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    Wavelength Dependence of Underwater Turbulence Characterized Using Laser-Based White Light

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    MS Thesis - Omar Alkhazragi.pdf
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    2.079Mb
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    Description:
    thesis
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    Type
    Thesis
    Authors
    Alkhazragi, Omar cc
    Advisors
    Ooi, Boon S. cc
    Committee members
    Alouini, Mohamed-Slim cc
    Shihada, Basem cc
    Ng, Tien Khee cc
    Program
    Electrical Engineering
    KAUST Department
    Computer, Electrical and Mathematical Sciences and Engineering (CEMSE) Division
    Date
    2019-04
    Embargo End Date
    2020-04-18
    Permanent link to this record
    http://hdl.handle.net/10754/631898
    
    Metadata
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    Access Restrictions
    At the time of archiving, the student author of this thesis opted to temporarily restrict access to it. The full text of this thesis became available to the public after the expiration of the embargo on 2020-04-18.
    Abstract
    The means of communication in oceanic environments is currently dominated by sonar. Although it is reliable for long-distance transmission, the vision of internet of underwater things (IoUT) requires an alternate means for high-data-rate transmission. It is also envisaged that a networked underwater and above-water objects, such as sensor nodes, and autonomous underwater vehicles will benefit seafloor exploration. The use of laser-based optical communication is poised to realize this dream while working hand-in-hand with acoustic and radio-frequency technologies from the littoral zone to deep blue sea. While blue and green lasers are typically utilized depending on the optical properties of the water, laser-based white light is attractive in a number of aspects. In this thesis, we proposed and realized the use of white light to model the channel and to provide the immediate decision for the preferred system configuration, which is critical for developing reliable communication links, particularly, in the presence of turbulence, which makes the alignment of underwater wireless optical communication (UWOC) links challenging. Temperature and salinity changes are among factors that change the refraction index, giving rise to beam wander. This thesis explores the dependence of underwater turbulence on the wavelength. After comparing the performance of red, green, and blue lasers, an ultra-fast comprehensive method that utilizes a white-light source that can produce a wide range of wavelengths is implemented. Experimental results show an 80%-decrease in the scintillation index as the wavelength is increased from 480 to 680 nm in weak turbulence caused by a 0.02-℃/cm temperature gradient with a 40-ppt salt concentration, which emulates conditions found in the Red Sea. The effect of turbulence on the bit error ratio (BER) is also investigated experimentally. Temperature gradients increased the BER especially for shorter wavelengths. The results along long-transmission distances were verified using Monte Carlo simulations. The correlation matrix between wavelengths was studied, which is important for designing multiple-input multiple-output systems. The results obtained show that as the difference in the wavelengths increases, the correlation decreases. Based on the interplay among scintillations, scattering, absorption, and the correlation between different wavelengths, it is possible to design a more reliable UWOC link.
    Citation
    Alkhazragi, O. (2019). Wavelength Dependence of Underwater Turbulence Characterized Using Laser-Based White Light. KAUST Research Repository. https://doi.org/10.25781/KAUST-508LQ
    DOI
    10.25781/KAUST-508LQ
    ae974a485f413a2113503eed53cd6c53
    10.25781/KAUST-508LQ
    Scopus Count
    Collections
    Theses; Electrical Engineering Program; Computer, Electrical and Mathematical Sciences and Engineering (CEMSE) Division

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