Elektrik Elektronik Mühendisliği Bölümü Yayın Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/411
Browse
16 results
Search Results
Article Citation - WoS: 13Citation - Scopus: 13Field Correlation of Flat-Topped Beams in Anisotropic Non-Kolmogorov Turbulent Atmosphere(Taylor & Francis Ltd, 2019) Baykal, Yahya; Ata, YalcinField correlation of flat-topped beams in anisotropic non-Kolmogorov turbulent atmosphere is formulated and evaluated. Larger anisotropic factor causes higher field correlations. Smaller field correlations are seen when the transverse distance at the receiver plane increases. Smaller field correlations are observed at large off-axis transverse receiver points, which are valid for any anisotropic factor and for any power-law exponent of non-Kolmogorov turbulence. When the flat-topped beam is composed of large number of Gaussian beams, the field correlation becomes smaller. In anisotropic non-Kolmogorov turbulence, longer propagation distances, larger structure constants, smaller inner scales and smaller source sizes decrease the field correlation. Larger power law exponent of non-Kolmogorov turbulence increases the field correlations at any anisotropic factor.Article Citation - WoS: 12Citation - Scopus: 14M-Ary Pulse Position Modulation Performance in Strong Atmospheric Turbulence(Optical Soc Amer, 2018) Baykal, Yahya; Ata, Yalcin; Gokce, Muhsin CanerThe performance of an M-ary pulse position modulated (PPM) optical wireless communication system operating in strong atmospheric turbulence is investigated. Bit error rate (BER) is employed as the measure for the performance. In our overall performance formulation, average received power as measured by a finite-sized avalanche photodiode (APD) detector is used by the help of the extended Huygens-Fresnel principle. For the aperture averaged scintillation evaluations, the asymptotic Rytov theory with the gamma-gamma intensity statistics is utilized. Gamma-gamma statistics together with the large-scale and the small-scale log-intensity variances yield the scintillation index valid both in weak and strong atmospheric turbulence regimes. BER variations versus the plane wave scintillation index are examined at different values of receiver aperture diameters, data bit rates, M values of M-ary PPM, quantum efficiency, and average APD gain. (C) 2018 Optical Society of AmericaArticle Citation - WoS: 8Citation - Scopus: 8Structure Parameter of Anisotropic Atmospheric Turbulence Expressed in Terms of Anisotropic Factors and Oceanic Turbulence Parameters(Optical Soc Amer, 2019) Ata, Yalcin; Gokce, Muhsin C.; Baykal, YahyaThe structure parameter of the anisotropic atmospheric turbulence is expressed in terms of atmospheric, oceanic anisotropic factors in x and y directions, and the oceanic turbulence parameters, which are the wavelength, the link length, 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. For the purpose of expressing the structure parameter of the anisotropic atmospheric turbulence in terms of atmospheric, oceanic anisotropic factors and the oceanic turbulence parameters, the spherical wave scintillation indices that are found in weak anisotropic atmospheric turbulence and in weak oceanic turbulence are equated to each other. We aim to utilize the structure parameter expressed in this paper in the evaluations of various physical entities such as the average intensity, scintillation index, and beam spread in anisotropic oceanic turbulence by exploiting the existing solutions for the same physical entities in anisotropic atmospheric turbulence. Use of this structure parameter will help us to obtain the anisotropic oceanic turbulence results easily because such results will be found by just inserting the structure parameter expressed in this paper to the already reported corresponding results of anisotropic atmospheric turbulence. (C) 2019 Optical Society of AmericaArticle Citation - WoS: 12Citation - Scopus: 11Error Performance of Optical Wireless Communication Systems Exercising Bpsk Subcarrier Intensity Modulation in Non-Kolmogorov Turbulent Atmosphere(Elsevier Science Bv, 2019) Baykal, Yahya; Gokce, Muhsin Caner; Ata, YalcinSubcarrier 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.Article Citation - WoS: 9Citation - Scopus: 11Effect of Strong Atmospheric Non-Kolmogorov Turbulence on the M-Ary Psk Subcarrier Intensity Modulated Free Space Optical Communications System Performance(Optical Soc Amer, 2019) Baykal, Yahya; Gokce, Muhsin C.; Ata, YalcinAtmospheric 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 AmericaArticle Citation - WoS: 12Citation - Scopus: 15M-Ary Phase Shift Keying-Subcarrier Intensity Modulation Performance in Strong Oceanic Turbulence(Spie-soc Photo-optical instrumentation Engineers, 2019) Baykal, Yahya; Ata, Yalcin; Gokce, Muhsin CanerIn 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).Article Citation - WoS: 4Citation - Scopus: 4The Analysis of Anisotropic the Non-Kolmogorov Turbulence Effect on Asymmetrical Gaussian Beam Propagation in a Marine Atmosphere(Iop Publishing Ltd, 2019) Ata, Yalcin; Baykal, YahyaThe 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.Article Citation - WoS: 9Citation - Scopus: 10Anisotropy Effect on Performance of Subcarrier Intensity Modulated Binary Phase Shift Keying Optical Wireless Communication Links in Weakly Turbulent Underwater Channel(Taylor & Francis Ltd, 2019) Gokce, Muhsin C.; Ata, Yalcin; Baykal, YahyaThe 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.Article Citation - WoS: 24Citation - Scopus: 26Average Channel Capacity in Anisotropic Atmospheric Non-Kolmogorov Turbulent Medium(Elsevier, 2019) Baykal, Yahya; Gokce, Muhsin Caner; Ata, YalcinThe 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.Article Citation - WoS: 32Citation - Scopus: 40Performance Analysis of M-Ary Pulse Position Modulation in Strong Oceanic Turbulence(Elsevier Science Bv, 2018) Baykal, Yahya; Ata, Yalcin; Gokce, Muhsin CanerIn this paper, we consider an underwater wireless optical communication (UWOC) system which consists of an M-ary pulse position modulated (PPM) Gaussian optical beam at the transmitter and an avalanche photodiode (APD) at the receiver. In strong oceanic turbulence, we aimed at investigating the system performance in terms of bit error rate (BER) by the help of gamma-gamma channel model. For this purpose, the average power and the aperture averaged scintillation at the finite sized detector are derived by using the extended Huygens-Fresnel principle and the asymptotic Rytov theory, respectively. BER variations are examined versus the average APD gain, modulation order, bit rate as well as 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 and the ratio of temperature to salinity contributions to the refractive index spectrum.