Generalized Framework for a Fair Comparison of Cellular and Cooperative Massive MIMO Systems

2026-06-12

AI Summary

This study addresses evaluation biases in comparing conventional cellular and cooperative cell-free massive MIMO systems, which often arise from conflating antenna distribution, site cooperation, and signal processing assumptions. To resolve this, the authors propose a unified graph-theoretic framework that explicitly decouples antenna distribution and site cooperation into two distinct dimensions, defining seven canonical architectures and deriving consistent uplink and downlink spectral efficiency expressions for each. A relative capacity metric is introduced to quantify how closely each architecture approaches the performance of an ideal centralized cell-free system, revealing that phase-aligned cooperative beamforming is the primary source of performance gains. Results demonstrate that, under dense deployments with few antennas per access point, cooperative distributed and hybrid cell-free architectures can closely match centralized performance while substantially reducing fronthaul bandwidth requirements; furthermore, simulation areas of at least 2.5×2.5 km² are necessary to ensure fair performance evaluation.

Abstract

Cooperative massive multiple-input multiple-output (MIMO) promises large gains over cellular deployments, but existing comparisons of different architectures often mix antenna distribution, inter-site coordination, and processing assumptions. This paper introduces a graph-based framework for fair comparison of cellular, coordinated, and cell-free massive-MIMO systems. We differentiate between two key properties, namely antenna distribution and inter-site cooperation, which yields seven representative system types. We derive compatible uplink and downlink spectral efficiency (SE) expressions, including an uplink bound for detectors with mixed instantaneous and statistical effective channel state information (CSI), and adapt scalable user association and processing rules to all considered architectures. We evaluate these systems using extensive numerical simulations and show that for a fair comparison much larger simulation areas (at least 2.5 $\times$ 2.5 km2) than commonly used are required. We introduce the relative capacity, which measures how closely each architecture approaches centralized cell-free processing. The results show that coordinated, phase-aligned beamforming across spatially distributed antennas is the main source of cooperation gains. In dense deployments with few antennas per access point (AP), coordinated Distributed Antenna System (DAS) and hybrid cell-free architectures achieve much of the centralized cell-free performance while requiring substantially weaker midhaul assumptions.

Problem

• massive MIMO
• fair comparison
• cellular systems
• cooperative systems
• antenna distribution

Innovation

• graph-based framework
• massive MIMO
• inter-site cooperation
• spectral efficiency
• relative capacity