Towards reliability analysis of IEEE 802.11p MAC for platooning in a heterogeneous traffic setup

We study the performance of the IEEE 802.11p medium access protocol for platooning of connected vehicles in the presence of interruptions from human-driven Motorised Two Wheelers (MTWs). We invoke specific mobility models for the movement of the vehicles—car-following models for connected vehicle platoons and gap-acceptance model to capture the interruptions by the MTWs—and use them to configure (i) the traffic setup and (ii) the rate at which data packets related to safety-critical messages are generated. A control-theoretic analysis of the car-following models yields a bound on the admissible communication delay to ensure non-oscillatory convergence of the platoon headway. We then use suitable Markov chain models to derive the distribution of the MAC access delay experienced by packets pertaining to safety-critical events as well as routine safety messages. Using the delay distribution and the bound on the admissible delay we compute the reliability of the 802.11p MAC protocol in terms of traffic and protocol parameters. It is seen that the MAC protocol may not always ensure timely delivery of packets for safe platooning. Our study highlights the need for redesign of MAC protocols for vehicular communications in heterogeneous conditions.