Spectral Efficiency and Scalability Analysis for Multi-Level Cooperative Cell-Free Massive MIMO Systems

TL;DR

This paper introduces a multi-level cooperative architecture for cell-free massive MIMO systems that enhances spectral efficiency and scalability by using spatial expansion units, with derived rate expressions and verified improvements.

Contribution

It proposes a novel multi-level cooperative architecture with spatial expansion units, providing closed-form rate expressions and demonstrating improved spectral efficiency and scalability trade-offs.

Findings

Closed-form uplink rate expressions derived and verified.

Multi-level architecture outperforms other cell-free MIMO architectures.

Enhanced balance between spectral efficiency and scalability achieved.

Abstract

This paper proposes a multi-level cooperative architecture to balance the spectral efficiency and scalability of cell-free massive multiple-input multiple-output (MIMO) systems. In the proposed architecture, spatial expansion units (SEUs) are introduced to avoid a large amount of computation at the access points (APs) and increase the degree of cooperation among APs. We first derive the closed-form expressions of the uplink user achievable rates under multi-level cooperative architecture with maximal ratio combination (MRC) and zero-forcing (ZF) receivers. The accuracy of the closed-form expressions is verified. Moreover, numerical results have demonstrated that the proposed multi-level cooperative architecture achieves a better trade-off between spectral efficiency and scalability than other forms of cell-free massive MIMO architectures.