Resultados de la búsqueda176 resultados

Subgaussian rotationinvariant features for steerable waveletbased image retrieval
Tzagkarakis, G.; BeferullLozano, B.; Tsakalides, P.
(2004). ArticleThis paper presents a new rotationinvariant image retrieval method, which extends a recently introduced classification technique based on steerable wavelet transforms. In the proposed procedure, the feature extraction step consists of estimating the covariations (lowerorder crosscorrelations) between the wavelet subband coefficients, which are modeled as subGaussian random vectors. The similarity measurement is carried out first by employing norms calculating the distance between the covariation matrices representing two distinct images and second by evaluating the KullbackLeibler Distance (KLD) between their corresponding subGaussian distributions. We provide analytical expressions...
This paper presents a new rotationinvariant image retrieval method, which extends a recently introduced classification technique based on steerable wavelet transforms. In the proposed procedure, the feature extraction step consists of estimating the covariations (lowerorder crosscorrelations) between the wavelet subband coefficients, which are modeled as subGaussian random vectors. The similarity measurement is carried out first by employing norms calculating the distance between the covariation matrices representing two distinct images and second by evaluating the KullbackLeibler Distance (KLD) between their corresponding subGaussian distributions. We provide analytical expressions relating the subGaussian features corresponding to a rotated image from the features of the original image. Finally, we relate the employed optimal lowerorder correlation (p≤2) to the degree of nonGaussianity of the wavelet coefficients, and we demonstrate the effectiveness of our method using real texture images.
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Lattice Sensor Networks: Capacity Limits, Optimal Routing and Robustness to Failures
Barreneche, G.; BeferullLozano, B.; Vetterli, M.
(2004). ArticleWe study network capacity limits and optimal routing algorithms for regular sensor networks, namely, square and torus grid sensor networks, in both, the static case (no node failures) and the dynamic case (node failures). For static networks, we derive upper bounds on the network capacity and then we characterize and provide optimal routing algorithms whose rate per node is equal to this upper bound, thus, obtaining the exact analytical expression for the network capacity. For dynamic networks, the unreliability of the network is modeled in two ways: a Markovian node failure and an energy based node failure. Depending on the probability of node failure that is present in the network, we...
We study network capacity limits and optimal routing algorithms for regular sensor networks, namely, square and torus grid sensor networks, in both, the static case (no node failures) and the dynamic case (node failures). For static networks, we derive upper bounds on the network capacity and then we characterize and provide optimal routing algorithms whose rate per node is equal to this upper bound, thus, obtaining the exact analytical expression for the network capacity. For dynamic networks, the unreliability of the network is modeled in two ways: a Markovian node failure and an energy based node failure. Depending on the probability of node failure that is present in the network, we propose to use a particular combination of two routing algorithms, the first one being optimal when there are no node failures at all and the second one being appropriate when the probability of node failure is high. The combination of these two routing algorithms defines a family of randomized routing algorithms, each of them being suitable for a given probability of node failure.
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RateDistortion Problem for Physics Based Distributed Sensing
BeferullLozano, B.; Konsbruck, Robert L.; Vetterli, M.
(2004). ArticleWe consider the ratedistortion problem for sensing the continuous spacetime physical temperature in a circular ring on which a heat source is applied over space and time, and which is also allowed to cool by radiation or convection to its surrounding medium. The heat source is modelled as a continuous spacetime stochastic process which is bandlimited over space and time. The temperature field is the result of a circular convolution over space and a continuoustime causal filtering over time of the heat source with the Green's function corresponding to the heat equation, which is space and time invariant. The temperature field is sampled at uniform spatial locations by a set of sensors...
We consider the ratedistortion problem for sensing the continuous spacetime physical temperature in a circular ring on which a heat source is applied over space and time, and which is also allowed to cool by radiation or convection to its surrounding medium. The heat source is modelled as a continuous spacetime stochastic process which is bandlimited over space and time. The temperature field is the result of a circular convolution over space and a continuoustime causal filtering over time of the heat source with the Green's function corresponding to the heat equation, which is space and time invariant. The temperature field is sampled at uniform spatial locations by a set of sensors and it has to be reconstructed at a base station. The goal is to minimize the meansquareerror per second, for a given number of nats per second, assuming ideal communication channels between sensors and base station. We find a) the centralized Rc (D) function of the temperature field, where all the spacetime samples can be observed and encoded jointly. Then, we obtain b) the Rsi (D) function, where each sensor, independently, encodes its samples optimally over time and c) the Rsti (D) function, where each sensor is constrained to encode also independently over time. We also study two distributed predictionbased approaches: a) with perfect feedback from the base station, where temporal prediction is performed at the base station and each sensor performs differential encoding, and b) without feedback, where each sensor locally performs temporal prediction.
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Visual Representation Of Enhanced Sand Pile Models
Pla Castells, M.; García Fernández, I.; Martínez Durá, R. J.
(2003). ArticleProceedings of the Industrial Simulation Conference 2003, 141146 This paper overviews some models based on the Chip Firing Game and propose a modification of the Abelian Sand Pile Model in a lattice in order to implement a realistic simulation of a pile of sand falling and finding an stable configuration. We have modified the update rule in the way that now is based on the comparision among neighbour nodes. We found that the simulations can be suitable for doing them in real time and propose as a future work a better solution to reduce the computational cost of the algorithms.

New Models for Fast Contact Force Computation
García Fernández, I.; Pla Castells, M.; martínez Durá, R. J.
(2003). ArticleProceedings of the Industrial Simulation Conference 2003, 401407 This work focuses on the subject of impact response modeling in Real Time rigid body simulation, and more precisely in those applications where a very high accuracy in the solution is not required. The problem of impact response has several aspects to overcome, such as the instantaneous nature of the forces that appear during the contact, the absence of a unique solution in the case of contacts with friction, of the stiffness of the resultant models. This makes the impact management to be one of the most problematic parts to resolve during the implementation of computational models for rigid body systems. We present a model...
Proceedings of the Industrial Simulation Conference 2003, 401407 This work focuses on the subject of impact response modeling in Real Time rigid body simulation, and more precisely in those applications where a very high accuracy in the solution is not required. The problem of impact response has several aspects to overcome, such as the instantaneous nature of the forces that appear during the contact, the absence of a unique solution in the case of contacts with friction, of the stiffness of the resultant models. This makes the impact management to be one of the most problematic parts to resolve during the implementation of computational models for rigid body systems. We present a model for contacts that is much simpler than the usual methods and that achieves an accuracy of the same order than the integration step size respect to the usual method. The model is valid both for frictional and nonfrictional contacts.
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Nested trellis codes and shaping for the transmitter side information problem
BeferullLozano, B.; Diggavi, S.
(2003). ArticleIn this paper, we specifically focus on the problem of power shaping and we examine nested constructions based on trellis codes, which build on simple low dimensional lattices. We propose the idea of performing shaping through a coarse lattice (source code) and we also show how this method can actually be combined with shaping through a fine lattice (channel code) so that a joint shaping can be performed by the fine and coarse lattices in the communication channel with transmitter sideinformation simultaneously.

Efficient Quantization for Overcomplete Expansions in R^n
BeferullLozano, B.; Ortega, A.
(2003). ArticleWe study construction of structured regular quantizers for overcomplete expansions in RN. Our goal is to design structured quantizers which allow simple reconstruction algorithms with low complexity and which have good performance in terms of accuracy. Most related work to date in quantized redundant expansions has assumed that the same uniform scalar quantizer was used on all the expansion coefficients. Several approaches have been proposed to improve the reconstruction accuracy, with some of these methods having significant complexity. Instead, we consider the joint design of the overcomplete expansion and the scalar quantizers (allowing different step sizes) in such a way as to produce...
We study construction of structured regular quantizers for overcomplete expansions in RN. Our goal is to design structured quantizers which allow simple reconstruction algorithms with low complexity and which have good performance in terms of accuracy. Most related work to date in quantized redundant expansions has assumed that the same uniform scalar quantizer was used on all the expansion coefficients. Several approaches have been proposed to improve the reconstruction accuracy, with some of these methods having significant complexity. Instead, we consider the joint design of the overcomplete expansion and the scalar quantizers (allowing different step sizes) in such a way as to produce an equivalent vector quantizer (EVQ) with periodic structure. The construction of a periodic quantizer is based on lattices in RN and the concept of geometrically scaled similar sublattices. The periodicity makes it possible to achieve good accuracy using simple reconstruction algorithms (e.g., linear reconstruction or a small lookup table).
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Quantizing using lattice intersections, Discrete and Computational Geometry
Sloane, N. J. A.; BeferullLozano, B.
(2003). ArticleThe usual quantizer based on an ndimensional lattice # maps a point x # R n to a closest lattice point. Suppose # is the intersection of lattices # 1 , . . . , # r . Then one may instead combine the information obtained by simultaneously quantizing x with respect to each of the # i . This corresponds to decomposing R n into a honeycomb of cells which are the intersections of the Voronoi cells for the # i , and identifying the cell to which x belongs. This paper shows how to write several standard lattices (the facecentered and bodycentered cubic lattices, the root lattices D 4 , E # 6 , E 8 , the CoxeterTodd, BarnesWall and Leech lattices, etc.) in a canonical way as intersections of a...
The usual quantizer based on an ndimensional lattice # maps a point x # R n to a closest lattice point. Suppose # is the intersection of lattices # 1 , . . . , # r . Then one may instead combine the information obtained by simultaneously quantizing x with respect to each of the # i . This corresponds to decomposing R n into a honeycomb of cells which are the intersections of the Voronoi cells for the # i , and identifying the cell to which x belongs. This paper shows how to write several standard lattices (the facecentered and bodycentered cubic lattices, the root lattices D 4 , E # 6 , E 8 , the CoxeterTodd, BarnesWall and Leech lattices, etc.) in a canonical way as intersections of a small number of simpler, decomposable, lattices. The cells of the honeycombs are given explicitly and the mean squared quantizing error calculated in the cases when the intersection lattice is the facecentered or bodycentered cubic lattice or the lattice D 4 . 1.
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Diseño Interactivo de Escenarios para Simulación de Conducción
Coma, Inmaculada;Rueda, Silvia; Sánchez, Mar; Fernández, Marcos
(2002). ArticleRevista de Enseñanza y Tecnología.
El diseño de escenarios para simulación de conducción es una tarea compleja ya que requiere, por una parte el diseño del escenario tridimensional, y por otra el diseño de las situaciones dinámicas de conducción. Habitualmente estos escenarios se diseñan utilizando herramientas de modelado de propósito general, y mediante un lenguaje de programación o un lenguaje script para el diseño de las situaciones dinámicas. En el presente trabajo se presenta una herramienta que permite tanto el diseño de la escena como las situaciones dinámicas mediante un interfaz. Esta herramienta funciona sobre plataforma Windows. El diseño de escenarios para simulación de conducción es una tarea compleja ya que...
El diseño de escenarios para simulación de conducción es una tarea compleja ya que requiere, por una parte el diseño del escenario tridimensional, y por otra el diseño de las situaciones dinámicas de conducción. Habitualmente estos escenarios se diseñan utilizando herramientas de modelado de propósito general, y mediante un lenguaje de programación o un lenguaje script para el diseño de las situaciones dinámicas. En el presente trabajo se presenta una herramienta que permite tanto el diseño de la escena como las situaciones dinámicas mediante un interfaz. Esta herramienta funciona sobre plataforma Windows. El diseño de escenarios para simulación de conducción es una tarea compleja ya que requiere, por una parte el diseño del escenario tridimensional, y por otra el diseño de las situaciones dinámicas de conducción. Habitualmente estos escenarios se diseñan utilizando herramientas de modelado de propósito general, y mediante un lenguaje de programación o un lenguaje script para el diseño de las situaciones dinámicas. En el presente trabajo se presenta una herramienta que permite tanto el diseño de la escena como las situaciones dinámicas mediante un interfaz. Esta herramienta funciona sobre plataforma Windows.
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Robust phoneme discrimination using acoustic waveforms
Cvetkovic, Z.; BeferullLozano, B.; Buja, A.
(2002). ArticleWe present a study of separability of acoustic waveforms of speech at phoneme level. The analyzed data consist of 64 ms segments of acoustic waveforms of individual phonemes from TIMIT data base, sampled at 16 kHz. For each phoneme, by means of principal component analysis, we identify subspaces which contain a given proportion of the total energy of the available waveforms in the timedomain, and also in the spectralmagnitude domain. In order to assess the separation between phonemes in the two domains, we perform pairwise classification of phonemes on clean data and on data immersed in white additive Gaussian noise up to 0 dB signal to noise ratio. While the classification based on...
We present a study of separability of acoustic waveforms of speech at phoneme level. The analyzed data consist of 64 ms segments of acoustic waveforms of individual phonemes from TIMIT data base, sampled at 16 kHz. For each phoneme, by means of principal component analysis, we identify subspaces which contain a given proportion of the total energy of the available waveforms in the timedomain, and also in the spectralmagnitude domain. In order to assess the separation between phonemes in the two domains, we perform pairwise classification of phonemes on clean data and on data immersed in white additive Gaussian noise up to 0 dB signal to noise ratio. While the classification based on spectral magnitudes exhibits high sensitivity to additive noise, the timedomain classification proves to be very robust.
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