Precoding for Uplink RIS-Assisted Cell-Free MIMO-OFDM Systems with Hardware Impairments

TL;DR

This paper proposes a joint precoding and RIS configuration method for uplink cell-free MIMO-OFDM systems with hardware impairments, improving sum-rate performance through an iterative WMMSE-based algorithm.

Contribution

It introduces a novel joint design framework for precoding, RIS coefficients, and receive combining in RIS-assisted CF-mMIMO systems considering hardware impairments.

Findings

Proposed BCD approach effectively maximizes uplink sum-rate.

Iterative methods outperform heuristic solutions in simulations.

System performance is robust to hardware impairments.

Abstract

This paper studies a reconfigurable intelligent surface (RIS)-assisted cell-free massive multiple-input multiple-output (CF-mMIMO) system with multiple RISs. Joint design of transmit precoding, RIS coefficients, and receive combining is investigated for uplink sum-rate maximization under in-phase and quadrature phase imbalance (IQI) at user equipments (UEs) and access points (APs). A weighted minimum mean squared error (WMMSE) based block coordinate descent (BCD) approach is proposed, where novel iterative methods are developed to efficiently solve the BCD subproblems. The efficiency of proposed approaches is demonstrated relative to heuristic methods via extensive simulations.