# Demonstration of a Hybrid B5G System Integrating VLC and RF-Based Technologies with Access Networks
## 3 Experimental Setup
This 5G NR base-band signal is then applied at VSG3, which is used to up-convert the signal to RF3. A 20 km single-mode fiber (SMF) optical link is used to transport the optical carrier, giving rise to the optical midhaul link. At the DU, an erbium-doped fiber amplifier (EDFA) (Golight) provides an optical gain of 15 dB. DU is connected to the remote radio head (RRH) via a fronthaul link, which can be either optical or wireless. A 1.5 m FSO fronthaul has been implemented as a proof-of-concept, integrating the hybrid RoF/FSO application. Two matched fiber-optic collimators were used to implement FSO link. It is important to note that FSO systems adhere to maximum allowable optical power levels to ensure a safe environment for human exposure. Infrared communication around 1.5 \(\upmu\)m does not reach the retina. Nevertheless,  
Figure 3: VLC system photographs. optical beams with a diameter smaller than 1 cm and power exceeding 10 dBm pose potential risks to human eyes [28; 29]. At RRH, the FSO signal is received by an optical power monitor (OPM) that is used only to monitor the input optical power. Next, this signal is photodetected by a 50 GHz bandwidth photodetector (DMX50 AF, Thorlabs, Newton, NJ, USA) (PD1). The received RF signals are then filtered by a diplexer (DPX2); thus, the RF3 is separated from RF1 and RF2, amplified in approximately 35 dB by an EA EA1, and next radiated using a 30 dBi gain horn antenna. From the other DPX2 output, we have RF1+RF2; these are amplified in approximately 24 dB by EA2, and then next split in power by SC2. To separate RF2 from RF1, a bandpass filter (BPF) and an LPF were used. RF2 is irradiated by a 5-dBi gain log-periodic antenna with a previous amplification of approximately 22 dB by EA3. RF1,  
Figure 4: Proposed system: (**a**) schematic diagram and (**b**) photograph. after being output from LPF, is amplified by a 51 dB gain EA (EA4), and next injected into the VLC transmitter. One may notice from the schematic diagram that three distinct access networks were considered in this study. The first one is a mm-wave wireless transmission at RF3, using a pair of identical horn antennas distanced 2.4 m from each other. The second one is another wireless transmission transporting a signal LTE in RF2, where two identical log-periodic antennas were used, distanced 3.5 m apart. And the third access network is the VLC link described above, where RF1 is transported by an incoherent white light. On the receiver side, at the end user (EU), the VLC receiver recovers the RF1 signal to be evaluated by VSA1 (MXA-N9020A, Keysigh, Santa Rosa, CA, USA). On the other hand, the radio-frequency wireless signals RF2 and RF3 are received directly from their respective antennas to be analyzed by the VSA2 (DSAV084A, Keysight, Santa Rosa, CA, USA) and VSA3 (FSW67, Rohde & Schwarz, Munich, Germany ), respectively. The indoor scenario is a research laboratory environment furnished with computers, tables, pieces of equipment, and desktops. The wireless measurements were performed during non-business hours to minimize human-induced shadowing. Table 1 presents a concise overview of the primary parameters pertaining to the proposed system.