Elektrik Elektronik Mühendisliği Bölümü Yayın Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/411
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Conference Object Citation - WoS: 2Flat-Topped Field Correlations in Extremely Strong Turbulence(Electromagnetics Acad, 2011) Baykal, Yahya Kemal; Baykal, Yahya; Elektrik-Elektronik MühendisliğiIn extremely strong turbulent horizontal atmospheric optical links, field correlations of flat-topped Gaussian incidence are evaluated. Field correlations are represented versus the diagonal distance at the receiver plane, for variations in the number of beams forming the flat-topped structure, receiver points, source sizes, link lengths, structure constants and the wave-lengths. Our results in extremely strong turbulence are compared to their free space counterparts which only reflect the diffraction patterns at the receiver plane. The effects of the inner scale of turbulence on the field correlations in extremely strong turbulence are examined in detail and it is observed that the size of the inner scale in extremely strong turbulence can considerably influence the field correlations of flat-topped beams.Article Citation - WoS: 3Citation - Scopus: 2Snr Advantage of Anisotropy in Oceanic Optical Wireless Communications Links(Optical Soc Amer, 2019) Baykal, YahyaSignal-to-noise ratio (SNR) of an optical wireless communication (OWC) link that operates in anisotropic oceanic turbulence is evaluated. To find the SNR advantage of the anisotropy in the oceanic turbulent medium, SNR in anisotropic oceanic turbulence is normalized by the SNR in isotropic oceanic turbulence. The dB values of this normalized SNR are examined versus the oceanic turbulence parameters of the ratio of temperature to salinity contributions to the refractive index spectrum, the rate of dissipation of mean-squared temperature, the rate of dissipation of kinetic energy per unit mass of fluid at various oceanic anisotropic factors, the avalanche multiplication factors, the radii of receiver aperture, link lengths, and detector responsivity values. It is found that as the oceanic turbulence becomes more anisotropic, at any link parameter, the SNR of the OWC link becomes advantageous over the isotropic counterpart. (c) 2019 Optical Society of AmericaConference Object Citation - Scopus: 1Intensity Fluctuations of Incoherently Superposed Gaussian Beams in Atmospheric Turbulence(Spie-int Soc Optical Engineering, 2010) Baykal, YahyaIntensity fluctuations of incoherently superposed Gaussian beams are formulated in weak turbulence by employing the extended Huygens-Fresnel principle. Each individual beam superposed is taken to be fully incoherent. The scintillation index evaluated for different number of beams indicates that as the number of beams increase, scintillations decrease. Incoherent superposition of smaller sized Gaussian sources exhibits smaller fluctuations. Comparing the scintillation index arising from incoherently superposed Gaussian beams to the scintillation index of coherently superposed Gaussian beams of the same structure shows that incoherent superposition yields lower intensity fluctuations, thus can be advantageous in atmospheric optical communication links.Article Citation - WoS: 11Citation - Scopus: 12Anisotropy Effect on Performance of Ppm Optical Wireless Oceanic Communication Links(Pergamon-elsevier Science Ltd, 2019) Baykal, YahyaThe performance, quantified by the bit-error-rate (BER), of M-ary pulse position modulated (PPM) optical wireless oceanic communication (OWOC) link is investigated when such a link operates in anisotropic weak oceanic turbulence. For this purpose, formulations of the average received power and the scintillation index of collimated Gaussian optical beam detected by a point detector are developed for anisotropic weak oceanic turbulence, which in turn are employed in the BER expression of the PPM OWOC links. BER is evaluated under various turbulence parameters of anisotropic oceanic turbulence, M of M-ary PPM, data bit rate, average current gain of avalanche photodiode (APD). For any investigated parameter, it is found that the BER performance of M-ary PPM OWOC links is improved as the ocean becomes more anisotropic. (C) 2019 Elsevier Ltd. All rights reserved.Article Citation - WoS: 21Citation - Scopus: 21Signal-To Ratio Reduction Due To Oceanic Turbulence in Oceanic Wireless Optical Communication Links(Elsevier Science Bv, 2018) Baykal, YahyaThe effect of oceanic turbulence on the signal-to-noise ratio (SNR) at the receiver of an oceanic wireless optical communication (OWOC) link is studied. To quantify such effect, the metric employed is the reduction in the SNR when oceanic turbulence is present. SNR reduction due to oceanic turbulence is formulated by subtracting the 10 log (SNR) evaluated at the receiver in the presence of turbulence from the 10 log (SNR) evaluated at the receiver in the absence of turbulence. Classical SNR formula which is function of the received optical power, noise and optical detector parameters is utilized. As the average received power, our earlier result that uses a Gaussian optical source field and a finite Gaussian receiver aperture in atmospheric turbulence is adapted for oceanic turbulence and such found average received power is inserted in the SNR expression. OWOC links that use collimated Gaussian optical sources at the transmitter and PIN photodiode, avalanche photodiode (APD) at the receiver, are analyzed. Results that present the variations of the SNR reduction due to oceanic turbulence against the changes in the source, oceanic turbulence and the optical receiver parameters are reported.Article Citation - WoS: 30Citation - Scopus: 32Bit Error Rate of Pulse Position Modulated Optical Wireless Communication Links in Oceanic Turbulence(Optical Soc Amer, 2018) Baykal, YahyaThe upper bound of the average bit error rate (BER) of a pulse position modulated (PPM) optical wireless communication (OWC) link operating in oceanic turbulence is formulated. BER variations against the changes in the ratio of temperature to salinity contributions to the refractive index spectrum, the rate of dissipation of mean-squared temperature, and the rate of dissipation of kinetic energy per unit mass of fluid are found at various data bit rates, average current gains of the avalanche photodiode (APD), and M values of the M-ary PPM. It is found that under any oceanic turbulence parameters, BER performance of the PPM OWC system becomes favorable at smaller data bit rates, M values, and at larger average current gains of APD. (c) 2018 Optical Society of AmericaArticle Citation - WoS: 28Citation - Scopus: 29Higher Order Mode Laser Beam Intensity Fluctuations in Strong Oceanic Turbulence(Elsevier Science Bv, 2017) Baykal, YahyaIntensity fluctuations of the higher order mode laser beams are evaluated when these beams propagate in a medium exhibiting strong oceanic turbulence. Out formulation involves the modified Rytov solution that extends the Rytov solution to cover strong turbulence as well, and our recently reported expression that relates the atmospheric turbulence structure constant to the oceanic turbulence parameters and oceanic wireless optical communication link parameters. The variations of the intensity fluctuations are reported against the changes of the ratio of temperature to salinity contributions to the refractive index spectrum, rate of dissipation of kinetic energy per unit mass of fluid, rate of dissipation of mean-squared temperature, viscosity and the source size of the higher order mode laser beam. Our results indicate that under any oceanic turbulence parameters, it is advantageous to employ higher order laser modes in reducing the scintillation noise in wireless optical communication links operating in a strongly turbulent ocean.Article Citation - WoS: 23Citation - Scopus: 23Ber of Asymmetrical Optical Beams in Oceanic and Marine Atmospheric Media(Elsevier Science Bv, 2017) Baykal, YahyaThe average bit-error-rate (BER) performances of asymmetrical optical Gaussian beams propagating in oceanic and marine atmospheric turbulence are examined. Both type of media are assumed to exhibit weak turbulence. The effect of asymmetry factor on the BER performance are investigated in conjunction with the oceanic turbulence parameters of the ratio of temperature to salinity contributions to the refractive index spectrum, the rate of dissipation of mean-squared temperature and the rate of dissipation of kinetic energy per unit mass of fluid, and with the marine atmospheric link parameters of the link length and the structure constant. Also, the variations of the BER against the source size of various asymmetrical beams are scrutinized in both oceanic and marine atmospheric media.Article Citation - WoS: 12Citation - Scopus: 12Scintillation Index of Higher Order Mode Laser Beams in Strong Turbulence(Elsevier Science Bv, 2017) Baykal, YahyaThe scintillation index of higher order laser modes is examined in strong atmospheric turbulence. In our formulation, modified Rytov theory is employed with the inclusion of existing modified turbulence spectrum which presents the atmospheric turbulence spectrum as a linear filter having refractive and diffractive spatial frequency cutoffs. Variations of the scintillation index in strong atmospheric turbulence are shown against the weak turbulence plane wave scintillation index for various higher order laser modes of different sizes. Use of higher order modes in optical wireless communication links operating in strongly turbulent atmosphere is found to be advantageous in reducing the scintillation noise.Article Citation - WoS: 28Citation - Scopus: 30Effect of Anisotropy on Intensity Fluctuations in Oceanic Turbulence(Taylor & Francis Ltd, 2018) Baykal, YahyaFor an optical spherical wave propagating in an oceanic turbulent medium, the effect of anisotropy on the received intensity fluctuations is investigated. For different anisotropy factors, the variations of the scintillation index vs. the ratio that determines the relative strength of temperature and salinity in the index fluctuations, the rate of dissipation of the mean squared temperature, the rate of dissipation of the turbulent kinetic energy, viscosity, link length and the wavelength are plotted. It is found that, for all the oceanic turbulence and the link parameters of interest, as the medium becomes more anisotropic, the intensity of the optical spherical wave fluctuates less. It is concluded that the performance of an optical wireless communication systems (OWCS) operating in anisotropic oceanic turbulence is better than the performance of OWCS operating in isotropic oceanic turbulence.