Research On Routing Protocols For Vehicular Ad HOC Networks

Vehicular Ad Hoc Networks(VANETs) have emerged as a new kind of wireless mobile networks. In which vehicles on roads act as mobile nodes, and communicate with each other by Dedicated Short Range Communication(DSRC) standards. Communications from vehicle to vehicle(V2V) or from vehicle to infrastructure(V2I) are both suported by VANETs. Services such as traffic accident alarming and traffic warning can be provided for drivers, passengers and traffic administrations to increase driving safety. Sharing traffic jam information between vehicles by VANETs can increase transportation efficiency and save energy consumptions.The routing protocols of VANETs focus on the messages delivery in a multi-hop manner between vehicles, which is one of the main problems in VANETs. Different from Mobile Ad Hoc Networks(MANETs), the vehicles in VANETs move faster, the network topologies change more rapidly, the network connections are often disconnected and in fragment, the communications between vehicles are often blocked by high-rise buildings, and the message delivery delay becomes longer and varies greatly. All these characters make the routing in VANETs face more serious challenges. Nowadays, the routing problems in VANETs are attracting more and more attentions of the researchers all over the world, and many routing protocols have been proposed.After survey and analysis the published routing protocols of VANET, the thesis classifies them into three categories of unicast routing, broadcast routing and geographic multi-cast routing, respectively. More detailed classifications are also made for each category, and the characteristics and limitations of the published routing protocols are discussed for every category. The thesis focuses on the routing problems of unicast. According to the differences of the number of copies generated by the message, and after analyzing the characteristics of the message delivery processes, together with the limitations of the published routing protocols, several research findings and innovations in single copy routing, epidemic routing and multi-copy routing are mainly achieved.1. The research of single copy routing based on junctions of roads and traffic populationsA single copy routing protocol named JTAR is proposed characterized by the minimized message delivery delay. Supported by the proposed delay model of message forwarding, the minimized delay and the optimal path from each junction to the destination can be got by Dijkstra’s least-weight path algorithm. In the proposed JTAR, the metric named critical-segment of non-optimal road is defined and proved for routing recovery, and the junction is not the only place to select the optimal next junction compared to other routing protocols. The pattern that messages can be only forwarded to the neighbor junction is reformed, and messages can be forwarded into the optimal street directly crossing the junction. Routing loops are also discussed and resolved. Simulation results suggest that the delivery ratio and delay achieved by JTAR are better than the compared protocols.2. The research of unicast epidemic routing based on zone division of neighborsA routing protocol named GZER is proposed characterized by greedy zone epidemic. In the proposed GZER, the neighbors of a vehicle are divided into different zones according to their physical locations, with the consideration of the directional and restricted characteristics of message forwarding progress. RSV is employed to indicate the messages that the zone do not have. In each zone, only the farthest neighbor will be infected decided by RSV, and all the vehicles in the network will be covered eventually. New infection trigger scheme is designed to improve the infection effect, and improved methods for SV update are designed to eliminate redundant infections. According to the research result that the vehicles on road are exponential distributed, the proportion of copies generated by GZER and Epidemic is derived. Simulation results show that GZER achieves better performances on delivery ratio, delivery delay, the number of copies, routing overhead and throughput, especially on the environments of high vehicle density together with heavy traffic loads.3. The research of multi-copy unicast routingA multi-copy unicast routing protocol named SAMOR is proposed based on the social-aware of vehicles. The multi-copy routings have the advantages of epidemic routing, but will not generate serious bandwidth contention and frequent collisions caused by too many copies. In the proposed SAMOR propotocal, the social network properties of vehicles in VANETs are utilized. The vehicles are classified into the categories of communities and global by exploring the contact intervals between nodes. Using the proposed parameter of utility, the allocation scheme of copies during spread period and the forwarding method of copy during focus period are designed. Simulation results suggest that SAMOR achieves better performances on delivery ratio and delay.4. The research of Epidemic routing protocolAfter analyzing the infection processes for unicast and percolation of Epidemic routing, absorbing finite-state Markov chains are presented for the unicast and percolation of Epidemic, respectively. The expressions of the expected number of copies and delivery delay for unicast, as well as the percolation delay of message broadcast are derived by the models. Simulation results confirmed the accuracy of the analysis obtained from the proposed model.