An efficient MAC protocol for provisioning fairness in vehicle to roadside communications

In this paper, we present an efficient medium access control (MAC) protocol based on IEEE 802.11 DCF, which minimizes the unfairness problem of two way vehicle ad hoc networks. Geographically highly dynamic topology in vehicle ad hoc networks lead to unfairness problem. Unfairness problem has two aspects: higher velocity vehicles cannot transmit a minimum number of packets and lower velocity vehicles cannot transmit above a minimum number of packets. To address the above mentioned issues, our proposed scheme adjusts the transmission probability for each vehicle according to its residence time by changing the value of MAC parameters dynamically. An analytical model is developed to analyze the performance of the proposed protocol in a non-saturated state. We derive the relationship between the transmission probability and the residence time. Furthermore, relation between the transmission probability and the minimum contention window size of a vehicle is also derived to correlated residence time with minimum contention window size. Analytical results show that our proposed scheme overcomes the limitations of existing MAC protocols by ensuring that packet transmission rate remains proportional to the residence time of the vehicles.