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IEEE 802.11n PHY Motorola HT Partial Proposal

IEEE 802.11n PHY Motorola HT Partial Proposal. Alexandre Ribeiro Dias, Stéphanie Rouquette-Léveil, Markus Muck, Marc de Courville, Jean-Noël Patillon, Sébastien Simoens, Karine Gosse, Keith Blankenship, Brian Classon Motorola Labs. Overview. Overall goal and key features of proposal

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IEEE 802.11n PHY Motorola HT Partial Proposal

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  1. IEEE 802.11n PHY Motorola HT Partial Proposal Alexandre Ribeiro Dias, Stéphanie Rouquette-Léveil, Markus Muck, Marc de Courville, Jean-Noël Patillon, Sébastien Simoens, Karine Gosse, Keith Blankenship, Brian Classon Motorola Labs

  2. Overview • Overall goal and key features of proposal • Turbo Codes • Multiple-Antenna schemes • OFDM modulator and data rates • Preamble definitions • Simulation results • Hardware complexity estimation

  3. Overall goal of the proposed PHY design Modification of IEEE 802.11a-1999 PHY in order to provide new OFDM PHY modes meeting the IEEE802.11n PAR with: • High spectrum efficiency for achieving target performance with increased data rates • Data streams transmitted in parallel using multi-antenna transceivers • Optimized multi-carrier modulation with lower overhead • Enhanced forward error correction schemes • Improved link budget for lower to medium data rates • Providing the IEEE802.11a PHY data rates with increased range/link quality • Adapted to the support of services requiring small packet size such as VoIP • Exploit multi-antenna capabilities for robust transmission modes • Turn gains in spectral efficiency into link budget advantages • Favored short term implementation and deployment with robust, low complexity techniques • Open-loop multi-antenna solutions: simple, robust and without protocol overhead (feedback signalization) • Improve operation in limited Outdoor environments with support of long channel impulse responses

  4. Key features (1/2) • Multi-antenna extension: • MIMO with at least 2Tx/2Rx antennas scaling up to 4Tx • Support for asymmetric antenna configurations to accomodate various classes of devices • Open-loop modulation technique • Second OFDM modulator (optional): • 2 bandwidths supported: 20MHz and 40MHz • Optionally 128 carriers in 20/40MHz with 104 data carriers, and guard interval of 32 samples • 8% PHY rate increase for 20MHz mode • 117% PHY rate increase for 40MHz mode vs 20MHz/64-carriers • Turbo Codes: Increase roubustness

  5. Key features (2/2) • New nPLCP preambles for MIMO support(same for 64- and 128-point IFFT/FFT) • High order modulation (optional): 256-QAM • Space/frequency interleaver • Compatibility to legacy systems: • IEEE 802.11a convolutional code with code rates 1/2, 2/3, 3/4 and 5/6

  6. Turbo Codes: Motivation • Stable, well-understood technology • Good performance • Block size and code rate flexibility • Padding can be used to reduce number of interleavers • Puncturing patterns simple to describe and implement • Incremental redundancy procedures easily defined • Highly parallelizable “parallel window” decoder architecture • Easily scaled to meet latency requirements • Motorola 2048-bit information block implementation benchmark of 10ms per iteration on 2001-era FPGA scales to 1.25ms per iteration on current technology ASIC with clock rate increase and window size decrease • Interleavers can be parallelized to avoid memory contentions without performance penalty • Known intellectual property landscape

  7. Coding Functional Description • Scrambling before padding insertion • Before decoding, receiver may insert large LLRs at known locations • Padding • Inserts minimum number of zeros to make block size multiple of 512 bits • Zeros are inserted uniformly across the SERVICE+PSDU at the ends of 256-bit sub-blocks • Turbo interleaver maps padding to odd-numbered positions in second encoder • Segmentation • Breaks padded sequence into 2048-bit segments plus at most one segment of length 512, 1024, or 1536 bits

  8. Turbo Encoder • Rate-1/3 3G turbo code polynomials • Code rates 1/2, 2/3, 3/4, and 5/6 can be achieved exactly through puncturing • Contention-free turbo interleavers • Performance nearly identical to WCDMA down to 10-4 frame error rates • Constituent encoders left unterminated • Helps preserve exact code rate • Negligible performance degradation

  9. Contention-Free Interleavers • Inter-window shuffle (IWS) interleaver i = output position p(i) = input position r() = bit reversal intra-window permutation (same for all windows) j(j) = {j0(j),j1(j),,jM-1(j)} = j-th permutation of {0,1,,M-1} (periodic) M = number of windows (2,4,6,8 for block size 512,1024,1536,2048, resp.)

  10. Non-Termination Performance • 8-th iteration static binary channel FER with IWS interleavers (no tail compared with full 12-bit tail) • Non-termination helps preserve exact code rate with negligible performance impact 512-bit block 2048-bit block

  11. Padding Removal • To preserve code rate, all padding bits and associated parity bits (i.e., on same trellis step) are removed prior to puncturing removed padding

  12. Multi-antenna aspects of the proposal • Transmission of 1, 2 or 3 parallel streams using: • Space-Time Block Coding (STBC), Spatial Division Multiplexing (SDM) or robust hybrid solutions (STBC/SDM) • optimize the rate vs link budget trade-off • 2, 3 or 4 transmit antennas • The number of receive antennas determines the maximum number of spatial streams that can be transmitted. • The capability of decoding 2 parallel data streams is mandatory • all the devices have to be able to decode all the modes where the number of spatial streams is lower or equal than the number of receive antennas in the device. • It is required for a device to exploit all its antennas in transmission even for optional modes. • 2 or more receive antennas • With STBC or STBC/SDM, asymmetric antenna configurations can be supported • Importance of configurations in which NTx≠ NRx • NTx > NRx e.g. between AP and mobile handset (in DL) • NTx < NRx e.g. between MT and AP (UL), or if MT have upgraded multi-antenna capabilities compared to AP (infrastructure upgrade cost)

  13. Asymmetric Modes for a robust hybrid solution 2 transmit antenna schemes proposed 3 transmit antenna schemes proposed 4 transmit antenna schemes proposed

  14. OFDM modulation • 1st OFDM modulation based on IEEE802.11a parameters: • 48 data subcarriers, 64-point IFFT/FFT, 20MHz Bandwidth • 180Mbps maximum PHY rate (120Mbps mandatory) • 2nd OFDM modulation (optional extension): • 104 data subcarriers, 128-point IFFT/FFT, 8 pilots, 20MHz Bandwidth  195Mbps maximum PHY rate • 3rd OFDM modulation (optional extension): • 128-point IFFT/FFT, 40MHz Bandwidth • 104 data subcarriers, 8 pilots • Guard interval duration: 0.8s • 234Mbps maximum PHY rate

  15. Data rate (Mbits/s) Data rate (Mbits/s) Number of spatial streams (NS) Number of spatial streams (NS) Modulation Modulation Coding rate (R) Coding rate (R) Coded bits per subcarrier per stream (NBPSC) Coded bits per subcarrier per stream (NBPSC) Coded bits/ symbol (NCBPS) Coded bits/ symbol (NCBPS) Data bits/ symbol (NDBPS) Data bits/ symbol (NDBPS) 6.5Mbps 1 BPSK 1/2 1 104 52 6Mbps 1 BPSK 1/2 1 48 24 13Mbps 1 QPSK 1/2 2 208 104 12Mbps 1 QPSK 1/2 2 96 48 19.5Mbps 1 QPSK 3/4 2 208 156 18Mbps 1 QPSK 3/4 2 96 72 24Mbps 1 16QAM 1/2 4 192 96 26Mbps 1 16QAM 1/2 4 416 208 36Mbps 1 16QAM 3/4 4 192 144 39Mbps 1 16QAM 3/4 4 416 312 48Mbps 1 64QAM 2/3 6 288 192 52Mbps 1 64QAM 2/3 6 624 416 60Mbps 1 64QAM 5/6 6 288 240 65Mbps 1 64QAM 5/6 6 624 520 72Mbps 2 16QAM 3/4 4 192 144 78Mbps 2 16QAM 3/4 4 416 312 96Mbps 2 64QAM 2/3 6 288 192 104Mbps 2 64QAM 2/3 6 624 416 108Mbps 2 64QAM 3/4 6 288 216 117Mbps 2 64QAM 3/4 6 624 468 120Mbps 2 64QAM 5/6 6 288 240 130Mbps 2 64QAM 5/6 6 624 520 144Mbps 2 256QAM 3/4 8 384 288 156Mbps 2 256QAM 3/4 8 832 624 Mode: 2-TX48 carriers20MHz Mode: 2-TX104 carriers20MHz

  16. Mode: 2-TX104 carriers40MHz Mode: 3/4-TX48 carriers20MHz

  17. Mode: 3/4-TX104 carriers20MHz Mode: 3/4-TX104 carriers40MHz

  18. OFDM Parameters Overview (I/2) • 20MHz • 48 Carriers • 20MHz • 104 Carriers

  19. OFDM Parameters Overview (II/2) • 40MHz • 104 Carriers

  20. Frequency and space interleaver • IEEE802.11a based frequency interleaver defined for both 48 and 104 data subcarriers • Spatial division: • NSD : number of data subcarriers

  21. nPLCP preamble (I/2)

  22. nPLCP preamble (II/2) • Overview on different frame structures:

  23. Simulation results • AWGN, TGnB, TGnD, TGnE channel comparisons for 20MHz Bandwidth • Essential points • Throughput increase with optional modes (FFT-128) at constant SNR requirements in AWGN channels • Robust modes based on STBC for good coverage and support of asymetric configurations • Unilateral modification of number of antennas in TX and RX can be exploited Useful for independent evolution of AP/MT

  24. Simulation results - AWGN • 2TX/2RX to 4TX/4RX configuration and SNR ~21dB:120Mbps  180Mbps (130Mbps  195Mbps) 

  25. Mode/ Mbps SNR for PER=10-1 180 XXX  42dB  34dB 120 36dB  28dB  24.5dB 96 32dB  24dB  21dB 48 20dB  16dB  14dB 12 10dB  7dB  6dB Simulation results - TGnB • Diversity gain for all streams • 120 Mbps lowers SNR ~ 36dB  28dB  24.5dB

  26. Simulation results - TGnB • For new schemes: Same behaviour is observed for diversity modes as for classical schemes • Clear improvements for 2 streams from 2x2  3x3 mode • Clear improvements for 3 streams from 2x2/3x3  4x4 mode

  27. Mode/Mbps Mode/Mbps SNR for PER=10-1 SNR for PER=10-1 120 120 26.5dB 31.5dB 96 96 24dB 28dB 48 48 16dB 20dB 12 12 5dB 11dB Simulation results - TGnB • # TX antennas < # RX antennas  e.g. Update of MT • # TX antennas > # RX antennas  e.g. Update of AP

  28. PHY Throughput Analysis – TGnB • Link adaptation is based on long term average SNR  sub-optimum  inferior bound • Finer grid possible with more modes

  29. Mode/ Mbps SNR for PER=10-1 180 (effect) XXX  36dB  29dB 180 XXX  36dB  29dB 120 35dB  25.5dB  23dB 96 27.5dB  21dB  19dB 48 18dB  14dB  11dB 12 5dB  4.5dB  3.5dB Simulation results - TGnD • Diversity gain for all streams • 120 Mbps lowers SNR ~ 35dB  25.5dB  23dB

  30. Mode/Mbps Mode/Mbps SNR for PER=10-1 SNR for PER=10-1 120 120 24dB 30dB 96 96 20dB 25.5dB 48 48 14.5dB 17dB 12 12 2dB 7dB Simulation results - TGnD • # TX antennas < # RX antennas  e.g. Update of MT • # TX antennas > # RX antennas  e.g. Update of AP

  31. PHY Throughput Analysis – TGnD • Link adaptation is based on long term average SNR  sub-optimum  inferior bound • Finer grid possible with more modes

  32. Mode/ Mbps SNR for PER=10-1 180 XXX  43dB  31dB 120 37dB  26.5dB  24dB 96 30dB  22.5dB  20dB 48 19dB  15dB  12dB 12 7dB  5dB  4dB Simulation results - TGnE • Diversity gain for all streams • 120 Mbps lowers SNR ~ 37dB  26.5dB  24dB

  33. Mode/Mbps Mode/Mbps SNR for PER=10-1 SNR for PER=10-1 120 120 25dB 31.5dB 96 96 21.5dB 26.5dB 48 48 15dB 18dB 12 12 4dB 9dB Simulation results - TGnE • # TX antennas < # RX antennas  e.g. Update of MT • # TX antennas > # RX antennas  e.g. Update of AP

  34. PHY Throughput Analysis – TGnE • Link adaptation is based on long term average SNR  sub-optimum  inferior bound • Finer grid possible with more modes

  35. Simulation results – TGnD/TGnE • Similar to TGnB: • 2Tx: • Diversity gain for 1 stream, but not for 2 streams • 120 Mbps requires SNR ~ 35dB (TGnD) 37dB (TGnE) • 3Tx: • Diversity gain for 2 streams, but not for 3 streams • 120 Mbps lowers SNR: • ~ 36dB  26dB (TGnD) • ~ 37dB  26.5dB (TGnE) • 4Tx: • Diversity gain for all streams • 120 Mbps lowers SNR • ~ 36dB  26dB  23dB (TGnD) • ~ 37dB  26.5dB  24dB (TGnD)

  36. Simulation results – Offset compensation • No significant impact at 10% PER in channel E (NLOS) Figure 42 - Offset impact in 4x4 antenna configuration

  37. Simulation results – Offset compensation • Impact of carrier frequency offset and symbol clock offset at SNR=50dB in channel E (LOS): • Small degradation of the PER performance • High data rate modes are more impacted: • PER (+40ppm) = 112/100xPER (0ppm) at 48Mbps • PER (+40ppm) = 163/100xPER (0ppm) at 120Mbps Figure 42 - Offset impact in 4x4 antenna configuration

  38. Simulation results – Offset compensation • High data rate modes are less impacted if spatial diversity: • 3x3: PER (+40ppm) = 158/100xPER (0ppm) at 180Mbps • 4x4: PER (+40ppm) = 121/100xPER (0ppm) at 180Mbps Figure 42 - Offset impact in 4x4 antenna configuration

  39. Implementation complexity

  40. Conclusion • Proposal: MIMO extension of IEEE802.11a addressing • Short term implementation needs through mandatory modes relying on a mix of STBC and SDM • Take into account device size constraints allowing asymmetric TX/RX antenna configuration independent upgrade of APs / MTs possible • Enable PHY throughput covering 54Mbits/s  180 (468) Mbps

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