Wongnigué Allassane Soro^1,, Amadou Soumahoro¹, Douatia Koné^{1, 2}, Aladji Kamagaté¹

Unmanned aerial vehicle (UAV)-assisted free-space optical (FSO) communication is a promising solution for rapidly deployable, high-capacity wireless networks. However, realistic channel characterization in tropical environments remains challenging because atmospheric attenuation, turbulence, pointing errors, and angle-of-arrival (AoA) fluctuations are often investigated independently and rarely using long-term site-specific meteorological data. This paper presents a unified statistical framework for modeling a UAV-assisted FSO link under the tropical savanna climate of Korhogo, northern Côte d’Ivoire. The proposed model jointly incorporates weather-dependent attenuation caused by rain, fog, humidity, and dust, Málaga-distributed atmospheric turbulence, pointing errors, and AoA fluctuations within a heterodyne-detection decode-and-forward relay architecture. Atmospheric attenuation parameters are derived from six years (2020–2025) of meteorological observations collected by the Korhogo station of the National Meteorological Agency (ANAM), enabling realistic channel characterization. Closed-form channel statistics are employed to evaluate the signal-to-noise ratio (SNR) and bit-error rate (BER). The results show seasonal atmospheric attenuation ranging from 0.81 dB/km during the dry season to 3.10 dB/km under severe rainy conditions. Increasing the UAV altitude from 200 m to 500 m extends the communication range from 2.5 km to 4.5 km for an SNR threshold of 10 dB, while the reliable transmission distance at a BER of 10⁻³ increases from 2.5 km to 3.2 km. More importantly, the analysis reveals a distance-dependent altitude trade-off. Beyond approximately 5 km, humidity-induced attenuation and beam divergence outweigh turbulence mitigation, challenging the common assumption that higher UAV altitudes always improve FSO performance. These findings provide practical design guidelines for deploying reliable UAV-assisted FSO systems in tropical environments.

Angle-of-Arrival fluctuations, Atmospheric attenuation, Atmospheric turbulence, Channel characterization, Málaga distribution, Pointing errors, UAV-FSO communications