doc.:ieee 802.11-10/0359r1 submission xx. xx, 2010 il-gu lee et al.slide 1 802.11ac preamble for vht...
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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: 2010-05-18Authors:
Name Affiliations Address Phone email Il-Gu Lee ETRI Daejeon, Korea +82 42 860 1633 [email protected]
In-Kyeong Choi ETRI Daejeon, Korea +82 42 860 5242 [email protected]
YuRo Lee ETRI Daejeon, Korea +82 42 860 5693 [email protected]
Jong-Ee Oh ETRI Daejeon, Korea +82 42 860 1758 [email protected]
Eun-Young Choi ETRI Daejeon, Korea +82 42 860 1633 [email protected]
Sok-Kyu Lee ETRI Daejeon, Korea +82 42 860 5919 [email protected]
Minho Cheong ETRI Daejeon, Korea +82 42 860 5635 [email protected]
Submission
doc.:IEEE 802.11-10/0359r1xx. 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.
Submission
doc.:IEEE 802.11-10/0359r1xx. xx, 2010
Slide 3
Proposal (1) in 10/0070r0
Il-Gu Lee et al.
VHT-STF VHT-LTFsL-STF L-LTF L-SIG VHTSIGA VHTSIGB VHTData
2 symbols 1 symbol
T
VHT auto-detection
Rate=6MbpsLength determined by T
• 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.
Submission
doc.:IEEE 802.11-10/0359r1xx. 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 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.
Submission
doc.:IEEE 802.11-10/0359r1xx. 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.
Submission
doc.:IEEE 802.11-10/0359r1xx. xx, 2010
Backward Compatibility with 802.11nin 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
Submission
doc.:IEEE 802.11-10/0359r1xx. xx, 2010
Slide 7
Our Proposal (2)
Il-Gu Lee et al.
L-STF L-LTF VHT-LTFsVHT-SIGB
VHT-DATAVHT-STF
L-SIGVHT-
SIGA1VHT-
SIGA2
• 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.
VHT-SIGA2(Alternative Q-BPSK/BPSK)
Q
I
Q
I
Q
I
L-SIG(BPSK)
VHT-SIGA1(BPSK)
Submission
doc.:IEEE 802.11-10/0359r1xx. 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
Submission
doc.:IEEE 802.11-10/0359r1xx. xx, 2010
1) 11ac Preamble Design Evaluation for 11n Receivers
Il-Gu Lee et al.Slide 9
Submission
doc.:IEEE 802.11-10/0359r1xx. 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 10 Il-Gu Lee et al.
Submission
doc.:IEEE 802.11-10/0359r1xx. xx, 2010
Proposal 1
Figure 1. High SNR (25dB) Figure 2. Low SNR (5dB)
High SNR Low SNR
VHT-SIGA1
VHT-SIGA2
Total EnergyEquality
VHT-SIGA1
VHT-SIGA2
Total EnergyEquality
I-phase 0.38 0.01 0.39 100% 0.39 0.11 0.50 96%
Q-phase 0.01 0.38 0.39 0.10 0.38 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
Blue: In-phaseRed: Quadrature-phase
Slide 11
-1 0 1
-1
0
1
Constellation of VHT-SIGA1
In-Phase
Qua
drat
ure-
Pha
se
-1 0 1
-1
0
1
Constellation of VHT-SIGA2
In-Phase
Qua
drat
ure-
Pha
se
0 20 40 60
-1
0
1
sample index
nom
aliz
ed a
mpl
itude
Equalized Output of VHT-SIGA1
0 20 40 60
-1
0
1
sample index
nom
aliz
ed a
mpl
itude
Equalized Output of VHT-SIGA2
-1 0 1
-1
0
1
Constellation of VHT-SIGA1
In-Phase
Qua
drat
ure-
Pha
se
-1 0 1
-1
0
1
Constellation of VHT-SIGA2
In-PhaseQ
uadr
atur
e-P
hase
0 20 40 60
-1
0
1
sample index
nom
aliz
ed a
mpl
itude
Equalized Output of VHT-SIGA1
0 20 40 60
-1
0
1
sample index
nom
aliz
ed a
mpl
itude
Equalized Output of VHT-SIGA2
Il-Gu Lee et al.
Submission
doc.:IEEE 802.11-10/0359r1xx. 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-phaseRed: Quadrature-phase
Figure 1. High SNR (25dB) Figure 2. Low SNR (5dB)
Slide 12
High SNR Low SNR
VHT-SIGA1
VHT-SIGA2
Total Energyequality
VHT-SIGA1
VHT-SIGA2
Total Energyequality
I-phase 0.38 0.18 0.56 39% 0.39 0.21 0.60 56%
Q-phase 0.01 0.21 0.22 0.10 0.24 0.34
-1 0 1
-1
0
1
Constellation of VHT-SIGA1
In-Phase
Qua
drat
ure-
Pha
se
-1 0 1
-1
0
1
Constellation of VHT-SIGA2
In-PhaseQ
uadr
atur
e-P
hase
0 20 40 60
-1
0
1
sample index
nom
aliz
ed a
mpl
itude
Equalized Output of VHT-SIGA1
0 20 40 60
-1
0
1
sample index
nom
aliz
ed a
mpl
itude
Equalized Output of VHT-SIGA2
-1 0 1
-1
0
1
Constellation of VHT-SIGA1
In-Phase
Qua
drat
ure-
Pha
se
-1 0 1
-1
0
1
Constellation of VHT-SIGA2
In-Phase
Qua
drat
ure-
Pha
se
0 20 40 60
-1
0
1
sample index
nom
aliz
ed a
mpl
itude
Equalized Output of VHT-SIGA1
0 20 40 60
-1
0
1
sample index
nom
aliz
ed a
mpl
itude
Equalized Output of VHT-SIGA2
Il-Gu Lee et al.
Submission
doc.:IEEE 802.11-10/0359r1xx. 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-phaseRed: Quadrature-phase
Figure 1. High SNR (25dB) Figure 2. Low SNR (5dB)
Slide 13
High SNR Low SNR
VHT-SIGA1
VHT-SIGA2
Total Energyequality
VHT-SIGA1
VHT-SIGA2
Total Energyequality
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 0.38
-1 0 1
-1
0
1
Constellation of VHT-SIGA1
In-Phase
Qua
drat
ure-
Pha
se
-1 0 1
-1
0
1
Constellation of VHT-SIGA2
In-Phase
Qua
drat
ure-
Pha
se
0 20 40 60
-1
0
1
sample index
nom
aliz
ed a
mpl
itude
Equalized Output of VHT-SIGA1
0 20 40 60
-1
0
1
sample index
nom
aliz
ed a
mpl
itude
Equalized Output of VHT-SIGA2
-1 0 1
-1
0
1
Constellation of VHT-SIGA1
In-Phase
Qua
drat
ure-
Pha
se
-1 0 1
-1
0
1
Constellation of VHT-SIGA2
In-PhaseQ
uadr
atur
e-P
hase
0 20 40 60
-1
0
1
subcarrier index
nom
aliz
ed a
mpl
itude
Equalized Output of VHT-SIGA1
0 20 40 60
-1
0
1
subcarrier index
nom
aliz
ed a
mpl
itude
Equalized Output of VHT-SIGA2
Il-Gu Lee et al.
Submission
doc.:IEEE 802.11-10/0359r1xx. xx, 2010
11n Auto-detection Error Rate in 11n DeviceSNR [dB] Proposal 1
(N=48)Proposal 2
(N=24)Proposal 2
(N=36)
14 0.56 0 0
12 0.55 0 0
10 0.54 0 0
8 0.56 0 0
6 0.52 0 0
4 0.54 0 0.009
2 0.49 0.004 0.054
- 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 14 Il-Gu Lee et al.
Submission
doc.:IEEE 802.11-10/0359r1xx. xx, 2010
2) 11ac/11a Auto-detection Performance for 11ac Receivers
Il-Gu Lee et al.Slide 15
Submission
doc.:IEEE 802.11-10/0359r1xx. 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 16 Il-Gu Lee et al.
Submission
doc.:IEEE 802.11-10/0359r1xx. 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 17 Il-Gu Lee et al.
Submission
doc.:IEEE 802.11-10/0359r1xx. 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 18 Il-Gu Lee et al.
Submission
doc.:IEEE 802.11-10/0359r1xx. 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.
Submission
doc.:IEEE 802.11-10/0359r1xx. 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
Submission
doc.:IEEE 802.11-10/0359r1xx. xx, 2010
Comparisons
Criterions Proposal 1
Proposal 2
1st VHT-SIG BPSK BPSK
2nd VHT-SIG Q-BPSK Alternative Q-BPSK/BPSK
11n fairness & safety Bad Good
11ac/11a reliability Sufficient Sufficient
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.
Submission
doc.:IEEE 802.11-10/0359r1xx. 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 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.
Submission
doc.:IEEE 802.11-10/0359r1xx. 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.