Industry and academia have been working towards the evolution from Centralized massive Multiple-Input Multiple-Output (CmMIMO) to Distributed mMIMO (DmMIMO) architectures. Instead of splitting a coverage area into many cells, each served by a single Base Station equipped with several antennas, the whole coverage area is jointly covered by several Access Points (AP) equipped with few or single antennas. Nevertheless, when choosing between deploying more APs with few or single antennas or fewer APs equipped with many antennas, one observes an inherent trade-off between the beamforming and macro-diversity gains that has not been investigated in the literature. Given a total number of antenna elements and total downlink power, under a channel model that takes into account a probability of Line-of-Sight (LoS) as a function of the distance between the User Equipments (UEs) and APs, our numerical results show that there exists a ``sweet spot" on the optimal number of APs and of antenna elements per AP which is a function of the physical dimensions of the coverage area.

翻译：工业界与学术界一直在推动从集中式大规模多输入多输出（CmMIMO）向分布式大规模MIMO（DmMIMO）架构的演进。不同于将覆盖区域划分为多个小区并由配备多天线的单个基站分别服务，整个覆盖区域由多个配备少量或单天线的接入点（AP）联合覆盖。然而，在部署更多配备少量或单天线的AP与部署较少但配备多天线的AP之间进行选择时，存在一种波束成形增益与宏分集增益之间的固有权衡，这一现象尚未在文献中得到研究。在给定总天线单元数量和总下行链路功率的条件下，考虑一种将用户设备（UE）与AP间距离的函数作为视距（LoS）概率的信道模型，我们的数值结果表明，存在一个关于AP数量与每个AP天线单元数量的“最佳平衡点”，该平衡点取决于覆盖区域的物理尺寸。