Distributed Contention Control in Heterogeneous 802.11b WLANs

Several feedback-based mechanisms have been proposed to maximize the IEEE 802.11 MAC protocol efficiency by guaranteeing an optimal time-spreading of users' channel accesses. However, these solutions suffer from a significant unfairness problem in the presence of stations adopting the standard binary exponential backoff algorithm. Generally, a few legacy stations are sufficient to completely starve enhanced stations employing a modified 802.11 MAC protocol that adapts the backoff to the network contention level. In this paper we propose a credit-based scheme to enforce fairness in heterogeneous networks. Specifically, enhanced stations earn credits when releasing transmission opportunities granted by the standard protocol. The credits are a virtual currency spent by the enhanced stations to reclaim new transmission opportunities. In this paper, we apply our solution to the distributed mechanism for contention control named AOB [5]. Simulation results show the effectiveness of the proposed mechanism in all the network scenarios considered