# Performance of Cooperative Relay NOMA with Large Antenna Transmitters
## 5 Conclusions and Future Scope  
In this paper, different from previous works on mMIMO CR-NOMA system, we have presented a 3D GBSM channel model between TX\(-\)RS and RS\(-\)UEs communication links. We examined a two-stage downlink mMIMO CR-NOMA system with the 3D GBSM channel model where the transmitter is represented by CA or URA. We have undertaken performance analyses of the proposed system model with simulations and compared it with the theoretical results of systems using CBSM. Generation of 3D GBSM channel model is complex, therefore, to minimize the computational complexity of the channel, we defined the antenna location vector based on the physical dimension of the antenna configuration. The proposed 3D GBSM channel model incorporates various network coding schemes such as DF and AF for better channel and system performance. For performance analysis, we derived the probability of an outage, the achievable rate and the bit-error rate for the two-stage system. According to the results, the combination of CA and AF gives a better outage probability. Finally, even though the proposed 3D GBSM channel model has a higher computational cost in terms of complexity, the results reveal that the performance difference between the theoretical channel model (CBSM) and GBSM is minimal. The work can further be extended to cover millimeter-wave CR-NOMA with multiple antenna at the TX, RS and UEs. Again, the effect of spatial correlation of antenna array configuration on the performance of 3D GBSM in CR-NOMA systems presents good future research opportunities.  
Conceptualization, S.T.-K. and E.A.A.; methodology, S.T.-K.; software, S.T.-K. and E.A.A.; validation, S.T.-K., E.A.A., K.A.-P.A. and S.A.A.; formal analysis, S.T.-K.; resources, E.A.A., S.A.A. and M.O.A.; writing\(-\)original draft preparation, S.T.-K., E.A.A. and K.A.-P.A.; writing\(-\)review and editing, S.T.-K., E.A.A., K.A.-P.A., S.A.A. and M.O.A.; supervision, E.A.A., S.A.A. and M.O.A. All authors have read and agreed to the published version of the manuscript.  
This research was supported by the University of Zululand and Tolkom SA LTD.  
Not applicable.  
The authors are grateful to the University of Zululand and Tolkom SA LTD, South Africa, and the Center for RFIC and System Technology, School of Communication and Information Engineering, University of Electronic Science and Technology of China for their contribution.  
The authors declare no conflict of interest.  
The following abbreviations are used in this manuscript:  
\begin{tabular}{l l} NOMA & Non-Orthogonal Multiple Access \\
5G & Fifth Generation \\ SIC & Successive Interference Cancellation \\ CR-NOMA & Cooperative Relay Non-Orthogonal Multiple Access \\ mMIMO & Massive Multiple-Input Multiple-Output \\ CBSM & Correlated-Based Stochastic Channel Model \\ GBSM & Geometric-Based Stochastic Channel Model \\
3 GPP & Third Generation Partnership Project \\
3D & Three Dimension \\ URA & Uniform Rectangular Array \\ CA & Cylindrical \\ Array & \\ OP & Outage Probability \\ AF & Amplify-and-Forward \\ DF & Decode-and-Forward \\ OMA & Orthogonal \\ \end{tabular}