## 1 Introduction
### Related Works  
In order to accurately analyze the impact of atmospheric turbulence on FSO communication systems, scholars have proposed many statistical decay models, including the Lognormal (LN) distribution [4], Negative Exponential distribution [5], \(\kappa\) distribution [6; 7], Gamma-Gamma distribution [8; 9], Malaga distribution [10], and Exponentiated Weibull (EW) distribution [11; 12]. For weak turbulence, [PERSON] et al. used LN distribution to model the probability density function of light irradiance. Negative Exponential and \(\kappa\) distributions are commonly used to simulate strong turbulent states. [PERSON] et al. proposed a modified Rytov theory, which led to the derivation of the Gamma-Gamma turbulence model. Due to its ability to simulate the changes from weak turbulence to strong turbulence, it has been widely used in the performance analysis of FSO systems. The Malaga distribution unifies most irradiance statistical models, including the LN distribution, \(\kappa\) distribution, and Gamma-Gamma distribution and is therefore considered a generalized turbulence model. Under all aperture averaging conditions, the EW distribution can provide good consistency with the probability density function (PDF) of light irradiance for simulation and experimental data in weak to strong turbulence and is commonly used to analyze the impact of aperture averaging technology on FSO system performance. In order to mitigate the impact of atmospheric environment on the performance of ground FSO communication systems and improve the reliability and availability of wireless optical communication links, a mixed FSO/RF transmission system combining FSO links and millimeter wave radio frequency (MMW-RF) links has been proposed. Mixed FSO/RF communication systems are generally divided into mixed FSO/RF dual-hop systems and hybrid FSO/RF parallel transmission systems. The mixed FSO/RF dual-hop system is an asymmetric dual-hop relay system that can effectively expand coverage and reduce the impact of atmospheric environment on the FSO system [13]. [PERSON] et al. [14] derived and analyzed the end-to-end average bit error rate (BER) expression for hybrid FSO/RF dual-hop systems based on the decode and forwarddecoding forwarding (DF) scheme under Exponential Weibull turbulence channels with nonzero boresight pointing error (PE) and Nakagami-m fading channels. The hybrid FSO/RF parallel transmission system is a cooperative communication system that can effectively improve communication system performance [15]. [PERSON] et al. [16] derived closed-form expressions of the bit error rate and outage probability of hybrid FSO/RF parallel systems based on a selective combination under Malaga turbulence with pointing errors and \(\eta-\mu\) fading RF channels. Due to the influence of turbulence, the performance of FSO communication systems deteriorates rapidly with the increase of transmission distance. A cooperative communication network based on multi-hop transmission (multi-hop relay-assisted network) is considered an effective solution to solve the problem [17]. [PERSON] et al. [18] derived mathematical expressions of the end-to-end average bit error rate and outage probability of parallel multi-hop FSO systems under Exponential Weibull turbulence with nonzero boresight pointing errors. [PERSON] et al. [19] deduced the expression of the end-to-end average bit error rate and outage probability of the parallel multi-hop relay FSO system under Gamma-Gamma turbulence with a pointing error and different weather conditions and analyzed the impact of plane wave and spherical wave beams on the performance of parallel multi-hop relay FSO system. In recent years, the development of unmanned aerial vehicle (UAV) technology has made UAV-assisted FSO communication a research hotspot for scientists [20; 21; 22; 23]. UAV-assisted FSO communication is achieved by installing laser transmitters, receivers, and other devices on the UAV to communicate with ground terminals.