Elektrik - Elektronik Mühendisliği Bölümü Koleksiyonu

Permanent URI for this collectionhttps://gcris.khas.edu.tr/handle/20.500.12469/47

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Now showing 1 - 17 of 17

Citation Count: 13
Bayesian Compressive Sensing For Primary User Detection
(Inst Engineering Technology-IET, 2016) Erküçük, Serhat; Erküçük, Serhat; Cirpan, Hakan Ali
In compressive sensing (CS)-based spectrum sensing literature most studies consider accurate reconstruction of the primary user signal rather than detection of the signal. Furthermore possible absence of the signal is not taken into account while evaluating the spectrum sensing performance. In this study Bayesian CS is studied in detail for primary user detection. In addition to assessing the signal reconstruction performance and comparing it with the conventional basis pursuit approach and the corresponding lower bounds signal detection performance is also considered both analytically and through simulation studies. In the absence of a primary user signal the trade-off between probabilities of detection and false alarm is studied as it is equally important to determine the performance of a CS approach when there is no active primary user. To reduce the computation time and yet achieve a similar detection performance finally the effect of number of iterations is studied for various systems parameters including signal-to-noise-ratio compression ratio mean value of accumulated energy and threshold values. The presented framework in this study is important in the overall implementation of CS-based approaches for primary user detection in practical realisations such as LTE downlink OFDMA as it considers both signal reconstruction and detection.
Citation Count: 1
Bayesian estimation of discrete-time cellular neural network coefficients
(TUBITAK Scientific & Technical Research Council Turkey, 2017) Şenol, Habib; Özmen, Atilla; Şenol, Habib
A new method for finding the network coefficients of a discrete-time cellular neural network (DTCNN) is proposed. This new method uses a probabilistic approach that itself uses Bayesian learning to estimate the network coefficients. A posterior probability density function (PDF) is composed using the likelihood and prior PDFs derived from the system model and prior information respectively. This posterior PDF is used to draw samples with the help of the Metropolis algorithm a special case of the Metropolis--Hastings algorithm where the proposal distribution function is symmetric and resulting samples are then averaged to find the minimum mean square error (MMSE) estimate of the network coefficients. A couple of image processing applications are performed using these estimated parameters and the results are compared with those of some well-known methods.
Citation Count: 1
Broadband matching via reflection function optimization
(Wiley, 2017) Şengül, Metin Y.
In this paper a practical approach is presented for designing broadband matching networks via reflection function optimization. In the proposed algorithm the input or output reflection function of the matching network is expressed in terms of three real polynomials describing the matching network load and generator reflection coefficients. Next one of the polynomials is optimized to get minimum reflection function values in the passband. Then matching network topology and element values are obtained via the formed input reflection coefficient expression. Two examples are presented to explain the usage of the new approach. Copyright (c) 2016 John Wiley & Sons Ltd.
Citation Count: 2
Broadband Matching via Unequal Length Cascaded Transmission Lines
(World Scientific Publ Co Pte Ltd, 2017) Şengül, Metin Y.
In this paper a new approach based on the real frequency technique (RFT) has been proposed to solve broadband matching problems using cascaded unequal length transmission lines. At the end of the design process optimum characteristic impedance and delay values of transmission lines are obtained. Two examples are given to illustrate the utilization of the proposed approach.
Citation Count: 0
Broadband Microwave Amplifier Design with Lumped Elements
(Walter De Gruyter Gmbh, 2016) Şengül, Metin Y.
This study introduces a broadband microwave amplifier design that utilizes the measured scattering parameters of active devices without assuming an initial topology for the matching networks or an analytic form of the system transfer function. The algorithm can be extended to design multistage broadband microwave amplifiers. An example is given to illustrate the application of the proposed method. It was found that the proposed method provides very good initials for CAD tools to further improve amplifier performance by working on the element values.
Citation Count: 5
Epidemic models for phase transitions: application to a physical gel
(Taylor & Francis Ltd, 2017) Bilge, Ayşe Hümeyra; Pekcan, Önder; Kara, Selim; Öğrenci, Arif Selçuk
Carrageenan gels are characterized by reversible sol-gel and gel-sol transitions under cooling and heating processes and these transitions are approximated by generalized logistic growth curves. We express the transitions of carrageenan-water system as a representative of reversible physical gels in terms of a modified Susceptible-Infected-Susceptible epidemic model as opposed to the Susceptible-Infected-Removed model used to represent the (irreversible) chemical gel formation in the previous work. We locate the gel point T-c of sol-gel and gel-sol transitions and we find that for the sol-gel transition (cooling) T-c > T-sg (transition temperature) i.e. T-c is earlier in time for all carrageenan contents and moves forward in time and gets closer to T-sg as the carrageenan content increases. For the gel-sol transition (heating) T-c is relatively closer to T-gs
Citation Count: 2
Explicit solutions of two-variable scattering equations describing lossless low-pass two-ports with mixed lumped and distributed elements
(Wiley, 2019) Şengül, Metin Y.; Eker, Göker
One of the methods to describe mixed lumped and distributed element two-port networks is to use two-variable scattering equations. In literature, the solutions of these explicit descriptive equations for some classes of low-order ladder networks are derived under some restrictions. In this paper, the complete and explicit solutions of the equations are derived to describe lossless low-pass two-port networks with mixed lumped and distributed elements, up to four elements, without any restrictions.
Citation Count: 6
Fault tolerant control with re-configuring sliding-mode schemes
(2005) Kerestecioğlu, Feza; Kerestecioğlu, Feza
In this paper a controller design method for linear MIMO systems is presented which a sliding mode controller is reconfigured in case of system faults. Faults are detected with the residual vector generated from a standard linear observer. Once a fault has been detected the fault distribution matrix can be obtained and used to update the corrective or equivalent control parts of the sliding mode controller. As a result fault tolerant adaptive controllers keep the system performance within acceptable limits or at least avoids the system to wind-up. © TÜBITAK.
Citation Count: 6
Foster impedance data modeling via singly terminated LC ladder networks
(TUBITAK Scientific & Technical Research Council Turkey, 2013) Şengül, Metin Y.
In this work a lossless model is developed for the given Foster impedance data. In the model a 2-port short-or open-terminated LC ladder is used. After applying the proposed algorithm a realizable driving-point reactance function that fits the given data is obtained. Next this function is synthesized resulting in the desired model. In the algorithm there is no need to select a circuit topology for the model. Two examples are given to illustrate the utilization of the proposed modeling algorithm.
Citation Count: 2
High-pass/low-pass section design for 0 degrees-360 degrees lumped-element phase shifters via the real frequency technique
(TUBITAK Scientific & Technical Research Council Turkey, 2017) Şengül, Metin Y.
In this paper an algorithm based on the real frequency technique (RFT) is proposed to design high-pass and low-pass sections of a 0 degrees-360 degrees wide range lumped-element phase shifter. The switching process however is not considered in this work. In the algorithm it is enough to define the section type (high-pass or low-pass) and the number of elements in the sections there is no need to select the exact circuit topologies for the high-pass and low-pass sections. This is a natural consequence of the proposed approach. Unlike in the methods described in the literature there is also no need to derive element value expressions. Two examples are given to illustrate the utilization of the proposed algorithm. The proposed algorithm and results are verified by simulation.
Citation Count: 8
Mathematical Characterization of Thermo-reversible Phase Transitions of Agarose Gels
(Taylor & Francis Inc, 2018) Bilge, Ayşe Hümeyra; Pekcan, Önder; Kara, Selim; Bilge, Ayşe Hümeyra
The thermal phase transition temperatures of high (HMP) and low melting point (LMP) agarose gels were investigated by using UV-vis spectroscopy techniques. Transmitted light intensities from the gel samples with different agarose concentrations were monitored during the heating (gel-sol) and cooling (sol-gel) processes. It was observed that the transition temperatures T-m defined as the location of the maximum of the first derivative of the sigmoidal transition paths obtained from the UV-vis technique slightly increased by increasing the agarose concentration in both the HMP and LMP samples. Here we express the phase transitions of the agar-water system as a representative of reversible physical gels in terms of a modified Susceptible-Infected-Susceptible epidemic model whose solutions are the well-known 5-point sigmoidal curves. The gel point is hard to determine experimentally and various computational techniques are used for its characterization. Based on previous work we locate the gel point T-0 of sol-gel and gel-sol transitions in terms of the horizontal shift in the sigmoidal transition curve. For the gel-sol transition (heating) T-0 is greater than T-m i.e. later in time and the difference between T-0 and T-m is reduced as the agarose content increases. For the sol-gel transition (cooling) T-0 is again greater than T-m but it is earlier in time for all agarose contents and moves forward in time and gets closer to T-m as the agarose content increases.
Citation Count: 2
Mathematical models for phase transitions in biogels
(World Scientific Publ Co Pte Ltd, 2019) Bilge, Ayşe Hümeyra; Öğrenci, Arif Selçuk; Pekcan, Önder
It has been shown that reversible and irreversible phase transitions of biogels can be represented by epidemic models. The irreversible chemical sol-gel transitions are modeled by the Susceptible-Exposed-Infected-Removed (SEIR) or Susceptible-Infected-Removed (SIR) epidemic systems whereas reversible physical gels are modeled by a modification of the Susceptible-Infected-Susceptible (SIS) system. Measured sol-gel and gel-sol transition data have been fitted to the solutions of the epidemic models, either by solving the differential equations directly (SIR and SEIR models) or by nonlinear regression (SIS model). The gel point is represented as the "critical point of sigmoid," defined as the limit point of the locations of the extreme values of its derivatives. Then, the parameters of the sigmoidal curve representing the gelation process are used to predict the gel point and its relative position with respect to the transition point, that is, the maximum of the first derivative with respect to time. For chemical gels, the gel point is always located before the maximum of the first derivative and moves backward in time as the strength of the activation increases. For physical gels, the critical point for the sol-gel transition occurs before the maximum of the first derivative with respect to time, that is, it is located at the right of this maximum with respect to temperature. For gel-sol transitions, the critical point is close to the transition point; the critical point occurs after the maximum of the first derivative for low concentrations whereas the critical point occurs after the maximum of the first derivative for higher concentrations.
Citation Count: 2
Modified Q-Based Real Frequency Design of Narrowband Impedance Equalizer with Complex Terminations
(World Scientıfic Publ Co Pte Ltd, 2019) Şengül, Metin Y.; Yeşilyurt, Gökmen
In this paper, real frequency design equations of narrowband impedance matching network with complex terminations are derived; which are used to design L, Pi and T type of networks. In the approach, there is no need to have termination models with component values, it is enough to have measurement values of termination impedances. A few examples are solved to exhibit the have measurement values of termination impedances. A few examples are solved to exhibit the merits and application of the derived equations.
Citation Count: 0
Reflection Modeling Based Broadband Matching Network Design
(Walter De Gruyter, 2017) Şengül, Metin Y.
In this paper a new broadband matching network design approach based on reflection modeling is proposed which has two parts: impedance data generation and modeling. In the approach firstly the output impedance data of the matching network is obtained to get the desired flat transducer power gain in the passband. Next the output reflection data are calculated using the obtained impedance data then they are modeled as a bounded real function. Then this function is synthesized and the desired lossless matching network with initial element values is obtained. A double matching example is solved to illustrate the use of the proposed approach. It is seen that proposed approach provides suitable initials for CAD tools for final trimming.
Citation Count: 2
Shifted-modified Chebyshev filters
(TUBITAK Scientific & Technical Research Council Turkey, 2013) Şengül, Metin Y.
This paper introduces a new type of filter approximation method that utilizes shifted-modified Chebyshev filters. Construction of the new filters involves the use of shifted-modified Chebyshev polynomials that are formed using the roots of conventional Chebyshev polynomials. The study also includes 2 tables containing the shifted-modified Chebyshev polynomials and the normalized element values for the low-pass prototype filters up to degree 6. The transducer power gain group delay and impulse and step responses of the proposed filters are compared with those of the Butterworth and Chebyshev filters and a sixth-order filter design example is presented to illustrate the implementation of the new method.
Citation Count: 7
Simple outage probability bound for two-way relay networks with joint antenna and relay selection over Nakagami-m fading channels
(Inst Engineering Technology-IET, 2015) Erdoğan, Eylem; Güçlüoğlu, Tansal
The performance of a multiple-input multiple-output amplify-and-forward two-way relay network with joint antenna and relay selection is analysed over Nakagami-m fading channels. Both approximate and asymptotic system outage probability expressions are derived and diversity and coding gains for an arbitrary number of antennas relays and fading severity are presented. Finally the analytical findings are verified by numerical examples.
Citation Count: 8
Throughput maximization in discrete rate based full duplex wireless powered communication networks
(John Wıley & Sons Ltd, 2020) Şadi, Yalçın; Şadi, Yalçın; Coleri, Sinem
In this study, we consider a discrete rate full-duplex wireless powered communication network. We characterize a novel optimization framework for sum throughput maximization to determine the rate adaptation and transmission schedule subject to energy causality and user transmit power. We first formulate the problem as a mixed integer nonlinear programming problem, which is hard to solve for a global optimum in polynomial-time. Then, we investigate the characteristics of the solution and propose a polynomial time heuristic algorithm for rate adaptation and scheduling problem. Through numerical analysis, we illustrate that the proposed scheduling algorithm outperforms the conventional schemes such as equal time allocation half-duplex and on-off transmission schemes for different initial battery levels, hybrid access point transmit power and network densities.

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