A Position-Based On-demand Routing Protocol in VANET

Abstract

a periodical beacon broadcast protocol to acquire accurate location and driving information of VANET nodes with shorter delay and lower overhead, a broadcast routing protocol to send a short message from source node to all nodes very rapidly and reliably by using multi-hop communications, and a unicast routing protocol to exchange data between source and destination nodes. The beacon broadcast protocol is designed to dynamically control the beacon period to minimize the waste of bandwidth. The beacon period is determined by predicting a travel distance based on vehicle speed and estimating a possible position error caused by instant acceleration speed of vehicle. A broadcast beacon is generated to correct the vehicle position when the possible position error exceeds an allowed tolerance. Therefore, position information of all vehicles is maintained accurate as much as the allowed tolerance while minimizing the waste of bandwidth due to unnecessarily frequent beaconing. This accurate position information of nodes can provide a foundation in providing safety-driving services and make the broadcast routing and unicast routing protocols run more efficiently. The broadcast routing protocol is a relay node selection protocol using adaptive-delay algorithm for low delay and reliable delivery based on the accurate information of neighbor nodes. Adaptive delay algorithm guarantees reliable transmission and minimizes delay which can occur in the process of multi-hop broadcasting protocol. Transmission by making a selected relay node has the shortest delay regardless of node density. In addition, it solves the problem of the waste of bandwidth and broadcasting storms generated by packet flooding due to the selective rebroadcasting Unicast routing protocol is also proposed based on the accurate information of beacon. The proposed protocol is designed under the condition that the routing path corresponds with the path of the road and the radio range of a node includes the road width. It prevents unstable nodes from participating in the establishment of the routing path and makes it possible to acquire the stable path considering node density and the environments of the road. The established routing path enables a reliable packet transmission by continuously maintaining routing path through maintenance and repair algorithm of routing path in the irregular traffic environment with a high mobility. This protocol overcomes the problems of the existing position-based protocols by applying the algorithm for establishment, maintenance and repair of the path of the topology-based routing protocol based on the information of neighbor vehicles and the features of VANET. The proposed POVRP is first evaluated in the ideal model of traffic mobility to judge the performance and accuracy in the operation of each protocol. In the following evaluation in the realistic traffic mobility model, the overall performance and effect of the proposed protocol is verified. When the margin of error for vehicle location is required to be less than 0.3m, Dynamic beacon transmission protocol reduce the waste of bandwidth by 80%, compared with beacon protocol whose transmission period is fixed as 0.1s. The proposed adaptive broadcasting routing protocol reduce the delay 95% more than a usual flooding broadcasting routing protocol and 80% more than greedy forwarding broadcasting routing protocol. In addition, the proposed broadcasting routing protocol retransmits broadcasting packets by a selected node, which reduces the waste of bandwidth by 90%, compared with flooding broadcasting routing protocol. The proposed unicast routing protocol shows 40~50% increase in data processing than AODV, and 30~60% increase than GSR, which is dependent on the node density.; VANET is a core technology to realize various ITS services which provide safe driving and efficient traffic condition. VANET has several different features from MANET. It consists of vary fast moving nodes, and hence its topology changes rapidly. Many routing protocols have been proposed and evaluated to improve the performance of VANET. However, the previous routing protocols have considered only the partial features among indispensible features necessary for a practical VANET. The position-based routing protocols have been reported to show superior performance than the other protocols by employing the exact location information of nodes as an important feature. However, they don?t account for how to get the location information and just assume that each node has already known all the location information of neighbor nodes. It is self-evident that inclusion of the information acquiring procedure would degrade their performance much and their application to a real VANET as itself would be restrictive. In this dissertation, a position-based on-demand routing protocol (POVRP) is proposed which guarantees the rapid and reliable data transmission in VANET. The proposed protocol consist of three distinct protocols