Edge-assisted Data Transmission Methods In Vehicular Networks

As an important part of the modern intelligent transportation system,the vehicular network is widely used in fault warning,autonomous driving,road flow monitoring,on-board entertainment,etc.The efficient data transmission technology in vehicular networks is of great significance in improving driving safety and driving experience.However,as the industry has increasingly higher requirements for data transmission efficiency for autonomous driving and intelligent driving,it is difficult for the current vehicular network to meet the requirements of low latency and high reliability.The main problems are as follows: the network topology changing rapidly makes it difficult to maintain an effective path between vehicle nodes,resulting in a higher packet loss rate and lower bandwidth utilization,retransmission can improve the reliability of data transmission,but it will cause delay.However,some applications in the vehicular networks have strict requirements on the quality of service(Qo S)such as delay.In addition,when a large number of users in the vehicular network initiate requests,especially for high-definition video,online games and other data,they need to download a large amount of data from the server.These requested data usually have repetitive parts.However,bandwidth resources in the vehicular network are limited,the repeated transmission of data will result in low network bandwidth utilization.In the vehicular network,due to the dynamics of the network,the unreliability of the link,the interference of wireless signals and other factors.In addition,in vehicular networks,due to network dynamics,link unreliability,wireless signal interference,etc.,problems such as low hit rate of the user request and large delay are caused.Therefore,designing a method that can not only satisfy the delay constraints of user requests,reduce the consumption of network bandwidth resources,but also improve the hit rate of user requests is a difficult and scenic spot problem for efficient data transmission in the vehicular network.To improve the efficiency of data transmission in the vehicular network,especially multimedia data,this thesis focuses on several key issues such as large V2 V transmission delay in the vehicular network,excessive network traffic load,low user request hit rate,and high response delay.The main work includes:1.This thesis proposed a space-time graph-based V2 V delay-bounded RSU deployment scheme.To solve the V2 V delay-bounded RSU deployment problem in the vehicular network,and consider the dynamic characteristics of the vehicular network topology,the space-time graph model is adopted to construct the topology of the vehicular network with a predictable trajectory into a space-time graph.Through analysis and proof,the problem is an NP-hard problem,and a heuristic greedy algorithm is proposed to solve the problem,i.e.,it will select the RSU that can reduce the delay of the spacetime graph from the RSU candidate positions to deploy.The time complexity of the algorithm is analyzed and its performance is verified through simulation experiments.2.This thesis proposed a transmission method of coded multicasting based on RSU cache.To solve the problem of excessive network load on the backhaul link caused by a large amount of repeated data in user requests in vehicular networks,a RSU cachebased data transmission method of coded multicasting is proposed.First,according to the user's request data and the user's cached data,a maximum degree priority algorithm is designed to divide users into multiple multicast groups.Secondly,RSU uses XOR encoding to delete duplicate requests for files requested by users,divides the requested files into multiple subfiles,and adopts the subfile coding method to formulate the problem into a bi-objective set cover problem(BOSCP),and proposes a heuristic algorithm to solve the problem.For scenarios where vehicle users are covered by multiple RSUs in the dense deployment of RSUs,the network flow method is used to assign users to the appropriate RSUs,furthermore,multicast group division and subfile encoding-based transmission methods are used to transmit data for each RSU.3.This thesis proposed an edge-assisted hierarchical cooperative content deployment and coded delivery strategy.To solve the problems of low hit rate of users' requests,high response delay,and heavy network traffic load in the vehicular network,an edge-assisted hierarchical cooperative content deployment,and coded delivery method are proposed.The method first uses the user's speed,distance,and link availability as the basis for selecting cluster heads,and proposes a vehicle clustering method and cluster fusion method,which can effectively reduce the impact of topology dynamics on communication between vehicles.At the same time,a hierarchical cooperative content deployment strategy based on cluster heads and RSUs is proposed,and the cooperative caching between different RSUs is considered,the problem is formulated into an optimization problem,and a heuristic method is designed to derive the hierarchical content deployment strategy of cluster heads and RSUs.In the cache node,the transmission method based on subfile coding is used to transmit data to the user to reduce the amount of data transmitted and improve the utilization of network bandwidth.