A Study On Rsu Deployment Approaches For Vehicular Ad Hoc Networks

Vehicular ad hoc network(VANET)is a kind of self-organizing network,which originated from the traditional mobile ad hoc networks.Its uniqueness mainly reflects in the high dynamic network topology,frequent disruption of network connectivity,predicable mobility model and so on.In recent years,its effects on alleviating traffic pressure,improving road safety,reducing traffic pollution and so on serves as the background of widespread interest in VANET by government,academic,and industrial bodies.VANET composed of vehicles equipped with On-Board Unit(OBU)and Road Side Units(RSU)can provide a variety of applications including active road safety applications,traffic efficiency and management applications and value-added applications.This thesis focuses on the RSU deployment problem in VANET.Firstly,we analyze the network connectivity after deploying RSUs.Then,we propose a RSU deployment approach based on centrality and a RSU deployment approach aimed to reduce application request delay to improve the effectiveness of the deployment of roadside units.Firstly,we studied the network connectivity problem in a VANET and derived an analytical model to calculate the downlink connectivity probability within the two-hop coverage of an RSU.The analytical model takes into account the road condition,traffic distribution,and vehicle capability.The simulation results show that the derived analytical model is basically accurate.It can be used to not only calculate the two-hop downlink connectivity probability and investigate the impacts of different parameters on the connectivity probability,including the distance between adjacent RSUs,the traffic density,and the ratio of each type of vehicles.Moreover,the derived analytical model is also useful in the deployment of RSUs in a VANET.It can be used to investigate if the deployment distance between two adjacent RSUs can meet the requirement in terms of the two-hop downlink connectivity probability,which has an impact on the transmission delay of the network.Secondly,we introduced the notion of centrality in a social network to RSU deployment,and proposed a centrality-based RSU deployment approach for a 2-D urban or suburban road scenario.This deployment approach on the basis of the road topology and traffic rules derives a better RSU deployment scheme without the time-varying statistical parameters.The centrality-based RSU deployment problem was formulated as a linear programing problem with the objective to maximize the total centrality of all position candidates selected for RSU deployment under the constraint of a given deployment budget.The formulated problem is analogous to a 0-1 Knapsack problem and can be solved by employing a 0-1 Knapsack algorithm.Simulation results show that the proposed centrality-based deployment approach can effectively improve the efficiency of RSU deployment in terms of the coverage time ratio as compared to a random deployment approach.And lastly,we first analyzed the message transmission delay on each road segment and then derived the average application request delay of each road segment.On the basis of this,a RSU deployment approach is proposed to reduce the average application request delay.This deployment method considering actual deployment scenarios reduces the average application request delay by deploying RSUs at intersections within given budget.Simulation results show that proposed deployment approach can effectively reduce the average application request delay compared to a random deployment approach.