LMMSE Receivers in Uplink Massive MIMO Systems with Correlated Rician Fading

TL;DR

This paper provides a theoretical analysis of uplink massive MIMO systems with correlated Rician fading, comparing LMMSE and statistical combining, revealing how LoS strength influences spectral efficiency and optimal training.

Contribution

It introduces a closed-form asymptotic analysis of spectral efficiency for both LMMSE and statistical combining in correlated Rician fading environments, highlighting the impact of LoS components.

Findings

Stronger LoS signals improve spectral efficiency.

Statistical combining outperforms LMMSE in high LoS conditions.

Optimal training length depends on Rician factor.

Abstract

We carry out a theoretical analysis of the uplink (UL) of a massive MIMO system with per-user channel correlation and Rician fading, using two processing approaches. Firstly, we examine the linear minimum-mean-square-error receiver under training-based imperfect channel estimates. Secondly, we propose a statistical combining technique that is more suitable in environments with strong Line-of-Sight (LoS) components. We derive closed-form asymptotic approximations of the UL spectral efficiency (SE) attained by each combining scheme in single and multi-cell settings, as a function of the system parameters. These expressions are insightful in how different factors such as LoS propagation conditions and pilot contamination impact the overall system performance. Furthermore, they are exploited to determine the optimal number of training symbols which is shown to be of significant interest at low Rician factors. The study and numerical results substantiate that stronger LoS signals lead to better performances, and under such conditions, the statistical combining entails higher SE gains than the conventional receiver.