The Research On Multi-Channel MAC Protocol In Vehicular Wireless Communication

With the continuous evolution and development of ITS(intelligent transportation systems),VANET(Vehicular Ad Hoc Network)has attracted widespread attention and research.VANET enables the interaction of information between car and car,and between the car and the road,which enriches the on-board application service,improves traffic safety,alleviates traffic pressure,and accelerates traffic construction.WAVE(Wireless Accession Vehicular Environment),as the implementation protocol for VANET,is mainly composed of IEEE802.11p and IEEE 1609.X.The issues exposed by the current WAVE system include low message transmission success rate,waste of channel resources,and high message transmission delay because of the IEEE802.11p/1609.4 hybrid protocol used in the MAC layer.This thesis mainly focuses on the research and improvement of IEEE802.11p and IEEE1609.4 protocols,and carries out corresponding verification and comparison.To address the issue of IEEE802.11p channel access scheme for broadcast safety messages in VANET,a Markov model of its backoff process is established.And,the Poisson process was used to establish the vehicle node distribution model.On the basis of calculating system optimal throughput,an improved CSMA/CA(Carrier Sense Multiple Access/Collision Avoidance)scheme based on node density to adjust the competition parameters is proposed,making the system can effectively reduce message collision probability,improving throughput and network adaptabilityThen,the issue of insufficient transmission performance in the high node density situation and the waste of channel resources in the IEEE 1609.4 multi-channel coordination scheme are improved and optimized.After reconfiguring the channel access priority of the node,a multi-channel coordination scheme based on the RSU is proposed,which effectively uses the channel resources,improves the transmission success rate of the message in limited time slots,and adapts to high node density situation while to reduce system delays,thus ensuring the safety message transmissionFinally,two different improvement schemes were simulated and compared with the current standard scheme,respectively.The results show that compared with the channel access scheme and multi-channel coordination scheme of the standard agreement,the improved scheme can achieve better system performance and adapt to different node density situation.