Experimental Multiport-Network Parameter Estimation and Optimization for Multi-Bit RIS

TL;DR

This paper presents a novel method for estimating multiport-network parameters of RIS in unknown environments, enabling optimized RIS configurations with minimal performance loss despite model inaccuracies.

Contribution

It introduces an efficient estimation technique for MNT parameters in practical scenarios involving multi-bit RIS elements, addressing a key research gap.

Findings

The proposed method accurately estimates MNT parameters in unknown environments.

RIS configurations optimized with the estimated model perform nearly as well as those with the true model.

Model inaccuracies can lead to up to 17 dB performance difference, but end-to-end results remain similar.

Abstract

Physics-consistent theoretical studies on RIS-parametrized wireless channels use models from multiport-network theory (MNT) to capture mutual-coupling (MC) effects. However, in practice, RIS design and radio environment are partially or completely unknown. We fill a research gap on how to estimate the MNT model parameters in such experimentally relevant scenarios. Our technique efficiently combines closed-form and gradient-descent steps, and it can be applied to multi-bit-programmable RIS elements. We discuss inevitable (but operationally irrelevant) parameter ambiguities. We experimentally validate our technique in an unknown rich-scattering environment parametrized by eight 6-bit-programmable RIS elements of unknown design. We experimentally evaluate the performance of RIS configurations optimized with the estimated MNT model and an MC-unaware cascaded model. While the models differ in accuracy by up to 17 dB, the end-to-end performance differences are small.