Enhancing IEEE 802.11 in Selfish Environments

Wireless access protocols currently deployed in MANET use distributed contention resolution mechanisms for sharing the wireless channel. In this environment, selfish hosts that fail to adhere to the MAC protocol may obtain an unfair share of the channel bandwidth at the expense of performance degradation of well-behaved hosts. We present a novel access method, Predictable Random Backoff (PRB), that is capable of mitigating the misbehavior of selfish hosts; particularly, hosts that deliberately do not respect the random deferment of the transmission of their packets [4]. PRB is based on minor modifications of the IEEE 802.11 Binary Exponential Backoff (BEB) and forces each node to generate a predictable backoff interval. Hosts that do not follow the operation of PRB are easily detected and isolated. We present an accurate analytical model to compute the system throughput using a three-dimensional Markov chain. We evaluate the performance of PRB under normal case and in the presence of selfish hosts. Our results show that PRB and BEB perform similarly in the former case. Selfish hosts, however, achieve substantially higher throughput than well behaved hosts under BEB. PRB, on the other hand, can effectively enhance IEEE 802.11 BEB by mitigating the impacts of these MAC selfish misbehaviors and guarantee a fair share of the wireless channel for well behaved hosts