Introducing Meta-Fiber into Stacked Intelligent Metasurfaces for MIMO Communications: A Low-Complexity Design with only Two Layers

2025-07-13

AI Summary

To address the challenges of high computational complexity in phase-shift optimization and severe multi-layer energy attenuation in stacked intelligent metasurfaces (SIMs) for MIMO beam-domain communications, this paper proposes a novel two-layer SIM architecture based on meta-fiber coupling. It innovatively employs programmable meta-fibers to establish interference-free, parallel channel mappings between the two metasurface layers—replacing conventional cascaded multi-layer structures. By integrating alternating optimization with closed-form phase control, the method jointly designs the phase profiles of transmit and receive meta-atoms to approximate the ideal channel matrix while minimizing mean-square error. Compared to a seven-layer baseline scheme, the proposed approach improves channel capacity by over 25%, reduces the total number of meta-atoms by 59%, and significantly lowers hardware overhead and optimization complexity. Furthermore, it provides a scalable, general-purpose optimization framework extendable to arbitrary numbers of layers.

Technology Category

• Search and Optimization: Metareasoning and Metaheuristics
• Machine Learning: Hardware-aware ML
• Multiagent Systems: Mechanism Design

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments
• User Modeling, Personalization and Recommendation: User modeling and simulation for interactive and conversational systems
• Search and Retrieval-Augmented AI: Efficiency and scalability of Web search engines

Abstract

Stacked intelligent metasurfaces (SIMs), which integrate multiple programmable metasurface layers, have recently emerged as a promising technology for advanced wave-domain signal processing. SIMs benefit from flexible spatial degree-of-freedom (DoF) while reducing the requirement for costly radio-frequency (RF) chains. However, current state-of-the-art SIM designs face challenges such as complex phase shift optimization and energy attenuation from multiple layers. To address these aspects, we propose incorporating meta-fibers into SIMs, with the aim of reducing the number of layers and enhancing the energy efficiency. First, we introduce a meta-fiber-connected 2-layer SIM that exhibits the same flexible signal processing capabilities as conventional multi-layer structures, and explains the operating principle. Subsequently, we formulate and solve the optimization problem of minimizing the mean square error (MSE) between the SIM channel and the desired channel matrices. Specifically, by designing the phase shifts of the meta-atoms associated with the transmitting-SIM and receiving-SIM, a non-interference system with parallel subchannels is established. In order to reduce the computational complexity, a closed-form expression for each phase shift at each iteration of an alternating optimization (AO) algorithm is proposed. We show that the proposed algorithm is applicable to conventional multi-layer SIMs. The channel capacity bound and computational complexity are analyzed to provide design insights. Finally, numerical results are illustrated, demonstrating that the proposed two-layer SIM with meta-fiber achieves over a 25% improvement in channel capacity while reducing the total number of meta-atoms by 59% as compared with a conventional seven-layer SIM.

Problem

• Reducing energy attenuation in multi-layer metasurfaces
• Simplifying phase shift optimization complexity
• Enhancing MIMO communication efficiency with meta-fibers

Innovation

• Meta-fiber-connected 2-layer SIM design
• Closed-form phase shift optimization
• Non-interference parallel subchannels system