1. doc.:IEEE 802.11-10/0359r0 Submission Mar. 16, 2010 Il-Gu Lee et al.Slide 1 802.11ac preamble for VHT auto-detection Authors: Date: 2010-03-16

2. Submission doc.:IEEE 802.11-10/0359r0 Mar. 16, 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 Two proposals in TGac on preamble –Proposal (1) 10/070r0 (Zhang, et al) VHT-SIGA1: BPSK VHT-SIGA2: Q-BPSK –Proposal (2) 10/130r0 (Tu, et al) VHT-SIGA1&2: Alternative 0/90 deg or +45/-45 deg BPSK Our proposal –Proposal (3-A) & (3-B) VHT-SIGA1: BPSK VHT-SIGA2: Alternative +45/-45 deg (or 0/90 deg) BPSK –Proposal (3-C) VHT-SIGA1: BPSK VHT-SIGA2: 3-A or 3-B for data tones & pilot assist Il-Gu Lee et al.

3. Submission doc.:IEEE 802.11-10/0359r0 Mar. 16, 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 BPSK 1 st symbol of VHTSIGA : Good approach for 11a/n devices. 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 802.11-10/0359r0 Mar. 16, 2010 Slide 4 Proposal (2) in 10/0130r0 Il-Gu Lee et al. Or the “90-deg Orthogonal shift” may be replaced by +-45-deg shift. Good approach to provide speed and reliability for 11ac devices. Need to consider about various existing HT auto-detection methods [1]. [1] Hongyuan Zhang, et. al., 802.11ac Preamble, IEEE 802.11-10/0070r1, Feb. 10, 2010

5. Submission doc.:IEEE 802.11-10/0359r0 Mar. 16, 2010 Slide 5 Issues with proposal (1) and (2) Both the proposal (1) and (2) are good approaches for 11ac devices, but they are risky and unfair for existing 11n devices. –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. 11n standard defines Q-BPSK in two symbols of HT-SIG. It is unfair and risky to use Q-BPSK in 2 nd symbol of VHT-SIG. –Proposal (2): Assumes that all 11n receivers can distinguish the existing 90 deg from the newly defined phase rotation. There are various algorithms and implementations of HT auto-detection. It is unfair and risky to manipulate modulation of the 1 st symbol of VHT-SIG. Il-Gu Lee et al.

6. Submission doc.:IEEE 802.11-10/0359r0 Mar. 16, 2010 Slide 6 Our Proposal (3-A) Il-Gu Lee et al. L-SIG (BPSK) VHT-SIGA1 (BPSK) VHT-SIGA2 (+45/-45 deg alternative BPSK) Proposal (3-A) is more fair and safer for 11a/n devices –VHT-SIGA1 gives certainty to 11a/n devices. –VHT-SIGA2 may give some uncertainty to 11n devices which use 2 nd symbol of HT-SIG for HT auto-detection. –11n devices can auto-detect well based on more reliable VHT-SIGA1. (Certainty of BPSK is always larger than uncertainty of +/-45 deg rotated BPSK) –11ac devices can auto-detect based on 45 deg difference.

7. Submission doc.:IEEE 802.11-10/0359r0 Mar. 16, 2010 Slide 7 Our Proposal (3-B) Il-Gu Lee et al. Proposal (3-B) is an alternative method of (3-A) –VHT-SIGA1 gives certainty to 11a/n devices. –VHT-SIGA2 may give some uncertainty to 11n devices which use 2 nd symbol of HT-SIG for HT auto-detection. –11n devices can auto-detect well based on more reliable VHT-SIGA1. –11ac devices can auto-detect based on 90 deg rotated BPSK in half sub-carriers. VHT-SIGA2 (0/90 deg alternative BPSK) L-SIG (BPSK) VHT-SIGA1 (BPSK)

8. Submission doc.:IEEE 802.11-10/0359r0 Mar. 16, 2010 Slide 8 Our Proposal (3-C) Il-Gu Lee et al. Proposal (3-C) is more reliable than proposal (3-A) and (3-B) –VHT-SIGA1 gives certainty to 11a/n devices. –VHT-SIGA2 may give some uncertainty to 11n devices which use 2 nd symbol of HT- SIG for HT auto-detection. –11n devices can auto-detect well based on more reliable VHT-SIGA1. –11ac devices can auto-detect based on 90 deg rotated BPSK in half sub-carriers. –In addition to 90 deg rotated data tones, 90 deg rotated pilots provide more reliability. L-SIG (BPSK data & normal pilot) VHT-SIGA1 (BPSK data & normal pilot) VHT-SIGA2 (0/90 deg alternative BPSK data & 90 deg pilots) Normal pilots 90 deg rotated pilots 90 deg rotated data

9. Submission doc.:IEEE 802.11-10/0359r0 Mar. 16, 2010 Slide 9 Summary Existing two proposals in TGac for VHT auto-detection –Proposal (1) 10/070r0 (Zhang, et al) and (2) 10/130r0 (Tu, et al) –Unfair and risky to pre-assume any HT auto-detection of 11n devices. Three possible methods proposed: –Proposal (3-A) and (3-B) maintain BPSK on 1 st VHT-SIG symbol. –(3-A) uses +/-45 deg alternative BPSK on 2 nd VHT-SIG symbol. –(3-B) uses 0/90 deg alternative BPSK on 2 nd VHT-SIG symbol. Guarantee more reliable auto-detection for existing 11n devices, regardless of what 11n auto-detect algorithm was implemented. –Proposal (3-C) uses 90 deg rotated pilots on 2 nd VHT-SIG symbol. Guarantees more reliable auto-detection for 11ac devices with additional tones. Conclusion –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.

10. Submission doc.:IEEE 802.11-10/0359r0 Mar. 16, 2010 Slide 10 References [1] Hongyuan Zhang, et. al., 802.11ac Preamble, IEEE 802.11- 10/0070r1, Feb. 10, 2010 [2] Hongyuan Zhang, et. al., 802.11ac Preamble, IEEE 802.11- 10/0070r0, Jan. 18, 2010 [3] Yung-Szu Tu, et. al., Proposed TGac Preamble, IEEE 802.11- 10/0130r0, Jan. 20, 2010 Il-Gu Lee et al.