Statistical distribution of intensity fluctuations for underwater wireless optical channels in the presence of air bubbles

Abstract

Abstract-In this paper, we experimentally investigate the statistical distribution of intensity fluctuations for underwater wireless optical channels under different channel conditions, namely fresh and salty underwater channels with and without air bubbles. To do so, we first measure the received optical signal with a large number of samples. Based on the normalized acquired data the channel coherence time and the fluctuations probability density function (PDF) are obtained for different channel scenarios. Our experimental results show that salt attenuates the received signal while air bubbles mainly introduce severe intensity fluctuations. Moreover, we observe that log-normal distribution precisely fits the acquired data PDF for scintillation index (σ 2 I ) values less than 0.1, while Gamma-Gamma and K distributions aptly predict the intensity fluctuations for σ 2 I > 1. Since neither of these distributions are capable of predicting the received irradiance for 0.1 < σ 2 I < 1, we propose a combination of an exponential and a log-normal distributions to perfectly describe the acquired data PDF for such regimes of scintillation index.

Performance evaluation of underwater wireless optical communications links in the presence of different air bubble populations

“…However, many relevant studies have mostly focused on the effects of absorption and scattering by particles on the optical channel [6][7][8][9], system level design and demonstrations [10][11][12][13], underwater turbulence [14][15][16], and there is little study on the effect of air bubbles in UWOC channels [17]. Air bubbles in the oceans are mainly produced by breaking surface waves and rain [18].…”

Light based underwater wireless communications

“…This fact has recently been proven by a series of recent experimental results in Refs. [45][46][47]171, studying respectively the impact of air bubbles, and inhomogeneous salinity and temperature.…”

“…174,175) It was only recently that the impact of bubbles on the distribution of the irradiance has been investigated through a set of laboratory experiments. 47,171) These works essentially show that in the presence of air bubbles the distribution of the irradiance is accurately modeled by a mixture of the exponential distribution and the log-normal distribution which can also be replaced by the Gamma distribution. The presence of the log-normal distribution or equivalently the Gamma distribution agrees with previous studies suggesting its use to model underwater optical channels.…”

“…47, it is used to model the loss in the received energy caused by air bubbles. 47,171) Moreover, the use of Gamma distribution instead of the lognormal in the mixture model has been found to achieve a slightly higher accuracy.…”

“…The probability density functions of laser beam intensity fluctuations due to salty and bubbly underwater channels under various channel conditions were experimentally obtained by Jamali. 44) Weibull distribution was used to describe the statistics of salinityinduced turbulent UWOC channels. 45) The model showed an excellent fit with the measured data under all channel conditions emulated.…”