Far- versus Near-Field RIS Modeling and Beam Design

TL;DR

This paper explores the mathematical modeling and beam design strategies for reconfigurable intelligent surfaces in both far- and near-field wireless communication scenarios, highlighting different phenomena and design approaches.

Contribution

It introduces comprehensive models for RIS-assisted channels in both regimes and compares optimization-based and analytical beam design methods with simulation results.

Findings

Different RIS beam design approaches have varying complexity and flexibility.

Simulation results demonstrate the impact of system parameters on performance.

Near- and far-field models capture distinct propagation phenomena.

Abstract

In this chapter, we investigate the mathematical foundation of the modeling and design of reconfigurable intelligent surfaces (RIS) in both the far- and near-field regimes. More specifically, we first present RIS-assisted wireless channel models for the far- and near-field regimes, discussing relevant phenomena, such as line-of-sight (LOS) and non-LOS links, rich and poor scattering, channel correlation, and array manifold. Subsequently, we introduce two general approaches for the RIS reflective beam design, namely optimization-based and analytical, which offer different degrees of design flexibility and computational complexity. Furthermore, we provide a comprehensive set of simulation results for the performance evaluation of the studied RIS beam designs and the investigation of the impact of the system parameters.