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Discussions on 11ac PHY Efficiency. Date: 2013-05-09. Authors:. Focus to Study. Straw Poll in [1] Do you support starting a new study group called “ high efficiency WLAN” to enhance 802.11 PHY and MAC in 2.4 and 5GHz with a focus on: Improving spectrum efficiency and area throughput
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Discussions on 11ac PHY Efficiency Date: 2013-05-09 Authors: Jianhan Liu, etc. Mediatek Inc.
Focus to Study • Straw Poll in [1] • Do you support starting a new study group called “high efficiency WLAN” to enhance 802.11 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.
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 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 • Maximum 8 spatial streams: 8x8 antenna array Jianhan Liu, etc. Mediatek Inc.
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.
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.
Case 1: 1 RX Antenna • Improves Efficiency when SNR is high Jianhan Liu, etc. Mediatek Inc.
Case 2: 2 RX antenna • Improves Efficiency when SNR is high Jianhan Liu, etc. Mediatek Inc.
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.
Reference [1] IEEE 802.11-13-/0339r10, “High-efficiency WLAN Straw poll”, Laurent Cariou, etc. Jianhan Liu, etc. Mediatek Inc.
Back UpsQAM BER In AWGN Channel Jianhan Liu, etc. Mediatek Inc.