View
233
Download
0
Category
Preview:
Citation preview
7/27/2019 Intron LTE
1/70
Europe & APAC
94 Duke StreetGlasgow G4 0UWScotland UK
Tel and Fax +44 (0)141 552 8855
www.steepestascent.cominfo@steepestascent.com
USA
200N. Westlake Blvd, #202Westlake VillageLos Angeles CA 91362, USA
Tel +1 805 413 4127
Introduction to LTEDaniel Garca-Als, Iain Stirling & Bob Stewart
7/27/2019 Intron LTE
2/70
Steepest Ascent Ltd. www.steepestascent.com 2
3GPP Evolution
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
3/70
Steepest Ascent Ltd. www.steepestascent.com 3
General Requirements Data rates (for a 20 MHz bandwidth):
100 Mbps in DL
50 Mbps in UL
Spectral efficiency associated to data rates shown above
5 bits/sec/Hz in DL 2.5 bits/sec/Hz in UL
Latency smaller than 5 msec for small IP packets
Voice service: at least same quality as WCDMA/HSPA
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
4/70 Steepest Ascent Ltd. www.steepestascent.com 4
Requirements: Mobility
Mobility :
Optimised for 0 to 15 km/h
High performance for up to 120 km/h
Should maintain a connection for up to 350 km/h (or even 500km/h for some frequency bands)
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
5/70 Steepest Ascent Ltd. www.steepestascent.com 5
Requirements: Coverage Coverage :
Up to 5 km cell radius: meet throughput, spectral efficiency andmobility targets
Up to 30 km cell radius: slight performance degradation istolerated
Up to 100 km cell radius: operation not precluded5 km
30 km100 km
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
6/70 Steepest Ascent Ltd. www.steepestascent.com 6
Requirements: E-MBMS Enhanced Multimedia Broadcast Multicast Service (E-MBMS):
Should provide MBMS better than Release 6;
Broadcast required spectral efficiency 1 bit/sec/Hz;
Should be possible to have MBMS only or a mixture of MBMSand non-MBMS services;
Can transmit MBMS over single frequency network (MBSFN);
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
7/70 Steepest Ascent Ltd. www.steepestascent.com 7
Requirements: Spectrum Flexibility Duplexing modes:
FDD : Frequency Division Duplex
TDD : Time Division Duplex Example bandwidths:
1.4 MHz3 MHz5 MHz
10 MHz15 MHz20 MHz
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
8/70 Steepest Ascent Ltd. www.steepestascent.com 8
Frame Structure FDD frame structure:
TDD frame structure:
slot (0.5ms)
0
subframe (1ms)
frame (10ms)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
subframe
frame
slot
0 2 3 4 5 7 8 9
DwPTS UpPTSGP DwPTS UpPTSGP
0 2 3 4 5 7 8 9610 msec
switch-point
5 msecswitch-point
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
9/70 Steepest Ascent Ltd. www.steepestascent.com 9
Resource Grid Two dimensional data structure:
...
0
...
...
...
...
...
...
. . .
. . .
a slot
s u
b c a r r
i e r s
OFDM symbols
time f r e q u e n c y
0 frame1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
a resource element
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
10/70 Steepest Ascent Ltd. www.steepestascent.com 10
Flexible Bandwidth LTE defined in a bandwidth independent way with:
resource blocks of 12 sub-carriers spaced 15 kHz
System bandwidth should be easily reconfigured
1 2
s u
b c a r r
i e r s
resourceblock
1 slot
f r e q u e n c y
time
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
11/70 Steepest Ascent Ltd. www.steepestascent.com 11
Transmission Time Interval (TTI) TTI:
length of independently decodable transmission link
In LTE a TTI is a subframe (2 slots): 1 msec
Minimum resource that can be allocated in LTE: 1 subframe in time: 1 msec
12 subcarriers in frequency:
0 2 3 4 5 7 8 91 6
subframe: 1 msec
frame: 10 msec
180 kHz 12 15 kHz=
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
12/70 Steepest Ascent Ltd. www.steepestascent.com 12
Multiple Access Scheme
Downlink
Orthogonal Frequency Division Multiple Access ( OFDMA ) withcyclic prefix (CP)
Uplink Single Carrier Frequency Division Multiple Access ( SC-
FDMA ) with cyclic prefix
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
13/70
Steepest Ascent Ltd. www.steepestascent.com 13
Adaptive Modulation and Coding Downlink modulation schemes
BPSK, QPSK, 16QAM, 64 QAM
Uplink modulation schemes
QPSK, 16QAM, 64QAM
Channel coding: Turbo coder with
coding rate of 1/3
two 8-state constituent encoders contention free internal interleaver
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
14/70
Steepest Ascent Ltd. www.steepestascent.com 14
MIMO Support Multiple input multiple output support (downlink only):
2 or 4 transmit antennas
2 or 4 receive antennas
Transmit diversity
Cyclic delay diversity (CDD)
Space frequency transmit diversity (transmit diversity codingapplied before IDFT)
Spatial multiplexing
Up to 4 layers or transmit streams
Codebook based precoding
Note: one antenna is used in non-MIMO mode.
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
15/70
Steepest Ascent Ltd. www.steepestascent.com 15
LTE Release 9 enhancements Multimedia Broadcast Multicast Service (MBMS)
completion of MBMS specification by adding related logicalchannels and clarifying physical layer details.
Home eNodeB (femtocells)
Interference scenarios such as WiFi and DECT interference;
Positioning support UE reception of satellite positioning signals (Galileo/GPS/
GLONASS)
UE reception of new downlink positioning reference signal Dual-layer UE-specific (non-codebook based) beamforming
Two new reference signals are defined (antenna ports 7 and 8)
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
16/70
Steepest Ascent Ltd. www.steepestascent.com 16
3GPP LTE Release 10 and beyond Has been submitted to the ITU as a candidate for IMT-Advanced;
Release 10 features:
Carrier aggregation to give up to 100MHz bandwidth;
Downlink transmission with 8 antennas and layers;
Uplink multi-antenna transmission with up to 4 antennas;
Co-ordinated Multi-Point (CoMP) transmission and reception; Relaying from Relay Nodes (RN) to eNB;
Latency improvements;
2.6GHz TDD support for USA
Self Optimising Networks (SON) enhancements
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
17/70
Europe & APAC
94 Duke StreetGlasgow G4 0UWScotland UK
Tel and Fax +44 (0)141 552 8855
www.steepestascent.cominfo@steepestascent.com
USA200N. Westlake Blvd, #202
Westlake VillageLos Angeles CA 91362, USA
Tel +1 805 413 4127
LTE UplinkDaniel Garca-Als, Iain Stirling & Bob Stewart
7/27/2019 Intron LTE
18/70
Steepest Ascent Ltd. www.steepestascent.com 2
Uplink Channels
Transport Channels (TrCH)
Control Information
UL-SCH Uplink - Shared ChannelRACH Random Access Channel
UCI Uplink Control Information
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
19/70
Steepest Ascent Ltd. www.steepestascent.com 3
Mapping to Physical Channels
Control information can be carried in PUSCH and PUCCH
UL-SCH
UCI
RACH
Uplink
PUSCH
PRACH
PUCCH
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
20/70
Steepest Ascent Ltd. www.steepestascent.com 4
Uplink Control Signalling Conveys L1 and L2 control information
HARQ acknowledgments for DL-SCH blocks
channel quality reports: CQI, RI and PMI
scheduling requests
Transmitted on PUCCH if no resources are allocated to UL-SCH
multiplexed with UL-SCH on to PUSCH (before SC-FDMA) if there is a valid schedule grant
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
21/70
7/27/2019 Intron LTE
22/70
Steepest Ascent Ltd. www.steepestascent.com 6
Control Information PUCCH The channel coding operations are:
codeblock
up to 11 bits
Indication (CQI) ACK / NACK
1 or 2 bits
Channel Qualityscheduling
0 bits
request
PUCCHformat 1
PUCCHformat 1a
or format 1b
PUCCHformat 2
codeblock
up to 11 bits
Indication (CQI)Channel Quality
PUCCHformat 2a
ACK / NACK
1 or 2 bits
20 bits 20 bits
or format 2b
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
23/70
Steepest Ascent Ltd. www.steepestascent.com 7
Channels and Signals A physical channel is defined as a set of resource elements carrying
information originating at a higher layer;
A physical signal is defined as a set of resource elements used in
support of the physical layer but not originating from a higher layer. For the uplink, the following physical channels are defined:
PUSCH : Physical Uplink Shared Channel;
PUCCH : Physical Uplink Control Channel;
PRACH : Physical Random Access Channel.
For the uplink, the following physical signals are defined: Sounding Reference Signal (SRS)
Demodulation Reference Signal (DMRS)
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
24/70
Steepest Ascent Ltd. www.steepestascent.com 8
Uplink Reference Signals There are two types of uplink reference signals:
Demodulation reference signal : associated with PUSCH or PUCCH
Sounding reference signal : not associated with any other transmission
They are time multiplexed with uplink data (not frequency multiplexed)
Used for channel estimation
0 1 2 3 4 5 6 0 1 2 3 4 5 6
slot slotsubframe
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
user #1
user #2
user #3
reference signal
dataf
t
PUSCH demodulation referencesignal example (normal CP)
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
25/70
Steepest Ascent Ltd. www.steepestascent.com 9
Demodulation Reference Signals: DRS There are two demodulation reference signals:
one for the PUSCH ;
and one for the PUCCH .
Used for channel estimation to allow for coherent demodulation
Desired attributes: small power variations in:
time: results in high power amplifier efficiency frequency: results in similar channel estimation quality for all
frequency components
DRS sequences used:
Cyclic extensions of Zadoff-Chu sequences (long sequences)
Special short QPSK sequences
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
26/70
Steepest Ascent Ltd. www.steepestascent.com 10
Sounding Reference Signal (SRS) I eNodeB needs channel quality information in order to assign resources
From DRS eNodeB can only get channel estimates on UE spectrum
No information available out of assigned spectrum
SRS overcome this problem
Used by base station to estimate channel quality of UEs
UE
allocatedresources
txed resource
grid
channel estimatesonly available on
rxed resourcegrid
this band
no channel estimates
available in other bands
DRS
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
27/70
Steepest Ascent Ltd. www.steepestascent.com 11
Sounding Reference Signal (SRS) II May cover large frequency span (not assigned to UE):
minimum of 4 resource block span
multiples of 4 resource blocks span
Can be transmitted as often as 2 msec (every 2nd subframe)
Can be transmitted as infrequently as 160 msec (every 16th frame)
Not necessarily transmitted with any physical channel (unlike DRS)
SRS modes
wideband: one transmission covers band of interest
frequency hopping: narrowband, location changes with time
subframe subframe subframe subframe subframe subframe
SRS
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
28/70
Steepest Ascent Ltd. www.steepestascent.com 12
SRS Transmission Transmitted on last symbol of subframe every 2nd subcarrier
Multiple UEs can transmit SRS s simultaneously
Interference is avoided by:
using different cyclic shifts (phase rotations): orthogonality
changing the comb transmission pattern
. . .
. . .
. . .
. . .
subframe
. . .
. . .
OFDM symbol
SRS subcarriers UE 1
used for SRS
SRS subcarriersUE 2
UE 3
using different
cyclic shifts for SRS
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
29/70
Steepest Ascent Ltd. www.steepestascent.com 13
Physical Uplink Control Channel PUCCH: Physical Uplink Control Channel
conveys uplink control information;
never transmitted simultaneously with PUSCH from the UE.
PUCCH used if UE has no valid schedule grant
Transmitted with frequency hopping (provides frequency diversity)
Transmitted on band edges: leaves contiguous bandwidth for PUSCHin the middle.
UE
uplink control
PUCCH:
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
30/70
Steepest Ascent Ltd. www.steepestascent.com 14
PUCCH Bandwidth One resource block (RB) allocated to each PUCCH This is too large for the amount of information transmitted
Therefore more than one PUCCH can share the same RB :
Use same base reference sequence
Use different phase rotations (cyclic shifts ) Use different orthogonal cover code (formats 1, 1a & 1b)
Inter-cell interference can be a problem Inter-cell interference is randomised by using hopping patterns in
and orthogonal codes with each symbol
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
31/70
Steepest Ascent Ltd. www.steepestascent.com 15
Physical Uplink Shared Channel PUSCH : Physical Uplink Shared Channel carries
data;
control information.
PUSCH processing chain:
UE
uplink data & control
PUSCH:
ScramblingModulation
mapper mapper Resource el.
modulationSC-FDMA
Precoding
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
32/70
Steepest Ascent Ltd. www.steepestascent.com 16
PUSCH Scrambling
Modulo 2 multiplication (XOR) with a scrambling sequence
Only applied to: coded data, channel quality coded bits, ACK codedbits
Not applied to ACK placeholders, these are set to predetermined value
ScramblingModulation
mapper mapper Resource el.
modulationSC-FDMA
PrecodingPUSCH
c
1 ACK bit placeholders Q m 4=( )
... 0 0 1 0 1 1 1 X X X 0 1 1 0 1 0 ...
coded datach. quality coded bits
ACK coded bits
.0 0 1 0 1 0 1 1 1 1 0 0 1 1 1 0b
i( )
b i( )
c i( )
b
i( ) b
i 1
( )=
b
i 1+( ) b
i 2+( ) 1= =
d l
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
33/70
Steepest Ascent Ltd. www.steepestascent.com 17
PUSCH Modulation
Maps bits into symbols
The modulation mapping defines 3 constellations as follows:
ScramblingModulation
mapper mapper Resource el.
modulationSC-FDMA
PrecodingPUSCH
Q
I
QPSK
1
100
01
10
11
Q
I1
1
16-QAM
Q
I3 5 7
3
5
7
64-QAM
0000
0001
0010
0011
1010
1011
1000
1001
3
3
0101
0100
0111
0110
1111
1110
1101
1100
1
1
101111 101101 100101 100111 000111 000101 001101 001111
101110 101100 100100 100110 000110 000100 001100 001110
101010 101000 100000 100010 000010 000000 001000 001010
101011 101001 100001 100011 000011 000001 001001 001011
111011 111001 110001 110011 010010 010001 011001 011011
111010 111000 110000 110010 010010 010000 011000 011010
111110 111100 110100 110110 010110 010100 011100 011110
111111 111101 110101 110111 010111 010101 011101 011111
PUSCHP di
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
34/70
Steepest Ascent Ltd. www.steepestascent.com 18
PUSCH Precoding
Not the same as downlink (multi-antenna) precoding
Produces SC-FDMA modulation;
Generation process:
Split the modulated symbols into sets; Each set (of size ) forms an SC-FDMA symbol ;
Perform a DFT (precoding part of SC-FDMA modulation);
DFT size: its prime must be a product of 2, 3 and/or 5
Smallest DFT size is 12
ScramblingModulation
mapper mapper Resource el.
modulationSC-FDMA
PrecodingPUSCH
Msymb Msymb MscPUSCH
Msc
PUSCH
PUSCHP di DFTSi
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
35/70
Steepest Ascent Ltd. www.steepestascent.com 19
PUSCH Precoding: DFT Size DFT can be implemented with FFT for efficiency; DFT size: its prime factors are 2, 3 and/or 5
Minimum DFT size (resource block size in the frequency domain): 12
MscPUSCH
NscRB
2 2
3 3
5 5
NscRB
NRBUL
=
. . .
. . .
. . .
. . .
...
...
subframefreq
time
1 2 s
u b c a
r r i er
s
DFT
N scRB 12=
R El tM i
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
36/70
Steepest Ascent Ltd. www.steepestascent.com 20
Resource Element Mapping
The final stage in PUSCH processing is to map the symbols to theallocated physical resource elements
Note that allocation sizes are limited to values whose prime factors are2, 3 & 5 (imposed by precoding stage)
Map in increasing order:
first subcarriers
then the time domain (SC-FDMA) Avoid SC-FDMA symbols with
Demodulation reference signals
Sounding reference signals
ScramblingModulation
mapper mapper Resource el.
modulationSC-FDMA
PrecodingPUSCH
z
PUSCHF H i g
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
37/70
Steepest Ascent Ltd. www.steepestascent.com 21
PUSCH Frequency Hopping Allocated spectrum to a UE can change every subframe ;
This is controlled by a frequency hopping function :
This provides for better frequency and interference diversity .
f hop .( )
frequency
time
subframeintervals
short-term narrowband interference Mobile 2
Mobile 3
Mobile 1
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
38/70
Europe & APAC94 Duke Street
Glasgow G4 0UWScotland UK
Tel and Fax +44 (0)141 552 8855
www.steepestascent.cominfo@steepestascent.com
USA200N. Westlake Blvd, #202
Westlake VillageLos Angeles CA 91362, USA
Tel +1 805 413 4127
LTE DownlinkDaniel Garca-Als, Iain Stirling & Bob Stewart
DownlinkChannels
7/27/2019 Intron LTE
39/70
Steepest Ascent Ltd. www.steepestascent.com 2
Downlink Channels
Transport Channels (TrCH):
Control Information:
DL-SCH Downlink - Shared ChannelBCH Broadcast ChannelPCH Paging ChannelMCH Multicast Channel
CFI Control Format Indicator
HI HARQ Indicator DCI Downlink Control Information
MappingtoPhysicalChannels
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
40/70
Steepest Ascent Ltd. www.steepestascent.com 3
Mapping to Physical Channels
DL-SCH
CFI
BCHPCH
MCHHI
DCI
Downlink
PDSCH
PBCH
PMCH
PCFICH
PDCCH
PHICH
DownlinkChannelsandSignals
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
41/70
Steepest Ascent Ltd. www.steepestascent.com 4
Downlink Channels and Signals A physical channel : set of resource elements carrying information
originating at a higher layer;
A physical signal : set of resource elements used in support of thephysical layer but not originating from a higher layer.
Reference Signals;
Synchronisation Signals;
PDSCH : Phy DL Shared Ch
PDCCH : Phy DL Control Ch.
PMCH : Phy Multicast Ch.
PBCH : Phy Broadcast Ch.
PCFICH : Phy Ctrl FormatIndicator Ch.
PHICH : Phy Hybrid ARQIndicator Ch.
Framestructure
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
42/70
Steepest Ascent Ltd. www.steepestascent.com 5
Frame structure
s u
b c a r r
i e r
OFDM symbol
ref. signalcontrol
PSS
SSS
BCH
unused
PCFICH
ref. signal
PDCCH
PDSCH
regions
unused
unused
SSS PSS
BCH
PCFICH
SSS PSS
DownlinkPCFICH
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
43/70
Steepest Ascent Ltd. www.steepestascent.com 6
Downlink PCFICH PCFICH: Downlink Physical Control Format Indicator Channel
specifies how many OFDM symbols are used for PDCCHtransmission;
Uses QPSK modulation
Transmitted in the same set of antenna ports as PBCH;
It has its own specific layer mapping, precoding and mapping to
resource elements.
UE
format of PDCCH
PCFICH:
PhysicalDownlinkControlChannel I
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
44/70
Steepest Ascent Ltd. www.steepestascent.com 7
Physical Downlink Control Channel I PDCCH: Physical Downlink Control Channel
carries control information including scheduling assignments;
Uses QPSK modulation
Transmitted in the same set of antenna ports as PBCH; It has its own specific layer mapping, precoding and mapping to
resource elements
UE
downlink and uplink scheduling assignmentsPDCCH:
PhysicalHybridARQIndicatorChannelI
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
45/70
Steepest Ascent Ltd. www.steepestascent.com 8
Physical Hybrid ARQ Indicator Channel I PHICH: Physical Hybrid ARQ Indicator Channel
hybrid-ARQ ACK and NACK indicators UEs;
Transmitted in the same set of antenna ports as PBCH;
The PHICH uses its own specific:
layer mapping; precoding;
mapping to resource elements.
UE
ACK / NACKPHICH:
PhysicalDownlinkSharedChannel
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
46/70
Steepest Ascent Ltd. www.steepestascent.com 9
Physical Downlink Shared Channel PDSCH: Physical Downlink Shared Channel
It is the main downlink channel;
Carries transport blocks to the mobiles ;
PDSCH uses the following antenna ports:
{0}, {0,1} or {0,1,2,3} if UE-specific reference signals are nottransmitted ;
{5} if UE-specific reference signals are transmitted .
UE
downlink data
PDSCH:
DownlinkPBCH
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
47/70
Steepest Ascent Ltd. www.steepestascent.com 10
Downlink PBCH PBCH: Physical Broadcast Channel
carries broadcast information (from the BCCH logical channel)
Uses a simplified and fixed transport format ; A coded block of 1920 samples for normal cyclic prefix or 1728
samples for extended cyclic prefix is produced by the channel coder
every 40ms; This block is QPSK modulated into 960 or 864 complex symbols;
Transmit diversity layer mapping and precoding is performed.
UE
UE
UEUE
UE
DownlinkReferenceSignalsI
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
48/70
Steepest Ascent Ltd. www.steepestascent.com 11
Downlink Reference Signals I
There are three types of downlink reference signal:
Cell-specific : its structure depends on the cell ID
MBSFN references for MBSFN transmission;
UE-specific references: used in non-codebook basedbeamforming.
Provided in support of coherent demodulation;
Used by UE to perform channel estimation and to obtain channelquality measurements.
DownlinkReferenceSignals II
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
49/70
Steepest Ascent Ltd. www.steepestascent.com 12
Downlink Reference Signals II References are arranged across time and frequency ; Only one reference signal is transmitted through per antenna port , this
allows for channel estimation for the different antenna ports ;
When an antenna port transmits a reference signal other ports aresilent;
time
f r e q u e n c y ANTENNA PORT 1
ANTENNA PORT 2
Antenna port 1 reference signal
Antenna port 2 reference signal
No transmission
SynchronisationSignals I
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
50/70
Steepest Ascent Ltd. www.steepestascent.com 13
Synchronisation Signals I There are two downlink synchronisation signals :
Primary synchronisation signal;
Secondary synchronisation signal.
This structure reduces cell search procedure complexity ;
Used to obtain:
UE
CELL
Primary/secondary synch signals
Cell identity
frame timing
Synchronisation Signals II
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
51/70
Steepest Ascent Ltd. www.steepestascent.com 14
y g Always transmitted in the same place regardless of bandwidth used.
first 72 carriers (around DC carrier);
OFDM symbols 5 and 6 of first slot in subframes 0 & 5.
10 msec radio frame
#0 #1 #2 #3 #4 #5 #6 #7 #8 #9
subframe
0 1 2 3 4 5 6 0 1 2 3 4 5 6
slot slot
7 2 s u
b c a
r r i e r s
OFDM symbol
0 1 2 3 4 5 6 0 1 2 3 4 5 6
slot slot
7 2 s u
b c a
r r i e r s
OFDM symbol
b a n
d w i d t h
f
t
secondary synch signal
primary synch signal
Channel Coding Procedures
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
52/70
Steepest Ascent Ltd. www.steepestascent.com 15
g
There are a number of procedures which are used for multipletransport channel or control information types:
CRC calculation; Code block segmentation ;
Channel coding (tail biting convolutional and turbo );
Rate matching ;
Tr. Channel & Ctrl. Information Processing
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
53/70
Steepest Ascent Ltd. www.steepestascent.com 16
g
Depending on the channel, a different set of processing steps occurs:
channelcoding
ratematching
code blocksegment.
bitstream e k E
b i t s
bitstream f k G
b i t s
CRCattachment
code blockconcat.
channelcoding
ratematching
CRCattachment
input bits a k A b i t s
input bits a k A b i t s
BCHDL-SCH, PCH and MCH
G C R C 1 6
D (
)
c o n v .
G C R C 2 4 A
D (
)
t u r b o
G C R C 2 4 B
D (
)
channelcoding
bitstream b k B
b i t s
CFI or HI
CFI or HI
H I : r a
t e 1 / 3 r e p e
t i t i o n c o
d e
C F I : r a
t e 1 / 1 6 b l o c
k c o
d e
bitstream e k E
b i t s
channelcoding
ratematching
CRCattachment
input bits a k A b i t s
DCI
G C R C 1 6
D (
)
c o n v .
Downlink Physical Channel Processing
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
54/70
Steepest Ascent Ltd. www.steepestascent.com 17
y g
The general structure of downlink physical channels processing is:
This structure applies to the PDSCH;
other channels have slightly different processing chains.
ScramblingModulation
mapper mapper Resource el.
layers antenna ports
mapper Layer
Precoding
modulationOFDM
ScramblingModulation
mapper mapper Resource el.
modulationOFDM
code words
. . .
. . .
. . .
. . .
Scrambling
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
55/70
Steepest Ascent Ltd. www.steepestascent.com 18
g
Produces a block of scrambled bits from the code word bits :
Modulo 2 multiplication (XOR) of the code word bits with a scrambling
sequence :
ScramblingModulation
mapper mapper Resource el.
layers antenna ports
mapper
Layer
Precoding
modulationOFDM
ScramblingModulation
mapper mapper Resource el.
modulationOFDM
code words
. . .
. . .
. . .
. . .
b q( ) b q( )
b q( )
i( ) bq( ) i( ) c
q( ) i( )+( ) mod 2;= i 0 Mbitq( ) 1 =
c q( )
block of bits bq( ) block of bits b
q( )
c q( )scrambling sequence
code word bits scrambled bits
Modulation
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
56/70
Steepest Ascent Ltd. www.steepestascent.com 19
Downlink supported modulation formats:
Physical Channel Modulation Schemes
PDSCH QPSK, 16QAM, 64QAMPMCH QPSK, 16QAM, 64QAM
PDCCH QPSK
PBCH QPSK
PCFICH QPSKPHICH BPSK
ScramblingModulation
mapper mapper Resource el.
layers antenna ports
mapper
Layer Precoding
modulationOFDM
ScramblingModulation
mapper mapper Resource el.
modulationOFDM
code words
. . .
. . .
. . .
. . .
Downlink Modulation Mapper
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
57/70
Steepest Ascent Ltd. www.steepestascent.com 20
The modulation mapping defines 4 constellations as follows:
Amplitude levels are normalised.
Q
I
QPSK
1
100
01
10
11
Q
I1
1
16-QAM
Q
I3 5 7
3
5
7
64-QAM
0000
0001
0010
0011
1010
1011
1000
1001
3
3
0101
0100
0111
0110
1111
1110
1101
1100
1
1
101111 101101 100101 100111 000111 000101 001101 001111
101110 101100 100100 100110 000110 000100 001100 001110
101010 101000 100000 100010 000010 000000 001000 001010
101011 101001 100001 100011 000011 000001 001001 001011
111011 111001 110001 110011 010010 010001 011001 011011
111010 111000 110000 110010 010010 010000 011000 011010
111110 111100 110100 110110 010110 010100 011100 011110
111111 111101 110101 110111 010111 010101 011101 011111
Q
I
QPSK
1
100
01
10
11
Q
I
BPSK
1
10
1
Multi-antenna Processing in LTE
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
58/70
Steepest Ascent Ltd. www.steepestascent.com 21
Includes
layer mapping : splits data sequence into a number of layers precoding
Under precoding the LTE standard can use
cyclic delay diversity (CDD)
spatial multiplexing (precoding)
transmit diversity
ScramblingModulation
mapper mapper Resource el.
layers antenna ports
mapper Layer
Precoding
modulationOFDM
Scrambling Modulationmapper mapper Resource el.
modulationOFDM
code words
. . .
. . .
. . .
. . .
Transmission Schemes I
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
59/70
Steepest Ascent Ltd. www.steepestascent.com 22
non codebook based beamforming (single antenna, Port 5):
Single antenna port, Port 0: Transmit Diversity:
UE
UE
S F B C
2 or 4 antennas supported
b e a m
f o r m
2 or 4 antennas supported
arbitrary beamforming vector
1 layer UE
Transmission Schemes II
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
60/70
Steepest Ascent Ltd. www.steepestascent.com 23
Open-loop spatial multiplexing (Large Delay CDD):
Closed-loop spatial multiplexing:
p r e c o
d i n g
2 or 4 antennas supported
codebook
2, 3 or 4 layersUE
UE
p r e c o
d i n g
2 or 4 antennas supported
codebook
2, 3 or 4 layers
codebook selection suggestion (PMI)
Transmission Schemes III
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
61/70
Steepest Ascent Ltd. www.steepestascent.com 24
Multi-user MIMO:
codebook based beamforming (Closed-loop spatial multiplexing usinga single transmission layer):
b e a m f o r m
b e a m
f o r m
2 or 4 antennas supported
codebook
2, 3 or 4
codebook selection suggestion (PMI)
layers
codebook codebook selection suggestion (PMI)
(shared resources)
UE
UE
b e a m f o r m
2 or 4 antennas supported
codebookcodebook selection suggestion (PMI)
1 layer UE
Physical Antennas and Antenna Ports
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
62/70
Steepest Ascent Ltd. www.steepestascent.com 25
LTE standard refers to antenna ports
Antenna ports and physical antennas are different
Antenna port: defined by the presence of an antenna port specificreference signal
There are up to 6 antenna port specific reference signals
Number of physical antennas is
Antenna ports map to physical antennas.
1 2 4, ,{ }
Precoding for Spatial Multiplexing
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
63/70
Steepest Ascent Ltd. www.steepestascent.com 26
Used with the layer mapping for spatial multiplexing Supports or antennas: &
Different coding used for:
precoding without CDD or closed loop spatial multiplexing
precoding with large delay CDD or open loop spatial mux.
Codebook based precoding: 7 element codebook for the 2 antenna port case
16 element codebook for the 4 antenna port case
For spatial multiplexing the number of layers is also known as thetransmission rank
P 2= P 4= p 0 1,{ } p 0 1 2 3, , ,{ }
Spatial Mux: Precoding without CDD
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
64/70
Steepest Ascent Ltd. www.steepestascent.com 27
Also known as closed loop precoding
Based on downlink channel estimates
UE reports recommendations : RI (rank indication) and PMI(precoder matrix indication)
eNodeB may or may not follow these recommendations whenselecting
layer 1
layer 2
layer
IDFT CP
precoding
IDFT CP
IDFT CP
W i( )P
ant 1
ant 2
ant P
x 0( ) i( )
x 1( ) i( )
x 1 ( ) i( )
W i( )
Spatial Mux: Large Delay CDD Precoding
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
65/70
Steepest Ascent Ltd. www.steepestascent.com 28
Also known as open loop precoding
matrices and are applied first, then precoding
codebook matrices used are predetermined
channel quality measurements are not required
layer 2
layer
IDFT CP
precodingCDD
IDFT CP
IDFT CP
W i( )P
ant 1
ant 2
ant P
1 0 0
0 e j2 k
0
0 0 e
j2 k 1 ( )
U
D i( )
layer 1
U D W i( )
Beamforming
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
66/70
Steepest Ascent Ltd. www.steepestascent.com 29
Supported by LTE: precoding applied to a single layer Codebook based beamforming:
Use precoding matrix from codebook
UE is informed of precoding matrix used
Non-codebook based beamforming:
Arbitrary beamforming applied UE is not notified of precoding matrix used
UE needs to estimate channel including effect of beamforming
UE specific reference signals used (antenna port 5)
Beamforming (UE specific) is applied to this reference signal
1=
Transmit Diversity Precoding
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
67/70
Steepest Ascent Ltd. www.steepestascent.com 30
For 2 antennas, precoding the Alamouti scheme is used as:
Note that any two columns of the coding matrix are orthogonal;
This is space-frequency transmit diversity (coding in frequencydomain)
A similar sparse mapping applies to the case of 4 antennas.
y 0( ) 2 i( )
y 1( ) 2 i( )
y 0( ) 2 i 1+( )
y 1( ) 2 i 1+( )
12
-------
1 0 j 0
0 1 0 j0 1 0 j1 0 j 0
Re x 0( ) i( ){ }
Re x 1( ) i( ){ }
Im x 0( ) i( ){ }
Im x 1( ) i( ){ }
=
Resource Element Mapping
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
68/70
Steepest Ascent Ltd. www.steepestascent.com 31
The final stage in the physical layer processing before OFDMmodulation is resource element mapping
Symbols are mapped to assigned resource elements
Resource elements used by reference signals are avoided
ScramblingModulation
mapper mapper Resource el.
layers antenna ports
mapper Layer Precoding
modulationOFDM
ScramblingModulation
mapper mapper Resource el.
modulationOFDM
code words
. . . . . . . . . . . .
OFDM Symbol Construction
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
69/70
Steepest Ascent Ltd. www.steepestascent.com 32
DC subcarrier is not modulated Subcarriers of resource blocks are arranged on both sides of the DC
subcarrier
For larger values of resource blocks in DL ( ) more resource blockslie to the left and right of the spectrum illustrated above.
OFDM symbols are transmitted in turn.
f
resourceblock
DC subcarrier
......
NRBDL
OFDM Modulation
http://www.steepestascent.com/http://www.steepestascent.com/7/27/2019 Intron LTE
70/70
Steepest Ascent Ltd. www.steepestascent.com 33
Implemented using an IFFT with 15kHz carrier spacing
Cyclic prefix also added at this stage
Each antenna port has its own OFDM modulation
ScramblingModulation
mapper mapper Resource el.
layers antenna ports
mapper Layer Precoding
modulationOFDM
ScramblingModulation
mapper mapper Resource el.
modulationOFDM
code words
. . . . . . . . . . . .
http://www.steepestascent.com/http://www.steepestascent.com/Recommended