1. September 2004
doc.: IEEE n
September 2004
Institute for Infocomm Research (I2R) TGn MIMO-OFDM PHY Partial Proposal - Presentation Sumei SUN, Chin Keong HO, Patrick FUNG, Yuan LI, Yan WU, Zhongding LEI, Woon Hau CHIN, Ying-Chang LIANG, Francois CHIN ( to:
Institute for Infocomm Research (I2R)
Sumei Sun et. al., I2R

2. Outline Summary of Key Points MIMO Structures and Data Rate
September 2004
doc.: IEEE n
September 2004
Outline
Summary of Key Points
MIMO Structures and Data Rate
PLCP Frame Format
Preamble
OFDM Processing
FEC
Performance
Conclusions
Institute for Infocomm Research (I2R)
Sumei Sun et. al., I2R

3. September 2004
doc.: IEEE n
September 2004
Summary of Key Points
OFDM modulation over 40MHz channel with FFT size of 128;
Support of two concurrent 11a transmissions in downlink;
Peak data rate of 216Mbps;
Mandatory support of 2×2 MIMO
Spatial multiplexing (SM);
Orthogonal STBC.
Optional support of 4×2 MIMO for downlink (from access point to terminal station )
groupwise STBC (GSTBC);
orthogonal STBC;
antenna beamforming;
antenna selection.
Institute for Infocomm Research (I2R)
Sumei Sun et. al., I2R

4. Summary of Key Points – Cont’d
September 2004
doc.: IEEE n
September 2004
Summary of Key Points – Cont’d
Efficient training signal design (preambles) that supports robust frequency and timing synchronization and channel estimation;
Bit-interleaved coded modulation (BICM)
Mandatory support of K=7 convolutional code;
Optional support of low-density parity check (LDPC) code.
An optional 2-D linear pre-transform in both frequency and spatial domain to exploit the frequency and spatial diversities.
Institute for Infocomm Research (I2R)
Sumei Sun et. al., I2R

5. MIMO Structures Mandatory 2×2 MIMO Optional 4×2 MIMO
September 2004
doc.: IEEE n
September 2004
MIMO Structures
Mandatory 2×2 MIMO
Spatial multiplexing (SM);
Orthogonal STBC.
Optional 4×2 MIMO
4 antennas at access point, and 2 at terminal station;
4 modes
Groupwise STBC (GSTBC);
Orthogonal STBC;
Fixed antenna beamforming;
Antenna selection.
Institute for Infocomm Research (I2R)
Sumei Sun et. al., I2R

6. Mandatory Mode 1 - 2×2 Spatial Multiplexing
September 2004
Mandatory Mode 1 - 2×2 Spatial Multiplexing
Source bits
scrambler
S/P
FEC
2-D Bit interleaver
OFDM
2-D Pre-transform
(optional)
Up to 216 Mbps information data rate;
Parallel FEC
Better scalability and less stringent decoder design requirement;
Little loss in spatial diversity with the 2-D interleaver.
2-D interleaver and 2-D pre-transform to exploit frequency and spatial diversity;
Lower PAPR with the use of PT.
Institute for Infocomm Research (I2R)

7. 11a compliant bit interleaver
September 2004
2-D Interleaver
2-D Bit interleaver
FEC
mapper
11a compliant bit interleaver
2-D symbol interleaver
Bit interleavers to exploit the frequency diversity;
Symbol interleaver operates in both frequency and spatial domain, to exploit the spatial domain diversity
Simple and effective.
Institute for Infocomm Research (I2R)

8. 2-D Pre-transform where T is the transformation matrix satisfying
September 2004
2-D Pre-transform
where
denotes the 1st data stream symbol vector
denotes the 2nd data stream symbol vector
T is the transformation matrix satisfying
If pre-transform is applied only in frequency domain, we have
Institute for Infocomm Research (I2R)

9. Mandatory Mode 2 - 2×2 STBC 2nd order transmit diversity
September 2004
Mandatory Mode 2 - 2×2 STBC
Source bits
scrambler
FEC
Bit interleaver
mapper PT
STBC
OFDM
2nd order transmit diversity
Improve wireless link quality;
Range extension.
Time-domain STBC implementation reduces transmitter complexity by using the FFT property
Institute for Infocomm Research (I2R)

10. September 2004
Time-domain STBC
The frequency-domain STBC shall satisfy the following in order to be backward compatible to 11a
Antenna 0
Antenna 1
time t
SF,0 = [SF,0(0), SF,0(1),… SF,0(N - 1)]
-S*F,1
time t+NT
SF,1 = [SF,1(0), SF,1(1),… SF,1(N - 1)]-
S*F,0
The corresponding time-domain STBC will be
Antenna 0
Antenna 1
time t
St,0=[ S t,0(0), S t,0(1),…, S t,0(N-1)]
[ -S t,1* (0), -S t,1* (N-1),…,-S t,1* (1)]
time t+NT
S t,1=[ S t,1(0), S t,1(1),…, S t,1(N-1)]
[ S t,0*(0), S t,0*(N-1),…,S t,0*(1)]
Institute for Infocomm Research (I2R)

11. Optional modes of 4×2 MIMO – WHY?
September 2004
Optional modes of 4×2 MIMO – WHY?
Rationale
AP usually has a large size and hence more antennas can be accommodated;
AP can afford higher power consumption.
Benefits
higher order of space diversity for both uplink (station to AP) and downlink (AP to Station);
More robust performance;
Possible range extension;
Little additional processing complexity.
Institute for Infocomm Research (I2R)

12. Optional modes of 4×2 MIMO – What?
September 2004
Optional modes of 4×2 MIMO – What?
Downlink
4×2 GSTBC;
4×2 STBC;
Fixed beamforming;
2×2 SM with transmit antenna selection.
Uplink
2×4 SM and 2×4 orthogonal STBC;
2×2 SM with receive antenna selection;
Fixed beamforming.
Institute for Infocomm Research (I2R)

13. Optional mode of 4×2 MIMO – 4×2 GSTBC
September 2004
Optional mode of 4×2 MIMO – 4×2 GSTBC
Source bits
scrambler
S/P
FEC
2-D Bit interleaver
OFDM
2-D Pre-transform
(optional)
STBC
Same data rate as 2×2 SM;
More robust performance and extended range than 2×2 SM with the 2nd order transmit diversity.
Very simple linear detection at the receiver;
No CSI needed at transmitter;
2 additional DAC and RF chains.
Institute for Infocomm Research (I2R)

14. Optional mode of 4×2 MIMO – 4×2 Orthogonal STBC
September 2004
Optional mode of 4×2 MIMO – 4×2 Orthogonal STBC
Source bits
randomization
FEC
Bit interleaver
mapper PT
STBC
OFDM
8th order space diversity (4th order transmit × 2nd order receive diversities)
range extension
robust performance
Linear processing for ML detection;
No CSI needed at transmitter;
2 additional DAC and RF chains;
Selection of the orthogonal STBC can be co-optimized with the coding rate and modulation scheme.
Institute for Infocomm Research (I2R)

15. Optional mode of 4×2 MIMO – Fixed Beam Multiplexing
September 2004
Optional mode of 4×2 MIMO – Fixed Beam Multiplexing
Used when the AP antenna correlation is high;
Time-domain beam-forming to achieve uncorrelated equivalent channels;
A set of beam-forming weights have been pre-stored, and AP just needs to select two on line which correspond to largest gains;
Multiplexing Gain
Beamforming Gain
No change to terminal station
Closed-loop.
Institute for Infocomm Research (I2R)

16. Optional mode of 4×2 MIMO – Fixed Beam Multiplexing (Cont’d)
September 2004
Optional mode of 4×2 MIMO – Fixed Beam Multiplexing (Cont’d) h1 s1 s2 + x1 x2 x3 x4 w1 w2 2
Conventional MIMO Detector 1
(1, 12)
(2, 21)
(2, 22)
(1, 11) h2
The overall channel
where
-- physical vector channel observed by each receive antenna;
for ULA, P = 2 in the example
Orthogonal beams w1 & w2
Uncorrelated h1 & h2
Institute for Infocomm Research (I2R)

17. Optional mode of 4×2 MIMO –Antenna Selection for 2×2 SM
September 2004
Optional mode of 4×2 MIMO –Antenna Selection for 2×2 SM s1 s2
switch
receiver
feedback bits
Station AP
Multiplexing Gain – higher throughput
Diversity Gain – full diversity as using four baseband + RF chains
Less complex AP – with two baseband + RF chains
Only three bits feedback needed
Institute for Infocomm Research (I2R)

18. 2×2 Spatial Multiplexing with Transmit Antenna Selection
September 2004
2×2 Spatial Multiplexing with Transmit Antenna Selection
Three bits feedback for all subcarriers per package
Bits
Selected antennas
000
#1 and #2
001
#1 and #3
010
#1 and #4
011
#2 and #3
100
#2 and #4
101
#3 and #4
110
reserved
111
Institute for Infocomm Research (I2R)

19. One Step Ahead - SVD Beamforming for 4×4 SM-OFDM
September 2004
One Step Ahead - SVD Beamforming for 4×4 SM-OFDM
Using
sub-channel grouping (SCG) to generate 4 grouped channels;
Multi-target overall-channel inversion (MT-OCI) power control to
convert the first three channels into “AWGN” channels, and the 4th channel not to be used;
Then optimal bit loading can be done for the three “AWGN” channels;
As high as 18 bits can be transmitted per data subcarrier.
Institute for Infocomm Research (I2R)

20. September 2004
Supported Data Rate - 2×2 SM, 4×2 GSTBC, SM with antenna selection and antenna beamforming
Data
Rate
(Mbps)
Modu-lation
Coding
rate
(R)
Coded bits per subcarrier
Coded bits per OFDM symbol
Data bits per OFDM symbol
Coded bits per MIMO- OFDM symbol
Data bits per MIMO-OFDM symbol 24
BPSK
1/2 1 96 48
192 36
3/4 72
144
QPSK 2
384
288
16-QAM 4
768
576
64-QAM 6
1152
216
432
864
Institute for Infocomm Research (I2R)

21. Supported Data Rate - 2×2 STBC
September 2004
Supported Data Rate - 2×2 STBC
Data
Rate
(Mbps)
Modu-lation
Coding
rate
(R)
Coded bits per subcarrier
Coded bits per OFDM symbol
Data bits per OFDM symbol
Coded bits per MIMO- OFDM symbol
Data bits per MIMO-OFDM symbol 12
BPSK
1/2 1 96 48 18
3/4 72 24
QPSK 2
192 36
144
16-QAM 4
384
288
64-QAM 6
576
108
432
Institute for Infocomm Research (I2R)

22. Supported Data Rate - 4×2 STBC
September 2004
Supported Data Rate - 4×2 STBC
To be determined later.
Institute for Infocomm Research (I2R)

23. September 2004
PLCP Frame Format
Institute for Infocomm Research (I2R)

24. PLCP Frame Format The rate bits are used to indicate
September 2004
PLCP Frame Format
The rate bits are used to indicate
Legacy mode or high throughput mode;
Coding scheme and code rate;
Modulation scheme;
Number of transmit antennas;
Transmission mode;
PT activated or de-activated;
Etc.
The length bits are used to indicate
The packet length.
Institute for Infocomm Research (I2R)

25. Preamble 8 short preambles Same for all transmit antennas;
September 2004
Preamble
17  0.8µs = 13.6µs
8  0.8µs = 6.4µs
SP5
SP1
SP2
SP3
SP4
SP7
SP6
SP8
CP2
LP1
LP2
LP4
LP3
= 20µs
= 4.0µs
Signal Detect,
AGC
Freq. Offset
Estimation,
Timing Synch
Channel Estimation,
Residual Frequency Offset Estimation CP
Data 1
Data 2
SF2
SF1

RATE, LENGTH
DATA
8 short preambles
Same for all transmit antennas;
Occupying 6.4 μs, for signal detection, AGC, frequency and time synchronization.
Institute for Infocomm Research (I2R)

26. Unique Long Preamble 4 long preambles
September 2004
Unique Long Preamble
4 long preambles
For channel estimation and residual frequency offset estimation
Data subcarriers  channel estimation
Pilot subcarriers  phase compensation starting in long preamble;
Resulting in more accurate channel estimation.
Overall time duration of 13.6 s;
Design Criteria
Orthogonal in space for all data subcarriers;
Last 32 points of the 4 LP’s have the same time-domain values.
Advantages
Simple and accurate channel estimation;
Low overhead.
Institute for Infocomm Research (I2R)

27. Construction of Long Preambles
September 2004
Construction of Long Preambles
Antenna 1: {L, L, L, L} + {P, P, P, P}
Antenna 2: {L, -L, L, -L} + {P, P, P, P}
Antenna 3: {L, L,-L, -L} + {P, P, P, P}
Antenna 4: {L, -L,-L, L} + {P, P, P, P} L P
Institute for Infocomm Research (I2R)

28. September 2004
4 Long Preamble – Why?
Robust channel estimation and residual frequency offset correction for 2×2 SM and STBC
Less degradation due to channel and frequency offset estimation errors;
Compensating the lack of diversity in 2×2 systems.
Higher diversity order in 4×2 systems, hence better tolerance for channel estimation errors
Institute for Infocomm Research (I2R)

29. OFDM Processing Requiring more stringent filtering than 11a.
September 2004
doc.: IEEE n
September 2004
OFDM Processing
Backward compatible with IEEE a;
Support of two concurrent downlink 11a transmissions;
The two “11a null subcarriers” can be used for noise power estimation.
Requiring more stringent filtering than 11a.
Institute for Infocomm Research (I2R)
Sumei Sun et. al., I2R

30. FEC - Mandatory Simple;
September 2004
FEC - Mandatory
Simple;
No additional hardware needed to support legacy 11a.
Institute for Infocomm Research (I2R)

31. FEC - Optional Rate-compatible partial-differential LDPC;
September 2004
FEC - Optional
Rate-compatible partial-differential LDPC;
H1 designed using progressive edge growth (PEG);
Same mother code optimized for R=3/4 to be used to generate R=1/2;
Unequal error protection for QAM signals in the interleaving pattern.
Institute for Infocomm Research (I2R)

32. Unequal Error Protection for QAM
September 2004
Unequal Error Protection for QAM
Basic Principle: Systematic bits in LDPC require more protection than parity check bits
put as many as possible the systematic bits in MSB
Step 1: Write coded sequence (systematic + parity) into a rectangular block of , put systematic bits into MSB positions.
Step 2: reshaped the block I into
Then permute columns by
Institute for Infocomm Research (I2R)

33. Simulation Conditions
September 2004
Simulation Conditions
Channel B and Channel E;
1 wavelength antenna spacing;
2×2 SM and 4×2 GSTBC
Packet length 1000 bytes
LMMSE filtering for detection;
Soft decision Viterbi decoding with truncation length of 70 for CONV;
Iterative sum-product decoding for LDPC;
LMMSE channel estimation;
Double correlation-based frequency synchronization and phase compensation.
Institute for Infocomm Research (I2R)

34. Simulated coding and modulation schemes
September 2004
Simulated coding and modulation schemes
Code rate
R=1/2
R=3/4
Modulation
QPSK
16QAM
64QAM
Data Rate
48 Mbps
96 Mbps
216 Mbps
Institute for Infocomm Research (I2R)

35. Performance – Channel B, Conv (2×2 SM vs. 4×2 GSTBC)
September 2004
Performance – Channel B, Conv (2×2 SM vs. 4×2 GSTBC)
Perfect channel estimation and synchronization;
SNR gain of 3, 3, and 5.8 dB for 48, 96, and 216 Mbps, respectively at PER =
Institute for Infocomm Research (I2R)

36. Performance – Channel E, Conv (2×2 SM vs. 4×2 GSTBC)
September 2004
Performance – Channel E, Conv (2×2 SM vs. 4×2 GSTBC)
Perfect channel estimation and synchronization;
SNR gain of 2.6, 2.8, and 6.3 dB for 48, 96, and 216 Mbps, respectively at PER =
Institute for Infocomm Research (I2R)

37. September 2004
Performance – Channel B, Conv (2×2 SM, Practical channel est and synchronization)
Performance degradation of only 1.04, 0.7, and 0.1 dB, respectively.
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38. September 2004
Performance – Channel E, Conv (2×2 SM, Practical channel est and synchronization)
Performance degradation of only 0.92, 0.8, and 1.52 dB, respectively.
Institute for Infocomm Research (I2R)

39. September 2004
Performance – Channel B, Conv (4×2 GSTBC, Practical channel est and synchronization)
Performance degradation of only 2.54, 1.82, and 1.67 dB, respectively.
Institute for Infocomm Research (I2R)

40. September 2004
Performance – Channel E, Conv (4×2 GSTBC, Practical channel est and synchronization)
Performance degradation of only 2.10, 1.66, and 1.78 dB, respectively.
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41. September 2004
Performance – Channel B, Conv (2×2 SM vs. 4×2 GSTBC, Practical channel est and synchronization)
Performance improvement of 1.50, 1.88, and 4.23 dB, respectively.
Institute for Infocomm Research (I2R)

42. September 2004
Performance – Channel E, Conv (2×2 SM vs. 4×2 GSTBC, Practical channel est and synchronization)
Performance improvement of 1.42, 1.94, and 6.04 dB, respectively.
Institute for Infocomm Research (I2R)

43. Summary of Performance Gains of GSTBC over SM
September 2004
Summary of Performance Gains of GSTBC over SM
Channel B
Channel E
QPSK, ½
1.42 dB
1.50 dB
16QAM, ½
1.94 dB
1.88 dB
64QAM, ¾
6.04 dB
4.23 dB
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44. 2×2 SM CONV-PT-OFDM, Chan E
September 2004
2×2 SM CONV-PT-OFDM, Chan E
Perfect channel estimation and synchronization;
QPSK modulation;
Rotated DFT used as the PT;
Block-iterative generalized decision feedback equalization (BI-GDFE);
2x2 SM, SNR gain w.r.t. coded OFDM is 1.1 dB at PER = (2.4 dB with feedback).
4x4 SM, SNR gain is 2.5 dB (4 dB with feedback).
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45. Performance – Conv vs LDPC, Chan B
September 2004
Performance – Conv vs LDPC, Chan B
Perfect channel estimation and synchronization;
LMMSE detection;
R=3/4, 64QAM, 216Mbps;
SNR gain of 2.8 and 2.5 dB for 2×2 SM and 4×2 GSTBC, respectively at PER =
Institute for Infocomm Research (I2R)

46. September 2004
Performance – Conv vs LDPC, Chan B (2×2 SM vs. 4×2 GSTBC, Practical channel est and synchronization)
Institute for Infocomm Research (I2R)

47. September 2004
Performance – Conv vs LDPC, Chan E (2×2 SM vs. 4×2 GSTBC, Practical channel est and synchronization)
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48. Summary of Performance Comparison between LDPC and CONV
September 2004
Summary of Performance Comparison between LDPC and CONV
Gain in dB of LDPC over CONV at PER=10-2
Channel B
Channel E
2x2 SM
QPSK, ½
0.25
1.50
16QAM, ½
1.20
2.20
64QAM, ¾
2.50
5.80
4x2 GSTBC
0.20
1.00
2.00
3.00
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49. September 2004
Summary & Conclusions
2×2 SM and STBC as the mandatory modes, and 4×2 GSTBC, STBC, beamforming, and antenna selection as the optional modes;
GSTBC provides significant performance gain over SM;
Subcarrier arrangement can support two concurrent 11a transmissions in downlink;
Novel and efficient preamble design that supports robust FOE and channel estimation;
Proposed LDPC in the optional mode which provides large performance gain over convolutional code for the peak data rate support;
Proposed PT in the optional mode which can be used for range extension .
Institute for Infocomm Research (I2R)

50. September 2004
doc.: IEEE n
September 2004
References
[1] S. M. Alamouti, “A simple transmit diversity technique for wireless communications”, IEEE JSAC, vol. 16, no. 8, pp – 1458, October 1998
[2] V. Tarokh, H. Jafarkhani, and A. R. Calderbank, “Space-time block codes from orthogonal designs,” IEEE Trans. Inform. Theory, vol. 45, pp. 1456–1467, July 1999.
[3] IEEE std a-1999 (Supplement to IEEE Std ), “Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: High-speed Physical Layer in the 5GHz Band”.
Institute for Infocomm Research (I2R)
Sumei Sun et. al., I2R

51. Thank You! September 2004 doc.: IEEE 802.11-04-0876-01-000n
Institute for Infocomm Research (I2R)
Sumei Sun et. al., I2R