Now showing items 1-20 of 177

  • A synthesis tool for the multiplierless realization of FIR-based multirate DSP systems 

    Authors:Yurdakul, Arda
    Publisher and Date:(IEEE, 2000)
    In this study a synthesis tool using a novel multirate folding technique which handles each FIR filter in a multirate DSP system as a single node is developed. A new architecture is presented for the multiplierless realization of a fold of multirate FIR filters. This synthesizer fully exploits the redundancies (i.e. `idle' and `missing' cycles) and common terms in multirate systems without sacrificing from overall system quality to produce multiplierless multirate systems. It also enables the usage ...

  • Cosmic ray intensity variation during a CME 

    The June 6 2000 coronal mass ejection was an exceptional full halo which made it possible to measure cosmic ray (CR) decrease with a simple experimental set-up. Variation in the local secondary cosmic ray density has been investigated by means of gamma rays. The experiment site was located in Istanbul (41.1N 29.0E). CR electrons and slow gamma rays have been eliminated. The CR density has dropped drastically starting on June 8 2000. The counts have been compared with the pre-shock levels and some ...

  • Zero-crossing based demodulation of minimum shift keying 

    Authors:Kalkan, Mine; Kerestecioǧlu, Feza
    Publisher and Date:(2003)
    Minimum shift keying (MSK) modulation has features such as constant envelope compact spectrum and good error performance which are all desirable in many digital applications including mobile radio. Numerous receiver structures to demodulate MSK have been suggested such as correlation receivers differential detectors and frequency discriminators MSK is a form of biphase keying and can be detected by a zero-crossing based phase demodulator which gives near optimum performance. In this paper the bit ...

  • Active reconfigurable control of a submarine with indirect adaptive control 

    Authors:Demirci, Ufuk; Kerestecioǧlu, Feza
    Publisher and Date:(2003)
    An indirect adaptive controller is designed for submersibles. The design is developed using a linearized MIMO model of a submarine. Standard recursive least squares estimation method is used to estimate the parameters. Depth and pitch angle of the submarine is controlled by means of the well-known indirect self-tuning method. In case of a system fault estimated parameters of the submarine model have been used to update the controller coefficients.

  • Nonuniform sampling for detection of abrupt changes 

    Authors:Kerestecioǧlu, Feza; Tokat, Sezai
    Publisher and Date:(Birkhauser Boston Inc, 2003)
    In this work detection of abrupt changes in continuous-time linear stochastic systems and selection of the sampling interval to improve the detection performance are considered. Cost functions are proposed to optimize both uniform and nonuniform sampling intervals for the well-known cumulative sum algorithm. Some iterative techniques are presented to make online optimization computationally feasible. It is shown that considerable improvement in the detection performance can be obtained by using ...

  • An open software architecture of neural networks: Neurosoft 

    Authors:Öǧrenci, Arif Selçuk; Arsan, Taner; Saydam, Tuncay
    Publisher and Date:(2004)
    Software architecture of generic distributed neural networks and its relevant information model have been developed. Principles of on-line architecture building training controlling (managing) and topological optimization guidelines are provided and extensively discussed.

  • Optimal input design for the detection of changes towards unknown hypotheses 

    Authors:Kerestecioǧlu, Feza; Cetin, I
    Publisher and Date:(Taylor & Francis Ltd, 2004)
    The effects of auxiliary input signals on detecting changes in ARMAX processes via statistical tests are discussed. Two extensions to the Cumulative Sum Test are considered. The first is applicable when the direction of the change in the parameter space is known but its magnitude is unknown. The second is applicable when neither is known. The performance criteria for the design of stationary stochastic inputs are based on the asymptotic properties of the tests. It is shown that power-constrained ...

  • A re-configuring sliding-mode controller with a ustable robustness 

    In this paper a controller design method for underwater vehicles is presented which is based on re-configuration of a sliding-mode controller in case of disturbances caused by shallow water conditions. The disturbance distribution information can be obtained and used to update the corrective gain vector of the sliding-mode controller. This increases the robustness of the controller and hence keeps the system performance within acceptable limits. Proposed method is validated with simulations on a ...

  • Pilot-aided bayesian MMSE channel estimation for OFDM systems: Algorithm and performance analysis 

    Authors:Şenol, Habib; Cirpan, Hakan Ali; Panayirci, Erdal
    Publisher and Date:(2004)
    This paper proposes a computationally efficient pilot-aided minimum mean square error (MMSE) channel estimation algorithm for OFDM systems. The proposed approach employs a convenient representation of the discrete multipath fading channel based on the Karhunen-Loeve (KL) orthogonal expansion and estimates uncorrelated series expansion coefficients. Moreover optimal rank reduction is achieved in the proposed approach by exploiting the optimal truncation property of the KL expansion resulting in a ...

  • A low-complexity KL expansion-based channel estimator for OFDM systems 

    Authors:Şenol, Habib; Cirpan, Hakan Ali; Panayirci, Erdal
    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 ...

  • Frequency selective fading channel estimation in OFDM systems using KL expansion 

    Authors:Şenol, Habib; Cirpan, Hakan Ali; Panayirci, Erdal
    Publisher and Date:(2005)
    This paper proposes a computationally efficient linear minimum mean square error (MMSE) channel estimation algorithm based on KL series expansion for OFDM systems. Based on such 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 ...

  • A low-complexity time-domain MMSE channel estimator for space-time/frequency block-coded OFDM systems 

    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 ...

  • Linear expansions for frequency selective channels in OFDM 

    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. ...

  • The effects of higher-order approximations in a fluid-filled elastic tube with stenosis 

    Authors:Demiray, Hilmi
    Publisher and Date:(Verlag der Zeitschrift fur Naturforschung, 2006)
    Treating arteries as thin-walled prestressed elastic tubes with a narrowing (stenosis) and blood as an inviscid fluid we study the propagation of weakly nonlinear waves in such a fluid-filled elastic tube by employing the reductive perturbation method in the long wave approximation. It is shown that the evolution equation of the first-order term in the perturbation expansion may be described by the conventional Korteweg-de Vries (KdV) equation. The evolution equation for the second-order term is ...

  • Influence of pH on the optical and structural properties of spin coated CeO2-TiO2 thin films prepared by sol-gel process 

    Optical and structural properties of mixed CeO2-TiO2 thin films have been investigated by varying the pH of the coating sol. The films were prepared by sol-gel process using spin-coating technique with a spin speed of 2500 rpm. The optical and structural properties of films were examined by a spectrophotometer AFM and XRD. Optical constants and thickness of the CeO2-TiO2 thin films have been determined with respect to the pH of the coating bath before deposition. The refractive index at 550 nm ...

  • The effect of a bump in an elastic tube on wave propagation in a viscous fluid of variable viscosity 

    Authors:Demiray, Hilmi
    Publisher and Date:(Elsevier Science, 2007)
    In the present work treating the arteries as a thin walled prestressed elastic tube with a bump and the blood as a Newtonian fluid of variable viscosity we have studied the propagation of weakly nonlinear waves in such a medium by employing the reductive perturbation method in the longwave approximation. Korteweg-deVries-Burgers equation with variable coefficients is obtained as the evolution equation. Seeking a progressive wave type of solution to this evolution equation it is observed that the ...

  • Optical and structural properties of Ta2O5-CeO2 thin films 

    In this study the sol-gel spin-coating method has been used to make Ta2O5-CeO2 thin films. These films have been prepared in various composition ratios to observe changes in their optical and structural properties. Reflectance and transmittance spectra were collected in the spectral range of 300-1000 nm and were accurately fit using the Tauc-Lorentz model. Film thicknesses refractive indices absorption coefficients and optical band gaps were extracted from the theoretical fit. The highest refractive ...

  • Distributed estimation with channel estimation error over orthogonal fading channels 

    Authors:Şenol, Habib; Tepedelenlioğlu, Cihan
    Publisher and Date:(IEEE, 2007)
    We study distributed estimation of a source corrupted by an additive Gaussian noise and observed by sensors which are connected to a fusion center with unknown orthogonal (parallel) flat Rayleigh fading channels. The fading communication channels are estimated with training. Subsequently source estimation given the channel estimates and transmitted sensor observations is performed. We consider a setting where the estimated channels are fed-back to the sensors for optimal power allocation which ...

  • Text area detection in digital documents images using textural features 

    Authors:Ar, İlktan; Karsligil, M. Elif
    Publisher and Date:(Springer, 2007)
    In this paper we propose a new texture-based method for extraction of text areas in a complex document image. Gabor filter motivated by the multi-channel filtering approach of Human Visual System (HVS) has been employed to create energy map of the document. In this energy map we assumed that text areas were rich in high frequency components. Connected components (probable text characters) were extracted by binarization of the energy map with Otsu's adaptive threshold method. First non-text components ...

  • An Integrated Software Architecture for Bandwidth Adaptive Video Streaming 

    Authors:Arsan, Taner
    Publisher and Date:(World Acad Sci Eng & Tech-Waset, 2008)
    Video streaming over lossy IP networks is very important issues due to the heterogeneous structure of networks. Infrastructure of the Internet exhibits variable bandwidths delays congestions and time-varying packet losses. Because of variable attributes of the Internet video streaming applications should not only have a good end-to-end transport performance but also have a robust rate control furthermore multipath rate allocation mechanism. So for providing the video streaming service quality some ...