On the Effect of Air Bubbles-Induced Scattering on Turbid Waters: An Experimental UOWC Channel Modeling Approach

Abstract

The influence of the oceanic medium on the underwater optical wireless communication (UOWC) highlights the need for an accurate mathematical channel characterization that models the properties of realistic oceanic environments, significantly optimizing the development of practical UOWC system designs. However, a need remains to provide a deeper insight into the behavior of air bubbles in turbid waters. This article presents an analysis and a statistical characterization of the received optical power fluctuations when considering different air bubble sizes and levels of particle-induced scattering. Experimental measurements were conducted in a water tank, manipulating water turbidity levels by dissolving a commercial antacid. Afterward, some evaluation metrics, such as the scintillation index, the average outage duration, and the coherence time, are calculated to provide an analytical framework of the air bubbles-induced fading in turbid environments. Additionally, the statistical behavior of small and large air bubbles are analytically described through the generalized Gamma distribution and a mixture of two generalized Gamma distributions, respectively, and validated with a coefficient of determination above 0.95 for all the considered turbid waters. Results demonstrate that water turbidity dramatically affects the stochastic behavior of the underwater channel in the presence of air bubbles, resulting in a significant reduction in light blockage due to the collection of scattered photons. As a result, the scintillation index and the average outage duration are noticeably reduced for more turbid water.

Keywords

• Air bubbles
• fading channel
• oceanic turbulence
• scattering
• turbid water
• underwater optical wireless communication