Research On Geocast In Vehicular Ad Hoc Network

Recent studies have shown that ITS (Intelligent Transportation System) has been recognized as the most effective solution to modern traffic problems. VANET (Vehicular Ad Hoc Networks), acts as the most important part of ITS, is a kind of MANET(Mobile Ad Hoc Networks) which is specifically designed for the vehicular communications to improve travel safety and enhance efficiency of information transmission. Driving comfort is also another application for VANET.Compared to the MANET, VANET faces many new characteristics: fast network topology change, frequent network partitioning, enough node processing capability, unlimited basic energy of vehicles, huge potential network scale, uncertain scope of the network, actual restrictions by the road conditions and driver behavior, hence VANET will require for more different applications than traditional MANET. Geocast is a special kind of multicast technology, which aims to transmit packets to all nodes located in a specific geographic area. With the popularity of vehicular positioning facilities, Geocast technology for VANET will be highly in demand.This paper studies a wide range technology of VANET, our research contains the basic frameworks, technical characteristics and existing applications of geocast strategy. The traditional geometry-based geocast schemes only considered the scenes limited to a fixed vehicle speed and fixed spacing situation. We propose a geometry-based framework, which can be adapted to the scenario with changeable vehicle relative position. We adjust the backoff strategy to make vehicles near the road intersection get the priority to geocast packets. We also design an appropriate control strategy, making the vehicles overtaking others can replace the opportunity of original sender. Simulation experiments show that our strategy can effectively reduce the average broadcast number and packets transmission delay.We hope to improve geocast transmission efficiency in the urban road intersection environment of multiple geocast regions with the application of multi-clustering technology. Traditional clustering-based geocast strategy would not only fluctuate when VANET changes its node density, but also in the scene of multiple geocast regions, VANET transmission efficiency would decrease significantly. We design a multi-stage clustering geocast strategy based on vehicular driving characteristics. We divide vehicles into some corresponding clusters in accordance with the direction of vehicles travel in road intersections. The cluster heads can build a set of clusters and elect a first-stage cluster head. The packets are transmitted from the first-stage cluster head to multiple geocast regions. Experiments show that our strategy can not only improve the transmission efficiency, but also can cope with the impact of frequent changes in...