Movable Antennas Meet Intelligent Reflecting Surface: When Do We Need Movable Antennas?

TL;DR

This paper explores the integration of movable antennas with intelligent reflecting surfaces in wireless systems, analyzing when and how movable antennas outperform fixed antennas in enhancing signal quality.

Contribution

It provides theoretical conditions for performance gains of movable antennas over fixed antennas and proposes an optimization algorithm for joint beamforming and antenna positioning.

Findings

Movable antennas can significantly outperform fixed antennas under certain LoS conditions.

Theoretical analysis identifies scenarios where MAs provide greater SNR improvements.

Numerical results validate the analytical conditions and demonstrate performance gains.

Abstract

Intelligent reflecting surface (IRS) and movable antenna (MA)/fluid antenna (FA) techniques have both received increasing attention in the realm of wireless communications due to their ability to reconfigure and improve wireless channel conditions. In this paper, we investigate the integration of MAs/FAs into an IRS-assisted wireless communication system. In particular, we consider the downlink transmission from a multi-MA base station (BS) to a single-antenna user with the aid of an IRS, aiming to maximize the user's received signal-to-noise ratio (SNR), by jointly optimizing the BS/IRS active/passive beamforming and the MAs' positions. Due to the similar capability of MAs and IRS for channel reconfiguration, we first conduct theoretical analyses of the performance gain of MAs over conventional fixed-position antennas (FPAs) under the line-of-sight (LoS) BS-IRS channel and derive the conditions under which the performance gain becomes more or less significant. Next, to solve the received SNR maximization problem, we propose an alternating optimization (AO) algorithm that decomposes it into two subproblems and solve them alternately. Numerical results are provided to validate our analytical results and evaluate the performance gains of MAs over FPAs under different setups.