Composite channel modeling and experimental investigation of free-space optical communications for urban scenario applications

In recent years, free space optical communication (FSO) has been extensively applied in the field of optical wireless communication due to its advantages of high bandwidth, low latency, and license-free spectrum. However, atmospheric turbulence, aerosol scattering and absorption, and platform pointing errors in urban environments severely impair communication reliability. To address these challenges, this paper proposes a composite channel model under the framework of an intensity modulation/direct detection (IM/DD) optical communication system, encompassing geometric transmission loss, atmospheric attenuation, turbulence-induced fading, and Rayleigh-distributed pointing errors. Based on this model, field tests were carried out with a self-developed FSOC terminal at a data rate of 2.5 Gbps under varying turbulence levels and meteorological conditions. The results demonstrate that, under weak to moderate turbulence, the system achieves stable transmission over link distances of 3 km to 13 km, with the average bit error rate approaching 10^-8 in favorable conditions. Experimental outcomes show close agreement with the model's predictions, thereby validating the accuracy and applicability of the composite channel model and providing a reliable reference for performance evaluation and link planning of urban FSO systems.