## 5 Results and Discussion  
This section validates the derived analytical expressions for the outage probability of the SUE and WUE, throughput, and SSE. It examines the proposed system's performance under iSIC and HWD conditions. The software used is MATLAB 2023a, and the parameters and the values used for simulation are tabulated in Table 4. The proposed IOS-aided C-HNOMA acts as the base system. It is integrated with existing pairing schemes [21, 27, 28] and traditional PA optimization techniques [4, 22], and a comparison between them is conducted to highlight the importance of pairing and PA optimization in improving system performance. The probability of outage is the metric that defines the reliability of the wireless connections in the system. It is the ratio of the number of transmissions under outage to the total number of transmissions. Figure 7 illustrates the average outage performance of the SUE across different pairing schemes considering no SIC error or HWDs. The derived closed-form expressions for the average outage probability of the WUE and SUE are presented as seen in (26) and (27), respectively, and closely align with the simulation results. This confirms the accuracy of the derived average outage probability expressions. The probability of outage with SW-SW pairing shows improvement over other pairing strategies. Similarly, Figure 8 demonstrates the effectiveness of SW-SW pairing in the average outage probability performance of the WUE. The average probability of outage for the WUE is better than for the SUE. This improvement is attributed to the cooperative communication within each pair and high PA to the WUE. The average SNR gain observed by the SW-SW scheme over other pairing schemes for the SUE and WUE is tabulated in Table 5. \begin{table}
\begin{tabular}{c c} \hline \hline
**Simulation Parameters** & **Values** \\ \hline Block length & \(10^{7}\) \\ Number of UE, \(M\) & 8 \\ Power fractions during direct relaying, \(\mu_{si}\) and \(\mu_{wi}\)[4] & 0.1 and 0.9 \\ Path-loss exponent, \(\eta\) (sub-urban region) & 3.8 \\ Channel gains of UE, \(\rho_{u}^{i}\), \(u=1,2,\ldots,8\)[12] & 8, 7, 6, 5, 4, 3, 2 and 1 \\ Target SE of SUE, \(R_{s,p}^{i}\)[31] & 0.5 bps/Hz, 1 bps/Hz \\ Target SE of WUE, \(\tilde{R}_{w,p}^{i}\)[31] & 0.5 bps/Hz, 1 bps/Hz \\ Threshold SNR of SUE, \(\rho_{s,p}^{i}\)[29] & 15 dB \\ Threshold SNR of WUE, \(\rho_{w,p}^{i}\)[29] & 15 dB \\ Target outage & \(10^{-3}\) and \(10^{-5}\) \\ Noise variance, \(\sigma_{u}^{2}\) & 1 \\ SIC error, \(\varepsilon\)[4] & 1\% \\ HWD, \(d=k_{g}^{2}=k_{g}^{2}=k_{u}^{2}=k_{u}\)[30] & 0.08, 0.09 and 0.15 \\ Number of IOS elements, \(L\)[12, 32] & 16, 32, 64 128 and 256 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Simulation set-up. Table 5 clearly indicates that the SW-SW pairing enhances the outage performance in the SUE and WUE compared to other pairing schemes. This improvement arises from the SW-SW pairing's provision of diverse channel gains within each pair. In contrast, the other pairing schemes exhibit similar channel gains, or some pairs in the system have similar channel gains while others demonstrate diverse channel gains, which ultimately diminishes the overall system performance. In terms of the SUE, SW-SW pairing offers \(\sim\)0.3 to \(\sim\)3.81 dB SNR gain, while for the WUE, it provides around \(\sim\)0.21 to \(\sim\)3.89 dB SNR gain. Three distinct cases of RP are presented here to evaluate the effectiveness of the pairing schemes. In RP, the UE is paired randomly, independent of channel gains or  
Figure 8: Average probability of outages for different pairing schemes of the WUE under ideal SIC and without HWD. Figure 7: Average probability of outages for different pairing schemes of the SUE under ideal SIC and without HWD. specific rules. As a result, they may not deliver consistent performance across various channel conditions. From Figures 7 and 8, it is evident that SW-SW pairing has significant improvement over other pairing schemes.