## 3 Interference Coordination Scheme Analysis
### User Pairing Scheme Combined with ABS
Moreover, the proposed user pairing scheme can achieve better performance in edge users and improve network fairness. The proposed power allocation scheme can effectively enhance the throughput of edge users as the network fairness index decreases slightly. Therefore, the proposed strategy in this paper can obtain better performance in edge users with a high level of network fairness than other schemes. Moreover, there are two numerical results for the joint optimization algorithm of adaptive CRE and ABS with the proposed method and the traversal method; the proposed method has less complexity than the traversal method. Due to the randomness of random pairing, the proposed adaptive optimization algorithm cannot efficiently obtain the optimal solution; however, the error of the proposed pairing scheme between the two methods is approximately 0.20% in terms of throughput performance. The simulation results under different network user scales in NOMA HetNets with the proposed strategy are shown in Table 3. The average throughput of edge users decreases with the scale of users increase. Because the more users there are, the fewer resources are allocated. Moreover, the proposed strategy can efficiently balance resources and keep network fairness at a high level. As the user scale increases, the throughput of single users decreases, but the total throughput of the network does not change significantly, so the energy efficiency basically remains unchanged. The simulation results under different network models are shown in Table 4. The network models as a comparison can be seen in [15]. The network models with NOMA have better performance in edge users and energy efficiency than network models with OMA. The proposed strategy can effectively enhance the performance of edge users and energy efficiency as the fairness index declined \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Scheme**} & **Average Throughput of Network Edge** & \multirow{2}{*}{**Fairness Index**} \\  & **Users (Mbps)** & \\  & **(Proposed/Traversal)** & \\ \hline Fixed power allocation + Proposed user pairing & 2.2808/2.2855 & 0.7600/0.7868 \\ Proposed power allocation + random user pairing & 1.4974/1.5931 & 0.4400/0.6984 \\ Proposed power allocation + Proposed user pairing & 2.5196/2.5244 & 0.7614/0.7657 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Simulation results under different schemes. Figure 4: Throughput performances of edge users and fairness index: (**a**) under random user pairing scheme with different power allocation factor; (**b**) under different power allocation schemes. in OMA HetNets. Moreover, the NOMA HetNets with the proposed strategy can improve the performance of edge users, fairness and energy efficiency by the proposed interference coordination strategy in the paper. ## 5 Conclusions

In this paper, a time-domain interference coordination optimization strategy of NOMA HetNets for network user fairness is proposed. In the strategy, CRE and ABS technology are applied to interference coordination. Novel user pairing schemes based on ABS ratio and dynamic power allocation schemes are proposed. Moreover, the idea of game theory is used to reduce the computational complexity of joint optimization algorithm of adaptive CRE and ABS. Simulation and numerical results present that the proposed user pairing scheme and power allocation scheme have better performance in edge users with a high level of network fairness than other schemes of similar complexity. Moreover, the proposed interference coordination optimization strategy can effectively improve the throughput performance of edge users and fairness in the network model of NOMA HetNets. Conceptualization and methodology, Z.Y. and J.H. ; software, validation, formal analysis, investigation, data curation and writing--original draft preparation, Z.Y. ; writing--review and editing, Z.Y. and J.H. ; supervision, project administration and funding acquisition, J.H. All authors have read and agreed to the published version of the manuscript.