VHTSIG Considerations Month Year doc.: IEEE 802.11-yy/xxxxr0 May 2010 VHTSIG Considerations Date: 2010-05-17 Authors: Hongyuan Zhang, et al. John Doe, Some Company

Overview Our earlier preamble proposal [1] shows a preamble structure with 2 VHTSIG segments: VHTSIGA as common PHY info for all MU clients, and VHTSIGB containing client-specific info. Our new proposal [2] showed that it is sufficient to use LSIG Length field in a VHT packet to signal the packet duration. Motivations: Without duration field, a lot of free bits in VHTSIGA may allow us to squeeze all the necessary PHY information bits into VHTSIGA. Assume up to 4 clients in each DLMU packet. Benefits by not having VHTSIGB in 11ac preamble: Save 4us for better efficiency. Cleaner receiver process: the whole flow will be similar to 11n (next slide). While VHTSIGB decoding and its corresponding PHY info processing requires extra handling compared with 11n. Slide 2 Hongyuan Zhang, et al.

Illustrations VHT Preamble structure in [1] 2 symbols 1 symbol L-STF L-LTF L-SIG VHTSIGA VHT-STF VHT-LTFs VHTSIGB VHTData VHT Preamble structure without VHTSIGB 2 symbols L-STF L-LTF L-SIG VHTSIG VHT-STF VHT-LTFs VHTData (48 Available bits) HT MM Preamble structure 2 symbols L-STF L-LTF L-SIG HTSIG HT-STF HT-LTFs HTData Slide 3 Hongyuan Zhang, et al.

Example of VHTSIG Bit Allocation for DLMU Bits: 2-4(TBD) 1 1 1 33(TBD) 4(TBD) 6 BW SGI STBC Coding GrpID Fields CRC Tail 6 25(TBD) 0-6(TBD) Grp ID>0 MU MCS Field Rsvd Example MU MCS (25 bits): 9 3-4(TBD) 3-4(TBD) 3-4(TBD) 3-4(TBD) Nsts LUT for 4 Clients MCS1 MCS2 MCS3 MCS4 MCS per user represents modulation and coding for the corresponding of spatial streams. STBC and LDPC are both common for all the clients The 9-bit Nsts LUT compresses all 493 possible stream assignment combinations, assuming: Up to 4 streams per user Up to 8 total number of streams Up to 4 users per MU packet The actual location of bits in VHT-SIG is subject to change if necessary Slide 4 Hongyuan Zhang, et al.

Example of VHTSIG Bit Allocation for SU Bits: 2-4 (TBD) 1 1 1 33 (TBD) 4(TBD) 6 BW SGI STBC Coding GrpID Fields CRC Tail 6 TBD TBD TBD Grp ID=0 SU MCS Field AID Rsvd The actual location of bits in VHT-SIG is subject to change if necessary Slide 5 Hongyuan Zhang, et al.

Feasibility of 4 bit CRC It might be possible to reduce CRC to 4 bit in VHTSIG and still get reliable false positive protection. Simulation of False positive prob as below: Hongyuan Zhang, et al. Slide 6

Conclusions It is possible to squeeze all the necessary VHT PHY info bits in 2 symbols of VHTSIGA, if VHT packet duration is signaled by LSIG Length field. Limit to at most 4 clients in each DLMU packet. No further PHY info bits needed in VHTSIGB. It may worth investigating this possibility. Slide 7 Hongyuan Zhang, et al.

March 2010 References [1] IEEE 802.11-10/0070r5, 802.11ac preamble. [2] IEEE 802.11-10/0534r0, Duration in L-SIG. Hongyuan Zhang, et al.