A fast-initializing digital equalizer with on-line tracking for data communications

A theory is developed for a digital equalizer for use in reducing intersymbol interference (ISI) on high speed data communications channels. The equalizer is initialized with a single isolated transmitter pulse, provided the signal-to-noise ratio (SNR) is not unusually low, then switches to a decision directed, on-line mode of operation that allows tracking of channel variations. Conditions for optimal tap-gain settings are obtained first for a transversal equalizer structure by using a mean squared error (MSE) criterion, a first order gradient algorithm to determine the adjustable equalizer tap-gains, and a sequence of isolated initializing pulses. Since the rate of tap-gain convergence depends on the eigenvalues of a channel output correlation matrix, convergence can be improved by making a linear transformation on to obtain a new correlation matrix

1D fast coded aperture camera

A fast (100 MHz) 1D coded aperture visible light camera has been developed as a prototype for imaging plasma experiments in the EUV/X-ray bands. The system uses printed patterns on transparency sheets as the masked aperture and an 80 channel photodiode array (9 V reverse bias) as the detector. In the low signal limit, the system has demonstrated 40-fold increase in throughput and a signal-to-noise gain of ≈7 over that of a pinhole camera of equivalent parameters. In its present iteration, the camera can only image visible light; however, the only modifications needed to make the system EUV/X-ray sensitive are to acquire appropriate EUV/X-ray photodiodes and to machine a metal masked aperture

A study on number theoretic construction and prediction of two dimensional acoustic diffusers for architectural applications

Thesis (Doctoral)--İzmir Institute of Technology, Architecture, İzmir, 2011Includes bibliographical references (leaves: 72-77)Text in English; Abstract: Turkish and Englishxiv, 172 leavesDefined as the scattering of sound independent from angle, optimum diffusion is very important for the perception of musical sound. For this purpose, Schroeder used mathematical number sequences to propose ʼreflection phase grating diffusersʼ, of two main types: Single plane or one-dimensional (1D) diffusers that scatter sound into a hemi-disc, and two dimensional (2D) diffusers that scatter into a hemisphere to disperse strong specular reflections without removing sound energy from the space, which is the main advantage of these devices. Currently, two methods are used to design 2D diffusers:Product Array and Folding Array Methods. Both are based on number theory and used methodologically in the field of acoustics, producing results that offer limited diffusion characteristics and design solutions for a variety of architectural spaces ranging from concert halls to recording studios where Schroeder diffusers are widely used. This dissertation proposes Distinct Sums Property Method originally devised for watermarking digital images, to construct adoptable 2D diffusers through number theoretical construction and prediction. At first, quadratic residue sequence based on prime number 7 is selected according to its autocorrelation properties as the Fourier transform of good autocorrelation properties gives an even scattered energy distribution. Then Distinct Sums Property Method is applied to construct 2D arrays from this sequence from which well depths and widths are calculated. Third, the aimed scattering and diffusion properties of the modeled 2D diffuser are predicted by Boundary Element Method which gives approximate results in accordance with the measurements based on Audio Engineering Society Standards. Fourth, polar responses (i.e. the scattering diagrams for specific angles) in each octave band frequency are obtained. Finally, predicted diffusion coefficients for uniform scattering are calculated and compared to the reference flat surfaceʼs coefficients and previous studieʼs results

A detector interferometric calibration experiment for high precision astrometry

Context: Exoplanet science has made staggering progress in the last two decades, due to the relentless exploration of new detection methods and refinement of existing ones. Yet astrometry offers a unique and untapped potential of discovery of habitable-zone low-mass planets around all the solar-like stars of the solar neighborhood. To fulfill this goal, astrometry must be paired with high precision calibration of the detector. Aims: We present a way to calibrate a detector for high accuracy astrometry. An experimental testbed combining an astrometric simulator and an interferometric calibration system is used to validate both the hardware needed for the calibration and the signal processing methods. The objective is an accuracy of 5e-6 pixel on the location of a Nyquist sampled polychromatic point spread function. Methods: The interferometric calibration system produced modulated Young fringes on the detector. The Young fringes were parametrized as products of time and space dependent functions, based on various pixel parameters. The minimization of func- tion parameters was done iteratively, until convergence was obtained, revealing the pixel information needed for the calibration of astrometric measurements. Results: The calibration system yielded the pixel positions to an accuracy estimated at 4e-4 pixel. After including the pixel position information, an astrometric accuracy of 6e-5 pixel was obtained, for a PSF motion over more than five pixels. In the static mode (small jitter motion of less than 1e-3 pixel), a photon noise limited precision of 3e-5 pixel was reached

Quantum dimer model with Z_2 liquid ground-state: interpolation between cylinder and disk topologies and toy model for a topological quantum-bit

We consider a quantum dimer model (QDM) on the kagome lattice which was introduced recently [Phys. Rev. Lett. 89, 137202 (2002)]. It realizes a Z_2 liquid phase and its spectrum was obtained exactly. It displays a topological degeneracy when the lattice has a non-trivial geometry (cylinder, torus, etc). We discuss and solve two extensions of the model where perturbations along lines are introduced: first the introduction of a potential energy term repelling (or attracting) the dimers along a line is added, second a perturbation allowing to create, move or destroy monomers. For each of these perturbations we show that there exists a critical value above which, in the thermodynamic limit, the degeneracy of the ground-state is lifted from 2 (on a cylinder) to 1. In both cases the exact value of the gap between the first two levels is obtained by a mapping to an Ising chain in transverse field. This model provides an example of solvable Hamiltonian for a topological quantum bit where the two perturbations act as a diagonal and a transverse operator in the two-dimensional subspace. We discuss how crossing the transitions may be used in the manipulation of the quantum bit to optimize simultaneously the frequency of operation and the losses due to decoherence.Comment: 11 pages, 7 (.eps) figures. Improved discussion of the destruction of the topological degeneracy and other minor corrections. Version to appear in Phys. Rev.

Interferometric synthetic aperture sonar system supported by satellite

Tese de doutoramento. Engenharia Electrotécnica e de Computadores. Faculdade de Engenharia. Universidade do Porto. 200

Secuencias binarias y sus aplicaciones

ABSTRACT: The generation of families of sequences with a bounded correlation, among other properties, is of interest in several fields such as cryptography, wireless communications and digital watermarks. Commercial applications such as GPS or military uses such as Radar have been developed and improved thanks to the search of these sequences and the analysis of their autocorrelation function and the correlation between members of the same family. In this project, we focus on a technique for the algebraic construction of sequences where a sequence of shifts and a sequence with good properties generate a new sequence. The aim is the exhaustive search of longer sequences then the ones already present in the literature. To do so, a software intended to provide support to a designer has been developed to assist in the search of said sequences and check their properties, which can be deployed in a supercomputer. The applications of these sequences are, among others, radars and location systems with higher spatial resolution.RESUMEN: Generar familias de secuencias con correlación acotada, entre otras propiedades, es de interés en diversas áreas como criptografía, comunicaciones inalámbricas y marcas de agua digitales. Aplicaciones comerciales como el GPS, o con usos militares como el Radar se han desarrollado y mejorado a partir de la búsqueda de estas secuencias mediante el estudio de su función tanto de autocorrelación como de la correlación entre los miembros de una misma familia. En este proyecto, nos centramos en una técnica para la construcción algebraica de secuencias donde, a través de una secuencia de desplazamientos y una secuencia con buenas propiedades, se genera una nueva secuencia. El objetivo es la búsqueda exhaustiva de secuencias de mayor longitud que las ya existentes en la literatura. Para este fin, se ha desarrollado un software de apoyo al diseñador con capacidad de ser desplegado en un nodo de supercomputación para asistir a la búsqueda de dichas secuencias y la comprobación de sus propiedades. La finalidad de estas secuencias, entre otros posibles usos, son radares y sistemas de localización con mayor resolución espacial.Grado en Ingeniería Informátic

Design of tch-type sequences for communications

This thesis deals with the design of a class of cyclic codes inspired by TCH codewords. Since TCH codes are linked to finite fields the fundamental concepts and facts about abstract algebra, namely group theory and number theory, constitute the first part of the thesis. By exploring group geometric properties and identifying an equivalence between some operations on codes and the symmetries of the dihedral group we were able to simplify the generation of codewords thus saving on the necessary number of computations. Moreover, we also presented an algebraic method to obtain binary generalized TCH codewords of length N = 2k, k = 1,2, . . . , 16. By exploring Zech logarithm’s properties as well as a group theoretic isomorphism we developed a method that is both faster and less complex than what was proposed before. In addition, it is valid for all relevant cases relating the codeword length N and not only those resulting from N = p

Transformées basées graphes pour la compression de nouvelles modalités d’image

Due to the large availability of new camera types capturing extra geometrical information, as well as the emergence of new image modalities such as light fields and omni-directional images, a huge amount of high dimensional data has to be stored and delivered. The ever growing streaming and storage requirements of these new image modalities require novel image coding tools that exploit the complex structure of those data. This thesis aims at exploring novel graph based approaches for adapting traditional image transform coding techniques to the emerging data types where the sampled information are lying on irregular structures. In a first contribution, novel local graph based transforms are designed for light field compact representations. By leveraging a careful design of local transform supports and a local basis functions optimization procedure, significant improvements in terms of energy compaction can be obtained. Nevertheless, the locality of the supports did not permit to exploit long term dependencies of the signal. This led to a second contribution where different sampling strategies are investigated. Coupled with novel prediction methods, they led to very prominent results for quasi-lossless compression of light fields. The third part of the thesis focuses on the definition of rate-distortion optimized sub-graphs for the coding of omni-directional content. If we move further and give more degree of freedom to the graphs we wish to use, we can learn or define a model (set of weights on the edges) that might not be entirely reliable for transform design. The last part of the thesis is dedicated to theoretically analyze the effect of the uncertainty on the efficiency of the graph transforms.En raison de la grande disponibilité de nouveaux types de caméras capturant des informations géométriques supplémentaires, ainsi que de l'émergence de nouvelles modalités d'image telles que les champs de lumière et les images omnidirectionnelles, il est nécessaire de stocker et de diffuser une quantité énorme de hautes dimensions. Les exigences croissantes en matière de streaming et de stockage de ces nouvelles modalités d’image nécessitent de nouveaux outils de codage d’images exploitant la structure complexe de ces données. Cette thèse a pour but d'explorer de nouvelles approches basées sur les graphes pour adapter les techniques de codage de transformées d'image aux types de données émergents où les informations échantillonnées reposent sur des structures irrégulières. Dans une première contribution, de nouvelles transformées basées sur des graphes locaux sont conçues pour des représentations compactes des champs de lumière. En tirant parti d’une conception minutieuse des supports de transformées locaux et d’une procédure d’optimisation locale des fonctions de base , il est possible d’améliorer considérablement le compaction d'énergie. Néanmoins, la localisation des supports ne permettait pas d'exploiter les dépendances à long terme du signal. Cela a conduit à une deuxième contribution où différentes stratégies d'échantillonnage sont étudiées. Couplés à de nouvelles méthodes de prédiction, ils ont conduit à des résultats très importants en ce qui concerne la compression quasi sans perte de champs de lumière statiques. La troisième partie de la thèse porte sur la définition de sous-graphes optimisés en distorsion de débit pour le codage de contenu omnidirectionnel. Si nous allons plus loin et donnons plus de liberté aux graphes que nous souhaitons utiliser, nous pouvons apprendre ou définir un modèle (ensemble de poids sur les arêtes) qui pourrait ne pas être entièrement fiable pour la conception de transformées. La dernière partie de la thèse est consacrée à l'analyse théorique de l'effet de l'incertitude sur l'efficacité des transformées basées graphes