Rate Analysis of Cell-Free Massive MIMO-NOMA With Three Linear Precoders

TL;DR

This paper evaluates the performance of cell-free massive MIMO-NOMA systems with three linear precoders, deriving sum rate expressions and analyzing the impact of interference, pilot contamination, and SIC imperfections.

Contribution

It provides a comprehensive analysis of three precoders in CF massive MIMO-NOMA, including closed-form sum rate expressions considering practical impairments.

Findings

mRZF and fpZF outperform MRT with perfect SIC

System supports more users than OMA at the same coherence interval

Pilot contamination and SIC imperfections degrade performance at low user counts

Abstract

Although the hybrid of cell-free (CF) massive multiple-input multiple-output (MIMO) and non-orthogonal multiple access (NOMA) promises massive spectral efficiency gains, the type of precoders employed at the access points (APs) impacts the gains. In this paper, we thus comprehensively evaluate the system performance with maximum ratio transmission (MRT), full-pilot zero-forcing (fpZF) and modified regularized ZF (mRZF) precoders. We derive their closed-form sum rate expressions by considering Rayleigh fading channels, the effects of intra-cluster pilot contamination, inter-cluster interference, and imperfect successive interference cancellation (SIC). Our results reveal that this system supports significantly more users simultaneously at the same coherence interval compared to its OMA equivalent. However, intra-cluster pilot contamination and imperfect SIC degrade the system performance when the number of users is low. Moreover, with perfect SIC, mRZF and fpZF significantly outperform MRT. Also, we show that this system with either mRZF or fpZF precoding outperforms OMA systems with MRT. The analytical findings are verified by numerical results.