RIS with Coupled Phase Shift and Amplitude: Capacity Maximization and Configuration Set Selection

TL;DR

This paper proposes a practical model for RIS reflection optimization considering coupled phase shift and amplitude, introducing efficient methods for capacity maximization and configuration set selection with linear complexity.

Contribution

It introduces a novel system model with coupled phase and amplitude, along with efficient algorithms for optimizing RIS reflection coefficients and configuration sets.

Findings

Capacity maximization achieved with linear complexity algorithms.

Optimal configuration set selection improves communication performance.

Practical coupled phase-amplitude model enhances RIS optimization accuracy.

Abstract

A reconfigurable intelligent surface (RIS) is a planar surface that can enhance the quality of communication by providing control over the communication environment. Reflection optimization is one of the pivotal challenges in RIS setups. While there has been lots of research regarding the reflection optimization of RIS, most works consider the independence of the phase shift and the amplitude of RIS reflection coefficients. In practice, the phase shift and the amplitude are coupled and according to a recent study, the relation between them can be described using a function. In our work, we consider a practical system model with coupled phase shift and amplitude. We develop an efficient method for achieving capacity maximization by finding the optimal reflection coefficients of the RIS elements. The complexity of our method is linear with the number of RIS elements and the number of discrete phase shifts. We also develop a method that optimally selects the configuration set of the system, where a configuration set means a discrete set of reflection coefficient choices that a RIS element can take.