Over-the-Air Equalization with Reconfigurable Intelligent Surfaces

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 a control over the wireless channel. In this paper, the potential of RIS technology is explored to perform equalization over-the-air for frequencyselective channels whereas, equalization is generally conducted at either the transmitter or receiver in conventional communication systems. Specifically, with the aid of an RIS, the frequencyselective 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 discretetime 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 demonstrated that with the proposed method, ISI can successfully be eliminated and the RIS-aided communication channel can be converted from frequency-selective to frequency-flat.

PhysFad: Physics-Based End-to-End Channel Modeling of RIS-Parametrized Environments with Adjustable Fading

“…Rigorous demonstrations of RIS-assisted over-the-air channel equalization were reported with experiments in the 2.5 GHz regime [19], and recently based on full-wave simulations in the context of WNoCs [20]. However, there is also a significant timely interest in studying these aspects based on channel models [55], [56]. To date, such studies emulate fading through cascaded random matrices as outlined in Sec.…”

Reconfigurable Intelligent Surfaces: Channel Characterization and Modeling

“…Here, we mainly introduce channel characteristics of reflection and transmission, Doppler effect and multipath fading mitigation, channel reciprocity, channel hardening, rank improvement, near field and far field, and half-power beamwidth (HPBW) and aperture efficiency. Other new channel characteristics include: multipath labeling [61], which intended to inject a label on propagation paths through the RISs; OTA equalization [62], which adjusted the phases of RIS elements according to the incoming signals to maximize the magnitude of the first tap and made the inter-symbol interference negligible; electromagnetic interference [63], which had a non-negligible impact on communication performance, especially when the size of the RIS grew large; etc.…”

Joint user and throughput maximization in re‐configurable intelligent surface assisted beyond 5G/6G networks

“…2 The communication technology's limitations also stem from its incapacity to control the wireless medium, resulting in adverse effects on system performance. 3,4 Various researchers have already expressed their opinions on sixth-generation (6G), and significant research endeavors have also already begun. They mainly focus on the lifetime of the battery of mobile devices and the type of services that they provide instead of the data rate and throughput of wireless networks.…”