The Research On Message Transmission Mechanism In MAC Layer Of Road-Vehicle Communications

A contradiction emerges gradually between the low traffic system efficiency and the increasingly high demand of citizens for travelling conditions. This is a fundamental problem needs to be resolved urgently by the current traffic industry. Therefore, the research of intelligent transportation based on vehicle to vehicle, vehicle to road communication also appears more urgent and important. Vehicle-road network composed of vehicle equipment, road-side equipment and traffic control center is a real-time, efficient, and reliable communication system. Compared to traditional wireless self-organized network, the nodes in vehicle road network move faster, which makes the network topology changes more frequently, link interruption more often and communication difficulties, which makes the study on vehicle road communication faces a great challenge. In this paper, the work has been done to message transmission mechanism in vehicle road communication as follows.1. This paper introduces the research background and significance first, then the characteristics of vehicle road network, advantages of DSRC technology, standard/protocol of WAVE/1609.4, mechanism of DCF and CSMA/CA are illustrated and analyzed in detail.2. A MAC layer dynamic priority scheduling mechanism is proposed. First, vehicle motion model and research on safety messages in vehicle road network are summarized. Then, some problems existing in the vehicle road network are analyzed and pointed out, like, the nodes communication mode in vehicle road network will result in the existence of massive redundant safety control messages, which makes the meaningful messages cannot be transmitted reliable and in time. Then, after we analyzed the characteristics of the message transmission mode,. Different priority is determined by the function of parameters of time, distance and direction,meaningless messages will be filtered according to the direction and absolute priority is introduced to ensure smooth communication for special vehicles.3.A channel access backoff mechanism for both V2 V and V2 I are presented on the basis of the node mobility characteristics considered. The unfairness of channel access were analyzed in vehicle network, This mechanism will adjust the contention window with nodes velocity, direction and location considered, so nodes would have an appropriate priority to access channel.4.With the NS2 platform and nodes motion model produced by VanetMobiSim, the throughput, time delay, link stability and channel access fairness were evaluated for both two mechanisms, the effectiveness and superiority of the proposed two mechanisms were verified.