Ensuring fair access in IEEE 802.11p-based vehicle-to-infrastructure networks

IEEE 802.11p is an approved amendment to the IEEE 802.11 standard to facilitate wireless access in vehicular environments (WAVE). In this article, we present an analytical model to evaluate the impact of vehicle mobility on the saturation throughput of IEEE 802.11p-based vehicle-to-infrastructure (V2I) networks. The throughput model is then used to investigate an unfairness problem that exists in such networks among vehicles with different mobility characteristics. Assuming a saturated network, if all the vehicles in the network use the same MAC parameters, IEEE 802.11p MAC protocol provides equal transmission opportunity for all of them, provided they have equal residence time in the coverage area of a road side unit (RSU). When vehicles have different mobility characteristics (e.g., extremely high and low speeds), they do not have similar chances of channel access. A vehicle moving with higher velocity has less chance to communicate with its RSU, as compared to a slow moving vehicle, due to its short residence time in the coverage area of RSU. Accordingly, the data transfer of a higher velocity vehicle gets degraded significantly, as compared to that of the vehicle with lower velocity, resulting in unfairness among them. In this article, our aim is to address this unfairness problem that exists among vehicles of different velocities in V2I networks. Analytical expressions are derived for optimal minimum CW (CWmin) required to ensure fairness, in the sense of equal chance of communicating with RSU, among competing vehicles of different mean velocities in the network. Analytical results are validated using extensive simulations.