Enhancing WLAN backoff procedures for downlink MU-MIMO support

The Enhanced Distributed Channel Access (EDCA) mechanism is the most commonly implemented medium access scheme in today´s wireless local area network (WLAN) products. With the introduction of the downlink multi-user MIMO (DL MU-MIMO) technology to the current IEEE 802.11 specification, the EDCA mechanism has been enhanced accordingly to support multiple simultaneous transmissions to different stations. In this paper, we report the work the IEEE 802.11ac task group has done for enhancing the backoff schemes of the EDCA mechanism and point out its issues. We then present two of our approaches which we believe perform better, in terms of fairness and network throughput, than the approach adopted by the current 802.11ac draft specification. OPNET simulations were conducted for performance evaluation.