802.11ac preamble for VHT auto-detection 2010-05-18 Month Year doc.: IEEE 802.11-yy/xxxxr0 doc.: IEEE 802.11-yy/xxxxr0 802.11ac preamble for VHT auto-detection Date: 2010-05-20 Authors: Il-Gu Lee et al. Page 1 Il-Gu Lee, ETRI

Overview Preamble design considerations for VHT auto-detection 2010-05-18 doc.: IEEE 802.11-yy/xxxxr0 Overview Preamble design considerations for VHT auto-detection Fairness / safety for 11a/n and 11ac devices Reliability for 11a/n and 11ac devices Proposals in TGac on preamble Proposal (1) 10/070r0 (Zhang, et al) VHT-SIGA1: BPSK VHT-SIGA2: Q-BPSK Proposal (2) 10/039r0 (Lee, et al) VHT-SIGA2: Alternative Q-BPSK/BPSK Evaluation results 11ac preamble design evaluation for 11n receivers 11ac/11a detection performance for 11ac receivers Il-Gu Lee et al. Il-Gu Lee, ETRI

2010-05-18 doc.: IEEE 802.11-yy/xxxxr0 Proposal (1) in 10/0070r0 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 For two symbols of VHT-SIGA, I energy equals to Q energy. Q-BPSK 2nd symbol of VHTSIGA: Need to consider about 11n devices which use 2nd symbol of HT-SIG for HT auto-detection. Il-Gu Lee et al. Il-Gu Lee, ETRI

Issues with proposal (1) 2010-05-18 doc.: IEEE 802.11-yy/xxxxr0 Issues with proposal (1) Backward compatibility issue 802.11n standard defines Q-BPSK in two symbols of HT-SIG. Given various existing implementations of 11n auto-detection. Not fair to pre-assume any 11n auto-detect method. Proposal (1) assumes that all 11n receivers do not use 2nd symbol of HT-SIG for HT auto-detection. It is unfair and risky to use Q-BPSK in 2nd symbol of VHT-SIG. Il-Gu Lee et al. Il-Gu Lee, ETRI

HT-SIG in IEEE 802.11n Standard [1] IEEE 802.11n, “Part 11: Wireless LAN Media Access Control (MAC) and Physical Layer (PHY) Specifications: Enhancements for Higher Throughput,” IEEE Std. 802.11n, Oct. 2009. Il-Gu Lee et al.

Backward Compatibility with 802.11n in TGac Functional Requirements [2] Peter Loc, et. al., TGac Functional Requirements and Evaluation Methodology Rev. 12, IEEE 802.11-09/00451r12, Mar. 18, 2010 Il-Gu Lee et al.

(Alternative Q-BPSK/BPSK) 2010-05-18 doc.: IEEE 802.11-yy/xxxxr0 Our Proposal (2) L-SIG (BPSK) VHT-SIGA1 (BPSK) VHT-SIGA2 (Alternative Q-BPSK/BPSK) 11n auto-detection in 11n devices with alternative Q-BPSK/BPSK VHT-SIGA1 gives certainty to 11a/n devices as I energy of full subcarriers. VHT-SIGA2 gives uncertainty to 11n devices which use 2nd symbol of HT-SIG for HT auto-detection. For two symbols, VHT-SIGA1 is only meaningful for 11n receiver. 11n devices detect the proposal (2) type 11ac packet as legacy packet. Il-Gu Lee et al. Il-Gu Lee, ETRI

Simulation Results 1) 11ac Preamble Design Evaluation for 11n Receivers 2) 11ac/11a Auto-detection Performance for 11ac Receivers Il-Gu Lee et al.

1) 11ac Preamble Design Evaluation for 11n Receivers Il-Gu Lee et al.

Simulation Conditions 1x1 802.11n configuration. 1 spatial stream 20MHz bandwidth mode. Transmitted packets (N : number of Q-BPSK tones); Proposal (1) N=48; Full Q-BPSK Proposal (2) N=24 : Alternative Q-BPSK(2n+1)/BPSK(2n) N=36 : Alternative Q-BPSK(4n+1,4n+2 and 4n+3)/BPSK(4n) AWGN added. HT auto-detection w/ 2 symbols of HT-SIG. Il-Gu Lee et al.

Proposal 1 Blue: In-phase Red: Quadrature-phase Figure 1. High SNR (25dB) Figure 2. Low SNR (5dB) High SNR Low SNR VHT-SIGA1 VHT-SIGA2 Total Energy Equality I-phase 0.38 0.01 0.39 100% 0.11 0.50 96% Q-phase 0.10 0.48 - Regardless the signal to noise ratio, I energy equals to Q energy over 2 symbols of HT-SIG. - 11n receivers which use 2 symbols of HT-SIG may have severe performance degradation Il-Gu Lee et al.

Proposal 2 (N=24) Blue: In-phase Red: Quadrature-phase Figure 1. High SNR (25dB) Figure 2. Low SNR (5dB) High SNR Low SNR VHT-SIGA1 VHT-SIGA2 Total Energy equality I-phase 0.38 0.18 0.56 39% 0.39 0.21 0.60 56% Q-phase 0.01 0.22 0.10 0.24 0.34 - Regardless the signal to noise ratio, I energy is larger than Q energy over 2 symbols of HT-SIG. - 11n receivers which use 2 symbols of HT-SIG can detect (2) type packet as a legacy mode Il-Gu Lee et al.

Proposal 2 (N=36) Blue: In-phase Red: Quadrature-phase Figure 1. High SNR (25dB) Figure 2. Low SNR (5dB) High SNR Low SNR VHT-SIGA1 VHT-SIGA2 Total Energy equality I-phase 0.38 0.09 0.47 64% 0.40 0.17 0.57 66% Q-phase 0.01 0.29 0.30 0.10 0.28 - Regardless the signal to noise ratio, I energy is larger than Q energy over 2 symbols of HT-SIG. - 11n receivers which use 2 symbols of HT-SIG can detect (2) type packet as a legacy mode Il-Gu Lee et al.

11n Auto-detection Error Rate in 11n Device SNR [dB] Proposal 1 (N=48) Proposal 2 (N=24) Proposal 2 (N=36) 14 0.56 12 0.55 10 0.54 8 6 0.52 4 0.009 2 0.49 0.004 0.054 Proposal (1) has about 50% 11n auto-detection error rate regardless of signal-to-noise ratio. On the other hand, proposal (2) doesn’t have auto-detection error in this simulation. Tradeoff relationship between 11n safety and 11ac/11a auto-detection. Depend on the number of Q-BPSK tones. The larger number of Q-BPSK tones allow 11ac receivers to auto-detect 11ac/11a better, but worse 11n safety for 11n standard. The smaller number of Q-BPSK tones give safety to 11n standard, but worse 11ac/11a auto-detection for 11ac receivers. Il-Gu Lee et al.

2) 11ac/11a Auto-detection Performance for 11ac Receivers Il-Gu Lee et al.

11ac Miss Detection Simulation Conditions 1x1 802.11ac configuration. 1 spatial stream 20MHz bandwidth mode. Transmitted packets; Proposal (1) Proposal (2) Channel D 11ac/11a auto-detection comparison; Proposal(1) Proposal(2) Il-Gu Lee et al.

11ac Miss Detection for 11ac Packet When 11ac packet sent to 11ac receiver, miss detection of 11ac packet as 11a packet 8.5dB Il-Gu Lee et al.

11ac False Detection Simulation Conditions 1x1 802.11ac configuration 1 spatial stream 20MHz bandwidth mode. Transmitted packets; 11a packet Channel D 11ac/11a auto-detection comparison; Proposal (1) Proposal (2) Il-Gu Lee et al.

11ac False Detection for 11a Packet When11a packet sent to 11ac receiver, false detection of 11a packet as 11ac packet 8.7dB Il-Gu Lee et al.

11ac/11a auto-detection performance Proposal 2 (N=24) Even/odd alternative Q-BPSK/BPSK. 24 Q-BPSK tones and 24 BPSK tones. 11ac auto-detection performance degradation due to the reduced Q-BPSK tones is ~1.5dB at 10-2 error rate. Proposal 2 (N=36) Modulo 4 alternative Q-BPSK/BPSK. For example, Q-BPSK for 4n+1, 4n+2, 4n+3, and BPSK for 4n (n=0,1,2..11) 36 Q-BPSK tones and 12 BPSK tones. 11ac auto-detection performance has only ~0.2dB loss at 10-2 error rate. For SNR range of interest for packet demodulation (> 10 dB) both proposals provide sufficient performance. Tradeoff relationship between 11n safety and 11ac/11a auto-detection performance. Il-Gu Lee et al.

Comparisons Criterions Proposal 1 2 1st VHT-SIG BPSK 2nd VHT-SIG Q-BPSK Alternative Q-BPSK/BPSK 11n fairness & safety Bad Good 11ac/11a reliability Sufficient - 11ac standard should be backward-compatible with 11n standard. Proposal (1) needs safety mechanism for concerns on the standard issue. Proposal (2) is a possible solution. Il-Gu Lee et al.

Summary Existing proposal in TGac for VHT auto-detection 2010-05-18 doc.: IEEE 802.11-yy/xxxxr0 Summary Existing proposal in TGac for VHT auto-detection Proposal (1) 10/070r0 (Zhang, et al) Unfair and risky to pre-assume any HT auto-detection of 11n devices. A possible method proposed: Proposal (2) uses alternative Q-BPSK/BPSK on 2nd VHT-SIG symbol. Guarantee more reliable auto-detection for existing 11n devices. Conclusion Proposal(1) has concerns about 11n auto-detection for 11n receivers. Our proposal guarantees more reliable auto-detection for existing 11n devices by simple modification, and at the same time, maintain sufficient 11a/11ac detection performance. Considering the fairness, safety, and reliability for HT/VHT auto-detection, our proposed method can be a good compromised solution for VHT preamble structure. Il-Gu Lee et al. Il-Gu Lee, ETRI

Strawpoll : Do you support to do the following insertion to the specification frame work document (IEEE 802.11-09/0992r9) R3.2.1.G: The 1st symbol of VHT-SIG-A shall be BPSK modulated. The subsequent symbol of VHT-SIG-A shall be 90-degree rotated BPSK (QBPSK) modulated on the data subcarriers whose indices are 4n+1, 4n+2, 4n+3 and BPSK modulated on the data subcarriers whose indices are 4n (n=0,1,2,..11) for VHT auto-detect. Yes No Abstain Il-Gu Lee et al.

2010-05-18 doc.: IEEE 802.11-yy/xxxxr0 References [1] IEEE 802.11n, “Part 11: Wireless LAN Media Access Control (MAC) and Physical Layer (PHY) Specifications: Enhancements for Higher Throughput,” IEEE Std. 802.11n, Oct. 2009. [2] Peter Loc, et. al., TGac Functional Requirements and Evaluation Methodology Rev. 12, IEEE 802.11-09/00451r12, Mar. 18, 2010 [3] Hongyuan Zhang , et. al., 802.11ac Preamble, IEEE 802.11-10/0070r1, Feb. 10, 2010 [4] Yung-Szu Tu, et. al., Proposed TGac Preamble, IEEE 802.11-10/0130r0, Jan. 20, 2010 [5] Il-Gu Lee, et. al., 802.11ac preamble for VHT auto-detection, 10/0359r0, Mar. 16, 2010 Il-Gu Lee et al. Il-Gu Lee, ETRI