Scintillation Index of Plane and Spherical Laser Beams Propagating in Arbitrary Oceanic Turbulence

Oceanic turbulence changes the propagation behavior of laser beams, causing degradation of light intensity, phase and degree of coherence at the received aperture. The degradation derives from fluctuations of light field statistics, and causes key metrics to deteriorate in underwater wireless optical communication (UWOC), e.g., the scintillation index. The analytical evaluation of turbulent effects on the scintillation index connects turbulence-induced refractive index fluctuation with tractable fading models, providing physically meaningful results for channel modeling, link budget analysis and system design of UWOC especially with intensity modulation and direct detection. In this work we apply the state-of-art oceanic turbulent model with generality and accuracy from [1] into the calculation of the scintillation index for plane and spherical waves, paving the way for fading channel modeling in UWOC directly. Specifically, we calculate the Rytov variances, present the analysis of the scintillation index, and derive the semi-analytical expressions. Since we adopt a large number of tunable parameters for oceanic turbulence optical spectrum, this work includes comprehensive considerations of the second- and fourth-order statistics related metrics under arbitrary turbulent settings. We numerically evaluate the Rytov variations and scintillation index, under different settings of the average temperature, salinity, dissipation rates for the fluid kinetic energy per unit mass, the ensemble-averaged variances of the temperature spectrum, link range, and receiving aperture diameter. Note that the evaluations are conducted under the model with the best trade-off on accuracy and generality describing the natural oceanic environments hitherto. The main contributions are summarized as follows: (1) We have extended the numerical analysis of spherical waves in prior works into the semi-analytical analysis of plane and spherical waves; (2) We further provide results under much more general and complex oceanic turbulence compared with prior works. It is plausible that this work provides fundamental insights for fading channel modeling, link predicting, system design, and deployment of UWOC in the natural oceanic environment.