212 Ref 21]
Channelization code set information (7 bits)
Modulation scheme information (1 bit) Transport block size information (6 bits)
Hybrid ARQ process information (3 bits)
Redundancy and constellation version (3 bits)
New data indicator (1 bit)
UE identity (16 bits) = H-RNTI
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High speed shared control channel (HS-SCCH)
49
Some of these parameters are more or less self-explanatory while oth-
ers require additional background information and closer examination
Modulation scheme information 1 bit
This single bit is used to inform the receiver whether the modulation
scheme QPSK or 16QAM is applied on the data channel HS-PDSCH
The interpretation of the bit x ms1 is as follows
ms1
x
if QPSK
otherwise
0
1
=
New data indicator 1 bit
The new data indicator bit field informs the receiving entity that the
prevailing PDU transmitted by the current HARQ process is either a
retransmission or contains new data This is done by setting the new
data bit to the value 0 for the first PDU on this particular HARQ process
and incrementing the value by 1 with every new data sent [TS 25321Ref 30] This leads to a toggled value In case the new data bit is not
incremented ie if it remains at its previous value it is an indicator for
retransmission
1st PDU of this
HARQ process
NDI = New data indicator
NDI = 0 NDI = 1
NACK
NDI = 1
ACK
NDI = 0
HS-SCCH HS-SCCH HS-SCCHHS-SCCH
ACK
Fig 2-19 New data indicator bit principle of incrementing value
Channelization code set information 7 bits
This field is used to indicate the number of channelization codes usedfor transmitting the transport block on the HS-PDSCH As was already
described the spreading factor applied on the HS-PDSCH is constant
with a value of 16 but the flexible values are the number of channeliza-
tion codes forming a cluster when using multiple codes and their posi-
tion in the code tree It is not allowed to distribute the code channels
over the code tree diagram For the sake of simplicity in signaling sev-
eral channelization codes form one cluster and these codes are con-
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HSDPA operation overview and physical channels
tiguous in the channelization code tree [TS 25213 Ref 22] Fig 2-20
illustrates the principle of indicating the channelization codes on the
HS-SCCH
SF = 16
Code ldquo0rdquo isreserved forcommonchannels
Code offset 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15P = 5O = 7
Code group indicatorx
ccs1 x
ccs2 x
ccs3 = min (Pminus 1 15 minusP)
Code offset indicatorx
ccs4 x
ccs5 x
ccs6 x
ccs7 = |Ominus 1minus P8 times15|
A cluster of codes
can be allocated to a UEC
ch16Ohellip C
ch16O + P minus 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1
2 2 2 2 2 2 2 2 2 2 2 2 2 2 14 14
1 2 3 4 5 6 7 8 9 10 11 12 13 14 2 1
3 3 3 3 3 3 3 3 3 3 3 3 3 13 13 13
1 2 3 4 5 6 7 8 9 10 11 12 13 3 2 1
4 4 4 4 4 4 4 4 4 4 4 4 12 12 12 121 2 3 4 5 6 7 8 9 10 11 12 4 3 2 1
5 5 5 5 5 5 5 5 5 5 5 11 11 11 11 11
1 2 3 4 5 6 7 8 9 10 11 5 4 3 2 1
6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10
1 2 3 4 5 6 7 8 9 10 6 5 4 3 2 1
7 7 7 7 7 7 7 7 7 9 9 9 9 9 9 9
1 2 3 4 5 6 7 8 9 7 6 5 4 3 2 1
8 8 8 8 8 8 8 8
8 7 6 5 4 3 2 1
0 (115)
1 (214)
2 (313)
3 (412)
4 (511)
5 (610)
6 (79)
7 (88) Redundant area
C l u s t e r c o d e i n d i c a t o r ( 3 b i t s )
Tree offset indicator (4 bits)
Signaled on HS-SCCH
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
PO
Decoding notation
Number ofmulti-codes
Offset fromleft right incode tree (SF = 16)
Fig 2-20 Channelization code set indicating the HS-PDSCH code cluster
The idea behind the code indication is a matrix with the rows repre-
senting the number of codes per cluster and the columns represent-
ing the position of that cluster the offset value in the code tree Recall-
ing that the maximum number of channelization codes per clusteris 15 and if the cluster size is 1 the offset values can also range from
1 to 15 the resulting matrix would have 15 rows and 15 columns Since
we know that four bits are needed to represent an integer from 1 to 15
we need a total of 4 + 4 = 8 bits for representation of the channeliza-
tion code set information It is a smart idea to save one bit The 15 times 15
matrix would contain much redundant information By way of analogy
like in a road map indicating distances between cities A table showing
8122019 hspa_e_lp
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High speed shared control channel (HS-SCCH)
51
the distance from city A to city B the opposite distance from city B to
city A is redundant information The useful information has the form
of a triangle The idea is to cut the lower part rotate it and append itto the spare part of the upper table In this manner a table is obtained
with 7 rows and 15 columns and it is possible to indicate each position
in it with just 7 bits
1 5 r o w s 7
r o w s
Matrix reduction for channeli-
zation code set information
15 columns
Fig 2-21 Matrix size reduction for channelization code set information
The content of the channelization code set matrix can be described as
a value with two numbers The upper number is the number of mul-
ticodes forming one cluster and the lower number is the offset in the
channelization code tree Accordingly the example in Fig 2-20 can be
interpreted to mean the HS-SCCH sends the bits as row number 4 and
column number 6 in the matrix The content of this element are the
values 5 over 7 which have to be interpreted as a cluster size of 5 codesand an offset of 7
Transport block size information 6 bits
With a length of six bits the transport block size (TBS) informa-
tion informs the receiving UE entity about the data block size of the
transport block sent on the HS-PDSCH We should keep in mind the
link adaptation performed with the adaptive modulation and coding
scheme that was described in section 12 page 10 The ratio errorcorrection and user data are flexible while the physical layer param-
eters such as the spreading factor modulation scheme and number of
channelization codes determine the physical block size This physical
block consists of the user data ratio or transport block size and the for-
ward error correction or redundancy information As this ratio is flex-
ible the HS-SCCH will inform the receiving UE entity about the size
of the transport block Here too there is a strategy of bit reduction the
8122019 hspa_e_lp
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52
HSDPA operation overview and physical channels
goal is to inform the receiver with as few bits as possible A non-effi-
cient approach would involve conversion of the decimal number repre-
senting the TBS into a binary sequence but the number of bits neededwould exceed the space available on the HS-SCCH Imagine that the
range of transport block sizes depends on the physical layer condi-
tions The ambient physical layer parameters modulation scheme and
number of channelization codes set a certain working point where the
remaining flexibility for a different TBS configuration can be obtained
by more or less puncturing resulting in a flexible ratio between for-
ward error correction and user data This will lead to a two-step proce-
dure when evaluating the transport block size First the receiver exam-
ines the information modulation scheme and number of channeliza-
tion codes scheduled via HS-SCCH which indicate the value k0 l as
shown in Fig 2-22 The 6-bit HS-SCCH control parameter transport
block size information will be the transport format resource indica-
tor (TFRI) named ki Let k t be the sum of the two values kt = ki + k0i
Both values kt and k0 i can be obtained from tables given by [TS 25321
Ref 30] The range for the TFRI is from 1 to 256 and the derived trans-port block size ranges from 137 bits to 27 952 bits The first table indi-
cates the value k 0 i based on the channelization code and the modula-
tion scheme
Combination i Modulation scheme Number of channelization codes k0 i
0
QPSK
1 1
1 2 40
2 3 633 4 79
4 5 92
5 6 102
Fig 2-22 Extract from TS 25321 table representing k0 i
The second table indicates the final transport block size based on kt
Index TB size Index TB size Index TB size1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
4 173 89 1456 174 6673
5 185 90 1483 175 6793
6 197 91 1509 176 6916
7 209 92 1537 177 7041
Fig 2-23 Extract from TS 25321 table representing kt
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High speed shared control channel (HS-SCCH)
53
J The transport block size used on HS-DSCH is not signaled explicitly on HS-SCCHJ Instead a transport block size index k
i is signaled to indicate the transport block size
First stepModulation scheme andnumber of channelizationcodes as signaled on HS-SCCHdetermine value k
0 i
Second step
Index kt = k
i + k
0i
determines HS-DSCH
transport block size
kt = k
i + k
0i
Table according to 3GPP TS 25321 extract from QPSK section
Table according to 3GPP TS 25321 254 entries in total
Combination i Modulation
scheme
Number of
channelization codes
k0 i
0
QPSK
1 1
1 2 40
2 3 63
3 4 79
4 hellip hellip
Index TB size Index TB size Index TB size
1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
helliphellip hellip hellip hellip hellip
Fig 2-24 Retrieval of transport block size information
Source Fig 2-22 to Fig 2-24 [TS 25321 Ref 30] reproduced by permission of 3GPP
Hybrid ARQ process information 3 bits
The concept behind the hybrid automatic repeat request (HARQ) was
introduced in section 13 page 14 One feature is the possibility of
multitasking ie having several HARQ processes activated at the same
time Fig 2-25 below shows the need to signal the process identity tothe receiver Remember that on the downlink there is a shared chan-
nel concept so the NodeB can flexibly decide which UE will be sched-
uled with a downlink transport block Up to eight HARQ processes
can be signaled via higher layers to one UE Note however that due to
the round-trip timing six HARQ processes must be active to achieve
the maximum throughput as shown in Fig 2-51 page 79 Compared
with HSUPA the HARQ processes on the downlink are asynchronous
so they have to be indicated but on the uplink they are synchronous sothey do not need to be signaled explicitly
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HSDPA operation overview and physical channels
Asynchronous DL minus Synchronous ULNumber of H-ARQ rocesses = 1 to 8 er UE
UL HS-DPCCH UE1
UE1 HARQ processes 1 to 4
3 4 1 42 11 1 32retrans
2
A N A A
A A
N A
UL HS-DPCCH UE2
HS-PDSCH
UE2 HARQ processes 1 to 2
Fig 2-25 HARQ process indication on HS-SCCH
Fig 2-25 shows a typical situation on the downlink (point-to-multi-
point) The NodeB sends data to several UEs sharing the HS-PDSCH
so therefore the HARQ process is asynchronous The time when a
transport block is retransmitted is not fixed For this reason the pro-
cess identifier is signaled on the HS-SCCH Based on the HARQ pro-
cess identity and the new data indicator bit the receiving entity knows
which part of the soft buffer memory has to be used in case of soft com-bining On the uplink the situation is slightly simpler The UE only
communicates with one NodeB so it is a point-to-point connection
Thus retransmission always occurs at a fixed time linked to the origi-
nal transmission
Redundancy and constellation version 3 bits
Adaptive modulation and coding involve flexible selection of modula-tion and coding schemes that are signaled to the receiving UE via the
parameters transport block size and modulation scheme information
Another concept used in HSDPA was previously discussed Chase com-
bining or incremental redundancy (see section 222 page 41) This
means that in case of retransmission the transmit entity can dynami-
cally select another puncturing scheme or keep the puncturing as it was
in the original transmission The applied puncturing scheme is signaled
as redundancy information to the receiver Additionally in case of the16QAM modulation scheme the transmitter can select another constel-
lation arrangement which is also signaled to the UE with the three bits
for the redundancy and constellation version see Fig 2-15 page 45
Depending on the modulation scheme (QPSK or 16QAM) there are
two different tables indicating the parameters ldquosrdquo ldquorrdquo and ldquobrdquo The
parameters ldquosrdquo and ldquorrdquo indicate which scheme is used for puncturing
ie if the puncturing mechanism prioritizes the systematic bits or not
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High speed shared control channel (HS-SCCH)
55
and which puncturing algorithm is used The parameter ldquobrdquo indicates
the constellation mapping version The receiver needs this information
to perform proper demodulation and decoding
Initial transmission
1st retransmission
2nd retransmission
3rd retransmission
r
0
0
1
1
2
2
3
xrv
(value)
s
0 1
1 0
2 1
3 0
4 1
5 0
6 1
7 0 3
s = 1 Systematic bits are prioritizeds = 0 Non-systematic bits are prioritized
r (range 0 to 3 for QPSK) influencesJ Input parameter for puncturing or (together with s) for repetition algorithm defined in TS 25212J Selection of parity bits
Redundancy version coding sequences are signaled on HS-SCCH egndash 0 2 5 6 One initial transmission + 3 retransmissions with different r and s parameters
Fig 2-26 Signaling of redundancy version parameters r and s QPSK case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
Initial transmission
2nd retransmission
1st retransmission
3rd retransmission
r (range 0 to 1 for 16QAM)influences input parameterfor puncturing or (togetherwith s) for repetitionalgorithm defined in
TS 25212 and thus selectionof parity bits
Redundancy version coding sequences are signaled on HS-SCCH egminus 6 4 0 5 Chase combining (no change in s and r parameters ie same redundancyversion) with four possible constellations
x rv (value) s r b
0 1 0 0
1 0 0 0
2 1 1 1
3 0 1 1
4 1 0 1
5 1 0 2
6 1 0 3
7 1 1 0
Definition of parameter s as for QPSK
b (range 0 to 3) describes constellationrearrangement to averagereliability of bits
Fig 2-27 Signaling of redundancy version parameters r s and b 16QAM case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
UE identity H-RNTI 16 bits
The HSDPA radio network transaction identifier (H-RNTI) unam-
biguously identifies the UE having an HS-PDSCH assignment within
a cell It is allocated to the UE via layer 3 signaling procedures at the
radio bearer setup if the radio bearer is an HSDPA connection This
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HSDPA operation overview and physical channels
value represents a temporary name of the UE used to address it when
scheduling data packets via HS-SCCH
HS-SCCH channel coding
The control information contained in the HS-SCCH is of course pro-
tected with channel coding mechanisms the whole coding chain is
described in Fig 2-28 Fig 2-18 page 48 presents the separation of
the control information into two code blocks which are sent consec-
utively mapped on slot 1 and slot 2 + 3 of one HS-SCCH subframe
This principle is also visible in the coding chain The first control block
consisting of channelization information modulation scheme and UE
identity is coded separately from the remaining control values to enable
the UE receiver to decode this first slot separately and prepare for pos-
sible HS-PDSCH reception The coding steps shown in Fig 2-28 such
as rate matching 1 and 2 are similar to the HS-PDSCH coding chain
and are further described in [TS 25212 Ref 21]
Channelcoding 1
R atematching 1
mux
Channelcoding 2
Ratematching 2
RVcoding
UE-specificCRC attachment
UE-specificmasking
Physical channelmapping
r s b
mux
Channelizationcode set
Modulationscheme
Transport block size information
HARQ processinformation
Redundancy andconstellation version
New data indicator
UE identity
UE identity
Fig 2-28 Channel coding for HS-SCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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High speed dedicated physical control channel (HS-DPCCH)
57
24 High speed dedicated physical control channel (HS-DPCCH)
In an active HSDPA connection the UE has to send acknowledgment ornon-acknowledgment reports (as described in section 13 page 14
where the HARQ process is described) as well as channel status infor-
mation to the network The reporting is performed on this physical
control channel HS-DPCCH
As ubiquitous in HSDPA the uplink is also configured into a subframe
structure of 2 ms corresponding to three slots The first slot of the sub-
frame carries the ACK NACK information the UE sends to the NodeB
while the following two slots ie slot 2 and 3 of the subframe convey
the CQI value the channel quality information to the NodeB
Subframe 0 Subframe i Subframe 4
Tslot
= 2560 chips J The spreading factor of theHS-DPCCH is 256 (10 bits peruplink slot)
J The HS-DPCCH can only existtogether with an UL DPCCH
(ded phys control channel)J The DPDCH (dedicated physical data channel) the DPCCH andthe HS-DPCCH are IQ codemultiplexed
HARQ-ACK CQI = Channel quality information
2 times Tslot
= 5120 chips
One radio frame Tf = 10 ms
One HS-DPCCH subframe 2 ms
Fig 2-29 HS-DPCCH configuration
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The slot format for HS-DPCCH describes a quantity of 30 bits per sub-frame resulting in a data rate of 15 kbps The spreading factor used for
the HS-DPCCH is constant and is always equal to 256 but the chan-
nelization code that is used as well as the mapping on either the I or
Q axis depends on several factors eg the co-existence of an HSDPA
connection with a circuit-switched connection meaning whether a
DPDCH established or not Fig 2-36 page 64 illustrates this IQ
mapping and Fig 2-35 page 63 shows the channelization code used
for HS-DPCCH
The HS-DPCCH builds a logical unit of one subframe but having the
independent control information HARQ-ACK and CQI included which
could be separately decoded at the NodeB Note that the slot carrying
the ACK NACK statement is active only when the UE has been sched-
uled by an HS-PDSCH subframe in the corresponding downlink sub-
frame previously Assuming the UE has not received a transport block
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HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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48
HSDPA operation overview and physical channels
overall UE reaction time when being scheduled is now seen as 1 slot
or 2560 chips This tough requirement for the UEs is due to the objec-
tive to obtain overall a much shorter latency than legacy standards Theadditional control information such as the new data indicator redun-
dancy version and transport block size is not that urgent since it is
needed after demodulation but before channel decoding So first the
UE will sample the whole three slots of the HS-PDSCH and demodu-
late them into a bit stream which is finally handed over to the channel
decoder This principle is known as post-processing and is used typi-
cally in mobile communications technologies
J Start of HS-SCCH subframe 0 is aligned with startof P-CCPCH frames
J The HS-PDSCH starts
τ HS-PDSCH
(2times Tslot
= 5120 chips)
after the start of the HS-SCCH
UE identity etc
processing timeof receiver
HS-DSCH subframe
3 times Tslot= 7680 chips
3 times Tslot
= 7680 chips
τ HS-PDSCH
(2times Tslot
= 5120 chips)
HS-SCCH
HS-PDSCH
Fig 2-18 Timing relation between HS-SCCH and HS-PDSCH
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
Content of the HS-SCCH control channelThe control information contained in the HS-SCCH control chan-
nel has already been mentioned so we will now consider the values
in more detail We will begin with an overview of what kind of control
information is contained in the HS-SCCH channel before proceeding
with further details about the single control elements The following
control information is present in the HS-SCCH [TS 25212 Ref 21]
Channelization code set information (7 bits)
Modulation scheme information (1 bit) Transport block size information (6 bits)
Hybrid ARQ process information (3 bits)
Redundancy and constellation version (3 bits)
New data indicator (1 bit)
UE identity (16 bits) = H-RNTI
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High speed shared control channel (HS-SCCH)
49
Some of these parameters are more or less self-explanatory while oth-
ers require additional background information and closer examination
Modulation scheme information 1 bit
This single bit is used to inform the receiver whether the modulation
scheme QPSK or 16QAM is applied on the data channel HS-PDSCH
The interpretation of the bit x ms1 is as follows
ms1
x
if QPSK
otherwise
0
1
=
New data indicator 1 bit
The new data indicator bit field informs the receiving entity that the
prevailing PDU transmitted by the current HARQ process is either a
retransmission or contains new data This is done by setting the new
data bit to the value 0 for the first PDU on this particular HARQ process
and incrementing the value by 1 with every new data sent [TS 25321Ref 30] This leads to a toggled value In case the new data bit is not
incremented ie if it remains at its previous value it is an indicator for
retransmission
1st PDU of this
HARQ process
NDI = New data indicator
NDI = 0 NDI = 1
NACK
NDI = 1
ACK
NDI = 0
HS-SCCH HS-SCCH HS-SCCHHS-SCCH
ACK
Fig 2-19 New data indicator bit principle of incrementing value
Channelization code set information 7 bits
This field is used to indicate the number of channelization codes usedfor transmitting the transport block on the HS-PDSCH As was already
described the spreading factor applied on the HS-PDSCH is constant
with a value of 16 but the flexible values are the number of channeliza-
tion codes forming a cluster when using multiple codes and their posi-
tion in the code tree It is not allowed to distribute the code channels
over the code tree diagram For the sake of simplicity in signaling sev-
eral channelization codes form one cluster and these codes are con-
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HSDPA operation overview and physical channels
tiguous in the channelization code tree [TS 25213 Ref 22] Fig 2-20
illustrates the principle of indicating the channelization codes on the
HS-SCCH
SF = 16
Code ldquo0rdquo isreserved forcommonchannels
Code offset 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15P = 5O = 7
Code group indicatorx
ccs1 x
ccs2 x
ccs3 = min (Pminus 1 15 minusP)
Code offset indicatorx
ccs4 x
ccs5 x
ccs6 x
ccs7 = |Ominus 1minus P8 times15|
A cluster of codes
can be allocated to a UEC
ch16Ohellip C
ch16O + P minus 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1
2 2 2 2 2 2 2 2 2 2 2 2 2 2 14 14
1 2 3 4 5 6 7 8 9 10 11 12 13 14 2 1
3 3 3 3 3 3 3 3 3 3 3 3 3 13 13 13
1 2 3 4 5 6 7 8 9 10 11 12 13 3 2 1
4 4 4 4 4 4 4 4 4 4 4 4 12 12 12 121 2 3 4 5 6 7 8 9 10 11 12 4 3 2 1
5 5 5 5 5 5 5 5 5 5 5 11 11 11 11 11
1 2 3 4 5 6 7 8 9 10 11 5 4 3 2 1
6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10
1 2 3 4 5 6 7 8 9 10 6 5 4 3 2 1
7 7 7 7 7 7 7 7 7 9 9 9 9 9 9 9
1 2 3 4 5 6 7 8 9 7 6 5 4 3 2 1
8 8 8 8 8 8 8 8
8 7 6 5 4 3 2 1
0 (115)
1 (214)
2 (313)
3 (412)
4 (511)
5 (610)
6 (79)
7 (88) Redundant area
C l u s t e r c o d e i n d i c a t o r ( 3 b i t s )
Tree offset indicator (4 bits)
Signaled on HS-SCCH
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
PO
Decoding notation
Number ofmulti-codes
Offset fromleft right incode tree (SF = 16)
Fig 2-20 Channelization code set indicating the HS-PDSCH code cluster
The idea behind the code indication is a matrix with the rows repre-
senting the number of codes per cluster and the columns represent-
ing the position of that cluster the offset value in the code tree Recall-
ing that the maximum number of channelization codes per clusteris 15 and if the cluster size is 1 the offset values can also range from
1 to 15 the resulting matrix would have 15 rows and 15 columns Since
we know that four bits are needed to represent an integer from 1 to 15
we need a total of 4 + 4 = 8 bits for representation of the channeliza-
tion code set information It is a smart idea to save one bit The 15 times 15
matrix would contain much redundant information By way of analogy
like in a road map indicating distances between cities A table showing
8122019 hspa_e_lp
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High speed shared control channel (HS-SCCH)
51
the distance from city A to city B the opposite distance from city B to
city A is redundant information The useful information has the form
of a triangle The idea is to cut the lower part rotate it and append itto the spare part of the upper table In this manner a table is obtained
with 7 rows and 15 columns and it is possible to indicate each position
in it with just 7 bits
1 5 r o w s 7
r o w s
Matrix reduction for channeli-
zation code set information
15 columns
Fig 2-21 Matrix size reduction for channelization code set information
The content of the channelization code set matrix can be described as
a value with two numbers The upper number is the number of mul-
ticodes forming one cluster and the lower number is the offset in the
channelization code tree Accordingly the example in Fig 2-20 can be
interpreted to mean the HS-SCCH sends the bits as row number 4 and
column number 6 in the matrix The content of this element are the
values 5 over 7 which have to be interpreted as a cluster size of 5 codesand an offset of 7
Transport block size information 6 bits
With a length of six bits the transport block size (TBS) informa-
tion informs the receiving UE entity about the data block size of the
transport block sent on the HS-PDSCH We should keep in mind the
link adaptation performed with the adaptive modulation and coding
scheme that was described in section 12 page 10 The ratio errorcorrection and user data are flexible while the physical layer param-
eters such as the spreading factor modulation scheme and number of
channelization codes determine the physical block size This physical
block consists of the user data ratio or transport block size and the for-
ward error correction or redundancy information As this ratio is flex-
ible the HS-SCCH will inform the receiving UE entity about the size
of the transport block Here too there is a strategy of bit reduction the
8122019 hspa_e_lp
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52
HSDPA operation overview and physical channels
goal is to inform the receiver with as few bits as possible A non-effi-
cient approach would involve conversion of the decimal number repre-
senting the TBS into a binary sequence but the number of bits neededwould exceed the space available on the HS-SCCH Imagine that the
range of transport block sizes depends on the physical layer condi-
tions The ambient physical layer parameters modulation scheme and
number of channelization codes set a certain working point where the
remaining flexibility for a different TBS configuration can be obtained
by more or less puncturing resulting in a flexible ratio between for-
ward error correction and user data This will lead to a two-step proce-
dure when evaluating the transport block size First the receiver exam-
ines the information modulation scheme and number of channeliza-
tion codes scheduled via HS-SCCH which indicate the value k0 l as
shown in Fig 2-22 The 6-bit HS-SCCH control parameter transport
block size information will be the transport format resource indica-
tor (TFRI) named ki Let k t be the sum of the two values kt = ki + k0i
Both values kt and k0 i can be obtained from tables given by [TS 25321
Ref 30] The range for the TFRI is from 1 to 256 and the derived trans-port block size ranges from 137 bits to 27 952 bits The first table indi-
cates the value k 0 i based on the channelization code and the modula-
tion scheme
Combination i Modulation scheme Number of channelization codes k0 i
0
QPSK
1 1
1 2 40
2 3 633 4 79
4 5 92
5 6 102
Fig 2-22 Extract from TS 25321 table representing k0 i
The second table indicates the final transport block size based on kt
Index TB size Index TB size Index TB size1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
4 173 89 1456 174 6673
5 185 90 1483 175 6793
6 197 91 1509 176 6916
7 209 92 1537 177 7041
Fig 2-23 Extract from TS 25321 table representing kt
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High speed shared control channel (HS-SCCH)
53
J The transport block size used on HS-DSCH is not signaled explicitly on HS-SCCHJ Instead a transport block size index k
i is signaled to indicate the transport block size
First stepModulation scheme andnumber of channelizationcodes as signaled on HS-SCCHdetermine value k
0 i
Second step
Index kt = k
i + k
0i
determines HS-DSCH
transport block size
kt = k
i + k
0i
Table according to 3GPP TS 25321 extract from QPSK section
Table according to 3GPP TS 25321 254 entries in total
Combination i Modulation
scheme
Number of
channelization codes
k0 i
0
QPSK
1 1
1 2 40
2 3 63
3 4 79
4 hellip hellip
Index TB size Index TB size Index TB size
1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
helliphellip hellip hellip hellip hellip
Fig 2-24 Retrieval of transport block size information
Source Fig 2-22 to Fig 2-24 [TS 25321 Ref 30] reproduced by permission of 3GPP
Hybrid ARQ process information 3 bits
The concept behind the hybrid automatic repeat request (HARQ) was
introduced in section 13 page 14 One feature is the possibility of
multitasking ie having several HARQ processes activated at the same
time Fig 2-25 below shows the need to signal the process identity tothe receiver Remember that on the downlink there is a shared chan-
nel concept so the NodeB can flexibly decide which UE will be sched-
uled with a downlink transport block Up to eight HARQ processes
can be signaled via higher layers to one UE Note however that due to
the round-trip timing six HARQ processes must be active to achieve
the maximum throughput as shown in Fig 2-51 page 79 Compared
with HSUPA the HARQ processes on the downlink are asynchronous
so they have to be indicated but on the uplink they are synchronous sothey do not need to be signaled explicitly
8122019 hspa_e_lp
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HSDPA operation overview and physical channels
Asynchronous DL minus Synchronous ULNumber of H-ARQ rocesses = 1 to 8 er UE
UL HS-DPCCH UE1
UE1 HARQ processes 1 to 4
3 4 1 42 11 1 32retrans
2
A N A A
A A
N A
UL HS-DPCCH UE2
HS-PDSCH
UE2 HARQ processes 1 to 2
Fig 2-25 HARQ process indication on HS-SCCH
Fig 2-25 shows a typical situation on the downlink (point-to-multi-
point) The NodeB sends data to several UEs sharing the HS-PDSCH
so therefore the HARQ process is asynchronous The time when a
transport block is retransmitted is not fixed For this reason the pro-
cess identifier is signaled on the HS-SCCH Based on the HARQ pro-
cess identity and the new data indicator bit the receiving entity knows
which part of the soft buffer memory has to be used in case of soft com-bining On the uplink the situation is slightly simpler The UE only
communicates with one NodeB so it is a point-to-point connection
Thus retransmission always occurs at a fixed time linked to the origi-
nal transmission
Redundancy and constellation version 3 bits
Adaptive modulation and coding involve flexible selection of modula-tion and coding schemes that are signaled to the receiving UE via the
parameters transport block size and modulation scheme information
Another concept used in HSDPA was previously discussed Chase com-
bining or incremental redundancy (see section 222 page 41) This
means that in case of retransmission the transmit entity can dynami-
cally select another puncturing scheme or keep the puncturing as it was
in the original transmission The applied puncturing scheme is signaled
as redundancy information to the receiver Additionally in case of the16QAM modulation scheme the transmitter can select another constel-
lation arrangement which is also signaled to the UE with the three bits
for the redundancy and constellation version see Fig 2-15 page 45
Depending on the modulation scheme (QPSK or 16QAM) there are
two different tables indicating the parameters ldquosrdquo ldquorrdquo and ldquobrdquo The
parameters ldquosrdquo and ldquorrdquo indicate which scheme is used for puncturing
ie if the puncturing mechanism prioritizes the systematic bits or not
8122019 hspa_e_lp
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High speed shared control channel (HS-SCCH)
55
and which puncturing algorithm is used The parameter ldquobrdquo indicates
the constellation mapping version The receiver needs this information
to perform proper demodulation and decoding
Initial transmission
1st retransmission
2nd retransmission
3rd retransmission
r
0
0
1
1
2
2
3
xrv
(value)
s
0 1
1 0
2 1
3 0
4 1
5 0
6 1
7 0 3
s = 1 Systematic bits are prioritizeds = 0 Non-systematic bits are prioritized
r (range 0 to 3 for QPSK) influencesJ Input parameter for puncturing or (together with s) for repetition algorithm defined in TS 25212J Selection of parity bits
Redundancy version coding sequences are signaled on HS-SCCH egndash 0 2 5 6 One initial transmission + 3 retransmissions with different r and s parameters
Fig 2-26 Signaling of redundancy version parameters r and s QPSK case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
Initial transmission
2nd retransmission
1st retransmission
3rd retransmission
r (range 0 to 1 for 16QAM)influences input parameterfor puncturing or (togetherwith s) for repetitionalgorithm defined in
TS 25212 and thus selectionof parity bits
Redundancy version coding sequences are signaled on HS-SCCH egminus 6 4 0 5 Chase combining (no change in s and r parameters ie same redundancyversion) with four possible constellations
x rv (value) s r b
0 1 0 0
1 0 0 0
2 1 1 1
3 0 1 1
4 1 0 1
5 1 0 2
6 1 0 3
7 1 1 0
Definition of parameter s as for QPSK
b (range 0 to 3) describes constellationrearrangement to averagereliability of bits
Fig 2-27 Signaling of redundancy version parameters r s and b 16QAM case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
UE identity H-RNTI 16 bits
The HSDPA radio network transaction identifier (H-RNTI) unam-
biguously identifies the UE having an HS-PDSCH assignment within
a cell It is allocated to the UE via layer 3 signaling procedures at the
radio bearer setup if the radio bearer is an HSDPA connection This
8122019 hspa_e_lp
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56
HSDPA operation overview and physical channels
value represents a temporary name of the UE used to address it when
scheduling data packets via HS-SCCH
HS-SCCH channel coding
The control information contained in the HS-SCCH is of course pro-
tected with channel coding mechanisms the whole coding chain is
described in Fig 2-28 Fig 2-18 page 48 presents the separation of
the control information into two code blocks which are sent consec-
utively mapped on slot 1 and slot 2 + 3 of one HS-SCCH subframe
This principle is also visible in the coding chain The first control block
consisting of channelization information modulation scheme and UE
identity is coded separately from the remaining control values to enable
the UE receiver to decode this first slot separately and prepare for pos-
sible HS-PDSCH reception The coding steps shown in Fig 2-28 such
as rate matching 1 and 2 are similar to the HS-PDSCH coding chain
and are further described in [TS 25212 Ref 21]
Channelcoding 1
R atematching 1
mux
Channelcoding 2
Ratematching 2
RVcoding
UE-specificCRC attachment
UE-specificmasking
Physical channelmapping
r s b
mux
Channelizationcode set
Modulationscheme
Transport block size information
HARQ processinformation
Redundancy andconstellation version
New data indicator
UE identity
UE identity
Fig 2-28 Channel coding for HS-SCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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High speed dedicated physical control channel (HS-DPCCH)
57
24 High speed dedicated physical control channel (HS-DPCCH)
In an active HSDPA connection the UE has to send acknowledgment ornon-acknowledgment reports (as described in section 13 page 14
where the HARQ process is described) as well as channel status infor-
mation to the network The reporting is performed on this physical
control channel HS-DPCCH
As ubiquitous in HSDPA the uplink is also configured into a subframe
structure of 2 ms corresponding to three slots The first slot of the sub-
frame carries the ACK NACK information the UE sends to the NodeB
while the following two slots ie slot 2 and 3 of the subframe convey
the CQI value the channel quality information to the NodeB
Subframe 0 Subframe i Subframe 4
Tslot
= 2560 chips J The spreading factor of theHS-DPCCH is 256 (10 bits peruplink slot)
J The HS-DPCCH can only existtogether with an UL DPCCH
(ded phys control channel)J The DPDCH (dedicated physical data channel) the DPCCH andthe HS-DPCCH are IQ codemultiplexed
HARQ-ACK CQI = Channel quality information
2 times Tslot
= 5120 chips
One radio frame Tf = 10 ms
One HS-DPCCH subframe 2 ms
Fig 2-29 HS-DPCCH configuration
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The slot format for HS-DPCCH describes a quantity of 30 bits per sub-frame resulting in a data rate of 15 kbps The spreading factor used for
the HS-DPCCH is constant and is always equal to 256 but the chan-
nelization code that is used as well as the mapping on either the I or
Q axis depends on several factors eg the co-existence of an HSDPA
connection with a circuit-switched connection meaning whether a
DPDCH established or not Fig 2-36 page 64 illustrates this IQ
mapping and Fig 2-35 page 63 shows the channelization code used
for HS-DPCCH
The HS-DPCCH builds a logical unit of one subframe but having the
independent control information HARQ-ACK and CQI included which
could be separately decoded at the NodeB Note that the slot carrying
the ACK NACK statement is active only when the UE has been sched-
uled by an HS-PDSCH subframe in the corresponding downlink sub-
frame previously Assuming the UE has not received a transport block
8122019 hspa_e_lp
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HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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High speed shared control channel (HS-SCCH)
49
Some of these parameters are more or less self-explanatory while oth-
ers require additional background information and closer examination
Modulation scheme information 1 bit
This single bit is used to inform the receiver whether the modulation
scheme QPSK or 16QAM is applied on the data channel HS-PDSCH
The interpretation of the bit x ms1 is as follows
ms1
x
if QPSK
otherwise
0
1
=
New data indicator 1 bit
The new data indicator bit field informs the receiving entity that the
prevailing PDU transmitted by the current HARQ process is either a
retransmission or contains new data This is done by setting the new
data bit to the value 0 for the first PDU on this particular HARQ process
and incrementing the value by 1 with every new data sent [TS 25321Ref 30] This leads to a toggled value In case the new data bit is not
incremented ie if it remains at its previous value it is an indicator for
retransmission
1st PDU of this
HARQ process
NDI = New data indicator
NDI = 0 NDI = 1
NACK
NDI = 1
ACK
NDI = 0
HS-SCCH HS-SCCH HS-SCCHHS-SCCH
ACK
Fig 2-19 New data indicator bit principle of incrementing value
Channelization code set information 7 bits
This field is used to indicate the number of channelization codes usedfor transmitting the transport block on the HS-PDSCH As was already
described the spreading factor applied on the HS-PDSCH is constant
with a value of 16 but the flexible values are the number of channeliza-
tion codes forming a cluster when using multiple codes and their posi-
tion in the code tree It is not allowed to distribute the code channels
over the code tree diagram For the sake of simplicity in signaling sev-
eral channelization codes form one cluster and these codes are con-
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50
HSDPA operation overview and physical channels
tiguous in the channelization code tree [TS 25213 Ref 22] Fig 2-20
illustrates the principle of indicating the channelization codes on the
HS-SCCH
SF = 16
Code ldquo0rdquo isreserved forcommonchannels
Code offset 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15P = 5O = 7
Code group indicatorx
ccs1 x
ccs2 x
ccs3 = min (Pminus 1 15 minusP)
Code offset indicatorx
ccs4 x
ccs5 x
ccs6 x
ccs7 = |Ominus 1minus P8 times15|
A cluster of codes
can be allocated to a UEC
ch16Ohellip C
ch16O + P minus 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1
2 2 2 2 2 2 2 2 2 2 2 2 2 2 14 14
1 2 3 4 5 6 7 8 9 10 11 12 13 14 2 1
3 3 3 3 3 3 3 3 3 3 3 3 3 13 13 13
1 2 3 4 5 6 7 8 9 10 11 12 13 3 2 1
4 4 4 4 4 4 4 4 4 4 4 4 12 12 12 121 2 3 4 5 6 7 8 9 10 11 12 4 3 2 1
5 5 5 5 5 5 5 5 5 5 5 11 11 11 11 11
1 2 3 4 5 6 7 8 9 10 11 5 4 3 2 1
6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10
1 2 3 4 5 6 7 8 9 10 6 5 4 3 2 1
7 7 7 7 7 7 7 7 7 9 9 9 9 9 9 9
1 2 3 4 5 6 7 8 9 7 6 5 4 3 2 1
8 8 8 8 8 8 8 8
8 7 6 5 4 3 2 1
0 (115)
1 (214)
2 (313)
3 (412)
4 (511)
5 (610)
6 (79)
7 (88) Redundant area
C l u s t e r c o d e i n d i c a t o r ( 3 b i t s )
Tree offset indicator (4 bits)
Signaled on HS-SCCH
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
PO
Decoding notation
Number ofmulti-codes
Offset fromleft right incode tree (SF = 16)
Fig 2-20 Channelization code set indicating the HS-PDSCH code cluster
The idea behind the code indication is a matrix with the rows repre-
senting the number of codes per cluster and the columns represent-
ing the position of that cluster the offset value in the code tree Recall-
ing that the maximum number of channelization codes per clusteris 15 and if the cluster size is 1 the offset values can also range from
1 to 15 the resulting matrix would have 15 rows and 15 columns Since
we know that four bits are needed to represent an integer from 1 to 15
we need a total of 4 + 4 = 8 bits for representation of the channeliza-
tion code set information It is a smart idea to save one bit The 15 times 15
matrix would contain much redundant information By way of analogy
like in a road map indicating distances between cities A table showing
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High speed shared control channel (HS-SCCH)
51
the distance from city A to city B the opposite distance from city B to
city A is redundant information The useful information has the form
of a triangle The idea is to cut the lower part rotate it and append itto the spare part of the upper table In this manner a table is obtained
with 7 rows and 15 columns and it is possible to indicate each position
in it with just 7 bits
1 5 r o w s 7
r o w s
Matrix reduction for channeli-
zation code set information
15 columns
Fig 2-21 Matrix size reduction for channelization code set information
The content of the channelization code set matrix can be described as
a value with two numbers The upper number is the number of mul-
ticodes forming one cluster and the lower number is the offset in the
channelization code tree Accordingly the example in Fig 2-20 can be
interpreted to mean the HS-SCCH sends the bits as row number 4 and
column number 6 in the matrix The content of this element are the
values 5 over 7 which have to be interpreted as a cluster size of 5 codesand an offset of 7
Transport block size information 6 bits
With a length of six bits the transport block size (TBS) informa-
tion informs the receiving UE entity about the data block size of the
transport block sent on the HS-PDSCH We should keep in mind the
link adaptation performed with the adaptive modulation and coding
scheme that was described in section 12 page 10 The ratio errorcorrection and user data are flexible while the physical layer param-
eters such as the spreading factor modulation scheme and number of
channelization codes determine the physical block size This physical
block consists of the user data ratio or transport block size and the for-
ward error correction or redundancy information As this ratio is flex-
ible the HS-SCCH will inform the receiving UE entity about the size
of the transport block Here too there is a strategy of bit reduction the
8122019 hspa_e_lp
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52
HSDPA operation overview and physical channels
goal is to inform the receiver with as few bits as possible A non-effi-
cient approach would involve conversion of the decimal number repre-
senting the TBS into a binary sequence but the number of bits neededwould exceed the space available on the HS-SCCH Imagine that the
range of transport block sizes depends on the physical layer condi-
tions The ambient physical layer parameters modulation scheme and
number of channelization codes set a certain working point where the
remaining flexibility for a different TBS configuration can be obtained
by more or less puncturing resulting in a flexible ratio between for-
ward error correction and user data This will lead to a two-step proce-
dure when evaluating the transport block size First the receiver exam-
ines the information modulation scheme and number of channeliza-
tion codes scheduled via HS-SCCH which indicate the value k0 l as
shown in Fig 2-22 The 6-bit HS-SCCH control parameter transport
block size information will be the transport format resource indica-
tor (TFRI) named ki Let k t be the sum of the two values kt = ki + k0i
Both values kt and k0 i can be obtained from tables given by [TS 25321
Ref 30] The range for the TFRI is from 1 to 256 and the derived trans-port block size ranges from 137 bits to 27 952 bits The first table indi-
cates the value k 0 i based on the channelization code and the modula-
tion scheme
Combination i Modulation scheme Number of channelization codes k0 i
0
QPSK
1 1
1 2 40
2 3 633 4 79
4 5 92
5 6 102
Fig 2-22 Extract from TS 25321 table representing k0 i
The second table indicates the final transport block size based on kt
Index TB size Index TB size Index TB size1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
4 173 89 1456 174 6673
5 185 90 1483 175 6793
6 197 91 1509 176 6916
7 209 92 1537 177 7041
Fig 2-23 Extract from TS 25321 table representing kt
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High speed shared control channel (HS-SCCH)
53
J The transport block size used on HS-DSCH is not signaled explicitly on HS-SCCHJ Instead a transport block size index k
i is signaled to indicate the transport block size
First stepModulation scheme andnumber of channelizationcodes as signaled on HS-SCCHdetermine value k
0 i
Second step
Index kt = k
i + k
0i
determines HS-DSCH
transport block size
kt = k
i + k
0i
Table according to 3GPP TS 25321 extract from QPSK section
Table according to 3GPP TS 25321 254 entries in total
Combination i Modulation
scheme
Number of
channelization codes
k0 i
0
QPSK
1 1
1 2 40
2 3 63
3 4 79
4 hellip hellip
Index TB size Index TB size Index TB size
1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
helliphellip hellip hellip hellip hellip
Fig 2-24 Retrieval of transport block size information
Source Fig 2-22 to Fig 2-24 [TS 25321 Ref 30] reproduced by permission of 3GPP
Hybrid ARQ process information 3 bits
The concept behind the hybrid automatic repeat request (HARQ) was
introduced in section 13 page 14 One feature is the possibility of
multitasking ie having several HARQ processes activated at the same
time Fig 2-25 below shows the need to signal the process identity tothe receiver Remember that on the downlink there is a shared chan-
nel concept so the NodeB can flexibly decide which UE will be sched-
uled with a downlink transport block Up to eight HARQ processes
can be signaled via higher layers to one UE Note however that due to
the round-trip timing six HARQ processes must be active to achieve
the maximum throughput as shown in Fig 2-51 page 79 Compared
with HSUPA the HARQ processes on the downlink are asynchronous
so they have to be indicated but on the uplink they are synchronous sothey do not need to be signaled explicitly
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54
HSDPA operation overview and physical channels
Asynchronous DL minus Synchronous ULNumber of H-ARQ rocesses = 1 to 8 er UE
UL HS-DPCCH UE1
UE1 HARQ processes 1 to 4
3 4 1 42 11 1 32retrans
2
A N A A
A A
N A
UL HS-DPCCH UE2
HS-PDSCH
UE2 HARQ processes 1 to 2
Fig 2-25 HARQ process indication on HS-SCCH
Fig 2-25 shows a typical situation on the downlink (point-to-multi-
point) The NodeB sends data to several UEs sharing the HS-PDSCH
so therefore the HARQ process is asynchronous The time when a
transport block is retransmitted is not fixed For this reason the pro-
cess identifier is signaled on the HS-SCCH Based on the HARQ pro-
cess identity and the new data indicator bit the receiving entity knows
which part of the soft buffer memory has to be used in case of soft com-bining On the uplink the situation is slightly simpler The UE only
communicates with one NodeB so it is a point-to-point connection
Thus retransmission always occurs at a fixed time linked to the origi-
nal transmission
Redundancy and constellation version 3 bits
Adaptive modulation and coding involve flexible selection of modula-tion and coding schemes that are signaled to the receiving UE via the
parameters transport block size and modulation scheme information
Another concept used in HSDPA was previously discussed Chase com-
bining or incremental redundancy (see section 222 page 41) This
means that in case of retransmission the transmit entity can dynami-
cally select another puncturing scheme or keep the puncturing as it was
in the original transmission The applied puncturing scheme is signaled
as redundancy information to the receiver Additionally in case of the16QAM modulation scheme the transmitter can select another constel-
lation arrangement which is also signaled to the UE with the three bits
for the redundancy and constellation version see Fig 2-15 page 45
Depending on the modulation scheme (QPSK or 16QAM) there are
two different tables indicating the parameters ldquosrdquo ldquorrdquo and ldquobrdquo The
parameters ldquosrdquo and ldquorrdquo indicate which scheme is used for puncturing
ie if the puncturing mechanism prioritizes the systematic bits or not
8122019 hspa_e_lp
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High speed shared control channel (HS-SCCH)
55
and which puncturing algorithm is used The parameter ldquobrdquo indicates
the constellation mapping version The receiver needs this information
to perform proper demodulation and decoding
Initial transmission
1st retransmission
2nd retransmission
3rd retransmission
r
0
0
1
1
2
2
3
xrv
(value)
s
0 1
1 0
2 1
3 0
4 1
5 0
6 1
7 0 3
s = 1 Systematic bits are prioritizeds = 0 Non-systematic bits are prioritized
r (range 0 to 3 for QPSK) influencesJ Input parameter for puncturing or (together with s) for repetition algorithm defined in TS 25212J Selection of parity bits
Redundancy version coding sequences are signaled on HS-SCCH egndash 0 2 5 6 One initial transmission + 3 retransmissions with different r and s parameters
Fig 2-26 Signaling of redundancy version parameters r and s QPSK case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
Initial transmission
2nd retransmission
1st retransmission
3rd retransmission
r (range 0 to 1 for 16QAM)influences input parameterfor puncturing or (togetherwith s) for repetitionalgorithm defined in
TS 25212 and thus selectionof parity bits
Redundancy version coding sequences are signaled on HS-SCCH egminus 6 4 0 5 Chase combining (no change in s and r parameters ie same redundancyversion) with four possible constellations
x rv (value) s r b
0 1 0 0
1 0 0 0
2 1 1 1
3 0 1 1
4 1 0 1
5 1 0 2
6 1 0 3
7 1 1 0
Definition of parameter s as for QPSK
b (range 0 to 3) describes constellationrearrangement to averagereliability of bits
Fig 2-27 Signaling of redundancy version parameters r s and b 16QAM case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
UE identity H-RNTI 16 bits
The HSDPA radio network transaction identifier (H-RNTI) unam-
biguously identifies the UE having an HS-PDSCH assignment within
a cell It is allocated to the UE via layer 3 signaling procedures at the
radio bearer setup if the radio bearer is an HSDPA connection This
8122019 hspa_e_lp
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56
HSDPA operation overview and physical channels
value represents a temporary name of the UE used to address it when
scheduling data packets via HS-SCCH
HS-SCCH channel coding
The control information contained in the HS-SCCH is of course pro-
tected with channel coding mechanisms the whole coding chain is
described in Fig 2-28 Fig 2-18 page 48 presents the separation of
the control information into two code blocks which are sent consec-
utively mapped on slot 1 and slot 2 + 3 of one HS-SCCH subframe
This principle is also visible in the coding chain The first control block
consisting of channelization information modulation scheme and UE
identity is coded separately from the remaining control values to enable
the UE receiver to decode this first slot separately and prepare for pos-
sible HS-PDSCH reception The coding steps shown in Fig 2-28 such
as rate matching 1 and 2 are similar to the HS-PDSCH coding chain
and are further described in [TS 25212 Ref 21]
Channelcoding 1
R atematching 1
mux
Channelcoding 2
Ratematching 2
RVcoding
UE-specificCRC attachment
UE-specificmasking
Physical channelmapping
r s b
mux
Channelizationcode set
Modulationscheme
Transport block size information
HARQ processinformation
Redundancy andconstellation version
New data indicator
UE identity
UE identity
Fig 2-28 Channel coding for HS-SCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
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High speed dedicated physical control channel (HS-DPCCH)
57
24 High speed dedicated physical control channel (HS-DPCCH)
In an active HSDPA connection the UE has to send acknowledgment ornon-acknowledgment reports (as described in section 13 page 14
where the HARQ process is described) as well as channel status infor-
mation to the network The reporting is performed on this physical
control channel HS-DPCCH
As ubiquitous in HSDPA the uplink is also configured into a subframe
structure of 2 ms corresponding to three slots The first slot of the sub-
frame carries the ACK NACK information the UE sends to the NodeB
while the following two slots ie slot 2 and 3 of the subframe convey
the CQI value the channel quality information to the NodeB
Subframe 0 Subframe i Subframe 4
Tslot
= 2560 chips J The spreading factor of theHS-DPCCH is 256 (10 bits peruplink slot)
J The HS-DPCCH can only existtogether with an UL DPCCH
(ded phys control channel)J The DPDCH (dedicated physical data channel) the DPCCH andthe HS-DPCCH are IQ codemultiplexed
HARQ-ACK CQI = Channel quality information
2 times Tslot
= 5120 chips
One radio frame Tf = 10 ms
One HS-DPCCH subframe 2 ms
Fig 2-29 HS-DPCCH configuration
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The slot format for HS-DPCCH describes a quantity of 30 bits per sub-frame resulting in a data rate of 15 kbps The spreading factor used for
the HS-DPCCH is constant and is always equal to 256 but the chan-
nelization code that is used as well as the mapping on either the I or
Q axis depends on several factors eg the co-existence of an HSDPA
connection with a circuit-switched connection meaning whether a
DPDCH established or not Fig 2-36 page 64 illustrates this IQ
mapping and Fig 2-35 page 63 shows the channelization code used
for HS-DPCCH
The HS-DPCCH builds a logical unit of one subframe but having the
independent control information HARQ-ACK and CQI included which
could be separately decoded at the NodeB Note that the slot carrying
the ACK NACK statement is active only when the UE has been sched-
uled by an HS-PDSCH subframe in the corresponding downlink sub-
frame previously Assuming the UE has not received a transport block
8122019 hspa_e_lp
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HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
8122019 hspa_e_lp
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50
HSDPA operation overview and physical channels
tiguous in the channelization code tree [TS 25213 Ref 22] Fig 2-20
illustrates the principle of indicating the channelization codes on the
HS-SCCH
SF = 16
Code ldquo0rdquo isreserved forcommonchannels
Code offset 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15P = 5O = 7
Code group indicatorx
ccs1 x
ccs2 x
ccs3 = min (Pminus 1 15 minusP)
Code offset indicatorx
ccs4 x
ccs5 x
ccs6 x
ccs7 = |Ominus 1minus P8 times15|
A cluster of codes
can be allocated to a UEC
ch16Ohellip C
ch16O + P minus 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1
2 2 2 2 2 2 2 2 2 2 2 2 2 2 14 14
1 2 3 4 5 6 7 8 9 10 11 12 13 14 2 1
3 3 3 3 3 3 3 3 3 3 3 3 3 13 13 13
1 2 3 4 5 6 7 8 9 10 11 12 13 3 2 1
4 4 4 4 4 4 4 4 4 4 4 4 12 12 12 121 2 3 4 5 6 7 8 9 10 11 12 4 3 2 1
5 5 5 5 5 5 5 5 5 5 5 11 11 11 11 11
1 2 3 4 5 6 7 8 9 10 11 5 4 3 2 1
6 6 6 6 6 6 6 6 6 6 10 10 10 10 10 10
1 2 3 4 5 6 7 8 9 10 6 5 4 3 2 1
7 7 7 7 7 7 7 7 7 9 9 9 9 9 9 9
1 2 3 4 5 6 7 8 9 7 6 5 4 3 2 1
8 8 8 8 8 8 8 8
8 7 6 5 4 3 2 1
0 (115)
1 (214)
2 (313)
3 (412)
4 (511)
5 (610)
6 (79)
7 (88) Redundant area
C l u s t e r c o d e i n d i c a t o r ( 3 b i t s )
Tree offset indicator (4 bits)
Signaled on HS-SCCH
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
PO
Decoding notation
Number ofmulti-codes
Offset fromleft right incode tree (SF = 16)
Fig 2-20 Channelization code set indicating the HS-PDSCH code cluster
The idea behind the code indication is a matrix with the rows repre-
senting the number of codes per cluster and the columns represent-
ing the position of that cluster the offset value in the code tree Recall-
ing that the maximum number of channelization codes per clusteris 15 and if the cluster size is 1 the offset values can also range from
1 to 15 the resulting matrix would have 15 rows and 15 columns Since
we know that four bits are needed to represent an integer from 1 to 15
we need a total of 4 + 4 = 8 bits for representation of the channeliza-
tion code set information It is a smart idea to save one bit The 15 times 15
matrix would contain much redundant information By way of analogy
like in a road map indicating distances between cities A table showing
8122019 hspa_e_lp
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High speed shared control channel (HS-SCCH)
51
the distance from city A to city B the opposite distance from city B to
city A is redundant information The useful information has the form
of a triangle The idea is to cut the lower part rotate it and append itto the spare part of the upper table In this manner a table is obtained
with 7 rows and 15 columns and it is possible to indicate each position
in it with just 7 bits
1 5 r o w s 7
r o w s
Matrix reduction for channeli-
zation code set information
15 columns
Fig 2-21 Matrix size reduction for channelization code set information
The content of the channelization code set matrix can be described as
a value with two numbers The upper number is the number of mul-
ticodes forming one cluster and the lower number is the offset in the
channelization code tree Accordingly the example in Fig 2-20 can be
interpreted to mean the HS-SCCH sends the bits as row number 4 and
column number 6 in the matrix The content of this element are the
values 5 over 7 which have to be interpreted as a cluster size of 5 codesand an offset of 7
Transport block size information 6 bits
With a length of six bits the transport block size (TBS) informa-
tion informs the receiving UE entity about the data block size of the
transport block sent on the HS-PDSCH We should keep in mind the
link adaptation performed with the adaptive modulation and coding
scheme that was described in section 12 page 10 The ratio errorcorrection and user data are flexible while the physical layer param-
eters such as the spreading factor modulation scheme and number of
channelization codes determine the physical block size This physical
block consists of the user data ratio or transport block size and the for-
ward error correction or redundancy information As this ratio is flex-
ible the HS-SCCH will inform the receiving UE entity about the size
of the transport block Here too there is a strategy of bit reduction the
8122019 hspa_e_lp
httpslidepdfcomreaderfullhspaelp 2430
52
HSDPA operation overview and physical channels
goal is to inform the receiver with as few bits as possible A non-effi-
cient approach would involve conversion of the decimal number repre-
senting the TBS into a binary sequence but the number of bits neededwould exceed the space available on the HS-SCCH Imagine that the
range of transport block sizes depends on the physical layer condi-
tions The ambient physical layer parameters modulation scheme and
number of channelization codes set a certain working point where the
remaining flexibility for a different TBS configuration can be obtained
by more or less puncturing resulting in a flexible ratio between for-
ward error correction and user data This will lead to a two-step proce-
dure when evaluating the transport block size First the receiver exam-
ines the information modulation scheme and number of channeliza-
tion codes scheduled via HS-SCCH which indicate the value k0 l as
shown in Fig 2-22 The 6-bit HS-SCCH control parameter transport
block size information will be the transport format resource indica-
tor (TFRI) named ki Let k t be the sum of the two values kt = ki + k0i
Both values kt and k0 i can be obtained from tables given by [TS 25321
Ref 30] The range for the TFRI is from 1 to 256 and the derived trans-port block size ranges from 137 bits to 27 952 bits The first table indi-
cates the value k 0 i based on the channelization code and the modula-
tion scheme
Combination i Modulation scheme Number of channelization codes k0 i
0
QPSK
1 1
1 2 40
2 3 633 4 79
4 5 92
5 6 102
Fig 2-22 Extract from TS 25321 table representing k0 i
The second table indicates the final transport block size based on kt
Index TB size Index TB size Index TB size1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
4 173 89 1456 174 6673
5 185 90 1483 175 6793
6 197 91 1509 176 6916
7 209 92 1537 177 7041
Fig 2-23 Extract from TS 25321 table representing kt
8122019 hspa_e_lp
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High speed shared control channel (HS-SCCH)
53
J The transport block size used on HS-DSCH is not signaled explicitly on HS-SCCHJ Instead a transport block size index k
i is signaled to indicate the transport block size
First stepModulation scheme andnumber of channelizationcodes as signaled on HS-SCCHdetermine value k
0 i
Second step
Index kt = k
i + k
0i
determines HS-DSCH
transport block size
kt = k
i + k
0i
Table according to 3GPP TS 25321 extract from QPSK section
Table according to 3GPP TS 25321 254 entries in total
Combination i Modulation
scheme
Number of
channelization codes
k0 i
0
QPSK
1 1
1 2 40
2 3 63
3 4 79
4 hellip hellip
Index TB size Index TB size Index TB size
1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
helliphellip hellip hellip hellip hellip
Fig 2-24 Retrieval of transport block size information
Source Fig 2-22 to Fig 2-24 [TS 25321 Ref 30] reproduced by permission of 3GPP
Hybrid ARQ process information 3 bits
The concept behind the hybrid automatic repeat request (HARQ) was
introduced in section 13 page 14 One feature is the possibility of
multitasking ie having several HARQ processes activated at the same
time Fig 2-25 below shows the need to signal the process identity tothe receiver Remember that on the downlink there is a shared chan-
nel concept so the NodeB can flexibly decide which UE will be sched-
uled with a downlink transport block Up to eight HARQ processes
can be signaled via higher layers to one UE Note however that due to
the round-trip timing six HARQ processes must be active to achieve
the maximum throughput as shown in Fig 2-51 page 79 Compared
with HSUPA the HARQ processes on the downlink are asynchronous
so they have to be indicated but on the uplink they are synchronous sothey do not need to be signaled explicitly
8122019 hspa_e_lp
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54
HSDPA operation overview and physical channels
Asynchronous DL minus Synchronous ULNumber of H-ARQ rocesses = 1 to 8 er UE
UL HS-DPCCH UE1
UE1 HARQ processes 1 to 4
3 4 1 42 11 1 32retrans
2
A N A A
A A
N A
UL HS-DPCCH UE2
HS-PDSCH
UE2 HARQ processes 1 to 2
Fig 2-25 HARQ process indication on HS-SCCH
Fig 2-25 shows a typical situation on the downlink (point-to-multi-
point) The NodeB sends data to several UEs sharing the HS-PDSCH
so therefore the HARQ process is asynchronous The time when a
transport block is retransmitted is not fixed For this reason the pro-
cess identifier is signaled on the HS-SCCH Based on the HARQ pro-
cess identity and the new data indicator bit the receiving entity knows
which part of the soft buffer memory has to be used in case of soft com-bining On the uplink the situation is slightly simpler The UE only
communicates with one NodeB so it is a point-to-point connection
Thus retransmission always occurs at a fixed time linked to the origi-
nal transmission
Redundancy and constellation version 3 bits
Adaptive modulation and coding involve flexible selection of modula-tion and coding schemes that are signaled to the receiving UE via the
parameters transport block size and modulation scheme information
Another concept used in HSDPA was previously discussed Chase com-
bining or incremental redundancy (see section 222 page 41) This
means that in case of retransmission the transmit entity can dynami-
cally select another puncturing scheme or keep the puncturing as it was
in the original transmission The applied puncturing scheme is signaled
as redundancy information to the receiver Additionally in case of the16QAM modulation scheme the transmitter can select another constel-
lation arrangement which is also signaled to the UE with the three bits
for the redundancy and constellation version see Fig 2-15 page 45
Depending on the modulation scheme (QPSK or 16QAM) there are
two different tables indicating the parameters ldquosrdquo ldquorrdquo and ldquobrdquo The
parameters ldquosrdquo and ldquorrdquo indicate which scheme is used for puncturing
ie if the puncturing mechanism prioritizes the systematic bits or not
8122019 hspa_e_lp
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High speed shared control channel (HS-SCCH)
55
and which puncturing algorithm is used The parameter ldquobrdquo indicates
the constellation mapping version The receiver needs this information
to perform proper demodulation and decoding
Initial transmission
1st retransmission
2nd retransmission
3rd retransmission
r
0
0
1
1
2
2
3
xrv
(value)
s
0 1
1 0
2 1
3 0
4 1
5 0
6 1
7 0 3
s = 1 Systematic bits are prioritizeds = 0 Non-systematic bits are prioritized
r (range 0 to 3 for QPSK) influencesJ Input parameter for puncturing or (together with s) for repetition algorithm defined in TS 25212J Selection of parity bits
Redundancy version coding sequences are signaled on HS-SCCH egndash 0 2 5 6 One initial transmission + 3 retransmissions with different r and s parameters
Fig 2-26 Signaling of redundancy version parameters r and s QPSK case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
Initial transmission
2nd retransmission
1st retransmission
3rd retransmission
r (range 0 to 1 for 16QAM)influences input parameterfor puncturing or (togetherwith s) for repetitionalgorithm defined in
TS 25212 and thus selectionof parity bits
Redundancy version coding sequences are signaled on HS-SCCH egminus 6 4 0 5 Chase combining (no change in s and r parameters ie same redundancyversion) with four possible constellations
x rv (value) s r b
0 1 0 0
1 0 0 0
2 1 1 1
3 0 1 1
4 1 0 1
5 1 0 2
6 1 0 3
7 1 1 0
Definition of parameter s as for QPSK
b (range 0 to 3) describes constellationrearrangement to averagereliability of bits
Fig 2-27 Signaling of redundancy version parameters r s and b 16QAM case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
UE identity H-RNTI 16 bits
The HSDPA radio network transaction identifier (H-RNTI) unam-
biguously identifies the UE having an HS-PDSCH assignment within
a cell It is allocated to the UE via layer 3 signaling procedures at the
radio bearer setup if the radio bearer is an HSDPA connection This
8122019 hspa_e_lp
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56
HSDPA operation overview and physical channels
value represents a temporary name of the UE used to address it when
scheduling data packets via HS-SCCH
HS-SCCH channel coding
The control information contained in the HS-SCCH is of course pro-
tected with channel coding mechanisms the whole coding chain is
described in Fig 2-28 Fig 2-18 page 48 presents the separation of
the control information into two code blocks which are sent consec-
utively mapped on slot 1 and slot 2 + 3 of one HS-SCCH subframe
This principle is also visible in the coding chain The first control block
consisting of channelization information modulation scheme and UE
identity is coded separately from the remaining control values to enable
the UE receiver to decode this first slot separately and prepare for pos-
sible HS-PDSCH reception The coding steps shown in Fig 2-28 such
as rate matching 1 and 2 are similar to the HS-PDSCH coding chain
and are further described in [TS 25212 Ref 21]
Channelcoding 1
R atematching 1
mux
Channelcoding 2
Ratematching 2
RVcoding
UE-specificCRC attachment
UE-specificmasking
Physical channelmapping
r s b
mux
Channelizationcode set
Modulationscheme
Transport block size information
HARQ processinformation
Redundancy andconstellation version
New data indicator
UE identity
UE identity
Fig 2-28 Channel coding for HS-SCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
8122019 hspa_e_lp
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High speed dedicated physical control channel (HS-DPCCH)
57
24 High speed dedicated physical control channel (HS-DPCCH)
In an active HSDPA connection the UE has to send acknowledgment ornon-acknowledgment reports (as described in section 13 page 14
where the HARQ process is described) as well as channel status infor-
mation to the network The reporting is performed on this physical
control channel HS-DPCCH
As ubiquitous in HSDPA the uplink is also configured into a subframe
structure of 2 ms corresponding to three slots The first slot of the sub-
frame carries the ACK NACK information the UE sends to the NodeB
while the following two slots ie slot 2 and 3 of the subframe convey
the CQI value the channel quality information to the NodeB
Subframe 0 Subframe i Subframe 4
Tslot
= 2560 chips J The spreading factor of theHS-DPCCH is 256 (10 bits peruplink slot)
J The HS-DPCCH can only existtogether with an UL DPCCH
(ded phys control channel)J The DPDCH (dedicated physical data channel) the DPCCH andthe HS-DPCCH are IQ codemultiplexed
HARQ-ACK CQI = Channel quality information
2 times Tslot
= 5120 chips
One radio frame Tf = 10 ms
One HS-DPCCH subframe 2 ms
Fig 2-29 HS-DPCCH configuration
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The slot format for HS-DPCCH describes a quantity of 30 bits per sub-frame resulting in a data rate of 15 kbps The spreading factor used for
the HS-DPCCH is constant and is always equal to 256 but the chan-
nelization code that is used as well as the mapping on either the I or
Q axis depends on several factors eg the co-existence of an HSDPA
connection with a circuit-switched connection meaning whether a
DPDCH established or not Fig 2-36 page 64 illustrates this IQ
mapping and Fig 2-35 page 63 shows the channelization code used
for HS-DPCCH
The HS-DPCCH builds a logical unit of one subframe but having the
independent control information HARQ-ACK and CQI included which
could be separately decoded at the NodeB Note that the slot carrying
the ACK NACK statement is active only when the UE has been sched-
uled by an HS-PDSCH subframe in the corresponding downlink sub-
frame previously Assuming the UE has not received a transport block
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HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
8122019 hspa_e_lp
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High speed shared control channel (HS-SCCH)
51
the distance from city A to city B the opposite distance from city B to
city A is redundant information The useful information has the form
of a triangle The idea is to cut the lower part rotate it and append itto the spare part of the upper table In this manner a table is obtained
with 7 rows and 15 columns and it is possible to indicate each position
in it with just 7 bits
1 5 r o w s 7
r o w s
Matrix reduction for channeli-
zation code set information
15 columns
Fig 2-21 Matrix size reduction for channelization code set information
The content of the channelization code set matrix can be described as
a value with two numbers The upper number is the number of mul-
ticodes forming one cluster and the lower number is the offset in the
channelization code tree Accordingly the example in Fig 2-20 can be
interpreted to mean the HS-SCCH sends the bits as row number 4 and
column number 6 in the matrix The content of this element are the
values 5 over 7 which have to be interpreted as a cluster size of 5 codesand an offset of 7
Transport block size information 6 bits
With a length of six bits the transport block size (TBS) informa-
tion informs the receiving UE entity about the data block size of the
transport block sent on the HS-PDSCH We should keep in mind the
link adaptation performed with the adaptive modulation and coding
scheme that was described in section 12 page 10 The ratio errorcorrection and user data are flexible while the physical layer param-
eters such as the spreading factor modulation scheme and number of
channelization codes determine the physical block size This physical
block consists of the user data ratio or transport block size and the for-
ward error correction or redundancy information As this ratio is flex-
ible the HS-SCCH will inform the receiving UE entity about the size
of the transport block Here too there is a strategy of bit reduction the
8122019 hspa_e_lp
httpslidepdfcomreaderfullhspaelp 2430
52
HSDPA operation overview and physical channels
goal is to inform the receiver with as few bits as possible A non-effi-
cient approach would involve conversion of the decimal number repre-
senting the TBS into a binary sequence but the number of bits neededwould exceed the space available on the HS-SCCH Imagine that the
range of transport block sizes depends on the physical layer condi-
tions The ambient physical layer parameters modulation scheme and
number of channelization codes set a certain working point where the
remaining flexibility for a different TBS configuration can be obtained
by more or less puncturing resulting in a flexible ratio between for-
ward error correction and user data This will lead to a two-step proce-
dure when evaluating the transport block size First the receiver exam-
ines the information modulation scheme and number of channeliza-
tion codes scheduled via HS-SCCH which indicate the value k0 l as
shown in Fig 2-22 The 6-bit HS-SCCH control parameter transport
block size information will be the transport format resource indica-
tor (TFRI) named ki Let k t be the sum of the two values kt = ki + k0i
Both values kt and k0 i can be obtained from tables given by [TS 25321
Ref 30] The range for the TFRI is from 1 to 256 and the derived trans-port block size ranges from 137 bits to 27 952 bits The first table indi-
cates the value k 0 i based on the channelization code and the modula-
tion scheme
Combination i Modulation scheme Number of channelization codes k0 i
0
QPSK
1 1
1 2 40
2 3 633 4 79
4 5 92
5 6 102
Fig 2-22 Extract from TS 25321 table representing k0 i
The second table indicates the final transport block size based on kt
Index TB size Index TB size Index TB size1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
4 173 89 1456 174 6673
5 185 90 1483 175 6793
6 197 91 1509 176 6916
7 209 92 1537 177 7041
Fig 2-23 Extract from TS 25321 table representing kt
8122019 hspa_e_lp
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High speed shared control channel (HS-SCCH)
53
J The transport block size used on HS-DSCH is not signaled explicitly on HS-SCCHJ Instead a transport block size index k
i is signaled to indicate the transport block size
First stepModulation scheme andnumber of channelizationcodes as signaled on HS-SCCHdetermine value k
0 i
Second step
Index kt = k
i + k
0i
determines HS-DSCH
transport block size
kt = k
i + k
0i
Table according to 3GPP TS 25321 extract from QPSK section
Table according to 3GPP TS 25321 254 entries in total
Combination i Modulation
scheme
Number of
channelization codes
k0 i
0
QPSK
1 1
1 2 40
2 3 63
3 4 79
4 hellip hellip
Index TB size Index TB size Index TB size
1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
helliphellip hellip hellip hellip hellip
Fig 2-24 Retrieval of transport block size information
Source Fig 2-22 to Fig 2-24 [TS 25321 Ref 30] reproduced by permission of 3GPP
Hybrid ARQ process information 3 bits
The concept behind the hybrid automatic repeat request (HARQ) was
introduced in section 13 page 14 One feature is the possibility of
multitasking ie having several HARQ processes activated at the same
time Fig 2-25 below shows the need to signal the process identity tothe receiver Remember that on the downlink there is a shared chan-
nel concept so the NodeB can flexibly decide which UE will be sched-
uled with a downlink transport block Up to eight HARQ processes
can be signaled via higher layers to one UE Note however that due to
the round-trip timing six HARQ processes must be active to achieve
the maximum throughput as shown in Fig 2-51 page 79 Compared
with HSUPA the HARQ processes on the downlink are asynchronous
so they have to be indicated but on the uplink they are synchronous sothey do not need to be signaled explicitly
8122019 hspa_e_lp
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54
HSDPA operation overview and physical channels
Asynchronous DL minus Synchronous ULNumber of H-ARQ rocesses = 1 to 8 er UE
UL HS-DPCCH UE1
UE1 HARQ processes 1 to 4
3 4 1 42 11 1 32retrans
2
A N A A
A A
N A
UL HS-DPCCH UE2
HS-PDSCH
UE2 HARQ processes 1 to 2
Fig 2-25 HARQ process indication on HS-SCCH
Fig 2-25 shows a typical situation on the downlink (point-to-multi-
point) The NodeB sends data to several UEs sharing the HS-PDSCH
so therefore the HARQ process is asynchronous The time when a
transport block is retransmitted is not fixed For this reason the pro-
cess identifier is signaled on the HS-SCCH Based on the HARQ pro-
cess identity and the new data indicator bit the receiving entity knows
which part of the soft buffer memory has to be used in case of soft com-bining On the uplink the situation is slightly simpler The UE only
communicates with one NodeB so it is a point-to-point connection
Thus retransmission always occurs at a fixed time linked to the origi-
nal transmission
Redundancy and constellation version 3 bits
Adaptive modulation and coding involve flexible selection of modula-tion and coding schemes that are signaled to the receiving UE via the
parameters transport block size and modulation scheme information
Another concept used in HSDPA was previously discussed Chase com-
bining or incremental redundancy (see section 222 page 41) This
means that in case of retransmission the transmit entity can dynami-
cally select another puncturing scheme or keep the puncturing as it was
in the original transmission The applied puncturing scheme is signaled
as redundancy information to the receiver Additionally in case of the16QAM modulation scheme the transmitter can select another constel-
lation arrangement which is also signaled to the UE with the three bits
for the redundancy and constellation version see Fig 2-15 page 45
Depending on the modulation scheme (QPSK or 16QAM) there are
two different tables indicating the parameters ldquosrdquo ldquorrdquo and ldquobrdquo The
parameters ldquosrdquo and ldquorrdquo indicate which scheme is used for puncturing
ie if the puncturing mechanism prioritizes the systematic bits or not
8122019 hspa_e_lp
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High speed shared control channel (HS-SCCH)
55
and which puncturing algorithm is used The parameter ldquobrdquo indicates
the constellation mapping version The receiver needs this information
to perform proper demodulation and decoding
Initial transmission
1st retransmission
2nd retransmission
3rd retransmission
r
0
0
1
1
2
2
3
xrv
(value)
s
0 1
1 0
2 1
3 0
4 1
5 0
6 1
7 0 3
s = 1 Systematic bits are prioritizeds = 0 Non-systematic bits are prioritized
r (range 0 to 3 for QPSK) influencesJ Input parameter for puncturing or (together with s) for repetition algorithm defined in TS 25212J Selection of parity bits
Redundancy version coding sequences are signaled on HS-SCCH egndash 0 2 5 6 One initial transmission + 3 retransmissions with different r and s parameters
Fig 2-26 Signaling of redundancy version parameters r and s QPSK case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
Initial transmission
2nd retransmission
1st retransmission
3rd retransmission
r (range 0 to 1 for 16QAM)influences input parameterfor puncturing or (togetherwith s) for repetitionalgorithm defined in
TS 25212 and thus selectionof parity bits
Redundancy version coding sequences are signaled on HS-SCCH egminus 6 4 0 5 Chase combining (no change in s and r parameters ie same redundancyversion) with four possible constellations
x rv (value) s r b
0 1 0 0
1 0 0 0
2 1 1 1
3 0 1 1
4 1 0 1
5 1 0 2
6 1 0 3
7 1 1 0
Definition of parameter s as for QPSK
b (range 0 to 3) describes constellationrearrangement to averagereliability of bits
Fig 2-27 Signaling of redundancy version parameters r s and b 16QAM case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
UE identity H-RNTI 16 bits
The HSDPA radio network transaction identifier (H-RNTI) unam-
biguously identifies the UE having an HS-PDSCH assignment within
a cell It is allocated to the UE via layer 3 signaling procedures at the
radio bearer setup if the radio bearer is an HSDPA connection This
8122019 hspa_e_lp
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56
HSDPA operation overview and physical channels
value represents a temporary name of the UE used to address it when
scheduling data packets via HS-SCCH
HS-SCCH channel coding
The control information contained in the HS-SCCH is of course pro-
tected with channel coding mechanisms the whole coding chain is
described in Fig 2-28 Fig 2-18 page 48 presents the separation of
the control information into two code blocks which are sent consec-
utively mapped on slot 1 and slot 2 + 3 of one HS-SCCH subframe
This principle is also visible in the coding chain The first control block
consisting of channelization information modulation scheme and UE
identity is coded separately from the remaining control values to enable
the UE receiver to decode this first slot separately and prepare for pos-
sible HS-PDSCH reception The coding steps shown in Fig 2-28 such
as rate matching 1 and 2 are similar to the HS-PDSCH coding chain
and are further described in [TS 25212 Ref 21]
Channelcoding 1
R atematching 1
mux
Channelcoding 2
Ratematching 2
RVcoding
UE-specificCRC attachment
UE-specificmasking
Physical channelmapping
r s b
mux
Channelizationcode set
Modulationscheme
Transport block size information
HARQ processinformation
Redundancy andconstellation version
New data indicator
UE identity
UE identity
Fig 2-28 Channel coding for HS-SCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
8122019 hspa_e_lp
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High speed dedicated physical control channel (HS-DPCCH)
57
24 High speed dedicated physical control channel (HS-DPCCH)
In an active HSDPA connection the UE has to send acknowledgment ornon-acknowledgment reports (as described in section 13 page 14
where the HARQ process is described) as well as channel status infor-
mation to the network The reporting is performed on this physical
control channel HS-DPCCH
As ubiquitous in HSDPA the uplink is also configured into a subframe
structure of 2 ms corresponding to three slots The first slot of the sub-
frame carries the ACK NACK information the UE sends to the NodeB
while the following two slots ie slot 2 and 3 of the subframe convey
the CQI value the channel quality information to the NodeB
Subframe 0 Subframe i Subframe 4
Tslot
= 2560 chips J The spreading factor of theHS-DPCCH is 256 (10 bits peruplink slot)
J The HS-DPCCH can only existtogether with an UL DPCCH
(ded phys control channel)J The DPDCH (dedicated physical data channel) the DPCCH andthe HS-DPCCH are IQ codemultiplexed
HARQ-ACK CQI = Channel quality information
2 times Tslot
= 5120 chips
One radio frame Tf = 10 ms
One HS-DPCCH subframe 2 ms
Fig 2-29 HS-DPCCH configuration
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The slot format for HS-DPCCH describes a quantity of 30 bits per sub-frame resulting in a data rate of 15 kbps The spreading factor used for
the HS-DPCCH is constant and is always equal to 256 but the chan-
nelization code that is used as well as the mapping on either the I or
Q axis depends on several factors eg the co-existence of an HSDPA
connection with a circuit-switched connection meaning whether a
DPDCH established or not Fig 2-36 page 64 illustrates this IQ
mapping and Fig 2-35 page 63 shows the channelization code used
for HS-DPCCH
The HS-DPCCH builds a logical unit of one subframe but having the
independent control information HARQ-ACK and CQI included which
could be separately decoded at the NodeB Note that the slot carrying
the ACK NACK statement is active only when the UE has been sched-
uled by an HS-PDSCH subframe in the corresponding downlink sub-
frame previously Assuming the UE has not received a transport block
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HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
8122019 hspa_e_lp
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52
HSDPA operation overview and physical channels
goal is to inform the receiver with as few bits as possible A non-effi-
cient approach would involve conversion of the decimal number repre-
senting the TBS into a binary sequence but the number of bits neededwould exceed the space available on the HS-SCCH Imagine that the
range of transport block sizes depends on the physical layer condi-
tions The ambient physical layer parameters modulation scheme and
number of channelization codes set a certain working point where the
remaining flexibility for a different TBS configuration can be obtained
by more or less puncturing resulting in a flexible ratio between for-
ward error correction and user data This will lead to a two-step proce-
dure when evaluating the transport block size First the receiver exam-
ines the information modulation scheme and number of channeliza-
tion codes scheduled via HS-SCCH which indicate the value k0 l as
shown in Fig 2-22 The 6-bit HS-SCCH control parameter transport
block size information will be the transport format resource indica-
tor (TFRI) named ki Let k t be the sum of the two values kt = ki + k0i
Both values kt and k0 i can be obtained from tables given by [TS 25321
Ref 30] The range for the TFRI is from 1 to 256 and the derived trans-port block size ranges from 137 bits to 27 952 bits The first table indi-
cates the value k 0 i based on the channelization code and the modula-
tion scheme
Combination i Modulation scheme Number of channelization codes k0 i
0
QPSK
1 1
1 2 40
2 3 633 4 79
4 5 92
5 6 102
Fig 2-22 Extract from TS 25321 table representing k0 i
The second table indicates the final transport block size based on kt
Index TB size Index TB size Index TB size1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
4 173 89 1456 174 6673
5 185 90 1483 175 6793
6 197 91 1509 176 6916
7 209 92 1537 177 7041
Fig 2-23 Extract from TS 25321 table representing kt
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High speed shared control channel (HS-SCCH)
53
J The transport block size used on HS-DSCH is not signaled explicitly on HS-SCCHJ Instead a transport block size index k
i is signaled to indicate the transport block size
First stepModulation scheme andnumber of channelizationcodes as signaled on HS-SCCHdetermine value k
0 i
Second step
Index kt = k
i + k
0i
determines HS-DSCH
transport block size
kt = k
i + k
0i
Table according to 3GPP TS 25321 extract from QPSK section
Table according to 3GPP TS 25321 254 entries in total
Combination i Modulation
scheme
Number of
channelization codes
k0 i
0
QPSK
1 1
1 2 40
2 3 63
3 4 79
4 hellip hellip
Index TB size Index TB size Index TB size
1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
helliphellip hellip hellip hellip hellip
Fig 2-24 Retrieval of transport block size information
Source Fig 2-22 to Fig 2-24 [TS 25321 Ref 30] reproduced by permission of 3GPP
Hybrid ARQ process information 3 bits
The concept behind the hybrid automatic repeat request (HARQ) was
introduced in section 13 page 14 One feature is the possibility of
multitasking ie having several HARQ processes activated at the same
time Fig 2-25 below shows the need to signal the process identity tothe receiver Remember that on the downlink there is a shared chan-
nel concept so the NodeB can flexibly decide which UE will be sched-
uled with a downlink transport block Up to eight HARQ processes
can be signaled via higher layers to one UE Note however that due to
the round-trip timing six HARQ processes must be active to achieve
the maximum throughput as shown in Fig 2-51 page 79 Compared
with HSUPA the HARQ processes on the downlink are asynchronous
so they have to be indicated but on the uplink they are synchronous sothey do not need to be signaled explicitly
8122019 hspa_e_lp
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54
HSDPA operation overview and physical channels
Asynchronous DL minus Synchronous ULNumber of H-ARQ rocesses = 1 to 8 er UE
UL HS-DPCCH UE1
UE1 HARQ processes 1 to 4
3 4 1 42 11 1 32retrans
2
A N A A
A A
N A
UL HS-DPCCH UE2
HS-PDSCH
UE2 HARQ processes 1 to 2
Fig 2-25 HARQ process indication on HS-SCCH
Fig 2-25 shows a typical situation on the downlink (point-to-multi-
point) The NodeB sends data to several UEs sharing the HS-PDSCH
so therefore the HARQ process is asynchronous The time when a
transport block is retransmitted is not fixed For this reason the pro-
cess identifier is signaled on the HS-SCCH Based on the HARQ pro-
cess identity and the new data indicator bit the receiving entity knows
which part of the soft buffer memory has to be used in case of soft com-bining On the uplink the situation is slightly simpler The UE only
communicates with one NodeB so it is a point-to-point connection
Thus retransmission always occurs at a fixed time linked to the origi-
nal transmission
Redundancy and constellation version 3 bits
Adaptive modulation and coding involve flexible selection of modula-tion and coding schemes that are signaled to the receiving UE via the
parameters transport block size and modulation scheme information
Another concept used in HSDPA was previously discussed Chase com-
bining or incremental redundancy (see section 222 page 41) This
means that in case of retransmission the transmit entity can dynami-
cally select another puncturing scheme or keep the puncturing as it was
in the original transmission The applied puncturing scheme is signaled
as redundancy information to the receiver Additionally in case of the16QAM modulation scheme the transmitter can select another constel-
lation arrangement which is also signaled to the UE with the three bits
for the redundancy and constellation version see Fig 2-15 page 45
Depending on the modulation scheme (QPSK or 16QAM) there are
two different tables indicating the parameters ldquosrdquo ldquorrdquo and ldquobrdquo The
parameters ldquosrdquo and ldquorrdquo indicate which scheme is used for puncturing
ie if the puncturing mechanism prioritizes the systematic bits or not
8122019 hspa_e_lp
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High speed shared control channel (HS-SCCH)
55
and which puncturing algorithm is used The parameter ldquobrdquo indicates
the constellation mapping version The receiver needs this information
to perform proper demodulation and decoding
Initial transmission
1st retransmission
2nd retransmission
3rd retransmission
r
0
0
1
1
2
2
3
xrv
(value)
s
0 1
1 0
2 1
3 0
4 1
5 0
6 1
7 0 3
s = 1 Systematic bits are prioritizeds = 0 Non-systematic bits are prioritized
r (range 0 to 3 for QPSK) influencesJ Input parameter for puncturing or (together with s) for repetition algorithm defined in TS 25212J Selection of parity bits
Redundancy version coding sequences are signaled on HS-SCCH egndash 0 2 5 6 One initial transmission + 3 retransmissions with different r and s parameters
Fig 2-26 Signaling of redundancy version parameters r and s QPSK case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
Initial transmission
2nd retransmission
1st retransmission
3rd retransmission
r (range 0 to 1 for 16QAM)influences input parameterfor puncturing or (togetherwith s) for repetitionalgorithm defined in
TS 25212 and thus selectionof parity bits
Redundancy version coding sequences are signaled on HS-SCCH egminus 6 4 0 5 Chase combining (no change in s and r parameters ie same redundancyversion) with four possible constellations
x rv (value) s r b
0 1 0 0
1 0 0 0
2 1 1 1
3 0 1 1
4 1 0 1
5 1 0 2
6 1 0 3
7 1 1 0
Definition of parameter s as for QPSK
b (range 0 to 3) describes constellationrearrangement to averagereliability of bits
Fig 2-27 Signaling of redundancy version parameters r s and b 16QAM case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
UE identity H-RNTI 16 bits
The HSDPA radio network transaction identifier (H-RNTI) unam-
biguously identifies the UE having an HS-PDSCH assignment within
a cell It is allocated to the UE via layer 3 signaling procedures at the
radio bearer setup if the radio bearer is an HSDPA connection This
8122019 hspa_e_lp
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56
HSDPA operation overview and physical channels
value represents a temporary name of the UE used to address it when
scheduling data packets via HS-SCCH
HS-SCCH channel coding
The control information contained in the HS-SCCH is of course pro-
tected with channel coding mechanisms the whole coding chain is
described in Fig 2-28 Fig 2-18 page 48 presents the separation of
the control information into two code blocks which are sent consec-
utively mapped on slot 1 and slot 2 + 3 of one HS-SCCH subframe
This principle is also visible in the coding chain The first control block
consisting of channelization information modulation scheme and UE
identity is coded separately from the remaining control values to enable
the UE receiver to decode this first slot separately and prepare for pos-
sible HS-PDSCH reception The coding steps shown in Fig 2-28 such
as rate matching 1 and 2 are similar to the HS-PDSCH coding chain
and are further described in [TS 25212 Ref 21]
Channelcoding 1
R atematching 1
mux
Channelcoding 2
Ratematching 2
RVcoding
UE-specificCRC attachment
UE-specificmasking
Physical channelmapping
r s b
mux
Channelizationcode set
Modulationscheme
Transport block size information
HARQ processinformation
Redundancy andconstellation version
New data indicator
UE identity
UE identity
Fig 2-28 Channel coding for HS-SCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
8122019 hspa_e_lp
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High speed dedicated physical control channel (HS-DPCCH)
57
24 High speed dedicated physical control channel (HS-DPCCH)
In an active HSDPA connection the UE has to send acknowledgment ornon-acknowledgment reports (as described in section 13 page 14
where the HARQ process is described) as well as channel status infor-
mation to the network The reporting is performed on this physical
control channel HS-DPCCH
As ubiquitous in HSDPA the uplink is also configured into a subframe
structure of 2 ms corresponding to three slots The first slot of the sub-
frame carries the ACK NACK information the UE sends to the NodeB
while the following two slots ie slot 2 and 3 of the subframe convey
the CQI value the channel quality information to the NodeB
Subframe 0 Subframe i Subframe 4
Tslot
= 2560 chips J The spreading factor of theHS-DPCCH is 256 (10 bits peruplink slot)
J The HS-DPCCH can only existtogether with an UL DPCCH
(ded phys control channel)J The DPDCH (dedicated physical data channel) the DPCCH andthe HS-DPCCH are IQ codemultiplexed
HARQ-ACK CQI = Channel quality information
2 times Tslot
= 5120 chips
One radio frame Tf = 10 ms
One HS-DPCCH subframe 2 ms
Fig 2-29 HS-DPCCH configuration
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The slot format for HS-DPCCH describes a quantity of 30 bits per sub-frame resulting in a data rate of 15 kbps The spreading factor used for
the HS-DPCCH is constant and is always equal to 256 but the chan-
nelization code that is used as well as the mapping on either the I or
Q axis depends on several factors eg the co-existence of an HSDPA
connection with a circuit-switched connection meaning whether a
DPDCH established or not Fig 2-36 page 64 illustrates this IQ
mapping and Fig 2-35 page 63 shows the channelization code used
for HS-DPCCH
The HS-DPCCH builds a logical unit of one subframe but having the
independent control information HARQ-ACK and CQI included which
could be separately decoded at the NodeB Note that the slot carrying
the ACK NACK statement is active only when the UE has been sched-
uled by an HS-PDSCH subframe in the corresponding downlink sub-
frame previously Assuming the UE has not received a transport block
8122019 hspa_e_lp
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HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
8122019 hspa_e_lp
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High speed shared control channel (HS-SCCH)
53
J The transport block size used on HS-DSCH is not signaled explicitly on HS-SCCHJ Instead a transport block size index k
i is signaled to indicate the transport block size
First stepModulation scheme andnumber of channelizationcodes as signaled on HS-SCCHdetermine value k
0 i
Second step
Index kt = k
i + k
0i
determines HS-DSCH
transport block size
kt = k
i + k
0i
Table according to 3GPP TS 25321 extract from QPSK section
Table according to 3GPP TS 25321 254 entries in total
Combination i Modulation
scheme
Number of
channelization codes
k0 i
0
QPSK
1 1
1 2 40
2 3 63
3 4 79
4 hellip hellip
Index TB size Index TB size Index TB size
1 137 86 1380 171 6324
2 149 87 1405 172 6438
3 161 88 1430 173 6554
helliphellip hellip hellip hellip hellip
Fig 2-24 Retrieval of transport block size information
Source Fig 2-22 to Fig 2-24 [TS 25321 Ref 30] reproduced by permission of 3GPP
Hybrid ARQ process information 3 bits
The concept behind the hybrid automatic repeat request (HARQ) was
introduced in section 13 page 14 One feature is the possibility of
multitasking ie having several HARQ processes activated at the same
time Fig 2-25 below shows the need to signal the process identity tothe receiver Remember that on the downlink there is a shared chan-
nel concept so the NodeB can flexibly decide which UE will be sched-
uled with a downlink transport block Up to eight HARQ processes
can be signaled via higher layers to one UE Note however that due to
the round-trip timing six HARQ processes must be active to achieve
the maximum throughput as shown in Fig 2-51 page 79 Compared
with HSUPA the HARQ processes on the downlink are asynchronous
so they have to be indicated but on the uplink they are synchronous sothey do not need to be signaled explicitly
8122019 hspa_e_lp
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54
HSDPA operation overview and physical channels
Asynchronous DL minus Synchronous ULNumber of H-ARQ rocesses = 1 to 8 er UE
UL HS-DPCCH UE1
UE1 HARQ processes 1 to 4
3 4 1 42 11 1 32retrans
2
A N A A
A A
N A
UL HS-DPCCH UE2
HS-PDSCH
UE2 HARQ processes 1 to 2
Fig 2-25 HARQ process indication on HS-SCCH
Fig 2-25 shows a typical situation on the downlink (point-to-multi-
point) The NodeB sends data to several UEs sharing the HS-PDSCH
so therefore the HARQ process is asynchronous The time when a
transport block is retransmitted is not fixed For this reason the pro-
cess identifier is signaled on the HS-SCCH Based on the HARQ pro-
cess identity and the new data indicator bit the receiving entity knows
which part of the soft buffer memory has to be used in case of soft com-bining On the uplink the situation is slightly simpler The UE only
communicates with one NodeB so it is a point-to-point connection
Thus retransmission always occurs at a fixed time linked to the origi-
nal transmission
Redundancy and constellation version 3 bits
Adaptive modulation and coding involve flexible selection of modula-tion and coding schemes that are signaled to the receiving UE via the
parameters transport block size and modulation scheme information
Another concept used in HSDPA was previously discussed Chase com-
bining or incremental redundancy (see section 222 page 41) This
means that in case of retransmission the transmit entity can dynami-
cally select another puncturing scheme or keep the puncturing as it was
in the original transmission The applied puncturing scheme is signaled
as redundancy information to the receiver Additionally in case of the16QAM modulation scheme the transmitter can select another constel-
lation arrangement which is also signaled to the UE with the three bits
for the redundancy and constellation version see Fig 2-15 page 45
Depending on the modulation scheme (QPSK or 16QAM) there are
two different tables indicating the parameters ldquosrdquo ldquorrdquo and ldquobrdquo The
parameters ldquosrdquo and ldquorrdquo indicate which scheme is used for puncturing
ie if the puncturing mechanism prioritizes the systematic bits or not
8122019 hspa_e_lp
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High speed shared control channel (HS-SCCH)
55
and which puncturing algorithm is used The parameter ldquobrdquo indicates
the constellation mapping version The receiver needs this information
to perform proper demodulation and decoding
Initial transmission
1st retransmission
2nd retransmission
3rd retransmission
r
0
0
1
1
2
2
3
xrv
(value)
s
0 1
1 0
2 1
3 0
4 1
5 0
6 1
7 0 3
s = 1 Systematic bits are prioritizeds = 0 Non-systematic bits are prioritized
r (range 0 to 3 for QPSK) influencesJ Input parameter for puncturing or (together with s) for repetition algorithm defined in TS 25212J Selection of parity bits
Redundancy version coding sequences are signaled on HS-SCCH egndash 0 2 5 6 One initial transmission + 3 retransmissions with different r and s parameters
Fig 2-26 Signaling of redundancy version parameters r and s QPSK case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
Initial transmission
2nd retransmission
1st retransmission
3rd retransmission
r (range 0 to 1 for 16QAM)influences input parameterfor puncturing or (togetherwith s) for repetitionalgorithm defined in
TS 25212 and thus selectionof parity bits
Redundancy version coding sequences are signaled on HS-SCCH egminus 6 4 0 5 Chase combining (no change in s and r parameters ie same redundancyversion) with four possible constellations
x rv (value) s r b
0 1 0 0
1 0 0 0
2 1 1 1
3 0 1 1
4 1 0 1
5 1 0 2
6 1 0 3
7 1 1 0
Definition of parameter s as for QPSK
b (range 0 to 3) describes constellationrearrangement to averagereliability of bits
Fig 2-27 Signaling of redundancy version parameters r s and b 16QAM case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
UE identity H-RNTI 16 bits
The HSDPA radio network transaction identifier (H-RNTI) unam-
biguously identifies the UE having an HS-PDSCH assignment within
a cell It is allocated to the UE via layer 3 signaling procedures at the
radio bearer setup if the radio bearer is an HSDPA connection This
8122019 hspa_e_lp
httpslidepdfcomreaderfullhspaelp 2830
56
HSDPA operation overview and physical channels
value represents a temporary name of the UE used to address it when
scheduling data packets via HS-SCCH
HS-SCCH channel coding
The control information contained in the HS-SCCH is of course pro-
tected with channel coding mechanisms the whole coding chain is
described in Fig 2-28 Fig 2-18 page 48 presents the separation of
the control information into two code blocks which are sent consec-
utively mapped on slot 1 and slot 2 + 3 of one HS-SCCH subframe
This principle is also visible in the coding chain The first control block
consisting of channelization information modulation scheme and UE
identity is coded separately from the remaining control values to enable
the UE receiver to decode this first slot separately and prepare for pos-
sible HS-PDSCH reception The coding steps shown in Fig 2-28 such
as rate matching 1 and 2 are similar to the HS-PDSCH coding chain
and are further described in [TS 25212 Ref 21]
Channelcoding 1
R atematching 1
mux
Channelcoding 2
Ratematching 2
RVcoding
UE-specificCRC attachment
UE-specificmasking
Physical channelmapping
r s b
mux
Channelizationcode set
Modulationscheme
Transport block size information
HARQ processinformation
Redundancy andconstellation version
New data indicator
UE identity
UE identity
Fig 2-28 Channel coding for HS-SCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
8122019 hspa_e_lp
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High speed dedicated physical control channel (HS-DPCCH)
57
24 High speed dedicated physical control channel (HS-DPCCH)
In an active HSDPA connection the UE has to send acknowledgment ornon-acknowledgment reports (as described in section 13 page 14
where the HARQ process is described) as well as channel status infor-
mation to the network The reporting is performed on this physical
control channel HS-DPCCH
As ubiquitous in HSDPA the uplink is also configured into a subframe
structure of 2 ms corresponding to three slots The first slot of the sub-
frame carries the ACK NACK information the UE sends to the NodeB
while the following two slots ie slot 2 and 3 of the subframe convey
the CQI value the channel quality information to the NodeB
Subframe 0 Subframe i Subframe 4
Tslot
= 2560 chips J The spreading factor of theHS-DPCCH is 256 (10 bits peruplink slot)
J The HS-DPCCH can only existtogether with an UL DPCCH
(ded phys control channel)J The DPDCH (dedicated physical data channel) the DPCCH andthe HS-DPCCH are IQ codemultiplexed
HARQ-ACK CQI = Channel quality information
2 times Tslot
= 5120 chips
One radio frame Tf = 10 ms
One HS-DPCCH subframe 2 ms
Fig 2-29 HS-DPCCH configuration
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The slot format for HS-DPCCH describes a quantity of 30 bits per sub-frame resulting in a data rate of 15 kbps The spreading factor used for
the HS-DPCCH is constant and is always equal to 256 but the chan-
nelization code that is used as well as the mapping on either the I or
Q axis depends on several factors eg the co-existence of an HSDPA
connection with a circuit-switched connection meaning whether a
DPDCH established or not Fig 2-36 page 64 illustrates this IQ
mapping and Fig 2-35 page 63 shows the channelization code used
for HS-DPCCH
The HS-DPCCH builds a logical unit of one subframe but having the
independent control information HARQ-ACK and CQI included which
could be separately decoded at the NodeB Note that the slot carrying
the ACK NACK statement is active only when the UE has been sched-
uled by an HS-PDSCH subframe in the corresponding downlink sub-
frame previously Assuming the UE has not received a transport block
8122019 hspa_e_lp
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HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
8122019 hspa_e_lp
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54
HSDPA operation overview and physical channels
Asynchronous DL minus Synchronous ULNumber of H-ARQ rocesses = 1 to 8 er UE
UL HS-DPCCH UE1
UE1 HARQ processes 1 to 4
3 4 1 42 11 1 32retrans
2
A N A A
A A
N A
UL HS-DPCCH UE2
HS-PDSCH
UE2 HARQ processes 1 to 2
Fig 2-25 HARQ process indication on HS-SCCH
Fig 2-25 shows a typical situation on the downlink (point-to-multi-
point) The NodeB sends data to several UEs sharing the HS-PDSCH
so therefore the HARQ process is asynchronous The time when a
transport block is retransmitted is not fixed For this reason the pro-
cess identifier is signaled on the HS-SCCH Based on the HARQ pro-
cess identity and the new data indicator bit the receiving entity knows
which part of the soft buffer memory has to be used in case of soft com-bining On the uplink the situation is slightly simpler The UE only
communicates with one NodeB so it is a point-to-point connection
Thus retransmission always occurs at a fixed time linked to the origi-
nal transmission
Redundancy and constellation version 3 bits
Adaptive modulation and coding involve flexible selection of modula-tion and coding schemes that are signaled to the receiving UE via the
parameters transport block size and modulation scheme information
Another concept used in HSDPA was previously discussed Chase com-
bining or incremental redundancy (see section 222 page 41) This
means that in case of retransmission the transmit entity can dynami-
cally select another puncturing scheme or keep the puncturing as it was
in the original transmission The applied puncturing scheme is signaled
as redundancy information to the receiver Additionally in case of the16QAM modulation scheme the transmitter can select another constel-
lation arrangement which is also signaled to the UE with the three bits
for the redundancy and constellation version see Fig 2-15 page 45
Depending on the modulation scheme (QPSK or 16QAM) there are
two different tables indicating the parameters ldquosrdquo ldquorrdquo and ldquobrdquo The
parameters ldquosrdquo and ldquorrdquo indicate which scheme is used for puncturing
ie if the puncturing mechanism prioritizes the systematic bits or not
8122019 hspa_e_lp
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High speed shared control channel (HS-SCCH)
55
and which puncturing algorithm is used The parameter ldquobrdquo indicates
the constellation mapping version The receiver needs this information
to perform proper demodulation and decoding
Initial transmission
1st retransmission
2nd retransmission
3rd retransmission
r
0
0
1
1
2
2
3
xrv
(value)
s
0 1
1 0
2 1
3 0
4 1
5 0
6 1
7 0 3
s = 1 Systematic bits are prioritizeds = 0 Non-systematic bits are prioritized
r (range 0 to 3 for QPSK) influencesJ Input parameter for puncturing or (together with s) for repetition algorithm defined in TS 25212J Selection of parity bits
Redundancy version coding sequences are signaled on HS-SCCH egndash 0 2 5 6 One initial transmission + 3 retransmissions with different r and s parameters
Fig 2-26 Signaling of redundancy version parameters r and s QPSK case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
Initial transmission
2nd retransmission
1st retransmission
3rd retransmission
r (range 0 to 1 for 16QAM)influences input parameterfor puncturing or (togetherwith s) for repetitionalgorithm defined in
TS 25212 and thus selectionof parity bits
Redundancy version coding sequences are signaled on HS-SCCH egminus 6 4 0 5 Chase combining (no change in s and r parameters ie same redundancyversion) with four possible constellations
x rv (value) s r b
0 1 0 0
1 0 0 0
2 1 1 1
3 0 1 1
4 1 0 1
5 1 0 2
6 1 0 3
7 1 1 0
Definition of parameter s as for QPSK
b (range 0 to 3) describes constellationrearrangement to averagereliability of bits
Fig 2-27 Signaling of redundancy version parameters r s and b 16QAM case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
UE identity H-RNTI 16 bits
The HSDPA radio network transaction identifier (H-RNTI) unam-
biguously identifies the UE having an HS-PDSCH assignment within
a cell It is allocated to the UE via layer 3 signaling procedures at the
radio bearer setup if the radio bearer is an HSDPA connection This
8122019 hspa_e_lp
httpslidepdfcomreaderfullhspaelp 2830
56
HSDPA operation overview and physical channels
value represents a temporary name of the UE used to address it when
scheduling data packets via HS-SCCH
HS-SCCH channel coding
The control information contained in the HS-SCCH is of course pro-
tected with channel coding mechanisms the whole coding chain is
described in Fig 2-28 Fig 2-18 page 48 presents the separation of
the control information into two code blocks which are sent consec-
utively mapped on slot 1 and slot 2 + 3 of one HS-SCCH subframe
This principle is also visible in the coding chain The first control block
consisting of channelization information modulation scheme and UE
identity is coded separately from the remaining control values to enable
the UE receiver to decode this first slot separately and prepare for pos-
sible HS-PDSCH reception The coding steps shown in Fig 2-28 such
as rate matching 1 and 2 are similar to the HS-PDSCH coding chain
and are further described in [TS 25212 Ref 21]
Channelcoding 1
R atematching 1
mux
Channelcoding 2
Ratematching 2
RVcoding
UE-specificCRC attachment
UE-specificmasking
Physical channelmapping
r s b
mux
Channelizationcode set
Modulationscheme
Transport block size information
HARQ processinformation
Redundancy andconstellation version
New data indicator
UE identity
UE identity
Fig 2-28 Channel coding for HS-SCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
8122019 hspa_e_lp
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High speed dedicated physical control channel (HS-DPCCH)
57
24 High speed dedicated physical control channel (HS-DPCCH)
In an active HSDPA connection the UE has to send acknowledgment ornon-acknowledgment reports (as described in section 13 page 14
where the HARQ process is described) as well as channel status infor-
mation to the network The reporting is performed on this physical
control channel HS-DPCCH
As ubiquitous in HSDPA the uplink is also configured into a subframe
structure of 2 ms corresponding to three slots The first slot of the sub-
frame carries the ACK NACK information the UE sends to the NodeB
while the following two slots ie slot 2 and 3 of the subframe convey
the CQI value the channel quality information to the NodeB
Subframe 0 Subframe i Subframe 4
Tslot
= 2560 chips J The spreading factor of theHS-DPCCH is 256 (10 bits peruplink slot)
J The HS-DPCCH can only existtogether with an UL DPCCH
(ded phys control channel)J The DPDCH (dedicated physical data channel) the DPCCH andthe HS-DPCCH are IQ codemultiplexed
HARQ-ACK CQI = Channel quality information
2 times Tslot
= 5120 chips
One radio frame Tf = 10 ms
One HS-DPCCH subframe 2 ms
Fig 2-29 HS-DPCCH configuration
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The slot format for HS-DPCCH describes a quantity of 30 bits per sub-frame resulting in a data rate of 15 kbps The spreading factor used for
the HS-DPCCH is constant and is always equal to 256 but the chan-
nelization code that is used as well as the mapping on either the I or
Q axis depends on several factors eg the co-existence of an HSDPA
connection with a circuit-switched connection meaning whether a
DPDCH established or not Fig 2-36 page 64 illustrates this IQ
mapping and Fig 2-35 page 63 shows the channelization code used
for HS-DPCCH
The HS-DPCCH builds a logical unit of one subframe but having the
independent control information HARQ-ACK and CQI included which
could be separately decoded at the NodeB Note that the slot carrying
the ACK NACK statement is active only when the UE has been sched-
uled by an HS-PDSCH subframe in the corresponding downlink sub-
frame previously Assuming the UE has not received a transport block
8122019 hspa_e_lp
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HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
8122019 hspa_e_lp
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High speed shared control channel (HS-SCCH)
55
and which puncturing algorithm is used The parameter ldquobrdquo indicates
the constellation mapping version The receiver needs this information
to perform proper demodulation and decoding
Initial transmission
1st retransmission
2nd retransmission
3rd retransmission
r
0
0
1
1
2
2
3
xrv
(value)
s
0 1
1 0
2 1
3 0
4 1
5 0
6 1
7 0 3
s = 1 Systematic bits are prioritizeds = 0 Non-systematic bits are prioritized
r (range 0 to 3 for QPSK) influencesJ Input parameter for puncturing or (together with s) for repetition algorithm defined in TS 25212J Selection of parity bits
Redundancy version coding sequences are signaled on HS-SCCH egndash 0 2 5 6 One initial transmission + 3 retransmissions with different r and s parameters
Fig 2-26 Signaling of redundancy version parameters r and s QPSK case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
Initial transmission
2nd retransmission
1st retransmission
3rd retransmission
r (range 0 to 1 for 16QAM)influences input parameterfor puncturing or (togetherwith s) for repetitionalgorithm defined in
TS 25212 and thus selectionof parity bits
Redundancy version coding sequences are signaled on HS-SCCH egminus 6 4 0 5 Chase combining (no change in s and r parameters ie same redundancyversion) with four possible constellations
x rv (value) s r b
0 1 0 0
1 0 0 0
2 1 1 1
3 0 1 1
4 1 0 1
5 1 0 2
6 1 0 3
7 1 1 0
Definition of parameter s as for QPSK
b (range 0 to 3) describes constellationrearrangement to averagereliability of bits
Fig 2-27 Signaling of redundancy version parameters r s and b 16QAM case
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
UE identity H-RNTI 16 bits
The HSDPA radio network transaction identifier (H-RNTI) unam-
biguously identifies the UE having an HS-PDSCH assignment within
a cell It is allocated to the UE via layer 3 signaling procedures at the
radio bearer setup if the radio bearer is an HSDPA connection This
8122019 hspa_e_lp
httpslidepdfcomreaderfullhspaelp 2830
56
HSDPA operation overview and physical channels
value represents a temporary name of the UE used to address it when
scheduling data packets via HS-SCCH
HS-SCCH channel coding
The control information contained in the HS-SCCH is of course pro-
tected with channel coding mechanisms the whole coding chain is
described in Fig 2-28 Fig 2-18 page 48 presents the separation of
the control information into two code blocks which are sent consec-
utively mapped on slot 1 and slot 2 + 3 of one HS-SCCH subframe
This principle is also visible in the coding chain The first control block
consisting of channelization information modulation scheme and UE
identity is coded separately from the remaining control values to enable
the UE receiver to decode this first slot separately and prepare for pos-
sible HS-PDSCH reception The coding steps shown in Fig 2-28 such
as rate matching 1 and 2 are similar to the HS-PDSCH coding chain
and are further described in [TS 25212 Ref 21]
Channelcoding 1
R atematching 1
mux
Channelcoding 2
Ratematching 2
RVcoding
UE-specificCRC attachment
UE-specificmasking
Physical channelmapping
r s b
mux
Channelizationcode set
Modulationscheme
Transport block size information
HARQ processinformation
Redundancy andconstellation version
New data indicator
UE identity
UE identity
Fig 2-28 Channel coding for HS-SCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
8122019 hspa_e_lp
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High speed dedicated physical control channel (HS-DPCCH)
57
24 High speed dedicated physical control channel (HS-DPCCH)
In an active HSDPA connection the UE has to send acknowledgment ornon-acknowledgment reports (as described in section 13 page 14
where the HARQ process is described) as well as channel status infor-
mation to the network The reporting is performed on this physical
control channel HS-DPCCH
As ubiquitous in HSDPA the uplink is also configured into a subframe
structure of 2 ms corresponding to three slots The first slot of the sub-
frame carries the ACK NACK information the UE sends to the NodeB
while the following two slots ie slot 2 and 3 of the subframe convey
the CQI value the channel quality information to the NodeB
Subframe 0 Subframe i Subframe 4
Tslot
= 2560 chips J The spreading factor of theHS-DPCCH is 256 (10 bits peruplink slot)
J The HS-DPCCH can only existtogether with an UL DPCCH
(ded phys control channel)J The DPDCH (dedicated physical data channel) the DPCCH andthe HS-DPCCH are IQ codemultiplexed
HARQ-ACK CQI = Channel quality information
2 times Tslot
= 5120 chips
One radio frame Tf = 10 ms
One HS-DPCCH subframe 2 ms
Fig 2-29 HS-DPCCH configuration
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The slot format for HS-DPCCH describes a quantity of 30 bits per sub-frame resulting in a data rate of 15 kbps The spreading factor used for
the HS-DPCCH is constant and is always equal to 256 but the chan-
nelization code that is used as well as the mapping on either the I or
Q axis depends on several factors eg the co-existence of an HSDPA
connection with a circuit-switched connection meaning whether a
DPDCH established or not Fig 2-36 page 64 illustrates this IQ
mapping and Fig 2-35 page 63 shows the channelization code used
for HS-DPCCH
The HS-DPCCH builds a logical unit of one subframe but having the
independent control information HARQ-ACK and CQI included which
could be separately decoded at the NodeB Note that the slot carrying
the ACK NACK statement is active only when the UE has been sched-
uled by an HS-PDSCH subframe in the corresponding downlink sub-
frame previously Assuming the UE has not received a transport block
8122019 hspa_e_lp
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HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
8122019 hspa_e_lp
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56
HSDPA operation overview and physical channels
value represents a temporary name of the UE used to address it when
scheduling data packets via HS-SCCH
HS-SCCH channel coding
The control information contained in the HS-SCCH is of course pro-
tected with channel coding mechanisms the whole coding chain is
described in Fig 2-28 Fig 2-18 page 48 presents the separation of
the control information into two code blocks which are sent consec-
utively mapped on slot 1 and slot 2 + 3 of one HS-SCCH subframe
This principle is also visible in the coding chain The first control block
consisting of channelization information modulation scheme and UE
identity is coded separately from the remaining control values to enable
the UE receiver to decode this first slot separately and prepare for pos-
sible HS-PDSCH reception The coding steps shown in Fig 2-28 such
as rate matching 1 and 2 are similar to the HS-PDSCH coding chain
and are further described in [TS 25212 Ref 21]
Channelcoding 1
R atematching 1
mux
Channelcoding 2
Ratematching 2
RVcoding
UE-specificCRC attachment
UE-specificmasking
Physical channelmapping
r s b
mux
Channelizationcode set
Modulationscheme
Transport block size information
HARQ processinformation
Redundancy andconstellation version
New data indicator
UE identity
UE identity
Fig 2-28 Channel coding for HS-SCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
8122019 hspa_e_lp
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High speed dedicated physical control channel (HS-DPCCH)
57
24 High speed dedicated physical control channel (HS-DPCCH)
In an active HSDPA connection the UE has to send acknowledgment ornon-acknowledgment reports (as described in section 13 page 14
where the HARQ process is described) as well as channel status infor-
mation to the network The reporting is performed on this physical
control channel HS-DPCCH
As ubiquitous in HSDPA the uplink is also configured into a subframe
structure of 2 ms corresponding to three slots The first slot of the sub-
frame carries the ACK NACK information the UE sends to the NodeB
while the following two slots ie slot 2 and 3 of the subframe convey
the CQI value the channel quality information to the NodeB
Subframe 0 Subframe i Subframe 4
Tslot
= 2560 chips J The spreading factor of theHS-DPCCH is 256 (10 bits peruplink slot)
J The HS-DPCCH can only existtogether with an UL DPCCH
(ded phys control channel)J The DPDCH (dedicated physical data channel) the DPCCH andthe HS-DPCCH are IQ codemultiplexed
HARQ-ACK CQI = Channel quality information
2 times Tslot
= 5120 chips
One radio frame Tf = 10 ms
One HS-DPCCH subframe 2 ms
Fig 2-29 HS-DPCCH configuration
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The slot format for HS-DPCCH describes a quantity of 30 bits per sub-frame resulting in a data rate of 15 kbps The spreading factor used for
the HS-DPCCH is constant and is always equal to 256 but the chan-
nelization code that is used as well as the mapping on either the I or
Q axis depends on several factors eg the co-existence of an HSDPA
connection with a circuit-switched connection meaning whether a
DPDCH established or not Fig 2-36 page 64 illustrates this IQ
mapping and Fig 2-35 page 63 shows the channelization code used
for HS-DPCCH
The HS-DPCCH builds a logical unit of one subframe but having the
independent control information HARQ-ACK and CQI included which
could be separately decoded at the NodeB Note that the slot carrying
the ACK NACK statement is active only when the UE has been sched-
uled by an HS-PDSCH subframe in the corresponding downlink sub-
frame previously Assuming the UE has not received a transport block
8122019 hspa_e_lp
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HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
8122019 hspa_e_lp
httpslidepdfcomreaderfullhspaelp 2930
High speed dedicated physical control channel (HS-DPCCH)
57
24 High speed dedicated physical control channel (HS-DPCCH)
In an active HSDPA connection the UE has to send acknowledgment ornon-acknowledgment reports (as described in section 13 page 14
where the HARQ process is described) as well as channel status infor-
mation to the network The reporting is performed on this physical
control channel HS-DPCCH
As ubiquitous in HSDPA the uplink is also configured into a subframe
structure of 2 ms corresponding to three slots The first slot of the sub-
frame carries the ACK NACK information the UE sends to the NodeB
while the following two slots ie slot 2 and 3 of the subframe convey
the CQI value the channel quality information to the NodeB
Subframe 0 Subframe i Subframe 4
Tslot
= 2560 chips J The spreading factor of theHS-DPCCH is 256 (10 bits peruplink slot)
J The HS-DPCCH can only existtogether with an UL DPCCH
(ded phys control channel)J The DPDCH (dedicated physical data channel) the DPCCH andthe HS-DPCCH are IQ codemultiplexed
HARQ-ACK CQI = Channel quality information
2 times Tslot
= 5120 chips
One radio frame Tf = 10 ms
One HS-DPCCH subframe 2 ms
Fig 2-29 HS-DPCCH configuration
Source [TS 25211 Ref 20] reproduced by permission of 3GPP
The slot format for HS-DPCCH describes a quantity of 30 bits per sub-frame resulting in a data rate of 15 kbps The spreading factor used for
the HS-DPCCH is constant and is always equal to 256 but the chan-
nelization code that is used as well as the mapping on either the I or
Q axis depends on several factors eg the co-existence of an HSDPA
connection with a circuit-switched connection meaning whether a
DPDCH established or not Fig 2-36 page 64 illustrates this IQ
mapping and Fig 2-35 page 63 shows the channelization code used
for HS-DPCCH
The HS-DPCCH builds a logical unit of one subframe but having the
independent control information HARQ-ACK and CQI included which
could be separately decoded at the NodeB Note that the slot carrying
the ACK NACK statement is active only when the UE has been sched-
uled by an HS-PDSCH subframe in the corresponding downlink sub-
frame previously Assuming the UE has not received a transport block
8122019 hspa_e_lp
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HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP
8122019 hspa_e_lp
httpslidepdfcomreaderfullhspaelp 3030
HSDPA operation overview and physical channels
in the corresponding previous HS-PDSCH subframes (this means
75 slots before the HS-DPCCH starts see section 26 page 71) it
will send discontinuous transmission (DTX) instead of ACK NACKinformation Similarly the transmission of the CQI value is not per-
manent as a result furthermore the CQI transmission depends on the
parameter CQI feedback cycle and is indicated by higher protocol lay-
ers at the radio bearer setup Thus it is also possible for the CQI to be
disabled in the contemplated HS-DPCCH subframe We understand
there are several possibilities for the HS-DPCCH configuration in one
subframe This is described in section 41 page 113 which presents
HS-DPCCH logging One consequence of this is that the TX power
used for sending the HS-DPCCH might not be constant Additional
analysis of this topic can be found in section 43 page 118 which
describes the code domain power vs time Fig 4-12 page 113 shows
there are four possibilities for how the HS-DPCCH can appear depend-
ing on the circumstances
The first slot contains ACK NACK and slots 2 and 3 contain CQI
The first slot contains ACK NACK and slots 2 and 3 contain DTX The first slot contains DTX and slots 2 and 3 contain CQI information
The first slot contains DTX and slots 2 and 4 contain DTX
Because one HS-DPCCH subframe forms one logical unit but consists
of two separate signaling parameters the channel coding chain is inde-
pendent for both values ie the decoding can be performed indepen-
dently for slot 1 containing ACK NACK statements and slot 2 and 3containing the CQI feedback Reception of these two control values
ACK NACK and CQI is thus non-correlated
Physical channelmapping
Channel codingChannel coding
PhCH
HARQ-ACK CQI
PhCH
Physical channelmapping
Fig 2-30 Coding chain for HS-DPCCH
Source [TS 25212 Ref 21] reproduced by permission of 3GPP