Time Division Wireless Power Transfer Using Receiver Grouping

Wireless power transfer (WPT) has attracted significant attention as a method of supplying energy to low-power devices, such as Internet of Things (IoT) and sensor devices. In WPT systems, beamforming techniques based on array antenna signal processing, such as multiple-input multiple-output (MIMO) and multiple-input single-output (MISO), are mandatory to improve energy conversion efficiency. In this study, to fairly and efficiently transfer energy for multiple receivers, we consider time-division WPT (TD-WPT) in a MISO-based WPT system, where the transmitter periodically switches weight vectors for receivers by assigning a time slot to each weight vector. From two properties, beneficial interference and channel dependency in WPT, we propose a TD-WPT system with receiver grouping, where the receivers are divided into some groups, and the weight vectors and slot lengths are optimized for the groups. In the proposed method, we consider two methods for receiver grouping, distance-based grouping and channel-based grouping, where the former and the latter divide receivers according to the distances between receivers and similarities of the channel coefficients, respectively. Additionally, we extend the channel-based grouping method by considering the homogeneity of the supplied power levels. Simulation experiments in a multipath indoor environment show that the proposed method improves the minimum and average harvested energy.