## 5 Experimental Results
### Performance Evaluation of Proposed Hardware D&F Co-Operative 5G Network
It can be seen from Figure 19 that the maximum throughput obtained by the SISO non-co-operative network was 3.27 Mbps; however, with 2 \(\times\) 2 MIMO, a capacity of 4.78 Mbps could be reached with the same \(\text{P}_{\text{\bf BS}}=15\) dBm, which represents a performance gain of about 1.51 Mbps. Nevertheless, when the SISO D&F protocol is considered, the average performance of the network is so much higher than the 2 \(\times\) 2 MIMO non-co-operative system--for example, the reached maximum throughput was 8.95 Mbps, which achieved a gain of 5.68 Mbps and 4.17 Mbps with respect to SISO and MIMO non-co-operative networks, respectively. It may also be seen that the throughput of the (2 \(\times\) 2 \(\times\) 2) MIMO D&F relay node co-operative system at \(\text{P}_{\text{\bf BS}}=10.3\) dBm was approximately 8.95 Mbps, corresponding to the maximum value reached by SISO D&F protocol, such that a performance gain of about 4.7 dBm was achieved. Furthermore, the obtained results in Figure 19 have been observed as a substantially improved system throughput of the D&F relay node with the MIMO technique in comparison with direct link, in which performance gains of 7.80 Mbps and 6.29 Mbps were reached, respectively, with respect to SISO and MIMO techniques. Finally, it should be noted that the maximum throughput of our downlink 5G NR for the 64-QAM constellation scheme is 11.066 Mbps. Therefore, from Figure 19, it can be seen that this value was reached by the (2 \(\times\) 2 \(\times\) 2) MIMO D&F protocol co-operative system from \(\text{P}_{\text{\bf BS}}=13\) dBm. Figure 18: BER vs. \(\text{P}_{\text{\bf BS}}\) of the relay node co-operative 5G network; 256-QAM. Here, the experimental results of the hardware interface downlink D&F relay node co-operative 5G network are given for 256-QAM modulation scheme over SISO and MIMO channels, as shown in Figure 20. It can be observed that the downlink SISO direct link reached a capacity of 1.87 Mbps at around \(\rm{P_{BS}}=15\) dBm, while with the 2 \(\times\) 2 MIMO antenna technique, the non-co-operative network reached the same average throughput at around \(\rm{P_{BS}}=11\) dBm; accordingly, a performance gain of 4 dBm was achieved. The maximum capacity of the 2 \(\times\) 2 MIMO direct link was 6.12 Mbps, but it is very far off the throughput reached by the D&F relay node. In this sense, when the SISO D&F relay node co-operative 5G network was taken into consideration, the user equipment reached 10.47 Mbps at around \(\rm{P_{BS}}=15\) dBm, implying that a 3.6 dB performance gain and 4.35 Mbps were successfully achieved compared to the 2 \(\times\) 2 MIMO direct link performance. It should be highlighted that the tremendous enhancement with the co-operative network is due to the impact of decoding and encoding stages the downlink FR1 received signal was subjected to before being retransmitted to the UE by means of the downlink D&F protocol. Additionally, it should be noted that the throughput maximum that could be reached without any channel for the 5G new radio PDSCH 256-QAM system (signal 2 of Table 1) is 15.206 Mbps, which only was achieved when employing the (2 \(\times\) 2 \(\times\) 2) MIMO D&F relay node at \(\rm{P_{BS}}=15\) dBm. In this context, it can be observed from the figure that D&F protocol with MIMO antenna technique achieved approximately the same average throughput as the SISO D&F relay node at 10.8 dBm. However, with respect to non-co-operative network, a gain of about 13.34 Mbps and 9.09 Mbps, respectively, for SISO and MIMO was obtained. Figure 19: Throughput vs. \(\rm{P_{BS}}\) of the relay node co-operative 5G network; 64-QAM.