Vol. 56, Issue 2, pp. 219-231 (2026)

Abstract

This paper presents an analytical framework for modeling atmospheric turbulence in free-space optical (FSO) communication systems using the zero-boresight double Rician fading model. Unlike previous studies that characterize this model only in terms of irradiance statistics, this work derives a closed-form expression for the average bit error rate (ABER) under intensity modulation with direct detection (IM/DD) and on–off keying (OOK). The resulting expression enables efficient and accurate performance evaluation of FSO links across a wide range of turbulence conditions. To further improve link robustness, the influence of adaptive optics (AO) is incorporated into the double Rician fading model. The analysis considers the correction of different sets of Zernike modes and demonstrates how variations in their coefficients affect received signal stability and overall link quality. Numerical results show that compensating lower-order Zernike modes significantly reduces turbulence-induced fading and leads to notable improvements in ABER performance. These findings provide a practical basis for designing AO-assisted FSO systems capable of dynamic adaptation to varying atmospheric conditions.