Beamforming Optimization for Active Intelligent Reflecting Surface-Aided SWIPT

Abstract

Active intelligent reflecting surface (IRS) has been recently proposed to alleviate the product path loss attenuation inherent in the IRS-aided cascaded channel. In this paper, we study an active IRS-aided simultaneous wireless information and power transfer (SWIPT) system. Specifically, an active IRS is deployed to assist a multi-antenna access point (AP) to convey information and energy simultaneously to multiple single-antenna information users (IUs) and energy users (EUs). Two joint transmit and reflect beamforming optimization problems are investigated with different practical objectives. The first problem maximizes the weighted sum-power harvested by the EUs subject to individual signal-to-interference-plusnoise ratio (SINR) constraints at the IUs, while the second problem maximizes the weighted sum-rate of the IUs subject to individual energy harvesting (EH) constraints at the EUs. The optimization problems are non-convex and difficult to solve optimally. To tackle these two problems, we first rigorously prove that dedicated energy beams are not required for their corresponding semidefinite relaxation (SDR) reformulations and the SDR is tight for the first problem, thus greatly simplifying the AP precoding design. Then, by capitalizing on the techniques of alternating optimization (AO), SDR, and successive convex approximation (SCA), computationally efficient algorithms are developed to obtain suboptimal solutions of the resulting optimization problems. Simulation results demonstrate that, given the same total system power budget, significant performance gains in terms of operating range of wireless power transfer (WPT), total harvested energy, as well as achievable rate can be obtained by our proposed designs over benchmark schemes (especially the one adopting a passive IRS). Moreover, it is advisable to deploy an active IRS in the proximity of the users for the effective operation of WPT/SWIPT.

Sum-Rate Maximization in Active RIS-Assisted Multi-Antenna WPCN

“…Inspired by the amplification characteristic of the active RIS, the active RIS is confirmed to be superior to the passive RIS in terms of performance enhancement, and thus has been considered a promising technique for IoT networks [19,20,[25][26][27][28][29]. The authors in [19] compare the capacity improvement achieved by the active RIS to the passive RIS, which demonstrats that the active RIS can fundamentally mitigate the double-fading effect.…”

“…The ac-tive RIS-aided multiuser MISO PS-SWIPT is studied in [27] to minimize the base station transmit power, which shows significant improvements compared to the passive RIS-aided system. Similarly, in [28], an active RIS is employed to assist SWIPT to boost the efficiency of both WET and WIT, while the conclusions and approaches are inapplicable to the WPCN system because of thire different system models.…”

“…In contrast to the passive RE, each active RE is equipped with an additionally integrated active reflection-type amplifier supported by a power supply. By appropriately setting the effective resistance, it is reasonable to assume that the reflection amplitude and phase of each element is independently [19,20,[25][26][27][28][29]. To power the operations of active RIS and users, the PS is equipped with a stable energy source.…”

Over-the-Air Beamforming with Reconfigurable Intelligent Surfaces

“…Further, for improving the data rate, a new RM design, which employs the sub-groups of a hybrid RIS as information transfer units, is presented in (Yigit et al, 2021b). In follow-up studies, the concept of the active RIS is deployed for beamforming optimization of the RIS-aided multi-user systems (Gao et al, 2022;Thanh Nguyen et al, 2022). Above all, the potential of the active RIS-aided systems for achieving enormous performance gains will enable to develop promising solutions for future research.…”