# Performance of Cooperative Relay NOMA with Large Antenna Transmitters
## 1 Introduction
### Contribution of the Work  
We consider a two-stage downlink network system model with a dedicated relay. We use the 3 GPP and WINNER+ models that follow the GBSM approach in [90; 91; 92] and provide a 3D GBSM channel model [93; 94] when the transmitter is either URA or CA. We use the channel model in a CR-NOMA system where the transmitter's antenna is a massive antenna array system. We analyse the performance of the proposed system when the RS uses either AF or DF network coding scheme. The reason is that research in [21; 95] shows that a significant component of energy is emitted in the elevation of the WINNER+ and 3 GPP models. As a result, specifying propagation pathways in azimuth alone does not improve performance [95]. Furthermore, the WINNER+ and 3 GPP models include the antenna boresight's elevation angle in the channel equation. We use URA and CA because their radiated MIMO signals can be adjusted in 3D space to boost system capacity [21]. Again, a massive antenna array can reduce clutter by using scanning acceleration and a space-time signal. Furthermore, it permits the creation of concentrated beams in any horizontal direction [21]. To reduce the computational complexity of the 3D GBSM channel model, we define the antenna element location vector using the physical dimension of the antenna array and incorporate it into the 3D channel model [21; 96; 97]. To enhance the performance of the proposed mMIMO CR-NOMA system, two coding schemes, AF and DF, are used with the channel model. The results present the performances of the \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Ref** & **Coding Scheme** & **Channel Model** & **Transmission Mode** & **Performance Metrics** & **Outcome** \\ \hline [86] & DF relay & CBSM (Rayleigh), single antenna with buffer capabilities & Downlink and outage probability & Average throughput and outage probability & There is a significant improvement in system throughput at both low and high SNR bands, as well as diversity order with an increased number of relays. \\ \hline [87] & DF relay & CBSM (Rayleigh), single antenna & Uplink & Weighted sum-rate maximization & The proposed cooperative NOMA outperforms both the non-cooperative NOMA benchmark and the traditional OMA in terms of attainable rate and throughput. \\ \hline [88] & DF relay & CBSM (Rayleigh), downlink single antenna & Ergodic sum-rate and outage probability & The proposed system provides better outage probability and superior ergodic sum rate over equivalent conventional systems. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._combination of coding schemes and large antenna transmitters regarding achievable rate, outage probability and Bit-error rate (BER). Again, to fill the gap in the above literature on the CR-NOMA system concerning the adoption of 3 GPP's 3D GBSM channel model with large antenna transmitters, this paper aims to assess the system usage performances using the proposed channel model. For clarity, the major contributions and objectives of the paper are:  
1. We examine a two-stage downlink mMIMO CR-NOMA GBSM system and introduce a new channel model when the transmitter is URA or CA. To reduce the computational complexity of the 3D GBSM channel, we define the antenna elements' location vector based on the physical dimension of the antenna array. We illustrate the transmitter with a massive antenna system following the models discussed in [17]. Here, the relay and user equipment only has a single antenna. 2. Two coding schemes, AF and DF, are incorporated into the channel model to improve the channel performance. 3. For performance analysis, evaluation and comparison, we present outage probability and achievable rate for the two-stage mMIMO CR-NOMA system. 4. Final findings show that the joint contribution between large antenna transmitters and coding schemes with 3D GBSM CR-NOMA presents possible advantages for future communications systems concerning achievable rate, outage probability and Bit-error rate (BER). The paper is organized as follows.