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Physics-Aware RIS Codebook Compilation for Near-Field Beam Focusing under Mutual Coupling and Specular Reflections

Alexandros I. Papadopoulos, Maria Anna Pistela, Dimitrios Tyrovolas, Antonios Lalas, Konstantinos Votis, Sotiris Ioannidis, George K. Karagiannidis, Christos Liaskos

TL;DR

This work tackles the challenge of configuring reconfigurable intelligent surfaces (RIS) in near-field programmable wireless environments, where mutual coupling and specular reflections complicate RIS responses. It introduces MATCH, a physics-based codebook compilation algorithm that initializes with geometric optics and progressively refines RIS phases through sensitivity analysis, a Pareto-based global search guided by EM energy distribution, and a final gradient refinement to maximize energy concentration in a prescribed focal region while minimizing leakage. Using a full-wave simulation framework that captures mutual coupling and wall reflections, MATCH demonstrates substantial improvements in focal energy concentration, achieving up to about 85–86% of the total energy within the focus region and markedly reduced leakage compared to GO or single-objective formulations. The results underscore the value of physics-consistent, codebook-based RIS optimization for practical, efficient near-field focusing in complex indoor environments, offering both performance gains and physical interpretability for RIS deployment in PWEs.

Abstract

Next-generation wireless networks are envisioned to achieve reliable, low-latency connectivity within environments characterized by strong multipath and severe channel variability. Programmable wireless environments (PWEs) address this challenge by enabling deterministic control of electromagnetic (EM) propagation through software-defined reconfigurable intelligent surfaces (RISs). However, effectively configuring RISs in real time remains a major bottleneck, particularly under near-field conditions where mutual coupling and specular reflections alter the intended response. To overcome this limitation, this paper introduces MATCH, a physics-based codebook compilation algorithm that explicitly accounts for the EM coupling among RIS unit cells and the reflective interactions with surrounding structures, ensuring that the resulting codebooks remain consistent with the physical characteristics of the environment. Finally, MATCH is evaluated under a full-wave simulation framework incorporating mutual coupling and secondary reflections, demonstrating its ability to concentrate scattered energy within the focal region, confirming that physics-consistent, codebook-based optimization constitutes an effective approach for practical and efficient RIS configuration.

Physics-Aware RIS Codebook Compilation for Near-Field Beam Focusing under Mutual Coupling and Specular Reflections

TL;DR

This work tackles the challenge of configuring reconfigurable intelligent surfaces (RIS) in near-field programmable wireless environments, where mutual coupling and specular reflections complicate RIS responses. It introduces MATCH, a physics-based codebook compilation algorithm that initializes with geometric optics and progressively refines RIS phases through sensitivity analysis, a Pareto-based global search guided by EM energy distribution, and a final gradient refinement to maximize energy concentration in a prescribed focal region while minimizing leakage. Using a full-wave simulation framework that captures mutual coupling and wall reflections, MATCH demonstrates substantial improvements in focal energy concentration, achieving up to about 85–86% of the total energy within the focus region and markedly reduced leakage compared to GO or single-objective formulations. The results underscore the value of physics-consistent, codebook-based RIS optimization for practical, efficient near-field focusing in complex indoor environments, offering both performance gains and physical interpretability for RIS deployment in PWEs.

Abstract

Next-generation wireless networks are envisioned to achieve reliable, low-latency connectivity within environments characterized by strong multipath and severe channel variability. Programmable wireless environments (PWEs) address this challenge by enabling deterministic control of electromagnetic (EM) propagation through software-defined reconfigurable intelligent surfaces (RISs). However, effectively configuring RISs in real time remains a major bottleneck, particularly under near-field conditions where mutual coupling and specular reflections alter the intended response. To overcome this limitation, this paper introduces MATCH, a physics-based codebook compilation algorithm that explicitly accounts for the EM coupling among RIS unit cells and the reflective interactions with surrounding structures, ensuring that the resulting codebooks remain consistent with the physical characteristics of the environment. Finally, MATCH is evaluated under a full-wave simulation framework incorporating mutual coupling and secondary reflections, demonstrating its ability to concentrate scattered energy within the focal region, confirming that physics-consistent, codebook-based optimization constitutes an effective approach for practical and efficient RIS configuration.
Paper Structure (5 sections, 13 equations, 2 figures, 2 tables)

This paper contains 5 sections, 13 equations, 2 figures, 2 tables.

Table of Contents

  1. Introduction
  2. System Model
  3. MATCH: A Novel Physics-Based Codebook Compilation Algorithm
  4. Simulation Results
  5. Conclusion

Figures (2)

  • Figure 1: Near-field beam-focusing patterns: (a); (b) Stage 1; (c,d) Stage 2 with/without minimization; (e,f) Stage 3 with/without minimization. Red star = transmitter; white circle = Receiver /focus area.
  • Figure :