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Indoor Channel Characterization with Extremely Large Reconfigurable Intelligent Surfaces at $300$ GHz

Fabio Cardoso, Sérgio Matos, Luís M. Pessoa, George C. Alexandropoulos

TL;DR

This work tackles indoor THz channel characterization in the presence of an extremely large RIS by designing a $100\times100$ RIS with $2$-bit unit cells tuned for a static non-specular reflection at $304$ GHz. Full-wave RCS simulations validate a compact three-ray RIS model that can be efficiently incorporated into ray-tracing tools, showing that near-field effects are manageable and that far-field approximations remain accurate beyond a short distance. The study details the unit-cell and metasurface designs, provides RIS-RCS characteristics (max $15.6$ dBm$^2$, HPBW $\approx 1^\circ$, $\sim65\%$ efficiency), and demonstrates how single- and multi-ray models capture RIS-induced multipath. The findings enable practical RIS-enabled THz indoor deployments by reducing modeling complexity while preserving key RIS scattering physics, thereby facilitating accurate and computationally efficient channel characterization for indoor high-capacity wireless systems.

Abstract

The technology of Reconfigurable Intelligent Surfaces (RISs) is lately being considered as a boosting component for various indoor wireless applications, enabling wave propagation control and coverage extension. However, the incorporation of extremely large RISs, as recently being considered for ultra-high capacity industrial environments at subTHz frequencies, imposes certain challenges for indoor channel characterization. In particular, such RISs contribute additional multipath components and their large sizes with respect to the signal wavelength lead to near-field propagation. To this end, ray tracing approaches become quite cumbersome and need to be rerun for different RIS unit cell designs. In this paper, we present a novel approach for the incorporation of RISs in indoor multipath environments towards their efficient channel characterization. An $100\times100$ RIS design with $2$-bit resolution unit cells realizing a fixed anomalous reflection at 300 GHz is presented, whose radar cross section patterns are obtained via full-wave simulations. It is showcased that the RIS behavior can be conveniently approximated by a three-ray model, which can be efficiently incorporated within available ray tracing tools, and that the far-field approximation is valid for even very small distances from the RIS.

Indoor Channel Characterization with Extremely Large Reconfigurable Intelligent Surfaces at $300$ GHz

TL;DR

This work tackles indoor THz channel characterization in the presence of an extremely large RIS by designing a RIS with -bit unit cells tuned for a static non-specular reflection at GHz. Full-wave RCS simulations validate a compact three-ray RIS model that can be efficiently incorporated into ray-tracing tools, showing that near-field effects are manageable and that far-field approximations remain accurate beyond a short distance. The study details the unit-cell and metasurface designs, provides RIS-RCS characteristics (max dBm, HPBW , efficiency), and demonstrates how single- and multi-ray models capture RIS-induced multipath. The findings enable practical RIS-enabled THz indoor deployments by reducing modeling complexity while preserving key RIS scattering physics, thereby facilitating accurate and computationally efficient channel characterization for indoor high-capacity wireless systems.

Abstract

The technology of Reconfigurable Intelligent Surfaces (RISs) is lately being considered as a boosting component for various indoor wireless applications, enabling wave propagation control and coverage extension. However, the incorporation of extremely large RISs, as recently being considered for ultra-high capacity industrial environments at subTHz frequencies, imposes certain challenges for indoor channel characterization. In particular, such RISs contribute additional multipath components and their large sizes with respect to the signal wavelength lead to near-field propagation. To this end, ray tracing approaches become quite cumbersome and need to be rerun for different RIS unit cell designs. In this paper, we present a novel approach for the incorporation of RISs in indoor multipath environments towards their efficient channel characterization. An RIS design with -bit resolution unit cells realizing a fixed anomalous reflection at 300 GHz is presented, whose radar cross section patterns are obtained via full-wave simulations. It is showcased that the RIS behavior can be conveniently approximated by a three-ray model, which can be efficiently incorporated within available ray tracing tools, and that the far-field approximation is valid for even very small distances from the RIS.
Paper Structure (10 sections, 2 equations, 8 figures, 1 table)

This paper contains 10 sections, 2 equations, 8 figures, 1 table.

Table of Contents

  1. Introduction
  2. Indoor System Model and Problem Description
  3. RIS Design at THz Frequencies
  4. Unit Cell Design
  5. Metasurface Design
  6. Far-Field Approximation
  7. Indoor Channel Characterization Results
  8. Single-Ray Approximation
  9. Multi-Ray Approximation
  10. Conclusion

Figures (8)

  • Figure 1: The considered indoor scenario for NLoS wireless communications assisted by an RIS at $304$ GHz. The room dimensions are $10\times10\times3$ m$^3$ and the RIS comprising $100\times100$ unit elements is a $5\times5$ cm$^2$ metasurface designed to facilitate the the TX-RX link.
  • Figure 2: The geometry of the designed single-layer patch-based unit cell at $304$ GHz.
  • Figure 3: Overview of the unit cell design corresponding to the 4 different states.
  • Figure 4: RCS patterns of the designed $100\times100$ static RIS with $2$-bit phase resolution unit cells.
  • Figure 5: Comparison between $E$-field calculated within CST at different distances from the RIS, considering the far-field approximation (blue curve, square markers) and the more accurate model that includes the near-field (red curve, round markers).
  • ...and 3 more figures