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PM104
LTE: Downlink Physical-Layer Overview and Throughput Simulation Results
Nov 5, 2008
Ian C. Wong, Ph.D. Jason WongSystems Engineer, Algorithms and Standards System & Application EngineerCellular Products Group R&D GSM
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Agenda
►Overview of LTE• LTE philosophy• LTE performance requirements
►LTE Physical Layer • General description• Physical channels• Channel coding• Modulation
►Throughput simulation results• Freescale’s LTE downlink simulator• Downlink shared channel• Control channel
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3GPP – LTE Philosophy and Criteria
►Philosophy• LTE focus is on:
Enhancement of the Universal Terrestrial Radio Access (UTRA)Optimization of the UTRAN architecture
• With HSPA (downlink and uplink), UTRA will remain highly competitive for several years
• LTE project aims to ensure the continued competitiveness of the 3GPP technologies for the future
►Criteria• Demand for higher data rates• Expectations of additional 3G spectrum allocations• Greater flexibility in frequency allocations• Continued cost reduction• Keeping up with other (unlicensed) technologies (eg WiMAX)
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Performance Requirements for LTE Category Requirement
Peak data rate DL: 100 Mbps in 20 MHz BW (5 bps/Hz)UL: 50 Mbps in 20 MHz BW (2.5 bps/Hz)
Control-plane latency < 100 ms for Idle to Active mode transition
Control-plane capacity > 200 users per cell in Active state within 5 MHz
User-plane latency < 5 ms for 1 user with 1 data stream and small IP packet
Average user throughput DL: 3-4 times of HSDPA per MHzUL: 2-3 of HSUPA per MHz
MobilityOptimized for 0-15 km/h
Support with high performance for 15-120 km/hSupport for 120-350 km/h or even 500 km/h
CoverageAll targets met for 5 km cells
Slight degradation for 5-30 km cellsSupport for 30-100 km cells
Spectrum flexibility Support for 1.25 – 20 MHz BandwidthsPaired or unpaired spectrum allocations
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LTE Protocol Architecture Around the Physical Layer
►PHY interfaces MAC sub-layer of Layer 2 and RRC of Layer 3
►PHY offers a transport channel to MAC
• Transport channel characterized by how information is transferred
►MAC offers logical channels to the RLC
• Logical channel characterized by the type of information transferred.
Radio Resource Control (RRC)
Medium Access Control (MAC)
Physical Layer(PHY)
Logical channels
Transport channels
Con
trol/M
easu
rem
ents Layer 2
Layer 1
Layer 3
Radio Link Control (RLC)
…
Physical channels
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Layer 1 General Description
►Multiple access• OFDMA in the downlink• SC-FDMA in the uplink
►Duplexing• Frequency-division duplexing (FDD) for paired spectrum• Time-division duplexing (TDD) for unpaired spectrum• Half-duplex FDD for paired spectrum (optional)
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Frame Structure
►Frame structure type 1 applicable to FDD and half duplex FDD►Each 10 ms radio frame is divided into ten equally sized sub-frames►Each sub-frame consists of two equally sized slots
Slot 0 Slot 1 Slot 2 Slot 3 … Slot 18 Slot 19
One radio frame = 10 ms
One subframe = 1 ms
One slot = 0.5 ms
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Slot Structure and Resource Elements
DLsymbN
slotT
0=l 1DLsymb −= Nl
RB scDL RB
NN
× RB scN
RBsc
DLsymb NN ×
),( lk
0=k
1RBsc
DLRB −= NNk
Transmission BW (MHz) 1.4 3 5 10 15 20
Slot duration 0.5 ms
Subcarrier spacing 15 kHz / 7.5 kHz (MBSFN)
Sampling frequency (MHz)
1.92 3.84 7.68 15.36 23.04 30.72
FFT size 128 256 512 1024 1536 2048
# downlink RBs(NDL
RB)6 15 25 50 75 100
# subarriers / RB (NRB
sc)12 / 24 (MBSFN)
# OFDM symbols / slot (NDL
symb)
7 (normal CP) 6 (extended CP)
3 (extended CP in MBSFN)
CP length (μs) 1 x 5.21, 6 x 4.69 (normal)16.6 (extended)
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Downlink Physical Channels
►Physical downlink shared channel (PDSCH)• Carries the downlink shared channel (DL-SCH) and paging channel (PCH)
►Physical downlink control channel (PDCCH)• Informs the UE about the resource allocation of PCH and DL-SCH, and Hybrid
ARQ information related to DL-SCH• Carries the uplink scheduling grant
►Physical control format indicator channel (PCFICH)• Informs the UE about the number of OFDM symbols used for the PDCCHs;• Transmitted in every subframe.
►Physical broadcast channel (PBCH)• The coded broadcast channel (BCH) transport block is mapped to four
subframes within a 40 ms interval• 40 ms timing is blindly detected• Each subframe is assumed to be self-decodable, i.e. the BCH can be decoded
from a single reception, assuming sufficiently good channel conditions.►Physical Hybrid ARQ Indicator Channel (PHICH)
• Carries Hybrid ARQ ACK/NAKs in response to uplink transmissions.►Physical multicast channel (PMCH)
• Carries the multicast channel (MCH) transport channel
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Channel Coding of Physical Channels
►Cyclic redundancy check• Error detection capability for transport block and each code block
►Code-block segmentation• Segment the transport block into smaller code blocks of roughly equal length
►Channel coding• Rate 1/3 turbo code – Downlink shared, paging, and multicast channels• Rate 1/3 tail-biting convolutional code – Broadcast channel and downlink control
information• Rate 1/16 block code – Control format indicator• Rate 1/3 repetition code – HARQ indicator
►Rate-matching• Includes sub-block interleaving, bit collection, and bit selection and pruning• Support hybrid ARQ transmissions
CRC
Code block
segment-ation
Channelcoding
Ratematching
UncodedTransport Channel bits
CodedPhysicalChannel bits
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Baseband Modulation of Downlink Physical Channels
►Scrambler breaks long strings of 1s and 0s of the coded bits►Modulation mapper converts scrambled bits into complex-valued symbols►Layer mapper and precoder performs symbol transformations to enable
multi-antenna transmission techniques►Resource element mapper maps the physical channel symbols to the
appropriate locations in the time-frequency grid ►OFDM signal generation converts the frequency domain symbols to time
domain complex baseband signals for each antenna port for transmission
ScramblerOFDM Signal
Generation
ModulationMapper
LayerMapper
+Precoder
ResourceElementMapper
Reference Signal Synchronization Signal
Reference & synch signalgenerator
Coded PhysicalChannel bits Complex
OFDM signal
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Downlink Reference Signals
► Transmitted in all subframes not used for MBSFN transmission
► Primarily used for channel estimation and tracking purposes
► Pseudo-random QPSK signals generated using length-31 gold sequence
► Orthogonal across time, frequency, and antennas within a cell
► Orthogonal in the code-domain among neighboring cells
One antenna port
Two antenna ports
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Downlink Synchronization Signals
►Primary synch signal• Half-frame timing reference• Frequency domain Zadoff-Chu
sequence• Occupies only middle 62
subcarriers in frequency►Secondary synch signal
• Frame timing reference• Interleaved concatenation of two
length-31 m-sequences
DL - RS
PSCH
1st SSCH
2nd SSCH
RS: Reference SignalPSCH: Primary Synchronization ChannelSSCH: Secondary Synchronization Channel
Frame (10ms)
Subframe(1ms)
1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7
Slot(0.5ms)
Slot 0 Slot 10
* Figure courtesy of Taeyoon Kim, Freescale
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Freescale’s Radio Link Simulator Architecture
PHY EncoderTS 36.212 –
Multiplexing and Channel Coding
Transportchannel raw bits
(generated by encoder) …
Physical channel coded bits
PHY ModulatorTS 36.211 –
Physical Channels and Modulation
PDSCHPDCCH
PBCH
TD-transmitted signal
Mobile MIMOChannel
PHY DemodulatorTS 36.211 –
Physical Channels and Modulation
Noise/Interference…
PDSCHPDCCH
PBCH
PHY DecoderTS 36.212 –
Multiplexing and Channel Coding
Decoded bits
Physical channel LLRs
Statistics Calculator (Coded/Uncoded BER, PER, Throughput)
PhyChanBits.txTrChanBits.tx
TrChanBits.rx PhyChanBits.rx
ReceiverImpairments
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Example RAN4 PDSCH Simulation Results
FDD 1x2 SIMO, 10MHz, 16-QAM 1/2, ETU300 channel
SIMO 16QAM 1/2 ETU300
0
2000000
4000000
6000000
8000000
10000000
12000000
14000000
16000000
-8 -6 -4 -2 0 2 4 6 8 10 12 14
SNR (dB)
Thro
ughp
ut (b
ps)
EricssonFreescaleInterDigitalLGEFujitsuNokiaNXPMotorolaNECTI
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Example RAN 4 PDSCH Simulation Results
►FDD 2x2-SFBC, 10MHz, ►1 codeword, 2 layers►16-QAM rate 1/2►EVA5, non-ideal channel
estimation
►FDD 2x2-SM with precoderfeedback for whole BW,
►10MHz MMSE receiver ►2 x 64QAM 3/4, ►EVA5, non-ideal channel
estimation
MIMO-SFBC 16QAM 1/2 EVA5
0
2000000
4000000
6000000
8000000
10000000
12000000
14000000
-8 -6 -4 -2 0 2 4 6 8 10 12 14 16
SNR (dB)
Thro
ughp
ut (b
ps)
EricssonFreescaleInterDigitalLGEFujitsuNokiaNXPMotorolaNECTI
MIMO-SM 64QAM 1/3 EPA5
0
10000000
20000000
30000000
40000000
50000000
60000000
70000000
2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32
SNR (dB)
Thro
ughp
ut (b
ps)
Ericsson
Freescale
InterDigital
LGE
Fujitsu
Nokia
NXP
Motorola
NEC
TI
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Example RAN4 PDCCH/PCFICH Simulations
0.10%
1.00%
10.00%
100.00%
-10 -8 -6 -4 -2 0 2 4 6
SNR [dB]PC
FIC
H/P
DC
CH
BLE
R
Ericsson
Freescale
TI
LGE
NTT DoCoMo
Motorola
Marvell
Nokia
Fujitsu
InterDigital
NEC
CATT
Qualcomm
AVERAGE
Sim 46.6: FDD 1x2 10MHz 8CCE Format1 ETU70 low
0.10%
1.00%
10.00%
100.00%
-10 -8 -6 -4 -2 0 2 4 6
SNR [dB]
PCFI
CH
/PD
CC
HB
LER
Ericsson
Freescale
TI
LGE
NTT DoCoMo
Motorola
Marvell
Nokia
Fujitsu
InterDigital
NEC
CATT
Qualcomm
Samsung
AVERAGE
Sim 47.10: FDD 2x2 SFBC 1.4MHz 2CCE Format2 EPA5 low
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References
►[1] Francois Coureau, “3GPP Evolution: LTE and SAE,” Beijing, China, 2004
►[2] TR 25.913 7.3.0, “Requirements for Evolved-UTRA and Evolved UTRAN,” March 2006
►[3] TS 36.201 v. 8.1.0, “E-UTRA: LTE Physical Layer – General Description,” Nov. 2007
►[4] TS 36.211 v. 8.2.0, “E-UTRA: Physical Channels and Modulation,” March 2008
►[5] TS 36.212 v. 8.2.0, “E-UTRA: Multiplexing and Channel Coding,”March 2008
►[6] TS 36.300 v. 8.4.0, “E-UTRA and E-UTRAN: Overall Description Stage 2,” March 2008
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Related Session Resources
SessionsSession ID
DemosPedestal ID
PM101 LTE: MIMO Techniques in 3GPP-LTE
Title
Demo Title
Session Location – Online Literature Libraryhttp://www.freescale.com/webapp/sps/site/homepage.jsp?nodeId=052577903644CB