Two-Layer Stacked Intelligent Metasurfaces: Balancing Performance and Complexity

TL;DR

This paper explores two-layer stacked intelligent metasurfaces (SIMs) for wireless signal processing, balancing performance and complexity, and demonstrating their potential in 6G communication systems.

Contribution

It introduces two novel 2-layer SIM architectures, analyzes their trade-offs, and validates their effectiveness in reducing power loss and complexity in communication applications.

Findings

Properly designed 2-layer SIMs reduce power loss.

They lower optimization complexity.

They maintain high signal processing performance.

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.