Protocol Optimization For Information Propagation Under Vehicular Ad Hoc Network

As an extension of Internet of Things(IoT),Vehicular Ad Hoc Networks(VANETs)accomplishes data sensing,processing and exchange in networks through the networking between vehicles,pedestrian and infrastructure,providing vehicular users and pedestrians with low latency,high reliability services.Low latency and high reliability information exchange in VANETs stands as the foundation of future implementation of Intelligent Transportation System(ITS)and safety-related services.Therefore,information propagation in VANETs should satisfy strict demands on latency and reliability regarding safety-related services.With progresses in the standardization and research,information propagation in VANETs is facing several live issues.Under the multi-channel environment specified by IEEE Standard for Wireless Access in Vehicular Environments(WAVE),existing propagation protocols in VANETs cannot achieve satisfying network performances regarding the propagation delay constraints of safety-related services.A novel channel sensing and access technology should be specifically designed for information propagation under IEEE WAVE multi-channel environment.Besides,the obstructing effect of vehicles on the propagation of radio is drawing more and more research focues,however the impact of this effect on information propagation in VANETs and its countermeasure has not been studied sufficiently.In this paper,we study the above two issues and proposed solutions that work effectively under highly dynamic VANETs.Specifically,we investigated the following research issues:Information propagation in VANETs mainly focuses on the propagations of Cooperative Awareness Messages(CAM)and Decentralized Environmental Notification Messages(DENM)on common control channel.As vehicles advance towards higher automation levels,VANETs should support more complex traffic services,which generates the demand for the propagation of Internet Protocol(IP)-based information and service data on service channels as specified by IEEE WAVE standard.Multi-source propagation in the multi-channel environments will incur Multi-source Relay Confliction(MRC)which leads to higher propagation delay and lower information propagation speed(IPS).However,the problem of how to mitigate the impact of MRC has not been studied sufficiently.In this paper,we propose the Success Probability base Relay Contention Algorithm(SRPCA)for mitigating the impact of MRC under WAVE channel environments.SPRCA uses a vital metric,i.e.Success Probability,to determine whether to join the relay candidate set of certain source and execute relay contention algorithm.SPRCA leverages both real time location information of vehicles and stochastic properties of vehicular distribution to mitigate the impact of MRC.Besides,as physical obstacles,vehicles have significant impact on the efficient propagation of safetyrelated information in VANETs by frequently obstructing the Line-Of-Sight(LOS)links between transmitters and receivers.Obstructing effect of vehicles will diminish the effective coverage of safety-related information and incur severe impact on road safety.However,this impact has not been addressed by existing propagation protocols.In this paper,we present the definition of broadcast efficiency(BE)as the metric for measuring the obstructing effect.We investigate the optimization issue for mitigating the impact of obstructing effect on the propagation of safety-related information and present a graph theory-based optimization(GTO)algorithm.For the capability of realistic implementation in VANETs,we further propose the Maximum Broadcast Efficiency Relaying(MBER)algorithm that can be embedded in VANETs.MBER maximizes the effective coverage of the broadcast,meanwhile,satisfies the constraints on both link state and delay by selecting relay according to broadcast efficiency and propagation delay.We evaluate the proposed protocols through theoretical analysis and network simulations.Network performances of proposed protocols are compared with related works.Evaluation results shed light on the effectiveness of proposed protocols and their advantages over related works in terms of propagation speed,reliability and other metrics.