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802.11ac preamble for VHT auto-detection

802.11ac preamble for VHT auto-detection. Date: 2010-03- 16. Authors:. 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)

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802.11ac preamble for VHT auto-detection

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  1. 802.11ac preamble for VHT auto-detection Date: 2010-03-16 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 • 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. 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. BPSK 1st symbol of VHTSIGA : Good approach for 11a/n devices. Q-BPSK 2nd symbol of VHTSIGA: Need to consider about 11n devices which use 2nd symbol of HT-SIG for HT auto-detection.

  4. Proposal (2) in 10/0130r0 [1] Hongyuan Zhang , et. al., 802.11ac Preamble, IEEE 802.11-10/0070r1, Feb. 10, 2010 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].

  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 2nd 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-BPSKin 2nd 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 1st symbol of VHT-SIG. Il-Gu Lee et al.

  6. Our Proposal (3-A) 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 2nd 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. Il-Gu Lee et al.

  7. Our Proposal (3-B) L-SIG (BPSK) VHT-SIGA1 (BPSK) VHT-SIGA2 (0/90 deg alternative BPSK) • 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 2nd 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. Il-Gu Lee et al.

  8. Our Proposal (3-C) L-SIG (BPSK data & normal pilot) VHT-SIGA1 (BPSK data & normal pilot) VHT-SIGA2 (0/90 deg alternative BPSK data & 90 deg pilots) 90 deg rotated data 90 deg rotated pilots Normal pilots • 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 2nd 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 pilotsprovide more reliability. Il-Gu Lee et al.

  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 1st VHT-SIG symbol. • (3-A) uses +/-45 deg alternative BPSK on 2nd VHT-SIG symbol. • (3-B) uses 0/90 deg alternative BPSK on 2nd 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 2nd 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. 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.

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