Cell-Free Massive MIMO with Multi-Antenna Users over Weichselberger Rician Channels

TL;DR

This paper analyzes cell-free massive MIMO systems with multi-antenna users over Weichselberger Rician channels, deriving spectral efficiency expressions and proposing a practical uplink precoding scheme to enhance performance.

Contribution

It introduces a novel uplink precoding scheme based on UE correlation eigenbasis and derives new closed-form spectral efficiency expressions for LSFD with MR combining.

Findings

Proposed precoding significantly improves spectral efficiency.

Derived accurate closed-form spectral efficiency expressions.

Numerical results validate the effectiveness of the precoding scheme.

Abstract

We consider a cell-free massive multiple-input multiple-output (MIMO) system with multi-antenna access points and user equipments (UEs) over Weichselberger Rician fading channels with random phase-shifts. More specifically, we investigate the uplink spectral efficiency (SE) for two pragmatic processing schemes: 1) the fully centralized processing scheme with global minimum mean square error (MMSE) or maximum ratio (MR) combining; 2) the large-scale fading decoding (LSFD) scheme with local MMSE or MR combining. To improve the system SE performance, we propose a practical uplink precoding scheme based on only the eigenbasis of the UE-side correlation matrices. Moreover, we derive novel closed-form SE expressions for characterizing the LSFD scheme with the MR combining. Numerical results validate the accuracy of our derived expressions and show that the proposed precoding scheme can significantly improve the SE performance compared with the scenario without any precoding scheme.