A Simple but Effective Contention Aware and Adaptive Back-off Mechanism for Improving the Performance of IEEE 802.11 DCF

Abstract

In IEEE 802.11 standard, Distributed Coordination Function (DCF) is used as a primary medium access mechanism to share the common wireless medium. It is now well established that performance of the DCF degrades, especially when there is a large number of stations in the network contending for the wireless medium. This occurs due to the traditional parameter setting of its Binary Exponential Back-off (BEB) mechanism, which is used for collision avoidance. Therefore, in this paper, we propose an effective Contention Window (CW) and Contention Slot Selection (CSS) mechanism, named Contention Aware and Adaptive Back-off (CAAB) mechanism, to enhance performance of the IEEE 802.11 DCF. This mechanism differs from the standard back-off mechanism in two ways. First, contention window is not reset after successful transmission. Instead, stations will be allowed to go back to the possible preceding back-off stage after successful packet transmission in order to maintain the CW selection as a continuous process. Second, back-off timer is also not uniformly chosen in the respective CW interval. Instead to it, a non-uniform CSS distribution is used to select back-off timer in order to make the selection process adaptive according to the contention level. A Markov chain model is developed to derive the throughput and delay performance of the DCF based on CAAB mechanism. Finally, performance of our mechanism is evaluated with respect to the BEB and Double Increment Double Decrement mechanisms. Simulation results show that the proposed mechanism outperforms the referenced mechanisms in almost each count.