WiMAX Physical Layer

Transcription

1 WiMAX Physical Layer lecturer: : 林杰龍 jielong@ttc.org.tw 009/03/10 Content I Baseband Technology I II III OFDM &OFDMA Signal Characteristics Modulation & Coding II III RF Technology Other Technology page-

2 Basic Architecture of an OFDM(A) System Tx Filter Add CP P/S IFFT S/P Mod. Interleaver FEC Encoder Randomizer Input Data Rx Filter S/P Remove CP FFT Detection P/S & De-Mod. De- Interleaver FEC Decoder De- Randomizer Output Data page-3 DFT and IDFT There is the orthogonal property between different subcarriers to avoid the interference when the spectrums overlap. j it e ω e j ω it page-4

3 DFT and IDFT Discrete Fourier Transform is implemented by the FFT and IFFT normally. IDFT _ x[ n] = DFT _ X [ k ] = 1 N N 1 n= 0 N 1 k = 0 x[ n] e X [ k ] e π j kn N π j kn N N: the number of subcarrier in OFDM x[n]: the complex input data in time domain X[k]: the data in frequency domain page-5 N Period: e WN Fourier Transform Characteristics j( π N ) = ( ) Complex Conjugate Symmetry: k N n kn kn W = W = W [ ] ( ) N N N ( π ) ( ) N N j N jπ W = e = e = 1 ( + ) ( + ) W = W = W kn k n N k N n N N N N DFT needs N multipliers and N(N-1) adders. This is a high calculating complexity method. FFT or IFFT is used to reduce the complexity to Nlog N page-6

4 DIT Radix- FFT x[0] x[] x[4] x[6] x[1] x[3] x[5] x[7] X[0] X[1] X[] X[3] X[4] X[5] X[6] X[7] page-7 Signals of Frequency Domain Single bit signal in frequency domain page-8

5 Signals of Frequency Domain Subcarrier Center Point page-9 Signals of Frequency Domain page-10

6 Physical Property Frequency Domain Nominal Channel Bandwidth, BW Sampling Frequency, F s = floor(n BW/8000) 8000 Sampling factor, n = F s / BW Used Channel, Bandwidth = N used f Carrier Spacing, f = Fs / N FFT N used N FFT page-11 Physical Property Time Domain Channel Effect : The different arrival time will cause the ISI. Cyclic Prefix : Copy the last part of OFDM symbol to the front in the time domain. CP Length : 1/4, 1/8, 1/16, 1/3 T s = T g + T b = CP x T b + T b T b : Useful OFDM Symbol Time T g : Cyclic Prefix T s : Transmitted OFDM Symbol Time CP prevents the discontinuous effect of the guard interval. T s T g T b Cyclic Cyclic Prefix Prefix Data Data Payload Payload page-1

7 Multipath Influence ISI (inter-symbol interference) T cp > T delay-spread CP CP Symbol CP CP Symbol Two path model T d CP CP Symbol CP CP Symbol ICI (inter-channel interference) T cp < T delay-spread CP CP Symbol CP CP Symbol T d CP CP Symbol CP CP Symbol page-13 Circular Convolution Path_1 Other Symbol Path_ Cyclic Cyclic Prefix Prefix Data Data Payload Payload Other Symbol Other Symbol Path_3 Cyclic Cyclic Prefix Prefix Data Data Payload Payload Other Symbol Other Symbol Cyclic Cyclic Prefix Prefix Data Data Payload Payload Other Symbol ISI Free Region T b Length Y[K] = H[K] X[k] page-14

8 OFDMA Scalability Parameters Values System B.W.(MHz) Sampling frequency(fs,mhz) FFT Size Subcarrier Frequency Spacing Useful Symbol Time Guard Time OFDMA Symbol Time kHz / khz us / us Tg = Tb/8 = 10.9 us / 11. us ( Others: Tb/4 =.8575 us /.401 us, Tb/16 = us / us ) us / us (based on 8/5, 8/7 sampling factor) Frame Sizes (msec) OFDM symbols page-15 Duplex Mode 80.16(e) supports both TDD, H-FDD and FDD 5 ms 5 ms F1 DL UL DL UL TDD F1 F DL UL DL UL H-FDD (TDD over FDD) F1 F DL UL DL UL True FDD F1 F ΔT DL1 DL UL1 DL1 UL DL UL1 Hybrid FDD page-16

9 Properties of FDD & TDD FDD: Simultaneous transmission in uplink and downlink is possible. Asymmetric uplink and downlink traffic can not be supported. Channel reciprocity does not exit which is a disadvantage in case of AAS. Paired frequency bands are required. TDD: Flexible allocation of bandwidth in DL and UL Allows more effective MIMO techniques Transceiver design is cheaper and less complex page-17 Channel Coding To overcome the effect of the channel, WiMAX adopt different channel coding for different situations. Channel coding is composed of 3 steps: randomizer, FEC and interleaving. Transmitter: Data Randomizer FEC Interleaving Receiver: Data Randomizer FEC Interleaving Randomizer ( ) FEC FEC (8.4.9.) Bit Bit Interleaver ( ) Repetition ( ) Modulation ( ) Burst data Mapping to OFDM(A) subchannels page-18

10 Randomizer The generator polynomial: 1+x 14 +x 15 Except the preamble and FCH. OFDMA randomizer initial vector page-19 Encoding - CC Convolutional Code is the most common code. Constraint length=7, Code rate=1/ G1 = 171 OCT For X G = 133 OCT For Y page-0

11 Convolutional Decoder Viterbi Decoding: Search through space of all possible sentences. Pick the one that is most probable given the waveform. Trellis Diagram: 0/00 0/00 0/00 0/00 0/00 1/11 1/11 1/11 0/10 0/11 1/00 0/11 0/11 1/01 0/10 1/01 0/10 0/01 0/01 t 1 t t 3 t t 4 5 t 6 page-1 Conventional Turbo Code Encoding - CTC RSC1 Interleaver RSC page-

12 Concatenated Code Combination of two codes provides the greater coding gain with less implementation complexity as a comparable single code Typically, inner code is a convolutional code while the outer code is a block code Convolutional code cleans up low-input SNR s Block code cleans up the remaining errors page-3 m j k k = s floor Interleaver Interleaver can avoid long runs of lowly reliable bits. The first permutation ensure that adjacent coded bits are mapped onto nonadjacent subcarriers. = ( N cbps /1) k mod 1 + floor ( k /1), k = 0,1,... N cbps 1 The second permutation ensure that adjacent coded bits are mapped onto less or more significant bits of the constellation. ( mk / s) + ( mk + N cbps floor (1 mk / N cbps )) mod( s ) k = 0,1,... N cbps 1 s = ceil ( N cpc / ) 1,, 4, 6 for BPSK, QPSK,16-QAM, 64-QAM page-4

13 M x N Matrix Simple Interleaver Concept N N+1 N+ N+3 N+4 N (M-1)N+1 (M (M-1)N+ (M-1)N+3 (M-1)N+4 MN Output 1, N+1, N+1, (M-1)N+1, N+, N+, (M-1)N+ page-5 Repetition Code It can be used to increase signal margin over the modulation and FEC. After FEC and interleaver, the data is segmented into slots. UL: Ns = multiple of R DL: Ns = [ R K, R K+(R-1) ] R =, 4,6 This scheme applies only to QPSK and in all coding schemes except HARQ with CTC. page-6

14 Modulation The data bits are entered serially to the constellation mapper. The support of 64-QAM is optional for license-exempt bands. BPSK QPSK 16-QAM 64-QAM page-7 Adaptive Modulation and Coding (AMC) FEC Tail Biting CC, CTC without H-ARQ CTC with Chase Combining H-ARQ CTC with Incremental Redundancy H-ARQ* Modulation Types for CC QPSK-1/, -3/4 16QAM-1/, -3/4 64QAM-1/, -/3, -3/4 (DL only) Modulation Types for CTC QPSK-1/, -3/4 16QAM-1/, -3/4 64QAM-1/, -/3, -3/4, -5/6 (DL only) Modulation QPSK 16-QAM 64-QAM Code rate 1/ 3/4 1/ 3/4 1/ /3 3/4 Receiver SNR page-8

15 ARQ (Automatic Repeat request) Conventional ARQ Stop-and-wait ARQ Go-back-N ARQ Selective-repeat ARQ Hybrid ARQ Chase Combining (CC) Incremental Redundancy (IR) page-9 Chase Combining (CC) Each retransmission repeats the first transmission or part of it. Soft combining of original and retransmitted signals are done at receiver before decoding Same Data Data channel Feedback channel Data1 Data ack Data nack Data nack Data nack Data3 ack time Soft Combination page-30

16 Incremental Redundancy (IR) Each retransmission transmit the new code bits from the mother code to lower the code rate. Reducing the effective data throughput/bandwidth of a user Combine with the CTC. Different Data Data channel Data1 Data IR IRdata IRdata IR IRdata IRdata IR IRdata IRdata Data3 Feedback channel ack nack nack nack ack time Check puncture table and do IR Combination page-31 Simple Throughput Calculation page-3

17 Content I II Baseband Technology RF Technology I II III IV V Multi-Input Multi-Output Space Time Coding Spatial Multiplexing Collaborative SM Beamforming III Other Technology page-33 Multi-Input Multi-Output MIMO Encoder MIMO Sub-channel Mapping IFFT IFFT IFFT x 0 (t) x 1 (t) x N (t) h 00 h 10 h M0 y 0 (t) y 1 (t) (t) y M (t FFT y MIMO Decoder Y = HS + N M 1 M N N 1 N y p ( t) = h pn x n ( t) + n = 0 n( t) H h00 h10 = M hm 0 h h h M M 1 L L O L h h h 0N 1N M MN page-34

18 Antenna Diversity Receive (SIMO) Transmit (MISO) Both (MIMO) page-35 Capacity of MIMO Shannon bound: Capacity of 1 to M: Capacity of N to M: C P log (1 + ) σ = (bps/hz) C n P log (1 + M ) σ = (bps/hz) n C min{ M 1 P H = log (det( I + HH )) = N σ K log P (1 + σ n ) n (bps/hz) i = 1, N } log (1 + P σ n λ ) i The Shannon Theorem has been broken by diversity method. page-36

19 Multipath Number vs SNR page-37 Advanced Technology on MIMO Space time code (STC) Reduce fade margin by spatial diversity Open loop Peak rate limit Spatial multiplexing (SM) Improve capacity Open loop Requires good SINR and low spatial correlation Adaptive MIMO switch (AMS) Optimally select STC or SM to adapt to channel condition Reduced feedback AAS (beamforming) Improve link budget Reduce interference #Antennas 4 for good beamforming effect Requires CSI feedback (e.g. sounding), good for slow varying channel Only extends range for unit transmission page-38

20 Space Time Code (STC) Encoder S/P S S S 1 S * * 1 STC Decoder Transmitter: Antenna 0: Tx transmit s1 and s Antenna 1: Tx transmit s* and s1* Receiver: x 1 = h 0 * r 0 + h 1 r 1 * x = h 1 * r 0 -h 0 r 1 * [s 1 s ] T = H H X = ( h 0 + h 1 )[s 1 s ] T + N Decoding is very similar to maximum ratio combining. page-39 Spatial Multiplexing (SM) Each transmit antenna transmits independent information stream for high throughput Collaborative spatial multiplexing Mobile stations have one or two antennas, BS has multiple antennas. Two single transmit antenna SS's can perform collaborative spatial multiplexing onto the same subcarrier Result in the uplink capacity increment by assigning same uplink resource to two SS s simultaneously page-40

21 Matrix Book of Tx DL For - antenna BS, the code books are shown as following: S A = Si C = i r S S * i+ 1 * i S S i + i+ 1 jr S r S S i B = S i+ 3 i+ i+1 r S i+ 1 jr S i + S + S i+ i+ 3 SM operation mode for data stream: Vertical Encoding Horizontal Encoding, r 1 + = Choose matrix type and MIMO architecture, according to the channel characteristics, system profile (permutation type, antenna number) and encoding schemes. 5 page-41 MIMO Architecture Matrix A, Vertical Matrix B A for,3,4 Tx Tx B for 3 or or 4 Tx Tx page-4

22 MIMO Architecture Matrix B for Horizontal Encoding Layers It is the same for Matrix C The number of layers depends on the number of encoding/modulation paths. The number of STC output paths is the same between vertical and horizontal. page-43 Antenna Grouping / Selection The proposed STC code for 3Tx-rate 1 configuration with diversity order 3 is given by 3 permutation types. ~ ~ * S1 S 0 0 ~ ~ ~ ~ * A1 = S S1 S 3 S ~ ~ 0 0 * S 4 S 3 * 4 A ~ ~ ~ ~ * * S1 S S 3 S ~ ~ * = S S1 0 ~ ~ * 0 0 S 4 S 3 0 * 4 ~ ~ S1 S A3 = 0 0 ~ ~ * S S1 * 0 0 ~ ~ * S4 S3 ~ ~ * S4 S3 Tx1, Tx at subcarrier 1 Tx, Tx3 at subcarrier Tx1, Tx at subcarrier 1 Tx1, Tx3 at subcarrier Tx1, Tx at subcarrier 1 Tx1, Tx3 at subcarrier S jθ i = xi e for I = 1,,, 8, where θ = tan 1 ( ) ~ S1 = S1I + js3q ~ S 3 = S3I + js1 Q ~ ~ S = SI + js4q S 4 = S4I + js S Q i = SiI + SiQ 1 3 page-44

23 Adaptive MIMO Switch page-45 Diversity Combination Switched combining: the current branch is used until a metric fails a certain threshold (e.g. Received Signal Strength Indicator) Cheap and simple, but not ideal Selection combining: the most appropriate branch is always selected. Slight performance advantage over switch diversity. All diversity branches must be analysed RSSI is not ideal unduly affected by interference Equal Gain Combining: simply co-phase and sum all branches Multiple receive chains are required Maximal Ratio Combining: each branch is combined according to its signal-to-noise ratio. Optimal performance Requires multiple receive chains and S/N calculation page-46

24 Diversity Improve Performance BER Frequency-selective channel (no equalization) AWGN channel (no fading) BER floor Flat fading channel Frequency-selective channel (equalization or Rake receiver) SNR page-47 MIMO Simulation Demodulation scheme = Zero-Forcing detection Center frequency =.3GHz OFDM Symbol B.W. = 1.75MHz FFT size = 56 Np = 8 Modulation = QPSK Sampling Factor = 8/7 Sampling Frequency = MHz Length of Symbol = 18 us Length of guard interval = 16 us Maximum delay spread = 5 us No Channel Coding Ref: A Fine Frequency Synchronization and Tracking for Mobile WiMAX Broadcasting Systems page-48

25 Adaptive Array System (AAS) Requirements: Requires CSI feedback (e.g. sounding), good for slow varying channel #Antennas 4 for good beamforming effect Advantages: Extend range for unit transmission Improve link budge Reduce interference page-49 Beamforming & Smart Antenna SIGNAL BEAMFORMER WEIGHTS λc: wave length INTERFERENCE INTERFERENCE Signal s(t) w(r): spatial signature vector Array data in Complex Baseband Format : π j x1 r λc x1 ( t) e n1 ( t) x( t) = s( t) M = M + = M π j xm r x λ M ( t) c e nm ( t) w( r) s( t) + n( t) page-50

26 Frequency Reuse Factor ( BS num per cluster, Sector Num per BS, Useable Frequency per BS ) page-51 Fractional Frequency Reuse page-5

27 Coverage page-53 DL Budget for WiMAX page-54

28 DL Budget for WiMAX page-55 I II III Content Baseband Technology RF Technology Data Allocation I II III IV Frame Structure Zone Burst Subcarrier allocation page-56

29 OFDMA Frame Structure TDD page-57 Return DL & UL Data Allocation Slot is the minimum allocation unit. The length of slot depends on the permutation type. The data allocation is according to dimensions subchannel & symbol page-58

30 OFDMA Preamble page-59 OFDMA Preamble Index : [0 : 113] IDcell : [0 : 31] Segment: 0,1, Totally 14*4=568 bits (forced to zero when fit into DC carrier) 3*568=1704, 1704-DC carrier=1703, 1703-out of range=170 page-60

31 Midamble and Postamble Frame n-1 Frame n Frame n+1 Frame m DL subframe UL subframe LP FCH DL Burst 1 M DL Burst DL Burst Y Postamble Preamble SP Midamble UL Data Symbol 1 M UL Data Symbol P+1 UL Data Symbol Q P page-61 Subframe Structure OFDMA Subframe Structure Zones STC AAS Permutation Common Sync Symbol Bursts Sub-Bursts page-6

32 Multiple Zones in Sub- Frame Zone types: Normal, STC, AAS, Common Sync Symbol Permutation types (FUSC,PUSC,AMC) Other Parameters: Midamble, Boosting, Preamble Configuration, SDMA page-63 Permutation Contiguous Permutation (Band AMC) Diversity Permutation (FUSC PUSC) Downlink Permutation Band AMC (1*6, *3, 3*) FUSC Optional FUSC PUSC TUSC1, TUSC Uplink Permutation Band AMC (1*6, *3, 3*) PUSC Optional PUSC page-64

33 Permutation Explanation PUSC Partial usage of subchannels. Divide the subcarrier into clusters. Optional PUSC Advanced cluster structure. Only for UL. FUSC Full usage of subchannels. Only for DL. Optional FUSC Advanced cluster structure. Only for DL. AMC Advanced Modulation/Coding Adjacent subcarrier permutation TUSC1 Tile usage of subcarriers Only for DL + AAS. TUSC Tile usage of subcarriers Only for DL + AAS page-65 Permutation Tradeoff Benefits Scheduling Channel Condition Contiguous Permutation (Band AMC) Sub-channelization gain Frequency selective loading gain Advanced frequency scheduler to explore frequency selectivity gain Stationary channel Diversity Sub-carrier Permutation (PUSC,FUSC) Sub-channelization gain Frequency Diversity Inter-cell interference averaging Simple scheduler, Rely on frequency diversity to achieve robust transmission Fast-changing channel Favorable Smart Antenna Tech. Beamforming MIMO page-66

34 Slot Definition Permutation AMC PUSC Optional PUSC FUSC Optional FUSC TDSC1 TDSC Downlink 1 subchannel by,3,6 OFDMA symbol 1 subchannel by OFDMA symbols n/a 1 subchannel by 1 OFDMA symbol 1 subchannel by 1 OFDMA symbol 1 subchannel by 3 OFDMA symbols 1 subchannel by 3 OFDMA symbols Uplink 1 subchannel by,3,6 OFDMA symbol 1 subchannel by 3 OFDMA symbols 1 subchannel by 3 OFDMA symbols n/a n/a n/a n/a page-67 Subframe Structure OFDM(A) Frame Structure Zones Bursts Allocation Boosting Modulation Coding Sub-Bursts page-68

35 Burst For DL Frame Control Header (FCH) Map Data Burst (DL-MAP UL-MAP) Normal Data Burst AAS Burst (Optional) For UL Initial Ranging/Handover Ranging Periodic Ranging/Bandwidth Request HARQ ACK Channel Fast Feedback Channel PAPR/Safety Zone Sounding Zone Normal Data Burst page-69 FCH Sub channel bit map RNG REP Coding DL-Map Len Reserved 6 bits 1 bit bits 3 bits 8 bits 4 bits Frame Control Header Used subchannels bitmap 6 groups Ranging Change Indicator Periodic/B.W. Request DL-Map Coding parameters Repetition Coding Indicator (1,,4,6) Coding Indicator CC (mandatory), BTC, CTC or ZT CC DL-MAP Length Total 4 bits Fixed Location and Coding Rate: None FFT-18 First 4 slots of the segment QPSK rate ½ with repetition coding of 4 FFT-18 Only the first slot No repetition code page-70

36 DL-MAP FCH DL-MAP Coded Information Data Coding Parameters FEC decoder Combine Collect a symbol block for FEC decoder S 0 S 1 S n S 0 S 1 S n MAC Message page-71 MAP Message Type page-7

37 Downlink Map page-73 OFDMA Ranging Initial-ranging / handover-ranging N1 = or 4 symbols Periodic-ranging / BW-request N1 = 1 or 3 symbols N = 6 for default 8 for optional page-74

38 CDMA_Allocation_IE Duration in units of OFDMA slots Ranging Code CDMA code sent by the SS Ranging Symbol the OFDMA symbol used by SS Ranging subchannel indicates the subchannel used BW request mandatory indicates whether SS shall include a BW request in the allocation page-75 Ranging Code A set of 56 special PN 144 bit-long ranging codes are divided into 4 groups for initial, periodic ranging, bandwidth requests and handover-ranging. 144bits are used to modulate the subcarriers in a group of 6 adjacent subchannels. These codes are BPSK modulated onto the subcarriers in the ranging channel. (1 bit per subcarrier) page-76

39 150 Auto Correlation decode ranging code autocorrelation 100 For six users R(t) 60 decode ranging code autocorrelation shift For one user R(t) shift page-77 UL ACK Channel Provides feedback for Downlink HARQ One ACK channel occupies half subchannel by three OFDMA symbols 3 pieces of 4x3 uplink tile in the case of PUSC 3 pieces of 3x3 uplink tile in the case of optional PUSC ACK coding If 0 for ACK, modulation vector 0,0,0 on ACK channel If 1 for NACK, modulation vector 4,7, on ACK channel ACK Channel Modulated by the QPSK symbol Even and odd half subchannel 1 ACK Channel (mini-subchannel) Tile(0) Tile(0) Tile(1) Tile(1) Tile() Tile() Tile(3) Tile(3) Tile(4) Tile(4) Tile(5) Tile(5) page-78

40 Fast Feedback Channel Slots are shared by multiple channels. Controlled by CQICH IE (control/allocation) Type: Normal fast feedback channel Used for STTD, SM, Permutation, Precoding Selection, MCS Enhanced fast feedback channel Normal + Anchor BS report Band AMC differential CINR feedback Indication Flag Feedback Primary/Secondary fast feedback channel Extended rtps bandwidth request MIMO feedback for transmit beamforming page-79 PAPR/Safety Zone PAPR Zone reduces the PAPR value. Safety Zone reduces the interference between BSs. PAPR reduction/safety zone/sounding zone allocation IE page-80

41 Sounding Zone UL Channel Sounding is a means of providing channel response information to the BS on an as-needed basis Intended for TDD systems where UL&DL RF reciprocity can be leveraged Simple, efficient, low complexity, and effective Periodicity feature can be used to significantly reduce sounding-command-ie overhead if continual sounding is required Frequency UL-MAP UL-MAP DL-MAP DL-MAP page-81 Subcarrier Allocation in DL PUSC Dividing the subcarriers into the number of physical clusters Renumbering the physical clusters into logical clusters For first DL Zone RenumberingSequence (PhysicalCluster) For others RenumberingSequence((PhysicalCluster) + 13 DL_PermBase)mod N clusters Allocate logical clusters to group Dividing the clusters into 6 major groups G0: cluster 0-11, G1:1-19, G5:5-59 for 104-FFT Allocating subcarriers to subchannel in each major group Even group: use basic permutation sequence 6 Odd group: use basic permutation sequence 4 page-8

42 Subcarrier Allocation in DL PUSC page OFDMA DL carrier allocation - PUSC page-84

43 Band AMC Allocation AMC allocation can be made by two mechanisms Subchannel index reference in DL / UL MAP A slot is defined as N bines by M symbols NxM = 6 Subchannel allocation in a band using HARQ map A group of 4 rows of bins is called a physical band A slot consists of 6 contiguous bins in a band AMC slot AMC slot page OFDMA DL carrier allocation - AMC page-86

44 FUSC Pilot in Diversity Permutation DL PUSC Cluster Structure Even symbol Odd symbol Symbol 0 Symbol 1 Symbol UL PUSC Tile Structure UL OPUSC Tile Structure page-87 Cluster Structure for FUSC For even symbols Antenna 0 uses VariableSet#0 and ConstantSet#0 Antenna 1 uses VariableSet#1 and ConstantSet#1 For odd symbols Antenna 0 uses VariableSet#1 and ConstantSet#0 Antenna 1 uses VariableSet#0 and ConstantSet#1 page-88

45 Subchannel Number for Permutation Downlink Uplink FUSC PUSC AMC 6 X 1 AMC 3 X AMC X 3 AMC 1 X 6 PUSC AMC 6 X 1 AMC 3 X AMC X 3 AMC 1 X 6 FFT FFT FFT FFT page-89 Pilot Modulation The polynomial for the PRBS generator is X 11 +X 9 +1 The sequence is The third 1 is W =1, shall be used in the first OFDM downlink symbol following the frame preamble page-90

46 Cluster Structure for PUSC using 4 antennas page-91 STC in Uplink For STTD (Space-Time Transmit Diversity) Mode Antenna 0 (Pattern A) Antenna 1 (Pattern B) For SM (Spatial Multiplexing) Mode Horizontal mode: First burst on antenna 0, Second burst on antenna 1 Vertical Mode: consecutive slots are mapped instead of a single slot. First slot of each slot pair on antenna 0. Second slot on antenna 1. For both modes, the pilot allocation is the same with STTD mode. page-9

47 Collaborative Spatial Multiplexing For single transmit antenna SS s One use uplink tile with pattern A Another one use tile with pattern B For dual transmit antennas SS s One use uplink tile with pattern A,B Another one use tile with pattern C,D Pattern C Pattern D page-93 Reference IEEE Standard for Local and metropolitan area networks IEEE Std 80.16e -005 and IEEE Std /Cor1-005 Performance of Convolutional Turbo Coded High-speed Portable Internet (WiBro) System, 007 OFDMA PHY SAP Interface Specification for Broadband Wireless Access Base Station IEEE 80.16e-005 Air Interface Overview Timing Recovery for OFDM Transmission, Baoguo Yang, Member, IEEE, Khaled Ben Letaief, Roger S. Cheng, Member, IEEE, and Zhigang Cao, Senior Member, IEEE Closed-Loop MIMO for Rel.1.x FDD Operation, Wen Tong, Peiying Zhu, Mo- Han Fong, SangYoub Kim, Michael Wang Nortel Networks, Aug, 007 page-94