Multiuser MISO PS-SWIPT Systems: Active or Passive RIS?

TL;DR

This paper investigates the use of active RISs in multiuser MISO SWIPT systems, demonstrating significant power savings and robustness over passive RISs through joint optimization of beamforming, PS ratios, and RIS parameters.

Contribution

It introduces an optimization framework for active RIS-assisted SWIPT systems with realistic energy harvesting models, showing notable improvements over passive RISs.

Findings

Active RISs reduce BS transmit power by up to 28%.

The proposed algorithm is robust against imperfect channel information.

Significant performance gains are achieved with low reflect power levels.

Abstract

Reconfigurable intelligent surface (RIS)-based communication networks promise to improve channel capacity and energy efficiency. However, the promised capacity gains could be negligible for passive RISs because of the double pathloss effect. Active RISs can overcome this issue because they have reflector elements with a low-cost amplifier. This letter studies the active RIS-aided simultaneous wireless information and power transfer (SWIPT) in a multiuser system. The users exploit power splitting (PS) to decode information and harvest energy simultaneously based on a realistic piecewise nonlinear energy harvesting model. The goal is to minimize the base station (BS) transmit power by optimizing its beamformers, PS ratios, and RIS phase shifts/amplification factors. The simulation results show significant improvements (e.g., 19% and 28%) with the maximum reflect power of 10 mW and 15 mW, respectively, compared to the passive RIS without higher computational complexity cost. We also show the robustness of the proposed algorithm against imperfect channel state information.