Over-the-Air Equalization with Reconfigurable Intelligent Surfaces

TL;DR

This paper explores how reconfigurable intelligent surfaces can be used to perform over-the-air equalization, transforming frequency-selective channels into flat ones to improve wireless communication performance.

Contribution

It introduces a novel RIS-based method for virtual equalization, eliminating ISI and converting frequency-selective channels to flat channels, supported by theoretical and simulation analysis.

Findings

RIS can successfully eliminate ISI in frequency-selective channels

RIS phase alignment methods convert frequency-selective channels to flat channels

Theoretical and simulation results confirm the effectiveness of RIS-based equalization

Abstract

Reconfigurable intelligent surface (RIS)-empowered communications is on the rise and is a promising technology envisioned to aid in 6G and beyond wireless communication networks. RISs can manipulate impinging waves through their electromagnetic elements enabling some sort of control over the wireless channel. In this paper, the potential of RIS technology is explored to perform a sort of virtual equalization over-the-air for frequency-selective channels whereas, equalization is generally conducted at either the transmitter or receiver in conventional communication systems. Specifically, with the aid of an RIS, the frequency-selective channel from the transmitter to the RIS is transformed to a frequency-flat channel through elimination of inter-symbol interference (ISI) components at the receiver. ISI is eliminated by adjusting the phases of impinging signals particularly to maximize the incoming signal of the strongest tap. First, a general end-to-end system model is provided and a continuous to discrete-time signal model is presented. Subsequently, a probabilistic analysis for the elimination of ISI terms is conducted and reinforced with computer simulations. Furthermore, a theoretical error probability analysis is performed along with computer simulations. It is analyzed and demonstrated that conventional RIS phase alignment methods, can successfully eliminate ISI and the RIS-aided communication channel can be converted from frequency-selective to frequency-flat.