Optimal Bilinear Equalizer for Cell-Free Massive MIMO Systems over Correlated Rician Channels

TL;DR

This paper develops low-complexity optimal bilinear equalizer schemes for cell-free massive MIMO systems over correlated Rician channels, providing closed-form spectral efficiency expressions and demonstrating high performance even with pilot contamination.

Contribution

It introduces novel centralized and distributed OBE schemes tailored to channel statistics, with explicit closed-form SE expressions and practical performance benefits.

Findings

OBE schemes achieve high spectral efficiency.

Closed-form SE expressions are derived for all schemes.

Proposed schemes perform well under severe pilot contamination.

Abstract

In this paper, we explore the low-complexity optimal bilinear equalizer (OBE) combining scheme design for cell-free massive multiple-input multiple-output networks with spatially correlated Rician fading channels. We provide a spectral efficiency (SE) performance analysis framework for both the centralized and distributed processing schemes with bilinear equalizer (BE)-structure combining schemes applied. The BE-structured combining is a set of schemes that are constructed by the multiplications of channel statistics-based BE matrices and instantaneous channel estimates. Notably, we derive closed-form achievable SE expressions for centralized and distributed BE-structured combining schemes. We propose one centralized and two distributed OBE schemes: Centralized OBE (C-OBE), Distributed OBE based on Global channel statistics (DG-OBE), and Distributed OBE based on Local channel statistics (DL-OBE), which maximize their respective SE expressions. OBE matrices in these schemes are tailored based on varying levels of channel statistics. Notably, we obtain new and insightful closed-form results for the C-OBE, DG-OBE, and DL-OBE combining schemes. Numerical results demonstrate that the proposed OBE schemes can achieve excellent SE, even in scenarios with severe pilot contamination.