Performance evaluation of a fair backoff algorithm for IEEE 802.11 DFWMAC

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Abstract
Due to hidden terminals and a dynamic topology, contention among stations in an ad-hoc network is not homogeneous. Some stations are at a disadvantage in opportunity of access to the shared channel and can suffer severe throughput degradation when the traffic load is high. This is the so-called "fairness problem" encountered mainly in existing MAC protocols such as IEEE 802.11 Distributed Foundation Wireless Medium Access Control (DFWMAC) that is used as a basis for most performance evaluation of routing protocols in mobile ad-hoc networks (MANET). The binary exponential backoff (BEB) used in DFWMAC protocol to resolve contention is known to always favor the last station that succeeds its transmission, which exacerbates the fairness problem in heavy traffic. This paper reviews a measurement-based backoff algorithm for the DFWMAC protocol that achieves statistical fair access to the shared medium, and then models analytically the resultant system as a feedback control system. The analytical model confirms the fairness property of the algorithm, as well as its convergence and show the impact of different parameters of the algorithm on the performance of the system