Browsing Elektrik-Elektronik Mühendisliği / Electrical - Electronics Engineering by Type "Article"
Now showing items 1-20 of 138
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A low-complexity KL expansion-based channel estimator for OFDM systems
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Publisher and Date:(2005)This paper first proposes a computationally efficient pilot-aided linear minimum mean square error (MMSE) batch channel estimation algorithm for OFDM systems in unknown wireless fading channels. The proposed approach employs a convenient representation of the discrete multipath fading channel based on the Karhunen-Loeve (KL) orthogonal expansion and finds MMSE estimates of the uncorrelated KL series expansion coefficients. Based on such an expansion no matrix inversion is required in the proposed ...
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A low-complexity time-domain MMSE channel estimator for space-time/frequency block-coded OFDM systems
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Publisher and Date:(Hindawi Publishing Corporation, 2006)Focusing on transmit diversity orthogonal frequency-division multiplexing (OFDM) transmission through frequency-selective channels this paper pursues a channel estimation approach in time domain for both space-frequency OFDM (SF-OFDM) and space-time OFDM (ST-OFDM) systems based on AR channel modelling. The paper proposes a computationally efficient pilot-aided linear minimum mean-square-error (MMSE) time-domain channel estimation algorithm for OFDM systems with transmitter diversity in unknown ...
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A Mobile Channel Model for VLC and Application to Adaptive System Design
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Publisher and Date:(IEEE-INST Electrical Electronics Engineers Inc, 2017)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 ...
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A Monte Carlo implementation of the SAGE algorithm for joint soft-multiuser decoding channel parameter estimation and code acquisition
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Publisher and Date:(2010)This paper presents an iterative scheme for joint timing acquisition multi-channel parameter estimation and multiuser soft-data decoding. As an example an asynchronous convolutionally coded direct-sequence code-division multiple-access system is considered. The proposed receiver is derived within the space-alternating generalized expectation-maximization framework implying that convergence in likelihood is guaranteed under appropriate conditions in contrast to many other iterative receiver ...
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A Reliable Successive Relaying Protocol
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Publisher and Date:(IEEE-INST Electrical Electronics Engineers Inc, 2014)Successive relaying has recently emerged as an effective technique for cooperative networks and provides significant improvements in bandwidth efficiency over traditional relaying techniques ;however to achieve full-diversity the available successive relaying protocols generally assume noise-free sourcerelay and interference-free inter-relay channels. In this paper a novel successive relaying protocol is proposed for N-relay wireless networks by removing these optimistic assumptions. The proposed ...
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Across dimensions: Two- and three-dimensional phase transitions from the iterative renormalization-group theory of chains
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Publisher and Date:(2020)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 ...
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AN ALTERNATIVE APPROACH TO DESIGN LUMPED ELEMENT DELAY EQUALIZERS
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Publisher and Date:(AVES YAYINCILIK, 2015)In this paper, an algorithm has been proposed to design lumped element delay equalizers which is considered as a single block as opposed to the existing methods in literature. Then after obtaining the desired delay performance, the designed delay equalizer is divided and realized as cascaded first-order and/or secondorder all-pass circuits. An example is given to illustrate the utilization of the proposed algorithm.
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Amplitude and Frequency Modulations with Cellular Neural Networks
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Publisher and Date:(Springer, 2015)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 ...
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An Alternative Approach To Design Lumped Element Delay Equalizers
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Publisher and Date:(Istanbul Univ Fac Engineering, 2015)In this paper an algorithm has been proposed to design lumped element delay equalizers which is considered as a single block as opposed to the existing methods in literature. Then after obtaining the desired delay performance the designed delay equalizer is divided and realized as cascaded first-order and/or second-order all-pass circuits. An example is given to illustrate the utilization of the proposed algorithm.
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An efficient joint channel estimation and decoding algorithm for turbo-coded space-time orthogonal frequency division multiplexing receivers
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Publisher and Date:(Inst Engineering Technology-IET, 2008)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 ...
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An Improved Adaptive Subspace Tracking Algorithm Based on Approximated Power Iteration
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Publisher and Date:(IEEE-INST Electrical Electronics Engineers Inc, 2018)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 ...
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Analysis of Mixed-Element Structures Formed With Shunt Capacitors Separated by Transmission Lines
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Publisher and Date:(IEEE-Inst Electrical Electronics Engineers Inc, 2019)In this brief, the analysis of mixed-element structures formed with shunt capacitors separated by commensurate transmission lines is performed first time in the literature. First, a low-pass lumped-element ladder network is considered. Then the series inductors are replaced with commensurate transmission lines. As a result, a practically important mixed-element structure is obtained. Then the description of the structure by means of two frequency variables (one for shunt capacitors and one for ...
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Analytic solution of the Feldtkeller equation
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Publisher and Date:(Elsevier GMBH Urban & Fischer Verlag, 2009)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 ...
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Bayesian Compressive Sensing For Primary User Detection
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Publisher and Date:(Inst Engineering Technology-IET, 2016)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 ...
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Bayesian compressive sensing for ultra-wideband channel estimation: algorithm and performance analysis
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Publisher and Date:(Springer, 2015)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 ...
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Bayesian estimation of discrete-time cellular neural network coefficients
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Publisher and Date:(TUBITAK Scientific & Technical Research Council Turkey, 2017)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 ...
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Blind-phase noise estimation in OFDM systems by sequential Monte Carlo method
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Publisher and Date:(John Wiley and Sons Ltd, 2006)One of the main drawbacks of orthogonal frequency division multiplexing (OFDM) systems is the phase noise (PN) caused by the oscillator instabilities. Unfortunately due to the PN the most valuable feature namely orthogonality between the carriers is destroyed resulting in a significant degradation in the performance of OFDM systems. In this paper based on a sequential Monte Carlo method (particle filtering) a computationally efficient algorithm is presented for estimating the residual phase noise ...
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Bound free electron-positron pair production accompanied by giant dipole resonances
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Publisher and Date:(Amer Physical Soc., 2011)At the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) for example virtual photons produce many particles. At small impact parameters where the colliding nuclei make peripheral collisions photon fluxes are very large and these are responsible for the multiple photonuclear interactions. Free pair productions bound free pair productions and nuclear Coulomb excitations are important examples of such interactions and these processes play important roles in the beam luminosity ...
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Bound-free electron-positron pair production in relativistic heavy-ion collisions
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Publisher and Date:(Amer Physical Soc., 2009)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 ...
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Broadband Decoupling and Matching of a Superdirective Two-Port Antenna Array
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Publisher and Date:(IEEE-INST Electrical Electronics Engineers Inc, 2008)Decoupling and matching networks may be used to improve the performance of compact antenna arrays where mutual radiator coupling has caused a degradation of the diversity capabilities. A popular network consists of a 180 degrees rat-race directional coupler which decouples the antenna ports followed by impedance matching networks at each port. Researchers however usually neglect the presence of losses both within the antenna array and the decoupling and matching network. For this reason we have ...