# Antenna Arrays for Line-of-Sight Massive MIMO: Half Wavelength is not Enough

## TL;DR

This paper demonstrates that non-uniform, non-equispaced antenna arrays outperform traditional half-wavelength uniform arrays in line-of-sight massive MIMO systems, offering improved channel conditions and spectral efficiency.

## Contribution

It introduces the use of non-uniform arrays for massive MIMO, showing their advantages over traditional uniform arrays in LOS conditions.

## Key findings

- Non-uniform arrays achieve better channel matrix condition numbers.
- Non-uniform arrays provide higher spectral efficiency.
- Increasing array size benefits circular arrays as well.

## Abstract

The aim of this paper is to analyze the array synthesis for 5 G massive MIMO systems in the line-of-sight working condition. The main result of the numerical investigation performed is that non-uniform arrays are the natural choice in this kind of application. In particular, by using non-equispaced arrays, we show that it is possible to achieve a better average condition number of the channel matrix and a significantly higher spectral efficiency. Furthermore, we verify that increasing the array size is beneficial also for circular arrays, and we provide some useful rules-of-thumb for antenna array design for massive MIMO applications. These results are in contrast to the widely-accepted idea in the 5 G massive MIMO literature, in which the half-wavelength linear uniform array is universally adopted.