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.

翻译：协作式大规模多输入多输出系统相较于蜂窝部署有望带来巨大增益，但现有不同架构的比较往往混杂了天线分布、站点间协作与处理假设。本文提出一种基于图的框架，用于公平比较蜂窝式、协调式与无小区式大规模MIMO系统。我们将天线分布与站点间协作这两个关键属性加以区分，从而得到七种代表性系统类型。我们推导了兼容的上行与下行频谱效率表达式，其中包含适用于混合瞬时与统计有效信道状态信息检测器的上行界，并将可扩展的用户关联与处理规则适配至所有架构。通过大量数值仿真评估这些系统，我们发现：为进行公平比较，所需仿真区域（至少2.5×2.5平方公里）远大于常规尺寸。我们引入相对容量指标，用以衡量各架构接近集中式无小区处理的程度。结果表明：在空间分布式天线上进行协调式相位对齐波束赋形是协作增益的主要来源。在每接入点天线数较少的密集部署中，协调式分布式天线系统与混合无小区架构在显著降低中传需求的同时，可实现大部分集中式无小区性能。