Research On Roadside Unit Deployment Strategy In Vehicular Ad-hoc Networks

The essence of VANET is a mobile ad hoc network with vehicles as nodes.To help vehicles build a stable and durable interconnection network,introducing roadside units into VANET is a reliable solution.Roadside units are a type of communication infrastructure similar to cellular base stations and are typically deployed at intersections or on both sides of the middle of a road segment.The roadside unit can be used as a relay node to provide assistance for vehicle-to-vehicle communication,and can independently supply resources to the vehicles in the network as an Internet access point,which makes the vehicle network well support road safety,traffic management,vehicle entertainment and other applications.According to the communication mode between the roadside units,the roadside unit is divided into two types:cable connected roadside unit and wireless roadside unit.Cable connected roadside unit has better performance in many aspects than wireless roadside unit,such as larger communication capacity,wider communication coverage radius,etc.The?_?2^?1metric is a standard used to judge the quality of a V2I connection provided by a roadside unit deployment scheme.Finding a deployment scheme consuming as few roadside units as possible to reach the?_?2^?1metric is called?deployment problem.In this paper,effective roadside unit deployment strategies are proposed for the two scenarios of local accident-prone areas and complete city scales.The characteristics of cable connected roadside unit make it more suitable for deploy-ment in urban accident-prone areas.However,there are few work focus on deploying cable connected roadside units in local areas,and cable deployment overhead introduced by cable connected roadside unit is easily overlooked.Therefore,this paper first discusses the strategy of deploying cable connected roadside units in local accident-prone areas.In order to ensure the economics and reliability of the deployment solution,we will minimize the roadside unit and cable deployment cost as the optimization goal,and require the deployment solution to achieve certain network coverage.In order to solve this optimization problem,we propose a two-layer emmbedded genetic algorithm TLEGA based on plane weighted undirected graph.TLEGA is nested by two inner and outer genetic operators.The inner GA is responsible for searching for the optimal edge individual matching the node individual from the outer layer representing the deployment position of the roadside unit.The outer GA's fitness calculation object is the complete individual consisting of edge individual and node individual,which makes TLEGA capable of global optimization under different cost ratios and coverage conditions and can solve cable connected roadside unit deployment problem well.Traditional?deployment problem only focuses on implementing?deployments based on historical traffic data,ignoring the fact that real-life traffic data dynamically changes over time.Therefore,this paper studies the deployment of virtual roadside units in rasterized city maps.We builds a multi-objective 0-1 integer programming model for real-time?deployment problem based on the single-objective 0-1 integer programming model of the traditional?deployment problem,and proposes a collaborative filtering based real-time deployment strategy CFBRDS to solve the optimization problem.CFBRDS performs similarity calculation based on the time and trace information of all vehicles in each time period,and predicts the time and trace information of the next time period according to the direction and speed of the vehicle.Then CFBRDS generates a new deployment scheme and updates the switch status of roadside units in real time,which makes up for the shortcomings of V2I connection instability provided by the roadside unit in traditional deployment strategy.By constructing an experimental simulation platform and conducting a series of simulation experiments,this paper verifies the effectiveness of the above two roadside unit deployment strategies.First,TLEGA can obtain an optimal deployment scheme after running in a limited number of times under different cost ratios and coverage conditions,reflecting the stability of the algorithm;from the perspective of cost and V2I transmission delay,it is proved that cable connected roadside unit is more suitable to be deployed in the accident-prone area than wireless roadside unit.Secondly,compared with the static deployment strategy SDS and the semi-dynamic deployment strategy SDDS,CFBRDS can achieve a larger real?₂value in each time period,reflecting the the real-time advantage resulted by accurate prediction.