Browsing by Author "Ata, Yalcin"

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Anisotropy effect on performance of subcarrier intensity modulated binary phase shift keying optical wireless communication links in weakly turbulent underwater channel
(Taylor & Francis Ltd, 2019) Baykal, Yahya; Gökçe, Muhsin Caner; Gokce, Muhsin C.; Ata, Yalcin; 7812
The effect of the anisotropy on the bit-error-rate (BER) performance of subcarrier intensity modulated (SIM) binary phase shift keying (BPSK) optical wireless communication (OWC) links operating in weakly turbulent underwater channels is examined. BER variations versus the anisotropic factor are examined when the bandwidth, photodetector responsivity, load resistor and the underwater turbulence parameters are varied. As anisotropy in the underwater channel becomes larger, SIM BPSK OWC links have better BER performance at any link and turbulence parameter.
Average channel capacity in anisotropic atmospheric non-Kolmogorov turbulent medium
(Elsevier, 2019) Ata, Yalcin; Gökçe, Muhsin Caner; Baykal, Yahya; Gokce, Muhsin Caner; 7812
The average channel capacity of a free space optical (FSO) communication system running an intensity modulated Gaussian beam is examined in anisotropic non-Kolmogorov atmospheric weak turbulence based on Rytov variance. Results are obtained by employing the log-normal distribution of irradiance fluctuations corresponding to weak turbulence regime. Our results show that average channel capacity increases together with the increase in anisotropy factor in x and y direction, non-Kolmogorov power law exponent, quantum efficiency of photo detector, Gaussian beam source size and the inner scale length. However, the average channel capacity is found to decrease when turbulence strength, link length and noise variance increase.
Average transmittance in non-Kolmogorov turbulence
(Elsevier Science Bv, 2013) Ata, Yalcin; Baykal, Yahya; Gercekcioglu, Hamza; 7812
Average transmittance in non-Kolmogorov turbulence is evaluated. Our recently published equivalent structure constant formulation is employed in our numerical evaluations. At the fixed propagation distance and wavelength, and at the corresponding equivalent structure constant, as the power law exponent of the non-Kolmogorov spectrum increases, the on-axis transmittance is found to decrease. At the same power law exponent of the non-Kolmogorov spectrum, the off-axis transmittance is obtained to be smaller than the on-axis transmittance. Off-axis transmittance variation versus the power law exponent shows that similar to the on-axis case, increase in the power law exponent eventually causes the off-axis transmittance to decrease, however this decrease occurs at larger power law exponent for larger off-axis distance. (C) 2013 Elsevier B.V. All rights reserved.
Binary Phase Shift Keying-Subcarrier Intensity Modulation Performance in Weak Oceanic Turbulence
(Elsevier, 2019) Gokce, Muhsin Caner; Gökçe, Muhsin Caner; Baykal, Yahya; Ata, Yalcin; 7812; 28643
The performance analysis of underwater wireless optical communication (UWOC) system that employs binary phase shift keying-subcarrier intensity modulation (BPSK-SIM) is investigated in weak oceanic turbulence. BPSK-SIM Gaussian beam and finite sized positive-intrinsic-negative (PIN) photodetector are employed at the transmitter and at the receiver, respectively. Bit error rate (BER) is taken as the performance indicator and in the evaluation of the BER, the required signal power and the aperture averaged scintillation index are obtained respectively by the use of the extended Huygens-Fresnel principle and the Rytov theory. Considering various noise types in underwater turbulence, BER variations are examined versus the oceanic turbulence parameters and the photodetector parameters, namely receiver aperture diameter, PIN-responsivity, noise factor, load resistor, and the electronic bandwidth. (c) 2019 Elsevier B.V. All rights reserved.
Effect of anisotropy on bit error rate for an asymmetrical Gaussian beam in a turbulent ocean
(Optical Soc Amer, 2018) Ata, Yalcin; Baykal, Yahya; 7812
Effect of anisotropy on the average bit error rate (BER) is investigated when an asymmetrical Gaussian beam is propagated in an anisotropic turbulent ocean. BER is found to decrease in response to an increase in anisotropy levels in the x and y directions. Higher average signal-to-noise ratio, wavelength, and microscale length yield smaller BER values. BER starts to rise with an increase in the asymmetrical beam source size in the x and y directions, source size ratio in the x and y directions, salinity and temperature contribution factor, the dissipation of the mean squared temperature, and the propagation distance. At the fixed source size ratio in the x and y directions of the asymmetrical beam source size, larger source sizes increase BER. An anisotropic turbulent ocean seems to exhibit better BER values as compared with an isotropic turbulent ocean. (c) 2018 Optical Society of America
Effect of strong atmospheric non-Kolmogorov turbulence on the M-ary PSK subcarrier intensity modulated free space optical communications system performance
(Optical Soc Amer, 2019) Ata, Yalcin; Gökçe, Muhsin Caner; Baykal, Yahya; Gokce, Muhsin C.; 7812
Atmospheric turbulence is one of the significant phenomena that degrades the free space optical (FSO) communications system performance, and thus designers need to define the requirements related to turbulence and optimize the system design to ensure optimum performance. The subcarrier intensity modulation (SIM) shows superiority in terms of bandwidth usage over the other modulation techniques. Performance of FSO communication systems exercising M-ary phase-shift-keying (PSK) SIM with the PIN photodiode receiver is evaluated in non-Kolmogorov strong atmospheric turbulence when a Gaussian beam is used as the excitation. Bit-error-rate (BER) of PSK SIM FSO communication systems is examined, and the results are presented versus the non-Kolmogorov atmospheric turbulence and positive-intrinsic-negative (PIN) photodetector parameters such as PIN photodetector responsivity, equivalent load resistor, modulation order, noise factor, bandwidth, propagation distance, and beam source size. (C) 2019 Optical Society of America
Error performance of optical wireless communication systems exercising BPSK subcarrier intensity modulation in non-Kolmogorov turbulent atmosphere
(Elsevier Science Bv, 2019) Ata, Yalcin; Gökçe, Muhsin Caner; Baykal, Yahya; Gokce, Muhsin Caner; 7812; 28643
Subcarrier intensity modulation (SIM) scheme is preferred due to efficient bandwidth usage superiority over other modulation techniques such as on-off keying (OOK), pulse position modulation (PPM). In this paper, we investigate the bit error rate (BER) performance of optical wireless communication (OWC) system using binary phase shift keying (BPSK) SIM in non-Kolmogorov turbulent atmosphere. We pay attention to the weak turbulence conditions by using Rytov approximation and considering that the receiver is a PIN photodetector. Propagating beam type is Gaussian. It is seen that BER performance of the BPSK SIM OWC is significantly affected from non-Kolmogorov power law exponent, load resistor, responsivity of the PIN photodetector, bandwidth, beam source size, turbulence strength and noise factor.
Fiber coupling efficiency in ocean with adaptive optics corrections
(2023) Gokce, Muhsin Caner; Ata, Yalcin; Baykal, Yahya; 7812
Underwater optical wireless communication (UOWC) is a very promising technology that enables high-speed data transfer through the use of laser beams in an oceanic turbulent medium. The high-tech fiber optical devices, which are already available in the market, can be integrated with the UOWC systems. When integration is achieved, oceanic turbulence, which distorts the wavefront of the propagating laser beam, plays an important role in reducing the fiber coupling efficiency (FCE), which in turn results in reducing the light power received from the fiber optical components. In this paper, we propose the use of the adaptive optics technique in a UOWC system to mitigate the effects of oceanic turbulence and boost the FCE. For this reason, the field correlation for a Gaussian laser beam is derived by using the Huygens-Fresnel principle. This way, the light power over the coupling lens and the light power accepted by the fiber core are formulated under the effect of adaptive optics corrections, which are repre-sented by the number of Zernike modes. The results demonstrate that under the oceanic turbulence effect, the FCE of the UOWC system employing adaptive optics is always larger than that of the UOWC system employing no adaptive optics.
Field correlation of spherical wave in underwater turbulent medium
(Optical Soc Amer, 2014) Ata, Yalcin; Baykal, Yahya; 7812
The absolute field correlation of the spherical wave in an underwater turbulent medium is investigated at the receiver plane by using the extended Huygens-Fresnel principle. Results denote that increase in the propagation distance, the rate of dissipation of the mean squared temperature, and microscale length cause reduction in the absolute field correlation. Field correlation increases when the wavelength and the rate of dissipation of the turbulent kinetic energy and parameters of temperature and salinity contribution to the turbulence decrease. Salinity dominated turbulence corrupts the absolute field correlation much more in comparison to the temperature dominated turbulence. Change in the receiver coordinate is found not to affect the absolute field correlation. (C) 2014 Optical Society of America
M-ary phase shift keying-subcarrier intensity modulation performance in strong oceanic turbulence
(Spie-soc Photo-optical instrumentation Engineers, 2019) Gokce, Muhsin Caner; Gökçe, Muhsin Caner; Baykal, Yahya; Ata, Yalcin; 7812
In strong oceanic turbulence, we investigate the bit error rate (BER) performance of underwater wireless optical communication links by employing phase shift keying subcarrier intensity modulated Gaussian laser beam at the transmitter and positive-intrinsic-negative photodetector having finite sized aperture at the receiver. Using the extended Huygens-Fresnel principle, which is conventionally used to analyze the optical beam propagation through turbulence, we evaluate the optical intensity and corresponding signal power over the receiver aperture. Gamma-gamma statistical model for the received intensity is adopted due to strong oceanic turbulence and the required aperture averaged scintillation for this model is obtained by the use of asymptotic Rytov theory. In our performance investigation, we consider the effects of various oceanic turbulences, modulation, receiver noise type, and the photodetector parameters on the BER performance. (C) 2019 Society of Photo-Optical Instrumentation Engineers (SPIE).
Performance of M-ary pulse position modulation for aeronautical uplink communications in an atmospheric turbulent medium
(Optical Soc Amer, 2019) Ata, Yalcin; Gökçe, Muhsin Caner; Baykal, Yahya; Gokce, Muhsin Caner; 7812
This paper discusses the bit-error-rate (BER) performance of an aeronautical uplink optical wireless communication system (OWCS) when a Gaussian beam is employed and the M-ary pulse position modulation technique is used in an atmospheric turbulent medium. Weak turbulence conditions and log-normal distribution are utilized. The Gaussian beam is assumed to propagate on a slant path, the transmitter being ground-based, and the airborne receiver is on-axis positioned. Variations of BER are obtained against the variations in the link length, Gaussian beam source size, zenith angle, wind speed, wavelength, modulation order, data bit rate, equivalent load resistor, avalanche photodetector gain, and detector quantum efficiency. It is observed that the performance of the aeronautical uplink OWCS is affected from atmospheric turbulence significantly. (C) 2019 Optical Society of America
Scintillations of optical plane and spherical waves in underwater turbulence
(Optical Soc Amer, 2014) Ata, Yalcin; Baykal, Yahya; 7812
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. (C) 2014 Optical Society of America
Structure functions for optical wave propagation in underwater medium
(Taylor & Francis Ltd, 2014) Ata, Yalcin; Baykal, Yahya; 7812
The features of the wave structure function (WSF) derived for spherical excitation in turbulent water are investigated. It is found that as the rate of the dissipation of turbulent kinetic energy e decreases, WSF increases. The rate of dissipation of the mean-squared temperature X-T is observed to be proportional to the WSF value. Deviation from the source and the receiver axis reveals greater turbulence effect. Salinity driven turbulence gives greater WSF values compared to the temperature driven turbulence. As expected, WSF is found to increase as the propagation distance increases.
The analysis of anisotropic the non-Kolmogorov turbulence effect on asymmetrical Gaussian beam propagation in a marine atmosphere
(Iop Publishing Ltd, 2019) Ata, Yalcin; Baykal, Yahya; 7812
The variations of the scintillation index of an asymmetrical Gaussian beam are investigated when the beam propagates in anisotropic non-Kolmogorov marine atmospheric turbulence. The results indicate that the scintillation decreases when the anisotropy factors in both x and y directions increase. Increases in the beam asymmetry ratio and the inner scale length increase the scintillation index level. The scintillations are found to increase as the propagation distance and structure constant increase, and as the wavelength decreases. Being valid for any asymmetry and anisotropic factor, for small values of the power law exponent, alpha of non-Kolmogorov marine atmospheric turbulence, the scintillation index tends to increase proportionally with alpha. However, as alpha is further increased, the scintillation index starts to decrease after reaching a peak value. Larger anisotropy in the non-Kolmogorov marine turbulence is found to be preferable since the scintillation index is found to decrease at large anisotropic factors.
Transmittance of multi Gaussian optical beams for uplink applications in atmospheric turbulence
(Ieee-inst Electrical Electronics Engineers inc, 2015) Ata, Yalcin; Baykal, Yahya; 7812
On-axis slant path uplink transmittance (used in short as transmittance throughout the text) for multi Gaussian optical beam in Kolmogorov atmospheric turbulent medium is investigated. It is observed that for both the flat-topped and the annular beams, as the propagation distance, wind speed and the zenith angle increase, the transmittance decreases. The transmittance of flat-topped beams increases when the number of beams, source size or the wavelength increases. For the annular beam, when the outer/inner beam size ratio is kept constant, larger source sizes yield larger transmittance values. Transmittance of the thicker annular beams is found to be larger than the transmittance of the thinner annular beams.
Turbulence effect on transmittance of atmospheric optics telecommunication system using dense wavelength division multiplexing
(Taylor & Francis Ltd, 2011) Ata, Yalcin; Baykal, Yahya; 7812
The effect of atmospheric turbulence on atmospheric optics telecommunication links employing dense wavelength division multiplexing (DWDM) systems is examined. For this purpose, transmittance obtained by using the MODTRAN (MODerate resolution atmospheric TRANsmission) code is modified by the transmittance due to turbulence when the incidence is a partially coherent optical beam. The spanned wavelengths cover the range employed in a practical DWDM system operating in the range of 1550 nm. The effect of turbulence is manifest as a decrease in the transmittance calculated by MODTRAN, being more effective when the incidence becomes less coherent.