Rayleigh Fading Modeling and Channel Hardening for Reconfigurable Intelligent Surfaces

TL;DR

This paper critiques the traditional Rayleigh fading model for RIS channels, proposing a more physically realistic alternative and analyzing its implications on RIS properties like channel hardening.

Contribution

It introduces a physically feasible Rayleigh fading model for RIS channels, replacing the traditional i.i.d. model, and revisits key RIS properties under this new model.

Findings

Traditional Rayleigh model is not physically consistent for RIS with rectangular geometry.

Proposes an alternative Rayleigh fading model that aligns with physical constraints.

Analyzes the impact of the new model on RIS properties like channel rank and hardening.

Abstract

A realistic performance assessment of any wireless technology requires the use of a channel model that reflects its main characteristics. The independent and identically distributed Rayleigh fading channel model has been (and still is) the basis of most theoretical research on multiple antenna technologies in scattering environments. This letter shows that such a model is not physically appearing when using a reconfigurable intelligent surface (RIS) with rectangular geometry and provides an alternative physically feasible Rayleigh fading model that can be used as a baseline when evaluating RIS-aided communications. The model is used to revisit the basic RIS properties, e.g., the rank of spatial correlation matrices and channel hardening.