Elektrik - Elektronik Mühendisliği Bölümü Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12469/47

Browse

Now showing 1 - 20 of 23

Citation - WoS: 2
Citation - Scopus: 2
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 - WoS: 2
Citation - Scopus: 3
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.
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 - WoS: 1
Citation - Scopus: 4
Channel Estimation in Underwater Cooperative Ofdm System With Amplify-And Relaying
(IEEE, 2012) Şenol, Habib; Panayırcı, Erdal; Erdoğan, Mustafa; Uysal, Murat
This paper is concerned with a challenging problem of channel estimation for amplify-and-forward cooperative relay based orthogonal frequency division multiplexing (OFDM) systems in the presence of sparse underwater acoustic channels and of the correlative non-Gaussian noise. We exploit the sparse structure of the channel impulse response to improve the performance of the channel estimation algorithm due to the reduced number of taps to be estimated. The resulting novel algorithm initially estimates the overall sparse channel taps from the source to the destination as well as their locations using the matching pursuit (MP) approach. The correlated non-Gaussian effective noise is modeled as a Gaussian mixture. Based on the Gaussian mixture model an efficient and low complexity algorithm is developed based on the combinations of the MP and the space-alternating generalized expectation-maximization (SAGE) technique to improve the estimates of the channel taps and their location as well as the noise distribution parameters in an iterative way. The proposed SAGE algorithm is designed in such a way that by choosing the admissible hidden data properly on which the SAGE algorithm relies a subset of parameters is updated for analytical tractability and the remaining parameters for faster convergence Computer simulations show that underwater acoustic (UWA) channel is estimated very effectively and the proposed algorithm has excellent symbol error rate and channel estimation performance.
Citation - WoS: 1
Citation - Scopus: 2
Data-Aided Autoregressive Sparse Channel Tracking for Ofdm Systems
(IEEE, 2016) Buyuksar, Ayse Betul; Şenol, Habib; Erküçük, Serhat; Cirpan, Hakan Ali
In order to meet future communication system requirements channel estimation over fast fading and frequency selective channels is crucial. In this paper Space Alternated Generalized Expectation Maximization Maximum a Posteriori (SAGE-MAP) based channel estimation algorithm is proposed for Orthogonal Frequency Division Multiplexing (OFDM) systems for Autoregressive (AR) modeled time-varying sparse channels. Also an initialization algorithm has been developed from the widely used sparse approximation algorithm Orthogonal Matching Pursuit (OMP) since the performance of SAGE algorithm strictly depends on initialization. The results show that multipath delay positions can be tracked successfully for every time instant using the proposed SAGE-MAP based approach.
Design of Phase Shifters With Ladder Stubs Via Real Frequency Technique
(World Scientific, 2020) Şengül, Metin Y.
Generally at high frequencies, lumped-elements are not preferred because of their limited range of values. Therefore, in this work, a kind of phase shifter formed with ladder stubs is studied and a new approach to design phase shifter's low pass and high pass sections which are composed of series or shunt connected open-ended or short-ended stubs is proposed. In the approach, since the main focus is to form low pass and high pass two-port sections, switching process is not considered. First, the designer selects the section type and the total number of stubs in the sections; it is not necessary to fix the two-port section topologies and not necessary to derive the characteristic impedance and delay expressions for the stubs. In the example, 5-stub two-port sections of a 180∘ phase shifter are designed by means of the proposed approach.
Citation - Scopus: 1
Edge Detection Using Steerable Filters and Cnn
(European Signal Processing Conference EUSIPCO, 2002) Özmen, Atilla; Akman, Emir Tufan
This paper proposes a new approach for edge detection using steerable filters and cellular neural networks (CNNs) where the former yields the local direction of dominant orientation and the latter provides iterative filtering. For this purpose steerable filter coefficients are used in CNN as a B template. The results are compared to the results where only CNN or steerable filters are used. As a result of this study the performance of the system can be improved since iterative filtering property of CNN and the ability of steerable filters for edge detection are used. © 2002 EUSIPCO.
Citation - WoS: 1
Citation - Scopus: 3
The Effect of Primary User Bandwidth on Bayesian Compressive Sensing Based Spectrum Sensing
(IEEE Computer Society, 2016) Başaran, Mehmet; Erküçük, Serhat; Cirpan, Hakan Ali
The application of compressive sensing (CS) theory has found great interest in wideband spectrum sensing. Although most studies have considered perfect reconstruction of the primary user signal it is actually more important to assess the presence or absence of the signal. Among CS based methods Bayesian CS (BCS) takes into consideration the prior information of signal coefficients to be estimated which improves signal reconstruction performance. On the other hand the sparsity level of the signal to be estimated has a direct impact on signal reconstruction and detection performances. Considering all of the above the effect of sparsity level on BCS based spectrum sensing is studied in this paper. More specifically a BCS based spectrum sensing scheme is considered and its mean-square error (MSE) performance is compared with the Bayesian Cramer-Rao bound for various user bandwidths. BCS MSE is also compared with the deterministic lower MSE (DL-MSE) which is a tight lower bound of the conventional basis pursuit approach. Furthermore complementary receiver operating characteristic (ROC) curves are obtained to examine the trade-off between probabilities of false alarm and detection depending on the user signal bandwidth.
Citation - WoS: 5
Citation - Scopus: 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 - WoS: 2
Citation - Scopus: 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 - WoS: 3
Citation - Scopus: 3
Explicit Synthesis Formulae for Cascaded Lossless Commensurate Lines
(Fachverlag Schiele Schon, 2008) Şengül, Metin Y.
In literature synthesis of cascaded lossless commensurate lines have been realized via some iterative methods. So to be able to obtain the value of an element which is not the first one the designer has to obtain all the values of the elements connected before the desired one. But in this paper explicit synthesis formulae of the networks containing cascaded lossless commensurate lines up to three have been derived analytically and all the element values can be calculated independently.
Citation - WoS: 10
Citation - Scopus: 9
Mathematical Characterization of Thermo-Reversible Phase Transitions of Agarose Gels
(Taylor & Francis Inc, 2018) Öğrenci, Arif Selçuk; 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 - WoS: 8
Citation - Scopus: 8
Minimum Length Scheduling for Discrete Rate Based Full Duplex Wireless Powered Communication Networks
(Springer, 2019) Iqbal, Muhammad Shahid; Şadı, Yalçın; Ergen, Sinem Coleri
In this study, we consider a wireless powered communication network where multiple users with radio frequency energy harvesting capabilities communicate to a hybrid energy and information access point in full duplex mode. We characterize an optimization framework for minimum length scheduling to determine the optimal rate adaptation and transmission scheduling subject to energy causality and traffic demand constraints of the users considering discrete-rate transmission model. 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, based on an analysis on the characteristics of the optimal solution, we derive optimality conditions for rate adaptation and scheduling using which we propose a fast polynomial-time complexity heuristic algorithm. We illustrate through numerical analysis that the proposed algorithm performs very close to optimal for various network scenarios.
Citation - Scopus: 1
Mixed Element Networks With Series Capacitors Separated by Unit Elements
(World Scientific, 2020) Şengül, Metin Y.; Çakmak, Gökhan
In this work, high-pass mixed-element networks with series capacitors separated by unit elements are analyzed. First, the description of the networks via two frequency variables is given. Then, explicit coefficient relations for the descriptive polynomials are derived in terms of the single-variable boundary polynomial coefficients. Finally, the derived relations are used to design a high-pass mixed-element matching network. The series capacitors can be converted to short-ended stubs by means of Richard's transformation. Thus, the obtained network is suitable for microstrip production.
Citation - WoS: 2
Citation - Scopus: 3
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 - WoS: 2
Citation - Scopus: 2
Noncoherent Ultra Wideband Wireless Sensor Networks for Primary User Detection
(IEEE Computer Society, 2016) Sabucu, Yağmur; Erküçük, Serhat
As a result of increasing demand for new technologies unlicensed usage of available spectrum has become very essential to provide an efficient usage of spectrum. For that reason sensor networks may be a reliable option to decide on the absence/presence of licensed users and to communicate without causing much interference as a secondary user network. These networks consist of two communication links for primary user detection. One link is between the primary user and the sensors and the other link is between the sensors and the fusion center. In this study we consider an IEEE 802.15.4a based ultra wideband (UWB) network with a noncoherent receiver structure for the first link. For the second link binary pulse position modulation is implemented to convey primary user information to the fusion center. Numerical expressions for probabilities of false alarm and detection for the overall system are obtained and validated by simulations where the performance of the system improves with number of sensors and the reliability of the first link. The results obtained from this study can be used for improving the primary user detection performance of UWB based wireless sensor networks in noncoherent operation mode. © 2016 IEEE.
Citation - Scopus: 1
Performance of Space Time Codes With Transmit Antenna Selection Over Frequency Selective Fading Channels in the Presence of Channel Estimation Errors
(2008) Güçlüoğlu, Tansal; Panayırcı, Erdal
This paper presents a performance analysis of space-time coded systems with transmit antenna selection over frequency selective fading channels when the erroneously estimated fading coefficients are available only at the receiver. An upper bound on the pairwise error probability is derived and numerical examples are presented. The analysis does not assume any specific coding or channel estimation algorithm. With imperfect channel state information (CSI) used both at the antenna selection and the space-time decoding processes the achievable diversity order does not decrease compared to perfect CSI scenario. copyright by EURASIP.
Citation - WoS: 8
Power Control-Based Multi-User Li-Fi Using a Compound Eye Transmitter
(IEEE, 2015) Çoğalan, Tezcan; Haas, Harald; Panayırcı, Erdal
In visible light communications (VLC) the transmitted signal is non-negative and real valued and these characteristics constrain the signal space and provide new challenges for waveform design in a multi-user system. In Light Fidelity (Li-Fi) a VLC technology and similar to radio frequency (RF) systems precoder designs can be used to serve multiple users. However a signal shaping algorithm is required to address the non-negativity of the transmitted signal in Li-Fi. In this study a power allocation algorithm is proposed to achieve a multi-user Li-Fi system. A compound eye transmitter consisting of several LEDs pointing in different directions is used. This means that the process of the obtaining the inverse of the channel matrix in precoder design is not required. Results show that when a 30 degrees semi-angle is used at the transmitter and the system has 4 users the proposed transmission model can achieve 10(-5) average bit error rate (BER) performance at 1 dBm average transmission power.
Citation - WoS: 4
Citation - Scopus: 4
Reflectance-Based Foster Impedance Data Modeling
(Fachverlag Schiele Schon, 2007) Şengül, Metin Y.
A reflectance-based method is presented to model a set of given Foster impedance data as a lossless singly terminated two-port consisting of lumped-elements in short or open termination. The basis of the new method rests on the interpolation of the given data as a realizable bounded-real (BR) reflection function. The desired circuit model is obtained by synthesizing this function. An algorithm to generate the circuit model is presented and an example is included which illustrates the utilization of the proposed modeling method.
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.

Browse

Browsing Elektrik - Elektronik Mühendisliği Bölümü Koleksiyonu by Scopus Q "Q3"