Irradiance probability density function for turbulence induced fading in free space optics

Area of Science:

• Optical Communications
• Atmospheric Optics
• Probability Theory

Background:

• Turbulence-induced fading significantly impacts free space optical (FSO) communication reliability.
• Existing models like lognormal and gamma-gamma distributions have limitations in accurately describing irradiance fluctuations under all scintillation conditions.

Purpose of the Study:

• To derive a novel irradiance probability density function (PDF) model for turbulence-induced fading in FSO systems.
• To enhance the accuracy of performance analysis for FSO systems operating under weak and strong scintillation.

Main Methods:

• The extended Rytov method was employed, incorporating a doubly stochastic process for large-scale scintillation.
• Small-scale irradiance fluctuations were modeled using a gamma distribution.
• Large-scale fluctuations were modeled using a combination of gamma and inverted gamma distributions, approximating lognormal behavior.

Main Results:

• Closed-form expressions for the probability density and cumulative density functions of the derived model were obtained.
• Model parameters were determined based on strong scintillation theory.
• The proposed model demonstrated excellent agreement with experimental data and previously published results, outperforming lognormal and gamma-gamma distributions.

Conclusions:

• The developed model provides a more accurate representation of irradiance fluctuations in FSO communications.
• The model's validity across weak and strong scintillation conditions, for both aperture averaging and point-like receivers, makes it suitable for performance analysis.
• This work contributes to the advancement of reliable optical wireless system design and analysis.