doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 1 Begonya Otal, Job Oostveen, Joerg Habetha, Monisha Ghosh, Pen Li, Ronald Rietman, TK Tan Philips August 13 th, 2004 Philips Partial Proposal to IEEE TGn Enhancements of a/g-based MIMO-OFDM System

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 2 Consumer Electronics market requirements Enabling a heterogeneous consumer multimedia network High throughput Improved Robustness Extended coverage Seamless coexistence

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 3 Overview of enhancements PHY I. 128-FFT in 20 MHz II. Advanced Coding ¼-rate Convolutional Code Concatenated RS-CC coding III. Embedded Signaling MAC IV. Multiple MCS and Receiver Aggregation

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 4 I. 128-FFT in 20MHz

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 5 Benefits Increase data rate by 11%. –2 x 2,rate ¾ 64QAM: goes from 108Mbps to 120Mbps (127 Mbps with half GI). Extra rate can be used as is, or combined with RS code to increase robustness with no extra overhead. Better performance in long delay spread channels –Longer symbol time relative to GI makes the 128-fft system more robust in long delay spread channels. –Better performance in half GI. Low overhead preamble design. –Channel estimation for 2 antennae can be accomplished in 8  sec, the same time that is currently used by a systems for 1 antenna.

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide FFT signaling over 20MHz Legacy Compatible Preamble L = Legacy HT = High Throughput STF = Short Training Field LTF = Long Training Field SIG = Signal Field HT Part 64-fft 128 fft L-STFL-LTFL-SIGHT-SIG0HT-STFHT-LTF DATA HT-SIG1

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide FFT signal structure over 20MHz 3 null carriers at DC (-1,0,+1) 6 pilots (–46, -28, -10, 10, 28, 46) 23 band-edge nulls (-64 to –53 and 53 to 63) 96 data carriers For comparison: –64-fft a system uses carriers (-52:2:-2) and (2:2:52) for data. –Proposed design uses (-52:-2) and (2:52) –Spectral mask is unchanged

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide FFT MIMO LTS Single, frequency interleaved LTS for 2 antennae. 52 tones per antenna for training. –Sequence used is same as for 11a, denoted as (a 1, a 2.. a 52 ) The PAR using the a long training sequence as is 3.8 dB. Band edge tones for improved channel estimation –Carriers -11 and 11 have training tones but no data Data on carriers (-62:-12) and (12:62), Antenna 1 training sequence on carriers (-62:-12) and (11:61), Antenna 2 training sequence on carriers (-61:-11) and (12:62). –help in channel estimation, especially for 150ns channel. –can be transmitted 12 db down from the other carriers, and hence do not affect the spectral shape appreciably.

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide FFT MIMO LTS Option 1: 8  sec per 2 antennae Pros: –Low overhead. –Channel delay spread up to 1.6usec can be estimated. Cons: –No additional fine frequency correction possible. Tone Interleaved odd/even, 6.4  sec GI, 1.6  sec

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide FFT MIMO LTS Option 2: 14.4 usec per 2 antennae Pros: –Fine frequency correction possible –Channel delay spread up to 1.6usec can be estimated with 3 dB better MSE performance as compared to Option 1 Cons: –Larger overhead. GI, 1.6 usec Tone Interleaved odd/even, 6.4 usec Tone Interleaved odd/even, 6.4 usec

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide FFT MIMO LTS Option 3: 14.4  sec per 2 antennae Pros: –Do not need frequency smoothing, per-tone estimation possible. Cons: –Channel estimation only up to 0.8usec. –No fine frequency estimation –Larger overhead. Not recommended. GI, 0.8  sec Tone Interleaved odd/even, 6.4  sec GI, 0.8  sec Tone Interleaved even/odd, 6.4 usec

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 12 Channel estimation Least Squares (LS) estimation. –Very good performance with Option 1 preamble. –Slightly higher complexity. Wiener Filtering. –4-tap filter has been designed to work well across a wide range of delay spreads. –Complexity is comparable to per-tone estimation used in current a systems. Simulation results. –Option 1 preamble requires LS estimation for good performance. –Option 2 preamble works well with the 4-tap filter, with only a 1-1.5dB loss in all channel models.

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 13 Channel estimation: Model B

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 14 Channel estimation: Model D

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 15 Channel estimation: Model E

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 16 Peak to average ratio (PAR) of 128-fft Vs. 64-fft

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 17 Performance in phase noise and frequency offset

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 18 Joint interleaving over 2 streams

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 19 II. Advanced Coding Concatenated Reed-Solomon ¼-rate Convolutional Coding

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 20 RS coder for 20Mhz and 40MHz. 10-byte error correcting code over GF(2 8 ). Polynomial: x 8 +x 4 +x 3 +x 2 +1 Codeword parameters: (220,200). –nominal 10% overhead. For shorter packets (< 200 bytes), always append 20 bytes of parity. –Example: 100 byte packet on 2 x 2, rate ¾ 64QAM, 40Mhz requires 166 pad bits. So: 20 parity bytes can be accommodated with no extra overhead. Packet does not have to be integral multiple of 200 bytes. –Start encoding in blocks of 200 bytes, last codeword will append 20 parity bytes to left-over bytes. Overhead can be less than 10%, even 0, if packet sizes are judiciously chosen. –Especially true for high data rates. Example: 990 data bytes on 2 x 2, ¾ 64QAM, 40Mhz has zero overhead. See figure on next slide

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 21 RS coding overhead for 243 Mbps data rate

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 22 RS performance: Channel Model B 2 dB gain

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 23 RS Performance: Channel Model D 2.5 dB gain

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 24 RS Performance: Channel Model E 3 dB gain

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 25 RS performance with impairments 3 dB gain for rate ½ 16QAM. 4.5 dB gain for rate ¾ 64QAM

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 26 ¼-rate Convolutional Code Improved coverage is important goal for 11n Challenge: –increase the coverage by using stronger FEC –without introducing too much complexity for the mandatory modes. The proposed solution is to –extend CC from ½ to ¼. –concatenate (220, 200) RS and Both are well known in the industry and have manageable complexity. Extended ¼ CC given by (133,171,135,175). –Extension of ½ CC (133,171).

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 27 Properties of Rate-¼ convolutional code Proposed Rate ¼ code: (133,171,135,175) It is a non-catastrophic extension of used rate-½ concolutional code (133,171) Among all codes that extend (133,171) it: – Has largest minimum free distance (21), – has minimum number (16) of paths at free distance 20. – has mimal number of paths at free distance 21, 22, 23, etc. Also want rate 1/3 code is optimal puncturing of (133,171,135,175) and still extension of (133,171): – Optimal code is (133, 171, 135) – free distance: 15.

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 28 Simulation Results for ¼ CC

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 29 Simulation Results for ¼ CC Conclusion: Additional 4 dB to improve the robustness and coverage

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 30 III. Embedded Signaling

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 31 Embedded signaling principle During legacy signal field, HT information is embedded by slightly distorting BPSK constellation points Legacy device can still decode legacy signal field 11n device is informed whether an HT transmission is following, –In addition encode the number of spatial streams

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 32 Comparing the preamble structure PreambleSignal Legacy Preamble Legacy Signal MIMO Training HT Sig-1 embedded signaling a: This proposal: MAC Header + Data HT Sig-0

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 33 Embedding On data sub-carriers and pilots, BPSK symbol x n = ±1 is replaced by Constellation points for legacy symbol Constellation points for symbol with embedding 

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 34 Embedding (ctd.) determines trade-off between legacy signal distortion and reliability of embedded bit: –1.0 dB loss ~  0.47 radians b n = ±1, n th bit from 48-bit codeword B m, –m = K, where K = #embedded bits Legacy transmission corresponds to B 0 =(0,…,0).

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 35 Simulation parameters : 0.47 radians 11a channel model with 0 and 50 ns delay spread Embedding 0,1,2,6 bits –0 bits: code words B 0 and B 1 => only HT signaling Error rates are “packet” error rates 1 – P(correct decoding) Decoding: –ML for embedded codeword –Viterbi (terminated) for signal field SISO system –Embedding is only difference w.r.t. 11a standard

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 36 Explanation of legend legacy without embedding –Error rate for decoding of signal field for standard 11a system legacy with embedding –Error rate for decoding of signal field for signal field in which embedded codeword is embedded 0 embedded bits –Error rate for decoding of embedded codeword, with 2 possible code words: B 0 =(0,…,0) and B 1 =(1,…,1) k embedded bits (k=1,2,3) –Error rate for decoding of embedded codeword, with 2 k possible code words:

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 37 Results: flat fading

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 38 Results: 50 ns

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 39 Conclusions from simulations At = 0.47 radians: –Up to 3 bits can be embedded and decoded reliably (reliable = error rate not worse than signal field) Embedded bits can be decoded correctly, even when signal field is decoded incorrectly

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 40 Proposal Use embedded signal on pilots and data sub-carriers to –Signal HT transmission –Embed 2: Communicate # antennas (2 bits) Move part of HT-Signal after HT-Training Embed at = 0.47 radians

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 41 IV. Multiple MCS and Receiver Aggregation

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 42 Multiple Receiver Aggregation Increases throughput efficiency significantly Reduces buffering delay because MPDUs of different receivers can be aggregated Receivers will have different link qualities and data rates: 54 Mbps 6 Mbps 108 Mbps Furthest receiver could limit throughput of all other stations  Aggregation of different Modulation and Coding Schemes (MCS) AP

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 43 General PPDU Format HT-SIG contains Multiple MCS and Receiver Aggregation part MMRA part has variable length Legacy Compatible Preamble HT Part 64-fft 128 fft L-STFL-LTFL-SIGHT-SIG0HT-STFHT-LTF DATA HT-SIG1

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 44 Different MCS codes included in HT-SIG as well as for each MCS: MAC-ADDR and LENGTH (or offset) of all MPDUs for each receiver HT-SIG MMRA part PSDU DATA Format of HT-SIG MMRA part & PSDU DATA

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 45 Power saving scheme MMRA allows for efficient power saving scheme Preambles inside the aggregate enable re-synchronization after wake-up Trade-off between throughput and power efficiency Compromise: Preambles only between sub-aggregates of different MCS Shorter (or no) delimiters between MPDUs inside an MCS sub-aggregate  STAs go into sleep-mode until beginning of their MCS aggregate  STAs stay awake inside the MCS aggregate until MPDUs have been received  STAs go back to sleep mode for the remainder of the aggregate

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 46 Active and sleep states of stations with MMRA

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 47 Performance evaluation and comparison to Single MCS Multiple Receiver Aggregation (SMRA)

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 48 Example: 2 Rx with MCS1 / 2 Rx with MCS2 / 1 Rx with MCS3 3 Complete PPDUs (PHY Header+DATA) must be send: one for each PSDU/MCS 2 SIFS are required to separate PPDUs at different data rates 3 PSDU Headers are required at the beginning of each Aggregate HT-SIG has no additional fields for the aggregates. Single MCS Multiple Receiver Aggregation (SMRA)

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 49 Active and sleep states of stations with SMRA

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 50 Scenario 1: 5 STA at 3 MCS: 24,54,108 Mbps

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 51 Scenario 2: 15 STA at 3 MCS: 24,54,108 Mbps

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 52 Scenario 3: 10 STA at 5 MCS: 18,24,48,54,108 Mbps

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 53 Scenario 4: 25 STA at 5 MCS: 18,24,48,54,108 Mbps

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 54 Conclusions Multiple receiver aggregation reduces delay compared to single receiver aggregation Aggregates with different MCS may either be aggregated or sent separately (MMRA versus SMRA) MMRA is much more power efficient than SMRA For MMRA trade-off between power and throughput efficiency Chosen MMRA is not only more efficient than SMRA in terms of power consumption but also in terms of throughput efficiency in most scenarios  MMRA should be always preferred over SMRA

doc.: IEEE /945r0 Submission August 2004 Pen C. Li, et al, Philips Slide 55 Summary In this presentation we have described PHY and MAC enhancements that optimize the throughput and robustness of n systems in both 20 and 40MHz bandwidth. These include : 1.128FFT for better data-rate efficiency in 20 MHz and lower overhead preamble design. 2.Advanced coding (concatenated RS and rate 1/4 convolutional code) for added robustness and range extension. 3.Embedded signaling as a means of coexistence and backward compatibility between legacy and HT devices. 4.Multiple MCS and receiver aggregation for improved MAC efficiency and power saving. These features can be easily incorporated into n devices at low complexity while at the same time improving the overall system performance, as shown by the simulation results presented.