Opportunistic Routing Protocol In Vehicular Ad Hoc Networks

Vehicular Ad Hoc Networks(VANETs)is a special kind of ad hoc networks,generated by vehicle nodes and roadside units.It can achieve vehicle communication in intelligent transportation systems(ITS).Compared with the traditional mobile ad hoc networks,it has lots of advantages,such as sufficient energy,auxiliary information and powerful computing ability.But some drawbacks like non-homogeneous distribution of nodes,frequent change of topology and unstable communication links,caused by high speed vehicles in the network,have brought challenges to the routing protocol design.In this paper,aiming at the network which has frequent network topology changes and short available time of link,opportunistic routing protocol for vehicular ad hoc networks is designed to minimize the data transmission delay when the source nodes and target nodes are moving vehicles.The main work is as follows:(1)A mobility model is presented to describe the real traffic scene.The mobility model includes the road model,the vehicle motion model and the link model.Based on graph theory,the law of node movement in the network is analyzed and summarized.It reflects the real road planning,law of vehicles' motion and the law variation of vehicle link so as to simulate the actual traffic scene for road planning.It is more consistent with the actual traffic scene mode and makes the routing protocol simulation more reliable.(2)An opportunistic routing protocol based on expected delay(EDOR)is proposed,which optimizes the data transmission delay between source nodes and target nodes when they are both moving vehicles.Trajectories of vehicles are predicted according to the law of vehicles' motion and the road topology.The expected delay of data forwarding in the routing process is computed on the basis of the predicted value and data timeliness.Besides,relay nodes are chosen to transmit data based on it.The strategy is a distributed opportunistic routing algorithm which has strong real-time performance.(3)Simulation results show that the performances of EDOR are better than GPSR routing protocol based on geographical location in data transmission delay,data transmission success rate,average forwarding times and data transmission linear distance.