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Discussions on 11ac PHY Efficiency

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

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  1. Discussions on 11ac PHY Efficiency Date: 2013-05-09 Authors: Jianhan Liu, etc. Mediatek Inc.

  2. 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.

  3. 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.

  4. 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 • 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 • Improves Efficiency when SNR is high Jianhan Liu, etc. Mediatek Inc.

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

  8. 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. 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. Reference [1] IEEE 802.11-13-/0339r10, “High-efficiency WLAN Straw poll”, Laurent Cariou, etc. Jianhan Liu, etc. Mediatek Inc.

  11. Back UpsQAM BER In AWGN Channel Jianhan Liu, etc. Mediatek Inc.

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