Downlink MIMO-RSMA with Successive Null-Space Precoding

TL;DR

This paper introduces a novel successive null-space precoding scheme for downlink MIMO-RSMA systems, improving interference management and robustness under imperfect channel knowledge.

Contribution

It proposes a new precoding method using null-space basis vectors and develops a suboptimal solution for rate optimization in MIMO-RSMA systems.

Findings

Enhanced system performance over baseline schemes

Improved robustness to channel estimation errors

Effective interference management with null-space precoding

Abstract

In this paper, we consider the precoder design for an underloaded or critically loaded downlink multi-user multiple-input multiple-output (MIMO) communication system. We propose novel precoding and decoding schemes which enhance system performance based on rate splitting at the transmitter and single-stage successive interference cancellation at the receivers. The proposed successive null-space (SNS) precoding utilizes linear combinations of the null-space basis vectors of the successively augmented MIMO channel matrices of the users as precoding vectors to adjust the inter-user-interference experienced by the receivers. We formulate a non-convex weighted sum rate optimization problem for the precoding vectors and the associated power allocation for the proposed SNS-based MIMO-rate-splitting multiple access (RSMA) scheme. We obtain a suboptimal solution for this problem via successive convex approximation. Moreover, we study the robustness of the proposed precoding scheme to imperfect channel state information (CSI) at the base station via derivative-based sensitivity analysis. Our analysis and simulation results reveal the enhanced performance and robustness of the proposed SNS-based MIMO-RSMA scheme over several baseline multi-user MIMO schemes, especially for imperfect CSI.