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N-BEB: New Binary Exponential Back-off Algorithm for IEEE 802.11
Mohammad Shurman and Bilal Al-Shua’b

In recent years, wireless ad-hoc networks have become increasingly popular because they are considered a de-facto alternative for infrastructureless environments. These networks are formed by a collection of independent wireless mobile nodes that can communicate and operate directly over wireless media without the need for a pre-existing communication infrastructure. Along with the hidden and exposed terminal problems, it has been observed that the fairness issue is responsible for DCF performance-degradation. The IEEE 802.11 DCF (Distributed Coordination Function) is considered the most popular technique used for the physical and MAC layers in ad-hoc networks. DCF is based on Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) mechanism. Since the IEEE 802.11 is the most implemented protocol, there has been countless research aimed at enhancing its performance in different ways, including modifying the Medium Access Control (MAC) algorithm (i.e. back-off algorithm). In this paper, a novel mechanism is suggested to resolve the IEEE 802.11 standard fairness problem, which results an unfair channel sharing between the stations due to the duplication of the Contention Window (CW) value each time an unsuccessful transmission occurs, while resets CW value in case of a successful transmission. To impose fairness in ad-hoc networks, our proposed idea dynamically tunes the CW value based on the previous transmission status of each node attempts to transmit. By studying the characteristics of the proposed algorithm using the NS2 simulator, we found that our proposed algorithm improves the fairness by fairly distributing channel between the competing nodes as well as has a remarkable reduction in the number of dropped packets. In addition, our proposed algorithm has a considerable improvement in the packet delivery ratio as well.

Keywords: IEEE802.11 back-off, BEB, QoS, chancel fairness, wireless MAC.

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