A Rate-Splitting Approach To Robust Multiuser MISO Transmission

TL;DR

This paper introduces a Rate-Splitting strategy for robust multiuser MISO systems with uncertain CSI, improving max-min rates and degrees of freedom compared to conventional methods, especially under high uncertainty.

Contribution

The paper proposes a novel Rate-Splitting approach that enhances robustness and performance in multiuser MISO systems with CSI uncertainties, outperforming traditional strategies.

Findings

RS achieves higher max-min DoF for large uncertainty regions.

RS attains non-saturating max-min rate for non-scaling uncertainties.

RS improves power minimization feasibility and performance.

Abstract

For multiuser MISO systems with bounded uncertainties in the Channel State Information (CSI), we consider two classical robust design problems: maximizing the minimum rate subject to a transmit power constraint, and power minimization under a rate constraint. Contrary to conventional strategies, we propose a Rate-Splitting (RS) strategy where each message is divided into two parts, a common part and a private part. All common parts are packed into one super common message encoded using a shared codebook and decoded by all users, while private parts are independently encoded and retrieved by their corresponding users. We prove that RS-based designs achieve higher max-min Degrees of Freedom (DoF) compared to conventional designs (NoRS) for uncertainty regions that scale with SNR. For the special case of non-scaling uncertainty regions, RS contrasts with NoRS and achieves a non-saturating max-min rate. In the power minimization problem, RS is shown to combat the feasibility problem arising from multiuser interference in NoRS. A robust design of precoders for RS is proposed, and performance gains over NoRS are demonstrated through simulations.