Elektrik - Elektronik Mühendisliği Bölümü Koleksiyonu

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

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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: 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: 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: 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: 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: 13
Effect of Power and Rate Adaptation on the Spectral Efficiency of Mqam/Ofdm System Under Very Fast Fading Channels
(Springer International Publishing Ag, 2012) Dong, Zhicheng; Fan, Pingzhi; Panayırcı, Erdal; Mathiopoulos, P. Takis
In this article the effect of power and rate adaptation on the spectral efficiency of orthogonal frequency division multiplexing (OFDM) systems using M-ary quadrature amplitude modulation (MQAM) is investigated in the presence of frequency selective and very rapidly time-varying fading channels under power and instantaneous bit error rate (BER) constraints. Lower bounds on the maximum spectral efficiency of adaptive OFDM/MQAM systems with perfect and imperfect channel state information (CSI) are obtained together with a closed-form expression for the average spectral efficiency of adaptive OFDM systems. The delay between the channel estimation and the actual transmission is also considered in this article. The theoretical and numerical results show that the adaptive MQAM/OFDM systems under fast fading channels have substantial gains in spectral efficiency over the non-adaptive counterparts with perfect CSI or moderate imperfect CSI. The theoretical and numerical results also show that a good way to deal with the delay CSI under very rapidly time-varying channels is to increase the subcarrier bandwidth of the OFDM system while ignoring the impact of the cyclic prefix.
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: 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 - 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
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.
Citation - WoS: 5
Citation - Scopus: 5
Information Theoretical Performance Limits of Single-Carrier Underwater Acoustic Systems
(Inst Engineering Technology-IET, 2014) Nouri, Hatef; Uysal, Murat; Panayırcı, Erdal; Şenol, Habib
In this study the authors investigate the information theoretical limits on the performance of point-to-point single-carrier acoustic systems over frequency-selective underwater channels with intersymbol interference. Under the assumptions of sparse and frequency-selective Rician fading channel and non-white correlated Gaussian ambient noise the authors derive an expression for channel capacity and demonstrate the dependency on channel parameters such as the number location and power delay profile of significant taps as well as environmental parameters such as distance temperature salinity pressure and depth. Then the authors use this expression to determine the optimal carrier frequency input signalling and bandwidth for capacity maximisation.
Citation - WoS: 10
Citation - Scopus: 13
Interpolation Based Pilot-Aided Channel Estimation for Stbc Spatial Modulation and Performance Analysis Under Imperfect Csi
(Inst Engineering Technology-IET, 2016) Acar, Yusuf; Dogan, Hakan; Basar, Ertugrul; Panayırcı, Erdal
A combination of space-time block coding and spatial modulation (STBC-SM) has been recently proposed for multiple input-multiple output systems to obtain both spatial diversity gain and more capacity simultaneously while assuming the perfect channel state information (P-CSI) was available at the receiver. However in practical scenarios the CSI is unknown to the receiver and should be estimated in order to detect the transmitted data in a reliable way. Therefore channel estimation (CE) is a major challenge in designing the STBC-SM systems. In this study the problem of CE is investigated and a new pilot-aided channel estimation (PA-CE) technique coupled with an interpolation is proposed for the STBC-SM systems operating in the presence of rapidly time-varying mobile channels. Several interpolation schemes such as the linear nearest neighbour piecewise cubic Hermite and the low-pass interpolations are applied and their performances are compared to determine the best suitable interpolation technique to be employed in STBC-SM systems. Bit error rate (BER) performance of the proposed CE technique is then investigated in time-varying channels with different modulation. Moreover the pairwise error probability of the STBC-SM scheme is derived and its average bit error probability is evaluated analytically in the presence of CE errors.
Citation - Scopus: 9
Iterative Joint Data Detection and Channel Estimation for Uplink Mc-Cdma Systems in the Presence of Frequency Selective Channels
(2010) Panayırcı, Erdal; Dogan, Hakan; Cirpan, Hakan Ali; Kocian, Alexander; Fleury, Bernard Henri
This paper is concerned with joint multiuser detection and multichannel estimation (JDE) for uplink multicarrier code-division multiple-access (MC-CDMA) systems in the presence of frequency selective channels. The detection and estimation implemented at the receiver are based on a version of the expectation maximization (EM) algorithm and the space-alternating generalized expectation-maximization (SAGE) which are very suitable for multicarrier signal formats. The EM-JDE receiver updates the data bit sequences in parallel while the SAGE-JDE receiver reestimates them successively. The channel parameters are updated in parallel in both schemes. Application of the EM-based algorithm to the problem of iterative data detection and channel estimation leads to a receiver structure that also incorporates a partial interference cancelation. Computer simulations show that the proposed algorithms have excellent BER end estimation performance. Crown Copyright © 2009.
Citation - WoS: 18
Citation - Scopus: 20
Joint Wavelet-Based Spectrum Sensing and Fbmc Modulation for Cognitive Mmwave Small Cell Networks
(Inst Engineering Technology-IET, 2016) Hosseini, Haleh; Anpalagan, Alagan; Raahemifar, Kaamran; Erküçük, Serhat; Habib, Salman
Millimetre-wave (mmWave) 5G communications is an emerging technology to enhance the capacity of existing systems by thousand-fold improvement. Heterogeneous networks employing densely distributed small cells can optimise the available coverage and throughput of 5G systems. Efficiently utilising the spectrum bands by small cells is one of the approaches that will considerably increase the available data rate and capacity of the heterogeneous networks. This challenging task can be achieved by spectrum sensing capability of cognitive radios and new modulation techniques for data transmission. In this study a wavelet-based filter bank is proposed for spectrum sensing and modulation in 5G heterogeneous networks. The proposed technique can mitigate the spectral leakage and interference by adapting the subcarriers according to cognitive information provided by wavelet packet based spectrum sensing (WPSS) and lowering sidelobes using wavelet-based filter bank multicarrier modulation. The performance improvement of WPSS compared with Fourier-based spectrum sensing is verified in terms of power spectral density comparison and probabilities of detection and false alarm. Meanwhile the bit error rate performance demonstrates the superiority of the proposed wavelet-based system compared with its Fourier-based counterpart over the 60 GHz mmWave channel.
Citation - Scopus: 26
Low-Complexity Joint Data Detection and Channel Equalisation for Highly Mobile Orthogonal Frequency Division Multiplexing Systems
(2010) Dogan, Hakan; Panayırcı, Erdal; Poor, H. Vincent
This study is concerned with the challenging and timely problem of channel equalisation and data detection for orthogonal frequency division multiplexing (OFDM) systems in the presence of frequency-selective and very rapidly time-varying channels. The algorithm is based on the space alternating generalised expectation-maximisation (SAGE) technique which is particularly well suited to multicarrier signal formats and can be easily extended to multi-input multi-output-OFDM systems. In fast fading channels the orthogonality between subcarriers is destroyed by the time variation of a fading channel over an OFDM symbol duration which causes severe inter-carrier interference (ICI) and in conventional frequency-domain approaches results in an irreducible error floor. The proposed joint data detection and equalisation algorithm updates the data sequences in series leading to a receiver structure that also incorporates ICI cancellation enabling the system to operate at high vehicle speeds. A computational complexity investigation as well as detailed computer simulations indicate that this algorithm has significant performance and complexity advantages over existing suboptimal detection and equalisation algorithms proposed earlier in the literature. © 2010 The Institution of Engineering and Technology.

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