802.11ac Preamble Date: 2010-03-15 Authors: Month Year Month Year doc.: IEEE 802.11-yy/xxxxr0 doc.: IEEE 802.11-yy/xxxxr0 802.11ac Preamble Date: 2010-03-15 Authors: Slide 1 Hongyuan Zhang et al. Page 1 John Doe, Some Company John Doe, Some Company

Abstract Changes from r1 (with italic font in slides) Month Year doc.: IEEE 802.11-yy/xxxxr0 Abstract Changes from r1 (with italic font in slides) Remove duration field in VHT-SIGA for bit allocation consideration Remove SU/MU bit in VHT-SIGA for bit allocation consideration Combine “Field/Bits consideration slides for SU and MU” into a single slide Update comparison slide for AutoDetection Update references with revision number Minor editorial changes Add a couple of strawpolls at the end Hongyuan Zhang et al. John Doe, Some Company

I. Numerology Hongyuan Zhang et al.

Proposed Basic Numerology (previously presented to TGac) Month Year doc.: IEEE 802.11-yy/xxxxr0 Proposed Basic Numerology (previously presented to TGac) Max number of transmit (Tx) antennas sounded: 8 Reasonable complexity, cost, and preamble length trade-off Max number of Nss (spatial streams) in the SU case: 8 Given that 8 Tx antennas are proposed to be sounded, then there is inherent support for up to 8 spatial streams Max number of Nss per user in the MU case: 4 Given that multiple users will share spatial streams, it is natural to make this number smaller than 8 Fits VHT-SIG size limitations, reduces number of representation bits required Maximum number of Nss summed over users in the MU case: 8 Max number of MU users: 4 Larger number significantly increases MAC/PHY complexity Hongyuan Zhang et al. John Doe, Some Company

Maximum number of transmit antennas sounded = 8 Month Year doc.: IEEE 802.11-yy/xxxxr0 Maximum number of transmit antennas sounded = 8 Meets PAR requirements For single user case 8 antenna with Nss=8 allows for > 500Mbps throughput For multi user case 8 antenna sounding allows for > 1 Gbps throughput Physical limitation on AP and STAs to put more than 8 antennas Going to 16 antenna sounding increases preamble length Number of bits required to indicate number of antennas sounded also increases – limited number of bits available in preamble Hongyuan Zhang et al. John Doe, Some Company

Max number of Nss (spatial streams) in the SU case = 8 Month Year doc.: IEEE 802.11-yy/xxxxr0 Max number of Nss (spatial streams) in the SU case = 8 Meets PAR requirements For single user case 8 spatial stream allows for > 500Mbps throughput Maximum number of Nss <= Maximum number of Antennas sounded Hongyuan Zhang et al. John Doe, Some Company

Max number of Nss per user in the MU case: 4 Month Year doc.: IEEE 802.11-yy/xxxxr0 Max number of Nss per user in the MU case: 4 Meets PAR requirements For multi user transmission two transmissions of Nss=4 allows for > 1Gbps throughput Given that multiple users will share spatial streams, it is natural to make this number smaller than 8 Fits VHT-SIG size limitations, reduces number of representation bits required 3 bits required to define Nsts per user for MU transmission For resolvable LTFs these bits have to be in VHT-SIGA Hongyuan Zhang et al. John Doe, Some Company

Maximum number of Nss summed over users in the MU case: 8 Month Year doc.: IEEE 802.11-yy/xxxxr0 Maximum number of Nss summed over users in the MU case: 8 Meets PAR requirements For multi user transmission sum of Nss equal to 8 leads to throughput > 1Gbps Given that 8 Tx antennas are proposed to be sounded, then there is inherent support for up to 8 spatial streams Hongyuan Zhang et al. John Doe, Some Company

Max number of MU users: 4 Meets PAR requirements Month Year doc.: IEEE 802.11-yy/xxxxr0 Max number of MU users: 4 Meets PAR requirements For multi user transmission 4 users with 2 streams per user > 1Gbps throughput Larger number significantly increases MAC/PHY complexity Each users stream has to be separately encrypted and modulated Fits VHT-SIG size limitations, reduces number of representation bits required Nss bits have to be pre-allocated for each user in VHT-SIGA. Even with 4 MU users, most of the VHT-SIGA bits are already allocated Hongyuan Zhang et al. John Doe, Some Company

II. Preamble Comparisons Hongyuan Zhang et al.

TGac Preamble Proposals Two proposals in TGac on preamble: (1) our proposal 10/070r1, and (2) 10/130r0 (Tu, et al). Major differences: Auto detection: (1) 90-deg rotation on 2nd VHTSIG symbol, (2) Manipulate constellation of 1st VHTSIG symbol, e.g. alternative 90-deg rotate, or 45-deg rotate. Modulation of VHT-SIG: (1) Same as 11n/a: BPSK r=1/2 (2) Allows QPSK from 2nd VHTSIG symbol Green Field: (1) A single preamble for SU/MU, no GF. (2) Allow GF Hongyuan Zhang et al.

Preamble Structure in (1)-0070r0 Rate=6Mbps Length determined by T 2 symbols 1 symbol L-STF L-LTF L-SIG VHTSIGA VHT-STF VHT-LTFs VHTSIGB VHTData T VHT auto-detection Hongyuan Zhang et al.

Preamble Structure in (2)-0130r0 Month Year doc.: IEEE 802.11-yy/xxxxr0 Preamble Structure in (2)-0130r0 Or the “90-deg Orthogonal shift” may be replaced by +-45-deg shift. Hongyuan Zhang et al. John Doe, Some Company

Comparisons—Auto Detection Proposal (1) is more reliable than (2): Guarantees the most reliable spoofing of existing 11n receivers (as 11a packet), regardless of what 11n auto-detect algorithm was implemented. Guarantees the most reliable 11ac auto detection, largest Euclidean Distance (BPSK vs QBPSK). It is risky to manipulate modulation of the 1st VHTSIG symbol. Given various existing implementations of 11n auto-detections. Not fair to pre-assume any 11n auto-detect approach as in proposal (2) More likely that an 11n device false-detects HTSIG, and goes into ED-CCA stage. On timing issue for detection VHT-STF AGC may be deferred by approximate FFT processing time (before VHT detection). 11ac will most likely run faster clock to support higher throughput; therefore AGC computation is faster than HT devices. May use partial GI of VHTLTF1 for AGC computation. There are much more complex functions (e.g. DLMU, faster decoder, etc) required for 11ac. VHT AGC enhancement is trivial. A reliable legacy spoofing is more important than the extra complexity of AGC enhancement. Hongyuan Zhang et al.

Comparisons—VHTSIG Modulation Preferable to keep using the lowest possible MCS to modulate VHTSIG fields: MCS0 is still necessary to guarantee the longest range. Make sure header is not worse than Data. Hongyuan Zhang et al.

Comparisons—Green Field Preferable not to define the second preamble format (GF): 11n GF has seen limited usage so far. One of the arguments in favor of GF in 11n was the existence of green space in 5 GHz due to the limited use of 11a If there are no 5 GHz deployments of 11n, then there is no point to TGac The assumption should be that there will be 5 GHz deployments of 11n. Like in 11n, multiple preamble types compounds the difficulty of auto-detection for small PHY efficiency improvement. GF protection exchanges offsets the PHY improvement. Hongyuan Zhang et al.

III. Re-present of Our Preamble Proposal (1) Hongyuan Zhang et al.

Preamble Design Goals Backward compatibility Robust legacy 11a deferral Robust legacy 11n deferral Reliable auto-detection among 11a, 11n (MM and GF), and VHT preambles Single preamble structure in SU and MU Signaling of VHT PHY information by VHTSIG. Training for wider channels, and detection and deferral in each sub-channel. Low PAPR Minimize overall preamble length Hongyuan Zhang et al.

Spoofing and Auto-detection Use L-SIG spoofing for both 11a and 11n receivers: As 11n spoofing for 11a/g receivers. Rate=6Mbps, Length/Rate indicates duration. Use 90-deg rotated BPSK (QBPSK) on VHTSIG symbol for VHT auto-detection. 11n receiver will treat the packet as 11a packet (L-SIG spoofing). Hongyuan Zhang et al.

Preamble Structure T Rate=6Mbps Length determined by T 2 symbols L-STF L-LTF L-SIG VHTSIGA VHT-STF VHT-LTFs VHTSIGB VHTData T VHT auto-detection Hongyuan Zhang et al.

Aggregation bit in VHT-SIGs for MU Packets? Last Symbol PHY Service VHT A - MPDU Tail Pad VHTSIG PHY L - TFs L - SIG VHTSIGA VHT - TFs Service VHT A - MPDU Tail B Pad PHY Service VHT A - MPDU Pad Tail MPDU MPDU - 3 Less than Length = Length = octets 8 - bit A - MPDU A - MPDU A - MPDU Null Null MAC Last byte subframe 1 subframe 2 subframe n subframe subframe Pad boundary There is no need to indicate the duration of the packet in VHT-SIG again Length information can be obtain from L-SIG Use A-MPDU structure to provide length information for individual MPDUs Require that A-MPDU always be used with VHT frame MAC provides an A-MPDU that fills the frame up to the last byte for each per-user stream, and PHY provides 0-7 bits of padding. Same padding scheme also defined in SU packets. “Aggregation” bit in VHTSIG is then not needed. Details refer to document 11-10-0064r1 (VHT frame padding). Hongyuan Zhang et al.

Summary on VHT-SIGs In MU, VHT-SIGA contains the “common” bits for all clients. Indicates number of space-time streams (NSTS) for each user. Need prior multiuser group and user ID assignment frame exchanges before DL-MU packets (e.g. by sounding and/or management frames). Each user will be able to get its own NSTS information from VHTSIGA.. Details refer to document 11-10-0073r2 (Group ID Concept for Downlink MU-MIMO Transmission). VHT-SIGB contains user-specific information (e.g. modulation and coding rate) and is spatially multiplexed for different clients. It is placed after all the VHT-LTFs to enable better receiver side interference mitigation in DL-MU before decoding VHT-SIGB. This requires each client getting as many LTFs as needed to train the total number of spatial streams across all users—named as “resolvable VHT-LTF”. “Non-resolvable VHT-LTF” may be selected if all clients do not support receiver side interference mitigation, or if interference mitigation is not required . Rx interference mitigation in DL-MU refer to document 11-09-1234r1 (Interference Cancellation for Downlink MU-MIMO). Hongyuan Zhang et al.

VHT-SIG Fields Considerations Bandwidth Short GI Group ID Field MCS STBC Sounding Smoothing Coding Type CRC & Tail For further investigation Full/partial MAC ID Number of Extension Streams Resolvable/Non-resolvable LTF Indication Details of bit allocation are subject to change if necessary Hongyuan Zhang et al.

Straw Poll on Numerology Do you support adding a basic guideline on the numerology for 11ac device described as in Section I of 11-10/0070r2 to the spec framework document, 11-09-0992? Yes: No: Abs: Hongyuan Zhang et al.

Straw Poll on Preamble Structure Do you support adding the 11ac preamble structure with two SIGNAL fields (VHT-SIGA with 2 OFDM symbols located before VHT-STF and VHT-SIGB with a single OFDM symbol located after VHT-LTFs) as in Section III (Slide 22) of 11-10/0070r2 to the spec framework document, 11-09-0992? Yes: No: Abs: Hongyuan Zhang et al.

Straw Poll on Spoofing Do you support to have BPSK on the 1st VHT-SIGA symbol and 90-deg rotated BPSK (QBPSK) on the 2nd VHT-SIGA symbol for VHT auto-detection as in Section III (Slide 20) of 11-10/0070r2, and to edit the spec framework document, 11-09-0992, accordingly? Yes: No: Abs: Hongyuan Zhang et al.