1. doc.:IEEE 802.11-10/0359r1 Submission xx. xx, 2010 Il-Gu Lee et al.Slide 1 802.11ac preamble for VHT auto-detection Date: 2010-05-18 Authors:

2. Submission doc.:IEEE 802.11-10/0359r1 xx. xx, 2010 Slide 2 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-SIGA1: BPSK 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.

3. Submission doc.:IEEE 802.11-10/0359r1 xx. xx, 2010 Slide 3 Proposal (1) in 10/0070r0 Il-Gu Lee et al. VHT-STFVHT-LTFsL-STFL-LTFL-SIGVHTSIGAVHTSIGBVHTData 2 symbols 1 symbol T VHT auto-detection Rate=6Mbps Length determined by T For two symbols of VHT-SIGA, I energy equals to Q energy. Q-BPSK 2 nd symbol of VHTSIGA: Need to consider about 11n devices which use 2 nd symbol of HT-SIG for HT auto-detection.

4. Submission doc.:IEEE 802.11-10/0359r1 xx. xx, 2010 Slide 4 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 2 nd symbol of HT-SIG for HT auto-detection. –It is unfair and risky to use Q-BPSK in 2 nd symbol of VHT-SIG. Il-Gu Lee et al.

5. Submission doc.:IEEE 802.11-10/0359r1 xx. xx, 2010 HT-SIG in IEEE 802.11n Standard Il-Gu Lee et al.Slide 5 [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.

6. Submission doc.:IEEE 802.11-10/0359r1 xx. xx, 2010 Backward Compatibility with 802.11n in TGac Functional Requirements Il-Gu Lee et al.Slide 6 [2] Peter Loc, et. al., TGac Functional Requirements and Evaluation Methodology Rev. 12, IEEE 802.11-09/00451r13, Mar. 18, 2010

7. Submission doc.:IEEE 802.11-10/0359r1 xx. xx, 2010 Slide 7 Our Proposal (2) Il-Gu Lee et al. 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 2 nd 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. VHT-SIGA2 (Alternative Q-BPSK/BPSK) L-SIG (BPSK) VHT-SIGA1 (BPSK)

8. Submission doc.:IEEE 802.11-10/0359r1 xx. xx, 2010 Simulation Results 1) 11ac Preamble Design Evaluation for 11n Receivers 2) 11ac/11a Auto-detection Performance for 11ac Receivers Il-Gu Lee et al.Slide 8

9. Submission doc.:IEEE 802.11-10/0359r1 xx. xx, 2010 1) 11ac Preamble Design Evaluation for 11n Receivers Il-Gu Lee et al.Slide 9

10. Submission doc.:IEEE 802.11-10/0359r1 xx. xx, 2010 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. Slide 10Il-Gu Lee et al.

11. Submission doc.:IEEE 802.11-10/0359r1 xx. xx, 2010 Proposal 1 Figure 1. High SNR (25dB)Figure 2. Low SNR (5dB) High SNRLow SNR VHT- SIGA1 VHT- SIGA2 TotalEnergy Equality VHT- SIGA1 VHT- SIGA2 TotalEnergy Equality I-phase0.380.010.39100%0.390.110.5096% Q-phase0.010.380.390.100.380.48 - 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 Blue: In-phase Red: Quadrature-phase Slide 11Il-Gu Lee et al.

12. Submission doc.:IEEE 802.11-10/0359r1 xx. xx, 2010 Proposal 2 (N=24) - 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 Blue: In-phase Red: Quadrature-phase Figure 1. High SNR (25dB)Figure 2. Low SNR (5dB) Slide 12 High SNRLow SNR VHT- SIGA1 VHT- SIGA2 TotalEnergy equality VHT- SIGA1 VHT- SIGA2 TotalEnergy equality I-phase0.380.180.5639%0.390.210.6056% Q-phase0.010.210.220.100.240.34 Il-Gu Lee et al.

13. Submission doc.:IEEE 802.11-10/0359r1 xx. xx, 2010 Proposal 2 (N=36) - 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 Blue: In-phase Red: Quadrature-phase Figure 1. High SNR (25dB)Figure 2. Low SNR (5dB) Slide 13 High SNRLow SNR VHT- SIGA1 VHT- SIGA2 TotalEnergy equality VHT- SIGA1 VHT- SIGA2 TotalEnergy equality I-phase0.380.090.4764%0.400.170.5766% Q-phase0.010.290.300.100.280.38 Il-Gu Lee et al.

14. Submission doc.:IEEE 802.11-10/0359r1 xx. xx, 2010 11n Auto-detection Error Rate in 11n Device SNR [dB]Proposal 1 (N=48) Proposal 2 (N=24) Proposal 2 (N=36) 140.5600 120.5500 100.5400 80.5600 60.5200 40.5400.009 20.490.0040.054 -Proposal (1) has about 50% 11n auto-detection error rate regardless 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. Slide 14Il-Gu Lee et al.

15. Submission doc.:IEEE 802.11-10/0359r1 xx. xx, 2010 2) 11ac/11a Auto-detection Performance for 11ac Receivers Il-Gu Lee et al.Slide 15

16. Submission doc.:IEEE 802.11-10/0359r1 xx. xx, 2010 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) Slide 16Il-Gu Lee et al.

17. Submission doc.:IEEE 802.11-10/0359r1 xx. xx, 2010 11ac Miss Detection for 11ac Packet When 11ac packet sent to 11ac receiver, miss detection of 11ac packet as 11a packet 8.5dB Slide 17Il-Gu Lee et al.

18. Submission doc.:IEEE 802.11-10/0359r1 xx. xx, 2010 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) Slide 18Il-Gu Lee et al.

19. Submission doc.:IEEE 802.11-10/0359r1 xx. xx, 2010 11ac False Detection for 11a Packet When11a packet sent to 11ac receiver, false detection of 11a packet as 11ac packet Slide 19 8.7dB Il-Gu Lee et al.

20. Submission doc.:IEEE 802.11-10/0359r1 xx. xx, 2010 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.Slide 20

21. Submission doc.:IEEE 802.11-10/0359r1 xx. xx, 2010 Comparisons CriterionsProposal 1 Proposal 2 1 st VHT-SIGBPSK 2 nd VHT-SIGQ-BPSKAlternative Q-BPSK/BPSK 11n fairness & safetyBadGood 11ac/11a reliabilitySufficient Il-Gu Lee et al.Slide 21 - 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.

22. Submission doc.:IEEE 802.11-10/0359r1 xx. xx, 2010 Slide 22 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: –(2A) uses alternative Q-BPSK/BPSK on 2 nd 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.

23. Submission doc.:IEEE 802.11-10/0359r1 xx. xx, 2010 Slide 23 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 802.11-09/00451r13, 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, Mar. 16, 2010 Il-Gu Lee et al.