Browsing by Author "Keskin, Aysan"

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Citation - WoS: 4
Citation - Scopus: 11
Effects of Focused and Collimated Laser Beams on the Performance of Underwater Wireless Optical Communication Links
(Ieee, 2015) Catmakas, Omer Kemal; Genc, Fatih; Baykal, Yahya; Arpali, Serap Altay; Arpali, Caglar; Keskin, Aysan
In this paper, the optical transmittance and bit error rate (BER) of focused and collimated laser beams are experimentally examined in an underwater optical wireless communication link with different water types. The water types used are fresh water, salty water and their variations with maalox in order to obtain turbid water. In bit error rate (BER) analysis, on-off keying (OOK) is used together with Bose-Chaudhuri-Hocquenghem (BCH) and convolutional codes. Results show that salt and maalox content decreases the transmittance, the convolution codes have better BER performance than BCH codes under the same modulation scheme (i.e., OOK) and focusing improves both the transmittance and BER performance as compared to collimated beams.
Citation - WoS: 5
Citation - Scopus: 4
Effects of Underwater Turbulence on Average Transmittance of Cos-Gaussian and Cosh-Gaussian Optical Beams
(Taylor & Francis Ltd, 2021) Baykal, Yahya; Keskin, Aysan
The impacts of underwater turbulence on the average optical transmittance are investigated when optical cosine-Gaussian and optical cosine-hyperbolic-Gaussian (cosh-Gaussian) beam propagate in weakly turbulent underwater medium. Findings obtained by using MATLAB reveal that when the displacement parameter is smaller (larger) for the cos-Gaussian (cosh-Gaussian) beam, the average transmittance increases. Also, an increase in the source size results in elevated average transmittance values. Rate of dissipation of kinetic energy per unit mass of fluid is found to be directly proportional to the average transmittance. However, the rate of dissipation of the mean-squared temperature is inversely proportional to the average transmittance. Average transmittance is found to be essentially the same when the temperature-induced optical turbulence is dominant. An increase in the salinity-induced optical turbulence suddenly reduces the average transmittance of the cos-Gaussian and cosh-Gaussian beam in underwater turbulence. Finally, it is observed that for the same sized beams in the same underwaterturbulent medium, cosh-Gaussian beam will have larger average transmittance than the corresponding cos-Gaussian beam. As the influence and value of our research conclusion on the development of our research, we comment that cosh-Gaussian beams can be preferred over the cos-Gaussian and Gaussian beams in obtaining larger average transmittance in underwater turbulence.
Citation - WoS: 11
Citation - Scopus: 14
Off-Axis Average Transmittance and Beam Spread of a Partially Coherent Flat-Topped Beam in a Turbulent Underwater Medium
(Optical Soc Amer, 2019) Keskin, Aysan; Baykal, Yahya
The effects of oceanic turbulence on the off-axis optical transmittance and beam spread are examined when a partially coherent flat-topped beam wave propagates in an underwater medium. To observe the oceanic turbulence effect, the power spectrum of homogeneous and isotropic oceanic water combining the effects of salinity and temperature is used. Employing the extended Huygens-Fresnel integral and Carter's definition for the general beam formulation that is applied to a partially coherent flat-topped beam, the effects of the parameters of power spectrum, the link on the off-axis average transmittance, and beam spread are analyzed. The results obtained with the help of the MATLAB program indicate that if the flatness of the optical beam increases, the average transmittance increases, and the beam spread decreases. Partial coherence is found to be inversely proportional to the average transmittance and directly proportional to beam spread. Increase in the source size is found to increase the average transmittance and to reduce the beam spread. Loss of the kinetic energy of fluid causes less turbulence. The rate of dissipation of kinetic energy per unit mass of fluid is directly proportional to the average transmittance, while it is inversely proportional to the beam spread. The rate of dissipation of the mean square temperature is inversely proportional to the average transmittance and directly proportional to the beam spread. When the temperature-induced optical turbulence is dominant, the average transmittance almost never decreases. However, the salinity-induced optical turbulence sharply reduces the average transmittance and increases the beam spread of the partially coherent flat-topped beam in underwater turbulence. When the off-axis parameter becomes larger, average transmittance decreases. (C) 2019 Optical Society of America
Citation - WoS: 5
Citation - Scopus: 5
Scintillation and Ber Analysis of Cosine and Cosine-Hyperbolic Beams in Turbulent Ocean
(Optical Soc Amer, 2021) Keskin, Aysan; Baykal, Yahya
Effects of source beam, link, and oceanic turbulence parameters on the scintillation index and bit error rate (BER) performance of cosine (cos) and cosine-hyperbolic (cosh) Gaussian light beams have been investigated in order to improve wireless optical communication link performance in oceanic turbulence. The Nikishov and Nikishov power spectrum of oceanic water and extendedHuygens Fresnel principle were used in our evaluations; the results were obtained viaMATLAB. The scintillation index andBERwere examined versus oceanic turbulence parameters, which are the rate of dissipation of mean-square temperature, the ratio of temperature and salinity contributions to the refractive index spectrum, and the dissipation rate of kinetic energy per unit fluid mass of fluid. Further, the scintillation index and BER are investigated against the source size, propagation distance, and complex displacement parameters of cos- and cosh-Gaussian beams. This study aimed to select the suitable sinusoidal beam to be employed in order to increase the performance of underwater wireless optical communication systems operating in oceanic turbulence. (C) 2021 Optical Society of America
Transmittance, scintillation and BER analysis in underwater optical wireless communication systems
(2020) Keskin, Aysan
Son yıllarda, yüksek hızlı veri iletiminin gereksinimleri nedeniyle sualtı kablosuz optik haberleşme sistemleri daha popüler olmuştur. Bu tezde, farklı ışık huzmelerinin ve performans kıstas ölçütlerinin sistem üzerine etkilerini inceleyerek, sualtı türbülansında kablosuz optik haberleşme performansının geliştirilmesi ele alındı. Geçirgenlik, ışın yayılması, parıldama, bit hata oranı gibi sualtı kablosuz optik haberleşme sistem performans ölçütleri üzerine okyanus türbülansının etkisi incelendi. Sistem performansını karşılaştırmak için kısmi eş fazlı düz tepeli, kosinüs Gauss, kısmi eş fazlı kosinüs Gauss, kosinüs hiperbolik Gauss ve kısmi eş fazlı kosinüs hiperbolik Gauss ışık huzmeleri kaynak olarak kullanıldı. Okyanus türbülansının sualtı kablosuz optik haberleşme sistemine etkisini incelemek için suyun güç spektrumu homojen ve izotropik olarak kabul edildi. Ortalama geçirgenliği analiz etmek için genişletilmiş Huygens Fresnel prensibi kullanıldı. Kısmi eş fazlı düz tepeli, kosinüs Gauss, kosinüs hiperbolik Gauss ve bunların kısmi eş fazlı formundaki ışık huzmeleri için eksen üzeri ve eksen dışı geçirgenlik incelendi. Carter tanımı yardımıyla kısmi eş fazlı düz tepeli ışık huzmesi için ışın yayılması gözlendi. Parıldama hesaplamaları için yine genişletilmiş Huygens Fresnel prensibinden yararlanıldı. Bunların dışında, okyanus türbülansının sualtı kablosuz optik haberleşme sistemlerinin önemli kriterlerden olan bit hata oranı üzerine etkisi gözlendi. Hesaplamalar MATLAB programı kullanılarak elde edildi. Bütün sistem performans ölçütlerine karşılık ortalama kare sıcaklık dağılım oranı, sıcaklık ve tuzluluk katkılarının kırılma indisi spektrumuna oranı, birim sıvı kütlesi için kinetik enerjinin dağılma hızı gibi önemli okyanus türbülansı parametreleri bu tez çalışmasında incelendi. Dahası eş fazlılık derecesi ve eksen dışı parametresi bu tezde gözlemlendi. Bu tez ile sualtı türbülanslı ortam için uygun huzmelerin seçilmesi hedeflenmiş ve çeşitli uyarımlar altında UWOC linklerinin performansları farklı yönlerden incelenmiştir.
Wireless optical wave propagation in underwater medium
(2013) Keskin, Aysan
In this thesis, the effects of the turbulence on the average transmittance are examined when the lowest order collimated Gaussian optical beam wave propagates in a wireless underwater medium. To observe the oceanic turbulence effect, the power spectrum of homogeneous and isotropic oceanic water combining the effects of salinity and temperature is used. Employing the Rytov method and the numeric integration, the effects of the parameters of power spectrum on the average transmittance are analyzed. Obtaining results with the help of Matlab program indicates that the rate of dissipation of the kinetic energy per unit mass of fluid is directly proportional to the average transmittance while the rate of dissipation of the mean-squared temperature is inversely proportional to the average transmittance. Increase in the link distance and decrease in the wavelength reduce the average transmittance. When the temperature-induced optical turbulence is dominant in the ratio of the salinity and temperature contributions to the refractive index spectrum, the average transmittance almost never decreases. However, the salinity-induced optical turbulence reduces the average transmittance sharply. Increasing the Kolmogorov microscale length, first the turbulence effect increases and the average transmittance decreases, but when the value of Kolmogorov microscale is further increased, the turbulence effect starts to decrease and the average transmittance increases, eventually a saturation is observed