Improved MAC protocols for DCF and PCF modes over fading channels in wireless LANs

Wireless LAN has become increasingly popular as a medium to connect portable devices to the network. Most of the existing wireless LAN protocols based on IEEE standard 802.11 assume that the wireless channel is time invariant and thus assign radio resources accordingly. In this paper, we devise a modified MAC level channel allocation method by carefully scheduling radio resource according to temporal channel characteristics, assuming the influence of channel fading. Based on this method we propose new protocols for the distributed coordination function (DCF) and the point coordination function (PCF), the two modes of communication defined in the IEEE standard for WLAN. The proposed protocols introduce minimum computational overhead. Our simulations show that the proposed PCF protocol improves the channel capacity up to 14% and the DCF protocol improves the channel capacity up to 90%, depending on the loss rate and temporal characteristics of the wireless channel. We also show that the proposed DCF protocol can lower SNR requirements thus potentially extending the battery life of portable devices that use WLAN.