Research And Improvement Of GPSR Protocol Based On The Density Of Vehicle Flow In Vehicular Ad Hoc Networks

Vehicular Ad hoc Networks(VANETs) is an application instance of Mobile Adhoc Networks(MANETs), with a lot of characteristics of MANETs. In VANETs, theestablishment of VANETs does not rely on any fixed facilities. All vehicles have thesame status and network spontaneously under certain protocols. The fast-moving ofvehicles makes the network topology change frequently. Designing the routingprotocols that meet the characteristics above can ensure good communication perfo-rmance.This paper focuses on the position-based routing protocols for VANETs, a typicalrepresentative of which is GPSR. The protocol includes position service and packetforwarding, and packet forwarding includes greedy forwarding and perimeterforwarding. GPSR protocol usually apply greedy forwarding to select the next hop,however, when local optimization phenomenon happens, the node starts perimeterforwarding to choose the next hop. With these two forwarding methods, the nodesestablish route. To design protocols suitable for real scene, it is essential to applyvehicular mobility models similar to real scene. VANETs Mobility Simulator(Vanet-MobiSim) can generate real vehicle flow model. Based on VanetMobiSim, this paperstudies the routing protocols of VANETs.This paper thinks that traditional GPSR protocol only considers the positionfactor. But it ignores the direction and speed factors. And it does not consider theeffects of obstacles and the density of vehicle flow. For the impact of traffic density,the paper presents the concept of the density of vehicle flow, demonstrates the criticalvalue of the density of vehicle flow, and studies a network model based on the densityof vehicle flow. Considering all the above factors, the paper proposes an improvementscheme of GPSR protocol based on the density of vehicle flow, including macro-directing algorithm, micro-forwarding algorithm and the maintenance of the neighborlist. According to the density of vehicle flow, macro-directing algorithm selects atransmission path from the source node to the destination node for the packet,avoiding the impact of the density of vehicle flow on communication link connectivity.The micro-forwarding algorithm provides that the protocol tries its best to make thepackets be transmitted over selected road sections. That is to say, to avoid the impactof the obstacles near the intersection, when the packet is transmitted from a road section to another road section, the protocol tries to choose the vehicle closest to theintersection as the next hop node. And it selects the vehicle node which moves to theintersection that macro-directing algorithm chooses as the next hop. When the schememaintains the neighbor list, the scheme forecasts the position of the vehicle node inthe dangerous zone by position prediction algorithm. According to the predictionresults, it deletes or saves the neighbor nodes.This paper builds a simulation platform using VanetMobiSim and the NS2simu-lator. It simulates traditional GPSR protocol and improved GPSR protocol. Thesimulation results show that, compared with the traditional GPSR protocol the newGPSR protocol improves data packet delivery ratio to some extent, but its averageend-to-end delay is slightly larger than before. Therefore, the new GPSR protocol issuitable for VANETs, which requires high reliability, and relatively low real-timeperformance.