RIS-Assisted Visible Light Communication Systems: A Tutorial

Abstract

Recent intensive and extensive development of the fifth-generation (5G) of cellular networks has led to their deployment throughout much of the world. As part of this implementation, one of the challenges that must be addressed is the skip-zone problem, which occurs when objects such as trees, people, animals, and vehicles obstruct the transmission of signals.In free-space optical (FSO) and radio frequency (RF) systems, dead zones are most often caused by buildings and trees, while in visible light communications (VLC), obstructions are caused by individuals moving around a room or objects placed in the room. A signal obstruction can significantly reduce the signal-to-noise ratio in RF and indoor VLC systems, whereas in FSO systems, where the transmitted signals are directional, the obstruction can completely disrupt data transmission. Therefore, the skipzone dilemma must be resolved to ensure the smooth and efficient operation of 5G and beyond networks. By placing a relay between a transmitter and a receiver, the effects of obstacles can be mitigated. As a result, the signal from the transmitter will reach the receiver. In recent years, reconfigurable intelligent surfaces (RISs) that are more efficient than relays have become widely accepted as a method of mitigating skip-zones and providing reconfigurable radio environments. However, there have been limited studies on RISs for optical wireless communication (OWC) systems. Through the RIS technology, OWC and RF communication channels can be reconfigured. This paper aims to provide a comprehensive tutorial on indoor VLC systems utilizing RIS technology. The article discusses the basics of VLC and RISs and reintroduces RISs for OWC systems, focusing on RIS-assisted indoor VLC systems. We also provide a comprehensive overview of optical RISs and examine the differences between optical RISs, RF-RISs, and optical relays. Furthermore, we discuss in detail how RISs can be used to overcome line-of-sight blockages and the device orientation issue in VLC systems while revealing key challenges such as RIS element orientation design, RIS elements to access point/user assignment design, and RIS array positioning design problems that need to be studied. Moreover, we discuss and propose several research problems on integrating optical RISs with other emerging technologies, including non-orthogonal multiple access, multiple-input multiple-output systems, physical layer security, and simultaneous lightwave and power transfer in VLC systems. Finally, we highlight other important research directions that can further improve the performance of RISassisted VLC systems.

Intelligent Omni-Surfaces: Simultaneous Refraction and Reflection for Full-Dimensional Wireless Communications

“…In the literature, some existing articles [17], [19], [43]- [52] have provided comprehensive tutorials or surveys of the state-of-the-art research work related to RISs from different perspectives, but the focus of this paper is quite different. Specifically, the authors in [19] discussed the applications of RISs as reflectors, especially the comparison with backscatter communications and reflective relays.…”

“…The authors in [49] discussed the machine learning and resource allocation techniques for RISaided wireless communications, while paper [50] emphasized the emerging use cases of RISs. The authors in [52] mainly discussed the applications of RISs in visible light communication (VLC) systems. These articles are summarized in Table I for reference.…”

Design and Optimization of Liquid Crystal RIS-Based Visible Light Communication Receivers

“…VLC has sparked the interest of the research community and the industry in recent years and is envisioned as a key evolutionary technology to enable ultrahigh data rate (potentially up to 100 Gb/s) in beyond fifth generation systems [1]. Inspired by the promising advantages of VLC, significant research efforts have been devoted to its design and performance analysis and can be categorized into areas such as network architecture design, user mobility, transmitter and receiver designs, access point (AP) assignment and resource allocation, interference management, and reconfigurable intelligent surfaces (RISs)-aided design [2]- [4]. Although the aforementioned areas are equally important in enhancing the performance gain of VLC systems, there has been few studies on the design and performance S. Aboagye, A. R. Ndjiongue, T. M. N. Ngatched * , and O.…”

Position Design for Reconfigurable Intelligent-Surface-Aided Indoor Visible Light Communication Systems

“…The relevant content in RF communication was considered by [24]. Motivated by the research prospect proposed by a survey [25], we set two indoor VLC scenarios with a VLC RIS and investigated the optimal position of the RIS array when taking the achievable rate as a utility function. Our main contributions are summarized as follows:…”