| In recent years, communication between vehicles has become a hot spot at domestic and overseas. Realize communication between vehicles can make drivers obtain real-time traffic information and other vehicles information in NLOS. That not only can improve road traffic safety and traffic conditions, but also can make a great convenience to the car travel. Mobile Ad Hoc network apply to vehicle communication has many good conditions. For example, the delay, network topology and network robustness have better advantage.Vehicular Ad Hoc Networks integrating mobile Ad Hoc networks technology is a center-free and special mobile Ad Hoc networks using between cars. Different from the traditional Ad Hoc networks, it is used in a new scenarios, and almost in mobile nodes vehicles run with a high-speed, for the network topology changes frequently, the traditional Ad Hoc networks technology can not meet the require of Vehicular Ad Hoc Networks. The routing protocols as a key technology of Vehicular Ad Hoc Networks determines the performance of the entire network in a great degree. Therefore, how to design an effective routing algorithm to support information timely and delivery reliable has been a hot spot research in Vehicular Ad Hoc Networks. Based on the analysis of the Vehicular Ad Hoc Networks architecture and features, this paper classified and compared some representative of Vehicular Ad Hoc networks routing protocols presently, and choose based on the geographic GPSR routing protocols to do re search. For require of the research, base on road network model is established firstly; on account of problems of GPSR protocol in city environment, this paper propose obstacles blocking algorithm, make improve on the GPSR routing protocol. Then, the work and research are introduced in detail in this paper:1. Describe the characteristics of the traditional Ad Hoc networks and Vehicular Ad Hoc Networks architecture. Comparing with traditional Ad Hoc networks, the Vehicular Ad Hoc Networks has its particular characteristics. Main features:there is no strict energy constraints; it can provide the location positioning for the node and provide geographic information by GPS and GIS; By traffic rules limit vehicle movement; wireless communications jamming by obstructions. These factors are all required to consider in Vehicular Ad Hoc Networks routing protocols. Then introduce the classification of Vehicular Ad Hoc Network routing protocol, By comparative analysis of based on topology and based on positional routing protocols, base on positional routing protocol has more goodness than that base on topology routing protocol.2. City traffic environment is extremely complicated, the movement of vehicle is restricted by the traffic rules and road conditions, so select an appropriate node mobility model is the basis for designing routing protocol. This paper describe several classical mobility models which are not applie to the urban environment by analysis, and subsequently introduced several node mobility models arc applie to the city environment. Finally, this paper make the abstract description of the city road network and make a detailed division to the road network structure, and use segment and junction points as the basis of design data structure package. It is laid a solid foundation for future routing protocols research and improves evaluation.3. After finished the above work, the paper analyzed defects of the GPSR routing protocol apply to city environment, and find the routing protocol performance affected by building blocking. Through the research to the loss from buildings, this paper defines the concept of block and the obstacles blocking algorithm to improve the availability of selecting neighbors'node in GPSR protocol. Then, Combining with road network information, this paer improve in choose of transmit strategy to avoid routing redundancy and routing cut in a certain degree. The simulation results show that the improved protocol is higher than GPSR protocol in the grouping delivery rate. |
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