Capacity Analysis of Supporting VoIP in IEEE 802.11e EDCA WLANs

Directly implementing voice over Internet protocol (VoIP) over infrastructure wireless local area networks (WLANs) will have the bottleneck problem in the access point (AP). In this paper, we propose to use the service differentiation provided by the new IEEE 802.11e standard to solve the bottleneck problem and improve the voice capacity. In particular, we propose to allocate higher priority access category (AC) to the AP while allocating lower priority AC to mobile stations. We develop a simple Markov chain model, which considers not only the important enhanced distributed channel access (EDCA) parameters but also the channel errors. Based on the developed analytical model, we analyze the performance of VoIP over EDCA. Through appropriately selecting the EDCA parameters, we are able to differentiate the services for the downlink and the uplink. The experimental results are very promising: with the adjustment of only one EDCA parameter, we improve the VoIP capacity by 20 similar to 30%.