Optimal Base-Station Deployment In Wireless Rechargeable Sensor Networks

With the development of wireless charging techniques,wireless charging problems have gradually attracted more and more attentions in wireless rechargeable sensor networks.In recent years,lots of researchers have studied various kinds of wireless charging problems based on different goals and models.A plenty of methods have been proposed by using either mobile chargers or fixed base-stations with the aim of prolonging the network lifetime together with maximizing the charging efficiency.Nowadays,some scholars have been focusing on how to best deploy fixed base-stations.The existing literatures reveal that both omnidirectional and directional base-stations have their respective limitations.The omnidirectional base-stations are confined to restricted locations,while rotation of the directional antenna is forbidden once deployed.On the basis of former frameworks,this paper considers the complex characteristics of omnidirectional charging base-stations and rotatable directional charging base-stations.Besides,based on the omnidirectional and directional charging base-station models,we propose a method to optimize the base-station deployment issues.Main contributions of this paper are listed below:(1)Deployment of the base-stations based on omnidirectional antenna.First of all,we conduct the analysis on the sensors,and extend the simple one-to-one(one sensor can be charged by only one base-station)situation to a complicated one-to-multiple(one sensor can be charged by more than one base-stations)condition.Second,we discuss the omnidirectional charging model.By proposing the concept of charging priority,we settle the problem of charging power distribution.Last,we develop an evaluation method on the charging utility of the omnidirectional base-station,and carry out the analysis of the approximation ratio of our proposed heuristic greedy algorithm which handles the whole problem.(2)Deployment of the rotatable base-stations based on directional antenna.To start with,based on the constraints of the charging time of the directional base-station,and with the help of an adaptation of the convergence algorithm of the generalized Fermat point,we obtain the solution to the optimum feasible base-station when the sensors' locations are pre-determined.Then we divide the sensors into different groups,and propose the localization algorithm of the rotatable directional charging base-station.After that,we prove the NP-hardness of minimizing the numbers of base-stations,and propose the concept of frequency of the sensors' appearance as well as discuss the situation with different frequency values.Once and for all,an approximation algorithm to the base-station selection is proposed based on the frequency of the sensors' appearance.Combining localization algorithm and selection algorithm of base-station,we solved the problem of how to deploy the directional base-station.(3)We code these heuristic algorithms on the DEV C++platform.A lot of simulation experiments are carried out,the results of which demonstrate the effectiveness and feasibility of our algorithms.