Spatial Characterization of Electromagnetic Random Channels

TL;DR

This paper develops a physical and statistical model for electromagnetic channels in the near-field region, extending beyond traditional far-field assumptions, with implications for large antenna array applications.

Contribution

It introduces a plane-wave scalar channel model valid in the reactive near-field, incorporating physical principles and stochastic Gaussian representations for near-field electromagnetic propagation.

Findings

Validates a deterministic plane-wave representation of near-field channels

Derives a stochastic Gaussian model for near-field channel coefficients

Shows spatial stationarity can be maintained in the near-field by excluding reactive mechanisms

Abstract

The majority of stochastic channel models rely on the electromagnetic far-field assumption, which allows to decompose the channel in terms of plane waves. The far-field assumption breaks down in future applications that push towards the electromagnetic near-field region, such as those where the use of electromagnetically large antenna arrays is envisioned. Motivated by this consideration, we show how physical principles can be used to derive a plane-wave scalar channel model that is also valid in the reactive near-field region. Precisely, we show that narrowband wave propagation through a three-dimensional scattered medium can be generally modeled as a linear and space-variant system. We first review the physics principles that lead to a closed-form deterministic plane-wave representation of the channel impulse response. This serves as a basis for deriving a stochastic representation of the channel in terms of statistically independent Gaussian random coefficients for spatially stationary random propagation environments. The very desirable property of spatial stationarity can always be retained in the radiative near-field region by excluding reactive propagation mechanisms confined in close proximity to the source. Remarkably, the provided stochastic representation is directly connected to the Fourier spectral representation of a general stationary spatial random field.