# Performance Analysis of Soft-Switching FSO/THz-RF Dual-Hop AF-NOMA Link Based on Cognitive Radio
## 4 Numerical Results  
In this section, we provide meaningful values to perform a numerical analysis of the proposed link. Unless otherwise specified, the NOMA system considered here has \(M=2\), \(a_{1}=0.51\), \(a_{2}=0.49\), \(\gamma_{th,1}=51/149\), \(\gamma_{th,2}=49/100\), and \(\Delta=5\%\). Regarding the frequency and wavelength, the RF frequency is taken as 60 GHz, the THz frequency is 0.1 THz, and the FSO wavelength is 1550 nm [31]. For atmospheric turbulence and pointing error scenarios, we set the moderate turbulence parameters as \(\alpha_{F}=1\), \(\beta_{F}=2\), \(\eta=2/\sqrt{\pi}\), \(\alpha_{T}=1.7\), \(\mu_{T}=1.5\), \(m_{1}=1\), and \(m_{2}=1\). For weak turbulence, the parameters are \(\alpha_{F}=1\), \(\beta_{F}=3\), \(\eta=2/\Gamma(4/3)\), \(\alpha_{T}=1.7\), \(\mu_{T}=1.7\), \(m_{1}=2\), and \(m_{2}=2\). The large pointing error is represented by \(g_{T}=1.6224\), whereas the small pointing error is denoted by \(g_{T}=2.9203\). The path loss exponent \(\alpha=2\), with distances \(d_{SR}=200\) m, \(d_{RU1_{2}}=20\) m, \(d_{RU2}=20\) m, and \(d_{RP}=5\) m. In the subsequent analysis, we primarily focus on the performance of OP under various conditions. Figure 3 investigates the relationship between OP and PAC under different \(I\) in weak turbulence. We set \(\gamma_{th,j}=\big{(}a_{j}\rho_{m}\big{)}/\left(1+\rho_{m}\sum_{i=j+1}^{M}a_ {i}\right)\), where \(\rho_{m}=\text{floor}[\rho+1]\) and \(\rho\) is a value on the ordinate of the function \(\rho\Big{(}\gamma_{th,j}\big{)}=\gamma_{th,j}/\left(a_{j}-\gamma_{th,j}\sum_{ i=j+1}^{M}a_{i}\right)\), and \(\text{floor}[\cdot]\) is rounded down. The results demonstrate that the link performance improves as the mean deviation of PAC decreases. Additionally, due to variations in channel gains, User2 outperforms User1. Comparing different \(I\), we observe that a larger \(I\) leads to better link performance, benefiting from the ability of the PN to withstand greater interference. Therefore, we consistently adopt the optimal PAC and SINR thresholds throughout the analysis. In Figure 4, numerous deductions may be discerned. Firstly, with the elevation of \(I\), the link's performance exhibits enhancement. Nevertheless, owing to the constraints imposed by both \(I\) and \(P_{Peak}\) upon \(P_{R}\), the link's performance reaches a state of equilibrium at a specific \(I\), as determined by (13). Furthermore, it is noteworthy that augmenting both \(P_{S}\) and \(P_{Peak}\) can amplify the link's performance, albeit the enhancement brought about by increasing \(P_{Peak}\) is notably more pronounced. This discrepancy arises from the operation of the link using AF-NOMA, wherein \(P_{S}\) contends with more extended link distances compared to \(P_{Peak}\). Consequently, for the ensuing analysis, we establish \(P_{S}=15\) dBm and \(P_{Peak}=40\) dBm. The comparison between (a), (c), and (e) with (b), (d), and (f) in Figure 5 reveals that User2 outperforms User1 due to the difference in channel gains. Moreover, by comparing the three columns (a) (b), (c) (d), and (e) (f), it is evident that the link performance increases with the increase in \(P_{S}\). Finally, we observe that a single change in either \(P_{Peak}\) or \(I\) does not significantly enhance the link performance. Only when both parameters are increased simultaneously is the link performance improved. Thus, the performance advantage is concentrated in the rectangular region in the upper right corner of the figure. Figure 4: The impact of different values of \(P_{S}\) and \(P_{Peak}\) on OP under weak turbulence. Figure 3: The relationship between OP and PAC under different \(I\) in weak turbulence. Figure 6 depicts three atmospheric scenarios: Case1 involves moderate turbulence with large pointing errors, Case2 features weak turbulence with large pointing errors, and Case3 exhibits weak turbulence with small pointing errors. Upon comparing these scenarios, it becomes evident that the link performance is superior in the cases of weak turbulence and small pointing errors.