## 3 Testbench Implementation of D&F Co-Operative 5G Network  
Our software defined radio platform and MatlabTM tool for co-operative LTE network was designed and explained in [29; 32]. However, to implement the decode-and-forward cooperative network, the 5G system has been upgraded from the hardware interface, which will allow approaching research in the future of the out-of-band D&F node in the mmWave frequency band. The relay node co-operative wireless communications testbench is realized with three nodes, base station (gnodeB), relay node (D&F protocol), and destination (UE). The baseband processes are based on and implemented using MatlabTM software and realize the digital algorithms, for example, waveform generation and M-QAM modulation in the base station, channel estimation and equalization, decoding, and coding of the PBCH, PDCCH, PDSCH, and other channels in the D&F relay node. Furthermore, the demodulation and comparison of the received signals from base station and D&F protocol are performed in UE. From the hardware interface, three separate universal software radio peripheral (USRP) devices, two NI-USRP 2944R, and one Ettus X310 are used as base station, D&F node, and UE, integrating digital/IF/RF units, respectively. The USRPs have tunable operating frequencies ranging from 70 MHz to 6 GHz and tunable transmission sample rates up to 200 mega samples per second. In order to assure a real-time relay node co-operative network implementation, we consider a specific computer configuration using three computers. Furthermore, USRPs can hold two RF chains (2 Tx/2 Rx). On the other hand, the connection from a PC to the NI-USRP 2944R/Ettus X310 is performed through the NI-IMAQdx GigE Vision High-Performance Driver, 10 gigabit ethernet card for desktop and 10 gigabit ethernet cable. The upgraded SDR platform consists of one PA to the output of USRP in the base station, guaranteeing extending of the coverage of the co-operative wireless communication 5G network, as shown in Figure 3. In addition, the base station with PA achieves a distance of 49 m with 8% of EVM, which is the requirement by the 3 GPP to the 64-QAM modulation scheme in a non-line-of-sight (NLOS) indoor-to-indoor scenario [33]. In addition, an OctoClock CDA-2990 has been added as an external source synchronizing multiple USRP devices (base station, D&F relay node, and UE) to improve the performance of the high channel count systems. On the other hand, the used antennas for the gnodeB node are R&S HL040E log-periodic broadband antennas. They work on 400 MHz to 6 GHz frequency band and their typical gain is 5.5 dBi. However, the D&F and UE nodes are equipped with Pasternack's PE51 RD1031 antennas, which cover the frequency band from 615 MHz to 4200 MHz and have a gain of 4.5 dBi. Figure 4 shows transmitted signal demodulation, occupied bandwidth, channel power, and spectrum from the emulated gnodeB measured through the MS2090A-Anritsu spectrum analyzer to the output of the ZHL-1042J power amplifier. It can be seen that there is synchronization and modulation full between base station and Anritsu spectrum analyzer, which demonstrates the correct functionality of the emulated gnodeB (5G downlink signal). The synchronization signal consists of two parts, namely primary synchronization signal (PSS) and secondary synchronization signal (SSS), which in Figure 4 present 7.82% and  
Figure 2: Baseband UE architecture. 8.03% of the error vector magnitude (EVM), respectively. In addition, the physical cell ID (0) of the implemented gnodeB and its time and frequency structure of a single SSB have been detected, which includes the demodulation of the physical broadcast channel (PBCH), as shown in Figure 5. The transmitted frequency error is about 288 Hz, which is perfectly correctable with the implemented frequency offset correction algorithms in the D&F and UE nodes. The channel total power of the gnodeB is, approximately, 17.30 dBm.