Research On Content Dissemination Scheme And Routing Protocol In Vehicular Ad Hoc Networks

As an emerging industry,Internet of Vehicles(Io V)creates a new market where lots of new applications involved with transportation safety,efficiency and infotainment may find their places.Apparently,the effective dissemination of content,e.g.,texts,images,music and video clips is the basis of any type of applications in Io V,such as social communications and video sharing.Vehicular Ad Hoc Network(VANET),as the concept in communication field of Io V,is just the technical approach for data dissemination.However,faced with a series of network characteristics,technical limitations and urgent users' demands in the VANET,the research on data dissemination is meaningful and challenging.Due to the presence of diverse node velocities,dynamic network topology,severe channel fading,as well as limit transmission coverage of vehicles and infrastructures in the VANET,vehicle-to-vehicle(V2V)and vehicle-to-infrastructure(V2I)communications both tend to be transient and unstable.On this basis,this thesis focuses on the following two problems.Firstly,the dissemination of large-size files from infrastructures to the target vehicle in highway vehicular communications suffers from the useless fragment content transmissions and low transmissions efficiency followed by low bandwidth utilization.This is because the transmission requirements of large-size files are more stringent and cannot be satisfied with existing communication resources and technologies.Secondly,the end-to-end transmission of packets is the basis of any scheme of data dissemination,which is related to routing design in the network layer.The existing geographic routing protocols shall cater for VANET's characteristics to some extent.However,they ignore the path quality including link state and forwarding quality inside nodes in the process of evaluating nodes' comprehensive quality,which influences the selection of relay nodes and the routing performance.In this thesis,a Cooperative Content Dissemination Scheme(CCDS)for highway vehicular communications and a Geographic Opportunistic Routing protocol based on Path Quality(PQ-GOR)are proposed for forthese two problems,respectively.To facilitate the access from vehicles to infrastructures and enable users to experience the efficient download of large-size files,CCDS utilizes multiple infrastructures,multiple vehicles in two moving directions and the mobility of vehicles to help the target vehicle to download.Detailed analysis is provided to characterize the file dissemination process using CCDS.Simulation and numerical results show that CCDS significantly increases the achievable data download volume and reveal the relationship between major performance-impacting parameters,such as distance between two adjacent infrastructures and vehicles' velocity.The results also give insight on the optimum deployment of network infrastructures,the effective division of target file among infrastructures and the adjustment of vehicles' velocity.To deal with frequent link breakage and low packet delivery rate,in PQ-GOR,both position information and path quality are considered to evaluate nodes' quality comprehensively.On this basis,a hybrid approach involved with filtering and prioritizing of candidate relay nodes as well as a flexible opportunistic forwarding strategy are put forward,which are aimed to make high-quality nodes forward packets as much as possible.Moreover,a comparison between PQ-GOR and two existing protocols is presented in the simulation.Corresponding results show that PQ-GOR has the higher packet delivery rate and throughput,and also the acceptable delay.