## 3 Testbench Implementation of D&F Co-Operative 5G Network
The obtained information from Figure 5 shows the root mean square EVM (%) of the PBCH, which can be seen to be considerably low, 2.60%. Figure 4: Transmitted signal demodulation, occupied bandwidth, channel power, and spectrum from the implemented gnodeB. Figure 3: Hardware interface testbench for D&F relay node co-operative 5G network. _Proposed D&F Protocol Radio Access Hardware Architecture_  
Taking into account the general-purpose system model in Section 2 and hardware interface testbench described in Section 3, this subsection proposes a decode-and-forward relaying radio access hardware architecture. The proposed D&F protocol is flexible due to the implementation through MatlabTM software, as well as the encoding and decoding algorithms, which are adjusted to the 3 GPP new radio standard [34]. In this sense, the 5G communication ToolBox of MatlabTM is employed. Furthermore, frequency division multiplexing (FDD) and MIMO antenna technique have been implemented, as well as in-band operation of the implemented protocol, that is, the backhaul and access links operate in the same frequency band, for which, in this work, the FR1 band (3.5 GHz) is considered. The overall hardware interface of D&F relay node consists of two major steps, the radio frequency and baseband, as shown in Figure 6. In the first step, a 5G NR signal from the gnodeB is received and saved to file as complex in-phase and quadrature (I/Q). This step is performed by means of RF receive chains of the MIMO Ettus x310 SDR platform. On the other hand, in the second step, using the saved signal is performed in the baseband processing through the MatlabTM software. Considering the flowchart in Figure 6, the first block in baseband step is _NR Basic Structure_, which has input signal similar to the sample rate of SDR platform (R\({}_{\rm P}^{\rm C}\)) and the received 5G signal (\(\hat{\textbf{Y}}_{\rm DF}^{\rm 1}\)). The output of this block (I\({}_{\rm OFDM}^{\rm NR}\)) supports the cyclic prefix, the desired number of iFFT points to use in the OFDM demodulator/modulator, the number of time-domain samples over which windowing and overlapping of OFDM symbols are applied, and the carrier frequency (Hz) allowing the phase precompensation applied for each OFDM symbol (as has been defined by the 3 GPP in [11]). For initial access, the D&F protocol should start by the cell search procedure. By using the SS block or synchronization/PBCH block, being the most important task for synchronization of the nodes in the 5G network, the D&F relay node can estimate and correct the frequency and time offsets, as is shown in the _Correlation Detector_ block. It should be mentioned that the SSB consists of four consecutive OFDM symbols with 240 subcarriers each, where the primary synchronization signal and secondary synchronization signal are placed in the first and third OFDM symbols, respectively. In addition, the physical broadcast channel carries on the PBCH payload and PBCH-DMRS, as can be seen in the proposed flowchart, and is placed in the second, third, and fourth OFDM symbols, being modulated with the Q-PSK constellation scheme. In architecture, the PSS block detects the primary reference signal and determines the N\({}_{\rm ID}^{\rm 2}\). This detection has been performed employing  
Figure 5: Q-PSK modulation scheme representation of the PBCH in the gnodeB measured through the MS2090A-Anritsu. the cross-correlation algorithm, in which the reference PSS sequence is created for the sector IDs (0, 1, and 2). Then, any significant frequency derivation must be estimated and eliminated, and the time offset must be performed without many errors being propagated. After the steps described previously, the 5G received signal is demodulated by means of the \(nrCP-OFDM\)_demodulation_ block. Thereafter, the output of the PSS block is employed by the SSS block; thus, the detection of SSS in the received 5G signal and the estimation of the N\({}_{\rm ID}^{\rm I}\) value is performed.