1. Discussions on 11ac PHY Efficiency
May 2013
doc.: IEEE hew
May 2013
Discussions on 11ac PHY Efficiency
Date:
Authors:
Jianhan Liu, etc. Mediatek Inc.
Osama Aboul-Magd (Huawei Technologies)

2. Focus to Study Straw Poll in [1]
May 2013
doc.: IEEE /xxxxr0
May 2013
Focus to Study
Straw Poll in [1]
Do you support starting a new study group called “high efficiency WLAN” to enhance PHY and MAC in 2.4 and 5GHz with a focus on:
Improving spectrum efficiency and area throughput
Improving real world performance in indoor and outdoor deployments
in the presence of interfering sources, dense heterogeneous networks
in moderate to heavy user loaded Aps
Jianhan Liu, etc. Mediatek Inc.
Jianhan Liu, (Mediatek Inc.)

3. Spectrum Efficiency in 11n and 11ac
May 2013
doc.: IEEE /xxxxr0
May 2013
Spectrum Efficiency in 11n and 11ac
Spectrum efficiency improvement from 11n to 11ac
Spectrum Efficiency defined as Bits/Second/Hz
Bandwidth from 20MHz to 80MHz does not improve spectrum efficiency
20MHz 11n and 80MHz 11ac, for the same MCS, achieve same spectrum efficiency
One can combine four 11n APs and Four 11n STAs using 4 different 20MHz channels to achieve similar BSS throughput as 11ac 80MHz BSS
From Physical Layer perspective, 11ac improve efficiency over 11n by introducing the following technologies
256QAM modulation
Down Link MU-MIMO
Increase Maximum number of spatial streams to 8
Jianhan Liu, etc. Mediatek Inc.
Jianhan Liu, (Mediatek Inc.)

4. Spectrum Efficiency Improvement in 11ac
May 2013
Spectrum Efficiency Improvement in 11ac
256 QAM:
Compared to 11n 64QAM, spectrum efficiency improves by 33%
Cons: Require about 30dB SNR and coverage area is reduced
8x8 MIMO
Maximum 8 Spatial streams in 11ac improves spectrum efficiency by 100% compared to maximum 4 Spatial streams in 11ac
Cons: Support of 8 spatial streams for SU is not very practical
Downlink MU-MIMO
Improves Spectrum efficiency in downlink
Unlink spectrum efficiency is not addressed
Jianhan Liu, etc. Mediatek Inc.

5. Efficiency Improvement from DL MU MIMO
May 2013
Efficiency Improvement from DL MU MIMO
We consider the BSS spectrum efficiency by comparing DL MU MIMO and SU MIMO case
11n only supports SU MIMO
Simulation Setting:
4 TX antennas at AP; 1 or 2 of RX antennas at STA
Linear pre-coding for MU
IEEE channel B
Real Channel estimation based on NDP sounding and feedback
Real 11ac waveform
Highest MCS is 7 (compared with 11n)
Jianhan Liu, etc. Mediatek Inc.

6. Case 1: 1 RX Antenna May 2013 Improves Efficiency when SNR is high
Jianhan Liu, etc. Mediatek Inc.

7. Case 2: 2 RX antenna May 2013 Improves Efficiency when SNR is high
Jianhan Liu, etc. Mediatek Inc.

8. May 2013
Possibility of Further Improvement of Spectrum Efficiency using 11ac ideas
Higher constellation modulation than 256 QAM is not a practical approach
512QAM (12.5% improvement) requires 4dB more SNR in AGWN than 256QAM
512QAM is vulnerable to phase noise and channel estimation error
Larger number of spatial streams (>8) for SU is not very practical approach
DL MU MIMO
Efficiency is not improved much in low SNRs
Uplink Efficiency is not improved
Jianhan Liu, etc. Mediatek Inc.

9. May 2013
Summary
Most technologies introduced in 11ac to enhance spectrum efficiency works in high SNR
More spatial streams for SU and higher constellation modulation are not very practical
DL-MU-MIMO does not help the uplink spectrum efficiency
Jianhan Liu, etc. Mediatek Inc.

10. May 2013
Reference
[1] IEEE /0339r10, “High-efficiency WLAN Straw poll”, Laurent Cariou, etc.
Jianhan Liu, etc. Mediatek Inc.

11. Back Ups QAM BER In AWGN Channel
May 2013
Back Ups QAM BER In AWGN Channel
Jianhan Liu, etc. Mediatek Inc.