## 6 Results and Analysis
The relationship between the SOP and the RF link's instantaneous SNR \(\lambda_{SR}\) in a mixed RF/FSO system is shown in Figure 4. The system is based on multi-user SWIPT, and the illegal eavesdropper experiences interference from the optimal user. Based on the simulation results, increasing \(\lambda_{SR}\) reduces the SOP of the system in a gradual manner. When \(\lambda_{SR}\)= 30 dB and \(\lambda_{IE}\) =2, 4, 6 and 8 dB, the mixed system's SOP are \(9.6\times 10^{-4}\), \(2.9\times 10^{-4}\), \(1.4\times 10^{-4}\) and \(4.0\times 10^{-5}\). Based on the findings, increasing \(\lambda_{IE}\) decreases the system's SOP, indicating that the optimal user's jamming signal to the eavesdropper improves PLS performance in the mixed system. Increasing the interference SNR of the optimal user can reduce eavesdropping channel quality, but it is restricted by transmission power. Thus, introducing optimal user interference and selecting appropriate transmit power can enhance the mixed system's secrecy performance. Figure 5 depicts the mixed system's SOP as a function of the RF link's Instantaneous SNR \(\lambda_{SR}\) when the optimal user at the source node adopts different values of energy  
Figure 4: Simulation of the SOP and the instantaneous SNR of the RF link of the RF/FSO system under different interference SNR \(\lambda_{IE}\) of the optimal user. Figure 3: Simulation of the SOP and the Instantaneous SNR of RF link for the RF/FSO system with the optimal user’s different numbers of interference antennas \(N_{I}\). conversion efficiency \(\eta\). The figure shows that the mixed system's SOP diminishes as \(\lambda_{SR}\) increases for different values of \(\eta\). When \(\lambda_{SR}\)= 30 dB and \(\eta\)= 0.3, 0.5, 0.7 and 0.9, the mixed system's SOP are \(9.7\times 10^{-4}\), \(4.2\times 10^{-4}\), \(2.2\times 10^{-4}\) and \(1.3\times 10^{-4}\), respectively. As the energy conversion efficiency of the optimal user increases, the SOP of the system decreases. The energy harvesting multi-user source node efficiently converts the relay's RF energy signal into DC, boosting both the stored energy and interference power of the optimal user relative to the illegal eavesdropper. Consequently, the jamming effect is improved, the communication quality of the illegal eavesdropper deteriorates, and the mixed system's PLS performance is improved. By improving the optimal user energy conversion efficiency scheme, the collected energy is more stable and that makes the system more secure. Figure 6 shows the ASC of the mixed RF/FSO system as a function of the instantaneous SNR \(\lambda_{SR}\) of the RF link when the optimal user adopts different time allocation factors \(\rho\). The simulation results show that the ASC of the system increases as \(\lambda_{SR}\) increases. When \(\lambda_{SR}\)= 30 dB and \(\rho=0.1\), 0.3, 0.5 and 0.7, the ASC values of the system are 1.8957, 1.9088, 1.9242 and 1.9464, respectively. This set of simulation data shows that the ASC of the mixed RF/FSO system can be effectively increased by increasing the time allocation factor \(\rho\). This is because as the time allocation factor \(\rho\) increases, the time taken by the relay to transmit the RF energy signal to the optimal user of the source node becomes longer in the first time slot and the RF energy received by the source node increases. The energy stored is higher, and the power of the optimal user to transmit interference signal to the eavesdropper is enhanced at the same time, which increases the interference effect of the optimal user on the illegal eavesdropper. Therefore, the communication quality and the mixed system's PLS performance are improved. Figure 5: Simulation of the security outage probability and the instantaneous signal-to-noise ratio of the RF link in RF/FSO system under different energy conversion efficiency \(\eta\) of the optimal user. Figure 6: Simulation of the average secrecy capacity and the instantaneous SNR of RF link in RF/FSO system when the optimal user uses different time allocation factors \(\rho\).