Position-based MAC forwarding methods for vehicular networks

Finding and maintaining communication paths in vehicular networks is challenging because of node mobility. Packet routing in Vehicular Ad-hoc Networks (VANET) has been studied recently and many different protocols have been proposed. In particular, geo-routing methods, which do not require maintenance of routes, have been proved to be particularly suitable for VANETs. As usual, these methods use a forwarding mechanism to route packets through intermediate nodes until reaching the destination. In this paper we evaluate two forwarding schemes for vehicular networks that modify the Medium Access Control (MAC) layer contention mechanism in order to prioritize access according to nodes position. In particular, we consider two approaches that use a geometrically-increasing probability distribution for choosing the contention slots but, in the first case, the distribution is appropriately weighted, and in the second case, vehicles (nodes) select the window size according to their position. We analytically evaluate the considered mechanisms with respect to the performance metrics: success probability and access delay. Finally, a detailed study on how to choose the most appropriate parameters and their influence is also conducted.