## 4 Related Works and Comparison to the State of the Art
The experiments consisted of evaluating the cascaded approach in terms of bit error rate (BER), EVM, and visibility range under the same dusty conditions. The experimental results demonstrated that the dust environment did not impair the RF link at 28 GHz, enabling the RF link to operate as a backup for FSO [25]. The FSO link has also been employed for extending the RoF fronthaul to sites where fiber optics do not reach, thus maintaining the optical communication advantages. In this way, [PERSON] et al. demonstrated a hybrid 4G/5G optical fiber-wireless system, including a free-space optics fronthaul [19]. The results showed that a 100 MHz bandwidth 5G signal transmission using A-RoF throughout a 8 km fiber-optic fronthaul could coexist on the same LTE fronthaul infrastructure. Additionally, a hybrid fiber and FSO fronthaul demonstrated the 4G and 5G operability at 2.6 and 3.5 GHz, respectively. [PERSON] et al. experimentally implemented a radio-over-fiber followed by an FSO fronthaul and mm-waves wireless transmission aimed at broadband wireless access [18]. The performance was evaluated by transmitting 4-, 16-, and 64-QAM LTE signals over the hybrid link and evaluating the EVM parameter as a function of weak-to-strong atmospheric turbulence regimes. Furthermore, [PERSON] et al. presented a radio-over-fiber combined with FSO and RF transmission for the 5G networks [24]. The authors used the 24-26 GHz frequency band and a particular direct intensity modulation solution for transmitting a 100 MHz bandwidth 64-QAM signal. The link performance was evaluated by exposing the FSO section to atmospheric turbulence and analyzing the SNR and EVM\({}_{\text{RMS}}\). In parallel with the wireless techniques for access point, VLC systems have been emerging as a potential technology to accomplish the 5G requirements and beyond. They are mainly composed of light-emitting diodes, which can be used for simultaneously lighting the environment and transmitting data. In this way, [PERSON] et al. reported a GaN LED-based visible light communication using a 4 \(\times\) 4 color polarization multiplexing and on-off keying (OOK) [38]. The system attained 2.3 Gbit/s over 1 m employing MIMO and pre-equalization under the illumination of 6.9-136.1 lux. Recent works have shown the use of VLC for 5G. For instance, [PERSON] et al. reported a comparison among 5G waveform candidates, namely filter bank multicarrier (FBMC), generalized frequency division multiplexing (GFDM), and OFDM, with regard to a single-input single-output VLC system [39]. On the other hand, VLC systems may employ lasers as a light source to achieve higher throughput. [PERSON] et al. reported a VLC system employing a white-light phosphor laser for illuminating and providing 6.9 Gbit/s over 1.5 m [40]. In this work, we examined an innovative proposal for optical-wireless architectures applied to the NSA 5G new radio framework. In contrast to previous works, we experimentally demonstrated 4G and 5G NR coexistence in the 700 MHz band taking into account a FiWi system. Regarding the dual wireless and FSO-based fronthaul architecture, our implementation employed the 5G NR standard. The parallel FSO at 1550 nm and mm-wave link at 38 GHz enabled a dynamic selection according to its transmission performance, whereas the other link operated as a backup. Its performance was investigated by assessing the EVM\({}_{\text{RMS}}\) for different power levels at the receiver to emulate the equivalent attenuation levels for visibility and rain conditions. The attenuation levels used for the FSO link were from 0 to 56 mm/h, whereas the values ranged from 0 to 102 mm/h for the wireless link. Overall, our 5G NR experimental results demonstrated 1.61 Gbit/s total throughput, which is within the 3 GPP EVM\({}_{\text{RMS}}\) requirements, for rain intensity less than 36.4 mm/h and visibility above 40 m.  
Moreover, we examined a fiber-optic and FSO-based 5G fronthaul followed by a dual-band 5G NR wireless access, including mm-waves.