Cooperative Charging as Service: Scheduling for Mobile Wireless Rechargeable Sensor Networks

Wireless Power Transmission (WPT) has been widely used to replenish energy for Wireless Rechargeable Sensor Networks. However, the charging service model, which is of the essence to commercial WPT, has not emerged so far. In this paper, we present a wireless charging service model from the perspective of cooperative charging economics, and formulate the Cooperative Charging Scheduling (CCS) problem for joint optimization of rechargeable devices' charging cost and moving cost. We first propose two intragroup cost sharing schemes to sustain the cooperation among devices. Then, the approximation algorithm CCSA of the CCS problem is proposed based on greedy approach and submodular function minimization. Furthermore, we model the large-scale CCS problem as a coalition formation game and present a game theoretic algorithm CCSGA. We show that CCSGA finally converges to a pure Nash Equilibrium. We conduct simulations, and field experiments on a testbed consisting of 5 chargers and 8 rechargeable sensor nodes. The results show that the average comprehensive cost of CCSA is 27.3% lower than the noncooperation algorithm and is only 7.3% higher than the optimal solution on average. In field experiments, CCSA outperforms the noncooperation algorithm by 42.9% in terms of comprehensive cost on average. Moreover, CCSGA is much faster than the approximation algorithm and is more suitable for large-scale cooperative charging scheduling.