Research Of Bidirectional Coupling Of Road Traffic Simulation And Network Simulation On VANET

Wireless networking technology continues to improve so that it is subjected to a wide range of concerns in all areas, particularly in the communications field. It has become a hot topic that many scholars competing in researching. Vehicle Ad Hoc Network is a wireless networking technology applied to the Inter-vehicle communication. Through the use of it vehicle drivers can obtain real-time traffic road conditions in the not visible circumstances. The ultimate goal of Vehicle Ad Hoc Network design is to build a mutually inter-vehicle communication network platform, which not only allows moving vehicles to avoid accidents and improve driving safety, and take the initiative in checking real-time traffic congestion information, improve transport efficiency, increase passengers ' comfort.However, the current research of Vehicle Ad Hoc Network still has many problems. First of all, the network simulation is still considered as the first step when study the communication between vehicles, but in Vehicle Ad Hoc Networks study it is difficult that network simulation tool to simulate real traffic scene. Traffic simulation is precisely the very important factor, it directly affects the accuracy of simulation results. Second, the current researchs of Vehicle Ad Hoc Network are based on the established models to study the mobile vehicle communication protocol. For the interaction of network simulation and traffic simulation has not been more in-depth explored. Based on the above two issues, this paper to improve urban transport mobility model to further study bi-directional coupling framework of traffic simulation and network simulation. The following describes in detail the work of this paper:Bi-directional coupling of network simulation and traffic simulation. Network simulation is the use of network simulation tool to build network model, and through the implementation of the model simulate network behavior. Traffic simulation is the use of traffic simulation tool to build the real traffic scene model, Through the analysis of the simulation data to obtain the optimal solution which solve the traffic problem. By extending OMNET++ and SUMO their own proprietary communication module based on TCP connection to exchange node information and command information for coupling network simulation and traffic simulation. Network simulation and traffic simulation run simultaneously, sharing the mobile nodes position, velocity and other information. This coupling framework breaks through the traditional research methods which is based on the established mobile to study the performance of the vehicle communication protocol. The coupling framework in-depth explore the interaction of network simulation and traffic simulation, that demonstrate Inter-vehicle communication directly affects the transportation system, contrary transportation system affects the communication between vehicles.Improvements of mobile vehicle model. The accuracy of simulation results depends on the choice of vehicle mobility model. Early mobility model in Vehicle Ad Hoc Network simulation is no longer applicable, because the complexity of today's urban environment determines the complexity of the mobile model, road conditions, traffic barriers, traffic signals, vehicle classification, traffic conditions and so on are the factors that mobile model design should be considered.In this paper, base on the analysis of vehicle movement and city road environment, we can propose a more realistic traffic model of urban traffic scenes. The improvement of mobile model for the following considerations: 1, consider the traffic barrier element. With particular attention to the city of artificial structures, as in a real traffic environment, traffic obstructions would do not transmit radio waves. This paper will give an algorithm to determine whether the radio waves are blocked by obstacles. 2, consider the factors of road control facilities. It mainly refers to the traffic lights. Traffic lights can control vehicle driving state. 3, consider the factors of vehicles node. Free vehicles, public transport vehicles. Free vehicles have bigger random mobility, faster speed, not subject to restrictions on fixed routes, and can stop anywhere. The public transport vehicles have low speed, and the range of speed is not large, they have a fixed stop time and fixed place stops.Simulation experiments. Based on the above preparations, this paper is based on the improving urban transport mobility model, analyzes the data of simulation experiment to study the various aspects of performance of the bi-directional coupling of network simulation and traffic simulation. In this simulation experiment, we consider two cases that have the traffic lights model and building model, and not have the traffic model and building model. Under the different sizes urban traffic environment in both cases, to simulate no warning information free traffic scenario; there is warning information, but there is no communication between vehicles scenario; there is warning information and inter-vehicle communication based on UDP connections traffic scenario; there is warning information and inter-vehicle communication based on TCP connection traffic scenarios.By analyzing the data extracted from the simulation results of the experiments, comparing different scenarios of the Inter-vehicle communication packet delivery rate and the average effective vehicle speed. Compared with pre-mobility model we can concluded: 1, Vehicle Ad Hoc Network's routing protocol significantly reduce the performance. The main reason is that the existence of urban obstacles leads to frequently change the wireless link, serious block the network, results in a large number of packet loss. 2, the average effective speed of vehicle nodes are also significantly reduced, mainly due to the traffic control facilities. 3, Using the bi-directional coupling framework of network simulation and traffic simulation can accurately describe the Inter-vehicle communication directly affects the performance of transport systems.Based on the improvement of urban traffic scenario modeling, we have studied the bi-directional coupling framework of network simulation and traffic simulation, and got the analysis result of framework for all aspects of performance, but there are still many areas require in-depth exploring. First, SUMO can import the electronic map of real city as an urban traffic scene to make the simulation more real. Second, because of this limited test conditions, for the simulation experiments, the number of nodes is relatively small, so the follow step of the experimental study will further increase the size of simulation experiments in order to really look forward to a more simulation real-world traffic environment.