Design of a Multi-User Wireless Powered Communication System Employing Either Active IRS or AF Relay

TL;DR

This paper develops an optimization framework for multi-user wireless powered communication systems utilizing either active IRS or AF relay, enhancing fairness and efficiency through joint waveform, power, and time allocation.

Contribution

It introduces a unified optimization approach for fair multi-user WPC systems employing IRS or relay, considering non-linear energy harvesting and using MM technique for non-convex problems.

Findings

Proposed method improves system performance in various setups.

Joint design enhances fairness among user pairs.

Algorithm converges quickly to optimal solutions.

Abstract

In this paper, we optimize a Wireless Powered Communication (WPC) system including multiple pair of users, where transmitters employ single-antenna to transmit their information and power to their receivers with the help of one multiple-antennas Amplify-and-Forward (AF) relay or an active Intelligent Reflecting Surface (IRS). We propose a joint Time Switching (TS) scheme in which transmitters, receivers, and the relay/IRS are either in their energy or information transmission/reception modes. The transmitted multi-carrier unmodulated and modulated waveforms are used for Energy Harvesting (EH) and Information Decoding (ID) modes, respectively. In order to design an optimal fair system, we maximize the minimum rate of all pairs for both relay and IRS systems through a unified framework. This framework allows us to simultaneously design energy waveforms, find optimal relay/IRS amplification/reflection matrices, allocate powers for information waveforms, and allocate time durations for various phases. In addition, we take into account the non-linearity of the EH circuits in our problem. This problem turns out to be non-convex. Thus, we propose an iterative algorithm by using the Minorization-Maximization (MM) technique, which quickly converges to the optimal solution. Numerical examples show that the proposed method improves the performance of the multi-pair WPC relay/IRS system under various setups.