Browsing by Author "Gokce, Muhsin Caner"

Now showing 1 - 20 of 41

Citation - WoS: 2
Citation - Scopus: 3
Adaptive Optics Compensation of M-Ary Pulse Position Modulated Communication Systems in Anisotropic Non-Kolmogorov Turbulent Atmosphere
(Elsevier, 2021) Ata, Yalcin; Baykal, Yahya; Gokce, Muhsin Caner
Adaptive optics compensation effect on the performance of an optical wireless communication system (OWC) employing M-ary pulse position modulation (PPM) scheme in anisotropic non-Kolmogorov turbulent atmosphere is investigated. Avalanche photodetector (APD) is used at the receiver side and log-normal channel that models the weak turbulence conditions is utilized. Anisotropy, generally resulting in better performance in OWC systems operating in the turbulent medium, combined with the adaptive optics applications will enhance the bit-error-rate (BER) of the OWC systems significantly. Results are obtained depending on various parameters for both the turbulent atmosphere and the receiver. Our work gives OWC system designers a perspective to optimize their design.
Citation - WoS: 13
Citation - Scopus: 15
Adaptive optics effect on performance of BPSK-SIM oceanic optical wireless communication systems with aperture averaging in weak turbulence
(Pergamon-elsevier Science Ltd, 2020) Gokce, Muhsin Caner; Baykal, Yahya; Ata, Yalcin; 7812; Elektronik ve Haberleşme Mühendisliği
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.
Citation - WoS: 8
Citation - Scopus: 11
Analysis of Optical Wireless Mimo Communication in Underwater Medium
(Ieee-inst Electrical Electronics Engineers inc, 2024) Ata, Yalcin; Baykal, Yahya; Gokce, Muhsin Caner
Leveraging on the multiple-input-multiple-output (MIMO) application for enabling high data rates and ensuring reliable communication between underwater platforms connected to underwater sensor network, this article presents a comprehensive analysis of the performance of optical wireless MIMO communication systems depending on the various phenomena. The outage performance of an underwater optical wireless communication (UOWC) is obtained in analytical form using the Meijer-G function. Aysmptotic expression of outage probability is also derived for high signal-to-noise ratio (SNR) regime. Results show that the destructive combined effect of the underwater turbulence, pointing error, attenuation, and angle of arrival (AOA) on the outage performance can be reduced by applying the MIMO spatial diversity technique.
Citation - WoS: 3
Citation - Scopus: 5
Analysis of wander and spreading of an optical beam by using the oceanic turbulence optical power spectrum
(Optica Publishing Group, 2022) Ata, YalcIn; Baykal, Yahya; Gokce, Muhsin Caner; Elektronik ve Haberleşme Mühendisliği
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. (C) 2022 Optica Publishing Group
Citation - WoS: 65
Citation - Scopus: 77
Aperture averaging and BER for Gaussian beam in underwater oceanic turbulence
(Elsevier Science Bv, 2018) Gokce, Muhsin Caner; Baykal, Yahya; 28643; 7812; Elektronik ve Haberleşme Mühendisliği
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.
Citation - WoS: 24
Citation - Scopus: 24
Aperture averaging in multiple-input single-output free-space optical systems
(Optical Soc Amer, 2016) Gokce, Muhsin Caner; Baykal, Yahya; Uysal, Murat; 28643; 7812; 124615; Elektronik ve Haberleşme Mühendisliği
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
Citation - WoS: 35
Citation - Scopus: 40
Aperture averaging in strong oceanic turbulence
(Elsevier Science Bv, 2018) Gokce, Muhsin Caner; Baykal, Yahya; 28643; 7812; Elektronik ve Haberleşme Mühendisliği
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. (C) 2017 Elsevier B.V. All rights reserved.
Citation - WoS: 21
Citation - Scopus: 25
Average channel capacity in anisotropic atmospheric non-Kolmogorov turbulent medium
(Elsevier, 2019) Ata, Yalcin; Baykal, Yahya; Gokce, Muhsin Caner; 7812; Elektronik ve Haberleşme Mühendisliği
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.
Citation - WoS: 0
Citation - Scopus: 1
BER performance ofM-ary pulse position modulated communication systems in anisotropic non-Kolmogorov turbulent atmosphere
(Taylor & Francis Ltd, 2022) Ata, Yalcin; Baykal, Yahya; Gokce, Muhsin Caner; 7812; Elektrik-Elektronik Mühendisliği; Elektronik ve Haberleşme Mühendisliği
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.
Citation - WoS: 13
Citation - Scopus: 13
Binary Phase Shift Keying-Subcarrier Intensity Modulation Performance in Weak Oceanic Turbulence
(Elsevier, 2019) Gokce, Muhsin Caner; Baykal, Yahya; Ata, Yalcin; 7812; 28643; Elektronik ve Haberleşme Mühendisliği
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.
Citation - WoS: 6
Citation - Scopus: 7
Bit error rate analysis of MISO FSO systems
(Taylor & Francis Ltd, 2016) Gokce, Muhsin Caner; Baykal, Yahya; Uysal, Murat; 28643; 7812; 124615; Elektronik ve Haberleşme Mühendisliği
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.
Citation - WoS: 4
Citation - Scopus: 5
Correlation of multimode fields in atmospheric turbulence
(Optica Publishing Group, 2023) Baykal, Yahya; Gokce, Muhsin Caner; Ata, Yalcin; Gercekcioglu, Hamza; 7812; Elektronik ve Haberleşme Mühendisliği
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 mul- timodes, 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.(c) 2023 Optica Publishing Group
Citation - WoS: 2
Citation - Scopus: 2
Correlations of multimode optical incidences in a turbulent biological tissue
(Optica Publishing Group, 2023) Baykal, Yahya; Gokce, Muhsin Caner; Gerekcioglu, Hamza; Ata, Yalin; 7812; Elektronik ve Haberleşme Mühendisliği
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. (c) 2023 Optica Publishing
Citation - WoS: 4
Citation - Scopus: 4
Coupling efficiency of multimode beam to fiber in atmospheric turbulence
(Pergamon-elsevier Science Ltd, 2023) Gokce, Muhsin Caner; Baykal, Yahya; Ata, Yalcin; 7812; Elektronik ve Haberleşme Mühendisliği
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 princi-ple. 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).(c) 2023 Elsevier Ltd. All rights reserved.
Citation - WoS: 5
Effect of anisotropy on performance of M-ary phase shift keying subcarrier intensity-modulated optical wireless communication links operating in strong oceanic turbulence
(Iop Publishing Ltd, 2020) Gokce, Muhsin Caner; Baykal, Yahya; Ata, Yalcin; 7812; Elektronik ve Haberleşme Mühendisliği
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.
Citation - WoS: 0
Citation - Scopus: 2
Effect of Partial Coherence on MISO FSO Systems
(Ieee, 2015) Gokce, Muhsin Caner; Baykal, Yahya; Uysal, Murat; 28643; Elektronik ve Haberleşme Mühendisliği
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.
Citation - WoS: 6
Citation - Scopus: 7
Effects of adaptive optics on bit error rate of M-ary PPM oceanic optical wireless communication systems with aperture averaging in strong turbulence
(Iop Publishing Ltd, 2021) Gokce, Muhsin Caner; Baykal, Yahya; Ata, Yalcin; 7812; Elektronik ve Haberleşme Mühendisliği
Scintillation is the result of oceanic turbulence reducing the bit error rate (BER) performance of oceanic optical wireless communication (OWC) systems. The scintillation, also known as intensity fluctuations, occurs due to the turbulence-induced wavefront deformations. The correction of deformations by adaptive optics (AO) reduces the scintillation effect of turbulence and results in improved BER performance. In this paper, an oceanic OWC (OOWC) system that has a Gaussian laser beam at the transmitter, finite-sized circular aperture at the receiver, employing M-ary pulse position modulation (PPM) and operating in strong oceanic turbulence, is considered. Improvement in the BER performance of the OOWC system is examined with the implementation of AO correction. Comparison of BER performances between the AO and non-adaptive optics OOWC systems is shown by calculating the metric defined. BER of M-ary PPM OOWC links is evaluated over gamma-gamma fading channels. The modified Rytov theory together with the Zernike filter functions is used to find the AO corrected aperture averaged scintillation index where extended Huygens-Fresnel technique is used to obtain the average received signal power.
Citation - WoS: 17
Citation - Scopus: 16
Effects of liver tissue turbulence on propagation of annular beam
(Elsevier Gmbh, 2018) Gokce, Muhsin Caner; Baykal, Yahya; 28643; 7812; Elektronik ve Haberleşme Mühendisliği
Effects of tissue turbulence on the propagation properties of an annular laser beam is examined. In this respect, the average intensity profile and the beam spread at the observation plane are formulated and evaluated after the annular laser beam propagates through the turbulent liver tissue. In our formulation, the extended Huygens-Fresnel method is utilized with the involvement of the turbulence power spectrum of the liver tissue. Results obtained from the performed simulations include the variations of the received average intensity and the effective beam size of the annular beam against the changes in the liver tissue turbulence and the laser beam parameters, i.e., against the laser wavelength, tissue length, primary and secondary source sizes of the annular laser beam. Our work in this paper will prove to be helpful in obtaining clues to diagnose abnormalities such as cancer and tumor in a liver tissue.
Citation - WoS: 12
Citation - Scopus: 12
Error performance of optical wireless communication systems exercising BPSK subcarrier intensity modulation in non-Kolmogorov turbulent atmosphere
(Elsevier Science Bv, 2019) Ata, Yalcin; Baykal, Yahya; Gokce, Muhsin Caner; 7812; 28643; Elektronik ve Haberleşme Mühendisliği
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.
Citation - WoS: 1
Citation - Scopus: 1
Fiber coupling efficiency in ocean with adaptive optics corrections
(Optica Publishing Group, 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. (c) 2023 Optica Publishing Group