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

TL;DR

This paper compares dual-polarized intelligent surfaces, showing that movable signals with fixed surfaces outperform reconfigurable surfaces, especially when polarizations differ, with significant performance gains.

Contribution

It introduces the concept of movable signals with fixed intelligent surfaces and demonstrates their superior performance over traditional RIS, especially with beyond-diagonal reflection matrices.

Findings

Movable signals with FIS outperform RIS by at least four times.

Beyond-diagonal FIS further improves performance when polarizations differ.

Fixed surfaces with movable signals achieve significant gains over reconfigurable surfaces.

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.