# Performance Analysis of Two-Hop mmWave Relay Nodes over the 5G NR Uplink Signal
###### Abstract  
In this paper, the uplink in a two-hop 5G new radio co-operative system using Relay Nodes (RNs) in millimeter bands has been simulated and studied. We focus on an uplink Amplify-and-Forward Relay Node (A&F RN) and Decode-and-Forward Relay Node (D&F RN) with an mmWave-band transceiver chain (Tx/Rx). We study two uplink mmWave MIMO D&F relaying protocols assuming, firstly, the complete knowledge of the uplink channel and, secondly, the uplink channel estimation through a Least Square (LS) algorithm. To verify the benefits of the proposed uplink mmWave MIMO co-operative network, a link-level co-operative simulator has been developed using Matlab(tm) and Simulink(tm) software, where an indoor-to-outdoor scenario and mmWave transceiver with off-the shelf components are considered. The main novelty of this link-level co-operative simulator and the implemented relay nodes is the usage of signals with 5G NR features, such as UL-SCH transport channel coding and PUSCH generation, which are the other main contributions of this article. Based on the numerical results in terms of the achievable Bit Error Rate (BER) and throughput, we show that the two-hop uplink co-operative network substantially improves the performance in the communications between the NR-User Equipment (NR-UE) and the logical 5G Radio Node (gNodeB). For example, the results from using uplink mmWave NR-D&F protocols far exceed those achieved with the uplink mmWave NR-A&F algorithm; in the case of the 64-QAM modulation scheme for the SISO technique, an improvement of 6.5 Mbps was achieved using the D&F PCE protocol, taking into account that the 256-QAM constellation is higher by 4.05 Mbps. On the other hand, an average throughput enhancement of 28.77 Mbps was achieved when an uplink mmWave (\(\times\) 4 \(\times\) 4) D&F PCE strategy was used versus an uplink mmWave SISO D&F LS protocol for a Signal-to-Noise Ratio (SNR) = 20 dB and 64-QAM signal. However, an improvement of 56.42 Mbps was reached when a 256-QAM modulation scheme was employed. Furthermore, this paper introduces the first study to develop an uplink mmWave MIMO 5G co-operative network platform through a Software Defined Radio (SDR) from a practical implementation point of view. millimeter-wave MIMO; uplink 5G NR; relay node cooperative system +
Footnote †: journal: Applied Sciences  
should require higher data rates, robustness, spectral efficiency, etc. Among the scenarios for 5G, mobile and wireless communications are expected: Direct Device-to-Device (D2D) communication [5], Massive Machine Communication (MMC) [6], Moving Networks (MNs) [7], Ultra-Dense Networks (UDNs) [8] and Ultra-Reliable Communication (URC) [9]. In order to solve the limitation of spectrum resources, the spectrum-rich mmWave has received special attention as the key spectrum of 5G and future technologies as 6G [10]. The wide spectrum available in millimeter bands [11] makes millimeter-wave technology an enabling technology for the deployment of 5G networks. It would provide a solution to address the challenges of bandwidth scarcity in 5G systems. However, the main challenge of the mmWave bands is undergone by the very high propagation loss, which substantially limits the communication distance in comparison with the FR1 frequency bands (<6 GHz) of 5G. For example, the free space path loss of a 20-m link at 60 GHz frequency can easily exceed 90 dB. On the other hand, thanks to the smaller wavelengths, it is easier to implement hardware massive MIMO (mMIMO) [12] systems, which can compensate for some of the limitations of millimeter band propagation. Consequently, millimeter waves and massive MIMO can be combined to achieve the maximum performance of both technologies [13; 14; 15]. In addition, it has been demonstrated that the co-operative networks using Relay Nodes (RNs) increase capacity and network coverage as well as decrease the path loss and total transmission power [16].