Energy Optimization for IRS-Aided SWIPT Under Imperfect Cascaded Channels

In this paper, intelligent reflecting surface is deployed in simultaneous wireless information and power transfer (SWIPT) system to improve the energy harvesting performance. We investigate the robust beamforming design considering the impact of the imperfect cascaded channels. We maximize the minimum received energy among all energy receivers to ensure fairness, while guaranteeing the worst-case information receivers rate requirement. To address with the coupling effect of multiple variables in the optimization problem, the alternate optimization method is utilized to decouple the optimization problem into two sub-problems, and the successive convex approximation and the semidefinite relaxation methods are used to solve the sub-problems. Simulation results reveal that employing IRS into SWIPT system can enhance the energy harvest performance, Additionally, our proposed two algorithms converges rapidly and can guarantee the robustness of the system.

I. Introduction

It Is believed that the next generation wireless communication will support massive Internet of Things (IoT) device with restricted energy storage capability. To support the above vision, energy harvesting technologies utilizing solar and wind energy have been proposed to enable possible self-sustainability of power-constrained communication devices. However, these technologies are vulnerable to environmental changes. Radio frequency (RF) energy harvesting has been emerged as a promising supplement, as it can enable simultaneous wireless information and power transfer (SWIPT) [1]. In [1], a multiuser multiple-input single-output (MISO) SWIPT system was studied, where weighted sum-power was maximized, while guaranteeing the minimum signal-to-interference-plus-noise ratio (SINR) requirements at the information receivers (IRs). In [2], the authors revealed that there exists a tradeoff between information rate attained and the amount of harvested energy in massive multiple-input-multiple-output (MIMO) SWIPT systems for maximizing the efficiency. The efficiencies of SWIPT depends on the signal attenuation, and the transmit power of IoT devices is typically in the order of mW. However, the harvested energy from the SWIPT technology typically ranges from 1W to tens of W [3]. In order to implement SWIPT, the researchers in [4] proposed a scheme of Unmanned aerial vehicle enabled SWIPT, where a UAV acts as a wireless charger to deliver energy to energy receiver. Moreover, various techniques such as massive MIMO [2], [5], [6], high-order modulation, etc., have been proposed to facilitate the energy efficiency, whereas they usually led to high capital expense [7].