Exploiting Multiple Polarizations in Extra Large Holographic MIMO

TL;DR

This paper investigates the use of multiple polarizations in holographic MIMO systems operating in near-field line-of-sight conditions, revealing optimal array dimensions for maximizing spectral efficiency.

Contribution

It introduces a holographic approximation for analyzing large multi-antenna arrays with multiple polarizations in near-field LOS scenarios, providing new insights into their multiplexing capabilities.

Findings

Optimal array dimensions exist for maximum spectral efficiency.

Holographic approximation effectively models large array behavior.

Achievable rates depend on array size and polarization diversity.

Abstract

The proliferation of large multi-antenna configurations operating in high frequency bands has recently challenged the conventional far-field, rich-scattering paradigm of wireless channels. Extra large antenna arrays must usually work in the near field and in the absence of multipath, which are far from traditional assumptions in conventional wireless communication systems. The present study proposes to analyze the spatial multiplexing capabilities of large multi-antenna configurations under line-of-sight, near field conditions by considering the use of multiple orthogonal diversities at both transmitter and receiver. The analysis is carried out using a holographic approximation to the problem, whereby the number of radiating elements is assumed to become large while their separation becomes asymptotically negligible. This emulates the operation of a continuous aperture of infinitesimal radiating elements, also recently known as holographic surfaces. The present study characterizes the asymptotic MIMO channel as seen by extra large uniform linear and planar arrays, as well as their associated achievable rates assuming access to perfect channel state information (CSI). It is shown, in particular, that for a given distance between the receiver and the center of the array and a given signal quality, there exists an optimum dimension of the multi-antenna surface that maximizes the spectral efficiency.