Energy harvesting sensor networks with a mobile control center: Optimal transmission policy

Wireless energy transfer, namely RF-based energy harvesting, is a potential way to prolong the lifetime of energy-constrained devices, such as wireless sensor networks. However, due to the huge propagation attenuation, energy efficiency is widely regarded as the biggest bottleneck for large-scale applications. Thus, it is significantly essential to explore appropriate transmission policies for the system to improve the global energy efficiency. To this end, this paper focuses on the optimum transmission policies in sensor networks scenario, where a mobile control center powers the sensor node by RF signal and then collects information from sensor node. Based on whether there is an energy storage at the sensor node, two related schemes, called as harvest-and-use scheme and harvest-store-use scheme, are investigated, respectively. In harvest-and-use scheme, as a baseline, both constant and optimal adaptive transmission strategies are discussed. In harvest-store-use scheme, an explicit closed-form expression of optimal transmission policy is derived in terms of throughput maximization, which can greatly enhance the system performance by opportunistic energy transfer with the help of energy storage. According to the simulation results, a considerably large improvement can be observed by employing the optimum transmission policy developed in this paper.