## 6 Discussion and Future Works  
In this work, a co-operative 5G network was designed and implemented, based on the SDR hardware interface and MatlabTM software, using a D&F protocol as an intermediate node to facilitate communication between source and destination. A decode-and-forward protocol symbolizes a layer 2 relay technology, in which the RF signal from the base station is first decoded, and then forwarded to the destination node where it is again encoded. It is worth noting that the 5G signal emulated in the D&F co-operative SDR platform and the developed algorithms comply with the requirements standardized by 3 GPP, being one of the main novelties of the presented work.  
Looking at the results of the backhaul link measurements, it can be seen that the algorithms implemented in the D&F protocol have an excellent behavior for the synchronization, correction, decoding, and coding of the 5G signal received from the gnodeB. In this respect, it should be noted that the obtained results are closely related to those obtained with the MS2090A-Arnitsu LTE/5G spectrum analyzer (see Figure 16). Besides, the analysis of the EVM over broadcast channel, control data channel, and downlink shared channel shows that the MMSE equalization stage decreases the error magnitude, which improves the system performance. It is worth noting that the EVM, before the equalization stage, does not decrease as the transmitted power increases, which is due to the fact that as the P\({}_{\mathbf{BS}}\) increases, the noise at the reception, in the experimentation scenario (Figure 7), is also amplified; however, when using the MMSE technique, the noise is considerably canceled out. In addition, the implemented algorithms were verified over controlled lab environment [33], obtaining one EVM of the PBCH which decreases as transmitted power increases.  
The results obtained in previously published works [36; 37; 38; 29; 39] are consistent with those obtained in this paper, demonstrating the improvements that the use of D&F relay nodes introduces in the performance of the network. Table 2 shows a comparative summary of the experimental results obtained in this paper. The presented results show the advantages of inserting D&F relay node in 5G mobile networks. Furthermore, it should be noted that  
Figure 20: Throughput vs. P\({}_{\mathbf{BS}}\) of the relay node co-operative 5G network; 256-QAM.  
in the case of mmWave communications, the use of relay nodes will be more necessary, as demonstrated in [30; 31].  
Future research work includes the development and implementation of algorithms for the uplink of the 5G signal. This would provide a co-operative 5G network with D&F relay nodes working bidirectionally (uplink and downlink). In this context, we will address the implementation of new algorithms to develop the hardware interface of the SDR platform for 5G uplink communication and upgrade the 5G signal to the 20 MHz bandwidth to improve the capacity of the co-operative network, as the SDR platform supports the requirements. Another future objective, which is currently being worked on, is the development of transceivers in millimeter bands (26 GHz), which will allow the implementation of D&F relay node in these frequency bands. This will allow analyzing the feasibility, through theoretical studies and measurements, of the use of relay nodes in some of the vertical markets proposed by 3 GPP, such as high-speed or high-vehicle-density transport. These works are a first step to analyze the advantages and disadvantages of using IAB (integrated access backhaul) in the deployment of 5G technology [17; 40].