# Experimental Evaluation of Hybrid Fibre-Wireless System for 5G Networks
## 4 Experimental Setup  
To validate the proposed FiWi 2 \(\times\) 2 MIMO equipped with the CNN DPD technique, we employed a 5G NR scenario at 3 GHz and 20 GHz, both comprising of 50 MHz bandwidth as demonstrated in the previous work [23; 24], but there was no integration of fibre-wireless, and also there was no DPD employed. The system represented in Figure 3 uses a dual drive Mach Zehnder modulator (MZM) with two distinct RF-driven signals and a 1310 nm DFB laser. The 5G transceiver transmits RF2, a 3 GHz flexible waveform signal, while the vector signal generator (VSG), labelled VSG, sends RF1, a 5G NR waveform at 20 GHz. The DPD procedure is divided into three steps. Firstly, the up-converted signal at their respective carrier frequencies of 3 and 20 GHz passes over 10 km of standard single-mode fibre (SSMF) and is collected by a photodetector (0.69 A/W) that receives and converts the signal back to the electrical domain. Because the multiband must be separated individually, an amplification phase is implemented. A diplexer (DPX) separates the 3 GHz and 20 GHz frequencies. The signals are then passed via a series of vector signal analyzers (VSA). Each VSA output is sent to the post-processing block to be evaluated for performance. This phase is carried out without the use of DPD, which implies that the output is assessed without the use of DPD. In the second phase, referred to as the DPD training phase, the DPD technique depicted in Figure 3 is applied, and training is performed until the error converges. To put it another way, DPD backs up the idea underlying inverting the amplitude and phase responses recorded at the EA electrical amplifiers. Depending on the user's wants and comparative criteria, CNN approaches can be employed. To achieve synchronization for the received waveforms, we employ the positioning reference signal (PRS) provided in the 5G NR framework (both input and output). The bandwidth of PRS is expected to be 20 MHz/106 resource blocks. The received and output reference broadcast signals are coupled in the time domain, and the power delay profile (PDP) is evaluated via threshold block to establish the first path of arrival [61]. The pre-distorted baseband signals are supplied into the DPD block in the third phase, where VSGs upconvert them to their carrier frequency before being fed into the optical link. Before being forwarded to the DPD training phase, the signal generated at the photodiode is passed via a diplexer DPX to isolate the different multibands. During the DPD validation stage, we flip the switches in the other manner. Pre-distortion and then transmitting the frames to the VSG complete the evaluation for 5G NR frames. We find that real-time operation in the adaptation is unnecessary since the nonlinearities of the RoF connectionslowly change owing to thermal effects and component ageing. Table 2 lists the parameters used, which have previously been discussed in [1,2] and other state of the art [18] studies. \begin{table}
\begin{tabular}{c c} \hline
**Parameters** & **Values** \\ \hline \multirow{3}{*}{Signal Types} & \(f_{c}=3,20\) GHz \\  & F/O/G—FDM waveform \\  & Modulation Data Rate = 256 QAM \\ \hline \multirow{2}{*}{Laser Diode} & \(\lambda\), \(wavelength=1310\) nm \\  & Dual Drive Mach Zehnder Modulator \\ \hline \multirow{3}{*}{Fibre} & SSMF \\  & Fibre Dispersion = 16 \(\frac{\text{ps}}{\text{mm}}\) \\  & Fibre Length = 10 \(\text{km}\) \\  & Attenuation = 0.44 \(\frac{\text{dB}}{\text{km}}\) \\ \hline \multirow{2}{*}{Photoreceiver} & \(\mathcal{R}\), \(Responsivity=0.69\) A/W \\ \end{tabular}
\end{table} 
Table 2: Link Parameters. Figure 3: 5G NR fibre–wireless system experimental block schematic. The functions are as follows: A: Selection switch for DPD or direct post-processing for performance evaluation; B: switch selection for synchronisation block or a performance post-processing block. C: B is turned towards synch and connected to train block, while C will be used to synch the DPD trained version. D: Training follows the synchronisation block.