Remaining Issues with New 11be Scrambler in IEEE 802.11-20
IEEE 802.11-20/1107r0 discusses the introduction of a new 11-bit scrambler in 11be to reduce payload PAPR. The document addresses issues related to the scrambler seed for CTS in response to MU-RTS transmissions, including the generation of PPDU synchronous scramblers, bit modulation in CTS and MU-RTS, and the handling of special conditions. Recommendations for ensuring robustness and simplicity in the scrambler seeding process are also provided.
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doc.: IEEE 802.11-20/1107r0 July 2020 Remaining Issues with New 11be Scrambler Date: 2020-07-21 Authors: Name Affiliations Address Phone Email Lin Yang Youhan Kim Qualcomm Bin Tian Submission Slide 1 Lin Yang (Qualcomm)
doc.: IEEE 802.11-20/1107r0 July 2020 Background 11be introduces new 11-bit scrambler to reduce payload PAPR. The passed SP says The following generator polynomial to generate the PPDU synchronous scrambler is used for EHT PPDU? ? ? = ?11+ ?9+ 1 The 11 bits used for the scrambler initialization are randomly assigned by the transmitter. The polarity of the pilot subcarrier is derived from the same sequence as 802.11ax. [#SP16] [20/0563r1 (EHT PPDU Scrambler, Xiaogang Chen, Intel), SP#1, Y/N/A: 36/12/12 To place the 11 bits scrambling seed we may need to re-define the bits in SERVICE field for EHT PPDU. A natural way to do it is using the 1st 11 LSB bits for 11be scrambling seed and keeping the remaining 5 bits still reserved 11be 11-bit scrambling seed legacy 7-bit scrambling seed Reserved s0 s1 s2 s3 s4 s5 s6 s7 s8 s9s10 0 1 2 3 4 5 6 7 8 9 101112131415 SERVICE field in EHT PPDU Submission Slide 2 Lin Yang (Qualcomm)
doc.: IEEE 802.11-20/1107r0 July 2020 Scrambler Seed for CTS in Response to MU-RTS (1) Multiple STAs send identical CTS in response to MU-RTS using non-HT DUP PPDU Modulated bits in CTS need to be same from all STAs, including scrambling sequence In 11ax, STA copies the 1st 7 bits of SERVICE field in MU-RTS as its scrambling seed for CTS and fill them into the 1st 7 bits of SERVICE field in CTS MU-RTS RX CTS TX SERVICE field of MU-RTS prior to descrambling During first 7 bits of SERVICE s6 s5 s4 s3 s2 s1 s0 SERVICE field of CTS after scrambling. First 7 bits are identical to MU-RTS. DataIn s0 s1 s2 s3 s4 s5 s6 Reserved 0 1 2 3 4 5 6 7 8 9 101112131415 X4 X3 X2 X1 X7 X6 X5 s0 s1 s2 s3 s4 s5 s6 Reserved 0 1 2 3 4 5 6 7 8 9 101112131415 Scrambled Data Out Submission Slide 3 Lin Yang (Qualcomm)
doc.: IEEE 802.11-20/1107r0 July 2020 Scrambler Seed for CTS in Response to MU-RTS (2) If MU-RTS is transmitted using EHT PPDU, MU-RTS has 11 bits of scrambling initial value Can still use the first 7 bits of the SERVICE field in MU-RTS only to scramble the CTS data and fill in the first 7 bits of the SERVICE field of the CTS Need to make sure those 7 bits can t be all 0 to guarantee scrambling Option 1: disallow 1st 7 bits to be all zero for MU-RTS Option 2: the receiving STAs use a default value for CTS scrambling seed, if the received scrambling seed in MU-RTS has 1st 7 bits being all zeros. For example, default value = 127 = all ones = 1111111 We recommend option 1 for its simplicity and robustness Option 2 needs all receiver to handle special condition MU-RTS RX CTS TX SERVICE field of MU-RTS prior to descrambling During first 7 bits of SERVICE s6 s5 s4 s3 s2 s1 s0 SERVICE field of CTS after scrambling. First 7 bits are identical to MU-RTS. Data In Reserved s0 s1 s2 s3 s4 s5 s6 s7 s8 s9s10 0 1 2 3 4 5 6 7 8 9 101112131415 X4 X3 X2 X1 X7 X6 X5 s0 s1 s2 s3 s4 s5 s6 Reserved 0 1 2 3 4 5 6 7 8 9 101112131415 s7-s10 not used for CTS scrambling initialization Scrambled Data Out Submission Slide 4 Lin Yang (Qualcomm)
doc.: IEEE 802.11-20/1107r0 July 2020 SP 1 Do you support using the first 11 LSB bits in SERVICE field for 11be scrambling seed and keeping the remaining 5 bits as reserved? 11be 11-bit scrambling seed legacy 7-bit scrambling seed Reserved s0 s1 s2 s3 s4 s5 s6 s7 s8 s9 s10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 SERVICE field in EHT PPDU Y/N/ABS Submission Slide 5 Lin Yang (Qualcomm)
doc.: IEEE 802.11-20/1107r0 July 2020 SP 2 Do you support using the first 7 LSB bits of the SERVICE field in MU-RTS to scramble the CTS data and fill in the first 7 LSB bits of the SERVICE field of the CTS, when MU- RTS is transmitted using an EHT PPDU? Y/N/ABS Submission Slide 6 Lin Yang (Qualcomm)
doc.: IEEE 802.11-20/1107r0 July 2020 SP 3 Do you support in 11be to disallow the 7 LSB bits of the SERVICE field in MU-RTS to be all zeros? Y/N/ABS Submission Slide 7 Lin Yang (Qualcomm)
