Research On Multi-Priority MAC Protocol Based On Clustering Itinvehicular Ad-Hoc Network

In order to alleviate traffic congestion and facilitate people's safer and more comfortable travel,as the core part of the intelligent transportation system,the vehicle self-organizing network came into being.The US IEEE 1609 working group improved on the basis of the IEEE 802.11 p standard and allocated a dedicated bandwidth of 75 MHz to the network.It is specified that the information is transmitted by the roadside unit and the onboard unit on one control channel and six service channels in a synchronization period of 100 ms.Due to the fixed synchronization period division,the problem of low channel utilization is caused,and the high-mobility vehicle environment and the high-speed change of the network topology also bring challenges to the research.Therefore,it is necessary to design a MAC protocol suitable for in-vehicle network environments with frequent dynamic changes.In this paper,the characteristics of the vehicle-mounted ad hoc network are designed to solve the problem of channel idleness and channel congestion in the network.An Asynchronous Cluster-based Multi-Priority Protocol(ACMP)is proposed.The contents are as follows:Firstly,a clustering algorithm based on mobile location awareness is proposed.By setting the cluster head coefficients in the beacon frame,additional information is used to occupy the control channel.The node selects the best cluster head based on the position,speed and driving direction information.The dynamic cluster head election method effectively extends the cluster head life and enhances the stability of the cluster.Other original nodes in the network sense that the message broadcast by the cluster head is successfully added to the cluster;the new node sends the request packet added to the cluster,and completes the clustering process according to whether there is a cluster head response around.At the same time,according to the four specific conditions specified,the maintenance mode of the cluster is proposed to avoid the phenomenon of frequently updating the cluster structure.Secondly,a multi-priority access channel mechanism and a cluster-based contention-free reservation and selection service channel strategy are proposed.The message transmitted by the control channel accesses the channel by priority through the mechanism,and divides the synchronization period into three phases,ensuring real-time security messages and reducing the number of nodes accessing the channel concurrently.In the service phase,a clustering algorithm is introduced.The cluster head represents the active nodes in the cluster,and the channels are reserved in order according to the proposed sorting process to realize a contention-free access channel.The node that successfully subscribes immediately switches to the corresponding channel for transmission of service information,and other nodes continue to listen to the control channel,so that the channel resources are fully utilized.Finally,in the NS-2 simulation environment,combined with the traffic scenario generated by the traffic simulation software SUMO,the experimental verification of ACMP is carried out.The experimental results show that the protocol can effectively alleviate the channel idle problem caused by time synchronization and has better adaptability to different traffic environments.