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Borde, Arnaud. "One-Dimensional Power Spectrum and Neutrino Mass in the Spectra of BOSS." Phd thesis, Université Paris Sud - Paris XI, 2014. http://tel.archives-ouvertes.fr/tel-01023004.
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The framework of the studies presented in this thesis is the one-dimensional power spectrum of the transmitted flux in the Lyman-alpha forests. The Lyman-alpha forest is an an absorption pattern seen in the spectra of high redshift quasars corresponding to the absorption of the quasar light by the hydrogen clouds along the line of sight. It is a powerful cosmological tool as it probes relatively small scales, of the order of a few Mpc. It is also sensible to small non-linear effects such as the one induced by massive neutrinos.First, we have developed two independent methods to measure the one-dimensional power spectrum of the transmitted flux in the Lyman-alpha forest. The first method is based on a Fourier transform, and the second on a maximum likelihood estimator. The two methods are independent and have different systematic uncertainties. The determination of the noise level in the data spectra was subject to a novel treatment, because of its significant impact on the derived power spectrum. We applied the two methods to 13,821 quasar spectra from SDSS-III/BOSS DR9 selected from a larger sample of over 60,000 spectra on the basis of their high quality, large signal-to-noise ratio, and good spectral resolution. The power spectra measured using either approach are in good agreement over all twelve redshift bins from =2.2 to =4.4, and scales from 0.001 (km/s)^−1 to 0.02 (km/s)^−1. We carefully determined the methodological and instrumental systematic uncertainties of our measurements.Then, we present a suite of cosmological N-body simulations with cold dark matter, baryons and neutrinos aiming at modeling the low-density regions of the IGM as probed by the Lyman-alpha forests at high redshift. The simulations are designed to match the requirements imposed by the quality of BOSS and eBOSS data. They are made using either 768^3 or 192^3 particles of each type, spanning volumes ranging from (25 Mpc/h)^3 for high-resolution simulations to (100 Mpc/h)^3 for large-volume ones. Using a splicing technique, the resolution is further enhanced to reach the equivalent of simulations with 3072^3 = 29 billion particles of each type in a (100 Mpc/h)^3 box size, i.e. a mean mass per gas particle of 1.2x10^5 solar masses. We show that the resulting power spectrum is accurate at the 2% level over the full range from a few Mpc to several tens of Mpc. We explore the effect on the one-dimensional transmitted-flux power spectrum of 4 cosmological parameters (n_s, sigma_8, Omega_m ,H_0), 2 astrophysical parameters (T_0, gamma) related to the heating rate of the IGM and the sum of the neutrino masses. By varying the input parameters around a central model chosen to be in agreement with the latest Planck results, we built a grid of simulations that allows the study of the impact on the flux power spectrum of these seven relevant parameters. We improve upon previous studies by not only measuring the effect of each parameter individually, but also probing the impact of the simultaneous variation of each pair of parameters. We thus provide a full second-order expansion, including cross-terms, around our central model. We check the validity of the second-order expansion with independent simulations obtained either with different cosmological parameters or different seeds for the initial condition generation. Finally, a comparison to the one-dimensional Lyman-alpha forest power spectrum obtained in the first part with BOSS data shows an excellent agreement.Eventually, even if there are still some potential biases and systematic errors that need to be studied in our simulation, we performed cosmological fits combining our measurement of the one-dimensional power spectrum and other cosmological probes such as the CMB results provided by Planck. These preliminary results are very encouraging as they lead to some of the tighest cosmological constraints as of today, especially on the sum of the neutrino masses with an upper limit of 0.1 eV.
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Stitz, Elizabeth H. "Instantaneous Power Spectrum." Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA229098.
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Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, March 1990.Thesis Advisor(s): Hippenstiel, Ralph D. Second Reader: Cristi, Roberto. "March 1990." Description based on signature page as viewed on August 25, 2009. DTIC Identifier(s): Signal analysis, Time varying spectra, Wigner Ville distribution functions, Rihaczek distribution functions. Author(s) subject terms: Instantaneous Power Spectrum, spectral estimation, nonstationary signal analysis. Includes bibliographical references (p. 108-112). Also available online.
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de, Oliveira Paulo M. D. Monica. "Instantaneous Power Spectrum." Thesis, Monterey, California. Naval Postgraduate School, 1989. http://hdl.handle.net/10945/26003.
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The need for tools capable of handling non-stationarities in the spectral content of the data was recognized as early as 1946. The Wigner-Ville Distribution (WD) has been extensively used since its introduction in 1948, but suffers from some associated problems (e.g., spectral cross-terms and requiring the use of analytic signals). An alternative Distribution is proposed, which has its origin in the definition proposed by Page of 'Instantaneous Power Spectrum' (IPS). Its characteristics are examined and, when pertinent, compared to the WD. It is shown to be less sensitive to the problems afflicting the WD, but provides less frequency resolution. The usefulness of a parametric (AR) version is investigated. Some typical test signals are examined, to demonstrate the performance and trade-offs of IPS and its parametric version
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Chiang, Chi-Ting. "Position-dependent power spectrum." Diss., Ludwig-Maximilians-Universität München, 2015. http://nbn-resolving.de/urn:nbn:de:bvb:19-183996.
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Perkins, Larry D. "Development and characterization of a low power helium microwave induced plasma for spectrometric determinations of metals and nonmetals." Diss., Virginia Polytechnic Institute and State University, 1989. http://hdl.handle.net/10919/54261.
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This dissertation centers on the development of a new helium microwave induced plasma. The analytical utility of this new plasma source is critically evaluated.
To sustain the helium plasma a TM ₀₁₀ high efficiency microwave induced plasma, HEMIP, was used. The HEMIP is a modification of the original Beenakker cavity that precludes the use of external matching devices, such as the highly popular double tuning stub.
The He-HEMIP was analytically characterized as an atomization source for metals and nonmetals with the use of atomic emission spectrometry (AES) and atomic fluorescence spectrometry (AFS). A torodial plasma was sustained in the cavity solely by the helium gas output of the nebulizer. Aqueous samples from a pneumatic glass nebulizer/Scott spray chamber were aspirated into the cavity without a desolvation apparatus. With AES, detection limits for metals and nonmetals were in the sub-ppm range. with AFS, detection limits for metals were determined to be in the low ppm to sub-ppb range and were found to be not statistically different from those reported for HCL-ICP-AFS. Linear ranges for AES and AFS ranged from four up to five and one-half orders of concentrative magnitude. The effect of sample uptake rate on the emission intensity was investigated. Ionization interferences were determined to be minimal and phosphate interferences were found not to occur.
Development and characterization also included studies of the He-HEMIP's physical characteristics. Excitation and ionization temperatures were found to be approximately equal, suggesting that the He—HEMIP approaches local thermodynamic equilibrium.
Evaluation of the He—HEMIP as a routine detector for sulfur during coal pyrolysis and coal extracted samples was investigated. Results showed that the He-HEMIP is selective and sensitive. Detection values compared favorably to those of certified coal samples.Ph. D.
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Hagerman, Karen Allyn. "Instantaneous power spectrum in 1 1 /." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from the National Technical Information Service, 1992. http://edocs.nps.edu/npspubs/scholarly/theses/1992/Jun/92Jun_Hagerman.pdf.
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Tadros-Attalla, Helen. "Power spectrum analysis of redshift surveys." Thesis, University of Oxford, 1996. https://ora.ox.ac.uk/objects/uuid:5a5786db-748e-4c78-bab8-c89a4eda2f07.
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This thesis describes a study of the clustering properties of galaxies and clusters of galaxies as measured by the power spectrum (P(k)) and the counts in cells statistic. The samples used are the optical Stromlo-APM galaxy survey, the APM cluster survey and the IRAS 1.2Jy, QDOT and PSCz surveys. Throughout, N-body simulations, for a variety of cosmological models, are used to test methods and to supplement analytic error estimates. For the Stromlo-APM sample the amplitude of the power spectrum is dependent on galaxy morphology. Early-type galaxies show a higher clustering amplitude than late-type galaxies by a factor of ~ 1.8. There is also tentative evidence for some dependence of the clustering amplitude on galaxy luminosity. The parameter Ω0.6/b is estimated via a comparison with the real-space power spectrum of the two-dimensional APM galaxy survey. For APM clusters the power spectrum is measured to very small wave numbers, with a possible detection of the expected turn-over. The results are inconsistent with the standard cold dark matter model. The shape of P( k) for clusters is approximately the same as that for Stromlo-APM galaxies but amplified by a factor of ~ 3.5. The power spectrum of the QDOT sample depends sensitively on the galaxy weighting scheme, probably due the manner in which the region of the Hercules supercluster is sampled. A best estimate of the power spectrum of IRAS galaxies is computed by combining the IRAS l.2Jy and QDOT samples. The PSCz galaxy power spectrum is also computed. The PSCz galaxies have a clustering amplitude twice that of optical galaxies. A similar result is found from a joint counts in cells analysis. Redshift-space distortions in the PSCz sample are analysed using a spherical harmonic decomposition of the density field. The value of Ω0.6/b = 1 is ruled out by this analysis at the 2σ significance level.
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Griffiths, Louise M. "The cosmic microwave background power spectrum." Thesis, University of Oxford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249266.
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Duniya, Didam Gwazah Adams. "Relativistic corrections to the power spectrum." University of the Western Cape, 2015. http://hdl.handle.net/11394/4787.
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Philosophiae Doctor - PhDThe matter power spectrum is key to understanding the growth of large-scale structure in the Universe. Upcoming surveys of galaxies in the optical and HI will probe increasingly large scales, approaching and even exceeding the Hubble scale at the survey redshifts. On these cosmological scales, surveys can in principle provide the best constraints on dark energy (DE) and modified gravity models and will be able to test general relativity itself. However, in order to realise the potential of these surveys, we need to ensure that we are using a correct analysis, i.e. a general relativistic analysis, on cosmological scales. There are two fundamental issues underlying the general relativistic (GR) analysis. Firstly, we need to correctly identify the galaxy overdensity that is observed on the past light cone. Secondly, we need to account for all the distortions arising from observing on the past light cone, including redshift distortions (with all general relativistic effects included) and volume distortions. These general elativistic effects appear in the angular power spectra of matter in redshift space. We compute these quantities, taking into account all general relativistic large-scale effects, and including the important contributions from redshift space distortions and lensing convergence. This is done for self-consistent models of DE, known as ‘quintessence’, which have only been very recently treated in the GR approach. Particularly, we focus mainly on computing the predictions (i.e. the power spectra) that need to be confronted with future data. Hence we compute the GR angular power spectra, correcting the 3D Newtonian calculation for several quintessence models. We also compute the observed 3D power spectra for interacting DE (which until now have not previously been studied in the GR approach) – in which dark matter and DE exchange energy and momentum. Interaction in the dark sector can lead to large-scale deviations in the power spectrum, similar to GR effects or modified gravity. For the quintessence case, we found that the DE perturbations make only a small contribution on the largest scales, and a negligible contribution on smaller scales. Ironically, the DE perturbations remove the false boost of large-scale power that arises if we impose the (unphysical) assumption that the DE perturbations vanish. However, for the interacting DE (IDE) case, we found that if relativistic effects are ignored, i.e. if they are not subtracted in order to isolate the IDE effects, the imprint of IDE will be incorrectly identified – which could lead to a bias in constraints on IDE, on horizon scales. Moreover, we found that on super-Hubble scales, GR corrections in the observed galaxy power spectrum are able to distinguish a homogeneous DE (being one whose density perturbation in comoving gauge vanishes) from the concordance model (and from a clustering DE) – at low redshifts and for high magnification bias. Whereas the matter power spectrum is incapable of distinguishing a homogeneous DE from the concordance model. We also found that GR effects become enhanced with decreasing magnification bias, and with increasing redshift.
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Hoi, Loison. "Cosmological inflation and the primordial power spectrum." Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:8881/R/?func=dbin-jump-full&object_id=92301.
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Hanson, D. "The microwave background beyond the power spectrum." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.603669.
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The minute fluctuations of the Cosmic Microwave Background (CMB) are a cornerstone of modern cosmology. They characterize the small perturbations in the distribution of matter and energy in the early Universe, and have been used with great success to hammer out the details of the current concordance model. We study in detail the analysis of the CMB fluctuations beyond the power spectra, treating statistical anisotropy and non-Gaussianity in a unified framework which is based on quadratic building blocks. We first demonstrate this formalism in application to the data of the WMAP satellite, constraining modulations of the observed and primordial fluctuations with quadratic maximum-likelihood estimators. The power of this approach lies in its speed and ability to test for systematic effects, which we use to resolve a previously unexplained nine sigma anomaly in the WMAP data as a result of contamination from the asymmetric instrumental beams. We then proceed to make a detailed study of the non-Gaussian effects due to gravitational lensing of the CMB by large-scale structure. In particular, we perform a detailed study of non-Gaussian estimators for the lensing potential power spectrum with simulated Planck data, discovering and correcting a number of small biases due to the high signal-to-noise with which lensing will be measured.
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Nicolson, Gavin. "Reconsturcting the modelling the primordial power spectrum." Thesis, Imperial College London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.508718.
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Hotchkiss, Shaun. "Inflation beyond the scalar fluctation power spectrum." Thesis, University of Oxford, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.526514.
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Mohapi, Setumo J. (Setumo James). "Power control for spread spectrum communications systems." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/39756.
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Macaulay, Edward Robert Mark. "Cosmology with power spectrum measurements from galaxy surveys." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:bb918260-6747-4133-bdcb-b393d080c6fa.
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The nature of dark matter and dark energy are currently two of the most important questions in cosmology. In this thesis, we consider studying the dark universe with the redshifts and peculiar velocities of galaxies. In the first half of the thesis, we analyse current peculiar velocity measurements of the bulk flow of our local volume to estimate the underlying dark matter power spectrum. In the second half of the thesis, we consider the prospects for measuring dark matter and dark energy with future galaxy redshift surveys, particularly via redshift space distortions. Fundamentally, bulk flow measurements and redshift space distortions are both sensitive probes of the power spectrum and growth rate of cosmic structure. In the final chapter, we directly compare power spectrum measurements with both methods.
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Loureiro, Arthur Eduardo da Mota. "Galaxy Power Spectrum Analysis: A Monte-Carlo Approach." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-06072015-060434/.
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Many galaxy surveys are planned to release their data over the next few years. Each different survey has its own geometrical limitations, which reflects upon the data as a selection function the spatial distribution of certain types of galaxies. Given a galaxy map (real or mock), the main goal of this work is to obtain information about how the selection function affects some of the cosmological parameters which can be probed from large-scale structure. A Monte-Carlo Markov Chain method is proposed in order to probe the effects of considering the selection functions parameters as nuisance parameters. The method consists in combining realizations of simulated galaxy catalogs using theoretical matter power spectra, combined with an optimal power spectrum estimator method. Theory and data are then compared in a multivariate Gaussian representing the likelihood function. This Monte-Carlo method has proven robust and capable of probing selection function effects on the cosmological parameters, showing that the simple marginalization over the nuisance parameters might lead to wrong estimates on the cosmology. The method is applied to obtain forecasts for these effects on the upcoming J-PAS Luminous Red Galaxies data and is employed to obtain constraints on the Hubble parameter (H0), the dark matter density (c) and two parameters of the equation of state of dark energy (w0 and wa).Nos próximos anos, diversos levantamentos de galáxias planejam lançar uma quantidade considerável de novos dados, marcando, assim, o início da chamda era da cosmologia de precisão. Cada levantamento possui suas próprias limitações geométricas, que manifestam- se perante os dados na forma de uma função de seleção, ou seja, uma distribuição espacial de cada tipo de galáxia. A partir de um mapa de galáxias (real ou simulado), o principal objetivo desse trabalho foi descobrir como a função de seleção afeta alguns dos parâmetros cosmológicos que podem ser obtidos através de dados futuros de estrutura em larga escala. Portanto, propôs-se um método de Monte-Carlo com cadeias de Markov para estudar os efeitos decorrentes da inclusão dos parâmetros da função de seleção como nuisance parameters. Esse método consiste em combinar simulações de catálogos de galáxias, usando um espectro de potências teórico da matéria junto com um estimador ótimo, a fim de obter ambos espectros (teórico e observacional) e compará-los em uma verossimilhança Gaussiana-multivariada. O método de Monte-Carlo provou-se robusto e capaz de demonstrar os efeitos da função de seleção sobre as estimativas dos parâmetros cosmológicos, comprovando que o simples ato de marginalizar sobre os parâmetros não desejados pode levar a estimativas equivocadas na cosmologia em quesão. Finalmente, esse método foi aplicado nas estimações do parâmetro de Hubble (H0), na densidade de matéria escura (c) e em dois dos parâmetros da equação de estado da energia escura (w0 e wa) com o objetivo de prever tais efeitos para dados futuros do levantamento J-PAS com Galáxias Vermelhas Luminosas.
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Lin, Yousi. "Spectrum Management Issues in Centralized and Distributed Dynamic Spectrum Access." Diss., Virginia Tech, 2021. http://hdl.handle.net/10919/104362.
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Dynamic spectrum access (DSA) is a powerful approach to mitigate the spectrum scarcity problem caused by rapid increase in wireless communication demands. Based on architecture design, DSA systems can be categorized as centralized and distributed. To successfully enable DSA, both centralized and distributed systems have to deal with spectrum management issues including spectrum sensing, spectrum decision, spectrum sharing and spectrum mobility. Our work starts by investigating the challenges of efficient spectrum monitoring in centralized spectrum sensing. Since central controllers usually require the presence information of incumbent users/primary users (IUs) for decision making, which is obtained during spectrum sensing, privacy issues of IUs become big concerns in some DSA systems where IUs have strong operation security needs. To aid in this, we design novel location privacy protection schemes for IUs. Considering the general drawbacks of centralized systems including high computational overhead for central controllers, single point failure and IU privacy issues, in many scenarios, a distributed DSA system is required. In this dissertation, we also cope with the spectrum sharing issues in distributed spectrum management, specifically the secondary user (SU) power control problem, by developing distributed and secure transmit power control algorithms for SUs.
In centralized spectrum management, the common approach for spectrum monitoring is to build infrastructures (e.g. spectrum observatories), which cost much money and manpower yet have relatively low coverage. To aid in this, we propose a crowdsourcing based spectrum monitoring system to capture the accurate spectrum utilization at a large geographical area, which leverages the power of masses of portable mobile devices. The central controller can accurately predict future spectrum utilization and intelligently schedule the spectrum monitoring tasks among mobile SUs accordingly, so that the energy of mobile devices can be saved and more spectrum activities can be monitored. We also demonstrate our system's ability to capture not only the existing spectrum access patterns but also the unknown patterns where no historical spectrum information exists. The experiment shows that our spectrum monitoring system can obtain a high spectrum monitoring coverage with low energy consumption.
Environmental Sensing Capability (ESC) systems are utilized in DSA in 3.5 GHz to sense the IU activities for protecting them from SUs' interference. However, IU location information is often highly sensitive in this band and hence it is preferable to hide its true location under the detection of ESCs. As a remedy, we design novel schemes to preserve both static and moving IU's location information by adjusting IU's radiation pattern and transmit power. We first formulate IU privacy protection problems for static IU. Due to the intractable nature of this problem, we propose a heuristic approach based on sampling. We also formulate the privacy protection problem for moving IUs, in which two cases are analyzed: (1) protect IU's moving traces; (2) protect its real-time current location information. Our analysis provides insightful advice for IU to preserve its location privacy against ESCs. Simulation results show that our approach provides great protection for IU's location privacy.
Centralized DSA spectrum management systems has to bear several fundamental issues, such as the heavy computational overhead for central controllers, single point failure and privacy concerns of IU caused by large amounts of information exchange between users and controllers and often untrusted operators of the central controllers. In this dissertation, we propose an alternative distributed and privacy-preserving spectrum sharing design for DSA, which relies on distributed SU power control and security mechanisms to overcome the limitations of centralized DSA spectrum management.Doctor of Philosophy
Due to the rapid growth in wireless communication demands, the frequency spectrum is becoming increasingly crowded. Traditional spectrum allocation policy gives the unshared access of fixed bands to the licensed users, and there is little unlicensed spectrum left now to allocate to newly emerged communication demands. However, studies on spectrum occupancy show that many licensed users who own the license of certain bands are only active for a small percentage of time, which results in plenty of underutilized spectrum. Hence, a new spectrum sharing paradigm, called dynamic spectrum access (DSA), is proposed to mitigate this problem. DSA enables the spectrum sharing between different classes of users, generally, the unlicensed users in the DSA system can access the licensed spectrum opportunistically without interfering with the licensed users. Based on architecture design, DSA systems can be categorized as centralized and distributed. In centralized systems, a central controller will make decisions on spectrum usage for all unlicensed users. Whereas in distributed systems, unlicensed users can make decisions for themselves independently. To successfully enable DSA, both centralized and distributed DSA systems need to deal with spectrum management issues, such as resource allocation problems and user privacy issues, etc. The resource allocation problems include, for example, the problems to discover and allocate idle bands and the problems to control users' transmit power for successful coexistence. Privacy issues may also arise during the spectrum management process since certain information exchange is inevitable for global decision making. However, due to the Federal Communications Commission's (FCC) regulation, licensed users' privacy such as their location information must be protected in any case. As a result, dynamic and efficient spectrum management techniques are necessary for DSA users. In this dissertation, we investigate the above-mentioned spectrum management issues in both types of DSA systems, specifically, the spectrum sensing challenges with licensed user location privacy issues in centralized DSA, and the spectrum sharing problems in distributed DSA systems. In doing so, we propose novel schemes for solving each related spectrum management problem and demonstrate their efficacy through the results from extensive evaluations and simulations. We believe that this dissertation provides insightful advice for DSA users to solve different spectrum management issues for enabling DSA implementation, and hence helps in a wider adoption of dynamic spectrum sharing.
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Law, Eugene. "How to Estimate the Unmodulated Carrier Power Level of a Modulated Telemetry Signal." International Foundation for Telemetering, 2006. http://hdl.handle.net/10150/604416.
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ITC/USA 2006 Conference Proceedings / The Forty-Second Annual International Telemetering Conference and Technical Exhibition / October 23-26, 2006 / Town and Country Resort & Convention Center, San Diego, CaliforniaThis paper will present methods to both measure the unmodulated carrier power of a modulated signal and to estimate the unmodulated carrier power level from the measured power spectrum. The unmodulated carrier power level is needed to convert measured spectra into units of dBc.
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Vázquez, Oliver Miguel Ángel. "Beamforming design and power control for spectrum sharing systems." Doctoral thesis, Universitat Politècnica de Catalunya, 2014. http://hdl.handle.net/10803/144654.
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In order to provide wireless services for the current demand of high data rate mobile applications, more spectrally efficient systems are needed. As a matter of fact, the current wireless systems are limited by a frequency splitting spectrum management which in one hand minimizes the multiuser interference but; on the other hand, it precludes the use of wider bandwidth signals. As a more aggressive frequency reuse is targeted (ideally, all transmitters might eventually share the same frequency band), the use of multiple antennas for interference reliving, jointly with a smart power allocation is compulsory. In addition, novel spectrum management regulatory policies are required for ensuring a peaceful coexistence between adjacent spectrum sharing networks and for promoting their development.
The aim of this dissertation is provide a beamforming and power allocation design for these novel spectrum sharing systems which are meant to exponentially increase the spectral efficiency of the systems. A mathematical framework based on multicriteria optimization for analyzing the beamforming design is provided which serves as a fundamental tool for describing the state-of-the-art studies in multiantenna interference networks. Indeed, the achievable rates are described and several ways of computing the Pareto rate region of MISO interference channel (i.e. the communication model that represents the spectrum sharing network when the transmitters use multiple antennas) are studied. Nevertheless, as the system designer aims to work in a single efficient rate point, the sum-rate optimal beamforming design is studied. Curiously, it results that under some realistic assumptions on both the desired and interference power levels, the obtained beamformer is the reciprocal version of a known receiving one and it optimizes a notion of antenna directivity for multiuser communications.
Neverthelss, it is important to remark that the higher transmit power is used, the more interference dominated is the medium, not only within the wireless network, but also to eventually adjacent networks that might suffer from inter-network interference. In order to cope with this problem, a spectrum licensing system is revisited, namely time-area-spectrum license. Under this spectrum management mechanism, a license holder is able to radiate signals under a certain portion of time, within a concrete area and in a given band. Moreover, the amount of signal strength within the area is constraint by a certain value. Since controlling the signal power levels in a given area is cumbersome, we propose to restrict the receive power as an estimation of the overall accumulated signal strength. Therefore, the optimal transmit beamformers and power allocations are studied. Concretely, the achievable rates are derived and an operational working point is envisaged. In addition, a suboptimal yet low computationally complex and decentralized beamforming design is presented and it shows a good performance in front of other decentralized designs.
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Last, Michael. "Finding abrupt changes in the time-varying power spectrum /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2005. http://uclibs.org/PID/11984.
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Mulye, Apoorva. "Power Spectrum Density Estimation Methods for Michelson Interferometer Wavemeters." Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/35500.
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In Michelson interferometry, many algorithms are used to detect the number of active laser sources at any given time. Conventional FFT-based non-parametric methods are widely used for this purpose. However, non-parametric methods are not the only possible option to distinguish the peaks in a spectrum, as these methods are not the most suitable methods for short data records and for closely spaced wavelengths. This thesis aims to provide solutions to these problems. It puts forward the use of parametric methods such as autoregressive methods and harmonic methods, and proposes two new algorithms to detect the closely spaced peaks for different scenarios of optical signals in wavemeters. Various parametric algorithms are studied, and their performances are compared with non-parametric algorithms for different criteria, e.g. absolute levels, frequency resolution, and accuracy of peak positions. Simulations are performed on synthetic signals produced from specifications provided by our sponsor, i.e., a wavemeter manufacturing company.
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Chen, Jia Yuan. "Spectrum and power optimisation in wireless multiple access networks." Thesis, University College London (University of London), 2008. http://discovery.ucl.ac.uk/1445389/.
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Emerging high-density wireless networks in urban area and enterprises offer great potential to accommodate the anticipated explosion of demand for wireless data services. To make it successful, it is critical to ensure the efficient utilisation of limited radio resources while satisfying predefined quality of service. The objective of this dissertation is to investigate the spectrum and power optimisation problem for densely deployed access points (APs) and demonstrate the potential to improve network performance in terms of throughput and interference. Searching the optimal channel assignment with minimum interference is known as an NP-hard problem. The increased density of APs in contrary to the limited usable frequencies has aggravated the difficulty of the problem. We adopt heuristic based algorithms to tackle both centralised and distributed dynamic channel allocation (DCA) problem. Based on a comparison between Genetic Algorithm and Simulated Annealing, a hybrid form that combines the two algorithms achieves good trade-off between fast convergence speed and near optimality in centralised scenario. For distributed DCA, a Simulated Annealing based algorithm demonstrates its superiority in terms of good scalability and close approximation to the exact optimal solution with low algorithm complexity. The high complexity of interactions between transmit power control (TPC) and DCA renders analytical solutions to the joint optimisation problems intractable. A detailed convergence analysis revealed that optimal channel assignment can strengthen the stability condition of TPC. Three distributed algorithms are proposed to interactively perform the DCA and TPC in a real time and open ended manner, with the ability to appropriately adjust power and channel configurations according to the network dynamics. A real network with practical measurements is employed to quantify and verify the theoretical throughput gain of their integration. It shows that the integrated design leads to a substantial throughput improvement and power saving compared with conventional fixed-power random channel allocation system.
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Maciel, de Paiva Junior Nilson. "Low-power and radiation resilient approaches for spectrum sensing." Electronic Thesis or Diss., Institut polytechnique de Paris, 2020. http://www.theses.fr/2020IPPAT040.
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Les progrès de la technologie ont permis une forte augmentation du nombre d'utilisateurs et de la quantité d'informations à transmettre. Ces dernières années, la demande de taux de téléchargement élevés, de connexions massives, de faibles latences et d'efficacité énergétique a augmenté, principalement en raison de la vulgarisation des appareils IoT et de l'introduction de l'industrie 4.0. Cela a conduit à une augmentation significative de la demande du spectre pour accueillir de nouveaux services ou pour améliorer les services existants. Une des alternatives pour traiter ce problème est l'utilisation de radios cognitives (CR). Elles sont capables de détecter le spectre et de voir quelles bandes ne sont pas actuellement utilisées. Parmi les divers défis liés à la CR, la détection du spectre est l'une des fonctions les plus importantes de ces radios. La détection de spectre à large bande présente plusieurs défis, notamment les antennes et le traitement d'un grand nombre de données. Cependant, en plusieurs instants, le spectre peut être considéré comme parcimonieux ce qui permet l'utilisation de l'acquisition comprimée (CS) afin de réduire la quantité d'échantillons nécessaires et ainsi réduire les ressources de traitement. En termes de matériel, l'utilisation de CS peut être traduite en convertisseurs analogique-information (AIC) au lieu d'implémenter des convertisseurs analogique-numérique (ADC) avec des taux d'échantillonnage élevés. De plus, il est intéressant de mettre en œuvre des dispositifs basse consommation. La réduction d'échelle des transistors en nanomètres permet de réduire la consommation et la surface. Cependant, d'autres alternatives ont été étudiées pour diminuer la puissance de fuite. Parmi ces alternatives, Magnetic Tunnel Junction (MTJ) a été très prometteur. De plus, les transistors de réduction d'échelle rendent les circuits plus sensibles au Single Event Transient (SET). Bien que le MTJ soit plus robuste que les transistors au rayonnement, il est nécessaire d'étudier quel est l'impact et comment le réduire. Dans ce contexte, cette thèse se concentre sur l'analyse des effets SET et les applications MTJ qui peuvent être utilisées dans un AIC pour effectuer la détection de spectre large bande. Les principales contributions de cette thèse sont l'analyse des effets SET dans un comparateur qui est l'un des principaux composants d'un ADC; l'analyse des effets SET dans les structures MTJ, et la proposition d'un ADC basé sur MTJ qui peut être utilisé dans un AIC pour effectuer la détection de spectre large bandeThe advancement of technology has enabled a great increase in the number of users and the amount of information to be transmitted. In recent years, the demand for high download rates, massive connection, low latencies, and energy efficiency has increased, mainly due the popularization of IoT devices and the introduction of industry 4.0. This has led to a significant increase in demand for the frequency spectrum to accommodate new services or to improve existing ones. One of the alternatives to deal with this problem is the use of cognitive radios (CRs). They are able to sense the spectrum and see which bands are not currently being used. Among the various challenges related to CR, spectrum sensing is one of the most important and one of the primary functions of these radios. Wideband spectrum sensing presents several challenges, including antennas and processing a lot of data. However, in several moments the spectrum can be considered sparse allowing the use of compressive sensing (CS) in order to reduce the amount of samples required and thereby reducing processing resources. In terms of hardware, the use of CS can be translated in analog-to-information converters (AICs) instead of implementing analog-to-digital converters (ADCs) with high sampling rates. Furthermore, it is interesting to implement low-power devices. Downscaling transistors to nanometers helps to reduce consumption and area. However, other alternatives have been studied to decrease the leakage power. Among these alternatives, Magnetic Tunnel Junction (MTJ) has been very promising. In addition, the downscaling transistors makes circuits more sensitive to Single Event Transient (SET), and although MTJ is more robust than transistors to radiation, it is necessary to study how this impact is and how to reduce it. In this context, this thesis focuses on the SET effects analysis and MTJ applications which can be used in an AIC to perform the wideband spectrum sensing. The main contributions of this thesis are the analysis of SET effects in a comparator which is one of the main components of an ADC, analysis of SET effects in MTJ structures, and the proposition of an MTJ-based ADC which can be used in an AIC to perform the wideband spectrum sensing
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Ma, Zheng. "Impeller Power Draw Across the Full Reynolds Number Spectrum." University of Dayton / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1406766474.
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Pearce, David Andrew James. "Improving spectrum efficiency in fixed cellular communication systems." Thesis, University of York, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341520.
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Taruya, Atsushi, Kazuya Koyama, and Takahiko Matsubara. "Signature of primordial non-Gaussianity on the matter power spectrum." American Physical Society, 2008. http://hdl.handle.net/2237/11326.
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Lazanu, Andrei. "The power spectrum and bispectrum of inflation and cosmic defects." Thesis, University of Cambridge, 2016. https://www.repository.cam.ac.uk/handle/1810/256999.
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Much of the recent progress in cosmology has come from studying the power spectrum of the cosmic microwave background (CMB). The latest results from the Planck satellite confirmed that the inflationary paradigm with the $\Lambda$CDM six-parameter model provides a very good description of the observed structures in the Universe. Even so, additional parameters, such as cosmic defects, are still allowed by current observational data. Additionally, many of the inflationary models predict a significant departure from Gaussianity in the distribution of primordial perturbations. Higher order statistics, such as the bispectrum, are required to test and constrain such models. The late-time distribution of matter in the Universe - large-scale structure (LSS) - contains much more information than the CMB that has not yet been used. In this thesis, we look at both problems: the effects of cosmic defects, in particular cosmic strings and domain walls on the CMB power spectrum through numerical simulations, and the dark matter bispectrum of large-scale structure. Topological defects are predicted by most inflationary theories involving symmetry breaking in the early Universe. In this thesis we study the effects of cosmic strings and domain walls on the CMB by determining their power spectrum. We use Nambu-Goto and field theory simulations for cosmic strings and domain walls respectively, and we determine the power spectra they produce with a modified Einstein-Boltzmann solver sourced by unequal time correlators from components of the energy-momentum tensor of the defects. We use these spectra together with CMB likelihoods to obtain constraints on the energy scales of formation of the cosmic defects, finding $G\mu/c^{2} < 1.29 \times 10^{−7}$ and $\eta < 0.93$ MeV (at 95% confidence level) for cosmic strings and domain walls respectively, when using the Planck satellite likelihoods. For the matter bispectrum of LSS, we compare different perturbative and phenomenological models with measurements from $N$-body simulations by using shape and amplitude correlators and we determine on which scales and for which redshifts they are accurate. We propose a phenomenological ‘three-shape’ model, based on the fundamental shapes we have observed by studying the halo model that are also present in the simulations. When calibrated on the simulations, this model accurately describes the bispectrum on all scales and redshifts considered, providing a prototype bispectrum HALOFIT-like methodology that could be used to describe and test parameter dependencies.
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Qu, Qi. "Power and spectrum efficient communications in wireless ad hoc networks." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2008. http://wwwlib.umi.com/cr/ucsd/fullcit?p3304197.
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Thesis (Ph. D.)--University of California, San Diego, 2008.Title from first page of PDF file (viewed June 16, 2008). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 105-114).
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Schlaich, Andreas [Verfasser]. "Time-dependent spectrum analysis of high power gyrotrons / Andreas Schlaich." Karlsruhe : KIT Scientific Publishing, 2015. http://www.ksp.kit.edu.
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Brannon, Raymond James. "The radio spectrum requirements of broadband power line telecommunications systems." Thesis, Open University, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.430560.
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Mirtavoosi, Mahyari Mohammad. "Power and rate optimization in shared-spectrum wireless communication networks." Thesis, King's College London (University of London), 2013. https://kclpure.kcl.ac.uk/portal/en/theses/power-and-rate-optimization-in-sharedspectrum-wireless-communication-networks(6945f10d-6434-4577-b557-4e3593a32b53).html.
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The growth of wireless applications and the emerging technologies require more efficient management of frequency spectrum. Adaptive resource allocation (i.e. transmission power and transmission rate) and opportunistic spectrum sharing are two key techniques with enormous potential to enhance the efficient utilization of the precious bandwidth and optimizing the performance. Adaptive algorithms are a vital feature of radio resource management (RRM) in third generation (3G) communication systems, and cognitive radio (CR) is a valuable technique with tremendous potential for improving the utilization of the radio spectrum. On the other hand, transition from the current 3G cellular communications systems to the fourth generation (4G) would happen gradually and take several years. During this period, both 3G and 4G technologies are expected to co-exist, and the aforementioned CR technology and adaptation techniques are suitable candidates to be used by service providers for achieving higher data rates in the future heterogeneous networks. In this thesis, novel adaptive transmission algorithms will be developed for shared-spectrum CR networks in the context of direct-sequence code division multiple access (DS-CDMA). This thesis makes several contributions. First, adaptive transmission is integrated into spectrum sharing problem. The joint optimization of power and rate is investigated, where optimality is in the sense of maximizing the average spectral efficiency of the reference cognitive user (CU). A close-form solution for the optimal outer loop power control target signal-to-noise ratio (SNR-target) of the reference CU is derived. The optimization is conducted when the reference CU is using interference-limited opportunistic spectrum access (IL-OSA) technique for utilizing the primary spectrum simultaneously with the primary users. The proposed optimization algorithm's performance is analyzed for a case, wherein the reference CU exploits the licensed spectrum subject to non-violation of the average and the peak received-interference constraints. Moreover, the evaluation is extended for more reliable scenario with better performance, wherein the imposed peak-interference constraint is dynamically set as a function of the number of active primary and cognitive users that exploit the licensed frequency band. Second, a shared-spectrum CR system is considered and the reference CU's total average spectral efficiency is derived when it uses access-bounded opportunistic spectrum access (AB-OSA) for exploiting the primary spectrum. The gain that can be attained by using a CR technology is highlighted and the reference CU performance investigated subject to average transmit power constraints. Finally, a novel access technique is proposed to overcome the AB-OSA limitation in CDMA/CDMA, CR networks. This method is referred to as access-bounded-interference-limited opportunistic spectrum access (AB-IL-OSA). This novel access strategy incorporates a mixed access-and interference- limited spectrum access strategy through spectrum sensing, to maximize the achievable spectral efficiency of the CUs. Various OSA strategies were proposed for CDMA-based CR networks to achieve a balance between the full exploitation of the primary spectrum and the inflicted interference on the primary service.
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Yang, Xianzhen. "Power Spectrum Prediction of Amplified Dual-Band LTE-Advanced Signals." PDXScholar, 2018. https://pdxscholar.library.pdx.edu/open_access_etds/4351.
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In wireless communication, the nonlinearity of a radio frequency (RF) power amplifier is an important issue for power amplifier designers. Since the nonlinearity is generated by the properties of physical components, it is hard to avoid it in producing power amplifiers. Power amplifier designers should know about the nonlinearity in order to compensate for it.
A two-tone test is a relatively widely used method to measure the nonlinearity of a power amplifier, which means the third order intercept point (IP3) can be measured from the two-tone test. Through the two-tone test, researchers have proposed some formulae to present what the amplified Code Division Multiple Access (CDMA) signal is like. They derived formulae in terms of output power, bandwidth, IP3, and IP5 to express the amplified CDMA signal and further to Orthogonal Frequency Division Multiplexing (OFDM) signals. With the development of wireless communication, researchers put their interest increasingly in Multiple Input Multiple Output (MIMO) systems. A formula expressing amplified dual two-tone signals has been proposed. In their research, they discussed what the expressions of intermodulation and cross modulation are and what their locations are.
In this research, dual band LTE-Advanced signals, whose modulation is OFDM are utilized, which means this research proposes a formula expression about the power spectrum of dual-band LTE-Advanced signals. Intermodulation and cross modulation caused by nonlinearity of power amplifiers are then specially discussed. This study will help RF designers to continuously compensate for them.
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Nayfeh, Mahir Ali. "Nonlinear dynamics in power systems." Thesis, Virginia Tech, 1990. http://hdl.handle.net/10919/41582.
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We use a perturbation analysis to predict some of the instabilities in a single-machine quasi-infinite busbar system. The system’s behavior is described by the so-called swing equation, which is a nonlinear second-order ordinary-differential equation with additive and multiplicative harmonic terms having the frequency Ω. When Ω≈ω₀, and Ω≈2ω₀, where ω₀ is the linear natural frequency of the machine, we use digital-computer simulations to exhibit some of the complicated responses of the machine, including period-doubling bifurcations, chaotic motions, and unbounded motions (loss of synchronism). To predict the onset of these complicated behaviors, we use the method of multiple scales to develop approximate closed-form expressions for the periodic responses of the machine. Then, we use various techniques to determine the stability of the analytical solutions. The analytically predicted periodic solutions and conditions for their instability are in good agreement with the digital-computer results.Master of Science
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Comley, Vivian Edward. "Aspects of synchronization in direct sequence spread spectrum systems." Thesis, University of Bath, 1985. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355305.
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A serial search process achieved by reference code clock frequency offset suffers from a degraded autocorrelation function between the two codes because of the differing chip rates. In this thesis a computer simulation is used to investigate the code decorrelation, and the results are employed to obtain the mean acquisition time for the serial search process. The analysis is extended to include a CCD. type of matched filter following the integrate and dump detector, and to investigate the improvements in acquisition time that may be achieved over the simple serial search process if a search-lock strategy is employed. The effects of jitter and phase offset upon the error probability of the recovered data are investigated both theoretically and by measurement for the particular case of code modulation by sequence inversion keying. A tracking loop is presented that has been shown to maintain reference code phase offset to within ~ 0.01 chips under conditions where the noise on the communications link has made the recovered data unusable for most purposes. Finally, an application of spread spectrum techniques to small local area networks is presented, and a discussion of the effects of the crosscorrelation noise from the other user spreading codes upon the tracking loop's discriminator characteristic is given.
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DITOLLA, ROBERT JOHN. "RANDOM VIBRATION ANALYSIS BY THE POWER SPECTRUM AND RESPONSE SPECTRUM METHODS (WHITE NOISE, FINITE-ELEMENT, VANMARCKE, DENSITY, NASTRAN)." Diss., The University of Arizona, 1986. http://hdl.handle.net/10150/183836.
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Determination of the stresses and displacements which occur in response to random excitations cannot be accomplished by traditional deterministic analysis methods. As the specification of the excitation and the response of the structure become more complex, solutions by direct, closed-form methods require extensive computations. Two methods are presented which can be used in the analysis of structures which are subjected to random excitations. The Power Spectrum Method is a procedure which determines the random vibration response of the structure based upon a frequency response analysis of a structural model. The Response Spectrum Method is a method which is based upon specified forces or displacements as a function of time. A derivation of each of the methods is presented and followed by comparisons of the results which were obtained for single and multiple-degree-of-freedom systems. Assumptions and limitations of the methods are discussed as well as their accuracy over ranges of frequency, damping and loading specification. As a direct application and comparison of the two methods, an analysis of the support system for the primary mirror of the Space Infrared Telescope Facility (SIRTF) has been performed. In addition, a method for the evaluation of the critical damping in a single-degree-of-freedom structure is demonstrated.
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Chakraborty, Joyraj, and Venkata Krishna chaithanya varma Jampana. "ANFIS BASED OPPURTUNISTIC POWER CONTROL FOR COGNITIVE RADIO IN SPECTRUM SHARING." Thesis, Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-5042.
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Cognitive radio is a intelligent technology that helps in resolving the issue of spectrum scarcity. In a spectrum sharing network, where secondary user can communicate simultaneously along with the primary user in the same frequency band, one of the challenges in cognitive radio is to obtain balance between two conflicting goals that are to minimize the interference to the primary users and to improve the performance of the secondary user. In our thesis we have considered a primary link and a secondary link (cognitive link) in a fading channel. To improve the performance of the secondary user by maintaining the Quality of Service (Qos) to the primary user, we considered varying the transmit power of the cognitive user. Efficient utilization of power in any system helps in improving the performance of that system. For this we proposed ANFIS based opportunistic power control strategy with primary user’s SNR and primary user’s channel gain interference as inputs. By using fuzzy inference system, Qos of primary user is adhered and there is no need of complex feedback channel from primary receiver. The simulation results of the proposed strategy shows better performance than the one without power control. Initially we have considered propagation environment without path loss and then extended our concept to the propagation environment with path loss where we have considered relative distance between the links as one of the input parameters.
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Jayalath, A. D. S. (Angiyaddage Dhammika Srilal) 1967. "OFDM for wireless broadband communications (peak power reduction, spectrum and coding)." Monash University, School of Computer Science and Software Engineering, 2002. http://arrow.monash.edu.au/hdl/1959.1/7995.
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Jayalath, A. D. S(Angiyaddage Dhammika Srilal) 1967. "OFDM for wireless broadband communications(peak power reduction, spectrum and coding) /." Monash University, School of Computer Science and Software Engineering, 2002. http://arrow.monash.edu.au/hdl/1959.1/7995.
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Jahren, Ole Henrik. "Emergent Behaviour in the Frequency-Power Spectrum of Discrete Dynamic Networks." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for datateknikk og informasjonsvitenskap, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-23038.
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In the fields of cellular automata and complex systems, emergence isoften used as an interpretation of system behaviour. Computation and theresulting output are both products of the systems trajectory in the basinof attraction, where the output data is a point or cyclic attractor. Assuch, the system outputs only a single variable, the states of all unitsin the system. This work diverges from the norm on two aspect. Instead ofexploring Cellular Automata as the computational architecture, BooleanNetworks, a specialisation of the more generalised Discrete DynamicNetworks, will be used. Secondly, a different approach in interpretingthe behaviour is taken. Instead of looking directly at the state of thesystem, the trajectory in the basin of attraction is instead transformedto a frequency-power spectrum representing the system output. This allowsan easy interpretation of the output (peeks) to several output variables,were each variables can be given as the power at different frequenciesin the frequency-power spectrum.Because of the difficulty in programming, i.e. designing, Discrete DynamicNetworks with the desired characteristics, a Genetic Algorithm will beused to evolve the networks. This thesis takes an experimental approach,evolving Discrete Dynamic Networks capable of producing differentnumber of peaks in the frequency-power spectrum. The results show thatDiscrete Dynamic Network exhibiting the desired emergent behaviour weresuccessfully evolved.
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Efroimsky, Michael. "Temperature power-spectrum of the primordial gravity-waves in inflationary cosmology." Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239355.
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Tang, Wing-shun, and 鄧榮信. "Study of power spectrum fluctuation in accretion disc by cellular automaton." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1999. http://hub.hku.hk/bib/B31221695.
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Uchaipichat, Nopadol. "The prediction of defibrillation outcome using time-frequency power spectrum methods." Thesis, Edinburgh Napier University, 2005. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.418238.
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Paykari, Paniez. "Binning of the primordial power spectrum and optimal galaxy survey design." Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/5547.
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The power spectrum describes the fluctuations in the Universe and encodes much of the cosmological information. Hence measuring different types of power spectra is of great importance in cosmology today. In this thesis we try to constrain two of these power spectra, the primordial power spectrum and the galaxy power spectrum. First we analyse the binning of the primordial power spectrum. The primordial power spectrum describes the initial perturbations in the Universe which eventually grew into the large-scale structure we observe today, and thereby provides an indirect probe of inflation or other structure-formation mechanisms. We will investigate which scales the primordial power spectrum can best be probed, in accordance with the knowledge about other cosmological parameters. The aim is to find the most informative way of measuring the primordial power spectrum at different length scales, using different types of surveys, such as Planck and SDSS (Bright Red Galaxy). For this we make use of the Fisher matrix formalism, principal component analysis and Hermitian square root of the Fisher matrix. This method of binning of the primordial power spectrum is then applied to the reconstruction of this power spectrum from WMAP and simulated Planck data. Here a new method for the reconstructing, directly from observations of the Cosmic Microwave Background (CMB), is introduced. Finally, we investigate the optimal observing strategy for measuring galaxy/matter power spectrum. These power spectra are of great importance in cosmology. Measuring this spectrum will enable us to measure other cosmological parameters. If we are only interested in the large scale power spectrum then we might gain more by sparsely observing a larger patch of sky, for the same observing time, rather than observing a smaller contiguous area. We will investigate the advantages and disadvantages of this strategy using Bayesian Experimental Design.
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Cresswell, Bevan. "Inflationary cosmology, phase transitions and primordial power spectra." Thesis, University of Canterbury. Physics and Astronomy, 2004. http://hdl.handle.net/10092/5578.
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We present the results of research into inflationary cosmology. This consists firstly of a basic overview of the inflationary scenario, including the currently accepted model of inflation as being driven by a weakly interacting scalar field with a slowly varying effective potential energy function. We then consider the theory of density perturbations, their quantum origins in the inflaton scalar field, and evolution in a rapidly expanding universe. This all acts as background material for the research carried out, which involves the generation of density perturbations by a non-standard effective potential for the inflaton field, and how their evolution is effected by features in the potential. The potentials are motivated by phase transitions in fields weakly coupled to the inflaton. These potentials violate the normally assumed slow roll conditions and the resulting power spectra do not have the scale independence characteristic of slow roll. Instead they exhibit scale dependent oscillations, whose nature depend on the details of the potential being considered. We finally consider the effect such power spectra would have on the Cosmic Microwave Background and compare this to the current observational data.
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Yoo, Byungseok. "Practical Aspects of Assessing Nonlinear Ultrasonic Response of Cyclically Load 7075-T6 Aluminum." Thesis, Virginia Tech, 2006. http://hdl.handle.net/10919/36335.
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The ultrasonic NDE technique to characterize the ultrasonic nonlinear response of the cyclically load 7075-T6 aluminum is described in this thesis. In order to estimate the nonlinear relation of the ultrasonic waves due to material fatigue damage or degradation, the spectral analysis techniques such as the power spectrum, bispectrum, and bicoherence spectrum are applied. The ultrasonic nonlinearity parameters by Cantrell and Jhang are introduced and presented as a function of the material fatigue growth, the number of fatigue cycles. This thesis presents the effectiveness of the bispectral analysis for evaluating the nonlinear aspects of the ultrasonic wave propagation. The results show that the nonlinearity parameters by Cantrell and Jhang are responsive to the output amplitude of the received signal and vary for the various materials, and independent of the input frequency and the ultrasonic wave propagation distance. By using the bispectral analysis tools, particularly the bicoherence spectrum, the increase of the coupling levels between the fundamental, its harmonic, and subharmonic frequency components is presented as the number of fatigue cycles is increased. This thesis suggests that the application of the bicoherence spectrum based on the nonlinear wave coupling relations be more effective for estimating the level of the material fatigue life.Master of Science
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Osborne, William P., Don Whiteman, and Sharmin Ara. "ON THE PERFORMANCE OF PCM/FM+ FM/FM SYSTEMS." International Foundation for Telemetering, 1993. http://hdl.handle.net/10150/608872.
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International Telemetering Conference Proceedings / October 25-28, 1993 / Riviera Hotel and Convention Center, Las Vegas, NevadaMuch modem telemetry is transmitted in a digital format and to be compatible with existing range equipment the digital data is impressed on the carrier using FM modulation. The receiving system in common use employs an FM limiter/discriminator as a detector followed by an integrate and dump matched filter for bit detection. This system has been studied by previous authors [1] and it is well known that in the absence of frequency uncertainty the optimum transmission parameters consist of a modulation index of .7 (peak-to-peak deviation divided by the bit rate) and an IF filter bandwidth equal to the bit rate followed by a limiter discriminator. In many cases, there is a need for some small amount of analog telemetry transmission in addition to the digital data discussed above. In these cases it is common practice to include analog subcarriers on the main carrier with the digital data modulating the carrier at baseband, the resulting system is called PCM/FM + FM/FM. These hybrid analog/digital systems are the subject of this paper. In particular this paper addresses the performance of these systems through simulation using the Block Oriented System Simulator (BOSS) from Comdisco and with analytical techniques to obtain the BER versus SNR curves for these systems. The simulation is used over a wide range of parameters to find the optimum values of modulation index and IF bandwidth for these systems.
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Moura, Tiago Sousa. "High efficiency energy harvesting system from D-TV spectrum." Master's thesis, Universidade de Aveiro, 2015. http://hdl.handle.net/10773/18868.
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Mestrado em Engenharia Eletrónica e TelecomunicaçõesA recolha de energia do meio ambiente para alimentar dispositivos como forma de os tornar auto-sustentáveis tem vindo cada vez mais a suscitar interesse. Por outro lado, o crescimento contínuo do espectro resultante das telecomunicações constitui uma grande oportunidade para a colheita de energia. Assim sendo, neste trabalho e proposto um sistema altamente e ciente de recolha de energia de rádio-frequência que utiliza o sinal da televisão digital (D-TV) portuguesa e que converte-o em tenso que poder a ser reaproveitada. De forma a ser vantajoso, o sistema e otimizado para operar a baixos níveis de potência. Assim, o presente trabalho pretende também fornecer orientações para o correto desenvolvimento do sistema de colheita de energia para baixa potência de entrada, contribuindo para o desenvolvimento de projetos futuros. O sistema e dividido numa antena recetora e num retificador. Para o retificador são propostas três soluções distintas: um díodo série, um díodo paralelo e um duplicador de tensão. A eficiência obtida e semelhante para as três configurações - cerca de 54% para um sinal de entrada sinusoidal com um nível de potência de -10.5 dBm. Medições com o multiplicador de tensão e o sinal real da D-TV como entrada mostraram uma eficiência de 63% para o mesmo nível de potência. Relativamente à antena, e proposta uma patch com slots e com um elemento parasita que utiliza como substrato dielétrico FR-4. Esta configuração resulta da necessidade de melhorar a largura de banda da microstrip simples. Medições mostraram um aumento da largura de banda em cerca de 4 vezes quando em comparação com uma patch simples.
Collect energy from the surroundings is being biased to power-up devices in order to turn them self-sustainable. On the other hand, the spectrum resultant from the telecommunications tends to progressively increase and becomes wide-reaching, constituting an enormous opportunity to energy harvesting. Thus, in this work a high e ciency radio-frequency energy harvesting system is proposed that takes uses of the Portuguese Digital Television (D-TV) signal to obtain Direct Current (DC) power. To be useful, the system is optimized to operate at low power conditions. So, this work also aims to provide reliable guidelines in the design of energy harvesting systems with low-input power. The system is divided into an antenna and a recti er. For the recti er, three di erent solutions are presented: a single-series diode, a singleshunt diode and a voltage doubler con guration. The e ciency is similar for the three recti ers { around 54% with a sine-wave excitation and -10.5 dBm input power. Field measurements with the voltage doubler has proven 63% e ciency for the same input power. As receiver antenna is proposed a slotted patch with a stacked parasitic based on FR-4 substrate. This con guration results from the need to improve the bandwidth of the basic microstrip patch. Measurements have proven and enhancement around 4 times in comparison with a basic patch.
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Josan, Amandeep Singh. "Constraints on the power spectrum of primordial perturbations from small-scale structure." Thesis, University of Nottingham, 2011. http://eprints.nottingham.ac.uk/11713/.
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In this thesis the Big Bang and inflation theory are reviewed. The success of inflation is largely due to the predicted generation of inhomogeneities. We review the dynamical equations of motion for an accelerating expansion of the Universe and the flow equations which describe the evolution of the Hubble slow-roll parameters. We use cosmological perturbation theory to find a new expression relating comoving curvature perturbations generated during inflation to density perturbations responsible for structure formation. Primordial black holes (PBHs) may form from primordial perturbations. We compile and update constraints on the abundance of PBHs. We then use our new relationship to translate these abundance limits into constraints on the power spectrum of primordial curvature perturbation. In addition we investigate the possible formation of ultracompact dark matter minihalos (UCMHs) which may also form from primordial pertubations. If dark matter is in the form of weakly interacting massive particles (WIMPs) then WIMP annihilation may produce a detectable gamma-ray signature. We calculate the potential constraints which would arise from a detection by the Fermi satellite. Finally, we investigate single field models of inflation using a stochastic technique to generate a large ensemble of models. Using a numerical approach along with a modified flow algorithm we find models of inflation compatible with all cosmological data which have large perturbations on small scales. Significant PBH formation occurs in models in which inflation can continue indefinitely and is ended via a secondary mechanism. We use our PBH constraints to eliminate such models which overproduce PBHs. In this work we demonstrate that PBH constraints, although weak, are effective at constraining models of inflation. We also demonstrate that a gamma-ray detection from UCMHs could potentially constrain the power spectrum of curvature perturbation on small scales very tightly in the near future.
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Salton, Grant. "The power spectrum of cosmic microwave background polarization from cosmic string wakes." Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=121559.
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We compute the integrated Sachs--Wolfe type contribution to the CMB polarization power spectrum from cosmic string wakes. An introduction to topological defects, cosmic strings, CMB polarization, and spin-s fields is given. We then use these tools to compute the angular power spectrum of E- and B-mode polarization due to cosmic string wakes, in the flat sky limit. We find that cross-correlation terms (i.e., EB, ET, BT) vanish, while the EE and BB power spectra are equal in shape and magnitude. This result is in stark contrast with B-mode polarization from Gaussian fluctuations, which vanishes identically. However, we find that the shape of the power spectrum from cosmic string wakes is very similar to the predicted B-mode power spectrum from gravitational lensing, but with a small overall amplitude. As such, the cosmic string wake signal is too small to be picked out from lensing, and background subtraction techniques would be very difficult. We find that the peak amplitude in the dimensionless power spectrum (sqrt(l(l+1)C_l/2pi)) is about 10^(-4) at a peak value of l~400.We briefly study the asymptotic version of the power spectrum and find that C_l is approximately constant until a turn around point set by the angular size of the dominant wakes. We then determine which cosmic string wakes give rise to the dominant contribution to the full, integrated power spectrum and find that the dominant wakes are those which were formed at the time of equal matter and radiation, and which intersect our past light cone at recombination. We conclude that the Fourier space signal (power spectrum) is too weak to detect cosmic string wakes in existing data, and future searches should focus on distinct position space features.Nous calculons la contribution intégrée au spectre de puissance de la polarisation du fond diffus cosmique (CMB) grâce aux sillages des cordes cosmiques. Une introduction aux défauts topologique, cordes cosmiques, de polarisation du CMB, et aux champs spin–s est donnée. Nous utilisons ensuite ces outils pour calculer le spectre de puissance angulaire de la polarisation des modes E et B grâce aux des sillages des cordes cosmiques, dans la limite du ciel plat. Nous trouvons que les termes de corrélation croisée (EB, ET, BT) sont zero, tandis que les spectres de puissance pour EE et BB ont la même forme et grandeur. Ce résultat contraste le polarisation du mode B causée par les fluctuations Gaussiennes, qui disparaîssent. Cependant, nous trouvons que la forme du spectre de puissance causée par les sillages de cordes cosmiques est très similaire au spectre en mode B prédite par lentille gravitationnelle, mais avec une amplitude globale trés faible. Donc, le signal du sillage de corde cosmique est trop faible pour être measuré au-dessus l'indicatif du lentille. Aussi, les méthodes de soustraction du fond serait très difficile. Nous trouvons que l'amplitude maximum dans le spectre de puissance sqrt(l(l+1)C_l/2pi) est d'environ 10^(-4) pour l~400.Nous étudions brièvement le forme asymptotique du spectre de puissance, et nous trouvons que Cl est quasi–constant en l jusqu'à un tournant correspondant à la taille angulaire du sillage le plus important. Nous déterminons alors quel sillage donne la contribution dominante au spectre de puissance complet. Nous trouvons que les sillages dominants sont ceux qui ont été formés à l'epoque de l'égalité de matière et de rayonnement, et qui croisent notre cône de lumière passé à l'époque de recombinaison. Nous concluons que l'indicatif dans l'espace Fourier est trop faible pour être détecté. Donc, les recherches futures devraient se concentrer sur les caractéristiques l'espace spatial.
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Parker, Michael Julian Reid. "Studies on power spectrum analysis of the fetal heart rate during labour." Thesis, Queen's University Belfast, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356874.
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