Adaptive window mechanism for the IEEE 802.11 MAC in wireless ad hoc networks

Abstract

The IEEE 802.11 MAC protocol adopts the distributed coordination function (DCF) with a binary exponential backoff as a medium access control mechanism. According to previous research results and our simulation study, the performance of IEEE 802.11 is highly dependent upon the number of contending stations and the initial value of contention window (CWmin). In this paper, we propose an adaptive contention window mechanism that dynamically selects the optimal backoff window by estimating the current number of contending stations in wireless ad hoc networks. In the proposed scheme, when there are small number of contending stations, a smaller CWmin value is selected, while a larger CWmin value is selected when there are large number of contending stations. We study the performance of the proposed mechanism by simulation and we got an improved performance over the IEEE 802-11 MAC protocol which uses a fixed CWmin value.