Research On Information Distribution Mechanisms For Vehicular Ad Hoc Networks

The number of vehicles is increasing, which causes plenty of problems such as traffic congestion, traffic safety, resource waste and environmental pollution. These tough questions bring great economic losses to the country. The concept of Vehicular Ad hoc Network is born in the process of trial and exploration. The communication nodes are vehicles. Thus, there is a lot of difference with the traditional Ad Hoc networks. They mainly include fast moving vehicles, highly dynamic topology structure, uneven distribution of node density and the wireless communication block because of obstacles such as buildings. Therefor traditional routing and MAC protocol is no longer suitable for VANET, which directly affect the communication performance such as packet delivery ratio, delay and network throughput. So routing and MAC protocol research have become the challenge of VANET.The thesis firstly introduces the current research status of VANET routing protocols. Their respective advantages and disadvantages are analyzed. Then, we put forward the improved GPCR-D routing protocol. Compared with the traditional geographic location based routing protocol, GPCR-D considers the network node density. It can dynamically determine the node density and build the areas with high node density in real time. The vehicle speed is slow and topology structure is relatively stable in the areas with high node density. Shortest path algorithm is used in these areas. GPCR-D adopts greedy forwarding routing idea outside the areas. At the same time, recovery strategy and routing void are improved in this thesis. The right-hand rule does not take into account the vehicle moving direction. The choosed next-hop routing is possible to be deliveryed in a direction away from the destination vehicle. The improved recovery strategy is a combination of vehicle position and angle.In need of Qos guarantee, single channel MAC protocol faces serious challenges. It can no longer meet the needs of bandwidth and high transmission rate. At this time multi-channel MAC protocol appears. The thesis puts forward multi-channel MAC protocol considered the node density and service traffic. The multi-channel MAC protocol can reduce switching times as little as possible in guarantee under the premise of communication performance. Mode α means node density and service information flow are large. Mode β means node density is large but service information flow is little. The rest of the nodes are divided into γ mode. Based on the characteristics of different patterns, message is delivered differently. Three modes can switch dynamically. Mode α can adjust the cycle dynamically using PID and adaptive algorithm. Under the condition of safety message reliable transmission, the multi-channel MAC protocol distributes SCH channels rationally, as much as possible to satisfy the user’s service demand and improve the data bandwidth.Finally, the thesis simulates the GPCR-D routing and multi-channel MAC protocol on OMNET++ platform. Sumo is selected as traffic simulator. Veins is an open source simulation framework to simulate vehicle communication. The experimental results show better communication performance reflected in packet delivery ratio and transmission delay.