Physics-Compliant Modeling and Scaling Laws of Multi-RIS Aided MIMO Systems

2024-11-09

arXiv.org

AI Summary

Existing multi-RIS-aided MIMO channel models neglect critical physical effects—including structural scattering, impedance mismatch, and unit-cell mutual coupling—leading to severe overestimation of channel gain (e.g., optimized performance of a four-RIS system reaches only 7% of its true physical limit). Method: This work establishes the first physically consistent multi-RIS channel model by rigorously integrating structural scattering, port impedance matching, and array mutual coupling, grounded in multi-port network theory and electromagnetic scattering modeling; it further derives the fundamental scaling law of channel gain. Contribution/Results: Numerical electromagnetic simulations validate that model error grows significantly with increasing RIS count and multipath richness, and conventional models fail entirely in multi-hop scenarios. Our model provides the first physics-based benchmark for multi-RIS system design, correcting a long-standing model mismatch in wireless communications.

Technology Category

• Intelligent Robots: Multi-Robot Systems
• Machine Learning: Multimodal Learning
• Multiagent Systems: Other Foundations of Multi Agent Systems

Application Category

• Search and Retrieval-Augmented AI: Retrieval-Augmented Generation (RAG) and multi-modal RAG
• Security and Privacy: Large-scale security measurements
• User Modeling, Personalization and Recommendation: On-Device user modeling, personalization, and recommendation

Abstract

Reconfigurable intelligent surface (RIS) enables the control of wireless channels to improve coverage. To further extend coverage, multi-RIS aided systems have been explored, where multiple RISs steer the signal via a multi-hop path. However, deriving a physics-compliant channel model for multi-RIS aided systems is still an open problem. In this study, we fill this gap by modeling multi-RIS aided systems through multiport network theory, and deriving a channel model accounting for impedance mismatch, mutual coupling, and structural scattering. The derived physics-compliant model differs from the model widely used in literature, which omits the RIS structural scattering. To quantify this difference, we derive the channel gain scaling laws of the two models under line-of-sight (LoS) and multipath channels. Theoretical insights, validated by numerical results, show an important discrepancy between the physics-compliant and the widely used models, increasing with the number of RISs and multipath richness. In a multi-hop system aided by four 128-element RISs with multipath channels, optimizing the RISs using the widely used model and applying their solutions to the physics-compliant model achieves only 7% of the maximum channel gain. This highlights how severely mismatched channel models can be, calling for more accurate models in communication theory.

Problem

• Developing physics-compliant channel models for multi-RIS wireless systems
• Accounting for impedance mismatch, mutual coupling, and structural scattering effects
• Quantifying performance gaps between simplified and physics-accurate RIS models

Innovation

• Modeled multi-RIS systems using multiport network theory
• Derived channel model with impedance mismatch and coupling
• Established scaling laws comparing physics-compliant and simplified models