On the Spectral Efficiency of Space-Constrained Massive MIMO with Linear Receivers

TL;DR

This paper analyzes the spectral efficiency of space-constrained massive MIMO systems with practical antenna topologies, deriving exact and approximate expressions for different linear receivers and highlighting the non-optimality of MRC.

Contribution

It provides new analytical expressions and bounds for spectral efficiency in realistic space-constrained massive MIMO scenarios, considering practical antenna arrangements.

Findings

ZF and MMSE receivers achieve increasing SE with more antennas.

MRC is non-optimal for space-constrained topologies.

Numerical results validate the analytical expressions.

Abstract

In this paper, we investigate the spectral efficiency (SE) of massive multiple-input multiple-output (MIMO) systems with a large number of antennas at the base station (BS) accounting for physical space constraints. In contrast to the vast body of related literature, which considers fixed inter-element spacing, we elaborate on a practical topology in which an increase in the number of antennas in a fixed total space induces an inversely proportional decrease in the inter-antenna distance. For this scenario, we derive exact and approximate expressions, as well as simplified upper/lower bounds, for the SE of maximum-ratio combining (MRC), zero-forcing (ZF) and minimum mean-squared error receivers (MMSE) receivers. In particular, our analysis shows that the MRC receiver is non-optimal for space-constrained massive MIMO topologies. On the other hand, ZF and MMSE receivers can still deliver an increasing SE as the number of BS antennas grows large. Numerical results corroborate our analysis and show the effect of the number of antennas, the number of users, and the total antenna array space on the sum SE performance.