1 / 51

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.

robertahall
Download Presentation

MIMO-OFDM PHY Proposal - Presentation

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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)

More Related