Unified Statistical Channel Model for Turbulence-Induced Fading in Underwater Wireless Optical Communication Systems

Abstract

A unified statistical model is proposed to characterize turbulence-induced fading in underwater wireless optical communication (UWOC) channels in the presence of air bubbles and temperature gradient for fresh and salty waters, based on experimental data. In this model, the channel irradiance fluctuations are characterized by the mixture Exponential-Generalized Gamma (EGG) distribution. We use the expectation maximization (EM) algorithm to obtain the maximum likelihood parameter estimation of the new model. Interestingly, the proposed model is shown to provide a perfect fit with the measured data under all channel conditions for both types of water. The major advantage of the new model is that it has a simple mathematical form making it attractive from a performance analysis point of view.Indeed, we show that the application of the EGG model leads to closed-form and analytically tractable expressions for key UWOC system performance metrics such as the outage probability, the average biterror rate, and the ergodic capacity. To the best of our knowledge, this is the first-ever comprehensive channel model addressing the statistics of optical beam irradiance fluctuations in underwater wireless optical channels due to both air bubbles and temperature gradient. E. Zedini and M. Hamdi are with the College Underwater wireless optical communication (UWOC), channel modeling, distribution fitting, maximum likelihood estimation, expectation maximization algorithm, mixture models, performance analysis, outage probability, bit-error rate (BER), ergodic capacity. I. INTRODUCTION Underwater wireless optical communication (UWOC) systems have recently attracted considerable research attention as an appropriate and efficient transmission solution for a variety of underwater applications including offshore oil field exploration, oceanographic data collection, maritime archaeology, environmental monitoring, disaster prevention, and port security among others [1]. This rapidly growing interest stems from the recent advances in signal processing, digital communication, and low-cost visible light-emitting diodes (LEDs) and laser diodes (LD) that have the lowest attenuation in seawater [2]-[5]. UWOC systems, operating in the blue/green portion of the spectrum in the 400-550 nm wavelength band, promise high data rates, low-latency, high transmission security, and reduced energy consumption, compared with their acoustic counterparts [1], [6], [7]. Nevertheless, the reliability of such systems is highly affected by absorption and scattering effects [1] as well as underwater optical turbulence (UOT). The identification of an accurate description for the absorption and scattering effects in UWOC channels has been extensively addressed in several recent works [8]-[10]. UOT results from rapid changes in the refractive index of the water caused by temperature fluctuations, salinity variations as well as the presence of air bubbles in seawater that affects the propagation of optical signals [11]-[13]. In oceans, air bubbles are produced by breakin...

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“…where E[·] is the expectation operator. The moment generating function (MGF) of the GGD can be derived in terms of the Fox's H function as [36,Eq. (27)]:…”

“…A closed-form expression for the ergodic capacity can be derived in terms of the Fox's H function as [36,Eq. (31)]:…”

“…where Γ(·, ·) is the upper incomplete Gamma function. The previous equation can also be derived in closed-form expression given by the Fox's H function as [36,Eq. (27)]:…”

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