Trade-Off Between Beamforming and Macro-Diversity Gains in Distributed mMIMO

TL;DR

This paper investigates the trade-off between beamforming and macro-diversity in distributed mMIMO systems, identifying an optimal balance of access points and antennas based on coverage area and channel conditions.

Contribution

It introduces a comprehensive analysis of the trade-off between deploying more APs with fewer antennas versus fewer APs with more antennas in distributed mMIMO, considering realistic channel models.

Findings

Existence of a 'sweet spot' for the optimal number of APs and antennas per AP.

Optimal configuration depends on the physical size of the coverage area.

Numerical results demonstrate the trade-off and optimal deployment strategies.

Abstract

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.