Development of Contention Window based MIDB algorithm for IEEE 802.11 based Wireless Networks

IEEE 802.11 is the most popular standard used in Wireless Local Area Networks (WLANs). Several Markov chain models have been developed to evaluate and to enhance the performance of the IEEE 802.11 Distributed Coordination Function (DCF) protocol. However, the existing models cannot accurately predict the performance of the network. Also, the existing models suffer with high packet collisions resulting in degradation of throughput and end-to-end delay, particularly under congested environments. The network performance also degrades due to propagation through erroneous channels. To overcome these problems, it is necessary to design an exact Markov chain model with an efficient Medium Access Control (MAC) algorithm for IEEE 802.11 based wireless networks in real traffic scenarios. This paper proposes an exact Markov chain model to accurately predict the performance of the wireless networks. To alleviate the collisions and to improve the throughput, a new backoff algorithm namely, Contention Window based Multiplicative Increase Decrease Backoff (CWMIDB) algorithm is proposed in this paper. A simple mathematical model is developed for transmission probability. Detailed results are presented which show the improvement in system throughput using CWMIBD algorithm compared to that of the existing backoff algorithms.