Elektrik - Elektronik Mühendisliği Bölümü Koleksiyonu

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

Browse

Now showing 1 - 20 of 41

Citation - WoS: 1
Citation - Scopus: 1
Across Dimensions: Two- and Three-Dimensional Phase Transitions From the Iterative Renormalization-Group Theory of Chains
(2020) Keçoğlu, İbrahim; Berker, A. Nihat
Sharp two- and three-dimensional phase transitional magnetization curves are obtained by an iterative renormalization-group coupling of Ising chains, which are solved exactly. The chains by themselves do not have a phase transition or nonzero magnetization, but the method reflects crossover from temperaturelike to fieldlike renormalization-group flows as the mechanism for the higher-dimensional phase transitions. The magnetization of each chain acts, via the interaction constant, as a magnetic field on its neighboring chains, thus entering its renormalization-group calculation. The method is highly flexible for wide application.
Amplitude and Frequency Modulations With Cellular Neural Networks
(Springer, 2015) Tander, Baran; Özmen, Atilla
Amplitude and frequency modulations are still the most popular modulation techniques in data transmission at telecommunication systems such as radio and television broadcasting gsm etc. However the architectures of these individual systems are totally different. In this paper it is shown that a cellular neural network with an opposite-sign template can behave either as an amplitude or a frequency modulator. Firstly a brief information about these networks is given and then the amplitude and frequency surfaces of the generated quasi-sine oscillations are sketched with respect to various values of their cloning templates. Secondly it is proved that any of these types of modulations can be performed by only varying the template components without ever changing their structure. Finally a circuit is designed simulations are presented and performance of the proposed system is evaluated. The main contribution of this work is to show that both amplitude and frequency modulations can be realized under the same architecture with a simple technique specifically by treating the input signals as template components.
Citation - WoS: 14
Citation - Scopus: 16
Bayesian Compressive Sensing for Primary User Detection
(Inst Engineering Technology-IET, 2016) Başaran, Mehmet; 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 - WoS: 3
Citation - Scopus: 3
Bayesian Compressive Sensing for Ultra-Wideband Channel Estimation: Algorithm and Performance Analysis
(Springer, 2015) Özgör, Mehmet; Erküçük, Serhat; Çırpan, Hakan Ali
Due to the sparse structure of ultra-wideband (UWB) channels compressive sensing (CS) is suitable for UWB channel estimation. Among various implementations of CS the inclusion of Bayesian framework has shown potential to improve signal recovery as statistical information related to signal parameters is considered. In this paper we study the channel estimation performance of Bayesian CS (BCS) for various UWB channel models and noise conditions. Specifically we investigate the effects of (i) sparse structure of standardized IEEE 802.15.4a channel models (ii) signal-to-noise ratio (SNR) regions and (iii) number of measurements on the BCS channel estimation performance and compare them to the results of -norm minimization based estimation which is widely used for sparse channel estimation. We also provide a lower bound on mean-square error (MSE) for the biased BCS estimator and compare it with the MSE performance of implemented BCS estimator. Moreover we study the computation efficiencies of BCS and -norm minimization in terms of computation time by making use of the big- notation. The study shows that BCS exhibits superior performance at higher SNR regions for adequate number of measurements and sparser channel models (e.g. CM-1 and CM-2). Based on the results of this study the BCS method or the -norm minimization method can be preferred over the other one for different system implementation conditions.
Citation - WoS: 1
Citation - Scopus: 1
Bayesian Estimation of Discrete-Time Cellular Neural Network Coefficients
(TUBITAK Scientific & Technical Research Council Turkey, 2017) Özer, Hakan Metin; 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 - WoS: 12
Citation - Scopus: 10
Bound-Free Electron-Positron Pair Production in Relativistic Heavy-Ion Collisions
(Amer Physical Soc., 2009) Şengül, Metin Y.; Güçlü, Mehmet C.; Fritzsche, S.
The bound-free electron-positron pair production is considered for relativistic heavy ion collisions. In particular cross sections are calculated for the pair production with the simultaneous capture of the electron into the 1s ground state of one of the ions and for energies that are relevant for the relativistic heavy ion collider and the large hadron colliders. In the framework of perturbation theory we applied Monte Carlo integration techniques to compute the lowest-order Feynman diagrams amplitudes by using Darwin wave functions for the bound states of the electrons and Sommerfeld-Maue wave functions for the continuum states of the positrons. Calculations were performed especially for the collision of Au+Au at 100 GeV/nucleon and Pb+Pb at 3400 GeV/nucleon.
Citation - WoS: 3
Citation - Scopus: 4
Busy Tone Based Coexistence Algorithm for Wran and Wlan Systems in Tv White Space
(Inst Engineering Technology-IET, 2018) Karatalay, Onur; Erküçük, Serhat; Baykaş, Tunçer
TV White Space (TVWS) refers to frequency band reserved only for licensed terrestrial TV broadcasting and is opened to unlicensed use under regulatory conditions. While regulations protect licensed systems from interference interference among unlicensed systems is left mainly to manufacturers. Consequently there is a need to develop new coexistence approaches between TVWS networks. Busy tone broadcasting is a coexistence method which can be used by TVWS networks to announce the selected frequency band is occupied. In this paper a busy tone based coexistence algorithm is proposed for IEEE 802.11af and IEEE 802.22 networks and analyzed by considering different client distributions experiencing log-normal shadowing where the exact interfering packet rate and successful packet transmission rate expressions are obtained and validated by simulations for different scenarios. The results show that with the proposed coexistence approach a WLAN can reliably detect the busy tone signal to change its frequency band and can reduce interference to WRAN. Even if there is no available frequency band for the WLAN the WRAN still maintains its enhanced successful packet transmission performance. The deployment of the proposed algorithm is important for successful coexistence between cognitive wireless networks where interference is not regulated such as in TVWS bands.
Citation - WoS: 4
Citation - Scopus: 6
Channel Estimation for Realistic Indoor Optical Wireless Communication in Aco-Ofdm Systems
(Springer, 2018) Özmen, Atilla; Şenol, Habib
In this paper channel estimation problem in a visible light communication system is considered. The information data is transmitted using asymmetrical clipped optical orthogonal frequency division multiplexing. Channel estimation and symbol detection are performed by the Maximum Likelihood and the Linear Minimum Mean Square Error detection techniques respectively. The system performance is investigated in realistic environment that is simulated using an indoor channel model. Two different channels are produced using the indoor channel model. Symbol error rate (SER) performance of the system with estimated channels is presented for QPSK and 16-QAM digital modulation types and compared with the perfect channel state information. As a mean square error (MSE) performance benchmark for the channel estimator Cramer-Rao lower bound is also derived. MSE and SER performances of the simulation results are presented.
Citation - WoS: 9
Citation - Scopus: 9
Complete Density Calculations of Q-State Potts and Clock Models: Reentrance of Interface Densities Under Symmetry Breaking
(Amer Physical Soc, 2020) Artun, E. Can; Berker, A. Nihat
All local bond-state densities are calculated for q-state Potts and clock models in three spatial dimensions, d = 3. The calculations are done by an exact renormalization group on a hierarchical lattice, including the density recursion relations, and simultaneously are the Migdal-Kadanoff approximation for the cubic lattice. Reentrant behavior is found in the interface densities under symmetry breaking, in the sense that upon lowering the temperature, the value of the density first increases and then decreases to its zero value at zero temperature. For this behavior, a physical mechanism is proposed. A contrast between the phase transition of the two models is found and explained by alignment and entropy, as the number of states q goes to infinity. For the clock models, the renormalization-group flows of up to 20 energies are used.
Citation - WoS: 12
Citation - Scopus: 14
Compressive Sensing for Ultra-Wideband Channel Estimation: on the Sparsity Assumption of Ultra-Wideband Channels
(Wiley-Blackwell, 2014) Başaran, Mehmet; Erküçük, Serhat; Cirpan, Hakan Ali
Due to the sparse structure of ultra-wideband (UWB) multipath channels there has been a considerable amount of interest in applying the compressive sensing (CS) theory to UWB channel estimation. The main consideration of the related studies is to propose different implementations of the CS theory for the estimation of UWB channels which are assumed to be sparse. In this study we investigate the suitability of standardized UWB channel models to be used with the CS theory. In other words we question the sparsity assumption of realistic UWB multipath channels. For that we particularly investigate the effects of IEEE 802.15.4a UWB channel models and the selection of channel resolution both on channel estimation and system performances from a practical implementation point of view. In addition we compare the channel estimation performance with the Cramer-Rao lower bound for various channel models and number of measurements. The study shows that although UWB channel models for residential environments (e.g. channel models CM1 and CM2) exhibit a sparse structure yielding a reasonable channel estimation performance channel models for industrial environments (e.g. CM8) may not be treated as having a sparse structure due to multipaths arriving densely. Furthermore it is shown that the sparsity increased by channel resolution can improve the channel estimation performance significantly at the expense of increased receiver processing. Copyright (c) 2013 John Wiley & Sons Ltd.
Citation - WoS: 16
Citation - Scopus: 17
Correlation of Experimental Liquid-Liquid Equilibrium Data for Ternary Systems Using Nrtl and Gmdh-Type Neural Network
(Amer Chemical Soc, 2017) Bekri, Sezin; Özmen, Dilek; Özmen, Atilla
In this work liquid liquid equilibrium (LLE) data for the ternary systems (water + propionic acid + solvent) were experimentally obtained at atmospheric pressure and 298.2 K. The ternary systems show type-1 behavior of LLE. Cyclopentane cyclopentanol 2-octanone and dibutyl maleate were chosen as solvent and it has been noted that there are no data in the literature on these ternary systems. The consistency of the experimental tie-line data was checked using the Hand and Othrner-Tobias correlation equations. A comparison of the extracting capabilities of the solvent was made with respect to the distribution coefficients and separation factors. The correlation of the experimental tie-line data was confirmed by the NRTL thermodynamic model. A Group Method of Data Handling (GMDH)-type neural network (NN) was also used to correlate the experimental tie-lines. It is shown that the results of the both models cohere with the experimental values.
Citation - WoS: 11
Citation - Scopus: 11
Devil's Staircase Continuum in the Chiral Clock Spin Glass With Competing Ferromagnetic-Antiferromagnetic and Left-Right Chiral Interactions
(Amer Physical Soc., 2017) Caglar, Tolga; Berker, A. Nihat
The chiral clock spin-glass model with q = 5 states with both competing ferromagnetic-antiferromagnetic and left-right chiral frustrations is studied in d = 3 spatial dimensions by renormalization-group theory. The global phase diagram is calculated in temperature antiferromagnetic bond concentration p random chirality strength and right-chirality concentration c. The system has a ferromagnetic phase a multitude of different chiral phases a chiral spin-glass phase and a critical (algebraically) ordered phase. The ferromagnetic and chiral phases accumulate at the disordered phase boundary and form a spectrum of devil's staircases where different ordered phases characteristically intercede at all scales of phase-diagram space. Shallow and deep reentrances of the disordered phase bordered by fragments of regular and temperature-inverted devil's staircases are seen. The extremely rich phase diagrams are presented as continuously and qualitatively changing videos.
Citation - WoS: 5
Citation - Scopus: 5
An Efficient Joint Channel Estimation and Decoding Algorithm for Turbo-Coded Space-Time Orthogonal Frequency Division Multiplexing Receivers
(Inst Engineering Technology-IET, 2008) Doğan, Hakan; Çırpan, Hakan Ali; Panayırcı, Erdal
The challenging problem in the design of digital receivers of today's and future high-speed high data-rate wireless communication systems is to implement the optimal decoding and channel estimation processes jointly in a computationally feasible way. Without realising such a critical function perfectly at receiver the whole system will not work properly within the desired performance limits. Unfortunately direct implementation of such optimal algorithms is not possible mainly due to their mathematically intractable and computationally prohibitive nature. A novel algorithm that reaches the performance of the optimal maximum a posteriori (MAP) algorithm with a feasible computational complexity is proposed. The algorithm makes use of a powerful statistical signal processing tool called the expectation-maximisation (EM) technique. It iteratively executes the MAP joint channel estimation and decoding for space-time block-coded orthogonal frequency division multiplexing systems with turbo channel coding in the presence of unknown wireless dispersive channels. The main novelty of the work comes from the facts that the proposed algorithm estimates the channel in a non-data-aided fashion and therefore except a small number of pilot symbols required for initialisation no training sequence is necessary. Also the approach employs a convenient representation of the discrete multipath fading channel based on the Karhunen-Loeve (KL) orthogonal expansion and finds MAP estimates of the uncorrelated KL series expansion coefficients. Based on such an expansion no matrix inversion is required in the proposed MAP estimator. Moreover optimal rank reduction is achieved by exploiting the optimal truncation property of the KL expansion resulting in a smaller computational load on the iterative estimation approach.
Citation - WoS: 2
Citation - Scopus: 3
Em-Based Map Channel Estimation and Data Detection for Downlink Mcc-Cdma Systems
(IEEE, 2007) Doğan, Hakan; Panayırcı, Erdal; Çırpan, Hakan Ali
In this work we propose a joint MAP channel estimation and data detection technique based on the Expectation Maximization (EM) method with paralel interference cancelation(PIC) for downlink multi-carrier (MC) code division multiple access (CDMA) systems in the presence of frequency selective channels. The EM algorithm derived estimates the complex channel parameters of each subcarriers iteratively and generates the soft information representing the data a posterior probabilities. The soft information is then employed in a PIC module to detect the symbols efficiently. Moreover the MAP-EM approach considers the channel variations as random processes and applies the Karhunen-Loeve (KL) orthogonal series expansion. The performance of the proposed approach are studied in terms of bit-error rate (BER) and mean square error (MSE). Throughout the simulations extensive comparisons with previous works in literature are performed showing that the new scheme can offer superior performance.
Citation - Scopus: 7
Fault Tolerant Control With Re-Configuring Sliding-Mode Schemes
(2005) Demirci, Ufuk; 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 - WoS: 6
Citation - Scopus: 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 - WoS: 3
Citation - Scopus: 3
Frustrated Potts Model: Multiplicity Eliminates Chaos Via Reentrance
(Amer Physical Soc, 2020) Türkoğlu, Alpar; Berker, A. Nihat
The frustrated q-state Potts model is solved exactly on a hierarchical lattice, yielding chaos under rescaling, namely, the signature of a spin-glass phase, as previously seen for the Ising (q = 2) model. However, the ground-state entropy introduced by the (q > 2)-state antiferromagnetic Potts bond induces an escape from chaos as multiplicity q increases. The frustration versus multiplicity phase diagram has a reentrant (as a function of frustration) chaotic phase.
Citation - WoS: 6
Citation - Scopus: 6
Growth and Shape Stability of Cu-Ni Core-Shell Nanoparticles: an Atomistic Perspective
(Royal Soc Chemistry, 2018) İlker, Efe; Madran, Melihat; Konuk, Mine; Durukanoğlu, Sondan
The growth and shape stability of bi-metallic cubic Cu-Ni nanoparticles are studied using atomic-level simulations. Cubic nano-crystals coated with an ultra-thin Cu layer can be readily obtained when Ni cubic nanoparticles are used as the seeds. At elevated temperatures the Cu seed with extending Ni branches preserves its shape compared to the Ni seed with extending Cu branches.
Citation - WoS: 3
Citation - Scopus: 3
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 - WoS: 15
Citation - Scopus: 20
Information Theoretical Performance Analysis and Optimisation of Cooperative Underwater Acoustic Communication Systems
(Inst Engineering Technology-IET, 2016) Nouri, Hatef; Uysal, Murat; Panayırcı, Erdal
In this study the authors investigate the information theoretical limits on the performance of single-carrier cooperative underwater acoustic communication systems in the presence of intersymbol interference. The authors assume decode-and-forward relaying and consider orthogonal half-duplex cooperation. Under the assumptions of sparse and frequency-selective Rician fading channel and non-white correlated Gaussian ambient noise the authors derive expressions for bounds on the individual and achievable rates for both cases where channel state information is available at the transmitter or not. Using these expressions the authors optimise input signalling and relay location to maximise average achievable rates.

Browse

Browsing Elektrik - Elektronik Mühendisliği Bölümü Koleksiyonu by Scopus Q "Q2"