Medium access control protocol for voice traffic in IEEE 802.11 WLANs

Recently, voice over WLAN has become an attractive service, and it is expected to be the most popular application in the near future due to its low cost and easy deployment. It has been reported that there occurs unfairness between downlink and uplink in the 802.11 WLAN. This is mainly caused by CSMA/CA employed in DCF. All stations including an AP fairly compete for shared wireless medium. Thus, in particular, the unfairness has an adverse impact on bi-directional voice calls. Downlink voice connections become a primary factor to limit voice capacity. In this paper, we propose a novel medium access protocol, so called DCFmm, in order to improve QoS of downlink voice traffic as well as fairness between bi-directional voice connections. DCFmm is designed to enhance 802.11 DCF, and is fully compatible with the legacy DCF. In addition, it requires only protocol modifications of an AP. Thus, it can be easily implemented into existing 802.11 WLANs. DCFmm is compared with two conventional techniques through computer simulations. Extensive simulation results show that the proposed DCFmm can improve fairness between downlink and uplink, and consequently, support larger number of voice calls than DCF.