Generalised Impedance Model of Wireless Links Assisted by Reconfigurable Intelligent Surfaces

TL;DR

This paper introduces a physics-based impedance model for RIS-assisted MIMO wireless links, providing accurate end-to-end channel descriptions and validating the model with numerical simulations, revealing capacity scaling laws.

Contribution

It develops a novel impedance matrix-based communication model for RIS-assisted links, bridging physics and system-level modeling with validated accuracy.

Findings

Channel capacity scales as R^{-2} for obstructed LOS links.

The impedance-based model is accurate for arbitrary RIS geometries.

Validated with numerical simulations for canonical scatterer geometries.

Abstract

We devise an end-to-end communication channel model that describes the performance of RIS-assisted MIMO wireless links. The model borrows the impedance (interaction) matrix formalism from the Method of Moments and provides a physics-based communication model. In configurations where the transmit and receive antenna arrays are distant from the RIS beyond a wavelength, a reduced model provides accurate results for arbitrary RIS unit cell geometry. Importantly, the simplified model configures as a cascaded channel transfer matrix whose mathematical structure is compliant with widely accepted, but less accurate, system level RIS models. A numerical validation of the communication model is presented for the design of binary RIS structures with scatterers of canonical geometry. Attained results are consistent with path-loss models: For obstructed line-of-sight between transmitter and receiver, the channel capacity of the (optimised) RIS-assisted link scales as $R^{-2}$, with $R$ RIS-receiver distance at fixed transmitter position. Our results shows that the applicability of communication models based on mutual impedance matrices is not restricted to canonical minimum scattering RIS unit cells.