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802.11ac preamble for VHT auto-detection

802.11ac preamble for VHT auto-detection. Date: 2010-05-18. Authors:. 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)

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802.11ac preamble for VHT auto-detection

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  1. 802.11ac preamble for VHT auto-detection Date: 2010-05-18 Authors: Il-Gu Lee et al.

  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. 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 Il-Gu Lee et al. 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.

  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 2nd symbol of HT-SIG for HT auto-detection. • It is unfair and risky to use Q-BPSKin 2nd symbol of VHT-SIG. Il-Gu Lee et al.

  5. 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.

  6. Backward Compatibility with 802.11nin TGac Functional Requirements [2] Peter Loc, et. al., TGac Functional Requirements and Evaluation Methodology Rev. 12, IEEE 802.11-09/00451r13, Mar. 18, 2010 Il-Gu Lee et al.

  7. 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.

  8. Simulation Results1) 11ac Preamble Design Evaluation for 11n Receivers 2) 11ac/11a Auto-detection Performance for 11ac Receivers Il-Gu Lee et al.

  9. 1) 11ac Preamble Design Evaluation for 11n Receivers Il-Gu Lee et al.

  10. 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.

  11. Proposal 1 Blue: In-phase Red: Quadrature-phase Figure 1. High SNR (25dB) Figure 2. Low SNR (5dB) - 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.

  12. Proposal 2 (N=24) Blue: In-phase Red: Quadrature-phase Figure 1. High SNR (25dB) Figure 2. Low SNR (5dB) - 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.

  13. Proposal 2 (N=36) Blue: In-phase Red: Quadrature-phase Figure 1. High SNR (25dB) Figure 2. Low SNR (5dB) - 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.

  14. 11n Auto-detection Error Rate in 11n Device • 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. Il-Gu Lee et al.

  15. 2) 11ac/11a Auto-detection Performance for 11ac Receivers Il-Gu Lee et al.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  21. Comparisons • - 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.

  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 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.

  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.

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