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VASCONCELLOS, EDMAR DA COSTA. "SUB-BAND IMAGE CODING". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1994. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=8635@1.
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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOREste trabalho aborda o problema da compressão de imagens explorando a técnica de codificação por sub-bandas(SBB). Como estrutura básica, usada na primeira parte do trabalho, tem-se a divisão da imagem em 16 sub-bandas buscando replicar os resultados de woods [1]. As componentes das 16 SBB são quantizadas e codificadas, e bits são alocados às SBB usando como critério a minimização do erro médio quadrático. Os quantizadores são projetados segundo uma distribuição Gaussiana Generalizada. Neste processo de codificação, a sub-banda de mais baixa freqüência é codificada com DPCM, enquanto as demais SBB são codificadas por PCM. Como inovação, é proposto o uso do algoritmo de Lempel-Ziv na codificação sem perdas (compactação) das sub-bandas quantizadas. Na compactação são empregados os algoritmos de Huffman e LZW (modificação do LZA). Os resultados das simulações são apresentados em termos da taxa (bits/pixel) versus relação sinal ruído de pico e em termos de analise subjetiva das imagens reconstruídas. Os resultados obtidos indicam um desempenho de compressão superior quanto o algoritmo de Huffman é usado, comparado com o algoritmo LZW. A melhoria de desempenho, na técnica de decomposição em sub-bandas, observada com o algoritmo de Huffman foi superior (2dB acima). Todavia, tendo em vista as vantagens da universalidade do algoritmo de Lempel-Ziv, deve-se continuar a investigar o seu desempenho implementado de forma diferente do explorado neste trabalho.
This work focus on the problem of image compression, with exploring the techniques of subband coding. The basic structure, used in the sirst part of this tesis, encompass the uniform decomposition of the image into 16 subbands. This procedure aims at reproducing the reults of Woods [1]. The component of the 16 subbands are quatized and coded and bits are optimally allocated among the subbands to minimize the mean-squared error. The quantizers desingned match the Generelized Gaussian Distribuition, which model the subband components. In the coding process, the lowest subband is DPCM coded while the higher subbands are coded with PCM. As an innovation, it is proposed the use of the algorithm LZW for coding without error (compaction) the quantized subbands. In the compactation process, the Huffamn and LZW algorithms are used. The simulation results are presented in terms of rate (bits/pel) versus peak signal-to-noise and subjective quality. The performance of the subband decomposition tecnique obtained with the Huffamn´s algorithm is about 2dB better than that obtained with the LZW. The universality of the Lempel-Ziv algorithm is, however, an advantage that leads us to think that further investigation should still be pursued.
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Simoncelli, Eero Peter. "Orthogonal sub-band image transforms". Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/14758.
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RILA, LUCIANO. "SUB-BAND CODING OF IMAGES USING INTER-BAND VECTOR QUANTIZATION". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1993. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=8746@1.
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICONeste trabalho são examinados métodos de codificação de imagens em sub-bandas utilizando quantização vetorial inter-bandas para faixas abaixo de 1 bit/pixel. O espectro de freqüências da imagem é decomposto em 16 sub-bandas uniformes através de um banco de filtros espelhados em quadratura bi-dimensionais. As amostras dos sinais das 16 sub-bandas são usadas para compor um vetor de 16 componentes que, posteriormente, é codificado por um esquema de quantização vetorial (QV). Com o objetivo de reduzir a complexidade e o espaço de memória, são investigadas duas estruturas de quantização vetorial. Uma delas utiliza QV particionada, com o objetivo não só de reduzir a complexidade, como também de explorar as propriedades espectrais. A outra realiza a quantização vetorial direta, enquanto a complexidade é reduzida significativamente. Resultados de simulações são apresentados para as taxas de 0,50 bit/pixel, 0,63 bit/pixel e 0,75 bit/pixel. Uma análise comparativa mostra que o desempenho dos dois esquemas é comparável ao que utiliza quantização vetorial direta, enquanto a complexidade é reduzida significativamente. Resultados de simulações mostram ainda que, a taxas abaixo de 1 bit/pixel, não é recomendável o uso de QV inter-bandas particionada com alocação de bits adaptativa, nem de QV inter-bandas multi-estágios com busca em árvore. A técnica QV inter-bandas quando a sub-banda dominante é codificada separadamente através de um quantizador vetorial intra-banda. Considera-se a decomposição do espectro de freqüências em 16 sub-bandas uniformes e em 13 sub-bandas. Para a decomposição em 16 sub-bandas, esse esquema apresenta desempenho comparável à QV inter-bandas direta e complexidade equivalente à QV inter-bandas multi- estágios.
In this thesis sub-band coding of images using inter-band vector quantization is examined at rates below 1 bit/pixel. The image spectrum is decomposed into 16 uniform bands using 2-D separable quadrature mirror filters. These 16 bands are used to create 16-dimension vectores, which are coded using vector quantization (VQ). In order to reduce the computational complexity and the storage requirements, two vector quantization structures are considered. One approach is to split the vectors not only to reduce complexity but also to exploit spectral properties of the data image. In the order approach the vector quantization is done in multiple stages. Simulation results are presented at rates of 0,50 bit/pixel, 0,63 bit/pixel and 0,75 bit/pixel. A comparative analysis shows that the performance of the two systems is comparable to the basic coding structure, while the complexity is significantly reduced. Simulation results also show that split VQ with adaptive bit allocation and multi-stage VQ with tree search are not recommended at these rates. The best trade-off between complexity and performance is achieved with the inter-band multi-stage VQ scheme using the sequential search procedure. At last, the use of inter- band VQ is examined when the dominant sub-band is separately coded using intra-band VQ. When the image spectrum is decomposed into 16 bands, this scheme has a performance comparable to the basic coding structure while the complexity and storage reduction is equivalent to the inter-band multi-stage VQ technique.
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Bhuvanendran, Nilesh. "SUB-OPTIMAL ULTRA-WIDE BAND RECEIVERS". Master's thesis, University of Central Florida, 2004. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4469.
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Ultra-wide Band (UWB) has sparked a lot of interest lately from the industry and academia. The growing capacity of the wireless industry is requires a new communication system that satisfies the high data rate which does not interfere with existing RF systems. UWB promises to be this new technology. UWB also promises low power, low cost and fexibility. The UWB Channel opens up a huge new wireless channel with Giga Hertz Capacities as well as the highest spatial capacities measured in bits per hertz per square meter. When properly implemented UWB channel can share spectrum with traditional radio systems without causing harmful interference. In this thesis we studied and compared several reduced complexity sub-optimal Ultra-Wide Band receivers. These receivers include auto correlation receiver, the square value detector and the absolute value detector are studied. We consider OOK and PPM modulation schemes. We examine these schemes and the receivers on Gaussian and UWB indoor channels. We compare the performance with optimal receivers. A transmitter receiver system using 0.1us pulses implemented using existing hardware. A packet consisting of 24 bits were transmitted and the received signal could be verified in real time using a vector signal analyzer. The results show sub-optimal receivers provide a better trade off between robust, complexity and performance.M.S.
Department of Electrical and Computer Engineering
Engineering and Computer Science
Electrical and Computer Engineering
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Romano, Pasquale. "Vector quantization for spatiotemporal sub-band coding". Thesis, Massachusetts Institute of Technology, 1989. http://hdl.handle.net/1721.1/69708.
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Song, Sewoong 1954. "Structural sub-band decomposition for adaptive filters". Thesis, The University of Arizona, 1990. http://hdl.handle.net/10150/291831.
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The theory of structural sub-band decomposition of an FIR filters is extended to adaptive filters. It is shown that this sub-band decomposition is equivalent to the transform of input data by orthogonal matrices, of which the Walsh-Hadamard Transform (WHT) is a special case. Thus, the proposed method is a generalization of the transform domain adaptive filtering (TDAF) using WHT, which is already known to enhance the convergence speed of adaptive filters. Furthermore, our method yields one possible hardware implementation of the fast WHT. The convergence behavior of the proposed sub-band adaptive filters is simulated using the Least Mean Squares (LMS) and Recursive Least Squares (RLS) algorithms. The results show the faster convergence speed of the proposed adaptive filters compared to conventional adaptive filters.
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Punya, Atchara. "Quasiparticle self-consistent GW band structures of III-N, II-IV-N2 semiconductors and band offsets". Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1380888317.
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Lefebvre, Pierre D. "Adaptive multiple sub-band common mode RFI suppression". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/MQ58475.pdf.
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Zemouri, Rachid. "Data compression of speech using sub-band coding". Thesis, University of Newcastle Upon Tyne, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316094.
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Fischer, Stefan [Verfasser] y Eicke [Akademischer Betreuer] Weber. "Upconversion of sub-band-gap photons for silicon solar cells = Hochkonversion von sub-band-gap Photonen zur Effizienzsteigerung von Silicium-Solarzellen". Freiburg : Universität, 2014. http://d-nb.info/1123480982/34.
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Ning, Paul. "A comparison of adaptive predictors in sub-band coding". Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/26799.
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Doherty, B. "Context dependency and sub-band based modelling for speech recognition". Thesis, Queen's University Belfast, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368773.
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CHACON, RAFAEL ANTONIO FLORES. "REAL TIME HARMONIC SINE WAVE ESTIMATION BY SUB-BAND DECOMPOSITION". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1999. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=7544@1.
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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORA medição da qualidade de energia é um aspecto cada vez mais importante com o avanço tecnológico. Um destes aspectos é a estimação dos harmônicos em sinais de potência. Este trabalho, apresenta um algoritmo para obter, simultaneamente, os valores reais de freqüência, amplitude e fase de cada componente do sinal, baseados em valores distorcidos originários do uso da FFT. Contrário a outros métodos, o algoritmo requer um número reduzido de dados, permitindo sua implementação em tempo real. Para estender este método a um sinal com componentes de harmônicos de ordem elevada utilizam-se bancos de filtros para decomposição em sub-bandas e eventual reconstrução numa estrutura de operação orientada ao tempo real. O trabalho apresenta resultados comprovando a correta operação e robustez do processo. O método é otimizado para implementação com reduzido número de operações em ponto flutuante.
Power quality measurement is a key issue with the technology advance in power systems. One fo these issues is harmonics estimation of power systems signals. This work shows an algorithm to obtain, simultaneously, the real values of frequency, amplitude and phase of each signal component, based in distorted values originated by the use of FFT. In contrast to other methods, the algorithm requires a small number of data, allowing its implementation in real time. To extended this method to a high harmonic order signal, filter banks are used to decompose it in sub bands and eventually reconstruct it, in a real time operation structure. This work shows results testing the correct operation and robustness of the process. Th eAlgorithm is optimized to its imlementation with a reduced number of float point operations.
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JOURDAN, MARCELO MOLLICA. "ADAPTIVE SUB-BAND COMPRESSION OF IMAGES AT LOW BIT RATES". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1995. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=8932@1.
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOEssa dissertação propõe um codificador de imagens adaptativo baseado em sub-bandas para baixas taxas de bits. O espectro de freqüência bi-dimensional é decomposto em 10 sub-bandas de maneira hierárquica através de um banco de filtros QMF de 9 coeficientes. Uma técnica de redução de irrelevância é usada para descartar vetores nas sub-bandas de número 2 a 10. Os vetores remanescentes nessas sub-bandas são classificadas em bordas ou texturas e codificados por ECVQ (Entropy Constrained Vector Quantization) multi-estágios. Já a primeira sub-banda é codificada por ADPCM com preservação de bordas. Um algoritmo ótimo de alocação de bits determina a distribuição adequada de bits entre as sub-bandas. Os resultados mostram excelentes desempenho para baixas taxas, sendo melhores que os obtidos pelo padrão JPEG e vários outros trabalhos apresentados na literatura recente.
This dissertation proposes an adaptative subband coder for low bit rate coding os still images. The bi-dimension frequency spectrum is decomposed in 10 subbands by means of a 9-coefficient QMF filter bank. Vector in subbands 2 to 10 are discarded by a new technique for irrelevancy reduction. The remanining vectors are classified in one of two classes, edges and textures, and coded by multistage ECVQ (Entropy Constrained Vector Quantization). The first subband is coded by an edge preserving ADPCM. An optimal bit allocation procedure is used to distribute bits along the subbands. The results obtained show excellent performance for low bit rate coding, outperforming JPEG and many other coders recently presented in literature.
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Stott, Chloe. "Optically detected magnetic resonance and sub-Kelvin EPR at Q-band". Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/optically-detected-magnetic-resonance-and-subkelvin-epr-at-q-band(fef4bd05-8b37-44a6-8ee7-21b961de2163).html.
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In this thesis I will discuss the development, construction and testing of a sub-Kelvin Q-band electron paramagnetic resonance (EPR) spectrometer and optically detected magnetic resonance (ODMR) of wide bandgap semiconductors at Q-band. The sub-Kelvin EPR spectrometer was developed to be integrated into a standard commercial system. Characterisation of the cryogenics and microwave components of the spectrometer will be discussed as well as the design and adaptations made to enable EPR experiments to be performed below 1 K. A waveguide thermal break design, previously only used in detectors for the cosmic microwave background radiation, was optimised using ANSYS High frequency structure simulator (HFSS) to operate at Q-band and was built and tested in this spectrometer. The sub-Kelvin EPR spectra of Cr3+ in Al2O3 and [Cr12O9(OH)3(O2CCMe3)15] were obtained. The resonant cavity of the spectrometer was also successfully tested at room temperature, with a pulsed microwave bridge, paving the way for further development of the system to enable sub-Kelvin pulsed EPR. A home-built Q-band ODMR spectrometer was used to investigate the wide band gap semiconductors ZnO and InGaN/GaN multiple quantum wells (MQWs). The ZnO was a natural crystal, and used to characterise the spectrometer. ODMR from a green c-plane InGaN/GaN MQW was studied to probe the method of carrier localisation in the QW. It was shown qualitatively that the ODMR results support current theories for carrier localisation mechanisms, but the noise on these measurements needs to be reduced to provide quantitative support.
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Jayatunga, Benthara Hewage Dinushi. "Heterovalent Semiconductors: First-Principles Calculations of the Band Structure of ZnGeGa2N4, and Metalorganic Chemical Vapor Deposition of ZnGeN2 - GaN Alloys and ZnSnN2". Case Western Reserve University School of Graduate Studies / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=case1619087038602758.
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Hart, Joanna Elizabeth. "Multirate sub-band structures with application to adaptive acoustic echo cancellation". Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.300759.
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Finan, Robert Andrew. "Towards the use of sub-band processing in automatic speaker recognition". Thesis, University of Abertay Dundee, 1998. http://eprints.soton.ac.uk/256266/.
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Darlington, David J. "The enhancement of noise-corrupted speech by sub-band adaptive filtering". Thesis, University of the West of Scotland, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388213.
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Khalab, Jamal M. "Multirate adaptive array techniques for cancellation of co-channel interference in direct sequence spread spectrum systems". Thesis, University of Nottingham, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294700.
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Wong, K. H. J. "Adaptive differential pulse code modulation and sub-band coding of speech signals". Thesis, University of Southampton, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380170.
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Yang, Wenjie. "Characterising and understanding Au-hyperdoped Si for sub-band gap optical absorption". Phd thesis, Canberra, ACT : The Australian National University, 2018. http://hdl.handle.net/1885/154257.
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The unparalleled technological maturity of silicon (Si) can be exploited to develop CMOS-compatible optoelectronics such as photodetectors and imaging arrays. However, the low-attenuation wavelengths commonly used in fibre-optics (up to 1650 nm) fall below the 1.12 eV band gap of Si (efficient absorption only occurs at wavelengths less than 1100 nm), thus requiring the realisation of sub-band gap photoresponse. A promising method to achieve this is to add an intermediate band within the band gap by incorporating appropriate impurities into the Si lattice at high concentrations (often beyond the thermodynamic solubility limit), or hyperdoping. Indeed, Au-hyperdoped Si made by ion implantation and pulsed laser melting (PLM) has been shown to exhibit strong sub-band gap optical absorption in the near-infrared and has led to the demonstration of a Si-based near-IR photodetector. The Au sub-band gap absorption has been shown to increase with the Au dose, and significant room for further improvement of the device performance has been predicted. While these results illustrate the potential of hyperdoped Si for photodetection in the near-infrared, the material properties of Au- and other transition-metal-hyperdoped Si remain elusive. With this as a premise, this PhD work has focused on characterising and understanding the properties of Au-hyperdoped Si. In this thesis, detailed Rutherford backscattering spectrometry and channeling measurements are undertaken to examine the lattice position of the Au atoms. It is shown that the Au occupies mostly substitutional lattice positions within the hyperdoped Si lattice. In addition, by varying the iplant energy and the implanted Au dose, thicker layers of Au-hyperdoped Si with higher Au concentrations are demonstrated. However, although the Au atoms remain significantly substitutional (more than 50% substitutional in most cases) at high Au concentrations, the Au distribution is found to be non-uniform. Further structural characterisation by transmission electron microscopy and energy dispersive spectroscopy reveals a new observation where filaments of single crystalline, Au-rich Si regions emerge after PLM. The local concentration within such filaments is estimated to be at least 3 at. %, and the proximate Si lattice is found to be slightly skewed. These features suggest a novel segregation regime in Au-hyperdoped Si that is distinctly different to conventional 'cellular breakdown' in hyperdoped Si, in which impurity precipitation might be observed at cell-walls. In spite of the inhomogeneous behaviour of Au-hyperdoped Si at high Au concentrations, the sub-band gap optical absorption is found to continue to increase with increasing substitutional Au dose. This is consistent with density functional theory calculations in which the isolated substitutional Au configuration is found to give rise to significant sub-band gap optical absorption. This enhancement in sub-band gap optical absorption is found to deactivate after subsequent thermal annealing. We show that this behaviour can be correlated with a loss of Au substitutionality. Furthermore, the detailed atomistic mechanism for the thermal relaxation of Au-hyperdoped Si is investigated by correlating the experimental observations with density functional theory results. We show that the thermal relaxation of Au-hyperdoped Si is a multi-step process which involves (1) the exchange of substitutional Au with interstitial Au, (2) the trapping of Au to local sinks, (3) the formation of Au dimers, and (4) the clustering and nucleation of Au precipitates. Furthermore, the activation energy associated with loss of Au substitutionality is found to be 1.6 eV, a similar value to the diffusion of Au in defective Si. In the final chapter of this work, experimental evidence for a vacancy trapping model is presented. We propose that vacancies are introduced during the resolidification process to minimise local strain around Au-rich regions. Furthermore, the trapped vacancies are shown to be decorated with Au after subsequent thermal annealing. We show that such a behaviour is not limited to Au-hyperdoped Si and may be a universal phenomenon that occurs during the incorporation of large size impurities into Si as the Si is rapidly resolidified from a laser-induced melt.
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Meredith, John Edwin Charles. "The use of a broad-band seismic network to study structures beneath the UK". Thesis, Cardiff University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284100.
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Smith, Cameron. "Restoration and registration of digital images using LMS adaptive filters". Thesis, University of the West of Scotland, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360228.
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HUANG, LING-YI. "Electronic Band Structure, Phonons and Exciton Binding Energies of Halide Perovskites CsSnX3 with X=Cl, Br, I". Case Western Reserve University School of Graduate Studies / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=case1436477745.
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Akbari, Mohsen. "Strategies for changing the redundancy of sub-band signals in oversampled filter banks". Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=107809.
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Communication channels are always vulnerable to noise sources. Thereby, any kind of data transmitted over these channels suffer from errors that happen during transmission which degrades the quality of the signal on the receiver side. To tackle this problem, some amount of redundancy should be added to the input signal so on the receiver side, this redundancy could be exploited to remove the errors. However, most of the existing schemes for adding redundancy to the signal have two main drawbacks. First, they are designed to work decently as long as the channel quality is always above a certain threshold. But when the channel quality falls under that threshold, the system tends to break down completely and is no longer capable of correcting the errors (threshold effect). Second, most of the current error correction schemes lack the inherent adaptability and flexibility for changing the added redundancy which is necessary due to the unavoidable change in channel characteristics.In this thesis, we will explore the methods of signal representation that are naturally amenable to transmission at flexible rates and offer graceful degradation in signal quality with degrading link quality. For such applications, we will consider the insertion of soft, structured redundancy in signals to be transmitted, through the use of Oversampled Filter Banks (OFBs). These codes enable a joint compression and protection of signals through the application of a redundant transform (or frame operator) to the signal, which serves both for signal conditioning for compression and for insertion of redundancy in the signal so as to be able to combat adverse channel effects. More specifically, in this thesis, we extend the framework of redundant expansions to the case where the amount of injected redundancy can be adjusted on the fly. This will be accomplished through two main approaches. The first method is called Adaptive Downsampling. Here, the idea is to change the downsampling rate of the OFB as a response to the changes in channel quality. We investigate the effect of such downsampling variation on filtering the input signal vectors on analysis side and propose suitable signal reconstruction method on the synthesis side of the OFB. In the second method, we introduce the notion of Instantaneous Erasures in OFBs which accounts for a situation when samples of sub-band vectors are erased arbitrarily in different time instances. We find the conditions under which the OFB maintains its perfect reconstruction property using time-domain analysis and we propose structures in order to be able to design implementable OFBs.Les canaux de communications sont vulnérables aux sources de bruit. De ce fait, n'importe quelle donnée transmise sur ces canaux peut être victime d'erreurs survenant lors de la transmission, dégradant ainsi la qualité du signal à la réception. Afin de résoudre ce problème, une certaine redondance doit être apportée au signal d'entrée pour qu'à la réception elle aide à corriger les erreurs. Cependant, la plupart des schémas ajoutant de la redondance aux signaux ont deux défauts majeurs. Premièrement, ces schémas sont conçus pour fonctionner décemment aussi longtemps que la qualité du canal reste au dessus d'un certain seuil. Mais dés que la qualité du canal tombe en dessous de ce seuil, le système est complètement perturbé et n'est plus capable de corriger les erreurs (effet de seuil). Deuxièmement, la plupart des schémas de correction d'erreurs courantes manquent d'adaptabilité et de flexibilité propres pour modifier la redondance ajoutée, ce qui est nécessaire au vue des changements inévitables des caractéristiques du canal. Dans cette thèse, nous explorons les méthodes de représentation du signal qui se prêtent naturellement à la transmission à des taux flexibles et qui offrent une dégradation graduelle (graceful degradation) en termes de qualité de signal par rapport à la détérioration du canal. Pour de telles applications, nous considérons l'insertion d'une redondance de type soft et structurée dans les signaux à transmettre en utilisant les bancs de filtres sur-échantillonnés (Oversampled Filter Bank : OFB). Ces codes offrent à la fois une compression et une protection des signaux grâce à l'application d'une transformation redondante (ou opérateur de frame) au signal, ce qui sert au prétraitement des signaux pour la compression et pour l'insertion de redondance dans le signal, permettant ainsi de contrer les effets indésirables du canal. Plus précisément, dans cette thèse, nous approfondissons le domaine des expansions redondantes de signal au cas où la quantité de redondance injectée peut être ajustée à la volée. Deux approches principales permettront cette entreprise. La première méthode est appelée sous-échantillonnage adaptatif. L'idée est de changer le taux de sous-échantillonnage de l'OFB en réponse aux variations de la qualité du canal. Nous étudions l'effet d'un tel sous-échantillonnage sur le filtrage des vecteurs du signal d'entrée du coté analyse et nous proposons une méthode de reconstruction du signal appropriée du coté synthèse de l'OFB. Pour la deuxième méthode, nous introduisons la notion d'effacement instantané dans les OFB, qui correspond au cas où les échantillons des vecteurs sous-bande sont effacés avec une distribution arbitraire à différents moments. Nous trouvons les conditions pour lesquelles l'OFB maintient sa propriété de reconstruction parfaite en utilisant une analyse temporelle et nous proposons des structures afin de permettre la conception d'OFB implémentables.
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Wong, Hok Ming. "Sub-band gap luminescence of ZnSe/GaAs heterojunction grown by hot wall epitaxy". HKBU Institutional Repository, 1996. http://repository.hkbu.edu.hk/etd_ra/61.
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Algarin, Paula C. "Effects of Zn Doping and High Energy Ball Milling on the Photocatalytic Properties of TiO2". [Tampa, Fla] : University of South Florida, 2008. http://purl.fcla.edu/usf/dc/et/SFE0002462.
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Sun, Bo. "Understanding and Modifying TiO2 for Aqueous Organic Photodegradation". Cincinnati, Ohio : University of Cincinnati, 2005. http://www.ohiolink.edu/etd/view.cgi?acc%5Fnum=ucin112361662.
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Thesis (Ph. D.)--University of Cincinnati, 2005.Title from electronic thesis title page (viewed Apr. 12, 2006). Includes abstract. Keywords: band structure; charge separation; 4-chlorophenol; CrO3; deactivation; Degussa P25; Electrospinning; environment decontamination.; Fibers; MCM-41; MCM-48; Mesoporous Molecular Sieves; oxidation state; photocatalysis; platinum; quantum efficiency; reactivation; reduction; SBA-15; surface modification; synergism; synergy; TiO2; titania; Titanium Dioxide; total carbon removal.; total organic carbon; TPR; Transition metals; visible light; UV-light; UV-Visible. Includes bibliographical references.
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Ahmed, Mamun. "Adaptive Sub band GSC Beam forming using Linear Microphone-Array for Noise Reduction/Speech Enhancement". Thesis, Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-6174.
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This project presents the description, design and the implementation of a 4-channel microphone array that is an adaptive sub-band generalized side lobe canceller (GSC) beam former uses for video conferencing, hands-free telephony etc, in a noisy environment for speech enhancement as well as noise suppression. The side lobe canceller evaluated with both Least Mean Square (LMS) and Normalized Least Mean Square (NLMS) adaptation. A testing structure is presented; which involves a linear 4-microphone array connected to collect the data. Tests were done using one target signal source and one noise source. In each microphone’s, data were collected via fractional time delay filtering then it is divided into sub-bands and applied GSC to each of the subsequent sub-bands. The overall Signal to Noise Ratio (SNR) improvement is determined from the main signal and noise input and output powers, with signal-only and noise-only as the input to the GSC. The NLMS algorithm significantly improves the speech quality with noise suppression levels up to 13 dB while LMS algorithm is giving up to 10 dB. All of the processing for this thesis is implemented on a computer using MATLAB and validated by considering different SNR measure under various types of blocking matrix, different step sizes, different noise locations and variable SNR with noise.Mamun Ahmed E-mail: mamuncse99cuet@yahoo.com
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Vieira-Ribeiro, Simon A. (Simon Albert) Carleton University Dissertation Engineering Systems and Computer. "Single-IF DECT receiver architecture using a quadrature sub-sampling band-pass sigma-delta modulator". Ottawa, 1995.
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Linaburg, Matthew Ronald. "Studies of Halide Perovskites CsPbX3, RbPbX3 (X=Cl-, Br-, I-), and Their Solid Solutions". The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1449074303.
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Castelli, Eleonora. "LISA Pathfinder noise performance results: disturbances in the sub-mHz frequency band and projection to LISA". Doctoral thesis, Università degli studi di Trento, 2020. http://hdl.handle.net/11572/254388.
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The LISA Pathfinder ESA mission was concluded on July 18th, 2017, after 18 months of operations as one of the most successful ESA missions ever. It was launched on December 3rd, 2015 with the purpose of assessing the feasibility of geodesic motion of two free-falling test masses at the level required by LISA, the first space-based gravitational wave observatory programmed for launch in 2034. This was achieved by measuring the relative acceleration between free-falling test masses with a sensitivity several {orders of magnitude} better than any other present or future mission. In addition to this, LISA Pathfinder constituted an advanced technological test for the flight hardware of the LISA mission.
In this thesis work I will illustrate the detail of the experimental results obtained in the course of the mission, whose best performance was published in February 2018, and discuss their consequences for LISA. I will, in particular, describe in some detail a series of observations for which a definitive physical model is still lacking.
I will then discuss possible explanations with the aim to reduce the number of available interpretations, and in order to lay the basis for a feasible on-ground experimental campaign in view of LISA.
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Al, lethawe Mohammed abdulridha. "Band gaps and waveguiding of surface acoustic waves in pillars-based phononics crystals". Thesis, Besançon, 2015. http://www.theses.fr/2015BESA2057.
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[…] Dans ce travail de thèse, nous nous sommes intéressés à ces bandes interdites et à ces modes de propagations dans le cas d’un cristal photonique constitué d’une matrice de piliers déposés en surface d’un milieu semi-fini. L’étude des interactions entre les piliers résonants localement avec la surface du milieu semi fini nous a permis d’identifier de nouveaux modes de propagation […]Nous avons également montré comment obtenir une réfraction négative omnidirectionnelle[…] La dernière partie de ce travail a été consacré à l’étude des mécanismes permettant la propagation et le confinement d’ondes guidées[…] .Nous avons également explicité les mécanismes qui permettent de crée ce type d’ondes guidées sub-longeur d’onde et le confinement des photons de surface[...] We present the features of the interaction between surface acoustic wave and locally resonant pillar on the top of demi infinite medium. We shown that the photonic crystal we proposed possess an acoustic metamaterial feature for surface acoustic waves in the manner that pillars on the top of the surface introduce new guide modes in the non radiative region of the substrate outside sound cone. We also demonstrate the these guided modes are resonant modes that have frequencies greatly lower than those expected from the Bragg mechanism. […]
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SILVA, HARRY ARNOLD ANACLETO. "INDEPENDENT TEXT ROBUST SPEAKER RECOGNITION IN THE PRESENCE OF NOISE USING PAC-MFCC AND SUB BAND CLASSIFIERS". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2011. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=18212@1.
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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORO presente trabalho é proposto o atributo PAC-MFCC operando com Classificadores em Sub-Bandas para a tarefa de identificação de locutor independente do texto em ruído. O sistema proposto é comparado com os atributos MFCC (Coeficientes Cepestrais de Frequência Mel), PAC- MFCC (Fase Autocorrelação-MFCC ) sem uso de classificadores em sub-bandas, SSCH(Histogramas de Centróides de Sub-Bandas Espectrais) e TECC (Coeficientes Cepestrais da Energia Teager). Nesta tarefa de reconhecimento, utilizou-se a base TIMIT a qual é composta de 630 locutores onde cada um deles falam 10 frases de aproximadamente 3 segundos cada frase, das quais 8 frases foram utilizadas para treinamento e 2 para teste, obtendo-se um total de 1260 locuções para o reconhecimento. Investigou-se o desempenho dos diversos sistemas utilizando diferentes tipos de ruídos da base Noisex 92 com diferentes relação sinal ruído. Verificou-se que a taxa de acerto da técnica PAC-MFCC com classificador em Sub-Bandas apresenta o melhor desempenho em comparação com as outras técnicas quando se tem uma relação sinal ruído menor que 10dB.
In this work is proposed the use of the PAC-MFCC feature with Sub-band Classifiers for the task of text-independent speaker identification in noise. The proposed scheme is compared with the features MFCC (Mel-Frequency Cepstral Coefficients ), PAC-MFCC (Phase Autocorrelation MFCC) without subband classifiers, SSCH (Subband Spectral Centroid Histograms) and TECC (Teager Energy Cepstrum Coefficients). In this recognition task, we used the TIMIT database which consists of 630 speakers, where every one of them speak 10 utterances of 3 seconds each one approximately, of which eight utterance were used for training and two for testing, thus obtaining a total of 1260 test utterance for the recognition. We investigated the performance of these techniques using differents types of noise from the base Noisex 92 with different signal to noise ratios. It was found that the accuracy rate of the PAC-MFCC feature with Sub-band Classifiers performs better in comparison with other techniques at a lower signal noise(less than 10dB).
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Gui, Le Jørgensen Palle E. T. "Use of operator theory and sub-band filters in the analysis and encoding of signals and images". Iowa City : University of Iowa, 2009. http://ir.uiowa.edu/etd/293.
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Gui, Le. "Use of operator theory and sub-band filters in the analysis and encoding of signals and images". Diss., University of Iowa, 2009. https://ir.uiowa.edu/etd/293.
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The thesis is motivated by recent advances in signal and image processing, a part of electrical and computer engineering.
In the first part, we begin with a new approach to the mathematical signal processing as used in the digital processing of images. We prove such results in the 2D case, and we explain their use. A key point we explore is the interplay between the two cases, continuous and discrete. Our discrete algorithms present fast matrix-operations to be applied to images in pixel form. This part of the thesis in turn is based on tools from wavelet analysis, and more generally from the theory of operators in Hilbert space.
In the second part, we address encoding and quantization of wavelet coefficients obtained after applying the DWT (mentioned in first part) to 1-D signals.This is the last crucial step in A/D conversion, i.e., analog to digital. By quantization we mean the conversion and encoding of processing-output into bits; bits that in turn are transmitted and fed into a decoder. We isolate and make mathematically precise a particular family of quantizers which are efficient in that they produce error terms of exponential fall-off. We do this with a family of discrete algorithms, each one governed by a quantizer. In Theorems 3.2, 3.5, 3.11, we obtain quite precise a priori estimates.
In the last part, we address the compression of a matrix (a 2-D image) obtained by applying the DWT on an image mentioned in the first part. Embedded Zerotree Wavelet algorithm is introduced and implemented.
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Park, Youngcheol. "Dual-Band Transmitters Using Digitally Predistorted Frequency Multipliers for Reconfigurable Radios". Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5107.
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The objective of the proposed research is to develop simplified reconfigurable transmission systems with frequency multipliers for the transmission of complex modulated signals. Because they rely on nonlinear properties, frequency multiplier-based transmission systems require proper linearization techniques and accurate modeling of the signal transfer function. To accomplish these two goals, the author has developed techniques to model and linearize frequency multipliers and to digitize feedback signals for nonlinear characterization.
First, adaptive predistortion techniques and zonal transfer theories have been developed for modeling and linearization. The predistortion system has been verified by applying an IS-95B signal to various frequency multipliers built by the author.
Second, because the output signals at higher harmonic zones occupy wider frequency bandwidths than the signal in the fundamental zone does and thus make it harder to use traditional sampling techniques, a simplified but effective method called the sub-Nyquist sampling rate was developed and verified.
Third, two methods for reconfigurable transmitters using frequency multipliers in conjunction with digital predistortion linearizers were developed. Both methods make it possible to transmit complex signals via frequency multipliers by using dual-band transmission systems that incorporate frequency multipliers that are based on linearization techniques. One of these methods uses a circuit topology that can be switched between a fundamental-mode in-phase combined amplifier and a push-push frequency doubler using input phasing. The second suggested method uses a fundamental-frequency power amplifier followed by a varactor multiplier that can be bypassed with an RF switch.
This work will contribute to the development of low-cost and size-effective reconfigurable transmission systems because it requires fewer transmitting components and needs less sampling of the feedback networks.
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Pítra, Kamil. "Antény pro oblasti (sub)milimetrových vln". Doctoral thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2014. http://www.nusl.cz/ntk/nusl-233662.
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Disertační práce se zabývá návrhem a optimalizací kruhově polarizované anténa pro oblast terahertzových kmitočtů. V práci se věnuji zjednodušené teorii terahertzového zdroje a návrhu vhodné antény pro tento zdroj. Návrh je zaměřen na dosažení kruhové polarizace z lineárně polarizovaných antén. Abych potlačil šíření povrchové vlny na elektricky tlustém dielektrickém substrátu, věnuji se návrhu a optimalizaci specifických periodických struktur. Návrh těchto struktur je poměrně komplikovaný, protože neexistuje přímočarý vztah mezi vlastnostmi struktur s elektromagnetickým zádržným pásmem (EBG) a geometrií buňky. Abych vhodně koncentroval vyzařovanou energii do úzkého svazku, věnuji se návrhu a optimalizaci částečně odrazného plochy (PRS), které působí jako planární čočka pro terahertzovou anténu.
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Gonçalves, Alison Arantes. "Estudo da condutividade térmica de cristais fonônicos em temperaturas sub-kelvin". Universidade Federal de Juiz de Fora, 2016. https://repositorio.ufjf.br/jspui/handle/ufjf/1769.
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CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Nesta tese estudamos a estrutura de bandas de fônons e a condutividade térmica de cristais fonônicos em temperaturas sub-Kelvin. O espectro fonônico de baixas frequências (até dezenas de GHz) foi obtido da solução da equação de onda generalizada através do método de Expansão em Ondas Planas. Os resultados para estruturas com periodicidade bidimensional da ordem de mícrons apresentam band gaps e faixas estreitas de transmissão. Este comportamento é interessante para o controle de vibrações mecânicas como em um filtro de frequências operando na frequência de GHz. A densidade de estados foi calculada com o objetivo de estudar problemas de transporte envolvendo materiais fonônicos. Além disso, calculamos a condutividade térmica cumulativa no regime de temperaturas de sub-Kelvin em micro cristais fonônicos visando possíveis aplicações em materiais termoelétricos. Esses cálculos se baseiam na teoria de transporte de Boltzmann a baixas temperaturas a fim de enfatizar o papel dos fônons de baixa frequência e negligenciar o espalhamento fônon-fônon. Em acordo com resultados recentes na literatura, mostramos que a condutividade térmica cumulativa das estruturas fonônicas cai acentuadamente em relação a suas matrizes (bulk). Dependendo da estrutura esta redução pode ser atribuída à velocidade de grupo dos fônons, à densidade de estados ou à presença de band gaps completos.
In this thesis we have studied the phononic band structure and the thermal conductivity of phononic crystals at sub-Kelvin temperatures. The low-frequency phonon spectra (up to tens of GHz) were obtained by solving the generalized wave equation with the Plane Wave Expansion method. The results for structures with two dimensional periodicity of the order of micrometers show the presence of GHz band gaps and narrow pass band. Such behavior is suitable for mechanical vibrations management like a GHz transversal phononic band pass filter. The phonon density of states was calculated aiming the study in transport problems involving phononic materials. Moreover, we have calculated the cumulative thermal conductivity at sub-Kelvin temperature regime of micro-phononic crystals aiming possible applications in thermoelectrics materials. The calculations were based in Boltzmann transport theory at low temperatures in order to highlight the role of low-frequency thermal phonons and to neglect phonon-phonon scattering. In accordance with recent results in the literature, our findings show that the cumulative thermal conductivity of the phononic crystals drops dramatically when compared with their bulk counterpart. Depending on the structural composition this reduction may be attributed to the phonon group velocity, the density of states or the presence of complete band gaps.
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Aouimeur, Walid. "Systèmes de mesure intégré sub-millimétrique en bande G (140-220 GHz) en technologie BiCMOS 55 nm". Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAT046.
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Les applications microélectroniques telles que les communications sans fil ou les radars nécessitent des traitements d’information avec des débits ou des résolutions de plus en plus élevés. Cela implique de travailler à des fréquences millimétriques voir sub-millimétriques. Grâce aux progrès des technologies silicium, des circuits intégrés travaillant dans les gammes de fréquences millimétriques émergent mais souffrent d'un manque de solution de caractérisation complète. Par exemple, il n’existe à ce jour aucun analyseur vectoriel de réseaux commercial qui soit capable de mesurer les paramètres S dans la bande G (140-220 GHz) en 4 ports. La caractérisation classique des circuits millimétriques en n ports (avec n>2) consiste alors à utiliser un analyseur vectoriel de réseaux 2 ports et à adapter les autres ports non utilisés à 50Ω. Par permutation circulaire, on arrive ainsi à extraire la matrice S d’un dispositif à n ports (avec n>2). Ce protocole de mesure est très long et délicat à mettre en place car il nécessite d’une part un investissement en appareil de mesure très couteux aux fréquences millimétriques et d’autre part de mettre en œuvre des méthodes de calibrage et de de-embedding précises et dédiées.Le travail développé dans le cadre de cette thèse a visé à intégrer dans la puce, des systèmes de caractérisation petits signaux (paramètres S) au plus près du Dispositif Sous Test (DST). Le fait d’être au plus près du DST permet de réduire les pertes d’insertion, de réduire l’amplitude des vecteurs d’erreurs et donc les erreurs résiduelles après calibrage. Par ailleurs, il est possible de mieux contrôler la puissance du signal envoyé et de considérer des méthodes de calibrage utilisant des charges intégrées, ce qui permet de réduire le temps de traitement et le cout. La technologie utilisée est la technologie SiGe BiCMOS 55 nm développée par la société STMicroelectronics, technologie particulièrement adaptée aux circuits en bande millimétrique. La solution développée dans cette thèse consiste à connecter le wafer avec des pointes de mesure qui amènent un signal hyperfréquence balayant le spectre 35-55 GHz. Une fois dans la puce, ce signal hyperfréquence est quadruplé en fréquence et amplifié afin d’atteindre des niveaux de puissance suffisant (bon rapport Signal/bruit) dans la bande G aux bornes du DST. Les paramètres de réflexion (S11 et S22) sont ensuite extraits grâce à deux coupleurs très directifs, placés sur l’entrée et la sortie du DST respectivement. Les sorties du coupleur sont ensuite ramenées en basse fréquence (0.5GHz < IF < 2.4 GHz) par l’intermédiaire de mélangeurs de fréquence.L’approche choisie est argumentée en se basant sur une étude des systèmes de mesures existant présentée dans la première partie de ce manuscrit. Puis la conception et la caractérisation de chacun des blocs composant le système sont détaillées : le quadrupleur de fréquence en bande G (constitué d’un doubleur de fréquence en bande W cascadé avec un doubleur de fréquence en bande G), le transfert switch en bande G permettant de commuter entre l’entrée et la sortie du DST, le coupleur directif à ondes lentes, les mélangeurs permettant de ramener les mesures en basse fréquence, etc…. Une fois tous les différents blocs présentés, le manuscrit aborde les deux systèmes de mesure conçus. Un premier système un port a été développé pour valider cette approche. Le second système conçu permet de mesurer un DST à deux ports (HBT). Ce second système conserve l’architecture hétérodyne du premier, intégrant en plus un transfert switch en bande G qui dirige le signal incident vers l’un des deux ports du DSTMicroelectronic applications such as wireless communications, radar or space detections require higher data rate resolutions, implying the use of millimeter wave and submillimeter frequencies. Thanks to the silicon technologies improvement, some microelectronic circuits are emerging working in the frequency range of 140-220 GHz (G-band) but they suffer from a lack of complete characterization tools involving costly investment. For example, there is currently no commercial vectorial network analyser (VNA) that can measure S parameters in the 4-ports G-band. The classical characterization of millimeter wave circuits in n ports (with n> 2) consists in using a vectorial analyzer of 2-ports networks and matching the other unused ports to 50Ω. By circular permutation, one thus manages to extract the S matrix from a device with n ports (with n> 2). This set up induces very long and difficult measurements and it requires on the one hand some very expensive measuring equipment at millimeter frequencies and on the other hand to implement accurate and dedicated calibration and de-embedding methods.Therefore, the work developed into this PhD study aimed to integrate in the die the measurement systems that would measure small signals "S-parameters" of the device under test (DUT). Being closer to the DST makes it possible to reduce the insertion losses, to reduce the amplitude of the error vectors and thus the residual errors after calibration. Moreover, it is possible to better control the power of the signal sent and to consider calibration methods using integrated loads, which reduces the time and cost processing. The technology used is the SiGe BiCMOS 55 nm technology developed by STMicroelectronics, a technology dedicated to RF and millimeter wave’s circuits.The system developed is a 1-port system. The solution developed consists on connecting the wafer with some probes and driving it with an external signal that spans the 35-55 GHz band. Once into the die, this signal is then quadrupled in frequency and amplified to reach good power level in G band at the DUT inputs. Some S-parameters (S11 and S22) are extracted from the DUT thanks to some very directive couplers designed respectively at the input and at the output of the DUT. The outputs of the couplers are then converted to low frequencies (IF =0.5-2.4 GHz) through passive frequency mixers.In a first part of the thesis manuscript, the way to work is argued, supported by a study of the state of the art concerning the measurement systems. Then, design and characterization of each blocks of the system are detailed: the frequency quadrupler in G band (composed of a W band frequency doubler, followed with a G band frequency doubler), the fully integrated transfer switch in G-band allowing driving the millimeter waves signal to the DUT input or to the DUT output, the directive couplers based on the slow wave lines, the frequency mixers used to bring back the results in base band frequency, etc… All the different blocks detailed, the measurement systems can be introduced. A first system, a one-port measurement system, has been designed as a proof of concept. Once the approach validated, a second system, two-ports measurement system, has been developed presenting an heterodyne architecture and a transfer switch in G band driving the input signal toward the DUT input or output
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Guadiana, Juan, Fil Macias y Chris Braun. "A Smarter Antenna". International Foundation for Telemetering, 2011. http://hdl.handle.net/10150/595731.
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ITC/USA 2011 Conference Proceedings / The Forty-Seventh Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2011 / Bally's Las Vegas, Las Vegas, NevadaThe Isotropic radiator, a device capable of radiating energy evenly in all directions is an abstraction, itsʼ real counterpart is called an omnidirectional (omni) antenna. The omnidirectional antenna is found on many vehicles. Ideally, only one receiving system is ever needed to acquire an omni, no matter the vehicle orientation, given the range is not excessive. There are trade-offs with antenna efficiency, with gain typically around -15 dBi (95% coverage). This paper proposes abandoning this paradigm. If a vehicle knows where the ground is why radiate energy up into the sky, where there are no receiving stations. This can be achieved by integrating some instrumentation with a discrete antenna array so that it radiates only from selected elements. The accuracy required is modest, an inexpensive Inertial Measurement Unit (IMU) is sufficient to improve link margin by 10, 20dB or more. These numbers are credible, as outlandish as they are, and substantiated in this paper. Ironically, from the ground this non-isotropic antenna looks very isotropic. Of significant benefit, this Smarter Antenna concept enables spatial discrimination and with that comes spectrum efficiency gains beyond that achieved by other means including advanced modulation formats.
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Tzou, Nicholas. "Low-cost sub-Nyquist sampling hardware and algorithm co-design for wideband and high-speed signal characterization and measurement". Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51876.
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Cost reduction has been and will continue to be a primary driving force in the evolution of hardware design and associated technologies. The objective of this research is to design low-cost signal acquisition systems for characterizing wideband and high-speed signals. As the bandwidth and the speed of such signals increase, the cost of testing also increases significantly; therefore, innovative hardware and algorithm co-design are needed to relieve this problem.
In Chapter 2, a low-cost multi-rate system is proposed for characterizing the spectra of wideband signals. The design is low-cost in the sense of the actual component cost, the system complexity, and the effort required for calibration. The associated algorithms are designed such that the hardware can be implemented with low-complexity yet be robust enough to deal with various hardware variations. A hardware prototype is built not only to verify the proposed hardware scheme and algorithms but to serve as a concrete example that shows that characterizing signals with sub-Nyqusit sampling rate is feasible. Chapter 3 introduces a low-cost time-domain waveform reconstruction technique, which requires no mutual synchronization mechanisms. This brings down cost significantly and enables the implementation of systems capable of capturing tens of Gigahertz (GHz) signals for significantly lower cost than high-end oscilloscopes found in the market today. For the first time, band-interleaving and incoherent undersampling techniques are combined to form a low-cost solution for waveform reconstruction. This is enabled by co-designing the hardware and the back-end signal processing algorithms to compensate for the lack of coherent Nyquist rate sampling hardware. A hardware prototype was built to support this work. Chapter 4 describes a novel test methodology that significantly reduces the required time for crosstalk jitter characterization in parallel channels. This is done by using bit patterns with coprime periods as channel stimuli and using signal processing algorithms to separate multiple crosstalk coupling effects. This proposed test methodology can be applied seamlessly in conjunction with the current test methodology without re-designing the test setup. More importantly, the conclusion derived from the mathematical analysis shows that only such test stimuli give unbiased characterization results, which are critical in all high-precision test setups. Hardware measurement results and analysis are provided to support this methodology. This thesis starts with an overview of the background and a literature review. Three major previously mentioned works are addressed in three separate chapters. Each chapter documents the hardware designs, signal processing algorithms, and associated mathematical analyses. For the purpose of verification, the hardware measurement setups and results are discussed at the end of these three chapters. The last chapter presents conclusions and future directions for work from this thesis.
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Wang, Shenhong. "High-gain planar resonant cavity antennas using metamaterial surfaces". Thesis, Loughborough University, 2006. https://dspace.lboro.ac.uk/2134/12481.
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This thesis studies a new class of high gain planar resonant cavity antennas based on metamaterial surfaces. High-gain planar antennas are becoming increasing popular due to their significant advantages (e.g. low profile, small weight and low cost). Metamaterial surfaces have emerged over the last few years as artificial structures that provide properties and functionalities not readily available from existing materials. This project addresses novel applications of innovative metamaterial surfaces on the design of high-gain planar antennas. A ray analysis is initially employed in order to describe the beamfonning action of planar resonant cavity antennas. The phase equations of resonance predict the possibility of low-profile/subwavelength resonant cavity antennas and tilted beams. The reduction of the resonant cavity profile can be obtained by virtue of novel metamaterial ground planes. Furthermore, the EBG property of metamaterial ground planes would suppress the surface waves and obtain lower backlobes. By suppressing the TEM mode in a resonant cavity, a novel aperture-type EBG Partially Reflective Surface (PRS) is utilized to get low sidelobes in both planes (E-plane and H-plane) in a relatively finite structure. The periodicity optimization of PRS to obtain a higher maximum directivity is also investigated. Also it is shown that antennas with unique tilted beams are achieved without complex feeding mechanism. Rectangular patch antennas and dipole antennas are employed as excitations of resonant cavity antennas throughout the project. Three commercial electromagnetic simulation packages (Flomerics Microstripes ™ ver6.S, Ansoft HFSSTM ver9.2 and Designer ™ ver2.0) are utilized during the rigorous numerical computation. Related measurements are presented to validate the analysis and simulations.
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Huet, Karim. "MODELISATION DU TRANSPORT SOUS CONTRAINTE MECANIQUE DANS LES TRANSISTORS SUB-65 NM POUR LA MICROELECTRONIQUE CMOS". Phd thesis, Université Paris Sud - Paris XI, 2008. http://tel.archives-ouvertes.fr/tel-00491513.
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La course à la miniaturisation des transistors MOS (Métal Oxyde Semiconducteur) implique l'utilisation de nouvelles technologies d'amélioration des performances. Notamment, l'ingénierie de contrainte mécanique est aujourd'hui devenue une étape incontournable. Dans ce contexte, les objectifs de ce travail sont de modéliser les dispositifs des prochains nœuds technologiques et de quantifier l'impact de la contrainte mécanique sur le transport. La mobilité est le facteur de mérite principalement exploité pour quantifier les performances d'une technologie et l'un des paramètres clés des simulateurs commerciaux. Dans ce cadre, le concept de mobilité effective et de mobilité de magnétorésistance dans les dispositifs courts est analysé et le rôle prépondérant des effets non stationnaires dans leur extraction est clairement identifié et quantifié par des modèles avancés. Ensuite, grâce à la version « Full Band » du simulateur particulaire Monte Carlo MONACO développée durant cette thèse, l'influence de la contrainte sur la structure de bandes et ses répercussions sur le transport dans les transistors courts sont étudiées. En bande de valence, le régime balistique est loin d'être atteint et la mobilité reste représentative des performances. Enfin, l'impact de la contrainte uniaxiale sur la mobilité des trous en couche d'inversion est étudiée par le biais d'expériences de flexion mécanique. Grâce à l'outil de calcul de mobilité Kubo-Greenwood (couplé à une résolution autocohérente des équations de k.p Schrödinger à 6 bandes et de Poisson) développé dans cette thèse, les tendances observées sont expliquées par les forts couplages existants entre les effets de contrainte et de confinement des trous.
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Cheriton, Ross. "Design and Characterization of InGaN/GaN Dot-in-Nanowire Heterostructures for High Efficiency Solar Cells". Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/37905.
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Light from the sun is an attractive source of energy for its renewability, supply, scalability, and cost. Silicon solar cells are the dominant technology of choice for harnessing solar energy in the form of electricity, but the designs are approaching their practical efficiency limits. New multijunction designs which use the tunable properties of the more expensive III-V semiconductors have historically been relegated to space applications where absolute power conversion efficiency, resilience to radiation, and weight are more important considerations than cost. Some of the more recent developments in the field of semiconductor materials are the so-called III-nitride materials which mainly use either indium, aluminum or gallium in combination with nitrogen. Indium gallium nitride (InGaN) is one of these III-nitride semiconductor alloys that can be tailored to span the vast majority of the solar spectrum. While InGaN growth traditionally requires expensive substrate materials such as sapphire, three-dimensional nanowire growth modes enable high quality lattice mismatched growth of InGaN directly on silicon without a metamorphic buffer layer. The absorption and electronic properties of InGaN can also be tuned by incorporating it into quantum confined regions in a GaN host material. This opens up a route towards cost-effective, high efficiency devices such as light emitted diodes and solar cells which can operate over a large range of wavelengths. The combination of the two material systems of InGaN/GaN and silicon can marry the low cost of silicon wafers with the desirable optoelectronic properties of III-nitride semiconductors. This thesis investigates the potential for highly nanostructured InGaN/GaN based devices using quantum-dot-in-nanowire designs as novel solar cells which can enable intermediate band absorption effects and multiple junctions within a single nanowire to absorb more of the solar spectrum and operating more efficiently. Such semiconductor nanostructures can in principle reach power conversion efficiencies of over 40\% on silicon, with a cost closer to conventional silicon solar cells as opposed to methods which use non-silicon substrates.
In the primary strategy, the nanowires contain InGaN quantum dots which act as photon absorption/carrier generation centres to sequentially excite photons within the large band gap semiconductor. By using this intermediate band of states, large operating voltages between contacts can be maintained without sacrificing the collection of long wavelength solar photons. In this work, we characterize the properties of such nanowires and experimentally demonstrate sub-bandgap current generation in a large area InGaN/GaN dot-in-nanowire solar cell.
Experimental characterization of InGaN / GaN quantum dots in nanowires as both LEDs and solar cells is performed to determine the nanowire material parameters to understand how they relate to the nanowire device performance. Multiple microscopy techniques are performed to determine the nanowire morphology and contact effectiveness. Optical characterization of bare and fabricated nanowires is used to determine the anti-reflection properties of nanowire arrays. Photoluminescence and electroluminescence spectroscopy are performed. Illuminated current-voltage characteristics and quantum efficiencies are determined. Specular and diffuse reflectivities are measured as a function of wavelength.
Technology computer-aided design (TCAD) software is used to simulate the performance of the overall nanowire device. The contribution from quantum dots or quantum wells is simulated by solving for the carrier wavefunctions and density of states with the quantum structures. The discretized density of states from the quantum dots is modelled and used in a complete drift-diffusion device simulation to reproduce electroluminescence results. The carrier transport properties are modified to demonstrate effects on the overall device performance.
An alternate design is also proposed which uses an InGaN nanowire subcell on top of a silicon bottom subcell. The dual-junction design allows a broader absorption of the solar spectrum, increasing the operating voltage through monolithically grown series-connected, current-matched subcells. The performance of such a cell is simulated through drift-diffusion simulations of a dual-junction InGaN/Si solar cell. The effects of switching to a nanowire subcell based on the nanowires studied in this thesis is discussed.
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Brouder, Christian. "Contribution à l'étude des structures d'absorption X dans les solides : Application à l'amorphisation par réaction à l'état solide". Nancy 1, 1987. http://www.theses.fr/1987NAN10330.
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Étude des structures fines d'absorption X dans les solides et plus particulièrement les multicouches métalliques. Application de la spectrométrie d'absorption X à l'étude de la réorganisation structurale et de la diffusion dans les multicouches ND/FE, CO/SN et CE/NI. Description, dans l'approximation à un électron, des approches actuelles du problème de l'absorption X (fonction d'onde, fonction de green, structure de bande)
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Aluru, Radha Krishna. "Voltage Droop Analysis and Mitigation in STTRAM-based Last Level Cache". Scholar Commons, 2016. http://scholarcommons.usf.edu/etd/6455.
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Preferred especially for a Last Level Cache (LLC) due to its high retention and tolerance capabilities, Spin-Transfer Torque Random Access Memory (STTRAM) is an emerging and a promising Non-Volatile Memory (NVM) technology. To switch the magnetization of a Magnetic Tunnel Junction (MTJ), the amount of current needed is very high (~100μA per bit). For a full cache line (512-bit) write, this extremely high current results in a voltage droop in the conventional cache architecture. Due to this droop, the write operation fails especially when the farthest bank of the cache is accessed. In this thesis, we perform an analysis of the voltage droop across the STTRAM Last Level cache and then propose a new cache micro-architecture to mitigate the droop problem and make the write operations successful.
Instead of continuously writing the entire cache line (512-bit) in a single bank, the proposed architecture writes 64-bits in multiple physically separated locations across the cache. The voltage droop issue for crossbar memories such as Resistive RAM (ReRAM) has been pointed out but however, similar issue for STTRAM has never been investigated. In this study, we perform voltage droop analysis on the conventional STTRAM LLC while performing write/read operation with a simulation circuit model. Our investigation reveals that this problem exists for the write operation in a STTRAM LLC when we try to access the farthest bank in the cache. We propose a droop-mitigation Architecture which reduces the droop significantly. The effectiveness of this proposed architecture on the cache parameters such as latency and energy are compared with the conventional architecture for against various benchmarks. From the simulation results obtained (both circuit and micro-architectural), compared to the conventional architecture, the proposed architecture incurs 1.95% IPC and 5.21% energy for a 8MB last level cache.
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TERENZI, Alessandro. "Innovative Digital Signal Processing Methodologies for Identification and Analysis of Real Audio Systems". Doctoral thesis, Università Politecnica delle Marche, 2021. http://hdl.handle.net/11566/287822.
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Esistono molti sistemi audio reali e ciascuno ha le proprie caratteristiche ma tutti sono accomunati dal fatto che sono sistemi in grado di generare o modificare un suono. Se un sistema naturale o artificiale può essere definito come sistema sonoro, allora è possibile applicare le tecniche del digital signal processing per studiare il sistema ed emularne il comportamento. In questo lavoro di tesi si propone di introdurre delle metodologie innovative di processamento del segnale applicate ad alcuni sistemi sonori reali.
In particolare, vengono studiati e discussi tre diversi sistemi: il mondo dei dispositivi non lineari basati su valvole, con particolare attenzione agli amplificatori per chitarra e hi-fi, l'ambiente acustico di una stanza ed il suo effetto sulla propagazione del suono ed infine il suono emesso dalle api in un alveare.
Per quanto riguarda il primo sistema, vengono proposti dei contributi innovativi per l'identificazione di modelli come la serie di Volterra ed il modello di Hammerstein; in particolare viene discusso un approccio per superare alcune limitazioni dell'identificazione tramite serie di Volterra e l'applicazione di una struttura in sottobande per ridurre il costo computazionale e incrementare la velocità di convergenza di un algoritmo adattativo per l'identificazione del modello di Hammerstein. In ultima analisi, viene proposto un approccio innovativo in grado di stimare con una singola misura vari parametri di distorsione sfruttando un modello di Hammerstein generallizato.
Per quanto riguarda il secondo ambito, vengono proposti i risultati relativi a due applicazioni di equalizzazione multipunto: nel primo caso si mostrerà come l'equalizzazione può essere usata non solo per compensare le anomalie sonore generate all'interno di una stanza, ma anche per migliorare la risposta in frequenza di particolari trasduttori a vibrazione ancorati ad un pannello rigido; nel secondo caso si illustra come un approccio in sottobande può migliorare l'efficienza computazionale e la velocità di un algoritmo di equalizzazione adattativo multipunto e multicanale.
Infine, viene presentato un sistema sonoro naturale, ovvero quello generato da un alveare. In questo caso si illustrerà un sistema di acquisizione innovativo sviluppato per monitorare gli alveari con particolare attenzione al suono; succesivamente si mostrano gli approcci messi a punto per analizzare il suono registrato in due condizioni reali ed infine verranno si illustrano i risultati ottenuti grazie allo studio del suono usando algoritmi di classificazione.
Inoltre, nella parte finale dell'elaborato sono presenti dei contributi secondari ma che hanno comunque come focus principale il signal processing applicato ad ambienti acustici reali, in particolare si discute di un'implementazione di un algoritmo di cancellazione attiva del rumore e di due algoritmi per effetti digitali in cui il primo migliora le performance sonore di altoparlanti compatti, ed il secondo genera un effetto stereofonico per chitarra elettrica.Many real word audio systems exist, each has its own characteristics but almost all of them can be identified from the fact that they are able to generate or modify a sound. If a natural or artificial system can be defined as a sound system, then it is possible to apply the techniques of digital signal processing for the studying and the emulation of the system. In this thesis, innovative methodologies for digital signal processing applied to real audio systems will be discussed. In particular, three different audio systems will be considered: the world of vacuum-based non linear audio devices with particular attention to guitar and hi-fi amplifiers; the room acoustic environment and its effect on the sound propagation; and finally the sound emitted by honey bees in a beehive. Regarding the first system, innovative approaches for the identification of the Volterra series and Hammerstein models will be proposed, in particular an approach to overcome some limitation of Volterra series identification. The application of a sub-band structure to reduce the computational cost and increase the convergence speed of an adaptive Hammerstein model identification will be proposed as well. Finally, an innovative approach for the measurement of several distortion parameters using a single measure, exploiting a generalized Hammerstein model, will be presented. For the second system, the results of the application of a multi-point equalizer to two different situations will be exposed. In particular, in the first case, it will be shown how a multi-point equalization can be used not only to compensate the acoustical anomalies of a room, but also to improve the frequency response of vibrating transducers mounted on a rigid surface. The second contribution will show how a sub-band approach can be used to improve the computational cost and the speed of an adaptive algorithm for a multi-point and multi channel equalizer. At the end, the focus will be on a natural sound system, i.e., a honey bees colony. In this case, an innovative acquisition system for honey bees sound monitoring will be presented. Then, the approaches developed for sound analysis will be exposed and applied to the recorded sounds in two different situations. Finally, the obtained results, achieved with the application of classification algorithms, will be exposed. In the final part of the work some minor contributions still related to signal processing applied to real sound systems are presented. In particular, an implementation of an active noise control system is discussed, and two algorithms for digital effects where the former improves the sound performances of compact loudspeakers and the latter generates a stereophonic effect for electric guitars are exposed.
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NGU, BRYAN y Tsegaye Mesfin. "MEASURING COMMERCIAL BANK PERFORMANCE AND EFFICIENCY IN SUB-SAHARAN AFRICA". Thesis, University of Skövde, School of Technology and Society, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:his:diva-3736.
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This paper offers to measure efficiency of banks in Sub Saharan Africa and its determining input andout put factors on two fonts. At this purpose, we applied the first font; Data Envelopment Analysis(DEA) for assessing efficiency level. The actual and target level of inputs/outputs to foster efficiencyare shown in the results. Secondly, the banks ratio analysis measuring banks performance throughreturns volatility for each bank, asset utilization and provision for bad and doubtful debts over thestudy period are all used as tools for this analysis. Our results suggest that Sub Saharan AfricanBanks are about 98.35% efficient. We are aware that the level of efficiency could be subject to up anddown swing if environmental factors influencing banks efficiency where taken into consideration.Finally, our result (DEA) is more sensitive to loans, other liabilities, other non interest expense,securities and deposit.