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  • 1.
    Irshad, Yasir
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    On some continuous-time modeling and estimation problems for control and communication2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The scope of the thesis is to estimate the parameters of continuous-time models used within control and communication from sampled data with high accuracy and in a computationally efficient way.In the thesis, continuous-time models of systems controlled in a networked environment, errors-in-variables systems, stochastic closed-loop systems, and wireless channels are considered. The parameters of a transfer function based model for the process in a networked control system are estimated by a covariance function based approach relying upon the second order statistical properties of input and output signals. Some other approaches for estimating the parameters of continuous-time models for processes in networked environments are also considered. The multiple input multiple output errors-in-variables problem is solved by means of a covariance matching algorithm. An analysis of a covariance matching method for single input single output errors-in-variables system identification is also presented. The parameters of continuous-time autoregressive exogenous models are estimated from closed-loop filtered data, where the controllers in the closed-loop are of proportional and proportional integral type, and where the closed-loop also contains a time-delay. A stochastic differential equation is derived for Jakes's wireless channel model, describing the dynamics of a scattered electric field with the moving receiver incorporating a Doppler shift.

  • 2.
    Irshad, Yasir
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Mossberg, Magnus
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    A comparison of estimation concepts applied to networked control systems2012In: 19th International Conference on Systems, Signals and Image Processing (IWSSIP), 2012, Piscataway: IEEE Press, 2012, p. 114-117Conference paper (Refereed)
    Abstract [en]

    A continuous-time description of networked control systems is considered and the parameters are estimated. The discrete-time description is time-varying due to the random time-delays in the wireless links and therefore difficult to work with. Off-line as well as on-line situations are considered for parameter estimation. In the off-line situation, a linear regression is formed and then the parameters are estimated by the least squares method. In the on-line situation, the estimates of the parameters are recursively updated for each time instance. A comparative study of two different parameter estimation approaches is presented. In the first approach, the parameters are estimated by a simple linear regression. In the second approach, transformation of the differentiation operator to another casual and stable linear operator is made in linear regression to estimate the parameters. A numerical study of these approaches is also presented for comparison.

  • 3.
    Kassler, Andreas
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Centre for HumanIT. Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Computer Science.
    Proceedings of The 1st Workshop on Wireless Broadband Access for Communities and Rural Developing Regions (WIRELESS4D'08, co-located with M4D 2008): 11-12 December, 2008, Karlstad University, Sweden2008Conference proceedings (editor) (Other academic)
  • 4.
    Mossberg, Magnus
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    A statistical inference method for a subset of long-range dependent FARIMA processes2012In: Statistical Signal Processing Workshop (SSP), 2012 IEEE, IEEE conference proceedings, 2012, p. 456-459Conference paper (Refereed)
    Abstract [en]

    A subset of long-range dependent FARIMA processes is considered. A method for estimating the parameter that describes the long-range dependency of such a process is suggested. The method is based on an asymptotic expression for the covariance function of the process and gives a closed form solution by means of a weighted linear least squares estimate. The variance of the estimate given by themethod is analyzed and, at the same time, the optimal choice of the weighting is expressed. A numerical illustration of the method and the material in the paper is provided

  • 5.
    Mossberg, Magnus
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Analysis of moments based methods for fractional Gaussian noise estimation2012In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 60, no 7, p. 3823-3827Article in journal (Refereed)
    Abstract [en]

    Fractional Gaussian noise, given as the increment of fractional Brownian motion, is a stationary Gaussian process characterized by the Hurst parameter. In the paper, moments based estimators of the Hurst parameter are presented and analyzed with respect to asymptotic variance

  • 6.
    Mossberg, Magnus
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Mossberg, Eva
    Karlstad University, Faculty of Technology and Science, Department of Mathematics.
    A Note on Parameter Estimation in Lamperti Transformed Fractional Ornstein-Uhlenbeck Processes2012In: IFAC Proceedings Volumes / [ed] Kinnaert, Michel, Elsevier, 2012, Vol. 45/16, p. 1067-1072Conference paper (Refereed)
  • 7.
    Mossberg, Magnus
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Sinn, Mathieu
    Cross-correlations of zero crossings in jointly Gaussian and stationary processes with zero means2017In: 2017 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), 5-9 March 2017, New Orleans, LA, IEEE, 2017, p. 4286-4290Conference paper (Refereed)
    Abstract [en]

    Zero crossing data contain information of a process in compact form and is therefore of interest in wireless sensor networks where only reduced amounts of data can be transmitted. When analyzing the properties of certain algorithms using zero crossing data, the cross-covariance between the zero crossing rates of two jointly Gaussian and stationary processes is needed. The evaluation of such a cross-covariance is considered in the paper and an exact numerical expression as well as an asymptotic expression are presented.

  • 8.
    Osesina, Olukayode Isaac
    et al.
    Karlstad University, Division for Information Technology.
    Zhang, Yafan
    Karlstad University, Division for Information Technology.
    Pagoti, Shirisha
    Karlstad University, Division for Information Technology.
    OFDM Carrier Frequency Offset Estimation2006Student thesis
    Abstract [en]

    This thesis discusses and investigates the estimation of carrier offset frequency in

    orthogonal frequency division multiplexing (OFDM) mobile systems. The investigation

    starts by using Mobile WiMAX wireless communication specifications described

    in IEEE 802.16e as the primary system setup. Under this setup orthogonal

    frequency division multiple access (OFDMA) is used as a physical layer scheme; it

    also involves the use of pilots in the OFDM symbol for channel estimation.

    Although OFDM is resistant to multipath fading, it requires a high degree of synchronisation

    to maintain sub-carrier orthogonality. Therefore the level of performance

    of the system depends first on the accuracy in estimating the carrier frequency

    offset and then the estimation of the channel. Maximum likelihood estimator

    is used for estimating carrier frequency offset; its performance under different conditions

    for example SNR, number of virtual carriers needed for estimation etc. are

    simulated and compared with theoretical results. The optimality of IEEE 802.16e

    specifications was also examined during the simulations and results analysis.

  • 9.
    Rathsman, Gustav
    Karlstad University, Faculty of Technology and Science.
    Framtagning av algoritm för artificiell efterklang2012Independent thesis Basic level (degree of Bachelor), 15 credits / 22,5 HE creditsStudent thesis
    Abstract [sv]

    Artificiell efterklang används i ljudinspelning och produktion för att placeraljud spatialt. En algoritm som simulerar efterklang med hjälp av ett filternätverk togs fram.Fokus vid resultat lades på objektiv analys och framför allt spektrogram ochvattenfallsdiagram. Den slutgiltiga modellen gav mätvärden lika målsättningen. Viktigaslutsatser drogs om justering av parametrar och filtermodeller.

  • 10.
    Yasir, Irshad
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics, Science, Mathematics and Engineering Education Research.
    A study of a stochastic differential equation based model for wireless channels2008Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    An autoregressive (AR) first order model is often used for modelling wireless channels. This is done in spite of the fact that a satisfactory physical explanation for this model has been missing. However, in the recent paper [Feng, Field and Haykin. 2007] derive a model in form of a first order stochastic differential equation (SDE) from a stochastic description of the scattered electric field. After discretizing this SDE, a physically motivated first order AR model is obtained.

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