Scattering regimes for underwater optical wireless communications using Monte Carlo simulation

Optical wireless communications has shown tremendous potential for underwater applications as it can provide higher bandwidth and better security compared to acoustic technologies. In this paper,  an investigation on scattering regimes for underwater links using Monte Carlo simulation has been presented.While the focus of this paper is on diffuse links, the simulation results of collimated links is also provided for comparison purpose. Three types of water namely clear, coastal and turbid water are being used in the simulation. It is shown that the effect of scattering on the path loss cannot be accurately modeled by the existing channel model; ie. Beers-Lambert (BL) law.  It has been shown that  the distance at which the unscattered light drops to zero can be used to estimate the transition point for the scattering regimes in case of diffuse links. The transition point for diffuse links in coastal water and turbid water can be estimated to be around 22 m and 4 m respectively. Further analysis on the scattering order probability at different scattering regimes illustrates how scattering is affected by beam size, water turbidity and distance. From the frequency response plot, it is estimated that the bandwidth of several order of GHz can be achieved when the links are operating in the minimal scattering region and will reduce to several hundreds of MHz when the link is operating in multiple scattering region

On the BER of Multiple-Input Multiple-Output Underwater Wireless Optical Communication Systems

In this paper we analyze and investigate the bit error rate (BER) performance of multiple-input multiple-output underwater wireless optical communication (MIMO-UWOC) systems. In addition to exact BER expressions, we also obtain an upper bound on the system BER. To effectively estimate the BER expressions, we use Gauss-Hermite quadrature formula as well as approximation to the sum of log-normal random variables. We confirm the accuracy of our analytical expressions by evaluating the BER through photon-counting approach. Our simulation results show that MIMO technique can mitigate the channel turbulence-induced fading and consequently, can partially extend the viable communication range, especially for channels with stronger turbulence

Investigation of Underwater Optical Wireless Communications with Turbulence

Turbulence is due to the random variations of the refractive index of the medium (in this case water), which leads to fluctuation or fading of the received light intensity. In wireless communications including underwater optical wireless communications the link performance is greatly affected. In this paper, we investigate the effect of turbulence on the probability density function (PDF) of the received light intensity. We show that lognormal and negative exponential distributions are fitted well with the PDFs of the received light intensity in weak-to-strong and saturated turbulence regimes. The goodness of fit test is performed to validate the conformity of these two distributions with the simulation results. Furthermore, we investigate the effect of the divergence angle of the Gaussian beam transmitter, the receiver’s aperture diameter and field of view on the scintillation index

Sea Water Channel for Underwater Communication

A potential underwater communication technology is water communication. Because of the limited physical scale, testing underwater data transmission in the laboratory differs from testing in a real-world water environment. Albeit fake dispersing specialists have been utilized to reproduce submerged correspondence through water channels under various correspondence climate conditions after the last many years, the comparability between test water and regular water isn’t dependable, for instance, the likeness of recurrence area qualities. It examines a number of distinct substances that precisely alter the water’s coefficients. As a reliability criterion for water recreation, the frequency range of data transmission through the test water’s water channel is then measured and compared. The findings demonstrate that the nature of the substances and the size of the particles have a significant impact on the properties of this water, and that the concentration of substances has an effect on the frequency domain portion of the water communication signal. If the water between the gaps contains a separate tx and rx module. Modules enable us to inform the onboard monitoring manager of marine scientist interactions and biomedical conditions

Cellular Underwater Wireless Optical CDMA Network: Potentials and Challenges

Underwater wireless optical communications is an emerging solution to the expanding demand for broadband links in oceans and seas. In this paper, a cellular underwater wireless optical code division multiple-access (UW-OCDMA) network is proposed to provide broadband links for commercial and military applications. The optical orthogonal codes (OOC) are employed as signature codes of underwater mobile users. Fundamental key aspects of the network such as its backhaul architecture, its potential applications and its design challenges are presented. In particular, the proposed network is used as infrastructure of centralized, decentralized and relay-assisted underwater sensor networks for high-speed real-time monitoring. Furthermore, a promising underwater localization and positioning scheme based on this cellular network is presented. Finally, probable design challenges such as cell edge coverage, blockage avoidance, power control and increasing the network capacity are addressed.Comment: 11 pages, 10 figure

Effects of Turbulence Induced Scattering on Underwater Optical Wireless Communications

This paper presents a comprehensive description of the relative effect of optical underwater turbulence in combination with absorption and scattering. Turbulence induced scattering is shown to cause and increase both spatial and temporal spreading at the receiver plane. It is also demonstrated that the relative impact of turbulence on a received signal is lower in a highly scattering channel. Received intensity distributions are presented confirming that fluctuations in received power from this method follow the commonly used Log-Normal fading model. The impact of turbulence induced scattering on maximum achievable data rate in the underwater channel is investigated.Comment: 9 pages, 10 figures and 3 table

Impulse response modeling for underwater optical wireless channels

In underwater optical wireless communication (UOWC) channels, impulse response is widely used to describe the temporal dispersion of the received signals. In this paper, we propose a new function to model the impulse response in most realistic cases in UOWC channels. By exploiting the inherent properties of such channels, our newly proposed model is superior to the conventional weighted double gamma functions (WDGF) model in explaining the behavior of the channel. We use Monte Carlo simulation to verify that our newly proposed model has a better accuracy of numerical fitting in most cases. Therefore, this new modeling approach offers a more convenient way to evaluate the performance of different kinds of UOWC channels

Investigation of the Scattering Noise in Underwater Optical Wireless Communications

In underwater optical wireless communications (UOWC), scattering of the propagating light beam results in both intensity and phase variations, which limit the transmission link range and channel bandwidth, respectively. Scattering of photons while propagating through the channel is a random process, which results in the channel-dependent scattering noise. In this work, we introduce for the first time an analytical model for this noise and investigate its effect on the bit error rate performance of the UOWC system for three types of waters and a range of transmission link spans. We show that, for a short range of un-clear water or a longer range of clear water, the number of photons experiencing scattering is high, thus leading to the increased scattering noise. The results demonstrate that the FEC limit of 3×10−3 and considering the scattering noise, the maximum link spans are 51.5, 20, and 4.6 m for the clear, coastal, and harbor waters, respectively

Modeling of underwater wireless optical communication channel by Monte Carlo based radiative transfer equation

Önemli askeri ve endüstriyel uygulama alanlarından dolayı, sualtı ortamında gerçek zamanlı ve yüksek hızlı bilgi iletişimi sağlayabilen sualtı kablosuz optik haberleşme (Underwater Wireless Optical Communication, UWOC) sistemlerine olan ilgi giderek artmaktadır. Güvenilir UWOC sistemlerinin tasarlanabilmesi için sualtı kablosuz optik haberleşme kanal karakteristiğinin gerçekçi ve doğru bir şekilde ortaya konulması önem arz etmektedir. Sualtı ortamının benzersiz optik özelliklerinden dolayı fazlasıyla karmaşık bir yapıya sahip olan UWOC kanalı, ışınım transfer denklemi (Radiative Transfer Equation, RTE) ile tamamen modellenebilmektedir. Fakat, RTE’nin kesin bir analitik çözümünü bulmak zordur. Bu çalışmada, RTE’nin yüksek doğrulukta çözümü ve UWOC kanal karakteristiğinin elde edilebilmesi için kullanılan Monte Carlo yaklaşımı ve işlem adımları detaylı olarak verilmiştir. Literatürde yaygın olarak kullanılan farklı su türleri için UWOC kanalının birim vuruş tepkileri elde edilmiş olup, kanal karakteristiklerinin yüksek doğruluğu ve hassasiyeti için yaklaşık modeller yerine literatürde kabul gören deneysel ölçümler dikkate alınmıştır. Elde edilen sonuçlara göre, UWOC sisteminin bilgi iletişim mesafeleri ele alınan su türleri için karşılaştırılmıştır.Due to the important military and industrial application areas, the interest in underwater wireless optical communication (UWOC) systems, which can support real-time and high-speed data communication in the underwater environment, gradually increases. In order to design reliable UWOC systems, it is important to reveal realistic and accurate underwater wireless optical communication channel characteristics. UWOC channel, which has a very complex structure due to the unique optical characteristics of the underwater environment, can be fully modeled by the radiative transfer equation (RTE). However, it is difficult to find an exact analytical solution of RTE. In this study, Monte Carlo approach and its operation steps are given in detail for the high accuracy solution of RTE and obtaining UWOC channel characteristic. For the different water types commonly used in the literature, the impulse responses of UWOC channel have been obtained and instead of approximate models experimental measurements recognized in the literature have been considered for the high accuracy and precision of the channel characteristics. According to the obtained results, data communication distances of the UWOC system are compared for the considered water type

CACA-UAN: a context-aware communication approach to efficient and reliable underwater acoustic sensor networks

Underwater Acoustic Sensor Networks (UANs) have emerged as a promising technology recently which can be applied in many areas such as military and civil, where the communication between devices is crucial and challenging due to the unique characteristics of underwater acoustic-based environment, such as high latency and low bandwidth. In this paper, context awareness is applied to the design of an underwater communication approach, called Context-Aware Communication Approach for a UAN (CACA-UAN), which aims to improve the overall performance of the underwater communication. According to the results, the proposed CACA-UAN can increase the efficiency and reliability of the underwater communication syste