Enabling Smart Radio Environments in the Frequency Domain With Movable Signals

TL;DR

This paper introduces the concept of movable signals in the frequency domain to enable smart radio environments, offering a new approach that can outperform existing reconfigurable surfaces in wireless communication systems.

Contribution

It proposes a novel frequency domain approach with movable signals, overcoming implementation challenges of existing technologies and demonstrating significant power gains in simulations.

Findings

Movable signals can achieve higher average received power than equal gain transmission in LoS conditions.

FIS-aided systems with movable signals can reach up to four times the power of RIS-aided fixed-frequency systems.

Movable signals remain effective in NLoS conditions by utilizing reflections from fixed intelligent surfaces.

Abstract

Smart radio environments (SREs) enhance wireless communications by allowing control over the channel. They have been enabled through surfaces with reconfigurable electromagnetic (EM) properties, known as reconfigurable intelligent surfaces (RISs), and through flexible antennas, which can be viewed as realizations of SREs in the EM domain and space domain, respectively. However, these technologies rely on electronically reconfigurable or movable components, introducing implementation challenges that could hinder commercialization. To overcome these challenges, we propose a new domain to enable SREs, the frequency domain, through the concept of movable signals, where the signal spectrum can be dynamically moved along the frequency axis. We first analyze movable signals in multiple-input single-output (MISO) systems under line-of-sight (LoS) conditions, showing that they can achieve higher average received power than quantized equal gain transmission (EGT). We then study movable signals under non-line-of-sight (NLoS) conditions, showing that they remain effective by leveraging reflections from surfaces made of uniformly spaced elements with fixed EM properties, denoted as fixed intelligent surfaces (FISs). Analytical results reveal that a FIS-aided system using movable signals can achieve up to four times the received power of a RIS-aided system using fixed-frequency signals.