Achieving Multi-beam Gain in Intelligent Reflecting Surface Assisted Wireless Energy Transfer

TL;DR

This paper explores how to leverage intelligent reflecting surfaces (IRS) for multi-beam wireless energy transfer, proposing dynamic beamforming strategies to maximize energy harvesting efficiency in multiuser systems.

Contribution

It introduces a novel time-division framework with dynamic IRS passive beamforming to achieve multi-beam gain, surpassing static schemes and existing methods.

Findings

Dynamic IRS beamforming significantly improves energy transfer efficiency.

Multi-beam transmission is essential for optimal performance.

Proposed scheme outperforms existing static and TDMA-based methods.

Abstract

Intelligent reflecting surface (IRS) is a promising technology to boost the efficiency of wireless energy transfer (WET) systems. However, for a multiuser WET system, simultaneous multi-beam energy transmission is generally required to achieve the maximum performance, which may not be implemented by using the IRS having only a single set of coefficients. As a result, it remains unknowns how to exploit the IRS to approach such a performance upper bound. To answer this question, we aim to maximize the total harvested energy of a multiuser WET system subject to the user fairness constraints and the non-linear energy harvesting model. We first consider the static IRS beamforming scheme, which shows that the optimal IRS reflection matrix obtained by applying semidefinite relaxation is indeed of high rank in general as the number of energy receivers (ERs) increases, due to which the resulting rank-one solution by applying Gaussian Randomization may lead to significant loss. To achieve the multi-beam gain, we then propose a general time-division based novel framework by exploiting the IRS's dynamic passive beamforming. Moreover, it is able to achieve a good balance between the system performance and complexity by controlling the number of IRS shift patterns. Finally, we also propose a time-division multiple access (TDMA) based passive beamforming design for performance comparison. Simulation results demonstrate the necessity of multi-beam transmission and the superiority of the proposed dynamic IRS beamforming scheme over existing schemes.