Adaptive Probabilistic NAV to Increase Fairness in Ad HOC 802.11 MAC Layer

The IEEE 802.11 MAC layer is known for its low performances in wireless ad hoc networks. For instance, it has been shown in the literature that two independent emitters nodes can easily monopolize the medium, preventing other nodes to send packets. The protocol we introduce in this article is a simple variation of the original IEEE 802.1 1 MAC layer which significantly increases the fairness while maintaining a high effective bandwidth. Its principle consists in avoiding systematic successive transmissions by the same emitter through the probabilistic introduction of a waiting time, a virtual NAV, after each emission. The probability to set a NAV is adaptively computed depending on the perceived utility of the previous virtual NAV. This protocol, called PNAV (Probabilistic NAV), is shown to be efficient by simulation and is compared to another IEEE 802.1 1 adaptation.