doc.: IEEE /913r4 Submission September 2004 Slide 1 IEEE n 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

doc.: IEEE /913r4 Submission September 2004 Slide 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

doc.: IEEE /913r4 Submission September 2004 Slide 3 Overall goal of the proposed PHY design Modification of IEEE a-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

doc.: IEEE /913r4 Submission September 2004 Slide 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

doc.: IEEE /913r4 Submission September 2004 Slide 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 a convolutional code with code rates 1/2, 2/3, 3/4 and 5/6

doc.: IEEE /913r4 Submission September 2004 Slide 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 10  s per iteration on 2001-era FPGA scales to 1.25  s 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

doc.: IEEE /913r4 Submission September 2004 Slide 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

doc.: IEEE /913r4 Submission September 2004 Slide 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

doc.: IEEE /913r4 Submission September 2004 Slide 9 Contention-Free Interleavers Inter-window shuffle (IWS) interleaver i = output position  (i) = input position  (  ) = bit reversal intra-window permutation (same for all windows)  (j) = {  0 (j),  1 (j), ,  M  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.)

doc.: IEEE /913r4 Submission September 2004 Slide 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 block2048-bit block

doc.: IEEE /913r4 Submission September 2004 Slide 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

doc.: IEEE /913r4 Submission September 2004 Slide 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 N Tx ≠ N Rx –N Tx > N Rx e.g. between AP and mobile handset (in DL) –N Tx < N Rx e.g. between MT and AP (UL), or if MT have upgraded multi-antenna capabilities compared to AP (infrastructure upgrade cost)

doc.: IEEE /913r4 Submission September 2004 Slide 13 2 transmit antenna schemes proposed3 transmit antenna schemes proposed 4 transmit antenna schemes proposed Asymmetric Modes for a robust hybrid solution

doc.: IEEE /913r4 Submission September 2004 Slide 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

doc.: IEEE /913r4 Submission September 2004 Slide 15 Mode: 2-TX 48 carriers 20MHz Mode: 2-TX 104 carriers 20MHz

doc.: IEEE /913r4 Submission September 2004 Slide 16 Mode: 2-TX 104 carriers 40MHz Mode: 3/4-TX 48 carriers 20MHz

doc.: IEEE /913r4 Submission September 2004 Slide 17 Mode: 3/4-TX 104 carriers 20MHz Mode: 3/4-TX 104 carriers 40MHz

doc.: IEEE /913r4 Submission September 2004 Slide 18 OFDM Parameters Overview (I/2) 20MHz 48 Carriers 20MHz 104 Carriers

doc.: IEEE /913r4 Submission September 2004 Slide 19 OFDM Parameters Overview (II/2) 40MHz 104 Carriers

doc.: IEEE /913r4 Submission September 2004 Slide 20 Frequency and space interleaver IEEE802.11a based frequency interleaver defined for both 48 and 104 data subcarriers Spatial division: –N SD : number of data subcarriers

doc.: IEEE /913r4 Submission September 2004 Slide 21 nPLCP preamble (I/2)

doc.: IEEE /913r4 Submission September 2004 Slide 22 nPLCP preamble (II/2) Overview on different frame structures:

doc.: IEEE /913r4 Submission September 2004 Slide 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

doc.: IEEE /913r4 Submission September 2004 Slide 24 Simulation results - AWGN 2TX/2RX to 4TX/4RX configuration and SNR ~21dB: 120Mbps  180Mbps (130Mbps  195Mbps) 

doc.: IEEE /913r4 Submission September 2004 Slide 25 Simulation results - TGnB Diversity gain for all streams 120 Mbps lowers SNR ~ 36dB  28dB  24.5dB XXX  42dB  34dB dB  7dB  6dB 12 20dB  16dB  14dB 48 32dB  24dB  21dB 96 36dB  28dB  24.5dB 120 SNR for PER=10 -1 Mode/ Mbps

doc.: IEEE /913r4 Submission September 2004 Slide 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

doc.: IEEE /913r4 Submission September 2004 Slide 27 Simulation results - TGnB # TX antennas < # RX antennas  e.g. Update of MT 26.5dB120 5dB12 16dB48 24dB96 SNR for PER=10 -1 Mode/Mbps 31.5dB120 11dB12 20dB48 28dB96 SNR for PER=10 -1 Mode/Mbps # TX antennas > # RX antennas  e.g. Update of AP

doc.: IEEE /913r4 Submission September 2004 Slide 28 PHY Throughput Analysis – TGnB Link adaptation is based on long term average SNR  sub-optimum  inferior bound Finer grid possible with more modes

doc.: IEEE /913r4 Submission September 2004 Slide 29 Simulation results - TGnD Diversity gain for all streams 120 Mbps lowers SNR ~ 35dB  25.5dB  23dB XXX  36dB  29dB 180 (effect) XXX  36dB  29dB 180 5dB  4.5dB  3.5dB 12 18dB  14dB  11dB dB  21dB  19dB 96 35dB  25.5dB  23dB 120 SNR for PER=10 -1 Mode/ Mbps

doc.: IEEE /913r4 Submission September 2004 Slide 30 Simulation results - TGnD # TX antennas < # RX antennas  e.g. Update of MT 24dB120 2dB dB48 20dB96 SNR for PER=10 -1 Mode/Mbps 30dB120 7dB12 17dB dB96 SNR for PER=10 -1 Mode/Mbps # TX antennas > # RX antennas  e.g. Update of AP

doc.: IEEE /913r4 Submission September 2004 Slide 31 PHY Throughput Analysis – TGnD Link adaptation is based on long term average SNR  sub-optimum  inferior bound Finer grid possible with more modes

doc.: IEEE /913r4 Submission September 2004 Slide 32 Simulation results - TGnE Diversity gain for all streams 120 Mbps lowers SNR ~ 37dB  26.5dB  24dB XXX  43dB  31dB 180 7dB  5dB  4dB 12 19dB  15dB  12dB 48 30dB  22.5dB  20dB 96 37dB  26.5dB  24dB 120 SNR for PER=10 -1 Mode/ Mbps

doc.: IEEE /913r4 Submission September 2004 Slide 33 Simulation results - TGnE # TX antennas < # RX antennas  e.g. Update of MT 25dB120 4dB12 15dB dB96 SNR for PER=10 -1 Mode/Mbps 31.5dB120 9dB12 18dB dB96 SNR for PER=10 -1 Mode/Mbps # TX antennas > # RX antennas  e.g. Update of AP

doc.: IEEE /913r4 Submission September 2004 Slide 34 PHY Throughput Analysis – TGnE Link adaptation is based on long term average SNR  sub-optimum  inferior bound Finer grid possible with more modes

doc.: IEEE /913r4 Submission September 2004 Slide 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)

doc.: IEEE /913r4 Submission September 2004 Slide 36 Simulation results – Offset compensation No significant impact at 10% PER in channel E (NLOS) Figure 42 - Offset impact in 4x4 antenna configuration

doc.: IEEE /913r4 Submission September 2004 Slide 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 Antenna configuration Data rate (Mbits/s) PER when carrier offset = -40ppm PER when carrier offset = 0ppm PER when carrier offset =+40ppm 2x212Mbps x248Mbps x296Mbps x2120Mbps

doc.: IEEE /913r4 Submission September 2004 Slide 38 Simulation results – Offset compensation Figure 42 - Offset impact in 4x4 antenna configuration Antenna configura tion Data rate (Mbits/s) PER when carrier offset = - 40ppm PER when carrier offset = 0ppm PER when carrier offset =+40ppm 3x312Mbps ~0 3x348Mbps x396Mbps x3120Mbps x3180Mbps Antenna configur ation Data rate (Mbits/s) PER when carrier offset = - 40ppm PER when carrier offset = 0ppm PER when carrier offset =+40ppm 4x412Mbps~0 4x448Mbps x496Mbps x4120Mbps x4180Mbps 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

doc.: IEEE /913r4 Submission September 2004 Slide 39 Implementation complexity

doc.: IEEE /913r4 Submission September 2004 Slide 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

doc.: IEEE /913r4 Submission September 2004 Slide 41