On Landau's Eigenvalue Theorem for Line-of-Sight MIMO Channels

TL;DR

This paper offers a new derivation of the degrees of freedom formula for line-of-sight MIMO channels using Landau's eigenvalue theorem, providing a general framework applicable to various environments.

Contribution

It specializes Landau's eigenvalue theorem to LOS channels, linking spatial bandwidth to geometry under the paraxial approximation, offering a novel analytical approach.

Findings

Provides an alternative derivation of DOF for LOS channels

Establishes a connection between spatial bandwidth and geometry

Offers a generalized framework for arbitrary environments

Abstract

An alternative derivation is provided for the degrees of freedom (DOF) formula on line-of-sight (LOS) channels via Landau's eigenvalue theorem for bandlimited signals. Compared to other approaches, Landau's theorem provides a general framework to compute the DOF in arbitrary environments, this framework is herein specialized to LOS propagation. The development shows how the spatially bandlimited nature of the channel relates to its geometry under the paraxial approximation that applies to most LOS settings of interest.