Browsing by Author "Gökçe, Muhsin Caner"

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Adaptive optics effect on performance of BPSK-SIM oceanic optical wireless communication systems with aperture averaging in weak turbulence
(2020) Gökçe, Muhsin Caner; Baykal, Yahya; Ata, Yalçın; 7812
Turbulence-induced wavefront deformations cause the irradiance of an optical signal to fluctuate resulting a in serious degradation in the bit-error-rate (BER) performance of optical wireless communication (OWC) system. Adaptive optics is an effective technique to compensate for the wavefront aberrations to reduce the fluctuations in the received intensity. In this paper, we investigate how the adaptive optics technique affects the BER performance of an oceanic OWC (OOWC) system employing binary phase shift keying-subcarrier intensity modulation (BPSK-SIM) and aperture averaging. To evaluate BER performance in weak oceanic turbulence, the required entities such as the received optical power captured by a circular aperture and the aperture averaged scintillation index measuring the fluctuations in the received irradiance are derived. The effect of adaptive optics correction of various wavefront aberrations (i.e., tilt, defocus, astigmatism and the coma) on the BER performance is illustrated and the performance of the adaptive optics-OOWC system is compared to that of a non-adaptive optics OOWC system by the metric defined. (C) 2020 Elsevier Ltd. All rights reserved.
Analysis of wander and spreading of an optical beam by using the oceanic turbulence optical power spectrum
(2022) Gökçe, Muhsin Caner; Baykal, Yahya; Gökçe, Muhsin Caner
Variance of beam displacement and short-term and long-term spreading of a Gaussian beam propagating in the presence of underwater turbulence are examined by using the oceanic turbulence optical power spectrum (OTOPS). Analytical expressions for both beam wander displacement variance and beam spreading are presented. Results show that the underwater turbulent channel causes deflection from the on-axis mean irradiance and brings significant wander and spreading effects to the propagating Gaussian beam wave. The variations of beam wander and short- and long-term spreading are obtained depending on the underwater medium parameters such as the average temperature, average salinity concentration, temperature-salinity gradient ratio, and temperature and energy dissipation rates. In particular, the real values of the average temperature and salinity concentration of turbulent water are used to obtain the results. In addition, the effects of propagation distance, Gaussian beam source size, and wavelength are shown. The results demonstrate that the underwater turbulent channel brings displacements in the centroid and spreading of the optical beam.
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.
Aperture averaging and BER for Gaussian beam in underwater oceanic turbulence
(Elsevier Science Bv, 2018) Gokce, Muhsin Caner; Gökçe, Muhsin Caner; Baykal, Yahya; 28643; 7812
In an underwater wireless optical communication (UWOC) link, power fluctuations over finite-sized collecting lens are investigated for a horizontally propagating Gaussian beam wave. The power scintillation index, also known as the irradiance flux variance, for the received irradiance is evaluated in weak oceanic turbulence by using the Rytov method. This lets us further quantify the associated performance indicators, namely, the aperture averaging factor and the average bit-error rate (). The effects on the UWOC link performance of the oceanic turbulence parameters, i.e., the rate of dissipation of kinetic energy per unit mass of fluid, the rate of dissipation of mean-squared temperature, Kolmogorov microscale, the ratio of temperature to salinity contributions to the refractive index spectrum as well as system parameters, i.e., the receiver aperture diameter, Gaussian source size, laser wavelength and the link distance are investigated. (c) 2017 Elsevier B.V. All rights reserved.
Aperture averaging in multiple-input single-output free-space optical systems
(Optical Soc Amer, 2016) Gokce, Muhsin Caner; Gökçe, Muhsin Caner; Baykal, Yahya; Uysal, Murat; 28643; 7812; 124615
Multiple-input single-output (MISO) techniques are employed in free-space optical (FSO) links to mitigate the degrading effects of atmospheric turbulence. In this paper, for the MISO FSO system, a partially coherent radial array and a finite-sized receiver aperture are used at the transmitter and the receiver, respectively. Using the extended Huygens - Fresnel principle, we formulate the average power and the power correlation at the finite-sized slow detector in weak atmospheric turbulence. System performance indicators such as the power scintillation index and the aperture averaging factor are determined. Effects of the source size, ring radius, receiver aperture radius, link distance, and structure constant and the degree of source coherence are analyzed on the performance of the MISO FSO system. In the limiting cases, the numerical results are found to be the same when compared to the existing coherent and partially coherent Gaussian beam scintillation indices. (C) 2016 Optical Society of America
Aperture averaging in multiple-input single-output free-space optical systems
(Spie-soc Photo-optical instrumentation Engineers, 2015) Gokce, Muhsin C.; Gökçe, Muhsin Caner; Baykal, Yahya; Kamacioglu, Canan; Uysal, Murat; 28643; 7812; 124615
Multiple-input single-output systems are employed in free-space optical links to mitigate the degrading effects of atmospheric turbulence. We formulate the power scintillation as a function of transmitter and receiver coordinates in the presence of weak atmospheric turbulence by using the extended Huygens Fresnel principle. Then the effect of the receiver aperture averaging is quantified. To get consistent results, parameters are chosen within the range of validity of the wave structure functions. Radial array beams and a Gaussian weighting aperture function are used at the transmitter and the receiver, respectively. It is observed that the power scintillation decreases when the source size, the ring radius, the receiver aperture radius, and the number of array beamlet increase. However, increasing the number of array beamlets to more than three seems to have negligible effect on the power scintillation. It is further observed that the aperture averaging effect is stronger when radial array beams are employed instead of a single Gaussian beam. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)
Aperture averaging in strong oceanic turbulence
(Elsevier Science BV, 2018) Gökçe, Muhsin Caner; Baykal, Yahya; 28643; 7812
Receiver aperture averaging technique is employed in underwater wireless optical communication (UWOC) systems to mitigate the effects of oceanic turbulence, thus to improve the system performance. The irradiance flux variance is a measure of the intensity fluctuations on a lens of the receiver aperture. Using the modified Rytov theory which uses the small-scale and large-scale spatial filters, and our previously presented expression that shows the atmospheric structure constant in terms of oceanic turbulence parameters, we evaluate the irradiance flux variance and the aperture averaging factor of a spherical wave in strong oceanic turbulence. Irradiance flux variance variations are examined versus the oceanic turbulence parameters and the receiver aperture diameter are examined in strong oceanic turbulence. Also, the effect of the receiver aperture diameter on the aperture averaging factor is presented in strong oceanic turbulence.
Application of adaptive optics on bit error rate of M-ary pulse-position-modulated oceanic optical wireless communication systems
(2020) Gökçe, Muhsin Caner; Gökçe, Muhsin Caner; Ata, Yalçın; 7812
An adaptive optics correction arising from the sum of tilt, focus, astigmatism and coma components is applied to the bit error rate (BER) of M-ary pulse-position-modulated (PPM) oceanic optical wireless communication systems. The percentage reduction in BER is evaluated 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 and that of kinetic energy per unit mass of fluid under different data bit rates, avalanche photodiode (APD) average current gains and the M values of the M-ary PPM. Our findings indicate that the percentage reduction in BER becomes larger when the ratio of temperature to salinity contributions to the refractive index spectrum or the rate of dissipation of mean-squared temperature or the data bit rate or the M value of the M-ary PPM is smaller, and when the rate of dissipation of kinetic energy per unit mass of fluid or the APD average current gain is larger.
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.
Beam shaping effects on MIMO free-space optical communication systems
(Çankaya Üniversitesi, 2016) Gökçe, Muhsin Caner
Multiple Input Multiple Output (MIMO) systems are employed in Free Space Optical (FSO) communication links to improve the link reliability in the presence of atmospheric turbulence. In this thesis, we consider a MIMO FSO system with practical transmitter and receiver configurations that consists of a radial laser array with Gaussian beams and a detector array with Gaussian apertures. Using the extended Huygens-Fresnel principle in weak atmospheric turbulence, we have derived formulations to find the average power and the power correlations on the finite sized detectors. This lets us to quantify the performance metrics such as the power scintillation index, the aperture averaging factor and the average bit error rate () as a function of system parameters, i.e., transmitter and receiver ring radius, number of Gaussian laser beams, number of detectors, laser source size, detector aperture radius, degree of source coherence, link distance and the structure constant of atmosphere. At first, by the help of the derivations the performance of multiple-input single-output (MISO) FSO system is investigated using both for coherent and for partially coherent Gaussian sources. Then, we improve our derivations and investigate the performance of MIMO FSO systems. In this way, the performance of MIMO FSO system is compared to that of MISO FSO, single-input multiple-output (SIMO) FSO and single-input single-output (SISO) FSO systems. MISO systems are then employed in underwater wireless optical communication (UWOC) links to mitigate the degrading effects of oceanic turbulence. To quantify the scintillation index of the MISO UWOC system, the Huygens - Fresnel principle is used with the novel equivalent structure constant of atmosphere. The oceanic turbulence parameters such as rate of dissipation of mean-squared temperature, rate of dissipation of kinetic energy per unit mass of fluid, Kolmogorov microscale, the ratio of temperature to salinity contributions to the refractive index spectrum, link distance and the wavelength which are expressed by the novel equivalent structure constant of atmosphere. Using the Matlab program, we present graphs and investigate the effect of system parameters on the performance metrics.
Ber anaylsis for super lorentz-gaussian laser beamspropagating in turbulent media
(Gazi Univ, Fac Engineering Architecture, 2013) Gökçe, Muhsin Caner; Sarı, Filiz; Özek, Faruk; 28643
In this work, BER-SNR variation of super Lorentz-Gaussian laser beam that propagating horizontally path in turbulent media is analyzed. Using scintillation index which is obtained by extented Huygens-Fresnel principle, BER - SNR value is calculated. Matlab program is used to show BER - SNR variation depending on link distance and beamwidth. To conclude, in short link range, super Lorentz-Gaussian beam is proven to be better link performance superior to commercially available Gaussian beam.
BER performance ofM-ary pulse position modulated communication systems in anisotropic non-Kolmogorov turbulent atmosphere
(2022) Baykal, Yahya Kemal; Gökçe, Muhsin Caner; Gökçe, Muhsin Caner; 7812
We investigated the effect of anisotropic non-Kolmogorov atmospheric turbulence on the performance of the optical wireless systems whenM-ary Pulse Position Modulation (PPM) is applied to a Gaussian beam. The performance of the optical wireless systems that use avalanche photodetector at the receiver is evaluated in terms of the bit error rate (BER). The effects of the parameters, such as the anisotropy factors inx-ydirections, modulation order, data bit rate, equivalent load resistor, photodetector quantum efficiency, non-Kolmogorov turbulence power law exponent, beam source size, link length, photodetector gain and structure constant on BER of theM-ary PPM Gaussian beam propagating in anisotropic non-Kolmogorov atmospheric turbulence, are examined.
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.
Bit error rate analysis of MISO FSO systems
(Taylor & Francis Ltd, 2016) Gokce, Muhsin Caner; Gökçe, Muhsin Caner; Baykal, Yahya; Uysal, Murat; 28643; 7812; 124615
Multiple-input single-output (MISO) systems are employed in free space optical (FSO) links to mitigate the degrading effects of atmospheric turbulence. In this paper, we consider a MISO FSO system with practical transmitter and receiver configuration that consists of radial laser array with Gaussian beams and a Gaussian receiver aperture function. We have employed our previously derived formulation of the power scintillation in which Huygens-Fresnel principle was employed. Therefore, we choose system parameters within the range of validity of the wave structure functions. Using the on-off keying modulation and the log-normal probability distribution function, we quantify the average bit error rate (< BER >) of laser array beams in weak turbulence. It is observed that the radial array beams at the transmitter are more advantageous than the single Gaussian beam. However, increasing the number of array beamlets to more than three seems to have negligible effects on < BER >. It is further observed that < BER > decreases when the source size, the ring radius and the receiver aperture radius increase.
Correlation of multimode fields in atmospheric turbulence
(2023) Gökçe, Muhsin Caner; Gökçe, Muhsin Caner; Ata, Yalçın; Gerçekcioğlu, Hamza; 7812
Multimode field correlations are evaluated in atmospheric turbulence. High order field correlations are special cases of the results that we obtained in this paper. Field correlations are presented for various numbers of multimodes, various multimode contents of the same number of modes, and various high order modes versus the diagonal distance from various receiver points, source size, link length, structure constant, and the wavelength. Our results will be of help especially in the design of heterodyne systems operating in turbulent atmosphere and fiber coupling efficiency in systems employing multimode excitation.
Correlations of multimode optical incidences in a turbulent biological tissue
(2023) Gökçe, Muhsin Caner; Gökçe, Muhsin Caner; Gerçekcioğlu, Hamza; Ata, Yalçın; 7812
In a turbulent biological tissue, field correlations at the observation plane are found when a multimode optical incidence is used. For different multimode structures, variations of the multimode field correlations are evaluated against the biological tissue turbulence parameters, i.e., the strength coefficient of the refractive-index fluctuations, fractal dimension, characteristic length of heterogeneity, and the small length-scale factor. Using a chosen multimode content, for specific biological tissue types of liver parenchyma (mouse), intestinal epithelium (mouse), upper dermis (human), and deep dermis (mouse), field correlations are evaluated versus the strength coefficient of the refractive-index fluctuations and small length-scale factor. Again, with a chosen multimode content, behavior of the field correlations is studied against the strength coefficient of the refractive-index fluctuations for various diagonal lengths and the transverse coordinate at the observation plane. Finally, the field correlation versus the strength coefficient of the refractive-index fluctuations is reported for different single modes, which are special cases of multimode excitation. This topic is being reported in the literature for the first time, to our knowledge, and the presented results can be employed in many important biological tissue applications.
Coupling efficiency of multimode beam to fiber in atmospheric turbulence
(2023) Gökçe, Muhsin Caner; Baykal, Yahya; Ata, Yalçın; 7812
Atmospheric turbulence causes wavefront distortions in the propagated laser beam. By the beam shaping of the transmitted laser, wavefront distortions can be mitigated effectively. In this paper, we consider a shaped laser modeled by multimode beams at the transmitter and investigate the coupling of the light wave to a single-mode fiber under the atmospheric turbulence effect. We derive the light power on the coupling lens and light power accepted by the fiber core using the extended Huygens-Fresnel principle. Then, the fiber coupling efficiency (FCE) is scrutinized for different system parameters such as the number of modes of the transmit laser, link distance, structure constant of atmosphere, focal length and radius of the coupling lens, wavelength, source size, and the number of speckles (NOS).
Effect of anisotropy on performance of M-ary phase shift keying subcarrier intensity-modulated optical wireless communication links operating in strong oceanic turbulence
(2020) Gökçe, Muhsin Caner; Baykal, Yahya; Ata, Yalçın; 7812
In strong oceanic turbulence, the performance of M-ary phase shift keying subcarrier intensity-modulated optical wireless communication (OWC) links is investigated in terms of the bit-error-rate (BER) by considering the effect of anisotropy of the oceanic channel. To calculate the BER of the OWC link, a gamma-gamma statistical channel model is adopted. The extended Huygens-Fresnel principle and the asymptotic Rytov theory are used to obtain the received optical power and the large-scale and small-scale log-intensity variances, respectively. Our graphical illustrations include the BER versus anisotropic factor for various system parameters such as the modulation order, filter bandwidth, link distance, peak amplitude of each subcarrier and the oceanic turbulence parameters.
Effect of Partial Coherence on MISO FSO Systems
(IEEE, 2015) Gökçe, Muhsin Caner; Baykal, Yahya; Uysal, Murat; 28643
Multiple-input single-output (MISO) techniques are employed in free space optical (FSO) systems to mitigate the degrading effects of atmospheric turbulence and therefore the link reliability is improved. In this paper, we consider an incoherent radial array beams and a finite sized slow detector for MISO FSO systems. We have derived the average power and power correlation formulas on the finite sized slow detector using the Huygens Fresnel principle in weak atmospheric turbulence. This helps us to find the system performance, such as power scintillation and aperture averaging factor. Effect of system parameters such as the source size, the ring radius, the degree of coherence, the link distance, the structure constant and the receiver aperture radius are analyzed on the performance of MISO FSO systems.
Effect of partial coherence on signal-to-noise ratio performance of free space optical communication system in weak turbulence
(2022) Gökçe, Muhsin Caner; Aymelek, Görkem; Yolcu, Begüm; Kayam, Orkun; Ünal, Onur; Gökçe, Muhsin Caner; Baykal, Yahya
The effect of source coherence on the average signal-to-noise ratio SNR performance of free space optical communication (FSOC) systems operating in weak atmospheric turbulence is investigated with the help of the extended Huygens–Fresnel principle. For an FSOC system that uses a partially coherent laser source, first, the received power at the finite-sized receiver aperture is derived. Then, the power scintillation index is evaluated that reflects the aperture averaging. Using these derived optical entities, the variations of SNR are examined versus parameters such as the degree of source coherence, wavelength, link distance, source size, structure constant of atmosphere and the receiver aperture radius. Obtained results show that a decrease in the degree of source coherence has a positive effect on SNR.