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VHTSIG Considerations

VHTSIG Considerations. Authors:. Date: 2010-05-17. 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.

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VHTSIG Considerations

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  1. VHTSIG Considerations Authors: Date: 2010-05-17 Hongyuan Zhang, et al.

  2. 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.

  3. Illustrations 2 symbols 1 symbol • VHT Preamble structure in [1] 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.

  4. Example of VHTSIG Bit Allocation for DLMU VHT-SIG: Bits: 2-4(TBD) 1 1 1 33(TBD) 4(TBD) 6 BW SGI STBC Coding GrpID Fields CRC Tail 25(TBD) 6 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.

  5. Example of VHTSIG Bit Allocation for SU • The actual location of bits in VHT-SIG is subject to change if necessary VHT-SIG: 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 Slide 5 Hongyuan Zhang, et al.

  6. 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

  7. 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.

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

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