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.

在智能汽车之间可靠，实时地发布基本安全消息（BSM）引起了学术界和工业界的广泛关注，在该领域中，一组相邻的车辆组成了车辆专用网络（VANET）来交换本地观察到的流量有关驾驶​​意识和道路安全的信息。但是，建筑物和卡车可能会降低车辆之间的无线链路质量，并导致BSM分发中的数据包频繁丢失。为了解决此问题，可以使用诸如智能交通信号灯之类的路边单元（RSU）与附近的车辆进行BSM转发，以帮助其他车辆恢复丢失的数据包。基于这一思想，已经提出了许多方案，但是很少研究BSM分发的效率。举例来说，他们总是假设广播链接的时间表是固定的，这可能与消息转发的顺序不一致，在恢复丢失的BSM时会产生较长的延迟，甚至导致数据过期。在本文中，我们提出了一种分散式转发感知协作调度（FACS）方案，用于可靠和实时的BSM分发，其中广播链路被精心安排以与附近车辆和RSU的本地资源一致，例如BSM的接收状态，即BSM恢复中分配的任务。从而，可以减少传播BSM的时间成本，并且其他车辆有更多机会进一步转发BSM，以实现可靠和实时的传播。我们分别使用带有/不带有RSU的VANET中的真实Wi-Fi跟踪评估FACS。仿真结果表明，平均安排了84.12％的无线链路，从而使消息接收率为96。33％（带RSU）和91.56％（不带RSU），即使车辆密度增加到0.35车辆/车道/米，也保持稳定。无线链路的调度还有助于将时间延迟从100减少到46.12毫秒，而不会触发额外的数据冲突（约3.7％），并且通过0.96的高网络平衡将消息隔离的任务平均分担给车辆和RSU。