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Two-Layer Stacked Intelligent Metasurfaces: Balancing Performance and Complexity

Hong Niu, Chau Yuen, Marco Di Renzo, Mérouane Debbah, H. Vincent Poor

Abstract

Stacked intelligent metasurfaces (SIMs) have emerged as a powerful paradigm for wave-domain signal processing, enabling fine-grained control over electromagnetic (EM) propagation in next-generation wireless systems. However, conventional multi-layer SIMs often suffer from excessive structural complexity, high computational overhead, and significant power attenuation across layers, limiting their performance. In this paper, we first characterize SIMs from the perspectives of functionality, application, and layer configuration, revealing the inherent trade-offs between signal processing flexibility and power efficiency. Then, two representative 2-layer architectures, the meta-fiber-connected SIM (MF-SIM) and the flexible intelligent layered metasurface (FILM), are introduced, each advocating a distinct 2-layer SIM design philosophy. Moreover, we identify several open challenges in topology optimization for MF-SIM, shape control for FILM, and hybrid 2-layer architectures. Finally, case studies considering 2-layer MF-SIM and FILM assisted point-to-point multiple-input multiple-output (MIMO) and multi-user communication systems validate that properly designed 2-layer SIMs can significantly reduce power loss and optimization burden while maintaining good signal processing performance, offering a promising pathway toward practical SIM-enabled 6G systems.

Two-Layer Stacked Intelligent Metasurfaces: Balancing Performance and Complexity

Abstract

Stacked intelligent metasurfaces (SIMs) have emerged as a powerful paradigm for wave-domain signal processing, enabling fine-grained control over electromagnetic (EM) propagation in next-generation wireless systems. However, conventional multi-layer SIMs often suffer from excessive structural complexity, high computational overhead, and significant power attenuation across layers, limiting their performance. In this paper, we first characterize SIMs from the perspectives of functionality, application, and layer configuration, revealing the inherent trade-offs between signal processing flexibility and power efficiency. Then, two representative 2-layer architectures, the meta-fiber-connected SIM (MF-SIM) and the flexible intelligent layered metasurface (FILM), are introduced, each advocating a distinct 2-layer SIM design philosophy. Moreover, we identify several open challenges in topology optimization for MF-SIM, shape control for FILM, and hybrid 2-layer architectures. Finally, case studies considering 2-layer MF-SIM and FILM assisted point-to-point multiple-input multiple-output (MIMO) and multi-user communication systems validate that properly designed 2-layer SIMs can significantly reduce power loss and optimization burden while maintaining good signal processing performance, offering a promising pathway toward practical SIM-enabled 6G systems.
Paper Structure (17 sections, 4 figures, 2 tables)

This paper contains 17 sections, 4 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Characterization of SIM
  3. Functional Capabilities
  4. Applications
  5. Number of Layers
  6. Design Concept of Two-Layer SIM
  7. MF-SIM Design Philosophy
  8. FILM Design Philosophy
  9. Comparison of MF-SIM and FILM
  10. Research Challenges for Two-Layer SIMs
  11. Topology Optimization for MF-SIMs
  12. Shape Control and Sensitivity Management for FILMs
  13. Hybrid Two-Layer Architectures
  14. Case Study
  15. Point-to-Point MIMO Communications
  16. ...and 2 more sections

Figures (4)

  • Figure 1: Representative classification and functional overview of SIM architectures.
  • Figure 2: Two design strategies for two-layer SIMs.
  • Figure 3: Channel capacity versus the power attenuation ratio per layer in point-to-point MIMO systems.
  • Figure 4: Bit-error rate versus the transmit power in multi-user MISO systems.