Capacity Analysis of Holographic MIMO Channels with Practical Constraints

TL;DR

This paper analyzes the capacity of holographic MIMO channels considering practical constraints like angle distribution and array aperture, revealing capacity limitations at high SNR and with increased antenna density.

Contribution

It introduces a wavenumber domain-based method to calculate spectral density for generalized angle distributions and analyzes capacity under realistic array constraints.

Findings

Capacity is affected by angle distribution at high SNR.

Capacity does not increase infinitely with antenna density due to aperture limits.

At low SNR, capacity is less sensitive to angle distribution.

Abstract

Holographic Multiple-Input and Multiple-Output (MIMO) is envisioned as a promising technology to realize unprecedented spectral efficiency by integrating a large number of antennas into a compact space. Most research on holographic MIMO is based on isotropic scattering environments, and the antenna gain is assumed to be unlimited by deployment space. However, the channel might not satisfy isotropic scattering because of generalized angle distributions, and the antenna gain is limited by the array aperture in reality. In this letter, we aim to analyze the holographic MIMO channel capacity under practical angle distribution and array aperture constraints. First, we calculate the spectral density for generalized angle distributions by introducing a wavenumber domain-based method. And then, the capacity under generalized angle distributions is analyzed and two different aperture schemes are considered. Finally, numerical results show that the capacity is obviously affected by angle distribution at high signal-to-noise ratio (SNR) but hardly affected at low SNR, and the capacity will not increase infinitely with antenna density due to the array aperture constraint.