Research On MAC Protocol For Vehicular Ad Hoc Networks Based On TDMA

Vehicular ad hoc network(VANET)that enables reliable communications between vehicles,between vehicles and roadside infrastructures,and between vehicles and pedestrians,has received widespread attention at the current moment.VANET can support a variety of services,including alarm information and entertainment applications,and is of great value in improving traffic efficiency and ensuring road traffic safety.Medium access control(MAC)protocols are proposed to provide fair and efficient access to wireless channel,which is the key to reliable data transmission in VANET.VANET has the specificities of rapid topology changes and high node mobility in the Network,therefore the traditional MAC protocols are no longer suitable to VANET.Meanwhile,VANET’s own characteristics also bring challenges to the MAC protocol design.To meet the requirements of delay sensitive services in VANET,contention-free MAC protocols,such as time division multiple access(TDMA)based MACs,have attracted much attention.The collision problem in network is a key factor affecting the reliability.In order to reduce collision and improve network reliability,this paper studies the design of VANET MAC protocol based on TDMA.The main work of this paper is as follows:(1)A protocol based on multi-carrier contention is proposed to resolve collisions caused by random access of nodes in frequent access scenarios.In a fully distributed scenario without centralized scheduling nodes,the proposed protocol utilizes a multi-carrier contention in the access process to confirm the unique owner node of control channel slot through several rounds of multi-carrier contention.The proposed mechanism can alleviate the access collision problems caused by random access.(2)To solve the problem of slot waste in VANET,a MAC scheme developed on vehicular mobility is proposed.In the existing fully distributed MAC,the node determines the status of the time slot resources by listening the control channel.However,due to the high mobility of nodes in VANET network,traditional protocols generally lag in the way of confirming slot status.Without additional network overhead,the proposed protocol utilizes the vehicular information,such as node position,in the current network,to make prediction on nodes’ position.By releasing idle time slots in advance,it can improve the time slot utilization and reduce the number of network access collision.(3)An adaptive time slot reservation protocol based on multiple service types is developed to solve the problem of channel resource allocation of different highpriority safety applications.In existing approaches,different high-priority safety applications are allocated with the same channel resources,which is not only inflexible but also a waste of channel resources.The proposed scheme improves resource utilization and reduces network collisions by supporting flexible channel resource assignment according to diverse high-priority safety applications.