Spatio-Temporal Mobile Cooperative Charging for Low-Power Wireless Rechargeable Devices

By deploying or scheduling wireless chargers, Wire-less Rechargeable Sensor Networks (WRSNs) can provide continu-ous energy supply for the rechargeable devices. Recently, a novel cooperative charging service model was proposed for WRSNs, which provides a business framework of on-demand wireless charging service. Based on such model, the existing work mainly considered the spatially cooperative charging scheduling problem but ignored the cooperation in temporal dimension. In practice, we can find that the QoS requirement of applications often requires an upper bound constraint on the out-of-service time for each device, which implies the charging service cost can benefit from the temporal cooperation of the devices. In this paper, we focus on the device-initiated mobile cooperative charging problem in both spatial and temporal dimensions. Our objective is to find a spatio-temporal cooperative charging scheduling strategy to minimize the total charging service cost, subject to the constraints that the out-of-service time of each device does not exceed a given upper bound. We first prove the NP-hardness of our target problem, and then devise a greedy-based Charging Service Cost Optimization Algorithm, which can achieve an approximation ratio of In $n+1$ in most of real situations. The extensive simulation results reveal that our solution always outperforms the other solutions in terms of charging service cost.