A Review of the Structure of Free-Space Optical Channel Models: Physical Meaning, Assumptions, and Atmospheric Conditions

Free-space optical (FSO) communication is an attractive high-capacity wireless technology for terrestrial, aerial, and satellite links. However, FSO performance is strongly affected by multiple impairments, including path loss, turbulence attenuation, pointing errors, and equipment loss. Therefore, accurate performance evaluation requires channel modelling that accounts for both deterministic power losses and stochastic channel effects. This paper presents a comprehensive and structured review of FSO channel modelling, covering the transmission, propagation medium, and receiver sections. The composite channel response is represented using a mathematical formulation. Commonly used FSO models are reviewed and organised, including Beer–Lambert and geometrical loss, Kim and Kruse path loss models, Lognormal, Gamma–Gamma, K, and Málaga distributions, along with pointing-error and angle-of-arrival models. Each model is explained in terms of its physical meaning, assumptions, and applicable operating conditions. Lastly, a numerical example is presented to demonstrate how deterministic losses and stochastic channel effects can be combined in FSO performance evaluation.