Optimal cosine modulated nonuniform linear phase FIR filter bank design via stretching and shifting frequency response of prototype filter

This paper proposes an optimal cosine modulated nonuniform linear phase finite impulse response (FIR) filter bank design. The frequency responses of all the analysis filters and the synthesis filters of the filter bank are derived based on both stretching and shifting the frequency response of the prototype filter. The total aliasing error of the filter bank is minimized subject to a specification on the maximum amplitude distortion of the filter bank as well as specifications on both the maximum passband ripple magnitude and the maximum stopband ripple magnitude of the prototype filter. This filter bank design problem is actually a functional inequality constrained optimization problem. Our recently developed integration approach is employed for solving the problem. Computer numerical simulation results show that our proposed design method outperforms existing design methods

Spectral estimation using nonuniform sampling

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1995.Includes bibliographical references (leaves 98-99).by James Martin Nohrden.M.S

Approximate trigonometric expansions with applications to signal decomposition and coding

Signal representation and data coding for multi-dimensional signals have recently received considerable attention due to their importance to several modern technologies. Many useful contributions have been reported that employ wavelets and transform methods. For signal representation, it is always desired that a signal be represented using minimum number of parameters. The transform efficiency and ease of its implementation are to a large extent mutually incompatible. If a stationary process is not periodic, then the coefficients of its Fourier expansion are not uncorrelated. With the exception of periodic signals the expansion of such a process as a superposition of exponentials, particularly in the study of linear systems, needs no elaboration. In this research, stationary and non-periodic signals are represented using approximate trigonometric expansions. These expansions have a user-defined parameter which can be used for making the transformation a signal decomposition tool. It is shown that fast implementation of these expansions is possible using wavelets. These approximate trigonometric expansions are applied to multidimensional signals in a constrained environment where dominant coefficients of the expansion are retained and insignificant ones are set to zero. The signal is then reconstructed using these limited set of coefficients, thus leading to compression. Sample results for representing multidimensional signals are given to illustrate the efficiency of the proposed method. It is verified that for a given number of coefficients, the proposed technique yields higher signal to noise ratio than conventional techniques employing the discrete cosine transform technique

On the detection of ionospheric waves, relationship with earthquakes and tsunamis

The research of this thesis addresses the detection and characterization of ionospheric waves and its application to traveling ionospheric disturbances (TIDs) induced by the natural events, such as earthquakes and tsunamis. The characterization is done from regional detrended Vertical Total Electron Content (VTEC) maps which are obtained from a set of Global Navigation Satellite System (GNSS) satellites. Note that from the mathematical and signal-processing point of view, the problem presents two key difficulties that are (a) the fact that ionospheric sampling is nonuniform, with different density of samples that somehow reflect the distribution of stations over the earth surface, and (b), that the estimation method can not introduce any constraints in the number of disturbances and their propagation parameters. In the first contribution of the thesis, we propose a method for detecting the number of simultaneous TIDs from a time series of high-pass-filtered VTEC maps and their parameters. The method, which we refer to as the Atomic Decomposition Detector of TIDs (ADDTID), is tested on the detrended VTEC map corresponding to a simulated realistic scenario from the dense GNSS network, Global Positioning System Earth Observation Network (GEONET) in Japan. The contribution consists of the detection of the exact number of independent TIDs from a nonuniform sampling of the ionospheric pierce points. The solution to the problem is set as the estimation of the representative perturbations from a dictionary of atoms that span a linear space of possible TIDs by means of a variation of the LASSO algorithm. These atoms consist of plane waves characterized by a wavelength, direction, and phase on a surface defined, the part of the ionosphere sounded by the GNSS observation. As the second contribution, we apply ADDTID on actual VTEC data to the GEONET network. We have studied the Medium Scale TIDs (MSTIDs) during the Spring Equinox day of 21 March 2011. The geophysical contribution is: (a) detection of circular MSTID waves compatible by time and center with a specific earthquake; (b) simultaneous superposition of two distinct MSTIDs, with almost the same azimuth; and (c) the presence of nighttime MSTIDs with velocities in the range 400-600 m/s. In the third contribution we provide a detailed characterization of the TIDs originated from the total solar eclipse of 21 August 2017, the shadow of which crossed the United States from the Pacific to the Atlantic ocean. This can be modeled in part as if the umbra and penumbra were moving cylinders that intersects with variable elevation angle a curved surface. The result of this is reflected in the time evolution of the TID wavelengths produced by the eclipse, which depend on the vertical angle of the sun with the surface of the earth, and also a double bow wave phenomenon, where the bow waves are generated in advance to the umbra. Finally, we detected a clear pattern of MSTIDs, which appeared in advance of the penumbra, which we could hypothesize as soliton waves associated with the bow wave. In the fourth contribution we characterized the MSTIDs generated during the Japan Tohoku earthquake of 11 March 2011. We found: (a) a confirmation of the performance of the algorithm in face of simultaneous multi-TID, the robustness to the curvature of the wave fronts of the perturbations and the accuracy of the estimated parameters. The results were double checked by the additional visual inspection from VTEC maps and keogram plots; (b) The detection of different wave fronts between the west and east MSTIDs around the epicenter, consistent in time and space with the post-earthquake tsunami; (c) The complete evolution of the circular MSTIDs driven by the tsunami during the GNSS observable area; (d) The detection of the fast and short circular TIDs related to the acoustic waves of earthquake.Esta tesis aborda la detección y caracterización de las ondas ionosféricas y su aplicación a las perturbaciones ionosféricas itinerantes (TID traveling ionospheric disturbances) inducidas por eventos naturales. La caracterización se realiza a partir de mapas regionales de Contenido Total Vertical de Electrones (VTEC) que se obtienen a partir de medidas de un conjunto de satélites del Sistema Navegación GNSS (Global Navigation Satellite System). Obsérvese que, desde el punto de vista matemático y de procesamiento de señales, el problema presenta dos dificultades: a) el hecho de que el muestreo ionosférico no es uniforme, con una densidad de muestras diferente que refleja de alguna manera la distribución de las estaciones sobre la superficie terrestre, y b) el hecho de que el método de estimación no puede introducir ninguna limitación en el número de perturbaciones y sus parámetros de propagación a detectar. En la primera contribución de la tesis, proponemos un método para detectar el número de TIDs simultáneas de una serie temporal de mapas VTEC filtrados por paso alto y sus parámetros. El método, al que denominamos como el Detector de Descomposición Atómica de TIDs (ADDTID), lo probamos con mapas VTEC, que corresponden a un escenario realista simulado en la red GEONET en Japón. La contribución consiste en la detección del número exacto de TIDs independientes a partir de un muestreo no uniforme de los IPPs de la ionosférica. La solución al problema se establece como la estimación de las perturbaciones representativas a partir de un diccionario de átomos que abarcan un espacio lineal de posibles TIDs mediante una variación del algoritmo LASSO. Estos átomos consisten en ondas planas caracterizadas por una longitud de onda, dirección y fase en una superficie definida. Como segunda contribución, aplicamos ADDTID a los datos VTEC a la red GEONET. Para probar el método, hemos estudiado los MSTIDs durante el día del Equinoccio de Primavera del 21 de marzo de 2011. La contribución geofísica es: (a) la detección de ondas circulares MSTID compatibles por tiempo y centro con un terremoto específico; (b) la superposición simultánea de dos MSTID distintos, con casi el mismo acimut; y (c) la presencia durante la noche de MSTID con velocidades en el rango de 400-600 m/s. En la tercera contribución presentamos una caracterización detallada de los TIDs originados por el eclipse solar total del 21 de agosto de 2017, cuya sombra atravesó los Estados Unidos desde el Pacífico hasta el Océano Atlántico. La evolución temporal de las TID producidas por el eclipse, que dependen del ángulo vertical del sol con la superficie de la tierra, y también aparece en un fenómeno de doble onda de choque. Finalmente, detectamos un patrón claro de MSTIDs, que aparecieron antes de la llegada de la penumbra, lo que podríamos hipotetizar como ondas de solitón asociadas con la onda de choque. En la cuarta contribución caracterizamos los MSTIDs generados durante el terremoto de Tohoku en Japón el 11 de marzo de 2011. Lo encontramos: a) una confirmación de la prestación del algoritmo frente al multi-TID simultáneas, la robustez frente a la curvatura de los frentes de onda de las perturbaciones y la precisión en la estimación de los parámetros. Los resultados se verificaron por duplicado mediante la inspección visual adicional de los mapas de VTEC y de los diagramas de keogramas; b) la detección de diferentes frentes de onda entre los MSTID del oeste y del este en torno al epicentro, coherentes en el tiempo y en el espacio con el maremoto posterior al terremoto; c) la evolución completa de las MSTID circulares que impulsó el maremoto durante el período observable en la zona de observación de los GNSS; y d) la detección de las MSTID circulares cortas y rápidas en el espacio en relación con las ondas acústicas asociadas con el terremoto.Postprint (published version

Optophone design: optical-to-auditory vision substitution for the blind

An optophone is a device that turns light into sound for the benefit of blind people. The present project is intended to produce a general-purpose optophone to be worn on the head about the house and in the street, to give the wearer a detailed description in sound of the'scene he is facing. The device will therefore consist'of an'electronic camera, some signal-processing electronics, earphones`, and a battery. The two major problems are the derivation of (a) the most suitable mapping from images to sounds, and (b) an algorithm to perform the mapping in real'time on existing electronic components. This thesis concerns problem (a). Chapter 2 goes into the general scene-to-sound mapping problem in some detail'and presents the work of earlier investigators. Chapter 3 1- discusses the design of tests to evaluate the performance of candidate mappings. A theoretical performance test (TPT) is derived. Chapter 4 applies the TPT to the most obvious mapping, the cartesian piano transform. Chapter 5 applies the TPT to a mapping based on the cosine transform. Chapter 6 attempts to derive a mapping by principal component analysis, using the inaccuracies of human sight and hearing and the statistical properties of real scenes and sounds. Chapter 7 presents a complete scheme, implemented in software, for representing digitised colour scenes by audible digitised stereo sound. Chapter 8 tries to decide how'many numbers are required to specify a steady spectrum with no noticeable degradation. Chapter 9 looks'at a scheme designed to produce more natural-sounding sounds related to more meaningful portions of the scene. This scheme maps windows in the scene to steady spectral patterns of short duration, the location of the window being conveyed by simulated free-field listening. Chapter 10 gives detailed recommendations as to further work

Signal processing for high-definition television

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mathematics, 1995.Includes bibliographical references (p. 60-62).by Peter Monta.Ph.D

Doctor of Philosophy in Physics

dissertationThe Telescope Array (TA) experiment is the largest Ultra High Energy cosmic ray observatory in the northern hemisphere and is designed to be sensitive to cosmic ray air showers above 1018eV. Despite the substantial measurements made by TA and AUGER (the largest cosmic ray observatory in the southern hemisphere), there remains uncertainty about whether the highest energy cosmic rays are galactic or extragalactic in origin. Locating features in the cosmic ray energy spectrum below 1018eV that indicate a transi- tion from galactic to extragalactic sources would clarify the interpretation of measurements made at the highest energies. The Telescope Array Low Energy Extension (TALE) is designed to extend the energy threshold of the TA observatory down to 1016.5eV in order to make such measurements. This dissertation details the construction, calibration, and operation of the TALE flu- orescence detector. A measurement of the flux of cosmic rays in the energy range of 1016.5 1018.5eV is made using the monocular data set taken between September 2013 and January 2014. The TALE fluorescence detector observes evidence for a softening of the cosmic spectrum at 1017.25±0.5eV. The evidence of a change in the spectrum motivates continued study of 1016.5 1018.5eV cosmic rays

Structures of atypical chemokine receptor 3 reveal the basis for its promiscuity and signaling bias

Both CXC chemokine receptor 4 (CXCR4) and atypical chemokine receptor 3 (ACKR3) are activated by the chemokine CXCL12 yet evoke distinct cellular responses. CXCR4 is a canonical G protein–coupled receptor (GPCR), whereas ACKR3 is intrinsically biased for arrestin. The molecular basis for this difference is not understood. Here, we describe cryo-EM structures of ACKR3 in complex with CXCL12, a more potent CXCL12 variant, and a small-molecule agonist. The bound chemokines adopt an unexpected pose relative to those established for CXCR4 and observed in other receptor-chemokine complexes. Along with functional studies, these structures provide insight into the ligand-binding promiscuity of ACKR3, why it fails to couple to G proteins, and its bias toward β-arrestin. The results lay the groundwork for understanding the physiological interplay of ACKR3 with other GPCRs