Fourier Plane-Wave Series Expansion for Holographic MIMO Communications

TL;DR

This paper introduces a Fourier plane-wave series expansion for electromagnetic channel modeling in Holographic MIMO systems, capturing near-field effects and providing a basis for capacity analysis beyond classical far-field assumptions.

Contribution

It presents a novel wave-based channel model derived from first principles, valid in near-field conditions, and offers a low-rank approximation for electromagnetic channels in holographic MIMO.

Findings

The model accurately captures electromagnetic propagation in arbitrary scattering environments.

It provides a low-rank approximation of the channel in the angular domain.

Capacity calculations show the impact of near-field effects on system performance.

Abstract

Imagine a MIMO communication system that fully exploits the propagation characteristics offered by an electromagnetic channel and ultimately approaches the limits imposed by wireless communications. This is the concept of Holographic MIMO communications. Accurate and tractable channel modeling is critical to understanding its full potential. Classical stochastic models used by communications theorists are derived under the electromagnetic far-field assumption, i.e. planar wave approximation over the array. However, such assumption breaks down when electromagnetically large (compared to the wavelength) antenna arrays are considered. In this paper, we start from the first principles of wave propagation and provide a Fourier plane-wave series expansion of the channel response, which fully captures the essence of electromagnetic propagation in arbitrary scattering and is also valid in the (radiative) near-field. The expansion is based on the Fourier spectral representation and has an intuitive physical interpretation, as it statistically describes the angular coupling between source and receiver. When discretized uniformly, it leads to a low-rank semi-unitarily equivalent approximation of the electromagnetic channel in the angular domain. The developed channel model is used to compute the ergodic capacity of a point-to-point Holographic MIMO system with different degrees of channel state information.