Stacked Intelligent Metasurface Enabled Near-Field Multiuser Beamfocusing in the Wave Domain

2024-06-24

IEEE Vehicular Technology Conference

AI Summary

Existing RIS research predominantly relies on the far-field plane-wave assumption, overlooking the near-field spherical wavefront characteristics induced by large-scale arrays at terahertz (THz) frequencies; moreover, conventional single-layer RIS lacks baseband signal processing capability. Method: This paper proposes Stacked Intelligent Metasurfaces (SIM), integrating multiple programmable metasurface layers at the base station. It pioneers the joint modeling of near-field spherical wave propagation and multi-layer cooperative modulation, embedding channel customization and wave-domain signal processing directly into hardware. SIM enables direct wave-domain near-field multi-user beam focusing, eliminating reliance on conventional digital baseband architectures. Contribution/Results: Numerical evaluations demonstrate that near-field focusing achieves higher spatial gain than far-field counterparts; SIM effectively suppresses multi-user interference while achieving sub-microsecond processing latency, thereby supporting high-density THz-band access with significantly reduced RF chain count and relaxed low-resolution DAC requirements.

Technology Category

• Search and Optimization: Metareasoning and Metaheuristics
• Intelligent Robots: Multi-Robot Systems
• Machine Learning: Large Multimodal Models (LMMs)

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Data management and stream processing for Web, mobile and wireless applications
• Search and Retrieval-Augmented AI: Retrieval-Augmented Generation (RAG) and multi-modal RAG
• Security and Privacy: Large-scale security measurements

Abstract

Intelligent surfaces represent a breakthrough technology capable of customizing the wireless channel cost-effectively. However, the existing works generally focus on planar wavefront, neglecting near-field spherical wavefront characteristics caused by large array aperture and high operation frequencies in the terahertz (THz). Additionally, the single-layer reconfigurable intelligent surface (RIS) lacks the signal processing ability to mitigate the computational complexity at the base station (BS). To address this issue, we introduce a novel stacked intelligent metasurfaces (SIM) comprised of an array of programmable metasurface layers. The SIM aims to substitute conventional digital baseband architecture to execute computing tasks with ultra-low processing delay, albeit with a reduced number of radio-frequency (RF) chains and low-resolution digital-to-analog converters. In this paper, we present a SIM-aided multiuser multiple-input single-output (MU-MISO) near-field system, where the SIM is integrated into the BS to perform beamfocusing in the wave domain and customize an end-to-end channel with minimized inter-user interference. Finally, the numerical results demonstrate that near-field communication achieves superior spatial gain over the far-field, and the SIM effectively suppresses inter-user interference as the wireless signals propagate through it.

Problem

• Enables near-field multiuser beamfocusing
• Reduces computational complexity at base station
• Suppresses inter-user interference effectively

Innovation

• Stacked Intelligent Metasurfaces (SIM)
• Near-field spherical wavefront utilization
• Ultra-low processing delay architecture