## 5 Conclusions  
In this paper, a two-hop 5G New Radio architecture was studied and analyzed in order to enhance the average system throughput and BER in outdoor-to-indoor environments. The system implements an NR-RN cooperative network, which uses outband NR-RNs. These NR-RNs translate the incoming signal into mmWave band of the 26 GHz for the access link inside an office environment. Two protocols of RNs were analyzed: Amplify-and-Forward (A&F) and Decode-and-Forward (D&F). Moreover, the channel estimation stage for the D&F relay was considered, taking into account the knowledge of the channel and applying the channel estimation through Least Square (LS) estimator. The cooperative system deploys NR-RN with one antenna at transmission and one antenna at reception, as well as multiple antennas. Furthermore, the 5G NR signal employs features that are standardized by the 3 GPP.  
In the simulations, the results demonstrated that the D&F NR-RN scheme can greatly enhance the KPIs of the system in comparison with A&F protocol. From the results, it follows that the implemented D&F NR-RN protocol with knowledge of channel has the best performance. For example, the maximum throughput of the proposed architecture (113.85 Mbps for 64-QAM signal) is reached from SNR = 12 dB. Nevertheless, with channel estimation, the obtained results are very near to the best performance, which has achieved approximately 93% of the maximum throughput at the SNR = 12 dB for the 64-QAM scheme. It can be noticed that is excellent results due to that, in a real environment, the channel needs to be estimated. On the other hand, the results showed that the 64-QAM modulation leads to better robustness in the evaluated scenario. Furthermore, it can be concluded from the results that employing mmWave NR-RNs together MIMO technique led to a substantial benefit, in terms of the KPIs of the network in the outdoor-to-indoor environment. The MIMO scheme achieved a reduction of the BER and increasing the throughput in the 256-QAM modulation scheme, which can be concluded increasing the number of antennas can lead to higher performance and spectral efficiency of the system.  
[PERSON] conceived the paper, designed the experiments, performed experiments, analyzed the data, and wrote the paper; [PERSON] and [PERSON] reviewed and edited the paper. All authors have read and agreed to the published version of the manuscript. This work was supported by the Spanish Ministry of Science, Innovation and Universities within the project TEC2017-87061-C3-1-R (CIENCIA/AEI/FEDER,UE) and by the China Science and Technology Exchange Center-MST of the People's Republic of China, within the project 23016 YFE0200200. The work of [PERSON] is supported by a Pre-doctoral Contract PRE2018-085032 from the Ministry of Science and Innovation.  
**Institutional Review Board Statement:** Not applicable.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Parameters** & [34; 35] & [36] & [37] & **Proposed** \\ \hline Signal Model & Conventional & Conventional & Conventional & NR standardization \\ A\&F RN & No & Yes & Yes & Yes \\ D\&F RN & Yes & No & No & Yes \\ Number of RN & 1 & 4 & 1 & 1 \\ Duplex Mode & Full & Full & Half & Half \\ BL Frequency & 60 GHz, 28 GHz & \textless{}6 GHz & \textless{}6 GHz & 3.5 GHz \\ AL Frequency & 60 GHz, 28 GHz & \textless{}6 GHz & \textless{}6 GHz & 26 GHz \\ Channel Estimation Algorithm & No & No & Yes & Yes \\ Knowledge Channel & Yes & Yes & Yes & Yes \\ Proposal of Hardware Implementation & No & No & No & Yes \\ \hline \hline \end{tabular}
\end{table}
Table 4: A comparison survey with previous works.