## 4 Simulation of Communication Performance  
Following this, the Monte Carlo method is employed to generate the phase screens simulating the atmospheric turbulence-induced phase distortions, thereby facilitating the simulation of the error rate relationship expressed in Equation (11) and yielding insights into the evolving error rate trends of the airborne laser link. The atmospheric structure constant \(C_{n}^{2}\) is \(5\times 10^{-15}\) m\({}^{-2/3}\), and the transmission rate of the OOK signal is 5 Gb/s. At an altitude of \(h=5\) km and a speed of \(v=0.4\) Ma, Figure 5 depicts how the relationship between \(R_{BER}\) and \(R_{SNR-\mathrm{aero}}\) varies as light propagates at different angles. From this graph, it is evident that, as \(R_{SNR-\mathrm{aero}}\) increases, \(R_{BER}\) decreases accordingly. Under static conditions, the propagation of the beam is hardly affected by the directional airflow. Hence, it can be observed that aero-optical effects independently interfere with optical signals. Figure 4: Comparison of the spot distortion under different motion conditions. (**a**) \(v=0\) Ma; (**b**) \(v=0.4\) Ma; (**c**) \(v=0.6\) Ma; (**d**) \(v=0.8\) Ma. Figure 3: Schematic diagram of the laser direction angle. For instance, when the \(R_{SNR-\text{aero}}\) is \(7.81\times 10^{-6}\), the average \(R_{BER}\) is approximately \(2.24\times 10^{-5}\) without aerodynamic optical disturbances. However, under the four typical angles specified in this study, the emitted beam along direction angle 1 experiences minimal density fluctuations in the flow field, resulting in slight variations in the refractive index and an \(R_{BER}\) of approximately \(2.24\times 10^{-5}\). Similar simulation results apply to direction 4, with an \(R_{BER}\) of approximately \(6.04\times 10^{-5}\). Conversely, the \(R_{BER}\) exceeds \(1\times 10^{-4}\) for other directions under the same conditions. Direction 2 is mainly considered for the following simulation since motion conditions have a significant impact on the changing of the light spot in that direction. Figure 6 illustrates the variation in the BER under various aircraft speeds, assuming a flying altitude of \(h=5\) km. The turret's more intense compression effect on the air causes the corresponding average BER to increase dramatically at high speeds compared to low speeds. This makes the impact of moving conditions evident when compared to static situations. Figure 5: BER curves of different emitted angles under the flight conditions of \(h=5\) km and \(v=0.4\) Ma. Figure 6: BER curve for the communication performance under several typical moving speed conditions. Taking the flight speed as a single variable and fixing the SNR, the communication performance under the condition of the selected SNR is studied, in order to more intuitively portray the influence of motion speed on laser communication connection. The outcomes are displayed in Figure 7. The BER steadily rises as flight speed is increased. For every 0.1 Ma increase in flying speed, the SNR increases by around \(0.87\times 10^{-4}\) when the SNR is 10 dB. When the SNR is high, the BER increases as the speed increases. For example, when the speed increases from 0.4 Ma to 0.5 Ma, the BER increases by approximately \(1.4\times 10^{-5}\); however, the BER increases by just \(1.02\times 10^{-5}\) when the speed increases from 0.8 Ma to 0.9 Ma. The simulation results indicate that, as the flight speed increases, the BER gradually rises. Moreover, under high SNR conditions, the influence of the flight speed on the communication performance becomes more pronounced. The simulation results are shown in Figure 8, which shows how the BER varies with the SNR at various altitudes. The BER of laser communication systems operating at high altitudes is often lower than that at low altitudes because the static air density decreases with height. Compared to lower altitudes, the rarefied air at higher altitudes is more prone to compression, which causes more noticeable variations in air density with increasing flight speed.