Optimization of RIS-aided SISO Systems Based on a Mutually Coupled Loaded Wire Dipole Model

TL;DR

This paper models RIS as coupled wire dipoles with tunable loads, proposing a gradient-based optimization algorithm for impedance tuning that improves performance and convergence in SISO systems.

Contribution

It introduces a circuit-based EM model of RIS using wire dipoles with mutual coupling and develops a gradient algorithm for optimal impedance tuning.

Findings

The proposed algorithm outperforms benchmark methods in performance.

The algorithm converges faster and is computationally efficient.

Numerical results validate the effectiveness of the model and optimization approach.

Abstract

The electromagnetic (EM) features of reconfigurable intelligent surfaces (RISs) fundamentally determine their operating principles and performance. Motivated by these considerations, we study a single-input single-output (SISO) system in the presence of an RIS, which is characterized by a circuit-based EM-consistent model. Specifically, we model the RIS as a collection of thin wire dipoles controlled by tunable load impedances, and we propose a gradient-based algorithm for calculating the optimal impedances of the scattering elements of the RIS in the presence of mutual coupling. Furthermore, we prove the convergence of the proposed algorithm and derive its computational complexity in terms of number of complex multiplications. Numerical results show that the proposed algorithm provides better performance and converges faster than a benchmark algorithm.