Movable Signals with Dual-Polarized Fixed Intelligent Surfaces: Beyond Diagonal Reflection Matrices

2025-12-03

AI Summary

This work addresses the performance limitation imposed by diagonal reflection matrices in dual-polarized intelligent surfaces (PIS)-assisted wireless systems. We propose a novel fixed intelligent surface (FIS) paradigm leveraging non-diagonal reflection matrices. Unlike conventional reconfigurable intelligent surface (RIS)-based approaches requiring dynamic element tuning, our method exploits frequency-shift modulation of mobile signals combined with the intrinsic polarization coupling of FIS to activate cross-polarization channels under transmit-receive polarization mismatch. Theoretical analysis and simulations demonstrate that the proposed FIS achieves over 4× higher achievable rate than the RIS benchmark while maintaining hardware simplicity—thereby overcoming the fundamental performance ceiling of diagonal reflection designs. Our key contribution is the first identification and exploitation of the capacity gain inherent in non-diagonal reflection matrices for dual-polarized channels, paving a new pathway toward low-overhead, high-performance intelligent surface deployment.

Technology Category

• Intelligent Robots: Multi-Robot Systems
• Search and Optimization: Non-convex Optimization
• Machine Learning: Matrix & Tensor Methods

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Novel mobile and WoT systems, and system-of-systems
• User Modeling, Personalization and Recommendation: On-Device user modeling, personalization, and recommendation
• Search and Retrieval-Augmented AI: Assisted, interactive, and conversational search

Abstract

This paper investigates wireless systems aided by dual-polarized intelligent surfaces. We compare reconfigurable intelligent surface (RIS), which adjust their reflection matrices, with movable signals operating with fixed intelligent surface (FIS), which adjust the signal frequency while the surface properties remain fixed. For both RIS and FIS, we consider surfaces with a diagonal reflection matrix, named diagonal RIS/FIS, and surfaces with a reflection matrix not limited to being diagonal, named beyond-diagonal RIS/FIS. Movable signals with FIS always outperform RIS, achieving at least a fourfold gain. When transmitter and receiver polarizations differ, beyond-diagonal FIS further enhances performance.

Problem

• Compares RIS and FIS in wireless systems with dual-polarized surfaces
• Analyzes diagonal vs beyond-diagonal reflection matrices for signal enhancement
• Demonstrates FIS outperforms RIS with at least fourfold gain

Innovation

• Fixed intelligent surfaces with movable signal frequencies
• Beyond-diagonal reflection matrices for enhanced polarization handling
• Dual-polarized surfaces outperforming reconfigurable intelligent surfaces