An Equivalence Principle-Based Hybrid Method for Propagation Modeling in
Radio Environments With Reconfigurable Intelligent Surfaces
Abstract
Most existing methods for analyzing reconfigurable intelligent surface
(RIS) channels are limited to free-space links and do not account for
the mutual coupling of unit cells, or they fail to accurately model
several types of realistic scenarios including near-field operation and
interaction of RISs with rich multipath environments. Alternatively,
some methods that can handle these scenarios are computationally
intensive, such as pure full-wave analysis. We present an equivalence
principle-based hybrid ray-tracing/full-wave method to model wave
propagation in wireless communication channels enabled by RISs. This
method uses ray-tracing to determine the incident waves on an RIS, then
applies full-wave analysis to model the response of the RIS to these
waves. Next, based on the equivalence principle, we introduce equivalent
surface electric and magnetic current densities that generate the
scattered fields produced by RIS. These equivalent sources are
integrated with ray-tracing to derive the site-specific propagation
model of the RIS channel. The proposed method readily accounts for
multiple incident waves on an RIS, enabling the accurate analysis of
propagation channels with RISs, with receivers in both the near and the
far region of an RIS. We show that the accuracy of our method is
comparable to that of full-wave analysis, through simple examples that
are manageable by the finite-element method. Also, we experimentally
validate the proposed technique by comparing simulation and measured
data for an actual indoor radio environment with an anomalous reflection
metasurface.