11ac Explicit Sounding and Feedback Month Year Month Year doc.: IEEE 802.11-yy/xxxxr0 doc.: IEEE 802.11-yy/xxxxr0 11ac Explicit Sounding and Feedback Date: 2010-11-08 Authors: Page 1 John Doe, Some Company John Doe, Some Company

Background (1) TGac decided the VHT Data stream parser being similar as 11n: Consecutive blocks of  s (num of bits on each constellation axis) bits are assigned to different spatial streams in a round robin fashion. If multiple encoders per user are present, the output of each encoder is used alternately in a round robin cycle, i.e., at the beginning S=NSSs bits from the output of first encoder are fed into all spatial streams, and then S bits from the output of the next encoder are used and so on.

Background(2) MCS Exclusion Rule: Month Year doc.: IEEE 802.11-yy/xxxxr0 Background(2) MCS Exclusion Rule: In order to avoid extra padding symbols, we will need to ensure that we have an integer number of punctured blocks from all encoders, i.e. both NCBPS/NES and NDBPS/NES are integers. Mathematically we need Sudhir Srinivasa et al. Page 3 John Doe, Some Company

Background (3) Same Stream Parser is also applied to 160MHz: which jointly parses bits of upper and lower 80MHz subbands. Intlv QAM Spatial Map CSD 234 tones Scrambler 512 IFFT Encoder Parser FEC 1 Stream Parser DAC FEC N Frequency Parser HW supporting VHT80

Issues with 160MHz Stream Parser For all 11n MCSs, as well as “allowed” 11ac MCSs in 20/40/80 MHz, each BCC is allocated multiple of S=NSSs coded bits per OFDM Symbol, i.e. NCBPS/NES is an integer (Guaranteed by MCS Exclusion Rule) (NCBPS/NES)/S is also an integer. Parsing/Deparsing are straightforward. In four 160MHz MCSs, (NCBPS/NES)/S is NOT an integer. 234 is multiple of 2 and 3, issues come when NES=5,7; and Nss=NES. Specifically, the following 160MHz MCSs have the issue: 64QAM, Rate 2/3, 5 streams—NES=5 64QAM, Rate 2/3, 7 streams—NES=7 64QAM, Rate 3/4, 5 streams—NES=5 64QAM, Rate 3/4, 7 streams—NES=7 Residue (relative to S=Nss.s) bits at each encoder leads to confusion at Rx. Note that NCBPS/NES are still multiples of s.

Propose to Change the SP Rules for These 4 MCSs Insert the following sentence on stream parser description text (3.2.4.3.1 ): “For 160MHz MCSs, if each BCC encoder does not generate integer blocks of S coded bits in each OFDM symbol, then apply the same stream parsing method until the last integer block (floor(NCBPS/NES/S)) of S bits at each encoder. Assuming that at this point in each OFDM symbol each BCC has M.s (M<NSS) residue bits, take the last M.s bits in the current OFDM symbol from the first encoder and allocate them to the first M spatial streams (s bits to each stream); then take the last M.s bits in the current OFDM symbol from the second encoder and distribute these among M spatial streams, starting from the (M + 1)-th spatial stream, and so on. Note that upon reaching the NSS’th spatial stream, we cycle back to the 1st spatial stream. Repeat till all bits are distributed in the current OFDM symbol.”

Pre-Motion #1 Do you agree to insert the following text into 3.2.4.3.1 (Stream Parser) of the spec framework? “For 160MHz MCSs, if each BCC encoder does not generate integer blocks of S coded bits in each OFDM symbol, then apply the same stream parsing method until the last integer block (floor(NCBPS/NES/S)) of S bits at each encoder. Assuming that at this point in each OFDM symbol each BCC has M.s (M<NSS) residue bits, take the last M.s bits in the current OFDM symbol from the first encoder and allocate them to the first M spatial streams (s bits to each stream); then take the last M.s bits in the current OFDM symbol from the second encoder and distribute these among M spatial streams, starting from the (M + 1)-th spatial stream, and so on. Note that upon reaching the NSS’th spatial stream, we cycle back to the 1st spatial stream. Repeat till all bits are distributed in the current OFDM symbol.” Y N A