Complexity Analysis And Routing Protocol Research For VANET In Urban Environment

With the development of wireless communication technologies, Vehicular Ad Hoc Network (VANET) becomes a research hotspot in both domestic and overseas. As Ad Hoc Network captures the characteristics of self-organizing, infrastructureless and all nodes have equal status, it has more wide applications in VANET. Applying the complex theory to VANET is meaningful, because it can reveal the complexity of VANET in different conditions along with the increasing number of the nodes and the changes of the network structure. With the high-speed movement, joint, exit of network nodes and dramatic changes of network topology, how to design an effective route to ensure data reliable and stable transmission has been the difficulty of VANET research.First, the paper introduces the origin, characteristics and applications of Mobile Ad Hoc Networks (MANET) and VANET. In order to simulate vehicle movement and get its trajectory, the paper sets up different scenarios under a real map of Dalian City with a VanetMobiSim software. Besides, the paper calculates the statistical properties such as the average path length, clustering coefficient, degree and degree distribution of VANET under different scenarios using the complex theory. The experimental results show that VANET has the properties of small world and scale-free property.Second, the paper introduces the "Connectionless Approach (CLA)" in detail. CLA mechanism is very suitable for the Ad Hoc networks without obstacles, but not for the Ad Hoc networks with irregular obstacles in urban VANET environment. Therefore, the CLA mechanism does not apply to urban VANET environment. This paper presents an improved CLA protocol-CLA with Urban Environment(CLA-UE), which abandons the practice of CLA mechanism in establishing the reference line and reference points and melts into the idea of "forwarding zone". Each forward zone is determined by the packet forwarding node in routing exploration. The routing protocol establish consecutive forwards zone along the road leading to the destination node, then the forwarding node can transmit data to the destination node along the forwarding zone.Finally, the paper constructs the random street mobility model with BonnMotion Software. The performances of the CLA-UE protocol were compared with DSR and AODV under "fixed-connection" status by GloMosim emulator and analyzed by simulation experiments on packet delivery fraction, routing overhead, average end-to-end delay of data packets. Simulation results show that the CLA-UE protocol can maintain a better network performance under situations of different node moving speed, node density and node traffic.