Study On Selfish Behavior In MAC Layer Of IEEE 802.11 Wireless Ad Hoc Networks

IEEE 802.11 DCF is one of the most popular protocols in MAC layer of wireless ad hoc networks nowadays. Most types of wireless devices are compatible with this protocol. However, with the devices, such as network adapters, becoming more and more programmable, it becomes much easier for some selfish nodes to modify the behavior of their wireless interface. Selfish behavior in MAC layer may lead to the performance degradation seriously. Therefore, it is very necessary to study and resolve the selfish behavior problem in MAC layer of wireless ad hoc networks.Selfish nodes may adopt a range of strategies to improve their share to wireless channel in MAC layer. As a side effect of this behavior, well-behaved nodes cannot use the channel for transmission. This dissertation investigates the saturated and non-saturated load throughputs of IEEE 802.11 DCF in the presence of selfish nodes. Using a modified Markov model, we have derived the throughput model of a node under various traffic loads. Meanwhile, based on a two-dimensional Markov chain model, we have analyzed the medium access delay when the nodes are saturated. The analytical models have been validated by a number of simulations.Selfish behavior detection is a very important problem to resolve. However, it is a hard task. The main difficulty comes from the random operation of the IEEE 802.11 MAC protocol, and is exacerbated by the nature of the wireless medium itself. Therefore, it is difficult to distinguish between selfish behavior and an occasional protocol malfunction due to wireless link impairment. In this dissertation, we have proposed a simple and robust mechanism based on CUSUM (Cumulative Sum) test by tracing the statistics characteristic in real time to detect the selfish behavior. This method can be used with any random access MAC protocols. Our simulation results show that the detection mechanism has short detection time and high detection accuracy.To prevent the behavior of selfish nodes, we have proposed a game-theoretic approach to investigate the selfish behavior problem. By using the ERC theory from economic field, we have given the strategy that a node may use when accessing the wireless channel, in which the equity, reciprocity, and competition property among nodes is considered. It is a Nash equilibrium strategy. Furthermore, we designed a new distributed protocol to detect selfish behavior based on the throughput, and to prevent the selfish behavior by jamming the packet transmissions of selfish nodes. Extensive simulation results show that the protocol is effective in detecting selfish nodes and eliminating selfish behavior.