Cooperative link scheduling for RSU-assisted dissemination of basic safety messages

The reliable and real-time dissemination of Basic Safety Message (BSM) among smart vehicles has attracted much attention in both academia and industry, where a group of adjacent vehicles form a Vehicular Ad-hoc NETwork (VANET) to exchange their local-observed traffic information for driving awareness and road safety. However, buildings and trucks may degrade the quality of wireless links between vehicles and cause frequent packet losses in BSM dissemination. To address this issue, road side units (RSU) such as intelligent traffic light could be involved to cooperate with nearby vehicles for BSM forwarding, aiming to help other vehicles recover their lost packets. Based on this idea, many schemes have been proposed but few studies the efficiency of BSM dissemination. For instance, they always assume the scheduling of broacast links are fixed, which may fail to coincide with the sequence of message forwarding, yielding a long time delay and even data expiration when recovering lost BSMs. In this paper, we propose a decentralized Forwarding-Aware Cooperative Scheduling (FACS) scheme for reliable and real-time BSM dissemination, where broadcast links are delicatedly scheduled to coincide with the local resource of neaby vehicles and RSUs, e.g., receiving status of BSM, the allocated task in BSM recovery. Thereby, the time cost in disseminating BSMs could be cut down and other vehicles have more chances to further forward BSMs for reliable and real-time dissemination. We evaluate FACS with real-world Wi-Fi traces in a VANET with/without RSU, respectively. Simulation results show that 84.12% wireless links are scheduld averagely, which yields a message reception ratio of 96.33% (with RSU) and 91.56% (without RSU) and remains stable even when vehicle density increases to 0.35 vehicle/lane/meter. The scheduling of wireless links also helps to cut down the time delay from 100 to 46.12 milliseconds without triggering extra data colloisions (around 3.7%), and the task of message diessmination is offloaded to vehicles and RSUs evenly with a high network balnace of 0.96.