# Demonstration of a Hybrid B5G System Integrating VLC and RF-Based Technologies with Access Networks
## 2 Literature Review  
Related works that consider VLC applications in 5G and B5G communication systems are briefly described in this section. [PERSON] and [PERSON] [20] conducted experiments on a micro-projection system for short-range communication in a 5G application. This system used LEDs along with a micro-liquid crystal display and transmitted various waveforms, including 4-PAM, 8-PSK, and 16-QAM. The study achieved a maximum throughput of 892 Mbps at a distance of 0.65 m between the transmitter and receiver. In [21], the implementation of a multicolored VLC system utilizing the 5G NR standard was reported. A red/green/blue (RGB)-based VLC system, employing three LEDs, was successfully demonstrated in accordance with the specifications of 3 rd-Generation Partnership Project (3 GPP) Release 15. The performance evaluation of the system was conducted in terms of the root mean square error vector magnitude (EVMRMS) as a function of the LED bias current, link length, and throughput. Additionally, digital pre-distortion (DPD) was successfully applied to the proposed RGB-based VLC system, achieving 1.92 Gbps of throughput. [PERSON] et al. [22] conducted an experimental study showcasing the integration of the 5G new radio (5G NR) standard within a VLC system. They transmitted quadrature phase shift keying (Q-PSK) modulated signals and attained a maximum throughput of 14.4 Mbps at a distance of 0.55 m. The work presented in [23] reported a proof of concept for a 12.5 km A-RoF fronthaul followed by a VLC-based access link, spanning 1.2 m, towards B5G solutions. The initial proof of concept achieved a data throughput of 60 Mbps, considering the technological convergence. In [24], the authors presented an experimental measurement campaign involving a hybrid architecture proposal based on A-RoF and FSO to compose the 5G fronthaul link. For this purpose, they utilized 10 km of optical fiber followed by a 50 m FSO link. For the access network, they transmitted a 5G NR signal at 39 GHz over a distance equivalent to 1 m, achieving a total throughput of 2.4 Gbps. The authors in [25] addressed the challenges encountered in VLC systems, particularly concerning modulation schemes, flickering, and dimming support, which impose limitations on data rates and real-time practical implementation. In response, they proposed Mach-Zehnder modulator (MZM) devices optimized for visible wavelengths at 520 and 530 nm. These devices exhibit enhanced performance characteristics, including an extinction ratio (ER) of 36.9 dB and insertion loss (IL) of 0.07 dB. Furthermore, the authors analyzed the performance of the proposed devices in an indoor environment, achieving a data rate of 1 Gbps within a bit error rate (BER) range of 10  
Figure 1: Hybrid FiWi system towards B5G applications within the C-RAN architecture. AP—access point; BH—backhaul; CO—central office; DU—distribution unit; FH—fronthaul; MH—midhaul. to \(10^{-4}\). [PERSON] et al. [26] conducted an experimental investigation focusing on the performance analysis of three modulation techniques: orthogonal frequency division multiplexing (OFDM), generalized frequency division multiplexing (GFDM), and filterbank multicarrier (FBMC). Their findings indicated that GFDM exhibited superior performance within the examined system, achieving a throughput of 9.94 Mbps at a distance of 2 m.  
Recently, our research group implemented an X-Haul system employing A-RoF, FSO, mm-wave, and VLC technologies towards 6G applications [17]. The main focus of the previous work was enabling picocells operating in the 39 GHz band for densely populated urban settings, as well as indoor connectivity using a laser-based VLC link operating at 550 MHz. The current work represents an evolution of [17], focusing on a novel architecture able to simultaneously deploy three different access networks, namely, a white-LED-based VLC system, a 5G NR wireless access operating in frequency range 2 (FR2) (26 GHz), and a Long-Term Evolution (LTE) wireless access operating at 2.5 GHz.