## 4 Conclusions and Discussion  
In this work, a strategy is proposed for the interference management, BER reduction, and throughput enhancement of the small-cell users. Using NOMA in small-cells not only results in better performance gains but also manages the interference by letting the ICI cause MUs to establish connection with the SBS. In the presented scheme, WHT-NOMA provides better throughput and BER performance even at low SNRs as compared to the conventional NOMA. As visible from the simulation analysis in the results section, it is shown that WHT-NOMA can improve the receiver performance gains up to a significant level. The WHT matrix works as a catalyst for the conventional NOMA and improves the BER with a SNR gain of approximately up to 5-10 dB. The receiver design of NOMA needs careful consideration as multiple users are paired together in the power domain, and this creates a lot of interference at the receiver. The presented technique improves BER and throughput performance of both the high- and low-channel-gain small-cell users, i.e., SCUs and SEUs, respectively. Furthermore, the work includes IRC for the ICI suppression, which further reduces the BER of the SUs, resulting in even better user throughput performance as visible from the presented results.  
Further, the work can be extended to include interference cancellation techniques like iterative SIC and parallel interference cancellation (PIC). The work may also be extended  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Complex Operations** & **NOMA** & **NOMA + WHT** & **NOMA + WHT + IRC** \\ \hline \
\begin{tabular}{c} Required No. of \\ Multiplications at the \\ Receiver \\ \end{tabular} & \(\frac{N_{C}}{2}log_{2}(N_{C})\) & \([(N_{C}/2)log_{2}(N_{C})]+[(N_{C})^{2}]\) & \([(N_{C}/2)log_{2}(N_{C})]+[(N_{C})^{2}]\) \\ \end{tabular} \\
\begin{tabular}{c} Multiplications at the \\ Receiver \\ \end{tabular} & \(+[2(N_{C})^{2}+K(N_{C})^{2}+(N_{C}^{2}+7/2N_{C}^{2}+5/2N_{C}-4)+KN_{C})]\) \\ \end{tabular}
\end{table}
Table 4: Computational Complexity[10; 34; 37].  
Figure 22: Number of operations for conventional NOMA, WHT-NOMA, and WHT-NOMA-IRC.  
to the multiuser system level case for checking the scalability performance of WHT-NOMA with IRC in more complex environments. The future extensions can analyze the performance of the proposed method with various transmit and receive diversity techniques such as multiple-input multiple-output (MIMO) NOMA.  
Conceptualization and methodology, M.R.U. and M.A.U.; mathematical modeling, M.R.U., M.A.U. and G.B.S.; data curation and visualization, M.R.U. and M.A.U.; simulation and validation, M.R.U., M.A.U. and R.A.N.; investigation and formal analysis, M.R.U., M.A.U. and G.B.S.; writing--original draft preparation, M.R.U., M.A.U. and R.A.N.; editing, S.Y.S., M.G.M. and C.P.; supervision, S.Y.S., M.G.M. and C.P.; project administration and funding acquisition, S.Y.S. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2019 RIA2C1089542).  
Not applicable for studies not involving humans or animals.  
Not applicable for studies not involving humans.  
The data presented in this study are available on request from the corresponding author. The data are not publicly available because this work is part of an ongoing funded project.  
The authors declare no conflict of interest.