MPMAC: Clustering Based MAC Protocol for VANETs

Vehicular safety messaging is warranted mostly in turbulent traffic situations in which even cluster based MAC protocols are beset by problems of cluster rupture, which leads to non-availability of channels to vehicles even when channels are idle. To solve this, motion parameters based cluster medium access (MPMAC) protocol is presented in this paper. The vehicles organize themselves into headless clusters without any messaging. The members of a cluster are not spatially bunched and may belong to different lanes. Each cluster has channels earmarked with the flexibility of utilizing idle channels belonging to other clusters. Safety messages are accorded higher priority with one channel dedicated exclusively for these messages. To enhance channel utilization and avoid the hidden station problem, the RSU monitors the channels and periodically advertises the channel usage map. The MPMAC protocol increases the system's throughput by enhancing channel utilization and facilitates the availability of channels during traffic conditions like phantom jams, lane changing and congestion. The delivery of safety messages to intended vehicles is ensured make provisions for flexible and prioritized channel access in addition to an earmarked channel. Simulation results show that the proposed MPMAC protocol is able to provide sufficient channels for dissemination of safety and other messages with enhanced throughput, fair access, and increased channel utilization while minimizing cluster formation overheads.