Improving WLAN voice capacity through dynamic priority access

Abstract

The most commonly deployed wireless local area network (WLAN) standard, IEEE 802.11b, provides no inherent quality of service (QoS) mechanisms to support delay sensitive applications. In particular, 802.11b WLANs exhibit poor voice capacity. This problem stems from limitations in the mandatory medium access control (MAC) protocol, called the distributed coordination function (DCF). WLANs commonly comprise an access point (AP) that must deliver all downlink packets, yet is afforded no special privileges under the DCF. This disparity leads to high downlink packet delays, which is the limiting factor in WLAN voice capacity. We believe that the main mechanism to improve capacity is to enable the AP to acquire the medium with a higher priority than the stations. This method is espoused in the forthcoming QoS-extension, IEEE 802.11e. In addition to the technique itself, knowing when and how long to apply it is critical for voice capacity improvement. We present such a technique, named aggrementing, for legacy 802.11b APs, as well as a generic approach that relates real-time system performance with the dynamics of such priority medium access techniques. We demonstrate that intelligently applying these techniques can improve WLAN voice capacity by as much as 25%.