KEYWORDS: Turbulence, Free space optics, Receivers, Atmospheric turbulence, Signal attenuation, Systems modeling, Signal to noise ratio, Free space optical communications, Telecommunications, Performance modeling
When the beam waist radius of the receiver is significantly larger than that of the receiver, the free-space optical link is vulnerable to some optical capture risks in the physical layer. In this paper, we propose a new method to analyze the average secrecy capacity performance of the FSO system under Fisher-Snedecor (F)-distribution turbulence combined with the unified pointing error. As a key feature, we evaluate security performance in the presence of an external eavesdropper that exists anywhere on the same receiving plane as the receiver. Based on this model, we derive the exact average secrecy capacity expression and verify it by accurate Monte Carlo simulation. By using the expression, we analyze in detail the influence of the electrical signal-to-noise ratio of the main channel, the influence of different waist radius of the beam in the receiver plane on the average secrecy capacity performance under different turbulence conditions.