Improving Padding Efficiency in HE SU PPDU with BCC

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IEEE 802.11-16/0080r2 proposes a method to enhance padding efficiency in High Efficiency Spatially Multiplexed (HE SU) PPDU with Block Concatenation Coding (BCC) in 20MHz transmission. By adjusting the duration of the last OFDM symbol based on the excess information bits, this method aims to reduce throughput padding inefficiency. It focuses on optimizing the use of 1x, 2x, and 4x HE-LTF while maintaining simplicity and compatibility with LDPC codewords. The approach involves careful consideration of PSDU_LENGTH calculation rules and efficient allocation of resources for different packet sizes.

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  1. January 2016 doc.: IEEE 802.11-16/0080r2 1x/2x/4x OFDM Symbol in HE SU PPDU with BCC Date: 2016-01-18 Authors: Name Affiliations Yeungnam Univ. (NEWRACOM) NEWRACOM Address Phone email Heejung Yu heejung@yu.ac.kr Daewon Lee Yujin Noh NEWRACOM Minho Cheong NEWRACOM Submission Slide 1 Heejung Yu, Yeungnam Univ./NEWRACOM

  2. January 2016 doc.: IEEE 802.11-16/0080r2 Background PHY padding and signal extension were included in SFD [1]. The pre-FEC padding, post-FEC padding and packet extension methods were included. Both pre-FEC and post-FEC padding bits fill up the last OFDM symbol with 12.8us (4x) duration. For packets with LDPC, the existing method looks a reasonable approach. By adjusting the duration of the last OFDM symbol, e.g., 1x, 2x, and 4x OFDM symbol, the padding inefficiency in terms of throughput can be reduced. Submission Slide 2 Heejung Yu, Yeungnam Univ./NEWRACOM Heejung Yu, Yeungnam Univ./NEWRACOM

  3. January 2016 doc.: IEEE 802.11-16/0080r2 Padding Efficiency Information bits need to be in units of NDBPS. 4x more tones in 11ax result in 4x larger NDBPS. Short packets (such as TCP/IP ACK) suffer the most. Quick SU transmissions from STAs suffer the most. In case of MU, it is possible to use smaller RU allocation and multiplex with other packets to reduce down the overall overhead inefficiency. Therefore, we focus on improving padding efficiency in HE SU PPDU and with 20MHz transmission. Short packets will not typically require larger transmission BW such as 40/80/160MHz. Submission Slide 3 Heejung Yu, Yeungnam Univ./NEWRACOM

  4. January 2016 doc.: IEEE 802.11-16/0080r2 Proposed Method Identical to 1x, 2x, and 4x HE-LTF, the duration of the last OFDM symbol is adjusted depending on the number of information bits (Excess information bits) in the last OFDM symbol. Limit the use of 1x/2x/4x last OFDM symbol to 20MHz SU transmission. Focus on resolving the biggest padding inefficiency. No changes to the packet padding and packet extension operations in [5]. Further limit the use of 1x/2x/4x OFDM symbol to BCC. Small size packets have smaller gain with LDPC. Do not need special processing for LDPC codeword size matching (i.e. puncturing/repetition). Simpler design. Submission Slide 4 Heejung Yu, Yeungnam Univ./NEWRACOM

  5. January 2016 doc.: IEEE 802.11-16/0080r2 Proposed PSDU_LENGTH Calculation 11ac PSDU_LENGTH calculation rules Time Last OFDM Symbol PHY Padding NCBPS NCBPS Data Payload EOF Padding PSDU_LENGTH APEP_LENGTH TOO MUCH! Proposed Method Time Last OFDM Symbol NCBPS,last NCBPS Data Payload EOF PSDU_LENGTH PSDU_LENGTH is approximately calculated to the nearest 1/4, 1/2, or 1 times NCBPS APEP_LENGTH 2x OFDM Symbol 4x OFDM Symbol Submission Slide 5 Heejung Yu, Yeungnam Univ./NEWRACOM

  6. January 2016 doc.: IEEE 802.11-16/0080r2 Proposed Frame Structure for HE SU PPDU 1x/2x OFDM symbol only applied to the last OFDM symbol. 1x OFDM symbol duration 4x OFDM symbol (12.8us) 1x OFDM symbol 3.2us CP CP TX waveform 2x OFDM symbol duration 4x OFDM symbol (12.8us) 2x OFDM symbol 6.4us CP CP TX waveform 4x OFDM symbol duration 4x OFDM symbol (12.8us) 4x OFDM symbol 12.8us CP CP TX waveform Submission Slide 6 Heejung Yu, Yeungnam Univ./NEWRACOM

  7. January 2016 doc.: IEEE 802.11-16/0080r2 PSDU_LENGTH Calculation Process 1. Calculate the numbers of OFDM symbols and bits in the last symbol (NSYM, NDbit,last). Determine the number of data subcarrier in the last symbol (NSD,1x, NSD,2x, NSD,4x) and NDPBS,last, NCBPS,last. Calculate the number of padding bits Npad. 2. 3. Details and examples shown in Appendix Submission Slide 7 Heejung Yu, Yeungnam Univ./NEWRACOM

  8. January 2016 doc.: IEEE 802.11-16/0080r2 OFDM modulation Cases of NSD,4x Normal operation as in other OFDM symbols Cases of NSD,2x The even tones(2k, k= 1, 2, 3, ) are used. The output of IDFT has two repeated waveform. The first half is transmitted. Cases of NSD,1x The every 4th tones(4k, k= 1, 2, 3, ) are used. The output of IDFT has 4 repeated waveform. The first half is transmitted. Submission Slide 8 Heejung Yu, Yeungnam Univ./NEWRACOM

  9. January 2016 doc.: IEEE 802.11-16/0080r2 The strong points Our proposal, support of 1x/2x/4x OFDM symbol, targets small payload transmissions in OFDM transmissions. (20MHz with BCC) In 2.4GHz operations, 20MHz OFDM transmissions are useful due to channel assignment and legacy operations. Direct link operations We reduce amount of EOF padding performed and transmit air-time. In a STBC case, we can reduce the symbol duration of last two OFDM symbols. Submission Slide 9 Heejung Yu, Yeungnam Univ./NEWRACOM

  10. January 2016 doc.: IEEE 802.11-16/0080r2 Conclusion By exploiting the repeated waveform in 1x, 2x symbol duration cases, we can achieve throughput gain as shown in [3]. The proposed method can be applied to 20MHz BCC OFDM packet transmission where the existing method may not be effective in terms of padding efficiency (or throughput). Submission Slide 10 Heejung Yu, Yeungnam Univ./NEWRACOM

  11. January 2016 doc.: IEEE 802.11-16/0080r2 Straw poll Do you support to add the following text in SDF? For HE SU-OFDM packets using BCC in 20MHz bandwidth, the symbol duration of 3.2us, 6.4us and 12.8us (without CP) in the last mSTBC OFDM symbols is optionally supported depending on the number of data bits. Details are TBD. Submission Slide 11 Heejung Yu, Yeungnam Univ./NEWRACOM

  12. January 2016 doc.: IEEE 802.11-16/0080r2 REFERENCES [1] 11-15-0132-13-00ax-Specification Framework for Tgax [2] 11-15-0572-01-00ax-PHY inefficiency of 256FFT per 20MHz [3] 11-15-0887-03-00ax-effcient padding for last OFDM symbol [4] 11-15-1092-00-00ax-support of 1x 2x 4x ofdm symbol in he su ppdu [5] 11-15-0810-00ax-HE PHY Padding and Packet Extension Submission Slide 12 Heejung Yu, Yeungnam Univ./NEWRACOM

  13. January 2016 doc.: IEEE 802.11-16/0080r2 APPENDIX: ENCODING PROCESS Submission Slide 13 Heejung Yu, Yeungnam Univ./Newracom

  14. January 2016 doc.: IEEE 802.11-16/0080r2 PSDU_LENGTH and PHY Padding Calculation Definition of variables NCBPS,1 = NSD,1 NSS NBPSCS, NCBPS,2 = NSD,2 NSS NBPSCS, NCBPS,4 = NCBPS NDBPS,1 = NCBPS,1 R NDBPS,2 = NCBPS,2 R NDBPS,4 = NDBPS ( )= NSD,4 NSS NBPSCS, ( )= NCBPS,4 R Calculate NSYM. 8 APEP_LENGTH + + N N N = for BCC tail ES service N m SYM STBC m N STBC DBPS Submission Slide 14 Heejung Yu, Yeungnam Univ./Newracom

  15. January 2016 doc.: IEEE 802.11-16/0080r2 PSDU_LENGTH and PHY Padding Calculation Calculate the number of data bits in the last OFDM symbol. ( ) = mod 8 APEP_LENGTH + + , for BCC N N N N m N , Dbit last tail ES service STBC DBPS Define NSD,1x , NSD,2x , and NSD,4x (=NSD). NSD,1x 48 NSD,2x 102 NSD,4x 234 20MHz NSD is defined in 11ax . Use of above parameters result in re-use of agreed BCC interleaver parameters. Submission Slide 15 Heejung Yu, Yeungnam Univ./Newracom

  16. January 2016 doc.: IEEE 802.11-16/0080r2 PSDU_LENGTH and PHY Padding Calculation If 0 <NDbit,last mSTBC NDBPS,1x, (1x OFDM symbol duration) NDBPS,last = NDBPS,1x (NCBPS,last = NCBPS,1x) BCC case: interleaver size = NSD,1x Data subcarrier with 4k (k=1,2 ) indices excluding DC and pilot tones are used. If mSTBC NDBPS,1x <NDbit,last mSTBC NDBPS,2x, (2x OFDM symbol duration) NDBPS,last = NDBPS,2x (NCBPS,last = NCBPS,2x) BCC case: interleaver size = NSD,2x Data subcarrier with 2k (k=1,2 ) indices excluding DC and pilot tones are used. If mSTBC NDBPS,2x <NDbit,last mSTBC NDBPS,4x , (4x OFDM symbol duration) NDBPS,last = NDBPS,4x(=NDBPS)(NCBPS,last = NCBPS,4x(=NCBPS)) BCC case: interleaver size = NSD,4x(=NSD) Data subcarrier with k (k=1,2 ) indices excluding DC and pilot tones are used. Submission Slide 16 Heejung Yu, Yeungnam Univ./Newracom

  17. January 2016 doc.: IEEE 802.11-16/0080r2 PSDU_LENGTH and PHY Padding Calculation PSDU_LENGTH + ( ) N m N m N N N N = , SYM STBC DBPS STBC DBPS last Tail ES service PSDU_LENGTH 8 Calculation of the number of PHY padding bits (0~7 bits) NPAD=(NSYM-mSTBC) NDBPS+mSTBC NDBPS,last-8 PSDU_LENGTH-NTail NES-Nservice Submission Slide 17 Heejung Yu, Yeungnam Univ./Newracom

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