An Adaptive Frame Based MAC Protocol In VANETs

Vehicle Ad Hoc Network(VANET)is a special mobile ad hoc network(MANET),which has a wide application prospect in Intelligent Transport System(ITS).However,in VANET,due to the high movement of the nodes,the frequent change of network topology,the instability of the communication links and the limited channel resources,it is urgent to study the channel access mechanism adapting to the high dynamic change of the channel.Therefore,by introducing the clustering algorithm to effectively control the topology of the network and the spatial reuse of network resources to expand the network capacity,while designing the effective MAC protocol to provide a fair channel access mechanism.In view of the current clustering algorithm,only the current state of the vehicle is considered,and only the state of the current time does not well reflect the problem of vehicle moving characteristics.This paper proposes a clustering algorithm based on movement prediction,predicting the position of the vehicle at the next moment through the vehicle movement model,and then calculates the weight as the measure of the cluster head according to the relative position and the relative velocity of the vehicle’s current time and next time.The measure factor is used to measure the stability of the node,the higher stability of the vehicle was selected as cluster head for cluster management,in order to improve the stability of the cluster.This paper also introduces the backup cluster head for the maintenance of the cluster to reduce the dissolution of the cluster and improve the life cycle of the cluster,the simulation verifies the reliability of the algorithm.Based on the clustering algorithm,this paper proposes a MAC protocol based on adaptive frame length for resource constraints and collision problems caused by fixed frame length in 802.11p.The frame length of the control channel is adaptively changed according to the number of cluster members,which can effectively utilize the channel resources.The security message is transmitted in a non-competitive manner,and the security message broadcast order of the cluster member is determined by the cluster head to ensure the successful transmission of the security message.The service channel is competed by the node and maximizes throughput through a reasonable frame length design.The simulation results show that the protocol designed in this paper can improve the stability of the cluster and reduce the access delay of the system,improve the delivery rate of the security packet and the throughput of the system.