Research Of Routing Protocols In Vehicular Ad Hoc Networks In Urban Environment

With road traffic accidents has become a global problem of public safety, ITS(Intelligent Transportation Systems) is getting increasing attention. VANET(Vehicular Ad Hoc Networks) is the important basis to realize the ITS,which is a self-organization network specifically designed for Inter-vehicle communication.It will be a creative way of network communication technology in vehicles to enable drivers to obtain information about the status of other vehicles and real-time traffic information of the scope of over-the-horizon. VANET for ITS provides a communication platform for the vehicle, not only make the road traffic safety and efficiency greatly improved but brings drivers more comfort and convenience.MANET(Mobile Ad Hoc Networks) as an emerging technology, achieves the intelligent inter-vehicle communications by the integration of Ad Hoc network technology, wireless LAN technology and battery technology. However, MANET is different with traditional Ad Hoc networks. It is a hybrid network architecture, having different nodes movement characteristics and the application of new scenes. Therefore, the traditional Ad Hoc network technology can not meet the vehicle mobile ad hoc network needs. As one of the main factors of the vehicle impact to the performance of mobile ad hoc network, routing technology becomes particularly important. Design of a real scene of automotive applications, and on this basis to study the performance of routing protocols is necessary. This paper discussed some of the challenges encountered in the research on on-board mobile ad hoc network technology , the present vehicle mobile ad hoc network routing protocols as well as the related mobile model, and come to a comprehensive, objective comprehensive conclusion by simulation.For research needs, we first classified and analysised some present representative vehicle routing protocols, and then summarized a variety of special scene and mobile models of domestic and international about vehicle network, through which to carry out simulation of the vehicle under urban scene, researching and analysising the differences in performance of urban scenes of the traditional vehicle routing protocol between GPSR protocol, and come to important conclusions. Finally, based on this work, adding a barrier into the NS2 simulation system, proposed a new barrier penetration model, Reproduce the real communication situation of the urban environment. Through simulation experiments, it shows that in the district where the obstacles has low block rate, the quality of communication is better. Next, we will details the work and research:Part 1. Traditional existing Ad Hoc network routing technology to on-demand routing and table-driven analysis of the two categories respectively. Although VANET is one kind of the Ad Hoc network, but when it is used in vehicle environment,it is very different with the traditional Ad Hoc networks, having many unique new features. The particularities of VANET is mainly expressed in: the movement of vehicles with high-speed and regularity, is restricted by the traffic; the speed of the vehicle causes channel instability, and buildings on the side of the road also interfere with wireless communications; vehicles also need to have enough power support and independent communication systems. These features are all problems in researching on VANET routing protocols. Therefore, under the car for the urban environment of the Ad Hoc network and application characteristics, we focus on the VANET routing protocols. By the topology based on two types of routing and location-assisted approach to vehicle routing protocol the principle of an in-depth analysis. And pointed out that location-based routing protocol based on network topology than the edge routing protocol.Part 2. We can not only get accurate simulation results to evaluate the performance of routing protocols, or predict the location of vehicles, as well as the next step to make more efficient routing judgments from real vehicle network environments and mobile models. The random mobile model of free-space which is used to be used in Traditional Ad Hoc network simulation is no longer applicable. Modeling on vehicle movement is far more complex than on traditional random movement under urban environment. Vehicle network nodes have its own characteristics of mobility and also have to face signal attenuation or interruption of communications caused by building block from time to time in the communications. And what's more, its characteristics of mobility also led to changes of network topology which cause impacts to the performance of routing protocols directly. In this paper, there are a few analysis of some kinds of the basic mobile model, and a lot of experimental studies about vehicle network mobile models under urban environment. We also expatiate the content and implementation processes and reappearance vehicle network under the actual urban environment from simple P2P Voronoi vehicle mobile model to limited urban mobile model based TIGER roads topology, and finally to General Connected Domain model in Complex connected domain, which lay a solid foundation of research and evaluation of routing protocol.Part 3. After the research and application of car scenes and mobile model completed, we successfully added the GPSR routing protocol to NS2, and detailed the process. A detailed analysis of the simulation results of GPSR protocol, make a comparison study with the theory greedy forwarding and perimeter forwarding, verified GPSR protocol code is correct, then in order to test the performance of three routing protocol: GPSR, AODV, DSR in cities environment. specify design work and process of the node mobile model in city enviroment in this paper, ans make a simulation in the specific urban environment. through the analysis of the three performance indicators, found the performance of GPSR is superior that of routing protocol based on the topological information such as aodv, dsr protocol, more suitable for VANET environment.Part 4. After that, we analyze the factor affecting network each in the urban environment, and we discovered that obstructing of a building is also getting all-important effect to the network. After the research of building penetration loss, we have built a barrier penetration probability model. Under that model, a part of signal can be passed through obstruction and continued propagation , yet a part of signal is to be obstructed and be abandoned.Be compared with simply block mean droping, penetration model based on probability is able to simulate the true world vehicle loaded network more status. NS2 is simulated experiment platform of this thesis, but now available code of NS2 does not have the obstruction element being able to reflect real world landform of the earth's surface. So it is required that obstacle and penetration model based on probability should be added to NS2 so that simulated environment approaches the true world. The result of GPSR Emulation is indicated that under existence of obstruction, the function of Ad Hoc network route agreement obvious went down. Especially, under the urban environment, the existence of building leads to wireless chain circuit change frequently and the network be jammed is grave. In that case, once the network loads heavily, it will lose packets. When obstruction obstructs rate is increasing highly, packets deliver rate is lower, and the delay of end to end is more obvious, but the route expense is not affected. Obstruct rate low area, it's the QoS communication is much better. This testified penetration model based on probability is able to reflect real city vehicle loaded network more status.Through the research work in this paper, we analyze the performance of routing protocols in VANET in detail. And pointed out the factors of affecting VANET routing protocol especially in the urban environment. Another work of this paper is establishing a platform for VANET simulation by re-developing NS2 by joining the obstacle model and the penetration model based on probability, established a VANET simulation platform which are close real network state, which provides the experimental basis for the further study of routing protocols for VANET.