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7/30/2019 4- Owa320010 Hspa & Hspa+ Introduction Issue 1.00
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HSPA & HSPA+ Introduction
Confidential Information of Huawei. No Spreading WithoutPermission
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Mobile network data rate evolution
WCDMA data transmission evolved from GSM/GPRS, inheriting much of theupper layer functionality directly from those systems. The first commercial
deployments of WCDMA are based on a version of the standards called
Release 99, with HSDPA introduced in Release 5 to offer higher speed
Downlink data services.
Enhanced Data rates for GSM Evolution (EDGE) is another system in the
GSM/GPRS family that some operators have deployed as an intermediate
step before deploying WCDMA.
Release 6 introduces the High Speed Uplink Packet Access (HSUPA) toprovide faster data services for the Uplink.
For HSUPA (Uplink) the theoretical maximum achievable peak data rate is
5.76 Mbps, while for HSDPA (Downlink) it is 14.4 Mbps.
Release 7 introduces HSPA+ to increase data rate and system capacity.
Some new features are used such as MIMO, DL 64QAM, CELL_FACH
operation and etc.
Release 8 introduces more new features to HSPA+ such as DL
MIMO+64QAM, DC-HSDPA (Dual Carrier-HSDPA), UL 16QAM and etc. TheDL/UL peak data rate can reach 42Mbps/11.5Mbps.
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Data Services and High Speed Downlink Packet Access (HSDPA)
Data Services are expected to grow significantly within the next few years.Current 2.5G and 3G operators are already reporting that a significant
proportion of usage is now due to data, implying an increasing demand for
high-data-rate, content-rich multimedia services. Although current Release
99 WCDMA systems offer a maximum practical data rate of 384 kbps, the
3rd Generation Partnership Project (3GPP) have included in Release 5 of
the specifications a new high-speed, low-delay feature referred to as High
Speed Downlink Packet Access (HSDPA).
HSDPA provides significant enhancements to the Downlink compared to
WCDMA Release 99 in terms of peak data rate, cell throughput, and round
trip delay. This is achieved through the implementation of a fast channel
control and allocation mechanism that employs such features as Adaptive
Modulation and Coding and fast Hybrid Automatic Repeat Request (HARQ).
Shorter Physical Layer frames are also employed.
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Release 99 Downlink Packet Data
There are different techniques defined in the Release 99 specification toenable Downlink packet data. Most commonly, data transmission is
supported using either the Dedicated Channel (DCH) or the Forward Access
Channel (FACH).
The DCH is the primary means of supporting packet data services. Each
user is assigned a unique Orthogonal Variable Spreading Factor (OVSF)
code dependent on the required data rate. Fast closed loop Power Control
is employed to ensure that a target Signal to Interference Ratio (SIR) is
maintained in order to control the block error rate (BLER). Macro Diversity
is supported using soft handover.
Data transfer can also be supported on the FACH. This common channel
employs a fixed OVSF code. As it needs to be received by all UEs, higher
data rates are generally not supported. Macro Diversity is also not
supported and the channel operates with a fixed (or slow changing) power
allocation. Each data block contains a unique UE identifier that allows a
given UE to keep itsown data and discard that belonging to other UEs.
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Although WCDMA Release 99 standard allows for maximum data rates of up to
2.0 Mbps, it has only been widely implemented with a maximum data rate of 384
kbps. This data rate is achieved by allocating a dedicated channel to each user.
The use of dedicated resources can be a limitation, especially for data applications
with bursty characteristics. Each dedicated channel uses an OVSF code. Shorter
codes are used for higher data rates and longer codes for lower data rates. When
an OVSF of a particular length is used, all longer OVSF codes derived from that
code become unavailable. This limits the number of simultaneous high speed data
users in a given cell. The Release 99 standards provide support for a Secondary
Scrambling Code, which eases this limitation, but it has not been widely
implemented in commercial systems and will likely be removed from future
versions of the specification. The data rate of a dedicated channel can be adjusted
to accommodate varying requirements of a data service application, but the
procedure for doing so is slow and thus inefficient. Capacity is controlled both by
the maximum amount of PA power that is available and by the power
requirement of each data service. In dedicated mode, fast power control is used
so that a target Eb/No is achieved on the Downlink. However, the required Eb/No
set point changes at a much slower rate. This can result in wasted resources
whereby a better than required Eb/No is achieved for the required BLER.
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In HSDPA, the NodeB allocates a set of high speed channels. These channels are
assigned to a user using a fast scheduling algorithm that allocates the channels
every 2 ms. All or part of the channels may be assigned to a given user during any
2 ms period.
The rapid scheduling of HSDPA is well-suited to the bursty nature of packet data.
During periods of high activity, a given user may get a larger percentage of the
channel bandwidth, while it gets little or no bandwidth during periods of low
activity.
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In HSDPA a common channel without closed loop power control is employed for
data transfer. Users are separated in both the time and code domains. A fixed
spreading factor is employed but multi codes operation is possible for increased
data rates.
Adaptive Modulation and Coding (AMC) replaces the role of power control so that
the modulation and coding rate are changed depending on the channel condition.
This is accomplished by locating the scheduling algorithm for channel allocation at
the NodeB instead of the RNC in Release 99.
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Comparison Summary
DCH and FACH are the two Release 99 channels typically used for packetswitched data in practice. The advantages and disadvantages of each
approach are apparent. Whereas DCH is suited for medium high data rates
(with a maximum rate of 384 kbps), rate switching is slow, making it
unsuitable and inefficient for bursty data such as a Web browsing
application. By contrast, FACH provides good support for bursty data but is
a common channel without power control or other mechanism to account
for channel conditions. This makes it unsuitable for higher data rates.
Switching from DCH to FACH is slow and inefficient, due in part to the
typical timer values used to detect inactivity
HSDPA is suitable to high date rates for a bursty application, though we
will see that the absence of soft handover makes it more suitable for
stationary or low-mobility users than for highly mobile users. HSDPA
typically operates at a fixed power, but feedback from the UE can instruct
the NodeB to use lower power when the UE is in good channel conditions.
Link adaptation is used to adjust data rate, coding, and modulation to
quickly respond to changing channel conditions.
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Data Services are expected to grow significantly within the next few years.
Current 2.5G and 3G operators are already reporting that a significant proportion
of usage is now devoted to data, implying an increasing demand for high-data-
rate, content-rich multimedia services. Although current Release 99 WCDMA
systems offer a maximum practical data rate in Uplink of 384 kbps, the 3rd
Generation Partnership Project (3GPP) has included in Release 6 of the
specifications a new high-speed, low-delay feature called High Speed Uplink
Packet Access (HSUPA).
HSUPA provides significant enhancements to the Uplink compared to WCDMA
Release 99 in terms of peak data rate, cell throughput, and latency. This is
achieved through the implementation of a fast resource control and allocation
mechanism that employs such features as Adaptive Coding, fast Hybrid Automatic
Repeat Request (HARQ) and Shorter Physical Layer frames. With the addition of
HSUPA, a better balance between Downlink HSDPA and Uplink traffic
performance is also achieved.
The High Speed Uplink Packet Access (HSUPA) is a 3GPP Release 6 feature, also
called Enhanced Uplink (EUL) or Enhanced DCH (E-DCH).
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Release 99 Uplink Packet Data
There are two different techniques defined in the Release 99 specificationto enable Uplink packet data. Most commonly, data transmission is
supported using either the Dedicated Channel (DCH) or the Random Access
Channel (RACH).
The DCH is the primary means of supporting packet data services. Each UE
uses an Orthogonal Variable Spreading Factor (OVSF) code, dependent on
the required data rate. Fast closed loop Power Control is employed to
ensure that a target Signal-to-Interference Ratio (SIR) is maintained in
order to control the block error rate (BLER). Macro Diversity is supported
using soft handover.
Data transfer can also be supported on the RACH. This common channel
employs an OVSF code, with a spreading factor between 32 and 256, as
negotiated with UTRAN during the Access procedure. Because it needs to
be shared among all UEs, higher data rates are generally not supported.
Macro Diversity is also not supported and the channel operates with a
fixed (or slow changing) power allocation.
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Release 99 Uplink Limitations
Among the available options for Uplink data transmissions in Release 99,the Common Channel (RACH) only allows for a small amount of data and a
limited duration of the transmission. Thus, from a practical point of view,
the Dedicated Channel (DCH) is the way to accommodate packet services in
a Release 99 network. However, significant limitations must also be faced
when using the Uplink DCH:
Large Scheduling Delay: In Release 99, the scheduling of resources is done
in the serving RNC and involves Layer 3 signaling messages to and from the
UE, which causes the mechanism to be relatively slow in assigning or
reconfiguring the resources assigned to a particular UE.
Large Latency: The transmission time interval can vary from 80 ms down to
10 ms as best case, posing an intrinsic boundary to the latency values. In
addition to that, the only available mechanism for retransmissions of
erroneous packets is located in RNC, thus significantly contributing to the
latency figures
Limited Uplink Data Rate: Though the standard allows for high data rate
on the Release 99 Uplink, typical values of maximum data rate observed in
deployed networks range from 64 kbps up to 384 kbps, while using aspreading factor of 4. In order to achieve higher peak data rates, lower
coding rates and multi-code transmission shaould be used, but these are
not available in R99 systems.
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HSUPA is realized by introducing the Enhanced Dedicated Channel (E-DCH)
In HSUPA, the Node B allows several UEs to transmit at a certain power level atthe same time. These grants are assigned to users by using a fast scheduling
algorithm that allocates the resources on a short-term basis (every 10ms or 2ms).
The rapid scheduling of HSUPA is well suited to the burst feature of packet
service. During periods of high activity, a given user may get a larger percentage
of the available resources, while getting little or no bandwidth during periods of
low activity.
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Enhancement methods in HSUPA
To overcome the Release 99 limitations previously mentioned, HSUPA hasbeen introduced in Release 6
The use of shorter TTI, fast resource scheduling, and fast retransmissions
at the physical layer improves uplink data services, while addressing the
release 99 limitations in terms of latency, peak data rate, coverage, and
capacity. Additionally, improved quality of service support helps to
optimize resource utilization and guarantee the promised quality
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The CQI table consists of 30 entries, where each entry indicates a different TFRC.
Transport Format Resource Combination (TFRC) points to the combination of
number of HS-PDSCH channelization codes, modulation scheme, and the HS-DSCH
transport block size. The 5-bit CQI reported by a UE is an index into this table
containing all possible TFRC combinations for that UE category. The TFRC
combinations are different for UEs with different HS-DSCH UE categories because
of the differences in the UE capabilities. Along with TFRC, CQI may also indicate a
power offset relative to the current HS-PDSCH power. The CQI table shown in the
slide is for UE categories supporting up to 15 HS-PDSCH codes (HSDPA terminal
category 10).
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HSDPA is advertised with data rates up to 14 Mbps. However, the actual HS-DSCH
peak data rate depends on the UEs HS-DSCH category. As shown in the table,
only a category 10 UE can achieve the maximum HSDPA throughput of 14 Mbps
when using all 15 HS-PDSCHs simultaneously.
Factors that decide the UEs HS-DSCH category are:
HS-PDSCH codes Determines the number of simultaneous HS-PDSCH channels
that can be decoded by a UE.
Inter-TTI interval Determines the minimum interval (in terms of HS-DSCH TTI)
between two successive HS-PDSCH assignments. The more HARQ processes a UE
supports, the shorter the inter-TTI interval. A minimum inter-TTI of 1 requires atleast 6 simultaneous HARQ processes.
Transport Block size Determines the maximum size of transport block that can
be sent on HS-DSCH in a TTI. It is dependent on the number of HS-PDSCH codes
and the modulation scheme.
IR buffer size Determines the maximum number of soft bits that can be buffered
by a UE across all simultaneously running HARQ processes.
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Example for Chase Combining ( CC ) Scheme
Example for Incremental Redundancy ( IR ) Scheme
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To support consecutive assignments, HSDPA defines a Hybrid Automatic Repeat
Request (HARQ) protocol. This protocol is implemented in both the NodeB and the
UE, and consists of procedures implemented in both the MAC-hs sublayer and the
Physical Layer. When the NodeB assigns an HSDPA subframe to a UE, it also
assigns a HARQ process to handle the data transfer. The UE HARQ process is
responsible for
Decoding the initial transmission
Sending an ACK or NACK
Soft-combining retransmissions of the data packet until it is successfully
decoded or until NodeB aborts the packet The maximum number of HARQ processes that a UE supports is a function of its
HSDPA category. The minimum number of HARQ processes supported by any UE
is 2, which corresponds to a UE that uses an inter-TTI interval of 3.
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Example of Code Allocation for a HSDPA cell:
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Shared channel transmission implies that a certain amount of radio resource of a cell
(code and power) is seem as a common resource that is dynamically shared between
users.
The NodeB transmit power allocation algorithm is not specified by the standard.
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There can be multiple (up to 15) HS-PDSCHs in a serving cell, which enables use of
both time division and code division multiple access methods.
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WCDMA R99 uses QPSK modulation scheme for downlink transmission. To
support higher data rate, 16QAM is introduced in HSDPA.
NodeB decides to use QPSK or 16QAM based on the CQI feedback from UE.
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The basic idea of fast scheduling is to transmit at the fading peaks of the channel
in order to increase the throughput and to use resource more efficiently. But this
might lead to large variations in data rate of the users. The trade-off is between
the cell throughput and fairness against users.
There are a number of scheduling algorithms that take into consideration the
trade-off between throughput and fairness:
Round Robin (RR): radio resource are allocated to communication links on a
sequential basis, not taking into account the instantaneous radio channel
conditions experienced by each link.
Max C/I: for maximum cell throughput ,the radio resource should be asmuch as possible be allocated to communication links with the best
instantaneous channel condition.
Proportional Fair (PF): allocates the channel to the user with relatively best
channel quality.
Enhanced Proportional Fair (EPF): allocates the channel to the user
according to relatively best channel quality, fairness, guarantee bit rate
requirement.
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Three new channels are introduced for HSDPA:
HS-PDSCH (High Speed Physical Downlink Shared Channel): This is adownlink shared channel. It is used to carry higher layer signaling or traffic
data.
HS-SCCH (High Speed Shared Control Channel): This is a downlink shared
channel. It is used to carry some physical indication which is used by the UE
to decode the higher layer data in HS-PDSCH. The following are some of
the information carried by HS-SCCH:
UE ID: Indicating which UE is scheduled in HS-PDSCH
Channelization Code Set: Indicating which codes allocated to the UEif it is scheduled
Modulation Scheme: Indicating the modulation scheme of HS-
PDSCH (QPSK or 16QAM)
Some other information
HS-DPCCH: This is a uplink dedicated channel. It is used to feedback CQI
and HARQ ACK/NACK by UE.
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DCCH and DTCH can be mapped to HS-DSCH.
A UE using HSDPA can also have additional Release 99 DCH. The HS-SCCH and HS-DPCCH are physical layer (control) channels. They carry no
upper layer information, and therefore have no logical or transport channel
mapping.
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5 OVSF code for HS-PDSCH
14.4Mbps / 3 = 4.8Mbps QPSK
4.8Mbps / 2 = 2.4Mbps
Turbo code rate =1/3
2.4Mbps / 3 = 0.8Mbps
Retransmission
0.8Mbps 0.8 = 640 kbps
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1 2 3 4 5
Decoded on 1st transmit Decoded on 2nd transmit
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Compared to R99 UL DCH, the enhance DCH specified for HSUPA in Release 6
offers the following features:
Shorter TTI of 2ms: which can reduce the latency and can be scheduled
faster
Lower SF: which can increase physical channel symbol rate , higher peak
data rate is available
Uplink L1 HARQ throughput: improve physical layer performance with fast
retransmissions
New transport and physical channels
Fast resource control: with new MAC entities in NodeB, radio resource canbe scheduled faster to optimize the total throughput
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This slide lists some important aspects for comparing HSDPA and HSUPA to help
understand HSUPA principles and operation.
The HSDPA concept is based on high speed shared channels with fast L1 HARQ
retransmission and rate and modulation adaptation to adjust to channel
conditions. The fast scheduler is located in the Node B and assigns the available
resources (power and codes) to several users. This enables cell power to be
directed to a single user (or to a small group of users) for a short period of time,
during which other users do not get any data. In this way, one Node B transmitter
can be shared among many UE receivers.
For HSUPA, the channel remains a dedicated channel, but with enhanced
capabilities such as fast scheduling and L1 HARQ retransmissions. Power control
and soft handover are still used to adapt to radio channel conditions. Because
each UE has an independent transmitter with its own power and code availability,
the HSUPA scheduler can accommodate many users to be received by the same
Node B, where the Rise-over-Thermal Noise level indicates the uplink loading of
the system.
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The Rise-over-Thermal noise level is a measure of the uplink load at the NodeB
receiver.
By increasing the number of UEs transmitting on the uplink and their
transmit power, the overall level of interference in the uplink band also
increases.
The NodeB receiver perceives this level as noise, and it directly affects the
decoding performance of uplink data transmissions.
The NodeB controls the interference level by adjusting the UE grant
assignments according to the current interference level.
When the UE receives a new grant, it uses it in combination with availableUE transmit power and amount of data in the buffer to determine the data
rate and the corresponding transmit power.
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Similar to HSDPA, HSUPA implements fast resource allocation and control with a
scheduler in the NodeB. While the HSDPA scheduler accommodates a common
resource to several users, the HSUPA scheduler has a different task: it coordinates
the reception of data transmitted from several UEs to a single NodeB. This can be
regarded as a very fast resource allocation of a dedicated channel (E-DCH), rather
than a sharing of a common channel (HS-DSCH).
On one side, each UE will tend to transmit as much as possible based on channel
conditions, the amount of data in the buffer, and the power available. On the
other side, the scheduler will try to satisfy each connected UE while preventing
overloading and maximizing resource utilization and cell throughput.
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This slide illustrates HSUPA operation :
1. The UE asks the NodeB for a grant to transmit data on uplink. 2. If the Node B allows the UE to send data, it indicates the grant in terms
of Traffic-to-Pilot (T/P) ratio. The grant is valid until a new grant is
provided.
3. After receiving the grant, the UE can transmit data starting at any TTI
and may include further requests. Data are transmitted according to the
selected transport format, which is also signaled to the NodeB.
4. After the Node B decodes the data, it sends an ACK or NAK back to the
UE. If the NodeB sends a NAK, the UE may send the data again with aretransmission.
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This slide illustrates a data transmission request from the UE through scheduling
information (SI), by which the UE asks the Node B for a grant to transmit data on
Uplink E-DCH.
UE power availability and UE buffer status are combined to determine the
scheduling information.
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This slide illustrates an HSUPA absolute grant assignment upon request from the
UE. The grant is determined based on uplink interference situation (Rise-over-
Thermal noise) at the NodeB receiver and on the UE transmission requests and
level of satisfaction.
The Node B indicates the Traffic-to-Pilot (T/P) grant by downlink grant channel.
The grant is valid until a new grant is given or modified.
SI is scheduling information. It includes the UL power usage and the buffer status
of UE. UE uses SI to request resource from NodeB.
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This slide illustrates an HSUPA Data Transmission for scheduled grants.
After receiving the grant, the UE can transmit data starting at any TTI and mayinclude additional scheduling information. The transport format is first selected
based on the received grant, on the available power and on the data in the buffer.
Data are transmitted on a set of E-DPDCH channels, and transport format
Information is signaled to the Node B on the corresponding E-DPCCH. The Happy
Bit (Happy Bit indicates the UEs level of satisfaction. ) is also included.
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This slide illustrates the acknowledgment of data at the NodeB and HARQ
retransmission.
After the NodeB attempts to decode the data, it sends an ACK or NACK to the UE.
If the NodeB sends a NACK, the UE may send the data again with a fast
retransmission.
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The main introduction in Release 6 is the new data channel, Enhanced Dedicated
Channel or E-DCH, which carries the uplink high speed data. New physical
channels are introduced to support E-DCH.
On the uplink, two new physical channels are introduced: E-DPDCH (Dedicated
Physical Data Channel for E-DCH) and E-DPCCH (Dedicated Physical Control
Channel for E-DCH). The E-DCH can be mapped to one to four uplink E-DPDCHs
(Dedicated Physical Data Channels for E-DCH), with improved coding and
modulation design. The physical layer control information, E-TFCI etc., is carried
on one E-DPCCH (Dedicated Physical Control Channel for E-DCH).
On the Downlink, three new physical channels are introduced to support E-DCH.
The downlink physical channels E-HICH (HARQ Indicator Channel for E-DCH) and
E-RGCH (Relative Grant Channel for E-DCH) are dedicated channels and they share
a single channelization code assigned by the higher layer to the UE. The UE
increases or decreases its E-DCH data rate based on the relative grant indicator on
E-RGCH. The downlink channel E-AGCH (Absolute Grant Channel for E-DCH) is a
common channel shared by all the users in the cell. The addressing on E-AGCH is
realized by masking CRC bits with E-RNTI (RNTI for E-DCH).
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DCCH and DTCH can be mapped to E-DCH.
A UE using HSUPA can also have additional Release 99 DCH and/or HSDPAchannels, although the standard specifies restrictions for the possible
combinations. Because power control and soft handover are supported for E-DCH,
the channel can be seen as an extension of the Release 99 DCH.
The E-DPCCH, E-HICH, E-AGCH, and E-RGCH are physical layer (control) channels.
They carry no upper layer information, and therefore have no logical or transport
channel mapping.
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Hybrid ARQ The hybrid ARQ for HSUPA consists of an N-Channels stop-and-wait
protocol. The number of HARQ processes is 4 for a 10 ms TTI and 8 for a 2 ms TTI
configuration. The retransmission is synchronous, with separate feedback
provided for each radio link. After requesting and receiving a grant for data
transmissions:
The UE transmits the data of the corresponding HARQ process to all
NodeBs for which a radio link exists.
Each Node B connected to the UE sends ACK/NAK back to the UE.
The transmission is successfully completed if an acknowledge (ACK) is
received.
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The E-DCH Active Set is limited to 4 cells, one of which is the E-DCH serving cell.
The radio links that are in softer handover with the E-DCH serving cell (i.e.,connected to the same NodeB) constitute the Serving E-DCH Radio Link Set (RLS).
All other links in the E-DCH active set, which are connected to other NodeBs, are
non-serving radio links.
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The following assumptions are needed to achieve the theoretical maximum data
rate of 5.76 Mbps:
Lower channel coding gain Using an effective code rate of 1 increases the
data rate, but the channel conditions must be very good for the NodeB to
correctly decode every data block on the first transmission.
Lower spreading factor UE must use SF 2.
Multi-code transmission Four codes (2 codes with SF2 and 2 codes with
SF4) are used by E-DPDCH.
Shorter TTI 2ms TTI is needed. Because the maximum transport block
size is 20000 bits with 10ms TTI, the maximum data rate for 10ms TTI is2Mbps.
In a practical scenario, the practical maximum data rate will be less than 5.76
Mbps, due to less than ideal channel conditions, the need for retransmission, and
the need to share the UE power with other channels.
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The examples presented so far have assumed a turbo code rate of 1/3 and BPSK
modulation. If we assume a single E-DPDCH and a transport block containing 640
data bits, rate 1/3 turbo coding produces 1920 symbols. BPSK modulation maps
one symbol onto one modulation symbol, which is then spread by the OVSF of
length 4. This results in 7680 chips sent every 2ms, corresponding to the
fundamental WCDMA chip rate of 3.84 Mcps.
If the transport block is not exactly 640 data bits, the rate matching step adjusts
the number of symbols after turbo coding to produce 1920 symbols.
By increasing the coding rate, more data bits can be transmitted in a 2 ms TTI,
thus increasing the data rate. Using a coding rate of 1, the data rate becomes 960
kbps, because 1920 bits can be transmitted in 1920 modulation symbols. This
corresponds to puncturing all the parity bits and transmitting only the systematic
bits.
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By changing the spreading factor from 4 to 2, the number of bits that can be
transmitted in a single TTI doubles from 640 to 1280, because now 7680/2 =
3840 symbols can be mapped onto 7680 chips. Again, a coding rate of 1 is
assumed.
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What determines the maximum data rate supported by different categories of UE?
It is a combination of the maximum number of E-DPDCH channels, the spreading
factor, and maximum bits in one TTI.
For 10 ms TTI, a maximum of 2 Mbps peak data rate can be achieved,
corresponding to a maximum transport block size of 20000 bits. To achieve
higher rates, a TTI of 2 ms shall be used.
With a single E-DPDCH channel, a spreading factor from 256 to 4 is allowed. For
multi-code transmissions, only SF4 and SF2 are allowed, in the following
combinations: (2 x SF4) or (2 x SF2) or (2 x SF4 + 2 x SF2). Note that SF=2 is not
permitted on a single code transmission.
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Downlink Enhanced L2: Downlink enhanced L2 allows flexible PDU sizes at the RLC layer
and segmentation at the MAC layer on the Uu interface. The feature prevents L2 from
becoming the bottleneck of Uu rate increasing by multiple-input multiple-output (MIMO)
and 64QAM.
Downlink MIMO: Downlink MIMO increases transmission rates through spatial
multiplexing and improves channel qualities through space diversity. The network side
can dynamically select single- or dual-stream transmission based on channel conditions.
The peak rate at the MAC layer can reach 28Mbps.
Downlink 64QAM: Downlink 64QAM allows the use of 64QAM in HSDPA to increase the
number of bits per symbol and thus to obtain higher transmission rates. The peak rate at
the MAC layer can reach 21Mbps.
Downlink Enhanced CELL_FACH Operation: Downlink Enhanced CELL_FACH Operation
allows the use of HSDPA technologies for the UEs in CELL_FACH, CELL_PCH, and
URA_PCH states (RAN11 only supports HSDPA reception in CELL_FACH state.). The
purpose is to increase the peak rates in these states, reduce the signaling transmission
delay during service setup or state transition, and improve user experience.
CPC: Continuous packet connectivity (CPC) allows uplink and downlink transmissions at
regular intervals. CPC reduces the transmit power and thus prolongs the UE battery life
because the UE does not have to monitor and transmit overhead channels in each TTl.
The reduction in the transmit power also helps to increase the uplink capacity by
decreasing the total interference. This improvement is significant when users such as VoIP
users transmit data discontinuously.
The CPC feature consists of DTX-DTX, and HS-SCCH Less Operation.
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Uplink 16QAM: 16QAM modulation can be used for HSUPA to improve uplink
peak date rate to around 11Mbps.
Uplink Enhanced L2: Some modifications are introduced in Uu interface layer 2 in
uplink direction to support higher data rate and improve uplink transmission
efficiency.
Downlink MIMO + 64QAM: Before RAN12 MIMO and 64QAM can not be used by
one UE simultaneously. In RAN12 downlink MIMO and 64QAM can be used
simultaneously by one UE to receive HSDPA data. With this technology, the
theoretical downlink peak rate can reach 42Mbps.
DC-HSDPA (Dual-cell HSDPA): DC-HSDPA allows a UE to set up HSDPAconnections with two inter-frequency time-synchronous cells that have the same
coverage. Theoretically, DC-HSDPA with 64QAM can provide a peak rate of
42Mbps in the downlink.
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HSPA+ can support three modulation modes: QPSK, 16QAM and 64QAM. Which
mode is used is stilled based on the channel condition of UE.
The AMC feature introduced with HSDPA enables adaptation of modulation and
coding to varying radio conditions. To improve the advantages of AMC even
further, a new modulation scheme, 64 QAM, is introduced with HSPA+.
Theoretically 64QAM can provide a peak rate of 21 Mbit/s to a single UE. It
enables the user with good channel conditions to download data at higher rates,
improves user experience.
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In wireless communications, MIMO refers to a wireless channel with multiple
inputs and multiple outputs.
In a MIMO system, there are N*M signal paths from the transmit antennas and the
receive antennas, and the signals on these paths are not identical.
3GPP Release 7 supports only 22 MIMO system.
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For HSDPA, the peak physical layer throughput is14.4Mbps. To achieve 14.4 Mbps
peak rate, all available SF-16 OVSF codes will be used.
With MIMO system, the multiplexing gain is obtained with independent data
streams on different antennas. The 2*2 MIMO system defined by 3GPP Release 7
can be 28Mbps.
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RAN 11.0 supports HSDPA in only the CELL_FACH state.
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DL DRX is discontinous downlink reception.
UL DTX is discontinousuplink transmission.
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All such UEs must support DL Enhanced L2. These categories do not indicate
whether CPC and Enhanced CELL_FACH operation are supported.
During the connection setup procedure or the service setup procedure, the UE
notifies the network of its capability to support these features.
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The MIMO and 64QAM features are introduced by 3GPP in R7. These two
features can be used respectively. In R7 restricted by the capabilities of UEs,
however, a single user cannot be configured with 64QAM and MIMO at the same
time.
In R8, 64QAM+MIMO can be used by one UE simultaneously to achieve a higher
throughput and better QoS, greatly improving user experience.
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Due to the rapid development of data services, the UMTS needs to improve the
spectrum resource utilization continuously to improve the downlink air interface
capabilities and enrich the service experience of users. The new DC-HSDPA
technology introduced in R8 aims to improve the user throughput through larger
spectrum bandwidth.
Dual-cell HSDPA (DC-HSDPA) enables users to receive the HSDPA data sent from
two inter-frequency downlink cells under the same coverage at the same time.
The network side can dynamically select between two carriers for HSDPA
transmission.
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DC-HSDPA users belong to both anchor and supplementary carrier cells. The DC-
HSDPA users can be scheduled in each cell. Compared with a single cell, the
number of users who can be scheduled is doubled, users with high-quality
channels can be selected through DL scheduling, and the system throughput is
increased. In addition, the channel attenuation of DC-HSDPA users is different in
the two cells, and the probability of high-quality channels is higher than that of
SC-HSDPA users (frequency-selective gain). Therefore, the throughput of users is
increased, and the service delay is reduced.
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Compared with the traditional HSPA technology, DC-HSDPA brings the following
gains:
Improving the peak throughput of users. When the DC-HSDPA and 64QAM
features are used together, the peak throughput can reach 42Mbps.
Compared with SC-HSDPA, DC-HSDPA features frequency-selective
scheduling and dynamic multi-carrier gain equalization, thus increasing the
system capacity. The gain is more obvious particularly when the load on
the two carriers is unequal.
Greatly reducing the burst service and HTTP service delay. As the user peak
rate is increased, the HTTP service response delay can be greatly reduced,and user service experience can be improved.
Improving the user experience of cell edge users and enhancing the DL
coverage.
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In implementation of RAN11.0 and earlier versions, a UL RLC works only in fixed
PDU mode, that is, the PDU size is fixed. Fixed-size PDUs cannot support high-
speed services effectively. When the window size is fixed, small PDUs cannot
support high-speed services. Large PDUs can support high-speed services, but the
power on the cell edge may be restricted. In addition, fixed-size PDUs may
introduce some extra headers and fill bits, which affects the transmission
efficiency. For example, when a UE moves from the cell center to the cell edge,
the transmit power of the UE is restricted when it reaches a certain distance. In
this case, the throughput drops rapidly, and data transmission may be easily
interrupted.
3GPP introduces uplink L2 enhancement in R8. The UL RLC (in UM or AM mode)
can support flexible PDUs and fixed PDUs. When working in flexible PDU mode,
the RLC can receive PDUs with different sizes flexibly to reduce the uplink PDU
size, and improve the throughput under the restricted uplink transmit power.
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Before RAN12, the modulation mode for HSUPA is QPSK. In RAN12, 16QAM for
HSUPA is introduced to improve the peak data.
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