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

2. Overview Preamble design considerations for VHT auto-detection
doc.: IEEE 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

3.
doc.: IEEE 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

4. Issues with proposal (1)
doc.: IEEE 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

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

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

7. (Alternative Q-BPSK/BPSK)
doc.: IEEE 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

8. Simulation Results 1) 11ac Preamble Design Evaluation for 11n Receivers ) 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
1x n 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)
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.

12. 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.

13. 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.

14. 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.

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

16. 11ac Miss Detection Simulation Conditions
1x ac 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
1x ac 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
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.

22. Summary Existing proposal in TGac for VHT auto-detection
doc.: IEEE 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

23. Strawpoll :
Do you support to do the following insertion to the specification frame work document (IEEE /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.

24.
doc.: IEEE yy/xxxxr0
References
[1] IEEE n, “Part 11: Wireless LAN Media Access Control (MAC) and Physical Layer (PHY) Specifications: Enhancements for Higher Throughput,” IEEE Std n, Oct
[2] Peter Loc, et. al., TGac Functional Requirements and Evaluation Methodology Rev. 12, IEEE /00451r12, Mar. 18, 2010
[3] Hongyuan Zhang , et. al., ac Preamble, IEEE /0070r1, Feb. 10, 2010
[4] Yung-Szu Tu, et. al., Proposed TGac Preamble, IEEE /0130r0, Jan. 20, 2010
[5] Il-Gu Lee, et. al., ac preamble for VHT auto-detection, 10/0359r0, Mar. 16, 2010
Il-Gu Lee et al.
Il-Gu Lee, ETRI