Position-based Routing Protocols In Vehicular Ad Hoc Networks At Specific Scenarios

In recent years, the rapid growth of wireless communication and the immediate problem of traffic informationization require the research on applications of wireless communication in intelligent traffic—Vehicular Ad Hoc Networks (VANET). VANET is categorized as a special mobile Ad Hoc network, which is able to establish a inter-vehicle communication network in a short time without any infrastructure. So it works regardless of the time and location. This feature enables the applications of early warning, computer-aided drive, traffic information inquiry, inter-vehicle communication, Internet access and so forth. Because of the high-speed movement, the predictability of road condition and the uncertainty of driver's behavior, it is hard to develop a effective routing protocol for Ad Hoc network. This paper analyzes the previous works in related fields at home and abroad, makes a comparison among the existing VANET protocol, and improves location-based route protocol. The main work is as follows:To solve the problem of excessive hops in urban crossroads, this paper proposes a novel geographical routing strategy based on priority of direction. Although the existing routing protocols can mitigate the problem of inefficiency by adding fixed nodes at crossroads, they require infrastructure, which is expensive and hard to deploy. In the approach proposed in this paper, the system obtains road information from electronic map, attaches them to the header of node packets and then broadcasts the messages periodically by beacons. By doing so, the node can be classified as normal node, predicted node or crossroads node. So the way of forwarding the data packets can be chose:greedy forwarding for the normal nodes, limited greedy forwarding for predicted nodes and the direction of forwarding is decided by the node at crossroads. The limited greedy forwarding at crossroads environment enables successful deliveries with less hops and shorter paths.To solve the problem of routing holes in suburban and high way, this paper proposes geographical routing protocol based on two-hop node information. Most of the current researches on VANET routing protocol are limited to greedy forwarding with one hop or multi hop with short-distance communication. They repair the holes only when one or more of them appear, which is not able to predict routing holes effectively. The system proposed by this paper obtains the positions of nodes in the range of two hops by exchanging information between neighbor nodes. It also stores the information of nodes of two hops in the neighbor tables. To search for routes for the data packets, the system can predict the holes when greedily forwarding in the nodes, which can avoid holes effectively. This algorithm proposed in this paper is able to decrease the probability of emergence of holes.This paper verifies the algorithm proposed in this paper by simulation. NS2 (network simulation platform) and MOVE (traffic simulator) are used. The scenes in the experiment are from Texas, US and locations around it. The traffic flow simulation scripts are generated by SUMO. Based on the comparison, this paper makes a comparison between the protocol proposed in this paper and the existing routing protocol, by rates of successful packet deliveries, end-to-end delay and packet delay. The result of the simulation reveals that geographical routing strategy based on priority of direction is able to deliver successfully with less and shorter routing paths, and geographical routing protocol based on two-hop node information has great performance in avoiding routing holes.