Tesi: "Time and frequency transfer"

1

Ilvedson, Corinne Rachel 1974. "Transfer function estimation using time-frequency analysis". Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/50472.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1998.
Includes bibliographical references (p. 135-136).
Given limited and noisy data, identifying the transfer function of a complex aerospace system may prove difficult. In order to obtain a clean transfer function estimate despite noisy data, a time-frequency analysis approach to system identification has been developed. The method is based on the observation that for a linear system, an input at a given frequency should result in a response at the same frequency, and a time localized frequency input should result in a response that is nearby in time to the input. Using these principles, the noise in the response can be separated from the physical dynamics. In addition, the impulse response of the system can be restricted to be causal and of limited duration, thereby reducing the number of degrees of freedom in the estimation problem. The estimation method consists of finding a rough estimate of the impulse response from the sampled input and output data. The impulse response estimate is then transformed to a two dimensional time-frequency mapping. The mapping provides a clear graphical method for distinguishing the noise from the system dynamics. The information believed to correspond to noise is discarded and a cleaner estimate of the impulse response is obtained from the remaining information. The new impulse response estimate is then used to obtain the transfer function estimate. The results indicate that the time-frequency transfer function estimation method can provide estimates that are often less noisy than those obtained from other methods such as the Empirical Transfer Function Estimate and Welch's Averaged Periodogram Method.
by Corinne Rachel Ilvedson.
S.M.

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2

HUANG, WEI. "Improved PPP for time and frequency transfer and real-time detection of GNSS satellite clock frequency anomalies". Doctoral thesis, Politecnico di Torino, 2020. http://hdl.handle.net/11583/2842527.

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3

McCune, Robert E. "Identification of Continuous-Time and Discrete-Time Transfer Function Models from Frequency Response Measurements". Ohio University / OhioLINK, 1989. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1239731009.

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4

Mohieldin, Ahmed Nader. "High performance continuous-time filters for information transfer systems". Texas A&M University, 2003. http://hdl.handle.net/1969/233.

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5

Babendreier, Justin Eric. "Near aggregation: a time and frequency domain analysis using state trajectories and transfer function residues". Thesis, Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/91080.

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In this thesis we investigate concepts associated with aggregation. The basic idea of aggregation is that there exists a reduced order model such that, for an appropriate initial condition, the trajectories of the reduced-order model are linear combinations of the trajectories of the ful 1-order model. We study systems which do not aggregate exactly, but which "nearly aggregate". It is shown that for "nearly aggregable" systems there exists a reduced-order model such that, for an appropriate initial condition, the trajectories of the reduced-order model are near a linear combination of the trajectories of the full-order model. Under certain conditions it has also been shown that near-aggregation is equivalent to near-unobservability (roughly, an invariant subspace close to the null space of C). Here we establish a relationship between near-unobservability and modal measures of observability as suggested by Selective Modal Analysis. With this result we then obtain an upper bound on the norm of the transfer function residue using near-unobservability measures. The Generalized Hessenberg Representation (GHR) and Dual GHR are examined throughout this analysis. It is finally shown that for SISO systems, the residue norm may be expressed in terms of certain parameters of the Dual GHR.
M.S.

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6

Bartůšek, Jan. "Time Frequency Analysis of ERP Signals". Master's thesis, Vysoké učení technické v Brně. Fakulta informačních technologií, 2007. http://www.nusl.cz/ntk/nusl-412769.

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Tato práce se zabývá vylepšením algoritmu pro sdružování (clustering) ERP signálů pomocí analýzy časových a prostorových vlastností pseudo-signálů získaných za pomocí metody analýzy nezávislých komponent (Independent Component Analysis). Naším zájmem je nalezení nových vlastností, které by zlepšily stávající výsledky. Tato práce se zabývá použitím Fourierovy transformace (Fourier Transform), FIR filtru a krátkodobé Fourierovy transformace ke zkvalitnění informace pro sdružovací algoritmy. Princip a použitelnost metody jsou popsány a demonstrovány ukázkovým algoritmem. Výsledky ukázaly, že pomocí dané metody je možné získat ze vstupních dat zajímavé informace, které mohou být úspěšně použity ke zlepšení výsledků.

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7

Yang, Taeyoung. "Fundamental Limits on Antenna Size for Frequency and Time Domain Applications". Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/39334.

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As ubiquitous wireless communication becomes part of life, the demand on antenna miniaturization and interference reduction becomes more extreme. However, antenna size and performance are limited by radiation physics, not technology. In order to understand antenna radiation and energy storage mechanisms, classical and alternative viewpoints of radiation are discussed. Unlike the common sense of classical antenna radiation, it is shown that the entire antenna fields contribute to both radiation and energy storage with varying total energy velocity during the radiation process. These observations were obtained through investigating impedance, power, the Poynting vector, and energy velocity of a radiating antenna. Antenna transfer functions were investigated to understand the real-world challenges in antenna design and overall performance. An extended model, using both the singularity expansion method and spherical mode decomposition, is introduced to analyze the characteristics of various antenna types including resonant, frequency-independent, and ultra-wideband antennas. It is shown that the extended model is useful to understand real-world antennas. Observations from antenna radiation physics and transfer function modeling lead to both corrections and extension of the classical fundamental-limit theory on antenna size. Both field and circuit viewpoints of the corrected limit theory are presented. The corrected theory is extended for multi-mode excitation cases and also for ultra-wideband and frequency-independent antennas. Further investigation on the fundamental-limit theory provides new innovations, including a low-Q antenna design approach that reduces antenna interference issues and a generalized approach for designing an antenna close to the theoretical-size limit. Design examples applying these new approaches with simulations and measurements are presented. The extended limit theory and developed antenna design approaches will find many applications to optimize compact antenna solutions with reduced near-field interactions.
Ph. D.

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8

Hon, Tsz Kin. "Time-frequency analysis and filtering based on the short-time Fourier transform". Thesis, King's College London (University of London), 2013. https://kclpure.kcl.ac.uk/portal/en/theses/timefrequency-analysis-and-filtering-based-on-the-shorttime-fourier-transform(de8bcca8-cd9d-42a3-bf79-281672478744).html.

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The joint time-frequency (TF) domain provides a convenient platform for signal analysis by involving the dimension of time in the frequency representation of a signal. A straightforward way to acquire localized knowledge about the frequency content of the signal at different times is to perform the Fourier transform over short-time intervals rather than processing the whole signal at once. The resulting TF representation is the short-time Fourier transform (STFT), which remains to date the most widely used method for the analysis of signals whose spectral content varies with time. Recent application examples of the STFT and its variants – e.g. the squared magnitude of the STFT known as the spectrogram – include signal denoising, instantaneous frequency estimation, and speech recognition. In this thesis, we first address the main limitation of the trade-off between time and frequency resolution for the TF analysis by proposing a novel adaptation procedure which properly adjusts the size of the analysis window over time. Our proposed approach achieves a high resolution TF representation, and can compare favorably with alternative time-adaptive spectrograms as well as with advanced quadratic representations. Second, we propose a new scheme for the time-frequency adaptation of the STFT in order to automatically determine the size and the phase of the analysis window at each time and frequency instant. This way, we can further improve the resolution of the conventional as well as the time-adaptive spectrograms. Finally, we focus on denoising non-stationary signals in the STFT domain. We introduced an optimized TF mask in the STFT domain, which is based on the concept of the multi-window spectrogram. Experimentation has shown that the introduced approach can effectively recover distorted signals based on a small set of representative examples of the noisy observation and the desired signal.

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9

Capus, Chris G. "Time-frequency methods based on the fractional fourier transform". Thesis, Heriot-Watt University, 2002. http://hdl.handle.net/10399/1194.

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10

Sucic, Victor. "Parameters selection for optimising time-frequency distributions and measurements of time-frequency characteristics of nonstationary signals". Thesis, Queensland University of Technology, 2004. https://eprints.qut.edu.au/15834/1/Victor_Sucic_Thesis.pdf.

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The quadratic class of time-frequency distributions (TFDs) forms a set of tools which allow to effectively extract important information from a nonstationary signal. To determine which TFD best represents the given signal, it is a common practice to visually compare different TFDs' time-frequency plots, and select as best the TFD with the most appealing plot. This visual comparison is not only subjective, but also difficult and unreliable especially when signal components are closely-spaced in the time-frequency plane. To objectively compare TFDs, a quantitative performance measure should be used. Several measures of concentration/complexity have been proposed in the literature. However, those measures by being derived with certain theoretical assumptions about TFDs are generally not suitable for the TFD selection problem encountered in practical applications. The non-existence of practically-valuable measures for TFDs' resolution comparison, and hence the non-existence of methodologies for the signal optimal TFD selection, has significantly limited the use of time-frequency tools in practice. In this thesis, by extending and complementing the concept of spectral resolution to the case of nonstationary signals, and by redefining the set of TFDs' properties desirable for practical applications, we define an objective measure to quantify the quality of TFDs. This local measure of TFDs' resolution performance combines all important signal time-varying parameters, along with TFDs' characteristics that influence their resolution. Methodologies for automatically selecting a TFD which best suits a given signal, including real-life signals, are also developed. The optimisation of the resolution performances of TFDs, by modifying their kernel filter parameters to enhance the TFDs' resolution capabilities, is an important prerequisite in satisfying any additional application-specific requirements by the TFDs. The resolution performance measure and the accompanying TFDs' comparison criteria allow to improve procedures for designing high-resolution quadratic TFDs for practical time-frequency analysis. The separable kernel TFDs, designed in this way, are shown to best resolve closely-spaced components for various classes of synthetic and real-life signals that we have analysed.

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11

Sucic, Victor. "Parameters Selection for Optimising Time-Frequency Distributions and Measurements of Time-Frequency Characteristics of Nonstationary Signals". Queensland University of Technology, 2004. http://eprints.qut.edu.au/15834/.

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The quadratic class of time-frequency distributions (TFDs) forms a set of tools which allow to effectively extract important information from a nonstationary signal. To determine which TFD best represents the given signal, it is a common practice to visually compare different TFDs' time-frequency plots, and select as best the TFD with the most appealing plot. This visual comparison is not only subjective, but also difficult and unreliable especially when signal components are closely-spaced in the time-frequency plane. To objectively compare TFDs, a quantitative performance measure should be used. Several measures of concentration/complexity have been proposed in the literature. However, those measures by being derived with certain theoretical assumptions about TFDs are generally not suitable for the TFD selection problem encountered in practical applications. The non-existence of practically-valuable measures for TFDs' resolution comparison, and hence the non-existence of methodologies for the signal optimal TFD selection, has significantly limited the use of time-frequency tools in practice. In this thesis, by extending and complementing the concept of spectral resolution to the case of nonstationary signals, and by redefining the set of TFDs' properties desirable for practical applications, we define an objective measure to quantify the quality of TFDs. This local measure of TFDs' resolution performance combines all important signal time-varying parameters, along with TFDs' characteristics that influence their resolution. Methodologies for automatically selecting a TFD which best suits a given signal, including real-life signals, are also developed. The optimisation of the resolution performances of TFDs, by modifying their kernel filter parameters to enhance the TFDs' resolution capabilities, is an important prerequisite in satisfying any additional application-specific requirements by the TFDs. The resolution performance measure and the accompanying TFDs' comparison criteria allow to improve procedures for designing high-resolution quadratic TFDs for practical time-frequency analysis. The separable kernel TFDs, designed in this way, are shown to best resolve closely-spaced components for various classes of synthetic and real-life signals that we have analysed.

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12

Sun, Pu. "Comparison of STFT and Wavelet Transform inTime-frequency Analysis". Thesis, Högskolan i Gävle, Avdelningen för elektronik, matematik och naturvetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-19072.

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The wavelet transform technique has been frequently used in time-frequency analysis as a relatively new concept. Compared to the traditional technique Short-time Fourier Transform (STFT), which is theoretically based on the Fourier transform, the wavelet transform has its advantage on better locality in time and frequency domain, but not significant as the solutions in spectrum. Wavelet transform has dynamic ‘window functions’ to represent time-frequency positions of raw signals, and can get better resolutions in time-frequency analysis. In this report, we shall first briefly introduce fuzzy sets and related concepts. And then we will evaluate their similarities and differences by not only the theoretic comparisons between STFT and wavelet transform, but also the process of the de-nosing to a noisy recorded signal.

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13

Schulte, Walter B. III. "The frequency response, impulse response, and transfer function of an ocean waveguide". Thesis, Monterey, California. Naval Postgraduate School, 2004. http://hdl.handle.net/10945/1516.

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Approved for public release, distribution is unlimited
In this thesis, the ocean was modeled as a waveguide with an ideal pressure - release surface, and an ideal rigid bottom. The ocean waveguide was then treated as a linear, time - invariant, space - variant (TISV) filter or communication channel. The filter is time - invariant because no motion was modeled and because the properties of the ocean were assumed to be constant. The filter is space - variant because of the presence of the two boundaries, that is, the ocean surface and ocean bottom. This thesis investigates the ocean as a linear TISV filter by evaluating 1) the complex frequency response, 2) the impulse response, and 3) the transfer function of the ocean with respect to depth. It is shown that the TISV impulse response of the ocean contains information that can be used to help localize a target in range and whether the target is above or below the receiver. Computer simulation results were obtained by evaluating the three filter functions for several different test cases.
Ensign, United States Navy

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14

Paneras, Demetrios E. "Efficient STFT analysis over limited frequency regions". Thesis, Boston University, 1992. https://hdl.handle.net/2144/34651.

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Thesis (M.S.)--Boston University
PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.
We address the problem of efficiently computing, over narrow frequency bands, the short-time Fourier transform (STFT) and approximations to the STFT. This problem is important for the design of signal understanding systems that have to efficiently carry out STFT reprocessing of signals in order to examine detailed features of signal components that have already been located within narrow frequency bands. In the computation of the exact STFT we use an "overlap pruning" approach (Covell et al. 1992) for exploiting the commonality of computations between successive slices of the STFT with unity decimation interval. We have also extended this approach to the STFT with non-unity decimation intervals and combined it with a frequency pruning method (Sreenivas et al. 1980) to provide additional computational savings. In the computation of approximations to the STFT we use an algorithm (Khan et al. 1988) for efficiently computing Taylor series approximations over narrow frequency bands. Through examples involving real data we demonstrate the feasibility of using the approximated STFT to obtain more accurate estimates of the center frequency of spectral peaks, and to resolve multiple peaks that have been smeared due to the use of short window lengths. The efficiency of all the algorithms we have investigated is less than 0(N log N) multiplications per STFT slice and can be as small as O(N) multiplications per STFT slice in certain cases. Consequently, all the algorithms compare favourably with the standard FFT implementation of the STFT which requires O(N log N) multiplications per slice. All the algorithms considered in this thesis were implemented in software and tested on synthetic and real sound signals.
2031-01-01

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15

Veroy, Karen Paula L. (Karen Paula Lavarro) 1975. "Time-frequency analysis of Lamb waves using the Morlet wavelet transform". Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/81540.

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16

Trombetta, Jacob J. "Time-Frequency Representation of Musical Signals Using the Discrete Hermite Transform". University of Akron / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=akron1304100211.

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17

Oliveira, Filho Itamar Sales de. "Time-frequency analysis : The bilinear Hilbert transform and the Carleson theorem". reponame:Repositório Institucional da UFC, 2016. http://www.repositorio.ufc.br/handle/riufc/18888.

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OLIVEIRA FILHO, Itamar Sales de. Time-frequency analysis : the bilinear Hilbert transform and the Carleson theorem. 2016. 109 f. Dissertação (Mestrado em Matemática em Rede Nacional) – Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2016.
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In 1966, Lennart Carleson proved that the Fourier series of a periodic function, square integrable over a fundamental domain of the real line converges to the same function almost everywhere. This result was revisited years later by Charles Fe erman (1973) and by Lacey and Thiele (2000). It is studied here Lacey and Thiele's work, where they approached the problem through time-frequency analysis. This proof was inspired in a previous work of theirs, where they establish boundedness for the bilinear Hilbert transform in Lebesgue spaces. The study of boundedness for this operator started with the attempts to establish boundedness for the first Calderon's commutator. Also through time-frequency analysis, it will be studied one of the works of Lacey and Thiele about the bilinear Hilbert transform.
Em 1966, Lennart Carleson provou que a série de Fourier de uma função periódica, quadrado-integrável em um domínio fundamental na reta converge para a prápria função em quase todo ponto. Esse resultado foi revisitado alguns anos depois por Charles Fefferman (1973) e por Lacey e Thiele (2000). É estudado aqui o trabalho desses ultimos, onde o problema é abordado através de análise de tempo e frequência. Essa demonstração foi inspirada em um trabalho anterior dos mesmos autores em que estabelecem limitação para a transformada de Hilbert bilinear em espaços de Lebesgue. O estudo da limitação desse operador começou com as tentativas de estabelecer limitação para o primeiro comutador de Calderón. Também sob o ponto de vista da análise de tempo e frequência, será estudado um dos trabalhos de Lacey e Thiele sobre a transformada de Hilbert bilinear.

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18

Akhanli, Deniz. "Radar Range-doppler Imaging Using Joint Time-frequency Techniques". Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12608325/index.pdf.

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Inverse Synthetic Aperture Radar coherently processes the return signal from the target in order to construct the image of the target. The conventional methodology used for obtaining the image is the Fourier transform which is not capable of suppressing the Doppler change in the return signal. As a result, Range-Doppler image is degraded. A proper time-frequency transform suppresses the degradation due to time varying Doppler shift. In this thesis, high resolution joint-time frequency transformations that can be used in place of the conventional method are evaluated. Wigner-Ville Distribution, Adaptive Gabor Representation with Coarse-to-Fine search algorithm, and Time-Frequency Distribution Series are examined for the target imaging system. The techniques applied to sample signals compared with each other. The computational and memorial complexity of the methods are evaluated and compared to each other and possible improvements are discussed. The application of these techniques in the target imaging system is also performed and resulting images compared to each other.

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19

Barkat, Braham. "Design, estimation and performance of time-frequency distributions". Thesis, Queensland University of Technology, 2000.

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20

Loza, Artur. "Image processing and time-frequency transform methods for radar characterisation and recognition". Thesis, University of Bristol, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.500445.

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This thesis covers research into radar target characterisation and recognition with the use of joint time-frequency representations and image processing techniques. Specifically, the recognition of the scatterers of ballistic missiles is of particular interest. The complex motion and composite structure of the targets result in highly nonstationary signal, and therefore its characteristics are investigated both in time and frequency. A novel method for time-frequency analysis of nonstationary radar signals is proposed facilitating formulation of a feature space suited to the problem at hand. This signal-adaptive procedure allows unsupervised computation of the Smoothed Wigner-Ville Distribution based on time and frequency moments of the time-segmented signal.

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21

Barbu, Madalina. "Acoustic Seabed and Target Classification using Fractional Fourier Transform and Time-Frequency Transform Techniques". ScholarWorks@UNO, 2006. http://scholarworks.uno.edu/td/480.

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An approach for processing sonar signals with the ultimate goal of ocean bottom sediment classification and underwater buried target classification is presented in this dissertation. Work reported for sediment classification is based on sonar data collected by one of the AN/AQS-20's sonars. Synthetic data, simulating data acquired by parametric sonar, is employed for target classification. The technique is based on the Fractional Fourier Transform (FrFT), which is better suited for sonar applications because FrFT uses linear chirps as basis functions. In the first stage of the algorithm, FrFT requires finding the optimum order of the transform that can be estimated based on the properties of the transmitted signal. Then, the magnitude of the Fractional Fourier transform for optimal order applied to the backscattered signal is computed in order to approximate the magnitude of the bottom impulse response. Joint time-frequency representations of the signal offer the possibility to determine the time-frequency configuration of the signal as its characteristic features for classification purposes. The classification is based on singular value decomposition of the time-frequency distributions applied to the impulse response. A set of the largest singular values provides the discriminant features in a reduced dimensional space. Various discriminant functions are employed and the performance of the classifiers is evaluated. A study of various classifiers' performance is carried-out for the proposed algorithm under two scenarios for determining the impulse response: FrFT method versus standard deconvolution method. Of particular interest for underwater under-sediment classification applications are long targets such as cables of various diameters, which need to be identified as different from other strong reflectors or point targets. Synthetic test data are used to exemplify and evaluate the proposed technique for target classification. The synthetic data simulates the impulse response of cylindrical targets buried in the seafloor sediments. Results are presented that illustrate the processing procedure. An important characteristic of this method is that good classification accuracy of an unknown target is achieved having only the response of a known target in the free field. The algorithm shows an accurate way to classify buried objects under various scenarios, with high probability of correct classification.

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Hammarqvist, Ulf. "Audio editing in the time-frequency domain using the Gabor Wavelet Transform". Thesis, Uppsala universitet, Centrum för bildanalys, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-153634.

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Visualization, processing and editing of audio, directly on a time-frequency surface, is the scope of this thesis. More precisely the scalogram produced by a Gabor Wavelet transform is used, which is a powerful alternative to traditional techinques where the wave form is the main visual aid and editting is performed by parametric filters. Reconstruction properties, scalogram design and enhancements as well audio manipulation algorithms are investigated for this audio representation.The scalogram is designed to allow a flexible choice of time-frequency ratio, while maintaining high quality reconstruction. For this mean, the Loglet is used, which is observed to be the most suitable filter choice. Re-assignmentare tested, and a novel weighting function using partial derivatives of phase is proposed. An audio interpolation procedure is developed and shown to perform well in listening tests.The feasibility to use the transform coefficients directly for various purposes is investigated. It is concluded that Pitch shifts are hard to describe in the framework while noise thresh holding works well. A downsampling scheme is suggested that saves on operations and memory consumption as well as it speeds up real world implementations significantly. Finally, a Scalogram 'compression' procedure is developed, allowing the caching of an approximate scalogram.

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E, Okwelume Gozie, e Ezeude Anayo Kingsley. "BLIND SOURCE SEPARATION USING FREQUENCY DOMAIN INDEPENDENT COMPONENT ANALYSIS". Thesis, Blekinge Tekniska Högskola, Avdelningen för signalbehandling, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-1312.

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Our thesis work focuses on Frequency-domain Blind Source Separation (BSS) in which the received mixed signals are converted into the frequency domain and Independent Component Analysis (ICA) is applied to instantaneous mixtures at each frequency bin. Computational complexity is also reduced by using this method. We also investigate the famous problem associated with Frequency-Domain Blind Source Separation using ICA referred to as the Permutation and Scaling ambiguities, using methods proposed by some researchers. This is our main target in this project; to solve the permutation and scaling ambiguities in real time applications
Gozie: modebelu2001@yahoo.com Anayo: ezeudea@yahoo.com

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Manser, Nathan Daniel. "Effects of Solids Retention Time and Feeding Frequency on Performance and Pathogen Fate in Semi-continuous Mesophilic Anaerobic Digesters". Scholar Commons, 2015. http://scholarcommons.usf.edu/etd/5735.

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Anaerobic digestion is a biochemical process in which organic carbon is biodegraded in an oxygen free environment through a microbial consortium. Engineered biological systems used for resource recovery often utilize anaerobic digestion to treat anthropogenic organic wastes by reclaiming the carbon as energy (methane gas) and a soil amendment (biosolids). Small-scale, or household, semi-continuous anaerobic digesters have been used in developed and developing countries for many decades to produce biogas from human and livestock waste, which is used for heating, lighting, and cooking. This application has been shown to improve the quality of life of the user. Although there is great potential for small-scale semi-continuous anaerobic digestion to provide much needed resource recovery functions and quality of life improvements in future development, the manner in which these systems are operated could lead to unintended consequences on human health because human waste often contains resistant pathogens. This paradigm is best demonstrated by soil-transmitted helminths that are known to be highly resilient in mesophilic anaerobic digestion environments and endemic to many developing countries. The idea that soil-transmitted helminths survive mesophilic anaerobic digestion is exacerbated when the biosolids from the digesters are land applied as a soil-amendment because this process fits perfectly into the lifecycle of soil-transmitted helminths that need soil environments to develop into infective larva. This research was divided into three sections to investigate the fate of human pathogens during semi-continuous anaerobic digestion and investigate techniques to enhance their removal. The sections were: 1) an examination into the fate (embryonation, development, inactivation, destruction) of Ascaris suum ova during mesophilic semi-continuous anaerobic digestion, with an emphasis on increased inactivation, 2) an investigation into the performance (volatile solids (VS) removal, E. coli and Salmonella destruction, methane production) of semi-continuous mesophilic anaerobic digesters and the effect of variations to solids retention time (SRT) and feeding frequency, and 3) development and application of mathematical models for pathogen inactivation kinetics and typical semi-continuous reactor residence time distributions to predict the removal efficiency of Ascaris suum ova during semi-continuous anaerobic digestion under different operating conditions. Results of these studies showed that during semi-continuous mesophilic anaerobic digestion variations in feeding frequency did not impact the fate of Ascaris suum ova or Salmonella; however it was observed that better removal of E. coli and higher methane production was achieved at the longer feeding interval (weekly). Additional results indicated that embryonated ova were destroyed faster than unembryonated ova under the experimental conditions, which suggests a potential mechanism to enhance removal of this common pathogen. Since an increased feeding interval proved to be beneficial for digester performance our findings suggest that wastes containing Ascaris suum ova could be stored in an aerated environment, for a period of time that does not negatively impact resource recovery, to lengthen the time between feedings and promote ova embryonation and ensuing destruction during digestion. Modeling results indicate that under mesophilic conditions (35oC) the ova of Ascaris suum could survive for 22 days and will not be completely removed from the effluent under typical feeding frequencies and average SRT were examined. Therefore, the use of anaerobic digestion as a resource recovery technology where soil-transmitted helminths proliferate should be applied with extra operational safeguards or be included as one step of several in a small-scale treatment train.

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25

Fredriksson, Henrik. "On the Short-Time Fourier Transform and Gabor Frames generated by B-splines". Thesis, Linnéuniversitetet, Institutionen för datavetenskap, fysik och matematik, DFM, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-20262.

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In this thesis we study the short-time Fourier transform. The short-time Fourier transform of a function f(x) is obtained by restricting our function to a short time segment and take the Fourier transform of this restriction. This method gives information locally of f in both time and frequency simultaneously.To get a smooth frequency localization one wants to use a smooth window, whichmeans that the windows will overlap. The continuous short-time Fourier transform is not appropriate for practical purpose, therefore we want a discrete representation of f. Using Gabor theory, we can write a function f as a linear combination of time- and frequency shifts of a fixed window function g with integer parameters a; b > 0. We show that if the window function g has compact support, then g generates a Gabor frame G(g; a; b). We also show that for such a g there exists a dual frame such that both G(g; a; b) and its dual frame has compact support and decay fast in the Fourier domain. Based on [2], we show that B-splines generates a pair of Gabor frames.

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26

Karaoglu, Bulent. "A comparison of frequency offset estimation methods in Orthogonal Frequency Division Multiplexing (OFDM) systems". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Dec%5FKaraoglu.pdf.

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Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, Dec. 2004.
Thesis Advisor(s): Roberto Cristi, Murali Tummala. Includes bibliographical references (p. 45-46). Also available online.

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27

Scaife, Bradley J. "DOPPLER SHIFTED SPREAD SPECTRUM CARRIER RECOVERY USING REAL-TIME DSP TECHNIQUES". International Foundation for Telemetering, 1998. http://hdl.handle.net/10150/607365.

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International Telemetering Conference Proceedings / October 26-29, 1998 / Town & Country Resort Hotel and Convention Center, San Diego, California
In any satellite communication, the Doppler shift associated with the satellite’s position and velocity must be calculated in order to determine the carrier frequency. If the satellite state vector is unknown then some estimate must be formed of the Doppler-shifted carrier frequency. One elementary technique is to examine the signal spectrum and base the estimate on the dominant spectral component. If, however, the carrier is spread (as in most satellite communications) this technique may fail unless the chip rate-to-data rate ratio (processing gain) associated with the carrier is small. In this case, there may be enough spectral energy to allow peak detection against a noise background. In this paper, we present a method to estimate the frequency (without knowledge of the Doppler shift) of a spread-spectrum carrier assuming a small processing gain and binary-phase shift keying (BPSK) modulation. Our method relies on a simple, averaged discrete Fourier transform along with peak detection. We provide simulation results indicating the accuracy of this method. In addition, we will describe an all-digital hardware design based around a Motorola DSP56303 and high-speed A/D which implements this technique in real-time. The hardware design is to be used in NMSU’s implementation of NASA’s demand assignment, multiple access (DAMA) service.

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28

Kothakapa, Vijayvardhan Reddy. "Investigation on the use of time-modulation technique for an ultra-wideband reader". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/14982/.

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Ultra-wideband Technology is a trusted key for future generation radio frequency identification systems to conquer them as high as the limitations of the ongoing narrow bandwidth radio frequency identification technology like decreasing the space coverage, insufficient ranging resolution for accurate localization, sensitivity to interference, and multiple access capabilities. The idea in practice is to apply the Time Modulation technique which means the presence of switches at the antenna ports, which is a new procedure, but typically adopted for narrowband antennas arrays. So, for the arrays working at a single frequency. Here we are trying to see if it is possible to apply this excitation technique also to ultra-wideband antennas. So, in this case, instead of having two monopoles for instance as well as our application, we have used two Ultra-wideband antennas working in the lower European UWB band [3.1 – 4.8]GHz. For single narrow band antennas, we see what it happens only at single band frequency. In this case, having UWB antennas, we must split our 2GHz band from 3 to 5GHz into windows of 500MHz. This dissertation mainly focuses on the two important characteristics. They are: localization and power transmission both realized by the time modulated antenna array and evaluates their application in the communication system. The first step of experiment localization is carried out on a computer by using the software tool called Computer Simulation Technology (CST) in the range from 3GHz to 5GHz and then merging the results with a MATLAB programming to extract the far-field results and by using Nonlin software which was developed by the researchers of DEI: with this procedure we are able to evaluate the simulation results of far-field by taking into account all the possible phenomena, both linear and non-linear, taking place in the radiating system under test.

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29

Zuo, Jian. "The Frequency Monitor Network (FNET) Design and Situation Awareness Algorithm Development". Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/26721.

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Wide Area Measurements (WAMs) have been widely used in the energy management system (EMS) of power system for monitoring, operation and control. In recent years, the advent of synchronized Phasor Measurements Unit (PMU) has added another dimension to the field of wide-area measurement. However, the high cost of the PMU, which includes the manufacture and deployment fee, is a hurdle to the wide use of the PMU in power systems. Unlike traditional PMUs, the frequency monitoring network (FNET) developed by the Virginia Tech Power IT lab is an Internetâ based, GPSâ synchronized, wide-area frequency monitoring network deployed at the distribution level, providing a low-cost and easily deployable WAMs solution. In this dissertation, the research work can be categorized into two parts: FNET Design and Situation Awareness Algorithm Development.
Ph. D.

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30

Seton, Ragnar. "Data acquisition system for optical frequency comb spectroscopy". Thesis, Umeå universitet, Institutionen för fysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-139117.

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The Optical Frequency Comb Spectroscopy (OFCS) Group at the Department of Physics at Umeå University develops new techniques for extremely high sensitivity trace gas detection, non invasive temperature measurements, and other applications of OFCS. Their setup used primarily for trace gas detection contains several components that have been developed in-house, including a Fourier Transform Spectrometer (FTS) and an auto-balancing detector. This is the one used in this thesis work and it includes a high frequency data acquisition card (DAC) recording interferograms in excess of 10^7 double-precision floating point samples per sweep of the FTS's retarder. For acquisition and analysis to be possible in both directions of the retarder the interferograms needs to be analysed in a sub-second timeframe, something not possible with the present software. The aim of this thesis work has thus been to develop a system with optimized analysis implementations in MATLAB. The latter was a prerequisite from the group to ensure maintainability, as all members are well acquainted with it.Fulfilling its primary purpose MATLAB performs vector and matrix computations quite efficiently, has mostly fully mutable datatypes, and with recent just-in-time (JIT) compilation optimizations vector resizing performance has improved to what in many instances is perceived as equivalent to preallocated variables. This memory management abstraction, however, also means that explicit control of when arguments are passed by value or by reference to a function is not officially supported. The following performance ramifications naturally increase with the size of the data sets (N) passed as arguments and become quite noticeable even at moderate values of N when dealing with data visualization, a key function in system. To circumvent these problems explicit data references were implemented using some of the undocumented functions of MATLAB's libmx library together with a custom data visualization function.The main parts of the near real time interferogram analysis are resampling and a Fourier transformation, both of which had functionally complete but not optimized implementations. The minimal requirement for the reimplementation of these were simply to improve efficiency while maintaining output precision.On experimentally obtained data the new system's (DAQS) resampling implementation increased sample throughput by a factor of 19 which in the setup used corresponds to 10^8 samples per second. Memory usage was decreased by 72% or in terms of the theoretical minimum from a factor 7.1 to 2.0. Due to structural changes in the sequence of execution DAQS has no corresponding implementation of the reference FFT function as the computations performed in it have been parallelized and/or are only executed on demand, their combined CPU-time can however in a worst-case scenario reach 75% of that of the reference. The data visualization performance increase (compared to MATLAB's own, as the old system used LabVIEW) depends on the size in pixels of the surface it is visualized on and N, decreasing with the former and increasing with the latter. In the baseline case of a default surface size of 434x342 pixels and N corresponding to one full sweep of the FTS's retarder DAQS offers a 100x speed-up to the Windows 7 version of MATLAB R2014b's plot.In addition to acquiring and analyzing interferograms the primary objectives of the work included tools to configure the DAC and controlling the FTS's retarder motor, both implemented in DAQS.Secondary to the above was the implementation of acquisition and analysis for both directions of the retarder, a HITRAN reference spectra generator, and functionality to improve the user experience (UX). The first, though computation time allows for it, has not been implemented due to a delay in the DAC-driver. To provide a generic implementation of the second, the HITRAN database was converted from the text-based format it is distributed in to a MySQL database, a wrapper class providing frequency-span selection and the absorption spectra generation was developed together with a graphical front-end. Finally the improved UX functionality mainly focused on providing easy-access documentation of the properties of the DAC.In summation, though the primary objectives of optimizing the data analysis functions were reached, the end product still requires a new driver for the DAC to provide the full functionality of the reference implementation as the existing one is simply too slow. Many of DAQS' components can however be used as stand-alone classes and functions until a new driver is available. It is also worth mentioning that National Instruments (NI), the DAC vendor, has according to their technical support no plans to develop native MATLAB drivers as MathWorks will not sell them licenses.

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31

Hussain, Zahir M. "Adaptive instantaneous frequency estimation: Techniques and algorithms". Thesis, Queensland University of Technology, 2002. https://eprints.qut.edu.au/36137/7/36137_Digitised%20Thesis.pdf.

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This thesis deals with the problem of the instantaneous frequency (IF) estimation of sinusoidal signals. This topic plays significant role in signal processing and communications. Depending on the type of the signal, two major approaches are considered. For IF estimation of single-tone or digitally-modulated sinusoidal signals (like frequency shift keying signals) the approach of digital phase-locked loops (DPLLs) is considered, and this is Part-I of this thesis. For FM signals the approach of time-frequency analysis is considered, and this is Part-II of the thesis. In part-I we have utilized sinusoidal DPLLs with non-uniform sampling scheme as this type is widely used in communication systems. The digital tanlock loop (DTL) has introduced significant advantages over other existing DPLLs. In the last 10 years many efforts have been made to improve DTL performance. However, this loop and all of its modifications utilizes Hilbert transformer (HT) to produce a signal-independent 90-degree phase-shifted version of the input signal. Hilbert transformer can be realized approximately using a finite impulse response (FIR) digital filter. This realization introduces further complexity in the loop in addition to approximations and frequency limitations on the input signal. We have tried to avoid practical difficulties associated with the conventional tanlock scheme while keeping its advantages. A time-delay is utilized in the tanlock scheme of DTL to produce a signal-dependent phase shift. This gave rise to the time-delay digital tanlock loop (TDTL). Fixed point theorems are used to analyze the behavior of the new loop. As such TDTL combines the two major approaches in DPLLs: the non-linear approach of sinusoidal DPLL based on fixed point analysis, and the linear tanlock approach based on the arctan phase detection. TDTL preserves the main advantages of the DTL despite its reduced structure. An application of TDTL in FSK demodulation is also considered. This idea of replacing HT by a time-delay may be of interest in other signal processing systems. Hence we have analyzed and compared the behaviors of the HT and the time-delay in the presence of additive Gaussian noise. Based on the above analysis, the behavior of the first and second-order TDTLs has been analyzed in additive Gaussian noise. Since DPLLs need time for locking, they are normally not efficient in tracking the continuously changing frequencies of non-stationary signals, i.e. signals with time-varying spectra. Nonstationary signals are of importance in synthetic and real life applications. An example is the frequency-modulated (FM) signals widely used in communication systems. Part-II of this thesis is dedicated for the IF estimation of non-stationary signals. For such signals the classical spectral techniques break down, due to the time-varying nature of their spectra, and more advanced techniques should be utilized. For the purpose of instantaneous frequency estimation of non-stationary signals there are two major approaches: parametric and non-parametric. We chose the non-parametric approach which is based on time-frequency analysis. This approach is computationally less expensive and more effective in dealing with multicomponent signals, which are the main aim of this part of the thesis. A time-frequency distribution (TFD) of a signal is a two-dimensional transformation of the signal to the time-frequency domain. Multicomponent signals can be identified by multiple energy peaks in the time-frequency domain. Many real life and synthetic signals are of multicomponent nature and there is little in the literature concerning IF estimation of such signals. This is why we have concentrated on multicomponent signals in Part-H. An adaptive algorithm for IF estimation using the quadratic time-frequency distributions has been analyzed. A class of time-frequency distributions that are more suitable for this purpose has been proposed. The kernels of this class are time-only or one-dimensional, rather than the time-lag (two-dimensional) kernels. Hence this class has been named as the T -class. If the parameters of these TFDs are properly chosen, they are more efficient than the existing fixed-kernel TFDs in terms of resolution (energy concentration around the IF) and artifacts reduction. The T-distributions has been used in the IF adaptive algorithm and proved to be efficient in tracking rapidly changing frequencies. They also enables direct amplitude estimation for the components of a multicomponent

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32

Nyman, Lina. "Estimation of Aerodynamic Parameters in Real-Time : Implementation and Comparison of a Sequential Frequency Domain Method and a Batch Method". Thesis, Linköpings universitet, Fluida och mekatroniska system, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-132807.

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The flight testing and evaluation of collected data must be efficient during intensive flight-test programs such as the ones conducted during development of new aircraft. The aim of this thesis has thus been to produce a first version of an aerodynamic derivative estimation program that is to be used during real-time flight tests. The program is to give a first estimate of the aerodynamic derivatives as well as check the quality of the data collected and thus serve as a decision support during tests. The work that has been performed includes processing of data in order to use it in computations, comparing a batch and a sequential estimation method using real-time data and programming a user interface. All computations and programming has been done in Matlab. The estimation methods that have been compared are both built on transforming data to the frequency domain using a Chirp z-transform and then estimating the aerodynamic derivatives using complex least squares with instrumental variables.The sequential frequency domain method performs estimates at a given interval while the batch method performs one estimation at the end of the maneuver. Both methods compared in this thesis produce equal results. The continuous updates of the sequential method was however found to be better suited for a real-time application than the single estimation of the batch method. The telemetric data received from the aircraft must be synchronized to a common frequency of 60 Hz. Missing samples of the data stream must be linearly interpolated and different units of measured parameters must be corrected in order to be able to perform these estimations in the real-time test environment.

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33

Girt, Lukáš. "Přenos přesného času a stabilní frekvence optickou sítí". Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2018. http://www.nusl.cz/ntk/nusl-376977.

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Diploma thesis focuses on the theoretical analysis of precise time and stable frequency transfer. It describes what time and frequency is, their properites and options of their generation. Next part deals with different possibilities of time and frequency transfer especially using fiber optics. In the practical part equipment for analysing effects of temperature changes on precise time transfer is puted into operation. Arduino platform is used for monitoring temperature changes on fiber. For testing of frequency stability in variable temperature conditions of environmental chamber device is created using highly coherent laser.

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34

El, Gemayel Tarek. "Feasibility of Using Electrical Network Frequency Fluctuations to Perform Forensic Digital Audio Authentication". Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/24383.

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Extracting the Electric Network Frequency (ENF) fluctuations from an audio recording and comparing it to a reference database is a new technology intended to perform forensic digital audio authentication. The objective of this thesis is to implement and design a range of programs and algorithms for capturing and extracting ENF signals. The developed C-program combined with a probe can be used to build the reference database. Our implementation of the Short-Time Fourier Transform method is intended for the ENF extraction of longer signals while our novel proposed use of the Autoregressive parametric method and our implementation of the zero-crossing approach tackle the case of shorter recordings. A Graphical User Interface (GUI) was developed to facilitate the process of extracting the ENF fluctuations. The whole process is tested and evaluated for various scenarios ranging from long to short recordings.

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35

McPhee, Hamish. "Algorithme d'échelle de temps autonome et robuste pour un essaim de nanosatellites". Electronic Thesis or Diss., Université de Toulouse (2023-....), 2024. http://www.theses.fr/2024TLSEP094.

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Un nouvel algorithme est proposé et validé pour générer une échelle de temps robuste. Prévu pour une utilisation dans un essaim de nanosatellites, l'Autonomous Time Scale using the Student's T-distribution (ATST) peut traiter les anomalies subies par les horloges et les liens inter-satellites dans un environnement hostile. Les types d'anomalies traités incluent les sauts de phase, les sauts de fréquence, un bruit de mesure élevé dans certains liens et les données manquantes. En prenant la moyenne pondérée des résidus contenus dans l'équation de l'échelle de temps de base (BTSE), la contribution des satellites avec des mesures anormales est réduite pour la génération de l'échelle de temps. Les poids attribués à chaque horloge sont basés sur l'hypothèse que les résidus suivent la loi de Student.La performance de l'algorithme ATST est équivalente à celle de l'algorithme AT1 oracle, qui est une version de l'échelle de temps AT1 avec la capacité de détecter parfaitement toutes les anomalies dans des données simulées. Bien que l'algorithme n'ait pas de méthode de détection explicite, l'ATST affiche toujours un niveau de robustesse comparable à celui d'un détecteur parfait. Cependant, l'ATST est conçu pour un essaim avec de nombreuses horloges de types homogènes et est limité par une complexité numérique élevée. De plus, les anomalies sont toutes traitées de la même manière sans distinction entre les différents types d'anomalies. Malgré ces limitations identifiées, le nouvel algorithme représente une contribution prometteuse dans le domaine des échelles de temps grâce à la robustesse atteinte.Une méthode de traitement des horloges ajoutées ou retirées de l'ensemble est également proposée dans cette thèse en conjonction avec l'ATST. Cette méthode préserve la continuité de phase et de fréquence de l'échelle de temps en attribuant un poids nul aux horloges pertinentes lorsque le nombre total d'horloges est modifié. Un estimateur des moindres carrés (Least Squares, LS) est présenté pour montrer comment les mesures des liens inter-satellites peuvent être traitées en amont pour réduire le bruit de mesure et en même temps remplacer les mesures manquantes. L'estimateur LS peut être utilisé avec une méthode de détection qui élimine les mesures anormales, puis l'estimateur LS remplace les mesures supprimées par les estimations correspondantes.Cette thèse examine également l'estimation optimale de l'estimateur du maximum de vraisemblance (MLE) pour les paramètres des lois de probabilités à queues lourdes : précisément la loi de Student et la loi des mélanges gaussiens. Les améliorations obtenues en supposant correctement ces lois par rapport à l'hypothèse de la loi gaussienne sont démontrées avec les bornes de Cramér-Rao mal spécifiées (MCRB). Le MCRB dérivé confirme que les lois à queues lourdes sont meilleures pour l'estimation de la moyenne en présence de valeurs aberrantes. L'estimation des paramètres des lois à queues lourdes nécessite au moins 25 horloges pour obtenir l'erreur minimale, c'est-à-dire que l'estimateur atteigne l'efficacité asymptotique. Cette méthodologie pourra nous aider à analyser d'autres types d'anomalies suivant des lois différentes.Des propositions pour des pistes de recherche futures incluent le traitement des limitations de l'algorithme ATST concernant les types et le nombre d'horloges. Une nouvelle moyenne pour attribuer les poids en utilisant le machine learning est envisageable grâce à la compréhension des résidus du BTSE. Les anomalies transitoires peuvent être mieux traitées par le machine learning ou même avec un estimateur robuste de la fréquence des horloges sur une fenêtre de données passées. Cela est intéressant à explorer et à comparer à l'algorithme ATST, qui est proposé pour des anomalies instantanées
A new robust time scale algorithm, the Autonomous Time scale using the Student's T-distribution (ATST), has been proposed and validated using simulated clock data. Designed for use in a nanosatellite swarm, ATST addresses phase jumps, frequency jumps, anomalous measurement noise, and missing data by making a weighted average of the residuals contained in the Basic Time Scale Equation (BTSE). The weights come from an estimator that assumes the BTSE residuals are modeled by a Student's t-distribution.Despite not detecting anomalies explicitly, the ATST algorithm performs similarly to a version of the AT1 time scale that detects anomalies perfectly in simulated data. However, ATST is best for homogeneous clock types, requires a high number of clocks, adds computational complexity, and cannot necessarily differentiate anomaly types. Despite these identified limitations the robustness achieved is a promising contribution to the field of time scale algorithms.The implementation of ATST includes a method that maintains phase and frequency continuity when clocks are removed or reintroduced into the ensemble by resetting appropriate clock weights to zero. A Least Squares (LS) estimator is also presented to pre-process inter-satellite measurements, reducing noise and estimating missing data. The LS estimator is also compatible with anomaly detection which removes anomalous inter-satellite measurements because it can replace the removed measurements with their estimates.The thesis also explores optimal estimation of parameters of two heavy-tailed distributions: the Student's t and Bimodal Gaussian mixture. The Misspecified Cramér Rao Bound (MCRB) confirms that assuming heavy-tailed distributions handles outliers better compared to assuming a Gaussian distribution. We also observe that at least 25 clocks are required for asymptotic efficiency when estimating the mean of the clock residuals. The methodology also aids in analyzing other anomaly types fitting different distributions.Future research proposals include addressing ATST's limitations with diverse clock types, mitigating performance loss with fewer clocks, and exploring robust time scale generation using machine learning to weight BTSE residuals. Transient anomalies can be targeted using machine learning or even a similar method of robust estimation of clock frequencies over a window of past data. This is interesting to research and compare to the ATST algorithm that is instead proposed for instantaneous anomalies

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36

Lee, Peter. "Wavelet Filter Banks in Perceptual Audio Coding". Thesis, University of Waterloo, 2003. http://hdl.handle.net/10012/927.

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This thesis studies the application of the wavelet filter bank (WFB) in perceptual audio coding by providing brief overviews of perceptual coding, psychoacoustics, wavelet theory, and existing wavelet coding algorithms. Furthermore, it describes the poor frequency localization property of the WFB and explores one filter design method, in particular, for improving channel separation between the wavelet bands. A wavelet audio coder has also been developed by the author to test the new filters. Preliminary tests indicate that the new filters provide some improvement over other wavelet filters when coding audio signals that are stationary-like and contain only a few harmonic components, and similar results for other types of audio signals that contain many spectral and temporal components. It has been found that the WFB provides a flexible decomposition scheme through the choice of the tree structure and basis filter, but at the cost of poor localization properties. This flexibility can be a benefit in the context of audio coding but the poor localization properties represent a drawback. Determining ways to fully utilize this flexibility, while minimizing the effects of poor time-frequency localization, is an area that is still very much open for research.

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37

SHI, Juanjuan. "Morphology-based Fault Feature Extraction and Resampling-free Fault Identification Techniques for Rolling Element Bearing Condition Monitoring". Thesis, Université d'Ottawa / University of Ottawa, 2015. http://hdl.handle.net/10393/33422.

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As the failure of a bearing could cause cascading breakdowns of the mechanical system and then lead to costly repairs and production delays, bearing condition monitoring has received much attention for decades. One of the primary methods for this purpose is based on the analysis of vibration signal measured by accelerometers because such data are information-rich. The vibration signal collected from a defective bearing is, however, a mixture of several signal components including the fault-generated impulses, interferences from other machine components, and background noise, where fault-induced impulses are further modulated by various low frequency signal contents. The compounded effects of interferences, background noise and the combined modulation effects make it difficult to detect bearing faults. This is further complicated by the nonstationary nature of vibration signals due to speed variations in some cases, such as the bearings in a wind turbine. As such, the main challenges in the vibration-based bearing monitoring are how to address the modulation, noise, interference, and nonstationarity matters. Over the past few decades, considerable research activities have been carried out to deal with the first three issues. Recently, the nonstationarity matter has also attracted strong interests from both industry and academic community. Nevertheless, the existing techniques still have problems (deficiencies) as listed below: (1) The existing enveloping methods for bearing fault feature extraction are often adversely affected by multiple interferences. To eliminate the effect of interferences, the prefiltering is required, which is often parameter-dependent and knowledge-demanding. The selection of proper filter parameters is challenging and even more so in a time-varying environment. (2) Even though filters are properly designed, they are of little use in handling in-band noise and interferences which are also barriers for bearing fault detection, particularly for incipient bearing faults with weak signatures. (3) Conventional approaches for bearing fault detection under constant speed are no longer applicable to the variable speed case because such speed fluctuations may cause “smearing” of the discrete frequencies in the frequency representation. Most current methods for rotating machinery condition monitoring under time-varying speed require signal resampling based on the shaft rotating frequency. For the bearing case, the shaft rotating frequency is, however, often unavailable as it is coupled with the instantaneous fault characteristic frequency (IFCF) by a fault characteristic coefficient (FCC) which cannot be determined without knowing the fault type. Additionally, the effectiveness of resampling-based methods is largely dependent on the accuracy of resampling procedure which, even if reliable, can complicate the entire fault detection process substantially. (4) Time-frequency analysis (TFA) has proved to be a powerful tool in analyzing nonstationary signal and moreover does not require resampling for bearing fault identification. However, the diffusion of time-frequency representation (TFR) along time and frequency axes caused by lack of energy concentration would handicap the application of the TFA. In fact, the reported TFA applications in bearing fault diagnosis are still very limited. To address the first two aforementioned problems, i.e., (1) and (2), for constant speed cases, two morphology-based methods are proposed to extract bearing fault feature without prefiltering. Another two methods are developed to specifically handle the remaining problems for the bearing fault detection under time-varying speed conditions. These methods are itemized as follows: (1) An efficient enveloping method based on signal Fractal Dimension (FD) for bearing fault feature extraction without prefiltering, (2) A signal decomposition technique based on oscillatory behaviors for noise reduction and interferences removal (including in-band ones), (3) A prefiltering-free and resampling-free approach for bearing fault diagnosis under variable speed condition via the joint application of FD-based envelope demodulation and generalized demodulation (GD), and (4) A combined dual-demodulation transform (DDT) and synchrosqueezing approach for TFR energy concentration level enhancement and bearing fault identification. With respect to constant speed cases, the FD-based enveloping method, where a short time Fractal dimension (STFD) transform is proposed, can suppress interferences and highlight the fault-induced impulsive signature by transforming the vibration signal into a STFD representation. Its effectiveness, however, deteriorates with the increased complexity of the interference frequencies, particularly for multiple interferences with high frequencies. As such, the second method, which isolates fault-induced transients from interferences and noise via oscillatory behavior analysis, is then developed to complement the FD-based enveloping approach. Both methods are independent of frequency information and free from prefiltering, hence eliminating the tedious process for filter parameter specification. The in-band vibration interferences can also be suppressed mainly by the second approach. For the nonstationary cases, a prefiltering-free and resampling-free strategy is developed via the joint application of STFD and GD, from which a resampling-free order spectrum can be derived. This order spectrum can effectively reveal not only the existence of a fault but also its location. However, the success of this method relies largely on an effective enveloping technique. To address this matter and at the same time to exploit the advantages of TFA in nonstationary signal analysis, a TFA technique, involving dual demodulations and an iterative process, is developed and innovatively applied to bearing fault identification. The proposed methods have been validated using both simulation and experimental data collected in our lab. The test results have shown that the first two methods can effectively extract fault signatures, remove the interferences (including in-band ones) without prefiltering, and detect fault types from vibration signals for constant speed cases. The last two have shown to be effective in detecting faults and discern fault types from vibration data collected under variable speed conditions without resampling and prefiltering.

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38

Zhang, Xiaojun. "Analysis and pre-processing of signals observed in optical feedback self-mixing interferometry". School of Electrical, Computer and Telecommunications Engineering - Faculty of Informatics, 2008. http://ro.uow.edu.au/theses/102.

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Since the laser technlology has been applied for providing highly precise measurement, laser interferometry based systems have found increasing applications in the distance, displace measurement and related applications. Recently, a simple construction of laser interferometer with the use of so-called optical feedback self-mixing interferometry (OFSMI) effect has become a popular technique in optical measurement field. In comparison with conventional interferometer, OFSMI enables simple, compact size and cheap interferometer devices to be implemented.This thesis studies the spectrum characteristics of OFSMI signals and outlines novel approaches to analysze and process the noisy signal at the time and frequency domain simultaneously. The work is motivated by the observation that, when OFSMI signal is given at weak feedback regime (feedback parameter C _ 1), the signal is strictly bandlimited, consequently an linear band-pass filter can be applied to remove the noise disturbance while preserving the signals waveform unchanged. On the other hand, in case of OFSMI signal is obtained with C > 1, an efficient denoising algorithm based on joint time-frequency representation (TFR) can be applied. It has been found that TFR approach provides an sufficient prospective for study the behavior of OFSMI signals for C > 1.This work contributes to the framework of pre-processing and analyzing of OFMSI signals. This thesis focus on the spectrum characteristics and the noise attenuation at weak and moderate feedback regime. To achieve this, the ability of band-pass FIR filters and TFR methods in OFSMI signal processing have been evaluated and compared. The results of this work lead to an significant improvement to the performance of OFSMI based laser measurement system.

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39

ZHU, XIANGDONG. "WAVELET-BASED SIGNAL ANALYSIS FOR THE ENVIRONMENTAL HEALTH RESEARCH". University of Cincinnati / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1085064472.

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40

Benhmad, François. "La WVaR (Wavelet Value at Risk) : une analyse temps-fréquence de la VaR du CAC40". Thesis, Montpellier 1, 2010. http://www.theses.fr/2010MON10024.

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Malgré la multiplicité des méthodes d'estimation de la VaR, elles souffrent d'une faiblesse fondamentale. En effet, elles ne font aucune distinction entre l'information captée à basse fréquence et celle captée à haute fréquence. Ce qui revient à supposer de façon implicite que l'information contenue dans les données historiques a la même importance quel que soit l'horizon temporel de l'investisseur c'est-à-dire sa fréquence de trading (intra-journalière, journalière, hebdomadaire, mensuelle,..). Mais, accepter une telle hypothèse revient à supposer que les marchés financiers sont homogènes. Ce qui est contraire à la réalité empirique. En effet, les marchés financiers sont caractérisés par une grande hétérogénéité d'acteurs. L'objet de notre thèse est d'apporter une contribution à l'estimation de la VaR basée sur la décomposition de la volatilité dans le domaine des fréquences. Ce qui nous permet de mette en évidence l'influence de l'hétérogénéité des horizons temporels des acteurs des marchés financiers sur l'estimation de la Value at Risk. Pour cela,nous faisons appel à un outil statistique susceptible de nous procurer de l'information temporelle sur la volatilité et de l'information fréquentielle sur la fréquence de trading des différents acteurs des marchés financiers: l'approche temps-fréquence de la transformée en ondelettes
Although multiplicity of VaR estimate approaches,they suffer from a fundamental weakness.They don't make any distiction between informations captured in a high frequency and in a low frequency manner.It is an implicit assumption of homogeneity of fiancial markets in contrast to empirical facts. In our thesis, we try to construct a VaR model based on volatility decomposition in the frequency domain.It enables us to show how the time horizons heterogeneity of financial markets participants could influence value at risk estimates.We use a statistical tool able to give us temporal information about volatility and frequencial information about trading frequencies of market participants:the time frequency approach of wavelet transform

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41

Fendrychová, Michaela. "Detekce elektrického oblouku". Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2016. http://www.nusl.cz/ntk/nusl-241952.

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Diplomová práce je zaměřena na problematiku analýzy signálů za účelem detekce poruchového oblouku, přičemž analýza signálů je prováděna v časové, frekvenční a smíšené časově-frekvenční oblasti. Práce stručně shrnuje existující normy pro zařízení pro detekci poruchového oblouku. Práce dokumentuje testy a měření, které byly realizovány v souladu s normami IEC 62606:2013 a UL 1699B. Z důvodu nedostatečnosti stávajících norem je v práci popsána nová metoda iniciace poruchového oblouku. naměřená data byla analyzována s využitím rychlé Fourierovy transformace, krátkodobé Fourierovy transformace a vlnkové transformace. Na základě provedeného literárního průzkumu a s využitím výsledků provedených analýz signálu je v práci proveden návrh nové detekční metody pro účely detekce poruchového oblouku v systémech napájených střídavým i stejnosměrným napětím.

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42

Vegh, Viktor. "Numerical modelling of industrial microwave heating". Thesis, Queensland University of Technology, 2003. https://eprints.qut.edu.au/37144/7/37144_Digitised%20Thesis.pdf.

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The numerical modelling of electromagnetic waves has been the focus of many research areas in the past. Some specific applications of electromagnetic wave scattering are in the fields of Microwave Heating and Radar Communication Systems. The equations that govern the fundamental behaviour of electromagnetic wave propagation in waveguides and cavities are the Maxwell's equations. In the literature, a number of methods have been employed to solve these equations. Of these methods, the classical Finite-Difference Time-Domain scheme, which uses a staggered time and space discretisation, is the most well known and widely used. However, it is complicated to implement this method on an irregular computational domain using an unstructured mesh. In this work, a coupled method is introduced for the solution of Maxwell's equations. It is proposed that the free-space component of the solution is computed in the time domain, whilst the load is resolved using the frequency dependent electric field Helmholtz equation. This methodology results in a timefrequency domain hybrid scheme. For the Helmholtz equation, boundary conditions are generated from the time dependent free-space solutions. The boundary information is mapped into the frequency domain using the Discrete Fourier Transform. The solution for the electric field components is obtained by solving a sparse-complex system of linear equations. The hybrid method has been tested for both waveguide and cavity configurations. Numerical tests performed on waveguides and cavities for inhomogeneous lossy materials highlight the accuracy and computational efficiency of the newly proposed hybrid computational electromagnetic strategy.

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43

Bensaibi, Mahmoud. "Identification de la fonction de transfert d'une structure ou d'une sous-structure par méthodes fréquentielles et temporelles". Châtenay-Malabry, Ecole centrale de Paris, 1996. http://www.theses.fr/1996ECAP0468.

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Le présent mémoire comporte deux parties. La première partie approfondit la méthode d'identification ARMA appliquée aux structures. Une connaissance approfondie de cette technique est nécessaire si l'on veut être capable de régénérer de manière précise à partir d'une identification, les fonctions de transfert données par un analyseur. Pour cette raison nous avons mené une étude dans le domaine fréquentiel, afin d'avoir des élements de comparaison et une étude dans le domaine temporel, qui a nécessité des développements concernant la méthode ARMA. Un exemple expérimental a éte teste pour valider les techniques proposees dans les deux domaines temporel et frequentiel. En deuxieme partie, on a developpe tant en fréquentiel qu'en temporel une méthode d'identification de sous-structures in situ. Cette identification s'oppose au problème bien connu de synthèse modale. Au contraire de celle-ci, qui a pour but de reconstruire le comportement globale de la structure à partir de ses sous-structures, on cherche à partir du comportement global d'une structure, à identifier les caractéristiques dynamiques d'une sous-structure appartenant à cette structure totale. C'est donc un problème d'identification locale. Cette étude ayant pour objet une analyse expérimentale, le bruit de mesure est pris en considération. Des exemples numériques ont été présentés et ont montrés qu'on obtenait de bon resultats jusqu'à un niveau de bruit de 5% dans le domaine temporel et 2% dans le domaine frequentiel. Enfin, une validation expérimentale a été réalisée dont le but principal est de montrer l'efficacité de l'algorithme sur un cas réel. La régéneration de la fonction de transfert de la sous-structure à partir des paramètres identifiées est abordée également

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44

Smigelski, Jeffrey Ralph. "Water Level Dynamics of the North American Great Lakes:Nonlinear Scaling and Fractional Bode Analysis of a Self-Affine Time Series". Wright State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=wright1379087351.

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45

Kerbal, Sofiane. "Development of new criteria for train detection and evaluation in critical conditions". Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-253201.

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Railway signaling is of paramount importance to ensure traffic management andsafety on the rail network. The main lines are divided into sections called ‘blocks’,which are governed by a fixed signal installation. To prevent trains from colliding,each block allows one train at once. In France (and most European countries),train detection is performed by an electrical device called track circuit that consistsof a transmitter and a receiver installed at the track-side, and connected via therails. In the absence of a train, an electrical signal flows from the transmitter tothe receiver through the rails. As a train enters a track circuit, its axles shuntthe rails, provoking a short circuit (also called ‘shunt’): the signal transmitted tothe receiver drops. The detection of that signal drop results in the detection of atrain. This method rarely fails throughout the network, but there can be criticalcases where it may be inefficient. In this Master’s Thesis, new detection criteriaproposed in previous studies have been tested on signals measured in poor shuntingconditions. Three approaches have been tested: one in the time domain and two inthe frequency domain. The time approach compares the short-term and long-termstatistics of the received signals. The observation of a change in the spectra of thereceived signals around the 3rd order harmonic (3OH) has led to the implementationof two frequency criteria: the estimation of the band power around the 3OH andthe detection of the 3OH peaks. The obtained results show that better detection isachieved when the new criteria and the existing one are combined.
Tågsignalsystem är väsentliga för att garantera trafikstyrning och säkerhet i tågnätet.Spåren är indelade i sektioner, s.k. block, som övervakas med fasta signalinstallationer.För att hindra tåg från att krocka, tillåts bara ett tåg i taget per block. IFrankrike (och de flesta andra europeiska länder), detekteras tågen med en elektriskspårkrets som består av en sändare och en mottagare som är installerad bredvidspåret och ansluten till rälsen. När inget tåg finns på spåret, flyter en elektrisk signalfrån sändaren till mottagaren via spåret. När ett tåg anländer, kortsluts kretsenav hjulaxeln och signalen försvinner från mottagaren. Minskningen i signalstyrkaanvänds för att detektera tåget. Denna metod sällan misslyckas i tågnätet, men iovanliga fall kan det uppstå farliga situationer. I detta examensarbete utvärderasnya detektionsmetoder, som har föreslagits i tidigare studier, på signaler som haruppmätts under förhållanden med dålig kontakt mellan hjul och spår. Tre olika metoderhar testats, en i tidsdomänen och två i frekvensdomänen. Tidsdomänsmetodenjämför kortvarig och långvarig statistik för den mottagna signalen. I spektrum förden mottagna signalen, har man observerat en förändring runt den tredje övertonen,samt detektering av frekvenstoppar vid tredje övertonen. De erhållna resultatenvisar på förbättrad detektering när de nya och existerande kriterierna kombineras.

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Coates, Mark J. "Time frequency modelling". Thesis, University of Cambridge, 1999. https://www.repository.cam.ac.uk/handle/1810/272036.

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47

Přikryl, Petr. "Porovnání úspěšnosti vícekanálových metod separace řečových signálů". Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2008. http://www.nusl.cz/ntk/nusl-217519.

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The separation of independent sources from mixed observed data is a fundamental problem in many practical situations. A typical example is speech recordings made in an acoustic environment in the presence of background noise or other speakers. Problems of signal separation are explored by a group of methods called Blind Source Separation. Blind Source Separation (BSS) consists on estimating a set of N unknown sources from P observations resulting from the mixture of these sources and unknown background. Some existing solutions for instantaneous mixtures are reviewed and in Matlab implemented , i.e Independent Componnent Analysis (ICA) and Time-Frequency Analysis (TF). The acoustic signals recorded in real environment are not instantaneous, but convolutive mixtures. In this case, an ICA algorithm for separation of convolutive mixtures in frequency domain is introduced and in Matlab implemented. This diploma thesis examines the useability and comparisn of proposed separation algorithms.

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Elayouty, Amira Sherif Mohamed. "Time and frequency domain statistical methods for high-frequency time series". Thesis, University of Glasgow, 2017. http://theses.gla.ac.uk/8061/.

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Advances in sensor technology enable environmental monitoring programmes to record and store measurements at high-temporal resolution over long time periods. These large volumes of high-frequency data promote an increasingly comprehensive picture of many environmental processes that would not have been accessible in the past with monthly, fortnightly or even daily sampling. However, benefiting from these increasing amounts of high-frequency data presents various challenges in terms of data processing and statistical modeling using standard methods and software tools. These challenges are attributed to the large volumes of data, the persistent and long memory serial correlation in the data, the signal to noise ratio, and the complex and time-varying dynamics and inter-relationships between the different drivers of the process at different timescales. This thesis aims at using and developing a variety of statistical methods in both the time and frequency domains to effectively explore and analyze high-frequency time series data as well as to reduce their dimensionality, with specific application to a 3 year hydrological time series. Firstly, the thesis investigates the statistical challenges of exploring, modeling and analyzing these large volumes of high-frequency time series. Thereafter, it uses and develops more advanced statistical techniques to: (i) better visualize and identify the different modes of variability and common patterns in such data, and (ii) provide a more adequate dimension reduction representation to the data, which takes into account the persistent serial dependence structure and non-stationarity in the series. Throughout the thesis, a 15-minute resolution time series of excess partial pressure of carbon dioxide (EpCO2) obtained for a small catchment in the River Dee in Scotland has been used as an illustrative data set. Understanding the bio-geochemical and hydrological drivers of EpCO 2 is very important to the assessment of the global carbon budget. Specifically, Chapters 1 and 2 present a range of advanced statistical approaches in both the time and frequency domains, including wavelet analysis and additive models, to visualize and explore temporal variations and relationships between variables for the River Dee data across the different timescales to investigate the statistical challenges posed by such data. In Chapter 3, a functional data analysis approach is employed to identify the common daily patterns of EpCO2 by means of functional principal component analysis and functional cluster analysis. The techniques used in this chapter assume independent functional data. However, in numerous applications, functional observations are serially correlated over time, e.g. where each curve represents a segment of the whole time interval. In this situation, ignoring the temporal dependence may result in an inappropriate dimension reduction of the data and inefficient inference procedures. Subsequently, the dynamic functional principal components, recently developed by Hor mann et al. (2014), are considered in Chapter 4 to account for the temporal correlation using a frequency domain approach. A specific contribution of this thesis is the extension of the methodology of dynamic functional principal components to temporally dependent functional data estimated using any type of basis functions, not only orthogonal basis functions. Based on the scores of the proposed general version of dynamic functional principal components, a novel clustering approach is proposed and used to cluster the daily curves of EpCO2 taking into account the dependence structure in the data. The dynamic functional principal components depend in their construction on the assumption of second-order stationarity, which is not a realistic assumption in most environmental applications. Therefore, in Chapter 5, a second specific contribution of this thesis is the development of a time-varying dynamic functional principal components which allows the components to vary smoothly over time. The performance of these smooth dynamic functional principal components is evaluated empirically using the EpCO2 data and using a simulation study. The simulation study compares the performance of smooth and original dynamic functional principal components under both stationary and non-stationary conditions. The smooth dynamic functional principal components have shown considerable improvement in representing non-stationary dependent functional data in smaller dimensions. Using a bootstrap inference procedure, the smooth dynamic functional principal components have been subsequently employed to investigate whether or not the spectral density and covariance structure of the functional time series under study change over time. To account for the possible changes in the covariance structure, a clustering approach based on the proposed smooth dynamic functional principal components is suggested and the results of application are discussed. Finally, Chapter 6 provides a summary of the work presented within this thesis, discusses the limitations and implications and proposes areas for future research.

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49

Mai, Cuong. "Frequency Estimation Using Time-Frequency Based Methods". ScholarWorks@UNO, 2007. http://scholarworks.uno.edu/td/571.

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Any periodic signal can be decomposed into a sum of oscillating functions. Traditionally, cosine and sine segments have been used to represent a single period of the periodic signal (Fourier Series). In more general cases, each of these functions can be represented by a set of spectral parameters such as its amplitude, frequency, phase, and the variability of its instantaneous spectral components. The accuracy of these parameters depends on several processing variables such as resolution, noise level, and bias of the algorithm used. This thesis presents some background of existing frequency estimation techniques and proposes a new technique for estimating the instantaneous frequency of signals using short sinusoid-like basis functions. Furthermore, it also shows that the proposed algorithm can be implemented in a popular embedded DSPmicroprocessor for practical use. This algorithm can also be implemented using more complex features on more resourceful processing processors in order to improve estimation accuracy

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Anoh, Kelvin Ogbonnaya Okorie. "Advanced MIMO-OFDM technique for future high speed braodband wireless communications : a study of OFDM design, using wavelet transform, fractional fourier transform, fast fourier transform, doppler effect, space-time coding for multiple input, multiple output wireless communications systems". Thesis, University of Bradford, 2015. http://hdl.handle.net/10454/14400.

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This work concentrates on the application of diversity techniques and space time block coding for future high speed mobile wireless communications on multicarrier systems. At first, alternative multicarrier kernels robust for high speed doubly-selective fading channel are sought. They include the comparisons of discrete Fourier transform (DFT), fractional Fourier transform (FrFT) and wavelet transform (WT) multicarrier kernels. Different wavelet types, including the raised-cosine spectrum wavelets are implemented, evaluated and compared. From different wavelet families, orthogonal wavelets are isolated from detailed evaluations and comparisons as suitable for multicarrier applications. The three transforms are compared over a doubly-selective channel with the WT significantly outperforming all for high speed conditions up to 300 km/hr. Then, a new wavelet is constructed from an ideal filter approximation using established wavelet design algorithms to match any signal of interest; in this case under bandlimited criteria. The new wavelet showed better performance than other traditional orthogonal wavelets. To achieve MIMO communication, orthogonal space-time block coding, OSTBC, is evaluated next. First, the OSTBC is extended to assess the performance of the scheme over extended receiver diversity order. Again, with the extended diversity conditions, the OSTBC is implemented for a multicarrier system over a doubly-selective fading channel. The MIMO-OFDM systems (implemented using DFT and WT kernels) are evaluated for different operating frequencies, typical of LTE standard, with Doppler effects. It was found that, during high mobile speed, it is better to transmit OFDM signals using lower operating frequencies. The information theory for the 2-transmit antenna OSTBC does not support higher order implementation of multi-antenna systems, which is required for the future generation wireless communications systems. Instead of the OSTBC, the QO-STBC is usually deployed to support the design of higher order multi-antenna systems other than the 2-transmit antenna scheme. The performances of traditional QO-STBC methods are diminished by some off-diagonal (interference) terms such that the resulting system does not attain full diversity. Some methods for eliminating the interference terms have earlier been discussed. This work follows the construction of cyclic matrices with Hadamard matrix to derive QO-STBC codes construction which are N-times better than interference free QO-STBC, where N is the number of transmit antenna branches.

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Tesi sul tema "Time and frequency transfer"

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