# Demonstration of a Hybrid B5G System Integrating VLC and RF-Based Technologies with Access Networks
## 1 Introduction  
The demand for data-intensive applications, ranging from the Internet of Everything (IoE) to augmented reality, has driven the evolution of fifth-generation (5G) networks towards enhanced speed, reliability, and efficiency [1]. Specifically, the next generations, which may be referred to as beyond-5G (B5G) networks, are expected to handle unprecedented data volumes (up to 1 Tbps), very low end-to-end latency (lower than 0.1 ms), extremely high connection density (more than \(1\times 10^{7}\) devices/km\({}^{2}\)), and high network availability and reliability (99.99999%) [2, 3]. In order to achieve such requirements and support new applications, B5G networks are envisaged to incorporate cutting-edge technologies, such as reconfigurable intelligent surface (RIS), extra-large multiple-input multiple-output (MIMO), cell-free systems, compressive sensing (CS), artificial intelligence (AI), THz, and millimeter-wave (mm-wave) communications [4, 5]. Notably, optical wireless communications (OWC) stand as a promising technology for implementing ultra-high-speed wireless communications in a variety of B5G applications. Using light as the medium for transmitting data offers several advantages, including high data transfer rates, immunity to electromagnetic interference, and secure communication [6]. In contrast to traditional radio-frequency (RF) communications, OWC covers the entire wavelength spectrum fromultraviolet to near-infrared (NIR) light, becoming a potential short-distance high-speed wireless-access technology [7]. Visible-light communication (VLC) is a subset of OWC that guarantees wireless data transmission using optical carriers from the visible-light spectrum [6; 8]. In contrast to alternative OWC technologies, such as infrared communication, VLC is attractive for indoor environments due to its integration with existing illumination systems [9]. In this context, light-emitting diodes (LEDs) are commonly used as light sources due to their beam divergence, enabling broader area illumination and coverage. As a result, VLC systems might perform data transmission and indoor illumination simultaneously. By contrast, VLC systems using laser diodes (LDs) may provide higher bandwidth and are required in scenarios where precise targeting is required (point-to-point transmission) [10]; nevertheless, recent works using LDs also report a broader coverage, along with illumination [11; 12]. Recent advancements in VLC research have reported peak data rates reaching the order of gigabits per second (Gbps), demonstrating its potential to be integrated into B5G networks [13]. Nevertheless, VLC may be integrated with other communication techniques, such as RF and infrared, to generate a novel high-capacity, stable, and reliable network [14]. In the context of B5G networks, the centralized radio access network (C-RAN) architecture has been proposed, in which the baseband processing is centralized in a central office (CO), whereas optical backhaul, midhaul, and fronthaul links connect the CO to the network core, distribution units (DUs), and base stations (BSs), respectively [13; 15]. In this scenario, analog radio-over-fiber (A-RoF) is a key technology for implementing midhaul and fronthaul links, owing to its band-efficient transmission, simple architecture, lower power consumption, and flexible implementation [16]. This process typically includes modulating light to carry analog radio frequency signals over fiber-optic communication infrastructure. Whereas optical fibers provide numerous advantages, such as low attenuation, long reach, high bandwidth, and immunity to electromagnetic interference (EMI), their implementation may be costly or impractical in some areas [17]. Consequently, free space optics (FSO) technology, which is a subset of OWC, may be an alternative medium for backhaul and fronthaul links. FSO uses infrared light propagation in free-space to transmit data rather than fiber cables.