Research On Networking Technology Of Hybrid Architecture Integrating VLC And IEEE 802.11p For VANET

With the rapid development of the automobile industry and continuous improvements of national economy and the technology level,traffic accidents occur frequently,which has aroused people's close attention to the road traffic safety.It is hoped that the potential traffic accidents warning information can be obtained prior to the accidents,which may provide longer response time for drivers to take corresponding contingency measures so as to avoid the occurrence of accidents as far as possible.However,due to the limited frequency resources of wireless communication,serious channel disturbance and power limitations of transmission systems,the vehicular ad hoc networks(VANETs)based on the wireless communication technology experience low throughput,long transmission latency and low reliabilities because of the system overload in the vehicle dense area or during the rush hour.To solve this problem,we propose a hybrid VANET architecture which integrates the visible light communication(VLC)and the wireless communication technology in vehicular environments.In these hybrid architecture,we use the VLC link as a second channel to assist IEEE 802.11 p between vehicles so as to reduce the number of competing nodes in the network and the IEEE 802.11 p network business load at the same time,which can improve the broadcast communication performance of road safety applications.Firstly,in this thesis,the direct(or one-hop)broadcast communication channels for the road safety applications based on IEEE 802.11 p protocol in the urban area are modeled.For the safety messages with different priorities,Markov chains are constructed to simulate their corresponding binary exponential backoff procedures,and the average duration and probability of the channel blocking in the backoff process are estimated.Secondly,an expression of the channel impulse response,considering the impacts of the light radiation mode,power attenuation and atmospheric turbulence effects on the receiving optical signal,is built.And a theoretical channel model of the VLC communication link between optical transceivers mounted on vehicles is constructed,with the disturbance of the thermal noise and shot noise.We define average delay and a packet reception rate as performance parameters,and make performance analyses of both the one-hop broadcast communication model based on the IEEE 802.11 p technology and the VLC communicationlink between vehicles in the city environment respectively.Then,we describe the hybrid VANET architecture which integrates IEEE 802.11 p and VLC communication technologies and the corresponding clustering algorithm of the hybrid architecture is designed.The selection criterion of cluster head in clustering algorithm is determined by the relative distance and the relative speed between the reference node and its neighboring nodes.After receiving the safety message,cluster head nodes have it copied and broadcast it to all the members of the cluster through their IEEE 802.11 p channels.And cluster members mainly use VLC channels to transmit and forward the messages.Finally,the hybrid VANET architecture and the clustering algorithm which combines IEEE 802.11 p and VLC communication technologies are verified on the OPNET network simulator,and compared with the typical multi-hop clustering algorithm(NHOP)which is on the basis of IEEE 802.11 p protocol.The analysis results demonstrate that the proposed hybrid VANET architecture and clustering algorithm outperform the NHOP scheme in terms of cluster structure stability,clustering overhead,time latency and reliability,and the performance of hybrid architecture is especially improved in dense area.