CSMA based inter-vehicle communication using distributed and polling coordination

Intelligent transportation systems rely heavily on inter-vehicle communication (IVC) systems to support, among other things, safe driving by relaying essential information in real time. It is very important to guarantee the delivery of an imminent collision warning in real time in order to make appropriate actions to avoid it. Several existing MAC layer protocols are modified to address real-time traffic in ad hoc vehicle environment; carrier sense multiple access (CSMA) is one such protocol. This paper implements a priority in CSMA using different backoff time spacing (BTS) to allow higher priority traffic to access the medium faster than those with medium-to-low priority. The backoff time spacing is inversely proportional to the priority; the higher the priority, the lower the backoff time. The paper also proposes a new media access control (MAC) protocol implementation that combines distributed and polling coordination functions to further enhance the BTS-priority-based CSMA and to ensure the absolute delivery of traffic with the highest priority. A computer simulation was carried out to evaluate the performance of the proposed protocol. When compared with the BTS-based CSMA implementation, the simulation results indicate significant improvements in the system throughput and successful packet rate for the traffic with highest priority.