Abstract: IEEE 802.11p protocol is a low layer standard of DSRC, the backoff algoritm which utilized is BEB（Binary Exponential Backoff）. BEB is widely used, but this algorithm cannot adapt to the DSRC network very well, because vehicles with high speed and the rapid changes of the network topology may easily lead to problems, such as unfairness of channel access and increasing rate of packet loss. To optimize and improve these situation, a backoff algorithm based on remaining time is proposed, this algorithm calculates the remaining time by the current speed of vehicle nodes to optimize the backoff mechanism. The experimental results show that, the mechanism proposed has a better performance in improving fairness of channel access and increasing the network throughput.

Key words: IEEE 802.11p, Dedicated Short Range Communications（DSRC）, fairness of channel access, backoff algorithm

摘要： IEEE 802.11p协议是DSRC技术的下层标准，而该协议采用的仍然是传统的二进制指数退避算法（BEB）。BEB算法虽已广泛使用，但并不能很好地适应DSRC中车载节点的高速移动及其拓扑结构快速变化的特点，易出现信道访问不公平，网络丢包率增加等问题。针对这些问题，提出一种考虑剩余时间的退避算法，由车辆节点的当前速度计算其剩余时间，优化退避机制。实验表明，提出的机制在改善信道访问公平性，提高网络吞吐量等方面均有较好的改善。

关键词: IEEE 802.11p, 专用短程通信（DSRC）, 信道访问公平性, 退避算法