A Design And Improvement In AODV Protocol Based On Roadside Unit Assist Routing Under Self-Organized Vehicle Network

VANET (Vehicle Ad Hoc Network) as a special Ad Hoc networks, is now an important part of the Intelligent Transportation System, which provides the infrastructure for the communication in vehicle or between vehicle and roadside equipment. VANET not only has common features of general Ad Hoc network, but also has its own characteristics:high-speed mobile nodes, frequently changing network topology, the not stable communication link, at the same time the trajectory of nodes within the network is regular, and always restricted by the static road. These characteristics make the existing routing protocols for Ad Hoc not have a good performance, not be suitable for VANET. Therefore, according to the VANET’s own characteristics, combined with relevant information, creating a stable and efficient routing quickly, which can be applied in the actual vehicle environment, is of great significance.First of all, this paper introduces the research background and overseas and domestic research status. And then there is a brief introduction to the Ad-Hoc, the basic concepts of VANET, VANET’s features and applications, and VANET’s routing technology and classification. In the paper we describe the AODV (Ad Hoc On-demand Distance Vector routing) routing protocol in detail, represent its two components-its route discovery and maintenance, analyze its design principle and the process flow, and point out its insufficiency. Nowadays most of the research on improving AODV protocol only just consider the part of moving vehicle. In our paper, we propose AODV’s improvement based on Roadside Unit assists in routing on the basis of the AODV algorithm, combining with the actual characteristics of VANET. RUAR-AODV (Roadside Unit Assist Routing based AODV) maintains two major improvements in route discovery and maintenance:(1)RSU (Road Side Unit) assists in routing. In the route discovery phase, we put RSU, another important component of the actual VANET, into the modified algorithm. The algorithm proposes RSU assisted in routing, combining traditional AODV’s route discovery, can improve the efficiency of routing; while we propose to find and choose two longest maintained routes, one named the main route while another used the alternate route. This mechanism can improve the continuity and stability of communication between nodes.(2) Switch and repair advanced. During maintenance phase, we set threshold to the using route, listening routing state. When the threshold is reached, switch to alternate route and repair the main route advanced. Such a mechanism can improve the continuity and stability of communication, and avoid network overhead caused by the routing restart.In the end of the paper, we use NS2, a popular network simulation tool, to simulate AODV and RUAR-AODV. Under the set of network environment, we measure the overall performance of two protocols, by analyzing the simulation results and comparing the four representative indicators of both:the hop count, the loss rate, the end to end delay and the protocol’s overhead. Experimental results show that, RUAR-AODV with help of RSU in routing, combining with the design of alternate routes can establish a stable and longer maintained route quickly. Advanced switching and repairing mechanism, to some extent, can extend the communication time, improve the stability of the route, and reduce network overhead caused by the routing restart. RUAR-AODV shows a good advantage in the hop count, the loss rate and the end to end delay. So the improved protocol can be more suitable for VANET.