Physically Consistent Modelling of Wireless Links with Reconfigurable Intelligent Surfaces Using Multiport Network Analysis

TL;DR

This paper emphasizes the importance of physically consistent modeling of reconfigurable intelligent surfaces (RIS) in wireless systems, revealing that common simplified models violate physical laws and proposing a multiport network analysis approach for accurate representation.

Contribution

It introduces a physically consistent modeling framework for RIS using multiport network analysis, addressing limitations of existing simplified models and ensuring adherence to physical laws.

Findings

Simplistic RIS models often violate physical laws.

Impedance-based analysis reveals inconsistencies in common models.

Proposed multiport network approach ensures physical consistency.

Abstract

RISs are an emerging technology for engineering the channels of future wireless communication systems. The vast majority of research publications on RIS are focussing on system-level optimization and are based on very simplistic models ignoring basic physical laws. There are only a few publications with a focus on physical modeling. Nevertheless, the widely employed model is still inconsistent with basic physical laws. We will show that even with a very simple abstract model based on isotropic radiators, ignoring any mismatch, mutual coupling, and losses, each RIS element cannot be modeled to simply reflect the incident signal by manipulating its phase only and letting the amplitude unchanged. We will demonstrate the inconsistencies with the aid of very simple toy examples, even with only one or two RIS elements. Based on impedance parameters, the problems associated with scattering parameters can be identified enabling a correct interpretation of the derived solutions.