## 6 Experimental Setup  
For the validation of this technique, a multiband 5G NR scenario for out/in-door environments working at 3 GHz (20 MHz bandwidth) and 20 GHz (50 MHz bandwidth), which was discussed in our previous work [35], but no DPD was implemented. As an upgradation of this architecture, the setup is integrated with a multiband DPD block to this setup for enhancing the performance of this link. The setup shown in Figure 11 comprises of a 1310 nm optical carrier is modulated by a MZM working with two distinct RF-driven signals and a 1310 nm DFB laser. VSG1 provides RF1 which is a 5G NR waveform at 20 GHz while 5G transceiver provides RF2 which is a 3 GHz flexible (O/G/F-FDM) signal. The process of DPD can be divided in to three main phases. In the first phase, we upconvert these signals at the respective carrier frequencies of 3 and 20 GHz, respectively, one after the other followed by the passing of these signals through 22 km of Standard Single-Mode Fiber (SSMF) and photodetector (0.71 A/W and  
Figure 11: Block Diagram of Experimental Analog Multi Band 5G-NR-OFH RoF. The following Switches have following functionalities: A: Selection between VSA 1 and 2. B: Selection between post processing block for performance or Synchronization block. C: Connected to Synch. Block for performing synchronization followed by DPD training. D: DPD blocks connection with training DPD block E: Required for time synchronization (TS) procedure. F: Required for performing validation to launch DPD inputs to the VSGs. For DPD training phase, architectures can be selected that are requires such as MSA, CPWL, ONN, etc. 40 GHz bandwidth) receives the signal and converts the received signal back to electrical domain. Since, the multiband needs to be isolated separately, an amplification stage is added. Followed by a diplexer (DPX) that separates the 20 GHz and 3 GHz signals. The signals then go to distinct vector signal analyzers (VSA). Here each VSA outputs is fed to the post processing block for performance evaluation. This step is carried out without DPD, this means that the output is evaluated without DPD process in this step. In the second phase called as DPD training phase, the DPD operation depicted in the Figure 10 is utilized in this section and training is employed unless the error converges. In simple words, DPD ensures that the phase and amplitude responses are inverse to that obtained at electrical amplifiers EA1 and EA2, respectively. The architectures such as GMP, CPWL, MSA and ONN can be utilized as per the user requirement and comparative requirements. In order to achieve synchronization for the received input and the output waveform, we exploit PRS (Position reference signal) presented in the 5G NR framework. The bandwidth for PRS is taken to be 20 MHz/106 resource blocks. The received and output reference transmitted signal are correlated in time domain and the PDP (power delay profile) is passed through the maximum block to find the strongest path of arrival. Moving on to the third phase, the predistorted basebands signal are passed into the DPD block upconverting the signals at their carrier frequency by their respective VSGs after which they are fed into the optical link. Then, the signal that is received at photodiode is passed through diplexer DPX to isolate the respective multi-bands at the VSA passes to the DPD training stage. In the phase where DPD validation is carried out, we move the switches to the opposite direction. The evaluation for 5G NR frames is achieved which involves predistortion followed by passing them to the VSG. The RoF link's nonlinearities slowly fluctuate owing to thermal effects and component ageing, from which we deduce that real-time processing in the adaptation is inessential. The parameters utilized are summarized in Table 5 that have been used previously in [35] and other state of the art [20; 21; 22; 23; 24; 25; 26; 27; 28]. The parameters of different architectures that are utilized in this study for the experimental setup are given in Tables 6-8, respectively.