# Demonstration of a Hybrid B5G System Integrating VLC and RF-Based Technologies with Access Networks
## 4 Results and Discussion
Figure 6 presents the EVM\({}_{\text{RMS}}\) measured at VSA3 as a function of bandwidths. One may notice that EVM\({}_{\text{RMS}}\) of 2.5, 3.2, 3.9, and 5.0% were measured respec  
Figure 6: 5G NR with 64-QAM scheme at 26 GHz—signal performance. FR2-1 bandwidths of 50, 100, 200, and 400 MHz. (**a**) Received spectra at FSW. (**b**) EVM\({}_{\text{RMS}}\) measured at VSA3 as a function of bandwidth. Maximum theoretical throughput calculated in each bandwidth. (**c**) Constellation comparison in mode back-to-back (B2B) and at the complete link (SYS). The yellow constellation represents user data, while the orange constellation serves as a demodulation reference signal. tively, comfortably meeting the 3 GPP requirements. Figure 6c displays the constellations for the four bandwidths for both back-to-back (B2B) mode and full link (SYS). It is observed that signal quality worsens with increasing bandwidth, which is due to the decrease in the signal-to-noise ratio (SNR) when increasing the bandwidth for a fixed radio frequency power transmission. On the other hand, Figure 7a presents the EVM\({}_{\text{RMS}}\) measured in VSA3 as a function of the injected RF power generated in VSG3. The best performance was achieved at +5 dBm, with EVM\({}_{\text{RMS}}\) of 4.7%. It can be observed that the EVM\({}_{\text{RMS}}\) increases for RF input powers above +5 dBm, reducing the signal quality. This degradation occurs due to the nonlinear response of the EAs, which generates significant intermodulation products at higher RF powers, distorting the signal. In conclusion, the 64-QAM modulation scheme with a 400 MHz bandwidth exhibited the best performance in terms of the quality of signal transmission for the mm-wave link. The third investigation concerns the LTE link. The VSG2 provides several closed communication standards, and, among these, the LTE signal was chosen, which transmits at 2.5 GHz and employs a 16-QAM modulation with a 6.84 MHz bandwidth and a maximal transmission power of 0 dBm. Figure 7b presents the EVM\({}_{\text{RMS}}\) measured in VSA2 as a  
Figure 7: EVM\({}_{\text{RMS}}\) as a function of the injected RF power. For the 5G NR signal (**a**), the LTE signal (**b**), and the VLC signal (**c**). function of the injected RF power generated in VSG2. In this case, the best performance was achieved at \(-4\) dBm, with EVM\({}_{\text{RMS}}\) of 6.5%. Figure 8 reports the EVM\({}_{\text{RMS}}\) measurements: 5.6% and 6.9% for the B2B mode and for the complete link, along with their respective spectrum and eye diagrams. Therefore, the EVM\({}_{\text{RMS}}\) falls by 1.3% when the signal travels through the complete system. Finally, the fourth investigation pertains to the VLC link. A Q-PSK modulation scheme with a 10 MHz bandwidth demonstrated the best performance. Figure 7c illustrates the EVM\({}_{\text{RMS}}\) measured in VSA1 relative to the injected RF power generated in VSG1. The optimal performance was attained at \(-10\) dBm, with an EVM\({}_{\text{RMS}}\) of 9.8%. Figure 9 displays the EVM\({}_{\text{RMS}}\) measurements: 2.2% and 10.1% for the B2B mode and for the complete link, accompanied by their respective spectrum and eye diagrams. Consequently, the EVM\({}_{\text{RMS}}\) decreases by 7.9% when the signal traverses through the complete system; this sharp drop is attributed to intermediate RF components, causing the electrical power to decrease. It is important to highlight that the RF and VLC links' distances are limited, as this is a proof-of-concept demonstration. These limitations are a result of the experimental setup and the controlled laboratory environment. Despite these constraints, we envision that future advancements in hardware and system design will enable these technologies to achieve greater distances, facilitating their integration into access networks. Furthermore, the current distance capabilities also make these technologies suitable for customer premises networks (CPNs) applications, such as indoor connectivity within homes or offices.