Research On The Multi-Channel MAC Based On RSU In Vanet

With the development of Intelligent Transportation System(ITS),the Vehicular Ad-hoc Network(VANET)has been paid more and more attention by academia and industry.VANET is a special self-organizing network,it has V2 V and V2 I communication ways,providing the users with safety and non-safety applications.With the development of economic,the demand for non-safety applications is also increasing.How to improve the efficiency of transmission of non-safety applications after the total transmission of safety information is an important subject for researchers.Before the study of non-safety service transmission,first the deployment of RSU on the roadside unit is introduced.The deployment of RSU has the important influence on the connectivity rate of the node.The deployment of RSU is excellent considering the connectivity rate.According to the communication characteristics of V2 V and V2 I,the deployment of roadside units based on a team of vehicles connectivity is proposed.The connectivity of the vehicle,the length of the team and the average number of vehicle nodes in the team are studied in the case of vehicle density and communication radius change.The results show that when the vehicle density is 10 vehicles per km and the communication radius of the vehicle is 300 m,the length of the team is 1608 m,the average number of vehicles in the team is 7,and the connectivity rate of the vehicle is about 75%.The connectivity of team-based research does not consider the special road segment of the RSU coverage,such as the high incidence of accidents,for this defect,a algorithm of based on the team on priority-road deployment is proposed,the road is divided into high incidence of accidents and ordinary sections.Then randomly intercepted three cases to verify the superiority of the algorithm.Experiments show that the connectivity based on the team on priority-road algorithm is higher than the team-based deployment algorithm,and the deployment number of nodes is not much bigger than the team-based deployment algorithm.Based on the WAVE MAC protocol,the control channel(CCH)and service channel(SCH)are analyzed and studied.The standard IEEE 802.11p/IEEE 1609.4 protocol adopts the multi-channel strategy of the fix-length CCH interval.This method can only transmit the safety information on the control channel,and the control channel and the service channel each account for 50 ms.In this way,when the node density changes,it has poor adaptability,resulting in a waste of channel time slot.Aiming at the problem,a SC-MMAC for adaptive adjustment of CCH and SCH slot length is proposed.Taking V2 I as the model structure and considering the immediate SCH access,when the number of vehicle change,the length of the CCH slot is dynamically adjusted by the margin of the CCH and SCH timeslot,and the three-dimensional markov chain is adopted for SC-MMAC.The experimental results show that the minimum timeslot of CCH can be reduced to 39.2ms and the maximum timeslot can reach 66 ms.The relationship between node density and throughput of SC-MMAC and WAVE MAC protocol is also simulated.The experiment shows that the throughput of SCMMAC is greater than the WAVE MAC.