Opportunistic Beamforming using an Intelligent Reflecting Surface Without Instantaneous CSI

TL;DR

This paper introduces an IRS-assisted opportunistic beamforming scheme that operates without instantaneous CSI, leveraging multi-user diversity to improve sum-rate performance in slow and fast fading environments.

Contribution

It proposes a novel IRS-assisted opportunistic beamforming method that does not require instantaneous CSI, enabling practical deployment and performance gains.

Findings

Approaches the performance of coherent beamforming with many users in slow-fading environments.

Achieves significant sum-rate improvements in correlated Rayleigh fast fading environments.

Utilizes random IRS rotations to exploit multi-user diversity without CSI.

Abstract

While intelligent reflecting surface (IRS) assisted wireless communication has emerged as an important research paradigm, channel state information (CSI) acquisition remains a critical challenge to design the IRS phase-shifts and yield the promised coherent beamforming gains. In this paper, we propose an IRS-assisted opportunistic beamforming (OBF) scheme under proportional fair scheduling, which does not require instantaneous CSI to design the IRS parameters. In a slow-fading environment, we show that with only random rotations at the IRS, the proposed scheme can capitalize on the multi-user (MU)-diversity effect to approach the performance of coherent beamforming as the number of users grows large. Next we study the sum-rate scaling of IRS-assisted OBF in the correlated Rayleigh fast fading environment under a deterministic beamforming scheme that results in a considerable sum-rate improvement.