The Experts below are selected from a list of 15885 Experts worldwide ranked by ideXlab platform
Yahya Baykal - One of the best experts on this subject based on the ideXlab platform.
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effect of eddy diffusivity ratio on underwater optical scintillation index
Journal of The Optical Society of America A-optics Image Science and Vision, 2017Co-Authors: Mohammed Elamassie, Murat Uysal, Yahya Baykal, Mohamed Abdallah, Khalid A QaraqeAbstract:The performance of underwater optical wireless communication systems is severely affected by the turbulence that occurs due to the fluctuations in the index of refraction. Most previous studies assume a simplifying, yet inaccurate, assumption in the turbulence spectrum model that the eddy diffusivity ratio is equal to unity. It is, however, well known that the eddy diffusivities of temperature and salt are different from each other in most underwater environments. In this paper, we obtain a simplified spatial power spectrum model of turbulent fluctuations of the seawater refraction index as an explicit function of eddy diffusivity ratio. Using the derived model, we obtain the scintillation index of optical plane and Spherical Waves and investigate the effect of the eddy diffusivity ratio.
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wave structure function and spatial coherence radius of plane and Spherical Waves propagating through oceanic turbulence
Optics Express, 2014Co-Authors: Yahya BaykalAbstract:The analytical formulae for the wave structure functions (WSF) and the spatial coherence radius of plane and Spherical Waves propagating through oceanic turbulence are derived. It is found that the Kolmogorov five-thirds power law of WSF is also valid for oceanic turbulence in the inertial range. The changes of the WSF and the spatial coherence radius versus different parameters of oceanic turbulence are examined.
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Scintillations of optical plane and Spherical Waves in underwater turbulence
Journal of The Optical Society of America A-optics Image Science and Vision, 2014Co-Authors: Yahya BaykalAbstract:The scintillation indices of optical plane and Spherical Waves propagating in underwater turbulent media are evaluated by using the Rytov method, and the variations in the scintillation indices are investigated when the rate of dissipation of mean squared temperature, the temperature and salinity fluctuations, the propagation distance, the wavelength, the Kolmogorov microscale length, and the rate of dissipation of the turbulent kinetic energy are varied. Results show that as in the atmosphere, also in underwater media the plane wave is more affected by turbulence as compared to the Spherical wave. The underwater turbulence effect becomes significant at 5–10 m for a plane wave and at 20–25 m for a Spherical wave. The turbulence effect is relatively small in deep water and is large at the surface of the water. Salinity-induced turbulence strongly dominates the scintillations compared to temperature-induced turbulence.
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formulation of correlations for general type beams in atmospheric turbulence
Journal of The Optical Society of America A-optics Image Science and Vision, 2006Co-Authors: Yahya BaykalAbstract:Log-amplitude and phase correlations of general-type beams are formulated in atmospheric turbulence. A general beam is described as the superposition of many sets of multimode contents, each mode being off-axis Hermite-Gaussian. Since the Rytov solution is utilized, the formulas are valid in the weakly turbulent regime. The results are presented in integral forms that should be numerically evaluated for the specific beam type of interest. Our general beam results correctly reduce to the existing solutions for the correlations of limiting-case beams such as higher-order single-mode, multimode, off-axis Hermite-Gaussian, Hermite-sinusoidal-Gaussian, higher-order-annular, flat-topped-Gaussian, and thus naturally fundamental mode, plane, and Spherical Waves. Scintillation index and phase fluctuations in atmospheric optical links employing such special beams will be examined in future using the results reported here.
Mohsen Kavehrad - One of the best experts on this subject based on the ideXlab platform.
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a novel statistical channel model for turbulence induced fading in free space optical systems
Journal of Lightwave Technology, 2015Co-Authors: Mohammadreza A Kashani, Murat Uysal, Mohsen KavehradAbstract:In this paper, we propose a new probability distribution function which accurately describes turbulence-induced fading under a wide range of turbulence conditions. The proposed model, termed double-generalized gamma (double GG), is based on a doubly stochastic theory of scintillation and developed via the product of two generalized gamma distributions. The proposed double GG distribution generalizes many existing turbulence channel models and provides an excellent fit to the published plane and Spherical Waves simulation data. Using this new statistical channel model, we derive closed form expressions for the outage probability and the average bit error as well as corresponding asymptotic expressions of free-space optical communication systems over turbulence channels. We demonstrate that our derived expressions cover many existing results in the literature earlier reported for gamma–gamma, double-Weibull and K channels as special cases.
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a novel statistical model for turbulence induced fading in free space optical systems
International Conference on Transparent Optical Networks, 2013Co-Authors: Mohammadreza A Kashani, Murat Uysal, Mohsen KavehradAbstract:In this paper, we propose a new probability distribution function which accurately describes turbulence-induced fading under a wide range of turbulence conditions. The proposed model, termed Double GG distribution, is based on a doubly stochastic theory of scintillation and developed via the product of two Generalized Gamma (GG) distributions. The proposed Double GG distribution generalizes many existing turbulence channel models in a closed-form expression and provides an excellent fit to the published plane and Spherical Waves simulation data. We finally evaluate the performance of a free-space optical system over the Double GG turbulence channel and derive closed-form expressions for the bit error rate, assuming intensity modulation/ direct detection with on-off keying.
Murat Uysal - One of the best experts on this subject based on the ideXlab platform.
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effect of eddy diffusivity ratio on underwater optical scintillation index
Journal of The Optical Society of America A-optics Image Science and Vision, 2017Co-Authors: Mohammed Elamassie, Murat Uysal, Yahya Baykal, Mohamed Abdallah, Khalid A QaraqeAbstract:The performance of underwater optical wireless communication systems is severely affected by the turbulence that occurs due to the fluctuations in the index of refraction. Most previous studies assume a simplifying, yet inaccurate, assumption in the turbulence spectrum model that the eddy diffusivity ratio is equal to unity. It is, however, well known that the eddy diffusivities of temperature and salt are different from each other in most underwater environments. In this paper, we obtain a simplified spatial power spectrum model of turbulent fluctuations of the seawater refraction index as an explicit function of eddy diffusivity ratio. Using the derived model, we obtain the scintillation index of optical plane and Spherical Waves and investigate the effect of the eddy diffusivity ratio.
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a novel statistical channel model for turbulence induced fading in free space optical systems
Journal of Lightwave Technology, 2015Co-Authors: Mohammadreza A Kashani, Murat Uysal, Mohsen KavehradAbstract:In this paper, we propose a new probability distribution function which accurately describes turbulence-induced fading under a wide range of turbulence conditions. The proposed model, termed double-generalized gamma (double GG), is based on a doubly stochastic theory of scintillation and developed via the product of two generalized gamma distributions. The proposed double GG distribution generalizes many existing turbulence channel models and provides an excellent fit to the published plane and Spherical Waves simulation data. Using this new statistical channel model, we derive closed form expressions for the outage probability and the average bit error as well as corresponding asymptotic expressions of free-space optical communication systems over turbulence channels. We demonstrate that our derived expressions cover many existing results in the literature earlier reported for gamma–gamma, double-Weibull and K channels as special cases.
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a novel statistical model for turbulence induced fading in free space optical systems
International Conference on Transparent Optical Networks, 2013Co-Authors: Mohammadreza A Kashani, Murat Uysal, Mohsen KavehradAbstract:In this paper, we propose a new probability distribution function which accurately describes turbulence-induced fading under a wide range of turbulence conditions. The proposed model, termed Double GG distribution, is based on a doubly stochastic theory of scintillation and developed via the product of two Generalized Gamma (GG) distributions. The proposed Double GG distribution generalizes many existing turbulence channel models in a closed-form expression and provides an excellent fit to the published plane and Spherical Waves simulation data. We finally evaluate the performance of a free-space optical system over the Double GG turbulence channel and derive closed-form expressions for the bit error rate, assuming intensity modulation/ direct detection with on-off keying.
Anders Bernland - One of the best experts on this subject based on the ideXlab platform.
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bandwidth limitations for scattering of higher order electromagnetic Spherical Waves with implications for the antenna scattering matrix
IEEE Transactions on Antennas and Propagation, 2012Co-Authors: Anders BernlandAbstract:Various physical limitations in electromagnetic theory and antenna theory have received considerable attention recently. However, there are no previous limitations on the scattering of higher order electromagnetic vector Spherical Waves, despite the widespread use of Spherical wave decompositions. In the present paper, bandwidth limitations on the scattering matrix are derived for a wide class of heterogeneous objects, in terms of their electrical size, shape and static material properties. In particular, it is seen that the order of the dominating term in the Rayleigh limit increases with the order of the Spherical wave. Furthermore, it is shown how the limitations place bounds on the antenna scattering matrix, thus introducing a new approach to physical limitations on antennas. Comparisons to other types of antenna limitations are given, and numerical simulations for two folded Spherical helix antennas and a directive Yagi-Uda antenna are included to illuminate and validate the theory. The results in this paper are derived using a general approach to derive limitations for passive systems: First, the low-frequency asymptotic expansion of the scattering matrix of a general scatterer is derived. This gives a set of sum rules, from which the limitations follow.
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bandwidth limitations for scattering of higher order electromagnetic Spherical Waves with implications for the antenna scattering matrix
Technical Report LUTEDX (TEAT-7214) 1-23 (2011); TEAT-7214 (2011), 2011Co-Authors: Anders BernlandAbstract:Various physical limitations in electromagnetic theory and antenna theory have received considerable attention recently. However, there are no previous limitations on the scattering of higher order electromagnetic vector Spherical Waves, despite the widespread use of Spherical wave decompositions. In the present paper, bandwidth limitations on the scattering matrix are derived for a wide class of heterogeneous objects, in terms of their electrical size, shape and static material properties. In particular, it is seen that the order of the dominating term in the Rayleigh limit increases with the order of the Spherical wave. Furthermore, it is shown how the limitations place bounds on the antenna scattering matrix, thus introducing a new approach to physical limitations on antennas. Comparisons to other types of antenna limitations are given, and numerical simulations for two folded Spherical helix antennas and a directive Yagi-Uda antenna are included to illuminate and validate the theory. The results in this paper are derived using a general approach to derive limitations for passive systems: First, the low-frequency asymptotic expansion of the scattering matrix of a general scatterer is derived. This gives a set of sum rules, from which the limitations follow. (Less)
Linyan Cui - One of the best experts on this subject based on the ideXlab platform.
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analysis of angle of arrival fluctuations for optical Waves propagation through weak anisotropic non kolmogorov turbulence
Optics Express, 2015Co-Authors: Linyan CuiAbstract:Analytical expressions for the variance of angle of arrival (AOA) fluctuations based on the Rytov approximation theory are derived for plane and Spherical Waves’ propagation through weak anisotropic non-Kolmogorov turbulence atmosphere. The anisotropic spectrum model based on the assumption of circular symmetry in the orthogonal plane throughout the path is adopted and it includes the same degree of anisotropy along the direction of propagation for all the turbulence cells size in the inertial sub-range. The derived expressions consider a single anisotropic coefficient describing the turbulence anisotropic property and a general spectral power law value in the range 3 to 4. They reduce correctly to the previously published analytic expressions for the cases of plane and Spherical Waves’ propagation through weak isotropic non-Kolmogorov turbulence for the special case of anisotropic factor equaling one. To reduce the complexity of the analytical results, the asymptotic-fit expressions are also derived and they fit well with the close-form ones. These results are useful for understanding the potential impact of deviations from the standard isotropic non-Kolmogorov turbulence atmosphere.
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analytical expressions for the angle of arrival fluctuations for optical Waves propagation through moderate to strong non kolmogorov refractive turbulence
Journal of The Optical Society of America A-optics Image Science and Vision, 2013Co-Authors: Linyan Cui, Bindang Xue, Fugen ZhouAbstract:The effects of moderate-to-strong non-Kolmogorov turbulence on the angle of arrival (AOA) fluctuations for plane and Spherical Waves are investigated in detail both analytically and numerically. New analytical expressions for the variance of AOA fluctuations are derived for moderate-to-strong non-Kolmogorov turbulence. The new expressions cover a wider range of non-Kolmogorov turbulence strength and reduce correctly to previously published analytic expressions for the cases of plane and Spherical wave propagation through both weak non-Kolmogorov turbulence and moderate-to-strong Kolmogorov turbulence cases. The final results indicate that, as turbulence strength becomes greater, the expressions developed with the Rytov theory deviate from those given in this work. This deviation becomes greater with stronger turbulence, up to moderate-to-strong turbulence strengths. Furthermore, general spectral power law has significant influence on the variance of AOA fluctuations in non-Kolmogorov turbulence. These results are useful for understanding the potential impact of deviations from the standard Kolmogorv spectrum.
