Performance Research On Broadcast Based MAC Layer In VANET

With the gradual improvement of people's living standard and the pursuit of a better life,cars become more and more important in family's life because of convenience.But at the same time there are lots of problems of traffic congestion and traffic accidents.So the focus of intelligent transportation system is to improving the safety and efficiency of road traffic,reduce traffic congestion and realize vehicle entertainment.The appearance of Vehicular Ad hoc Network(Vehicular Ad hoc Network,VANET)is to solve these problems and through the broadcasting and communications of information especially the security information.The information always transmitted between vehicles or vehicles and roadside facilities.The focus is the performance research and simulation about MAC layer protocol based on broadcast in VANET.The main contributions of the paper are summarized as follows:1.This paper studies and analyzes the t random access mode and cluster based access mode based on broadcast in VANET.By modeling the vehicle generated data packet into the channel as an M/G/1 queue with unlimited transmission buffers,two access modes are modeled respectively,and two parameters for packet arrival rate and system delay are derived for evaluating the robustness of the system.It is more direct to find the reasons for the performance of the system by modeling and analysis.2.A threshold analysis algorithm based on node density is proposed in this paper.The algorithm normalizes the arrival rate and the system delay of the two access modes,and combines the standardized results with the weighted method.The corresponding density is obtained as threshold through the intersection of the two curves,which is used as the switching point of the random access mode and the cluster based access mode.The performance of the random access mode is good at low density of road vehicles,and the performance drops sharply with the increase of density.However,the cluster based access mode is prolonged when the density is low,and is more suitable for the scene with higher vehicle density.Therefore,through the result of the algorithm,we can get the random access mode to switch to the density threshold of cluster based access mode with the increase of vehicle density,and it can maintain system performance with less overhead,which has practical application significance.3.This paper simulates the two access modes and sets up different parameter groups to verify the correctness of the model by more scenes.The simulation results show that the two kinds of package to rate decreased with the increase of road vehicle density data access mode,the system delay is increased with the increase of density,and reduce or increase the amplitude and the model results are roughly the same,which verified the model.At the same time,the simulation results and model results also proved that the random access mode of transmission within the scope of direct collision is not the main cause of packet loss,mainly due to the degradation of the system is around the hidden terminal effect,which also serves as the foundation to improve the system performance by clustering method.