Resolving Collisions in IEEE 802.11 by means of Contention Window Reservation Scheduling

The random backoff contention window algorithm implemented in the IEEE 802.11 Distributed Coordination Function (DCF) provides a certain degree of collision mitigation. However, the issue of high collision rates within the IEEE 802.11 contention mode in a wireless local area network (WLAN) with high number of nodes is still not resolved. High packet collision rates result in throughput degradation and increased delay and thus unable to support QoS for multimedia traffic. In this paper, we propose a Contention Window Reservation Scheduling (CWRS) algorithm to resolve packet collisions in the contention mode of 802.11 WLANs. Through proper scheduling, this algorithm provides collision free transmission and optimized throughput. Within the proposed algorithm, saturation throughput increases by more than 30% when there are more than 20 nodes in the network and medium access delay is also reduced by up to 90% as compared to 802.11. This enables WLAN to support QoS for multimedia traffic.