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MIMO-OFDM PHY Proposal - Presentation

This presentation provides a summary of key points, MIMO structures and data rate, PLCP frame format, OFDM processing, FEC, and performance of the MIMO-OFDM PHY proposal by the Institute for Infocomm Research (I2R). The proposal supports various MIMO configurations and optional modes for improved performance and range extension.

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MIMO-OFDM PHY Proposal - Presentation

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  1. Institute for Infocomm Research (I2R)TGn MIMO-OFDM PHY Partial Proposal - PresentationSumei SUN, Chin Keong HO, Patrick FUNG, Yuan LI, Yan WU, Zhongding LEI, Woon Hau CHIN, Ying-Chang LIANG, Francois CHIN(email to: sunsm@i2r.a-star.edu.sg) Institute for Infocomm Research (I2R)

  2. Outline • Summary of Key Points • MIMO Structures and Data Rate • PLCP Frame Format • Preamble • OFDM Processing • FEC • Performance • Conclusions Institute for Infocomm Research (I2R)

  3. Summary of Key Points • OFDM modulation over 40MHz channel with FFT size of 128; • Peak data rate of 216Mbps; • Mandatory support of 2×2 MIMO • Spatial multiplexing (SM); • Orthogonal STBC. • Optionalsupport of4×2 MIMO for downlink (from access point to terminal station ) • groupwise STBC (GSTBC); • orthogonal STBC; • antenna beamforming; • antenna selection. • Support of two concurrent 11a transmissions in downlink. Institute for Infocomm Research (I2R)

  4. 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)

  5. 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)

  6. scrambler FEC 2-D Bit interleaver 2-D Pre-transform (optional) OFDM Source bits S/P scrambler FEC OFDM Mandatory Mode 1 - 2×2 Spatial Multiplexing • Up to 216 Mbps information data rate; • Parallel FEC • Better scalability andless stringent decoder design requirement; • Littleloss 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. 2-D Bit interleaver 11a compliant bit interleaver mapper FEC 2-D symbol interleaver 11a compliant bit interleaver mapper FEC 2-D 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 • denotes the 1st data streamsymbol 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. Source bits OFDM STBC Bit interleaver scrambler FEC mapper PT Mandatory Mode 2 - 2×2 STBC • 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. Time-domain STBC • The frequency-domain STBC shall satisfy the following in order to be backward compatible to 11a • The corresponding time-domain STBC will be Institute for Infocomm Research (I2R)

  11. 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? • 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. scrambler FEC 2-D Bit interleaver 2-D Pre-transform (optional) STBC Source bits OFDM S/P STBC OFDM scrambler FEC Optional mode of 4×2 MIMO – 4×2 GSTBC • Same data rate as 2×2 SM; • More robust performance and extended range than2×2 SM with the2nd 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. Source bits STBC OFDM Bit interleaver randomization FEC mapper PT Optional mode of 4×2 MIMO – 4×2 Orthogonal STBC • 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 • 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. w1 s1 x1 + (1, 12) 1 x2 (1, 11) (2, 21) 2 x3 w2 s2 x4 (2, 22) h2 h1 Conventional MIMO Detector Optional mode of 4×2 MIMO – Fixed Beam Multiplexing (Cont’d) 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. switch s1 receiver s2 feedback bits Optional mode of 4×2 MIMO –Antenna Selection for 2×2 SM 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 • Three bits feedback for all subcarriers per package Institute for Infocomm Research (I2R)

  19. 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. Supported Data Rate - 2×2 SM, 4×2 GSTBC, SM with antenna selection and antenna beamforming Institute for Infocomm Research (I2R)

  21. Supported Data Rate - 2×2 STBC Institute for Infocomm Research (I2R)

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

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

  24. 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. 6.4 + 13.6 = 20µs 8  0.8µs = 6.4µs 17  0.8µs = 13.6µs LP1 LP2 LP4 SP1 SP5 LP3 CP2 SP6 SP8 Freq. Offset Estimation, Timing Synch Channel Estimation, Residual Frequency Offset Estimation Signal Detect, AGC 0.8 + 3.2 = 4.0µs 0.8 + 3.2 = 4.0µs 0.8 + 3.2 = 4.0µs SP2 SP3 SP7 SP4 0.8 + 3.2 = 4.0µs CP CP Data 1 Data 2  CP SF1 CP SF2 RATE, LENGTH DATA DATA Preamble • 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 • 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 • 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. 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 • Backward compatible with IEEE 802.11a; • 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)

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

  31. 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 • 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 • 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 Institute for Infocomm Research (I2R)

  35. 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 = 10 -2. Institute for Infocomm Research (I2R)

  36. 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 = 10 -2. Institute for Infocomm Research (I2R)

  37. Performance – Channel B, Conv(2×2 SM, Practical channel est and synchronization) • Performance degradation of only 1.04, 0.7, and0.1 dB, respectively. Institute for Infocomm Research (I2R)

  38. Performance – Channel E, Conv(2×2 SM, Practical channel est and synchronization) • Performance degradation of only 0.92, 0.8, and1.12dB, respectively. Institute for Infocomm Research (I2R)

  39. Performance – Channel B, Conv(4×2 GSTBC, Practical channel est and synchronization) • Performance degradation of only 2.54, 1.82, and1.67dB, respectively. Institute for Infocomm Research (I2R)

  40. Performance – Channel E, Conv(4×2 GSTBC, Practical channel est and synchronization) • Performance degradation of only 2.10, 1.66, and1.78dB, respectively. Institute for Infocomm Research (I2R)

  41. Performance – Channel B, Conv(2×2 SM vs. 4×2 GSTBC, Practical channel est and synchronization) • Performance improvement of 1.50, 1.88, and4.23 dB, respectively. Institute for Infocomm Research (I2R)

  42. Performance – Channel E, Conv(2×2 SM vs. 4×2 GSTBC, Practical channel est and synchronization) • Performance improvement of 1.42, 1.94, and5.64 dB, respectively. Institute for Infocomm Research (I2R)

  43. Summary of Performance Gains of GSTBC over SM Institute for Infocomm Research (I2R)

  44. 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 = 10 -2 (2.4 dB with feedback). • 4x4 SM, SNR gain is 2.5 dB (4 dB with feedback). Institute for Infocomm Research (I2R)

  45. 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 = 10 -2. Institute for Infocomm Research (I2R)

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

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

  48. Summary of Performance Comparison between LDPC and CONV Institute for Infocomm Research (I2R)

  49. 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. References [1] S. M. Alamouti, “A simple transmit diversity technique for wireless communications”, IEEE JSAC, vol. 16, no. 8, pp. 1451 – 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 802.11a-1999 (Supplement to IEEE Std 802.11 -1999), “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)

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