Robust MMSE Precoding and Power Allocation for Cell-Free Networks

TL;DR

This paper introduces a robust RMMSE precoding method for cell-free massive MIMO systems that effectively mitigates interference under imperfect CSI, improving performance over existing schemes.

Contribution

It develops an iterative RMMSE precoder based on generalized loading and analyzes its achievable rate and computational cost, advancing interference mitigation techniques.

Findings

RMMSE precoder outperforms linear MMSE, ZF, and conjugate beamforming under imperfect CSI.

Optimal and uniform power allocation schemes are proposed and analyzed.

Numerical results confirm the effectiveness of the RMMSE approach.

Abstract

We consider the downlink of a cell-free massive multiple-input multiple-output (MIMO) system with \textcolor{red}{single}-antenna access points (APs) and single-antenna users. An iterative robust minimum mean-square error (RMMSE) precoder based on generalized loading is developed to mitigate interference in the presence of imperfect channel state information (CSI). An achievable rate analysis is carried out and optimal and uniform power allocation schemes are developed based on the signal-to-interference-plus-noise ratio. An analysis of the computational costs of the proposed RMMSE and existing schemes is also presented. Numerical results show the improvement provided by the proposed RMMSE precoder against linear minimum mean-square error, zero-forcing and conjugate beamforming precoders in the presence of imperfect CSI.