Research On Connectivity For Vehicular Ad Hoc Networks In Fading Channels

Intelligent transportation systems lead the wisdom city.As an important part of intelligent transportation systems,vehicular ad hoc network has become a hot topic in the field of academia and industry researches.VANET is a special kind of mobile ad hoc networks and the connectivity is one of main performance parameters of VANET.The study of connectivity characteristics for VANET can provide routing protocol design,data distribution mechanism and mobility management with guidance.This paper aims at studying connectivity of VANET in deterministic channel and Nakagami-m fading channel based on VANET simulated by VanetMobiSim in detail.The main work concludes the following three aspects:(1)Topology characteristics of VANET are studied.Firstly,VANET is built based on deterministic channel model and Nakagami fading channel model.Then,the experiment analyzes the variation characteristics with time of complex networks statistical parameters,such as degree and degree distribution,clustering coefficient and network efficiency as well as influences on them by channel model parameters.The experimental results show that VANET topology does not have scale-free and small-world properties under the two kinds of channel models.(2)The instantaneous topology connectivity of VANET with the time evolution is studied.On the basis of connectivity metrics including the number of isolated nodes and connected components companied by the scale of the largest connected component,the effects on connectivity of VANET by network density,path loss index and decline factor is discussed.The results show when the network connectivity is poorer,all the connectivity indexes present heavy tail phenomenon and network connectivity has a strong time correlation,but if VANET is fully connected,the network time correlation is weak.(3)Topology characteristics and connectivity of VANET based on temporal network are studied.The change tendency of temporal shortest path length,clustering coefficient and global network efficiency of VANET over time is analyzed.The results show that with the extension of time,the average temporal distance and clustering coefficient both increase.When time reaches a certain threshold,the temporal distance and clustering coefficient tend to be saturated,indicating the network structure is stable.Moreover,with the nodes increasing,connectivity will get better.Based on temporal in and out connected components,the connectivity of VANET based on temporal network under Nakagami-m fading channel models is analyzed.The experiment indicates that as time goes on,the number of in and out connected components under fading channel model increases,and the connectivity of VANET based on temporal network is highly correlated with time.