Elektrik Elektronik Mühendisliği Bölümü

Permanent URI for this communityhttps://hdl.handle.net/20.500.12416/410

Browse

Now showing 1 - 4 of 4

Citation - WoS: 4
Citation - Scopus: 5
Accurate Method To Calculate Noise Figure in a Low Noise Amplifier: Quantum Theory Analysis
(Elsevier Sci Ltd, 2022) Salmanogli, Ahmad; Gecim, H. Selcuk
In this study, a low-noise amplifier is quantum-mechanically analyzed to study the behavior of the noise figure. The analysis view has been changed from classic to quantum, because using quantum theory produces some degrees of freedom, which may be ignored when a circuit is analyzed using classical theory. For this purpose, the Lagrangian is initially derived by considering the related nonlinearity of the transistor, and then using the Legendre transformation and canonical quantization procedure, the quantum Hamiltonian is derived. As an interesting point of this study, the low-noise amplifier is deliberately considered as two oscillators connecting to each other to share the photonic modes between them; accordingly, the voltage and current as measurable observations and the noise figure as a critical quantity in a low-noise amplifier are theoretically expressed in terms of the oscillator's mean photon number. The main goal of this work is to study quantities such as the noise figure in a sufficient detail using quantum theory. In addition, as an advantage of this theory, one can control and manipulate the noise figure only by manipulation of the oscillator's mean photon number and coupling it between two oscillators. Finally, the circuit is classically designed and simulated to verify the derived results using quantum theory. The comparison results show that there is a partial consistency between the two approaches; as the frequency increases, the noise figure becomes minimized at a particular frequency.
Citation - WoS: 8
Citation - Scopus: 9
Joint Parameter and State Estimation of the Hemodynamic Model by Iterative Extended Kalman Smoother
(Elsevier Sci Ltd, 2016) Akin, Ata; Aslan, Serdar; Cemgil, Ali Taylan; Aslan, Murat Samil; Toreyin, Behcet Ugur
The joint estimation of the parameters and the states of the hemodynamic model from the blood oxygen level dependent (BOLD) signal is a challenging problem. In the functional magnetic resonance imaging (fMRI) literature, quite interestingly, many proposed algorithms work only as a filtering method. This makes the estimation of hidden states and parameters less reliable compared with the algorithms that use smoothing. In standard implementations, smoothing is performed only once. However, joint state and parameter estimation can be improved substantially by iterating smoothing schemes such as the extended Kalman smoother (IEKS). In the fMRI literature, extended Kalman filtering is thought to be less accurate than standard particle filtering (PF). We compared EKF with PF and observed that the contrary is true. We improved the EKF performance by adding smoother. By iterative scheme joint hemodynamic and parameter estimation is improved substantially. We compared IEKS performance with the square-root cubature Kalman smoother (SCKS) algorithm. We show that its accuracy for the state and the parameter estimation is better and much faster than iterative SCKS. SCKS was found to be a better estimator than the dynamic expectation maximization (DEM), EKF, local linearization filter (LLF) and PP methods. We show in this paper that IEKS is a better estimator than iterative SCKS under different process and measurement noise conditions. As a result, IEKS seems to be the best method we evaluated in all aspects. (C) 2015 Elsevier Ltd. All rights reserved.
Citation - WoS: 38
Citation - Scopus: 45
Propagation of Modified Bessel-Gaussian Beams in Turbulence
(Elsevier Sci Ltd, 2008) Eyyuboglu, Halil Tanyer; Hardalac, Firat
We investigate the propagation characteristics of modified Bessel-Gaussian beams traveling in a turbulent atmosphere. The source beam formulation comprises a Gaussian exponential and the summation of modified Bessel functions. Based on an extended Huygens-Fresnel principle, the receiver plane intensity is formulated and solved down to a double integral stage. Source beam illustrations show that modified Bessel-Gaussian beams, except the lowest order case, will have well-like shapes. Modified Bessel-Gaussian beams with summations will experience lobe slicing and will display more or less the same profile regardless of order content. After propagating in turbulent atmosphere, it is observed that a modified Bessel-Gaussian beam will transform into a Bessel-Gaussian beam. Furthermore it is seen that modified Bessel-Gaussian beams with different Bessel function combinations, but possessing nearly the same profile, will differentiate during propagation. Increasing turbulence strength is found to accelerate the beam transformation toward the eventual Gaussian shape. (c) 2007 Elsevier Ltd. All rights reserved.
Citation - WoS: 72
Citation - Scopus: 92
Underwater Turbulence, Its Effects on Optical Wireless Communication and Imaging: a Review
(Elsevier Sci Ltd, 2022) Baykal, Yahya; Ata, Yalcin; Gokce, Muhsin C.
Theory of optical turbulence in underwater medium and the effects of underwater turbulence on various ap-plications done in underwater or under ocean are reviewed. A detailed survey of underwater turbulence studies in literature is reported. Underwater physics covering salinity, temperature and dissipation rates, various power spectra such as Hill, Nikishov and Nikishov, Li, new form and the oceanic turbulence optical power spectrum (OTOPS) spectra are explained. Wave and phase structure functions, related coherence length, anisotropy, in-tensity, field correlations in underwater turbulence are elaborated. Scintillation indices of spherical, plane, Gaussian, and other types of optical beams are mentioned. Bit-error-rate (BER), signal-to-noise-ratio (SNR) performances of optical wireless communication systems operating in underwater, and the effects of modulation types of these systems on the performances are reported. Channel capacity of underwater optical wireless communication systems when the channel experiences log-normal, gamma-gamma, Weibull, and negative exponential statistics are reflected. Underwater imaging and the related modulation transfer function, under-water turbulence mitigation techniques in the form of aperture averaging, adaptive optics, receiver, transmitter and multiple-input, multiple-output (MIMO) spatial diversity techniques are revised.

Browse

Browsing Elektrik Elektronik Mühendisliği Bölümü by browse.metadata.publisher "Elsevier Sci Ltd"