## 4 Custom A-IFOF Transceiver Preliminary Evaluation and Integration to Deployed MNO's Infrastructure
The FiWi and its symmetrical wireless-fiber (WiFi) layouts apply to a bidirectional wired-wireless scenario, while the extended fiber -wireless-fiber (FiWiFi) layout served as a wireless bridge interconnecting the terminals of two spatially separated fiber transport segments [40; 41; 42]. It should be noted that, due to the lack of laboratory equipment, the alternative layoutswere implemented in one direction, while in the other direction the IF signals were propagated over a passive RF cable. Regarding the WiFi layout, an inverted but symmetrical link of the FiWi layout was implemented, as depicted in Figure 6b. In addition, as it is shown Figure 6c, the FiWi layout was extended with an extra EML and a photoreceiver in order to setup the FiWiFi layout and evaluate its performance. It should be also mentioned that the voltage input levels of all of the electro-optic and active RF components were carefully selected in order to ensure their operation in the linear regime. Figure 5: (**a**) EVM values for 204 MHz BW after 25 km fiber–V-band wireless transmission, (**b**) EVM values for 398 MHz BW after 25 km fiber–V-band wireless transmission and (**c**) Constellation diagrams for both cases. Figure 7 shows the EVM results of the received IF signal after its converged FiWi, WiFi and FiWiFi transmission and the corresponding constellation diagrams after real-time processing. The initial signal that was generated by the RFSoC exhibited an EVM of 2.7% (Figure 7a), while the use of the optical and RF modules through the FiWi setup introduced an EVM increase of 4.6%. As it was originally expected, the FiWi (Figure 7b) and WiFi (Figure 7c) transmission performances were similar, with an EVM offset of 0.2%. The identical EVM measurements in both links are a strong indication that the active RF/optoelectronic units of the FiWi and WiFi testbeds were operating at their linear region. The extension of the FiWi link with an additional optoelectronic conversion stage was responsible for an increase in the EVM value of 2.3% (Figure 7d) compared to the FiWi case. Nevertheless, in all of the cases the transmission was well below the 3 GPP threshold of 17.5% EVM for the successful demodulation of the QPSK modulation [33], indicating the robustness of the proposed A-IFoF-V-band-IFoF transport solution and thus its scale-up capabilities. Figure 6: Experimental setup of (**a**) FiWi, (**b**) Wireless-Fiber (WiFi) and (**c**) FiWiFi downlink segments of the FPGA-enabled EPC-to-small cell interconnection. Figure 7: EVM measurements and constellation diagrams after (**a**) btb (**b**) FiWi, (**c**) WiFi and (**d**) FiWiFi real-time transmission, (**e**) Iperf measurements of the FiWi segment, (f) photo of the implemented testbed and screenshot of 4K video streaming. Aside from the performance metrics in the physical transport layer, the end-to-end EPC-to-small cell bidirectional connectivity over the presented layouts was presented, using real-world services. Mobile user equipment (MUE) was employed in order to perform Iperf measurements using Transmission Control Protocol (TCP) traffic exhibiting 100 Mbps stable connectivity (Figure 7e). Finally, 4K online video streaming (Figure 7f), uninterrupted live IP-video teleconferences and web browsing were successfully demonstrated over the presented A-IFoF-mmWave network configurations.