The Cooperative Downloading And Simulation In Urban VANET

VANET (Vehicular Ad hoc Network) is a type of mobile Ad hoc networks consisting of vehicles and RSUs (Road Side Units), which is basis of inter-vehicle network, international vehicle network and vehicle-mounted mobile Internet and proceeds wireless communication and information exchange between vehicle-vehicle and vehicle-Internet, according to the contract standard communication protocol and data interaction. It is an extension of things technology in the field of intelligent transportation systems. VANET performs well not only in terms of driving safety, navigation and intelligent transportation, but has better prospects for development in some other information services including entertainment, news and video conferences, which has become a hot research topic. However, in VANET vehicles move fast and the limited communication range of RSUs, there must be dark area between the adjacent RSUs where vehicles cannot communicate with RSUs directly and so vehicles cannot download files from RSUs continuously. In this paper, in order to solve the problem of file cannot being sustain transfer; we present a cooperative download scheme. When downloading task cannot be completed in one RSU’s communication range, selecting a group of vehicles to carry the required data to the user, thus the information transfer limitations out of the RSU communication of users is changed.In this paper, we first introduce the knowledge and technology of VANET, and for the characteristics of VANET and application requirements, a cooperative download scheme with the same direction as users is proposed. In this scheme, this paper designs redundant vehicles selection algorithm. When a vehicle does not finish the downloading task in the communication range of an RSU, it will choose a group of cooperative vehicles in the same direction, and pre-store the requested files in these cooperative vehicles when they are in the communication range of the RSU. Once the vehicle meets cooperative vehicles in the dark area, they can transmit pre-stored packets between each other. Thus, the limitation that vehicles cannot download file in the dark area is changed.In order to verify the effectiveness of the proposed mechanism in a real scene and a more realistic reflection of the topology of the road and the running track of the vehicles, we use the traffic simulation software VanetMobiSim. We take into account the topology of the road, traffic sign, acceleration, deceleration and the behavior of the crossroads and traffic lights, generating approximate real trace files, and then use network simulation tool NS-2to simulate the scheme. The results show the presented scheme can effectively extend the valid downloading area and improve the throughput of downloading files.