Joint 3D placement and multi-beam design for UAV-assisted wireless power transfer networks

Abstract

Abstract This paper investigates an unmanned aerial vehicle (UAV)-enabled wireless power transfer (WPT) system, where a UAV acts as the energy transmitter (ET) to deliver radio frequency (RF) energy to a set of energy receivers (ERs). Our aim is to maximize the total harvested energy at all ERs by jointly optimizing the three-dimensional (3D) position of the UAV and beam pattern. However, the optimization problem which takes into account the coverage radius of the UAV and beam scanning range, is formulated as a non-convex problem and hence is difficult to solve. To address this problem, we propose a low-complexity iterative algorithm that decomposes the original problem into three sub-problems and solves the 2D position of the UAV, flight altitude and beam pattern in an iterative manner. In particular, we first apply the exhaustive search algorithm to find the global optimal 2D position of the UAV. Subsequently, we can obtain the optimal UAV’s flight altitude via monotonicity theory. Finally, by applying the Butler Matrix feed network, we propose a multi-beam generation scheme to optimize the beam patterns. Numerical results validate that the theoretical findings and demonstrate that significant performance gain in terms of energy harvesting of all ERs can be achieved by the proposed algorithm in UAV-assisted WPT networks.