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  • 1.
    Abd-Elrady, Emad
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Nonlinear Approaches to Periodic Signal Modeling2005Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Periodic signal modeling plays an important role in different fields. The unifying theme of this thesis is using nonlinear techniques to model periodic signals. The suggested techniques utilize the user pre-knowledge about the signal waveform. This gives these techniques an advantage as compared to others that do not consider such priors.

    The technique of Part I relies on the fact that a sine wave that is passed through a static nonlinear function produces a harmonic spectrum of overtones. Consequently, the estimated signal model can be parameterized as a known periodic function (with unknown frequency) in cascade with an unknown static nonlinearity. The unknown frequency and the parameters of the static nonlinearity are estimated simultaneously using the recursive prediction error method (RPEM). A treatment of the local convergence properties of the RPEM is provided. Also, an adaptive grid point algorithm is introduced to estimate the unknown frequency and the parameters of the static nonlinearity in a number of adaptively estimated grid points. This gives the RPEM more freedom to select the grid points and hence reduces modeling errors.

    Limit cycle oscillations problem are encountered in many applications. Therefore, mathematical modeling of limit cycles becomes an essential topic that helps to better understand and/or to avoid limit cycle oscillations in different fields. In Part II, a second-order nonlinear ODE is used to model the periodic signal as a limit cycle oscillation. The right hand side of the ODE model is parameterized using a polynomial function in the states, and then discretized to allow for the implementation of different identification algorithms. Hence, it is possible to obtain highly accurate models by only estimating a few parameters.

    In Part III, different user aspects for the two nonlinear approaches of the thesis are discussed. Finally, topics for future research are presented.

  • 2.
    Abd-Elrady, Emad
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Harmonic signal modeling based on the Wiener model structure2002Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The estimation of frequencies and corresponding harmonic overtones is a problem of great importance in many situations. Applications can, for example, be found in supervision of electrical power transmission lines, in seismology and in acoustics. Generally, a periodic function with an unknown fundamental frequency in cascade with a parameterized and unknown nonlinear function can be used as a signal model for an arbitrary periodic signal. The main objective of the proposed modeling technique is to estimate the fundamental frequency of the periodic function in addition to the parameters of the nonlinear function.

    The thesis is divided into four parts. In the first part, a general introduction to the harmonic signal modeling problem and different approaches to solve the problem are given. Also, an outline of the thesis and future research topics are introduced.

    In the second part, a previously suggested recursive prediction error method (RPEM) for harmonic signal modeling is studied by numerical examples to explore the ability of the algorithm to converge to the true parameter vector. Also, the algorithm is modified to increase its ability to track the fundamental frequency variations.

    A modified algorithm is introduced in the third part to give the algorithm of the second part a more stable performance. The modifications in the RPEM are obtained by introducing an interval in the nonlinear block with fixed static gain. The modifications that result in the convergence analysis are, however, substantial and allows a complete treatment of the local convergence properties of the algorithm. Moreover, the Cramér–Rao bound (CRB) is derived for the modified algorithm and numerical simulations indicate that the method gives good results especially for moderate signal to noise ratios (SNR).

    In the fourth part, the idea is to give the algorithm of the third part the ability to estimate the driving frequency and the parameters of the nonlinear output function parameterized also in a number of adaptively estimated grid points. Allowing the algorithm to automatically adapt the grid points as well as the parameters of the nonlinear block, reduces the modeling errors and gives the algorithm more freedom to choose the suitable grid points. Numerical simulations indicate that the algorithm converges to the true parameter vector and gives better performance than the fixed grid point technique. Also, the CRB is derived for the adaptive grid point technique.

  • 3.
    Abd-Elrady, Emad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Söderström, Torsten
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Wigren, Torbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Periodic signal analysis using orbits of nonlinear ODEs based on the Markov estimate2004Conference paper (Refereed)
  • 4.
    Abd-Elrady, Emad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Söderström, Torsten
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Wigren, Torbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Periodic signal modeling based on Liénard's equation2004In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 49, no 10, 1773-1778 p.Article in journal (Refereed)
  • 5.
    Abd-Elrady, Emad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Söderström, Torsten
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Wigren, Torbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Periodic signal modeling based on Liénard's equation2003Report (Other academic)
  • 6.
    Abrahamsson, Richard
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Estimation Problems in Array Signal Processing, System Identification, and Radar Imagery2006Doctoral thesis, monograph (Other academic)
    Abstract [en]

    This thesis is concerned with parameter estimation, signal processing, and applications.

    In the first part, imaging using radar is considered. More specifically, two methods are presented for estimation and removal of ground-surface reflections in ground penetrating radar which otherwise hinder reliable detection of shallowly buried landmines. Further, a study of two autofocus methods for synthetic aperture radar is presented. In particular, we study their behavior in scenarios where the phase errors leading to cross-range defocusing are of a spatially variant kind.

    In the subsequent part, array signal processing and optimal beamforming is regarded. In particular, the phenomenon of signal cancellation in adaptive beamformers due to array perturbations, signal correlated interferences and limited data for covariance matrix estimation is considered. For the general signal cancellation problem, a class of improved adaptive beamformers is suggested based on ridge-regression. Another set of methods is suggested to mitigate signal cancellation due to correlated signal and interferences based on a novel way of finding a characterization of the interference subspace from observed array data. Further, a new minimum variance beamformer is presented for high resolution non-parametric spatial spectrum estimation in cases where the impinging signals are correlated. Lastly, a multitude of enhanced covariance matrix estimators from the statistical literature are studied as an alternative to other robust adaptive beamforming methods. The methods are also applied to space-time adaptive processing where limited data for covariance matrix estimation is a common problem.

    In the third and final part the estimation of the parameters of a general bilinear problem is considered. The bilinear model is motivated by the application of identifying submarines from their electromagnetic signature and by the identification of a Hamerstein-Wiener model of a non-linear dynamic system. An efficient approximate maximum-likelihood method with closed form solution is suggested for estimating the bilinear model parameters.

  • 7.
    Abuzohri, Ahmed
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Effektförstärkare med strömkontroll2012Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Energin är ett begrepp som används dagligen i vårt samhälle. Energin kan inte skapas men däremot kan den omvandlas till olika former, förbrukas och lagras i vissa fall. Men att omvandla energi från en form till en annan form för att sedan lagra den är en av dagens stora utmaningar inom tekniken då vi måste följa de regler som naturen dikterar. Forskning på detta område har pågått i flera decennier för att kunna ta fram lämpliga och effektiva sätt att lagra energi på. Svänghjul-system är ett sådant sätt där man kan lagra energi under begränsad tid.

    I mitt examensarbete har jag utnyttjat kunskapen som jag har lärt mig från elektronik kurserna för att konstruera en effektförstärkare med strömkontroll som användes för att driva ett svänghjul-system. Förstärkaren har byggts med elektronikkomponenter och styrs från datorn med m.h.a. styrprogrammet LabVIEW som kommunicerar med hårdvaran och kontrollerar svänghjulets rörelse.

  • 8.
    af Ekenstam, Love
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Modellering av signalbehandlingen i ett cochleaimplantat och utvärdering av modellen.2014Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    A program that simulates the signal processing in a cochlear implant using the signal processing strategy ACE (Advanced Combination Encoder) was constructed. Its main purpose is to, in advance, predict and test different implant settings with the purpose to be able to predict individual patient's differences in implant settings.

     

    The program was validated using output signals processed by Cochlear Limited using their own Matlab Toolbox for implant research, NMT (Nucleus Matlab Toolbox). Identical signals were processed by the program and then compared with NMT:s output. The outputs, produced with several different identical settings matched each other well.

     

    The amplitude compression function, a vital part of the signal processing, also matched well, apart from a relative loss of strength at high input amplitudes. The program will now be used by the cochlear implant section at Uppsala University Hospital to try out individual settings for cochlear implant users. The hope for the future is that better implant settings will lead to improved speech and sound experience, especially, in the long run, with regards to music.

  • 9. Ahlgren Peters, Adam
    et al.
    Söderholm, Robin
    Wahlmark, Rickard
    Analog gitarrförstärkare: med rörliknande egenskaper2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
  • 10.
    Ahlén, A
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Signal Processing. Signals and systems.
    Lindbom, L
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Signal Processing. Signals and systems.
    Sternad, M
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Signal Processing. Signals and systems.
    Analysis of stability and performance of adaptation algorithms with time-invariant gains2004In: IEEE Transactions on Signal Processing, Vol. 52, 103-116 p.Article in journal (Refereed)
  • 11.
    Ahlén, A
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. SIGNALS AND SYSTEMS.
    Sternad, M
    Lindbom, L
    Iterative Wiener design of adaptation laws with constant gains2001In: IEEE International Conference on Acoustics, Speech and Signal Processing, Salt Lake City, UT, 2001Conference paper (Refereed)
  • 12.
    Alavanja, Bojan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Application of SCADA Data Monitoring Methodology and Reliability Analysis of Wind Farm Operational Data2016Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Reliability of wind turbine components and maintenance optimisation are among the critical aspects of wind power development closely related to profitability and future development. The main reason for research in these areas is lowering the cost of energy production for wind power, specifically important in offshore environment. Continuous monitoring of specific wind turbine components can be valuable for wind farm operators and, subsequently, wind farm owners.  Also, health assessment of critical components can be useful in estimating the possibilities for life extension of wind turbines. Expensive Condition Monitoring Systems (CMSs) are not always available, particularly in older wind farms, and additionally installing CMSs on wind turbines is not always economically feasible. However, most of modern wind turbines are equipped with the Supervisory Control And Data Acquisition (SCADA) system which is recording 10-minute average values of parameters that depict operation of the turbine. That being said, SCADA data contains a vast amount of information that can be used for analysis of wind turbine components health. Therefore, this project will present an application of previously published methodology for SCADA data condition monitoring on real wind farm data. The goal of this project is to investigate on the possibilities of the SCADA monitoring methodology and what can be the added value of the application for wind farm operators, owners and other stakeholders.

    The methodology for condition monitoring through SCADA data was applied on real data gathered from two wind farms in Germany and one in the Netherlands. During the project the methodology had to be modified in order to ensure the best possible industrial application. Results of the project showed that the SCADA data condition monitoring approach is not capable of predicting failures. However, the technique has been proven successful for detecting the changes of trends in dependencies of working parameters, specifically monitoring parameters related to the turbine generators. Continuously monitoring the dependencies of working parameters can be used as an additional source of information for maintenance scheduling and assessment of components health. The approach presented in this paper can be valuable to asset managers and wind farm owners.

  • 13.
    Alfredsson, Stefan
    et al.
    Karlstad universitet.
    Brunström, Anna
    Karlstad universitet.
    Sternad, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Impact of 4G wireless link configurations on VoIP network performance2008In: IEEE International Symposium on Wireless Communication Systems 2008, ISWCS2008, Reykjavik, Iceland, 2008Conference paper (Refereed)
  • 14.
    Ambrozinski, Lukasz
    et al.
    Department of Robotics and Mechatronics, Faculty of Mechanical Engineering and Robotics, AGH University of Science and Technology, Kraków, Polen.
    Packo, Pawel
    Department of Robotics and Mechatronics, Faculty of Mechanical Engineering and Robotics, AGH University of Science and Technology, Kraków, Polen.
    Stepinski, Tadeusz
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Uhl, Tadeusz
    Department of Robotics and Mechatronics, Faculty of Mechanical Engineering and Robotics, AGH University of Science and Technology, Kraków, Polen.
    Ultrasonic guided waves based method for SHM: Simulations and an experimental test2011In: 5th World Conference on Structural Control and Monitoring, Tokyo, Japan, 2011Conference paper (Refereed)
  • 15.
    Ambrozinski, Lukasz
    et al.
    AGH University of Science and Technology, Kraków, Polen.
    Stepinski, Tadeusz
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Packo, Pawel
    AGH University of Science and Technology, Kraków, Polen.
    Uhl, Tadeusz
    AGH University of Science and Technology, Kraków, Polen.
    Self-focusing Lamb waves based on the decomposition of the time-reversal operator using time-frequency representation2012In: Mechanical systems and signal processing, ISSN 0888-3270, E-ISSN 1096-1216, Vol. 27, 337-349 p.Article in journal (Refereed)
    Abstract [en]

    Active ultrasonic arrays are very useful for structural health monitoring (SHM) of large plate-like structures. Large areas of a plate can be monitored from a fixed position but it normally requires precise information on material properties. Self-focusing methods can perform well without the exact knowledge of a medium and array parameters. In this paper a method for selective focusing of Lamb waves will be presented. The algorithm is an extension of the DORT method (French acronym for decomposition of time-reversal operator) where the continuous wavelet transform (CWT) is used for the time-frequency representation (TFR) of nonstationary signals instead of the discrete Fourier transform. The performance of the methods is compared and verified in the paper using both simulated and experimental data. It is shown that the extension of the DORT method with the use of TFR considerably improved its resolving ability. To experimentally evaluate the performance of the proposed method, a linear array of small piezoelectric transducers attached to an aluminum plate was used to obtain interelement responses, required for beam self-focusing on targets present in the plate. The array was used for the transmission of signals calculated with the DORT-CWT algorithm. To verify the self-focusing effect the backpropagated field generated in the experiment was sensed using laser scanning vibrometer.

  • 16.
    Ambrozinski, Lukasz
    et al.
    AGH University of Science and Technology, Kraków, Polen.
    Stepinski, Tadeusz
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Uhl, Tadeusz
    AGH University of Science and Technology, Kraków, Polen.
    Self focusing of 2D arrays for SHM of plate-like structures using time reversal operator2011In: 8th Workshop on SHM, Stanford, CA, 2011, 2011Conference paper (Refereed)
  • 17.
    Andersson, Claes R.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, The Linnaeus Centre for Bioinformatics. Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Clinical Pharmacology.
    Fryknäs, Mårten
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Clinical Pharmacology. Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Genetics and Pathology.
    Rickardson, Linda
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Clinical Pharmacology.
    Larsson, Rolf
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Clinical Pharmacology.
    Isaksson, Anders
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Clinical Pharmacology.
    Gustafsson, Mats G.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Clinical Pharmacology. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    In vitro drug sensitivity-gene expression correlations involve a tissue of origin dependency2007In: Journal of chemical information and modeling, ISSN 1549-9596, Vol. 47, no 1, 239-248 p.Article in journal (Refereed)
    Abstract [en]

    A major concern of chemogenomics is to associate drug activity with biological variables. Several reports have clustered cell line drug activity profiles as well as drug activity-gene expression correlation profiles and noted that the resulting groupings differ but still reflect mechanism of action. The present paper shows that these discrepancies can be viewed as a weighting of drug-drug distances, the weights depending on which cell lines the two drugs differ in.

  • 18.
    Andersson, Claes R.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, The Linnaeus Centre for Bioinformatics.
    Hvidsten, Torgeir R.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, The Linnaeus Centre for Bioinformatics.
    Isaksson, Anders
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences.
    Gustafsson, Mats G.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Clinical Pharmacology. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Komorowski, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, The Linnaeus Centre for Bioinformatics.
    Revealing cell cycle control by combining model-based detection of periodic expression with novel cis-regulatory descriptors2007In: BMC Systems Biology, ISSN 1752-0509, Vol. 1, 45- p.Article in journal (Refereed)
    Abstract [en]

    Background: We address the issue of explaining the presence or absence of phase-specific transcription in budding yeast cultures under different conditions. To this end we use a model-based detector of gene expression periodicity to divide genes into classes depending on their behavior in experiments using different synchronization methods. While computational inference of gene regulatory circuits typically relies on expression similarity (clustering) in order to find classes of potentially co-regulated genes, this method instead takes advantage of known time profile signatures related to the studied process. Results: We explain the regulatory mechanisms of the inferred periodic classes with cis-regulatory descriptors that combine upstream sequence motifs with experimentally determined binding of transcription factors. By systematic statistical analysis we show that periodic classes are best explained by combinations of descriptors rather than single descriptors, and that different combinations correspond to periodic expression in different classes. We also find evidence for additive regulation in that the combinations of cis-regulatory descriptors associated with genes periodically expressed in fewer conditions are frequently subsets of combinations associated with genes periodically expression in more conditions. Finally, we demonstrate that our approach retrieves combinations that are more specific towards known cell-cycle related regulators than the frequently used clustering approach. Conclusion: The results illustrate how a model-based approach to expression analysis may be particularly well suited to detect biologically relevant mechanisms. Our new approach makes it possible to provide more refined hypotheses about regulatory mechanisms of the cell cycle and it can easily be adjusted to reveal regulation of other, non-periodic, cellular processes.

  • 19. Andersson, Tobias
    et al.
    Sellergren, Albin
    Toft, Jonathan
    Signal processing through electroencephalography: Independent project in electrical engineering2016Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
  • 20.
    Apelfröjd, Rikke
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Design Aspects of Coordinated Multipoint Transmission: A Study of Channel Predictions, Resource Allocation, User Grouping and Robust Linear Precoding for Coherent Joint Transmission2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Shadowed areas and interference at cell borders pose great challenges for future wireless broadband systems. Coordinated Multipoint (CoMP) coherent joint transmission has shown the potential to overcome these challenges by turning harmful interference into useful signal power. However, there are obstacles to overcome before coherent joint transmission CoMP can be deployed. Some of these are the investigated in this thesis.

    First, coherent joint transmission requires very accurate Channel State Information (CSI), but unfortunately long system latencies cause outdating of the CSI. This can to some extend be counteracted by channel predictions. Two schemes are here investigated for predicting downlink Frequency Division Duplex (FDD) Orthogonal Frequency Division Multiplexing (OFDM) channels; Kalman filters and “predictor antennas”. The first is well suited for slow moving users, e.g. pedestrians or cyclists, as it does not require any special antenna setup. The second, which utilizes an extra antenna, located in front of the main receive antennas, is well suited for vehicular users, such as buses or trams, as these require long spatial prediction horizon.

    Second, a user grouping and resource allocation scheme is investigated. This scheme forms CoMP groups by local resource allocations and provides multi-user diversity gains very close to the optimal gains, found through an extensive combinatorial search. It has very low complexity, requires less feedback capacity than other schemes and places no demands on backhaul capacity.

    Finally, a linear precoder, which is robust to errors in the CSI, is investigated. This precoder takes the covariances of the channel errors into account while optimizing a Mean Squared Error (MSE) criterion. The MSE criterion includes design parameters that can be used as flexible tools for low dimensional searches with respect to an arbitrary optimization criterion, e.g. a weighted sum-rate criterion. The precoder design is also extended to handle backhaul constraints.

    Results show that with the combination of these three schemes: channel predictions, the proposed user grouping and resource allocation scheme and the robust linear precoder, then coherent joint transmission will indeed provide large capacity gains.

    List of papers
    1. Measurement-based evaluation of robust linear precoding for downlink CoMP
    Open this publication in new window or tab >>Measurement-based evaluation of robust linear precoding for downlink CoMP
    2012 (English)In: IEEE International Conference on Communications, ICC, Ottawa, Canada, 2012Conference paper, Published paper (Refereed)
    Abstract [en]

    We study the design and evaluation of joint processing coordinated multipoint (CoMP) downlink transmission. Precoders will then be designed based on outdated channel state information (CSI), so interference cannot be eliminated completely as by an ideal zero-forcing (ZF) solution. We here strive to design and evaluate realistic linear transmit schemes. Kalman predictors are used for orthogonal frequency-division multiplexing (OFDM) channels. They provide optimal linear predictions and also estimates of their uncertainty. Robust linear precoders are designed based on these uncertainty estimates. We introduce and use robust linear quadratic optimal feedforward control, with the criterion averaged (marginalized) over the CSI uncertainty. This flexible solution performs minimum mean square error (MSE) minimization. It can also iteratively optimize other criteria, such as sum-rate. The prediction- and transmission performance is evaluated using measured data on 20 MHz OFDM downlinks from three base stations, for users at fast pedestrian velocities. Downlink CoMP is here also compared to cellular transmission, that uses orthogonal resources within cells but allows uncontrolled interference between cells.

    National Category
    Signal Processing
    Research subject
    Electrical Engineering with specialization in Signal Processing
    Identifiers
    urn:nbn:se:uu:diva-181051 (URN)
    Conference
    IEEE International Conference on Communications, ICC, June 10 - 15, Ottawa, Canada.
    Available from: 2012-09-17 Created: 2012-09-17 Last updated: 2014-06-04Bibliographically approved
    2. Design and measurement based evaluations of coherent JT CoMP: a study of precoding, user grouping and resource allocation using predicted CSI
    Open this publication in new window or tab >>Design and measurement based evaluations of coherent JT CoMP: a study of precoding, user grouping and resource allocation using predicted CSI
    2014 (English)In: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, 100- p.Article in journal (Other academic) Published
    Abstract [en]

    Coordinated multipoint (CoMP) transmission provides high theoretic gains in spectral efficiency with coherent joint transmission (JT) to multiple users. However, this requires accurate channel state information at the transmitter (CSIT) and also user groups with spatially compatible users. The aim of this paper is to use measured channels to investigate if significant CoMP gains can still be obtained with channel estimation errors. This turns out to be the case, but requires the combination of several techniques. We here focus on coherent downlink JT CoMP to multiple users within a cluster of cooperating base stations. The use of Kalman predictors is investigated to estimate the complex channel gains at the moment of transmission. It is shown that this can provide sufficient CSIT quality for JT CoMP even for long (> 20 ms) system delays at 2.66 GHz at pedestrian velocities or, for lower delays, at 500 MHz, at vehicular velocities. A user grouping and resource allocation scheme that provides appropriate groups for CoMP is also suggested. It provides performance close to that obtained by exhaustive search at very low complexity, low feedback cost and very low backhaul cost. Finally, a robust linear precoder that takes channel uncertainties into account when designing the precoding matrix is considered. We show that, in challenging scenarios, this provides large gains compared with zero-forcing precoding. Evaluations of these design elements are based on measured channels with realistic noise and intercluster interference assumptions. These show that high JT CoMP gains can be expected, on average over large sets of user positions, when the above techniques are combined - especially in severely intracluster interference limited scenarios.

    Keyword
    Coordinated Multipoint, channel predictions, user grouping, resource allocation, robust precoding
    National Category
    Signal Processing
    Research subject
    Electrical Engineering with specialization in Signal Processing
    Identifiers
    urn:nbn:se:uu:diva-224254 (URN)10.1186/1687-1499-2014-100 (DOI)000347399300001 ()
    Available from: 2014-05-07 Created: 2014-05-07 Last updated: 2015-02-11Bibliographically approved
    3. Robust Linear Precoder for Coordinated Multipoint Joint Transmission under Limited Backhaul with Imperfect CSI
    Open this publication in new window or tab >>Robust Linear Precoder for Coordinated Multipoint Joint Transmission under Limited Backhaul with Imperfect CSI
    (English)Manuscript (preprint) (Other academic)
    National Category
    Engineering and Technology
    Research subject
    Electrical Engineering with specialization in Signal Processing
    Identifiers
    urn:nbn:se:uu:diva-224255 (URN)
    Available from: 2014-05-07 Created: 2014-05-07 Last updated: 2014-06-04
    4. Analysis and Measurement of Multiple Antenna Systems for Fading Channel Prediction in Moving Relays
    Open this publication in new window or tab >>Analysis and Measurement of Multiple Antenna Systems for Fading Channel Prediction in Moving Relays
    Show others...
    2014 (English)In: 2014 8TH EUROPEAN CONFERENCE ON ANTENNAS AND PROPAGATION (EUCAP), 2014, 2015-2019 p.Conference paper, Published paper (Other academic)
    Abstract [en]

    The performance of wireless data transmission to mobile vehicles is improved if channel state information is available at the transmitter but movement of vehicles causes outdating of channel estimates. The concept of a predictor antenna has recently been proposed, where an antenna is placed in front of other antennas on the roof of the vehicle to sense the radio environment in advance. This can comparatively provide an order-of-magnitude improvement in channel prediction performance. A potential problem with this idea is that closely placed antennas will experience mutual electromagnetic couplings. These may reduce the efficiency of the predictor antenna concept if they are not taken into account. In this paper, we discuss about how to treat the forgoing issue and eventually evaluate a promising candidate on measured channels. We argue that only open-circuit voltage method would be realistic for the present application. The usefulness of the proposed decoupling method is demonstrated on field measurements obtained in downtown Dresden, Germany. We also partly address the sensitivity of the open-circuit decoupling method to the accuracy of the utilized network parameters.

    Series
    Proceedings of the European Conference on Antennas and Propagation, ISSN 2164-3342
    Keyword
    Multi-element antennas; channel state prediction; moving relays; multipath measurement
    National Category
    Engineering and Technology
    Research subject
    Electrical Engineering with specialization in Signal Processing
    Identifiers
    urn:nbn:se:uu:diva-224256 (URN)978-88-907018-4-9 (ISBN)
    Conference
    The 8th European Conference on Antennas and Propagation (EuCAP), to be held at the World Forum in The Hague, The Netherlands, on 6-11 April 2014.
    Note

    This paper has been presented as a poster on: the 8th European Conference on Antennas and Propagation (EuCAP), in The Hague, The Netherlands, on 6-11 April 2014, and will appear in the proceedings

    Available from: 2014-05-08 Created: 2014-05-07 Last updated: 2015-11-06Bibliographically approved
    5. Kalman Predictions for Multipoint OFDM Downlink Channels
    Open this publication in new window or tab >>Kalman Predictions for Multipoint OFDM Downlink Channels
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Coordinated Multipoint (CoMP) transmission provides high theoreticgains in spectral eciency with coherent Joint Transmission (JT) to mul-tiple users. However, this requires accurate Channel State Information atthe Transmitter (CSIT). Unfortunately, coherent JT CoMP often is accom-panied by long system delays, due to e.g. data sharing over backhaul links.Therefore, the CSIT will be outdated.This report provides a detailed description on how to increase the accu-racy of the CSIT by utilizing Kalman lters to predict Orthogonal FrequencyDivision Multiplexing (OFDM) downlink channels. The small scale fading ofthese channels are modeled by Auto Regressive (AR) models of nite order.The report includes descriptions on how to estimate these models basedon past knowledge of the channel as well as analytical result on the pre-dictability of such models. Dierent technical design aspects for deployingthe Kalman lters in communication, such as pilot patterns, AR model esti-mations and the location of Kalman lters that predict downlink FrequencyDivision Duplex (FDD) channels, are also discussed.The aim of the report is to in detail describe the prediction procedureused in previous work. Some of the results from this previous work arehere presented and extended to provide a complete overview. All simulationresults are based on measured channels.The report also includes a description on how to model block-fading chan-nels with a specied channel accuracy that would have been obtained withKalman predictions. This model can then be used for system simulations.V:

    Keyword
    Linear predictions of OFDM channels, outdated channel state information (CSI), Coordinated Multipoint (CoMP), Predictability of radio channles, AR modelling of radio channels
    National Category
    Engineering and Technology
    Research subject
    Electrical Engineering with specialization in Signal Processing
    Identifiers
    urn:nbn:se:uu:diva-224263 (URN)
    Available from: 2014-05-08 Created: 2014-05-08 Last updated: 2014-06-04
  • 21.
    Apelfröjd, Rikke
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Sternad, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Design and measurement based evaluations of coherent JT CoMP: a study of precoding, user grouping and resource allocation using predicted CSI2014In: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, 100- p.Article in journal (Other academic)
    Abstract [en]

    Coordinated multipoint (CoMP) transmission provides high theoretic gains in spectral efficiency with coherent joint transmission (JT) to multiple users. However, this requires accurate channel state information at the transmitter (CSIT) and also user groups with spatially compatible users. The aim of this paper is to use measured channels to investigate if significant CoMP gains can still be obtained with channel estimation errors. This turns out to be the case, but requires the combination of several techniques. We here focus on coherent downlink JT CoMP to multiple users within a cluster of cooperating base stations. The use of Kalman predictors is investigated to estimate the complex channel gains at the moment of transmission. It is shown that this can provide sufficient CSIT quality for JT CoMP even for long (> 20 ms) system delays at 2.66 GHz at pedestrian velocities or, for lower delays, at 500 MHz, at vehicular velocities. A user grouping and resource allocation scheme that provides appropriate groups for CoMP is also suggested. It provides performance close to that obtained by exhaustive search at very low complexity, low feedback cost and very low backhaul cost. Finally, a robust linear precoder that takes channel uncertainties into account when designing the precoding matrix is considered. We show that, in challenging scenarios, this provides large gains compared with zero-forcing precoding. Evaluations of these design elements are based on measured channels with realistic noise and intercluster interference assumptions. These show that high JT CoMP gains can be expected, on average over large sets of user positions, when the above techniques are combined - especially in severely intracluster interference limited scenarios.

  • 22.
    Apelfröjd, Rikke
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Sternad, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Aronsson, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Measurement-based evaluation of robust linear precoding for downlink CoMP2012In: IEEE International Conference on Communications, ICC, Ottawa, Canada, 2012Conference paper (Refereed)
    Abstract [en]

    We study the design and evaluation of joint processing coordinated multipoint (CoMP) downlink transmission. Precoders will then be designed based on outdated channel state information (CSI), so interference cannot be eliminated completely as by an ideal zero-forcing (ZF) solution. We here strive to design and evaluate realistic linear transmit schemes. Kalman predictors are used for orthogonal frequency-division multiplexing (OFDM) channels. They provide optimal linear predictions and also estimates of their uncertainty. Robust linear precoders are designed based on these uncertainty estimates. We introduce and use robust linear quadratic optimal feedforward control, with the criterion averaged (marginalized) over the CSI uncertainty. This flexible solution performs minimum mean square error (MSE) minimization. It can also iteratively optimize other criteria, such as sum-rate. The prediction- and transmission performance is evaluated using measured data on 20 MHz OFDM downlinks from three base stations, for users at fast pedestrian velocities. Downlink CoMP is here also compared to cellular transmission, that uses orthogonal resources within cells but allows uncontrolled interference between cells.

  • 23.
    Aronsson, Daniel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Svensson, Tommy
    Chalmers University of Technology, Dept of Signals and Systems.
    Sternad, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Performance evaluation of memory-less and Kalman-based channel estimation for OFDMA2009In: IEEE Vehicular Technology Conference, Barcelona, Spanien, April 26-29, 2009, 2009, 2314-2318 p.Conference paper (Refereed)
    Abstract [en]

    The next generation wireless systems based on Orthogonal Frequency Division Multiple Access (OFDMA) need to operate in widely different deployment and usage scenarios. Thus, support for flexible resource allocation is important. In this paper we investigate the performance or different memory-less and memory-based channel estimators for different OFDMA subcarrier allocation schemes and different pilot patterns. We evaluate the performance in various fading environments and for different user terminal velocities. The results show that channel estimation can perform well enough for time-frequency localized resources as small as 22 channel symbols with two pilots in many important scenarios. The results provided can be used to identify appropriate subcarrier allocations for the next generation OFDMA based wireless systems.

  • 24.
    Asraf, Daniel
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Optimal Detectors for Transient Signal Families and Nonlinear Sensors: Derivations and Applications2003Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is concerned with detection of transient signal families and detectors in nonlinear static sensor systems. The detection problems are treated within the framework of likelihood ratio based binary hypothesis testing.

    An analytical solution to the noncoherent detection problem is derived, which in contrast to the classical noncoherent detector, is optimal for wideband signals. An optimal detector for multiple transient signals with unknown arrival times is also derived and shown to yield higher detection performance compared to the classical approach based on the generalized likelihood ratio test.

    An application that is treated in some detail is that of ultrasonic nondestructive testing, particularly pulse-echo detection of defects in elastic solids. The defect detection problem is cast as a composite hypothesis test and a methodology, based on physical models, for designing statistically optimal detectors for cracks in elastic solids is presented. Detectors for defects with low computational complexity are also formulated based on a simple phenomenological model of the defect echoes. The performance of these detectors are compared with the physical model-based optimal detector and is shown to yield moderate performance degradation.

    Various aspects of optimal detection in static nonlinear sensor systems are also treated, in particular the stochastic resonance (SR) phenomenon which, in this context, implies noise enhanced detectability. Traditionally, SR has been quantified by means of the signal-to-noise ratio (SNR) and interpreted as an increase of a system's information processing capability. Instead of the SNR, rigorous information theoretic distance measures, which truly can support the claim of noise enhanced information processing capability, are proposed as quantifiers for SR. Optimal detectors are formulated for two static nonlinear sensor systems and shown to exhibit noise enhanced detectability.

    List of papers
    1. An analytical series expansion solution to the problem of noncoherent detection
    Open this publication in new window or tab >>An analytical series expansion solution to the problem of noncoherent detection
    2004 (English)In: IEEE Transactions on Information Theory, ISSN 0018-9448, Vol. 50, no 12, 3369-3375 p.Article in journal (Refereed) Published
    Abstract [en]

    The well-known noncoherent detection problem concerns optimal detection of an amplitude-modulated sinusoid, with an unknown phase angle, corrupted by additive Gaussian noise. The classical solution to this problem is the noncoherent detector which is known to be optimal if the envelope belongs to a specific set of functions or satisfies the narrow-band approximation i.e., that the bandwidth of the envelope is narrow in comparison with the (carrier) frequency of the sinusoid. In this work, an analytical series expansion solution to the likelihood ratio for the noncoherent detection problem is derived. This solution offers a generalization of the noncoherent detector in which the conditions imposed on the envelope stated above have been relaxed. Analytical expressions for the joint probability density functions (pdfs) of the in-phase and quadrature components, jointly expressed in polar coordinates, are also derived under the signal-plus-noise and the noise-only hypotheses, respectively. Numerical simulations of the detector performance are presented in the form of receiver operating characteristics (ROC) and minimum probability of error curves. The results from a comparison of the general analytical solution with the classical noncoherent detector show significant differences between the two detectors when the narrow-band approximation does not hold.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-90173 (URN)10.1109/TIT.2004.838396 (DOI)
    Available from: 2003-03-17 Created: 2003-03-17 Last updated: 2013-10-01Bibliographically approved
    2. Detection of Multiple Transient Signals with Unknown Arrival Times
    Open this publication in new window or tab >>Detection of Multiple Transient Signals with Unknown Arrival Times
    2005 (English)In: IEEE Transactions on Information Theory, ISSN 0018-9448, Vol. 51, no 5, 1856-1860 p.Article in journal (Refereed) Published
    Abstract [en]

    The problem of optimal detection of signal transients with unknown arrival times contaminated by additive Gaussian noise is considered. The transients are assumed to be time continuous and belong to a parameterized family with the uncertainty about the parameters described by means of an a priori distribution. Under the assumption of a negligible probability that the independent transient observations overlap in time, a likelihood ratio is derived for the problem of detecting an unknown number of transients from the family, each transient with unknown arrival time. The uncertainty about the arrival times is assumed to be equal for all transients and is also described by means of a distribution. Numerical simulations of the performance of detecting a particular transient signal family are presented in the form of receiver operating characteristics (ROCs) for both the optimal detector and the classical generalized likelihood ratio test (GLRT). The results show that the optimal detector yields noticeable performance improvements over the GLRT. Moreover, the results show that the optimal detector may still outperform the GLRT when the true and modeled uncertainties about arrival times no longer agree.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-90174 (URN)10.1109/TIT.2005.846445 (DOI)
    Available from: 2003-03-17 Created: 2003-03-17 Last updated: 2014-01-21Bibliographically approved
    3. Optimal Detection of Crack Echo Families in Elastic Solids
    Open this publication in new window or tab >>Optimal Detection of Crack Echo Families in Elastic Solids
    2003 (English)In: The Journal of the Acoustical Society of America, Vol. 113, no 5, 2732-2741 p.Article in journal (Refereed) Published
    Abstract [en]

    Optimal detection of a striplike crack residing in an isotropic elastic solid with coarse microstructure by means of ultrasonic nondestructive evaluation (NDE) is considered. A physics-based approach to derive an optimal detector, which achieves the theoretical limitations constrained by the underlying physics, is presented. State-of-the-art physical models of crack echoes and of stochastic backscattering from the material structure in elastic solids are introduced and unified with the theory of optimal detection to yield a practically useful nonlinear filter bank implementation of the optimal detector. Monte Carlo simulations of the detection performance for the special case of a striplike crack with uncertain angular orientation are presented in the form of receiver operating characteristics (ROCs). These new results represent the physical limitations for detecting a crack under the stated conditions and serve as performance bounds to which other detectors should be compared. A physics-based generalized likelihood ratio (GLR) detector, which relies on the same nonlinear filter bank as the optimal detector, is also presented for the special case of a striplike crack. A comparison between the optimal and the GLR detectors shows that the GLR detector only slightly reduces the performance.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-90175 (URN)12765391 (PubMedID)
    Available from: 2003-03-17 Created: 2003-03-17 Last updated: 2013-06-14Bibliographically approved
    4. Phenomenological detectors for crack echo families in elastic solids
    Open this publication in new window or tab >>Phenomenological detectors for crack echo families in elastic solids
    2004 (English)In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 116, no 1, 379-388 p.Article in journal (Refereed) Published
    Abstract [en]

    The potential performance of low-complexity phenomenological detectors for crack echo families in elastic solids is evaluated. Ultrasonic echoes from a strip-like crack residing in an isotropic elastic solid with coarse microstructure are considered and the achieved detector performance is compared to the theoretical upper bounds (constrained only by the underlying physics) obtained by means of a recently presented physics-based optimal detector. A phenomenological signal model for the scattering process is formulated based on the time-domain impulse-response method and used to derive detectors of low numerical complexity which are dependent on a small number of parameters. The proposed detectors are compared in terms of receiver operating characteristic curves, which are computed by means of Monte Carlo simulations for the case of a strip-like crack with uncertain angular orientation. The minimum probability of error criterion is used to optimize the detector parameters for the simulation study and shown to be useful even for small training data sets. These results show that the proposed detectors have close to optimal performance in particular for the case of high signal-to-noise ratios.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-90176 (URN)
    Available from: 2003-03-17 Created: 2003-03-17 Last updated: 2013-10-01Bibliographically approved
    5. Information-Theoretic Distance Measures and a Generalization of Stochastic Resonance
    Open this publication in new window or tab >>Information-Theoretic Distance Measures and a Generalization of Stochastic Resonance
    1998 In: Physical Review Letters, Vol. 81, no 14, 2850-2853 p.Article in journal (Refereed) Published
    Identifiers
    urn:nbn:se:uu:diva-90177 (URN)
    Available from: 2003-03-17 Created: 2003-03-17Bibliographically approved
    6. Information-Theoretic Characterization of System Performance for a Nonlinear Magneto-Resistive Sensor
    Open this publication in new window or tab >>Information-Theoretic Characterization of System Performance for a Nonlinear Magneto-Resistive Sensor
    Show others...
    2000 In: Stochastic and Chaotic Dynamics in the Lakes, AIP Conference Proceedings 502, 2000, 603-608 p.Chapter in book (Other academic) Published
    Identifiers
    urn:nbn:se:uu:diva-90178 (URN)1-56396-915-7 (ISBN)
    Available from: 2003-03-17 Created: 2003-03-17Bibliographically approved
  • 25.
    Aubry, Augusto
    et al.
    CNR, IREA.
    De Maio, Antonio
    Universit`a degli Studi di Napoli “Federico II”.
    Piezzo, Marco
    Universit`a degli Studi di Napoli “Federico II”.
    Naghsh, Mohammad Mahdi
    Isfahan University of Technology.
    Soltanalian, Mojtaba
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control.
    Stoica, Petre
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control.
    Cognitive Radar Waveform Design for Spectral Coexistence in Signal-Dependent Interference2014Conference paper (Refereed)
  • 26.
    Ayyalasomayajula, Kalyan Ram
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Visual Information and Interaction. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computerized Image Analysis and Human-Computer Interaction.
    Brun, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Visual Information and Interaction. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computerized Image Analysis and Human-Computer Interaction.
    Document binarization using topological clustering guided Laplacian Energy Segmentation2014In: Proceedings International Conference on Frontiers in Handwriting Recognition (ICFHR), 2014, 2014, 523-528 p.Conference paper (Refereed)
    Abstract [en]

    The current approach for text binarization proposesa clustering algorithm as a preprocessing stage toan energy-based segmentation method. It uses a clusteringalgorithm to obtain a coarse estimate of the background (BG)and foreground (FG) pixels. These estimates are used as a priorfor the source and sink points of a graph cut implementation,which is used to efficiently find the minimum energy solution ofan objective function to separate the BG and FG. The binaryimage thus obtained is used to refine the edge map that guidesthe graph cut algorithm. A final binary image is obtained byonce again performing the graph cut guided by the refinededges on a Laplacian of the image.

  • 27.
    Babu, Prabhu
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Spectral Analysis of Nonuniformly Sampled Data and Applications2012Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Signal acquisition, signal reconstruction and analysis of spectrum of the signal are the three most important steps in signal processing and they are found in almost all of the modern day hardware. In most of the signal processing hardware, the signal of interest is sampled at uniform intervals satisfying some conditions like Nyquist rate. However, in some cases the privilege of having uniformly sampled data is lost due to some constraints on the hardware resources. In this thesis an important problem of signal reconstruction and spectral analysis from nonuniformly sampled data is addressed and a variety of methods are presented. The proposed methods are tested via numerical experiments on both artificial and real-life data sets.

    The thesis starts with a brief review of methods available in the literature for signal reconstruction and spectral analysis from non uniformly sampled data. The methods discussed in the thesis are classified into two broad categories - dense and sparse methods, the classification is based on the kind of spectra for which they are applicable. Under dense spectral methods the main contribution of the thesis is a non-parametric approach named LIMES, which recovers the smooth spectrum from non uniformly sampled data. Apart from recovering the spectrum, LIMES also gives an estimate of the covariance matrix. Under sparse methods the two main contributions are methods named SPICE and LIKES - both of them are user parameter free sparse estimation methods applicable for line spectral estimation. The other important contributions are extensions of SPICE and LIKES to multivariate time series and array processing models, and a solution to the grid selection problem in sparse estimation of spectral-line parameters.

    The third and final part of the thesis contains applications of the methods discussed in the thesis to the problem of radial velocity data analysis for exoplanet detection. Apart from the exoplanet application, an application based on Sudoku, which is related to sparse parameter estimation, is also discussed.

  • 28.
    Babu, Prabhu
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Gudmundson, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Stoica, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Automatic cepstrum-based smoothing of the periodogram via cross-validation2008In: Proc. 16th European Signal Processing Conference, European Association for Signal Processing , 2008Conference paper (Refereed)
  • 29.
    Babu, Prabhu
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Gudmundson, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Stoica, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Optimal Preconditioning for Interpolation of Missing Data in a Band-Limited Sequence2008In: Proc. 42nd Asilomar Conference on Signals, Systems and Computers, Piscataway, NJ: IEEE , 2008, 561-565 p.Conference paper (Refereed)
  • 30.
    Babu, Prabhu
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Pelckmans, Kristiaan
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Stoica, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Li, Jian
    Linear Systems, Sparse Solutions, and Sudoku2010In: IEEE Signal Processing Letters, ISSN 1070-9908, E-ISSN 1558-2361, Vol. 17, no 1, 40-42 p.Article in journal (Refereed)
  • 31.
    Babu, Prabhu
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Stoica, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Spectral analysis of nonuniformly sampled data — a review2010In: Digital signal processing (Print), ISSN 1051-2004, E-ISSN 1095-4333, Vol. 20, no 2, 359-378 p.Article in journal (Refereed)
  • 32.
    Babu, Prabhu
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Stoica, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Comments on "Iterative Estimation of Sinusoidal Signal Parameters"2010In: IEEE Signal Processing Letters, ISSN 1070-9908, E-ISSN 1558-2361, Vol. 17, no 12, 1022-1023 p.Article in journal (Refereed)
  • 33.
    Babu, Prabhu
    et al.
    Department of Electronic and Computer Engineering, HKUST, Hong Kong.
    Stoica, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Connection between SPICE and Square-Root LASSO for sparse parameter estimation2014In: Signal Processing, ISSN 0165-1684, E-ISSN 1872-7557, Vol. 95, 10-14 p.Article in journal (Refereed)
    Abstract [en]

    In this note we show that the sparse estimation technique named Square-Root LASSO (SR-LASSO) is connected to a previously introduced method named SPICE. More concretely we prove that the SR-LASSO with a unit weighting factor is identical to SPICE. Furthermore we show via numerical simulations that the performance of the SR-LASSO changes insignificantly when the weighting factor is varied. SPICE stands for sparse iterative covariance-based estimation and LASSO for least absolute shrinkage and selection operator.

  • 34.
    Babu, Prabhu
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Stoica, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    A combined linear programming-maximum likelihood approach to radial velocity data analysis for extrasolar planet detection2011In: ICASSP2011, the 36th International Conference on Acoustics, Speech and Signal Processing, Prague, Czech Republic, 2011, 4352-4355 p.Conference paper (Refereed)
    Abstract [en]

    In this paper we introduce a new technique for estimating the parameters of the Keplerian model commonly used in radial velocity data analysis for extrasolar planet detection. The unknown parameters in the Keplerian model, namely eccentricity e, orbital frequency f, periastron passage time T, longitude of periastron., and radial velocity amplitude K are estimated by a new approach named SPICE (a semi-parametric iterative covariance-based estimation technique). SPICE enjoys global convergence, does not require selection of any hyperparameters, and is computationally efficient (indeed computing the SPICE estimates boils down to solving a numerically efficient linear program (LP)). The parameter estimates obtained from SPICE are then refined by means of a relaxation-based maximum likelihood algorithm (RELAX) and the significance of the resultant estimates is determined by a generalized likelihood ratio test (GLRT). A real-life radial velocity data set of the star HD 9446 is analyzed and the results obtained are compared with those reported in the literature.

  • 35.
    Babu, Prabhu
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Stoica, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Sparse spectral-line estimation for nonuniformly sampled multivariate time series: SPICE, LIKES and MSBL2012In: 2012 Proceedings Of The 20th European Signal Processing Conference (EUSIPCO), 2012, 445-449 p.Conference paper (Refereed)
    Abstract [en]

    In this paper we deal with the problem of spectral-line analysis ofnonuniformly sampled multivariate time series for which we introduce two methods: the first method named SPICE (sparse iterativecovariance based estimation) is based on a covariance fitting framework whereas the second method named LIKES (likelihood-basedestimation of sparse parameters) is a maximum likelihood technique. Both methods yield sparse spectral estimates and they donot require the choice of any hyperparameters. We numericallycompare the performance of SPICE and LIKES with that of the recently introduced method of multivariate sparse Bayesian learning(MSBL).

  • 36.
    Babu, Prabhu
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Stoica, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Li, Jian
    Chen, Zhaofu
    Ge, Jian
    Analysis of radial velocity data by a novel adaptive approach2010In: Astronomical Journal, ISSN 0004-6256, E-ISSN 1538-3881, Vol. 139, no 2, 783-793 p.Article in journal (Refereed)
  • 37.
    Babu, Prabhu
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Stoica, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Marzetta, Thomas L.
    An IQML type algorithm for AR parameter estimation from noisy covariance sequences2009In: Proc. 17th European Signal Processing Conference, European Association for Signal Processing , 2009, 1022-1026 p.Conference paper (Refereed)
  • 38.
    Baghirli, Orkhan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Comparison of Lavenberg-Marquardt, Scaled Conjugate Gradient and Bayesian Regularization Backpropagation Algorithms for Multistep Ahead Wind Speed Forecasting Using Multilayer Perceptron Feedforward Neural Network2015Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Wind speed forecasting is critical for wind energy conversion systems since it greatly influences the issues such as scheduling of the power systems, and dynamic control of the wind turbines. Also, it plays an essential role for siting, sizing and improving the efficiency of wind power generation systems. Due to volatile and non-stationary nature of wind speed time series, wind speed forecasting has been proven to be a challenging task that requires adamant care and caution. There are several state-of-the-art methods, i.e., numerical weather prediction (NWP), statistical, and hybrid models, developed for this purpose. Recent studies show that artificial neural networks (ANNs) are also capable of wind speed forecasting to a great extent. 

    In this paper, 3-layer perceptron feedforward neural network is employed for comparison of three different training algorithms, i.e., Lavenberg-Marquardt (LM), Scaled Conjugate Gradient (SCG) and Bayesian Regularization (BR) backpropagation algorithms, in the view of their ability to perform 12 multistep ahead monthly wind speed forecasting. Horizontal wind speed, absolute air temperature, atmospheric pressure and relative humidity data collected between November 1995 - June 2003 and July 2007 – April 2015 for city of Roskilde, Denmark is used for training, validation and testing of the network model. The performed experiment shows that for 12 multistep ahead wind speed forecasting, SCG algorithm has obvious preference in terms of prediction accuracy with mean absolute percentage error (MAPE) of 3.717%, followed by LM and BR algorithms with MAPE of 4.311% and 4.587% accordingly. As a result, within the scope of this study, SCG algorithm is found to be more suitable to build a multistep ahead wind speed forecasting model.

  • 39.
    Bahne, Adrian
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Perceived Sound Quality of Small Original and Optimized Loudspeaker Systems2012In: Journal of The Audio Engineering Society, ISSN 0004-7554, Vol. 60, no 1-2, 29-37 p.Article in journal (Refereed)
    Abstract [en]

    The perceived sound quality of small loudspeaker systems with and without digital optimization was empirically evaluated in a listening experiment. Further, it was investigated how the presentation order in the performed paired comparisons influenced the results, as well as whether a self-evaluation was of potential use for variance reduction. The systems were optimized by means of FIR filters. The two versions of each loudspeaker system were rated in a paired comparison test for music stimuli. For the purpose of analysis a linear Gaussian model was applied, resulting in an interval scale revealing interesting information about certainty and discrimination ability of the listeners. The test investigated whether linear pre-compensation of small and inexpensive loudspeaker systems results in a significant improvement of the perceived audio quality in a typical listening situation. The results indicated a significant preference for the optimized version and a significant dependency on the presentation order was detected. The self-evaluation was found to be uncorrelated to the test results.

  • 40.
    Bahne, Adrian
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Multichannel Audio Signal Processing: Room Correction and Sound Perception2014Doctoral thesis, monograph (Other academic)
    Abstract [en]

    This thesis concerns and combines multichannel sound reproduction, digital room correction, audio signal processing, and human sound perception. It investigates perceived sound quality and new methods to improve timbral and spatial fidelity of loudspeaker-based multichannel sound reproduction in reverberant environments.

    In the first part of the thesis, the perceived sound quality of regular optimized stereo sound systems is investigated by means of a listening experiment based on subjective comparison judgments. It is shown that average listeners' preferences are in favor of the optimized version of the systems.

    The second part of the thesis takes on with three novel equalization schemes, which are based on insights from human perception. First, a general filter design framework based on multiple-input multiple-output (MIMO) feedforward control is introduced. The main objective is to provide means to jointly equalize a single loudspeaker by utilizing all available loudspeakers in a multichannel sound system.

    Well-known drawbacks of standard multichannel sound reproduction are (a) that symmetrical system setups are generally assumed, and (b) that high fidelity sound reproduction is limited to a tight region in space, the so-called sweet spot. In order to ease drawback (a), the MIMO similarity framework incorporating a pairwise channel similarity requirement is introduced, which is based on a mathematical description of the perception of virtual sound sources created in multichannel sound reproduction. The aim is to obtain similar (symmetrical) room transfer functions in the listening area of a given listening environment. In order to ease drawbacks (a) and (b), the personal audio framework is introduced. It aims at producing filters which improve spatial and timbral sound reproduction in multiple listening positions simultaneously.

    Evaluations based on simulations and measurements acquired in representative listening environments strongly indicate that the proposed methods successfully treat several causes which are known to impair sound quality and thus yield improved sound reproduction.

  • 41.
    Bahne, Adrian
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Perceived sound quality of small original and optimized loudspeaker systems2010In: 3rd International Workshop on Perceptual Quality of Systems (PQS), Dresden, Tyskland, 2010Conference paper (Refereed)
  • 42.
    Bahne, Adrian
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Brännmark, Lars-Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Ahlén, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Improved loudspeaker-room equalization for stereo systems regarding channel similarity2012In: Proceedings - International Conference on Audio, Language and Image Processing, 2012, 254-259 p.Conference paper (Refereed)
    Abstract [en]

    In this paper, a new approach to robust singlechannel loudspeaker-room equalization for stereo systems based on psychoacoustic insights is presented. Traditionally, in single-channel equalization each channel is equalized individually according to a desired target. In case the target cannot be reached for at least one of the two channels, this approach results in different loudspeaker-room transfer functions of the two channels at the listening position. However, reproducing the intended sound image of stereo recordings requires equal acoustic transfer functions from the input to the two loudspeakers to the listening region. In this paper we aim not only at equalizing the individual channels according to a desired target, but also at explicitly requiring symmetry between the two channels of a stereo system. To this end we propose a two-channel similarity SIMO controller structure, which is an extension to an earlier approach by the authors. The new approach is evaluated based on measurements in a room and is found to reduce differences between the room transfer functions of the two channels in both frequency and time domain.

  • 43.
    Barkefors, Annea
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Berthilsson, Simon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Sternad, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Extending the area silenced by active noise control using multiple loudspeakers2012In: Acoustics, Speech and Signal Processing (ICASSP), 2012 IEEE International Conference, 2012, 325-328 p.Conference paper (Refereed)
    Abstract [en]

    Active noise control is of increasing interest in e.g. cars, but the zone of noise damping becomes limited in reverberant environments. We investigate the possibility of extending this spatial zone significantly, by using multiple control loudspeakers. MIMO feedforward controllers designed by linear quadratic control theory are here shown to increase the limiting frequency for uniform damping in a 0.3×0.3 m test area, from 200 Hz to around 600 Hz.

  • 44.
    Barkefors, Annea
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Berthilsson, Simon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Sternad, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    An investigation of a theoretical tool for predicting performance of an active noise control system.2012In: 19th International Congress on Sound and Vibration, ICSV19, Vilnius, Lithuania, 2012, 1-8 p.Conference paper (Refereed)
  • 45. Barral, Joëlle K.
    et al.
    Gudmundson, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Stikov, Nikola
    Etezadi-Amoli, Maryam
    Stoica, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Nishimura, Dwight G.
    A Robust Methodology for In Vivo T1 Mapping2010In: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 64, no 4, 1057-1067 p.Article in journal (Refereed)
  • 46. Bartnitzek, T
    et al.
    Schönlinner, B
    Gautier, W
    Cheng, Shi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Rydberg, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Purtova, T
    Vähä-Veikkilä, T
    Ziaei, A
    Ceramic systems in package for RF and microwave2008In: IMAPS Advanced Technology Workshop on RF and Microwave Packaging, 2008Conference paper (Refereed)
  • 47.
    Ben Dhaou, I
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science. SIGNALS AND SYSTEMS.
    Carlemalm, C
    Tennunen, H
    On the robustness and performance tradeoffs for OFDM channel estimation2001In: Proceedings Wireless 2001, New York, 2001, Vol. 1, 41-48 p.Conference paper (Refereed)
  • 48.
    Berthilsson, Simon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Barkefors, Annea
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Brännmark, Lars-Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Sternad, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Acoustical zone reproduction for car interiors using a MIMO MSE framework.2012In: AES 48th International Conference, Munich, Germany, 2012Conference paper (Refereed)
  • 49.
    Berthilsson, Simon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Barkefors, Annea
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Sternad, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    MIMO design of active noise controllers for car interiors: Extending the silenced region at higher frequencies2012In: 2012 American Control Conference, Montréal, Canada, 2012, 6140-6147 p.Conference paper (Refereed)
  • 50.
    Bhikkaji, Bharath
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Model Reduction and Parameter Estimation for Diffusion Systems2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Diffusion is a phenomenon in which particles move from regions of higher density to regions of lower density. Many physical systems, in fields as diverse as plant biology and finance, are known to involve diffusion phenomena. Typically, diffusion systems are modeled by partial differential equations (PDEs), which include certain parameters. These parameters characterize a given diffusion system. Therefore, for both modeling and simulation of a diffusion system, one has to either know or determine these parameters. Moreover, as PDEs are infinite order dynamic systems, for computational purposes one has to approximate them by a finite order model. In this thesis, we investigate these two issues of model reduction and parameter estimation by considering certain specific cases of heat diffusion systems.

    We first address model reduction by considering two specific cases of heat diffusion systems. The first case is a one-dimensional heat diffusion across a homogeneous wall, and the second case is a two-dimensional heat diffusion across a homogeneous rectangular plate. In the one-dimensional case we construct finite order approximations by using some well known PDE solvers and evaluate their effectiveness in approximating the true system. We also construct certain other alternative approximations for the one-dimensional diffusion system by exploiting the different modal structures inherently present in it. For the two-dimensional heat diffusion system, we construct finite order approximations first using the standard finite difference approximation (FD) scheme, and then refine the FD approximation by using its asymptotic limit.

    As for parameter estimation, we consider the same one-dimensional heat diffusion system, as in model reduction. We estimate the parameters involved, first using the standard batch estimation technique. The convergence of the estimates are investigated both numerically and theoretically. We also estimate the parameters of the one-dimensional heat diffusion system recursively, initially by adopting the standard recursive prediction error method (RPEM), and later by using two different recursive algorithms devised in the frequency domain. The convergence of the frequency domain recursive estimates is also investigated.

    List of papers
    1. Reduced order models for diffusion systems
    Open this publication in new window or tab >>Reduced order models for diffusion systems
    2001 In: International Journal of Control, Vol. 75, no 15, 1543-1557 p.Article in journal (Refereed) Published
    Identifiers
    urn:nbn:se:uu:diva-91720 (URN)
    Available from: 2004-05-06 Created: 2004-05-06Bibliographically approved
    2. Reduced order models for diffusion systems using singular perturbations
    Open this publication in new window or tab >>Reduced order models for diffusion systems using singular perturbations
    2001 In: Energy and Buildings, Vol. 33, no 8, 769-781 p.Article in journal (Refereed) Published
    Identifiers
    urn:nbn:se:uu:diva-91721 (URN)
    Available from: 2004-05-06 Created: 2004-05-06Bibliographically approved
    3. Reduced order model for a two-dimensional diffusion system
    Open this publication in new window or tab >>Reduced order model for a two-dimensional diffusion system
    In: International Journal of ControlArticle in journal (Refereed) Submitted
    Identifiers
    urn:nbn:se:uu:diva-91722 (URN)
    Available from: 2004-05-06 Created: 2004-05-06Bibliographically approved
    4. Reduced order models for diffusion systems via Collocation methods
    Open this publication in new window or tab >>Reduced order models for diffusion systems via Collocation methods
    2000 In: Proc of 12th IFAC Symposium on System Identification, Santa Barbara, CA, USA, JuneArticle in journal (Refereed) Published
    Identifiers
    urn:nbn:se:uu:diva-91723 (URN)
    Available from: 2004-05-06 Created: 2004-05-06Bibliographically approved
    5. Bias and variance of parameter estimates of a one-dimensional heat diffusion system
    Open this publication in new window or tab >>Bias and variance of parameter estimates of a one-dimensional heat diffusion system
    2002 In: Proc of 15th IFAC Congress, Barcelona, Spain, JulyArticle in journal (Refereed) Published
    Identifiers
    urn:nbn:se:uu:diva-91724 (URN)
    Available from: 2004-05-06 Created: 2004-05-06Bibliographically approved
    6. Recursive algorithm for estimating parameters in a one-dimensional heat diffusion system
    Open this publication in new window or tab >>Recursive algorithm for estimating parameters in a one-dimensional heat diffusion system
    2002 In: Proc of Reglermöte, Linköping, SwedenArticle in journal (Refereed) Published
    Identifiers
    urn:nbn:se:uu:diva-91725 (URN)
    Available from: 2004-05-06 Created: 2004-05-06Bibliographically approved
    7. Recursive algorithms for estimating parameters in a one-dimensional diffusion system: derivation and implementation
    Open this publication in new window or tab >>Recursive algorithms for estimating parameters in a one-dimensional diffusion system: derivation and implementation
    In: International Journal of Adaptive Control and Signal ProcessingArticle in journal (Refereed) Submitted
    Identifiers
    urn:nbn:se:uu:diva-91726 (URN)
    Available from: 2004-05-06 Created: 2004-05-06Bibliographically approved
    8. Recursive algorithms for estimating parameters in a one-dimensional diffusion system: analysis
    Open this publication in new window or tab >>Recursive algorithms for estimating parameters in a one-dimensional diffusion system: analysis
    In: International Journal of ControlArticle in journal (Refereed) Submitted
    Identifiers
    urn:nbn:se:uu:diva-91727 (URN)
    Available from: 2004-05-06 Created: 2004-05-06Bibliographically approved
1234567 1 - 50 of 527
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