Elektrik - Elektronik Mühendisliği Bölümü Koleksiyonu

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

Browse

Now showing 1 - 20 of 21

Analytic Solution of the Feldtkeller Equation
(Elsevier GMBH Urban & Fischer Verlag, 2009) Şengül, Metin Y.
In every reflectance-based application like broadband matching circuit modeling etc. a nonlinear equation following from energy conservation the Feldtkeller equation must be solved in order to obtain real networks. In the literature however there is no analytic solution available but only numerical solutions. Consequently the resulting error depends on the accuracy of the numerical tools. In this paper an analytic solution is proposed which is based on the modified ABCD-parameters of a lossless reciprocal two-port network. An algorithm is presented and examples are included to illustrate the implementation of the analytical method. (C) 2008 Elsevier GmbH. All rights reserved.
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: 1
Citation - Scopus: 4
Broadband Impedance Matching Via Lossless Unsymmetrical Lattice Networks
(Elsevier GMBH Urban & Fischer Verlag, 2012) Şengül, Metin Y.
In this paper a broadband impedance matching network (equalizer) design algorithm has been proposed. In the equalizer a lossless unsymmetrical lattice network has been utilized. The branch impedances of the lattice network are considered as singly terminated lossless LC networks since it is not desired to dissipate power in the equalizer. After giving the algorithm its usage has been illustrated via an example. (C) 2011 Elsevier GmbH. All rights reserved.
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: 3
Citation - Scopus: 4
Design of Broadband Microwave Amplifiers With Mixed-Elements Via Reflectance Data Modeling
(Elsevier GMBH Urban & Fischer Verlag, 2008) Şengül, Metin Y.; Yarman, Sıddık Binboğa
A practical method is introduced to design single-stage broadband microwave amplifiers with mixed lumped and distributed elements via modeling the reflectance data obtained from lumped-element input and output matching network prototypes. The same transducer power gain level is obtained by using less number of lumped-elements in the mixed-element amplifier than that of the lumped-element amplifier prototype. A mixed-element amplifier design is presented to exhibit the utilization of the method. It is expected that the method will be employed to design microwave amplifiers for broadband communication systems. (C) 2007 Elsevier GmbH. All rights reserved.
Citation - WoS: 6
Citation - Scopus: 8
Design of Broadband Single Matching Networks
(Elsevier GMBH Urban & Fischer Verlag, 2009) Şengül, Metin Y.
In general commercially available software tools are preferred to design broadband matching networks for wireless communication systems. But they need a properly selected matching network topology with good initial element values. Therefore in this paper a new real frequency technique is presented to generate broadband single matching networks with suitable initial element values. In the proposed method load impedance is written in terms of ABCD-parameters of the desired matching network and the source resistor. Then free parameters are optimized which in turn yields the desired matching network with initial element values. It is not needed to select a circuit topology for the matching network which is the natural consequence of the matching processes. Also there is no need to select the desired transducer power gain level , the proposed technique naturally provides a gain curve fluctuating around the final available level. Eventually the initial design is improved by optimizing the performance of the matched system employing the commercially available computer-aided design (CAD) packages. An algorithm and two examples are given to illustrate the utilization of the proposed technique. (C) 2007 Elsevier GmbH. All rights reserved.
Citation - WoS: 11
Design of Distributed-Element Rf Filters Via Reflectance Data Modeling
(Elsevier GMBH Urban & Fischer Verlag, 2008) Şengül, Metin Y.; Yarman, Sıddık Binboğa; Volmer, Christian; Hein, Matthias A.
A reflectance-based modeling method is presented to obtain the distributed-element counterpart of a lumped-element network which is described by measured or computed reflectance data at a set of frequencies. Numerical generation of the scattering parameters forms the basis of this modeling tool. It is not necessary to select a circuit topology for the distributed-element model which is the natural consequence of the modeling process. Our approach supplements the known interpolation methods by a simple technique that does not involve complicated cascaded circuit topologies and whose numerical convergence is proven. To illustrate the utilization of the proposed method a lumped-element low-pass Chebyshev filter is transformed to its distributed-element counterpart. The filter designed for a frequency band around 1 GHz was fabricated and experimentally characterized. We find excellent agreement between measured and simulated transducer power gain over the entire frequency band. (c) 2007 Elsevier GmbH. All rights reserved.
Citation - WoS: 3
Citation - Scopus: 5
Design of Practical Broadband Matching Networks With Commensurate Transmission Lines
(Elsevier GMBH Urban & Fischer Verlag, 2013) Şengül, Metin Y.
To design broadband matching networks for microwave communication systems commercially available computer aided design (CAD) tools are always preferred. But these tools need proper matching network topology and element values. Therefore in this paper a practical method is proposed to generate distributed-element matching networks with good initial element values. Then the gain performance of the designed matching network can be optimized employing these tools. The utilization of the proposed method is illustrated by means of the given example. It is shown that proposed method provides very good initials for CAD tools. (C) 2013 Elsevier GmbH. All rights reserved.
Citation - WoS: 7
Citation - Scopus: 9
Detection of Interdependent Primary Systems Using Wideband Cognitive Radios
(Elsevier GMBH Urban & Fischer Verlag, 2013) Yılmaz, Burak; Erküçük, Serhat
Cognitive radios (CRs) may be sharing multiple frequency bands with primary systems if the CR is a wideband or an ultra wideband (UWB) system. In that case the CR should ensure all the coexisting primary systems in these bands are detected before it can start data transmission. In this work we study the primary system detection performance of a wideband CR assuming that there are multiple coexisting primary systems and that these primary systems may be jointly active. Accordingly we consider the implementation of energy detection scheme in multiple bands followed by two detection methods: (i) a maximum-a-posteriori (MAP) based detection (i.e. joint detection) that takes into account the statistics of simultaneously operating systems in independent bands and (ii) a Neyman-Pearson (NP) test based detection that optimizes the threshold values independently in each band (i.e. independent detection). For a simpler implementation of the independent detection we show that the threshold values obtained from joint detection can be used in order to achieve the optimum NP test based independent detection results. In addition to quantifying the gain of joint detection over independent detection in terms of probabilities of false alarm and detection for practical scenarios we also present the operation capability of CRs in terms of the fractions of time the CR can access the channel without interfering with the primary systems. The results are important for the practical implementation of multiband detection when the primary systems are known to be interdependent. (C) 2013 Elsevier GmbH. All rights reserved.
Citation - WoS: 4
Citation - Scopus: 6
Dual-Hop Amplify-And Multi-Relay Maximum Ratio Transmission
(Korean Inst Communicatıons Sciences (KICS), 2016) Erdoğan, Eylem; Güçlüoğlu, Tansal
In this paper the performance of dual-hop multi-relay maximum ratio transmission (MRT) over Rayleigh flat fading channels is studied with both conventional (all relays participate the transmission) and opportunistic (best relay is selected to maximize the received signal-to-noise ratio (SNR)) relaying. Performance analysis starts with the derivation of the probability density function cumulative distribution function and moment generating function of the SNR. Then both approximate and asymptotic expressions of symbol error rate (SER) and outage probability are derived for arbitrary numbers of antennas and relays. With the help of asymptotic SER and outage probability diversity and array gains are obtained. In addition impact of imperfect channel estimations is investigated and optimum power allocation factors for source and relay are calculated. Our analytical findings are validated by numerical examples which indicate that multi-relay MRT can be a low complexity and reliable option in cooperative networks.
Citation - WoS: 13
Citation - Scopus: 13
Energy Efficient Scma Supported Downlink Cloud-Rans for 5g Networks
(IEEE, 2020) Ferdouse, Lilatul; Erküçük, Serhat; Anpalagan, Alagan; Woungang, Isaac
Cloud-radio access networks (C-RANs) are regarded as a promising solution to provide low cost services among users through the centralized coordination of baseband units for 5G wireless networks. The coordinated multi-point access, visualization and cloud computing technologies enable C-RANs to provide higher capacity and wider coverage, as well as manage the interference and mobility in a centralized coordinated way. However, C-RANs face many challenges due to massive connectivity and spectrum scarcity. If not properly handled, these challenges may degrade the overall performance. Recently, the non-orthogonal multiple access (NOMA) scheme has been suggested as an attractive solution to support multi-user resource sharing in order to improve the spectrum and energy efficiency in 5G wireless networks. In this paper, among various NOMA schemes, we consider and implement the sparse code multiple access (SCMA) scheme to jointly optimize the codebook (CB) and power allocation in the downlink of C-RANs, where the utilization of SCMA in C-RANs to improve the energy efficiency has not been investigated in detail in the literature. To solve this NP-hard joint optimization problem, we decompose the original problem into two sub-problems: codebook allocation and power allocation. Using the conflict graph, we propose the throughput aware SCMA CB selection (TASCBS) method, which generates a stable codebook allocation solution within a finite number of steps. For the power allocation solution, we propose the iterative level-based power allocation (ILPA) method, which incorporates different power allocation approaches (e.g., weighted and NOMA successive interference cancellation (SIC)) into different levels to satisfy the maximum power requirement. Simulation results show that the sum data rate and energy efficiency performances of SCMA supported C-RANs depend on the selected power allocation approach. In terms of energy efficiency, the performance significantly improves with the number of users when the NOMA-SIC aware geometric water-filling based power allocation method is used.
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: 8
Citation - Scopus: 11
An Improved Adaptive Subspace Tracking Algorithm Based on Approximated Power Iteration
(IEEE-INST Electrical Electronics Engineers Inc, 2018) Wu, Qiang; Zheng, Jian-Sheng; Dong, Zhicheng; Panayırcı, Erdal; Wu, Zhi-Qiang; Ren, Qingnuobu
A subspace tracking technique has drawn a lot of attentions due to its wide applications. The main objective of this approach is to estimate signal or noise subspace basis for the sample covariance matrix. In this paper we focus on providing a fast stable and adaptive subspace tracking algorithm that is implemented with low computational complexity. An alternative realization of the fast approximate power iteration (FAPI) method termed modified FAPI (MFAPI) is also presented. Rather than solving an inverse square root of a matrix employed in the FAPI the MFAPI applies the matrix product directly to ensure the orthonormality of the subspace basis matrix at each recursion. This approach yields a simpler derivation and is numerically stable while maintaining a similar computational complexity as compared with that of the FAPI. Furthermore we present a detailed mathematical proof of the numerical stability of our proposed algorithm. Computer simulation results indicate that the MFAPI outperforms many classical subspace tracking algorithms particularly at the transient-state step.
Citation - WoS: 3
Citation - Scopus: 3
Linear Expansions for Frequency Selective Channels in Ofdm
(Elsevier GMBH Urban & Fischer Verlag, 2006) Şenol, Hande; Çırpan, Hakan Ali; Panayırcı, Erdal
Modeling the frequency selective fading channels as random processes we employ a linear expansion based on the Karhumen-Loeve (KL) series representation involving a complete set of orthogonal deterministic vectors with a corresponding uncorrelated random coefficients. Focusing on OFDM transmissions through frequency selective fading this paper pursues a computationally efficient pilot-aided linear minimum mean square error (MMSE) uncorrelated KL series expansion coefficients estimation algorithm. Based on such an expansion no matrix inversion is required in the proposed MMSE estimator. Moreover truncation in the linear expansion of channel is achieved by exploiting the optimal truncation property of the KL expansion resulting in a smaller computational load on the estimation algorithm. The performance of the proposed approach is studied through analytical and experimental results. We first exploit the performance of the MMSE channel estimator based on the evaluation of minimum Bayesian MSE. We also provide performance analysis results studying the influence of the effect of SNR and correlation mismatch on the estimator performance. Simulation results confirm our theoretical results and illustrate that the proposed algorithm is capable of tracking fast fading and improving performance. (c) 2005 Elsevier GmbH. All rights reserved.
Citation - WoS: 92
Citation - Scopus: 106
A Mobile Channel Model for Vlc and Application To Adaptive System Design
(IEEE-INST Electrical Electronics Engineers Inc, 2017) Miramirkhani, Farshad; Narmanlıoğlu, Ömer; Uysal, Murat; Panayırcı, Erdal
In this letter we propose a realistic channel model for visible light communication (VLC) assuming a mobile user. Based on non-sequential ray tracing we first obtain channel impulse responses for each point over the user movement trajectories and then express path loss and delay spread as a function of distance through curve fitting. Our results demonstrate large variations in received power. In system design this necessitates the use of adaptive schemes where transmission parameters can be selected according to channel conditions. To demonstrate the benefits of link adaptation over a mobile VLC channel we propose an adaptive system with luminary selection and demonstrate improvements in spectral efficiency over non-adaptive systems.
Citation - WoS: 6
Citation - Scopus: 7
Modeling Based Real Frequency Technique
(Elsevier GMBH Urban & Fischer Verlag, 2008) Şengül, Metin Y.
Usually commercially available software tools are used to design matching networks for wireless communication systems. But a properly selected matching network topology with good initial element values must be supplied to these tools. Therefore in this paper a modeling-based real frequency technique (M-RFT) is presented to generate matching networks with initial element values. In the proposed method output impedance data of the matching network are obtained in terms of ABCD-parameters of the load model. Then they are modeled which in turn yields the desired matching network with initial element values. It is not needed to select a circuit topology for the matching network which is the natural consequence of the matching processes. Also there is no need to select the desired transducer power gain level
Citation - WoS: 10
Citation - Scopus: 12
On Channel Estimation for Spatial Modulated Systems Over Time-Varying Channels
(Academic Press Inc Elsevier Science, 2015) Acar, Yusuf; Doğan, Hakan; Panayırcı, Erdal
Spatial Modulation (SM) has been proposed recently for multiple-input multiple-output (MIMO) systems to cope with the interchannel interference and to reduce the detection complexity as compared to the conventional MIMO systems. In SM system the data symbols are transmitted by a randomly selected active antenna of a MIMO transmitter to the receiver through a wireless channel. The information is carried both by the data symbol from any signal constellation such as M-ary phase shift keying (M-PSK) or M-ary quadrature amplitude modulation (M-QAM) by the index of the selected antenna. The channel estimation is a critical process at the receiver during the coherent detection of the transmitted symbol and the antenna index randomly selected. Recently the channel estimation of channel for SM systems has been investigated by the recursive least square (RLS) algorithm for only quasi-static fading channels. In this paper a novel channel estimation is proposed for SM systems in the presence of rapidly time-varying channels. The Bayesian mean square error (MSE) bound has been derived as a benchmark and the performance of the proposed approaches is studied in terms of MSE and bit-error rate (BER). Computer simulation results have confirmed that the proposed iterative channel estimation technique has significant BER/MSE performance advantages compared with existing channel estimation algorithm proposed earlier in the literature. (C) 2014 Elsevier Inc. All rights reserved.
Citation - WoS: 150
Citation - Scopus: 164
Performance of Spatial Modulation in the Presence of Channel Estimation Errors
(IEEE-INST Electrical Electronics Engineers Inc, 2012) Basar, Ertuğrul; Aygölü, Ümit; Panayırcı, Erdal; Poor, H. Vincent
This work investigates the negative effects of channel estimation errors on the performance of spatial modulation (SM) when operating over flat Rayleigh fading channels. The pairwise error probability of the SM scheme is derived in the presence of channel estimation errors and an upper bound on the average bit error probability is evaluated for M-PSK and M-QAM signalling. It is shown via computer simulations that the derived upper bound becomes very tight with increasing signal-to-noise ratio (SNR) and the SM scheme is quite robust to channel estimation errors.
Citation - WoS: 30
Citation - Scopus: 35
Performance of Transmit and Receive Antenna Selection in the Presence of Channel Estimation Errors
(IEEE-INST Electrical Electronics Engineers Inc, 2008) Güçlüoğlu, Tansal; Panayırcı, Erdal
This letter considers the effect of channel estimation errors on the performance of space-time coded (STC) systems with transmit and receive antenna selection over quasi-static flat fading channels. By performing pairwise error probability analysis and presenting numerical examples we show that the diversity order achieved with perfect channel state information (CSI) is still achievable with imperfect CSI used both at the antenna selection and the space-time decoding processes. We note that our results apply to general STC systems with both transmit and/or receive antenna selection based on largest received powers which can be estimated by any channel estimator.
Citation - WoS: 5
Citation - Scopus: 7
Power and Rate Adaptation Based on Csi and Velocity Variation for Ofdm Systems Under Doubly Selective Fading Channels
(IEEE-INST Electrical Electronics Engineers Inc, 2016) Dong, Zhicheng; Fan, Pingzhi; Lei, Xianfu; Panayırcı, Erdal
In this paper a novel joint continuous power and rate adaptation scheme is proposed fordoubly selective fading channels in orthogonal frequency division multiplexing (OFDM) systems based on terminal velocity and perfect or imperfect channel state information (CSI). The analysis and simulation results show that the continuous power and rate adaptation scheme is very effective and improve the performance of OFDM systems substantially under time-varying fading channels as compared with the traditional adaptation schemes operating without a priori knowledge of velocity and mobility adaptation without CSI.