Research On Routing Technology In Urban VANET

In recent years,in urban setting,the number of motor vehicles remains high and has been steadily increasing,which puts forward higher demand for the quality of data transmission in VANET(Vehicular ad hoc network).It continues to be a challenge to design efficient routing strategies for vehicular communication in urban VANET.Because of environmental characteristics in urban setting,there are three difficulties in design of routing protocol: one is that the high mobility of vehicles causes the frequent change of network topology,another is that the movement of vehicles is limited by the road topology,traffic condition and traffic lights,and the third is that irregular movement of vehicles results in uneven distribution of nodes along road.In addition,it's difficult to deployment infrastructures in urban,so it is not advisable to deploy a large amount of infrastructure to improve the communication quality in VANET.Considering that the routing strategy should be adjusted according to the mobility model of communication objects,in this thesis,according to the mobility model of communication objects,vehicular communications are divided into two types: communication between vehicles and static nodes and communication between vehicles and moving nodes.And combining with the characteristic of urban VANET,the author of this thesis proposes corresponding routing strategies for these two kinds of communication,aiming at reducing the average end-to-end delay and improving the packet transmission radio on the premise of limited infrastructures.In this thesis,the major research contents include the following two parts:(1)For communications between vehicles and static nodes in urban VANET,in view of the advantages of bus in urban setting such as wide coverage,fixed driving trajectory and regular service,this thesis proposes the bus trajectory-based street-centric routing algorithm.The algorithm first constructs the bus trajectory-based routing graph according to the trajectories of buses,then computes a routing trajectory for every communication by using shortest path algorithm.In the process of transmitting packet,it adopts two-layer relay mode,in which buses work as the main relay to make routing decisions and forward packets,and other vehicles play as secondary relay to provide multiple hop communication between two main relays.Simulation results show that the proposed routing algorithms have efficient performances including the packet transmission ratio and the end-to-end delay.(2)For communication between vehicles and moving nodes in urban VANET,this thesis proposes an intersection fog-based distributed routing algorithm.The algorithm first proposes the intersection vehicle fog model,in which waiting vehicles dynamically form a vehicle fog at an intersection,making full use of the storage and computing resources of waiting vehicles.Intersection vehicle fogs proactively establish multihop links with adjacent intersections,which can reduce the transmission delay between two adjacent intersections,and they periodically evaluate the traffic condition on adjacent road segments,thus according to the traffic condition,road segments with high density of vehicles are preferentially selected as routing trajectory when making routing decisions.During routing,intersection vehicle fog adjusts the routing direction according to the realtime position of the destination,thus avoiding rerouting.Simulation results demonstrate that the proposed algorithm features relatively strong performance and can adapt to the dynamic change of urban VANET.