Energy-Efficient and Delay-Minimizing Charging Method With a Multiple Directional Mobile Charger

Abstract

To prolong the battery lifetime of Internet-of-Things (IoT) devices, they can be charged by a mobile charger (MC) equipped with radio frequency (RF)-based wireless power transfer (WPT) capability. By concentrating power toward IoT devices, the energy efficiency of the MC increases when using a directional antenna instead of an omnidirectional counterpart. However, directional antennas have a narrow beamwidth, and thus, several IoT devices cannot be charged simultaneously. In this article, we propose a multiple-directional MC (MDMC) scheme that exploits multiple-directional beams to reduce the charging delay while maintaining the advantages of directional antenna with a higher charging efficiency. In our MDMC, an MC determines its charging points to visit and the directions of its beams at each charging point. The charging points can be determined in consideration of the distribution of the devices and the remaining energy. After selecting charging points, the travel paths are determined by considering the remaining energy of the IoT devices. In addition, to relax the problem complexity, we propose an efficient two-stage multiple-directional beam selection (MDBS) algorithm. In the first stage, the directions of beams are determined. The second stage calculates the charging time of each beam for minimizing delay. The simulation results show that the MDMC outperforms the existing single-directional antenna-based charging schemes in terms of the energy efficiency and charging delay approximately 15% and 25%, respectively.