# Research on Polarization Coding Cooperative Communication Scheme for FSO System
## 5 Simulation Results and Analysis
Figure 5: BER of cooperative FSO communication system with different code lengths. In the FSO communication system, the outage probability performance of cooperative communication is better than that of a direct transmission link. Figure 6 compares the outage probability of the FSO cooperative communication system under different turbulence intensities. It can be seen from the figure that the system outage performance reaches the peak when the turbulence intensity is the smallest. With the increase in turbulence intensity, the interruption performance of the system decreases. When the turbulence intensity increases to a certain intensity, the FSO cooperative communication system can suppress the occurrence of interruption events under strong turbulence, and the interruption performance of the system is improved. For example, when the turbulence intensity increases from 1.00 to 2.00, the interruption performance of the system continues to decline. However, with the continuous enhancement of turbulence intensity, the deterioration of the system outage probability is restrained. When the turbulence intensity increases from 1.00 to 1.25, the interruption performance of the system decreases by several dB; when the turbulence intensity increases from 1.75 to 2.00, the outage performance of the system only deteriorates by about 2 dB--much less than the initial deterioration--so the deterioration degree of the outage probability of the system is improved. The impact of different communication distances on the outage probability of the FSO cooperative communication system when the fixed refractive index structure constant \(C_{n}^{2}\) is \(1.41\times 10^{-14}\) is shown in Figure 7. As can be seen from the figure, the interruption performance of the FSO cooperative communication system decreases with the increase in communication distance between the source node \(S\) and destination node \(D\). When the distance increases to a certain extent, the FSO cooperative communication system can suppress the deterioration of interruption performance. For example, when the communication distance increases from 2000 m to 4000 m and the signal-to-noise ratio is 5 dB, the outage probability of the FSO cooperative communication system increases by about one order of magnitude. At this time, the performance of outage probability decreases due to the increasing communication distance between the source node \(S\) and the destination node \(D\) and the long distance of the relay link. When the communication distance is greater than 4000 m, the interruption performance of the FSO cooperative communication system is improved. When the communication distance rises to 6000 m, the interruption probability of the FSO cooperative communication system drops below \(10^{-7}\). This results from the improved outage probability performance of the system by the use of a cooperative communication system. Although the increase in communication distance leads to an increase in atmospheric turbulence intensity, the addition of a relay link can effectively improve the outage probability performance of the communication system. Figure 6: Outage probability of cooperative FSO communication system under different turbulence intensity.