Minimizing the service cost of mobile chargers while maintaining the perpetual operations of WRSNs

The wireless energy transfer technology based on magnetic resonant coupling has been emerging as a promising technology for lifetime prolongation of wireless sensor networks, by providing controllable yet perpetual energy to sensors. As a result, we can employ mobile chargers (i.e., charging vehicles) to charge sensors with wireless energy transfer when the mobile charger approach lifetime-critical sensors. It is however very costly to dispatch mobile chargers to travel too long to charge sensors since their mechanical movements are energyconsuming too. To minimize the operational cost of wireless sensor networks, in this chapter we study the deployment of multiple mobile chargers to charge sensors in a large-scale wireless sensor network so that none of the sensors will run out of energy and aim to minimize the service cost of the mobile chargers. Specifically, we study the problem of minimizing the total traveling distance of mobile chargers for a given monitoring period, and the problem of deploying the minimum number of mobile chargers to replenish a set of lifetime-critical sensors while ensuring that none of the sensors will run out of energy, respectively. For the former, we propose a novel approximation algorithm with a guaranteed approximation ratio, assuming that the energy consumption rate of each sensor does not change for the given monitoring period. Otherwise, we devise a heuristic algorithm through modifications to the approximation algorithm. Simulation results show that the proposed algorithms are very promising. For the latter, we develop an approximation algorithm with a provable performance guarantee, and experimental results demonstrate that the solution delivered by the proposed approximation algorithm is fractional of the optimal one.