Performance improvement of IEEE 802.11e to support QoS in saturated conditions

The IEEE 802.11 protocol has achieved worldwide acceptance with WLANs with minimum management and maintenance costs. However, IEEE 802.11 can only provide a best effort service and does not support the quality of services (QoS). Furthermore, the performance of the distributed coordination function (DCF) degrades significantly under heavy load due to the increasing time wasted during collision. In this paper, we pay attention to the enhanced distributed coordination function (EDCF) of IEEE 802.11e. We propose a new 802.11 Markov chain model of the station and study the behavior, and then extend the model to support EDCF. We present a more accurate analysis of the EDCF, and also study the saturation throughput when the maximum load that the system can support is reached.