Research On MAC Protocol Of Vehicle Ad Hoc Network Based On TDMA

Vehicular Ad hoc Network(VANET)is an essential part of the information platform of the intelligent transportation systems.And it is an open mobile self-organizing network consisting of vehicles and infrastructure communicating with each other through short-distance wireless communication technology.In the VANET,the characteristics of the high driving speed,frequent network topology changes and decentralization,make vehicles easy to be interfered in data transmission.Therefore,how to ensure the transmission data of vehicles with low collision rate and low packet loss rate at high speed is the focus of researches on VANET Media Access Control(MAC)protocol.In order to reducing the collision rate and packet loss rate,this thesis studies different MAC protocols to the VANET with or without infrastructure respectively.The main contents are as follows:(1)Aiming at the VANET with infrastructure,a time division multiple access(TDMA)MAC protocol based on interference-free graph is proposed.In this protocol,subnets are divided according to RSU communication range,and then orthogonal channels are allocated to adjacent subnets,to solve the interference problem of vehicle transmission among subnets.After that,RSU constructs the conflict graph according to the conflict relationship of vehicles within their subnet,and then allocates time slots to vehicles by solving the maximum independent set to solve the conflict problem of vehicle transmission.(2)Aiming at the VANET without infrastructure,a distributed TDMA MAC protocol based on competition is proposed.The protocol first divides the road into segments according to the vehicle communication radius,and then organizes the communication for vehicles on each road segment in a periodic manner.Each communication cycle is divided into two parts: a static segment and a dynamic segment according to the function.The static segment uses time division multiplexing to communicate.The dynamic segment is used for newly accessed vehicles competing for the transmission slot in the static segment.(3)The MAC protocols proposed in this thesis are verified through simulation experiments.The experimental results show that the two proposed protocols have significantly improvement in reducing the collision rate and reducing access delay.