## 5 Experimental Results
### Synchronization and Performance of the Backhaul Link in the D&F Relay Node  
In this subsection, the performance of the developed synchronization stages in the D&F relay node are evaluated. The first task of the D&F protocol after capturing the received signal through the SDR on the backhaul link is cell search, which is achieved by decoding the SSB to establish the synchronization between gnodeB and D&F relay node. In this sense, D&F protocol finds out time and frequency synchronization with a cell and decodes the cell ID of the gnodeB. Thus, relay node decodes the PSS and SSS to determine the physical cell ID. Figure 8 shows the PPS correlation versus frequency offset (kHz) for three sector IDs 0, 1, and 2. From the figure, it can be seen that N\({}_{\text{ID}}^{2}\) = 0 was selected due to that it has the highest magnitude. In the next step, decoding of the secondary synchronization signal is processed, for which SSS correlation is shown in Figure 9. Therefore, the cell ID group (N\({}_{\text{ID}}^{1}\)) with the highest correlation is determined, in this case, the cell ID group 0 was selected. Now, the D&F protocol can know the cell ID (N\({}_{\text{ID}}^{C}\)) by 3 \(\times\) 0 + 0 = 0. In order to further verify the developed synchronization algorithms, the values obtained before are compared with those obtained with the Anritsu spectrum analyzer. As can be seen in Figures 4 and 5 in Section 2, both values are 0. After that, the strength of signal for PBCH demodulation reference signal (DM-RS) for each set of SSB is detected (in this paper the authors have considered one SSB by frame) by the D&F relay node. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **Signal 1** & **Signal 2** \\ \hline Channel bandwidth, \(F_{s}\) & 5 MHz & 5 MHz \\ Carrier frequency, \(f_{s}\) & 3.5 GHz & 3.5 GHz \\ Tx/Rx schemes & SISO and 2 \(\times\) 2 MIMO & SISO and 2 \(\times\) 2 MIMO \\
5G duplex scheme & NR-FDD & NR-FDD \\ Modulation & 64-QAM & 256-QAM \\ Target code rate & 3/4 & 4/5 \\ Samples rate & 7.68 MHz & 7.68 MHz \\ Cyclic prefix (CP) & Normal & Normal \\ Number of FFT & 512 & 512 \\ Allocated resource blocks & 25 & 25 \\ Subcarriers per resource block & 12 & 12 \\ Information bit payload per slot & 12,296 & 16,896 \\ SS/PBCH block transmission & slot 0 & slot 0 \\ Subcarrier spacing & 15 kHz & 15 kHz \\ Number of cell ID & 0 & 0 \\ Max. throughput over 1 frame & 11.066 Mbps & 15.206 Mbps \\ Number of transmission & 20 & 20 \\ Number of frames per transmission & 80 & 80 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Main parameters to emulate the gnodeB. Figure 10 shows the PBCH DM-RS estimated SNR versus iSSB, where the index of PBCH DM-RS with the highest correlation (0) defines the LBSs of SS/PBCH block required for PBCH scrambling initialization. This beam is also identified as the best beam for the D&F protocol. Figure 8: Primary synchronization signal correlations versus frequency offset. Figure 9: Secondary synchronization signal correlations. Once successful decoding information by the D&F protocol is achieved, downlink control and the physical channels are now enabled by the obtained data symbols of the PBCH, in which the required information (I\({}_{\text{MB}}\)) is obtained to demodulate these channels. In this sense, Figure 11 shows the downlink constellation diagram for the physical broadcast channel. The left subfigure represents the received signal without equalization technique, and the right illustrates the equalized data symbols after applying the MMSE equalization algorithm. It should be noted from Figure 11 that the MMSE technique introduces significant improvement over the received PBCH symbols. Furthermore, it should be highlighted that the previous measurements have been performed considering the parameters of Signal 1 and the scenario of Figure 7. On the other hand, experimental results have been obtained, taking into account signal 2, and similar results have been drawn.