A survey of the state-of-the-art and focused research in range systems

In this one-year renewal of NASA Contract No. 2-304, basic research, development, and implementation in the areas of modern estimation algorithms and digital communication systems have been performed. In the first area, basic study on the conversion of general classes of practical signal processing algorithms into systolic array algorithms is considered, producing four publications. Also studied were the finite word length effects and convergence rates of lattice algorithms, producing two publications. In the second area of study, the use of efficient importance sampling simulation technique for the evaluation of digital communication system performances were studied, producing two publications

Efficient BER simulation of orthogonal space-time block codes in Nakagami-m fading

In this contribution, we present a simple but efficient importance sampling technique to speed up Monte Carlo simulations for bit error rate estimation of orthogonal space-time block codes on spatially correlated Nakagami-m fading channels. While maintaining the actual distributions for the channel noise and the data symbols, we derive a convenient biased distribution for the fading channel that is shown to result in impressive efficiency gains up to multiple orders of magnitude

A simple importance sampling technique for orthogonal space-time block codes on Nakagami fading channels

In this contribution, we present a simple importance sampling technique to considerably speed up Monte Carlo simulations for bit error rate estimation of orthogonal space-time block coded systems on spatially correlated Nakagami fading channels

Transient behavior of an adaptive synchronous CDMA receiver

A steepest descent algorithm is used to update the adaptive weights of a two-stage synchronous Code-Division Multiple-Access (CDMA) receiver that was proposed recently. An issue of the adaptive CDMA system - the convergence and stability property of the receiver is investigated in this thesis. This adaptive synchronous CDMA receiver uses a decorrelator at the first stage and adopts a neural network which acts as an interference canceler at the second stage. It can achieve near-optimum performance. Furthermore, its computational complexity is just a square function of the number of users. The only requirement is the knowledge of the users\u27 signature sequences. The analysis shows that the algorithm for the adaptive weights is convergent and straightforward in implementation. The guaranteed fast convergence of the receiver weights and the tractable theoretical analysis on it, as revealed in this thesis, make this adaptive receiver a promising approach for wireless communications

Influencia del porcentaje de finos en la permeabilidad de materiales areno-arcillosos

Las mezclas areno-arcillosas son uno de los suelos más comunes en la ingeniería geotécnica Estos suelos presentan una permeabilidad que dependen mayormente de su contenido de finos, de la presión de confinamiento y de la distribución espacial del contenido de finos. Esta dependencia se puede complicar si se considera la migración de finos debido al flujo de agua. Existen diferentes métodos para realizar los ensayos de permeabilidad: el método más empleado corresponde a los permeámetros convencionales. Estos aparatos lamentablemente no garantizan la saturación de la muestra, en especial cuando contiene un porcentaje de finos, y tampoco controlan la presión de confinamiento de la muestra. Existen equipos más sofisticados sin estas limitaciones, por ejemplo, la Celda de Rowe, también llamado Hidrocom, que cuenta con un sistema de contrapresión para la saturación de muestra y un pistón para ejercer presión de confinamiento. Esta investigación busca comparar los resultados de permeabilidad en materiales areno – arcillosos obtenidos en un permeámetro de cabeza constante contra los adquiridos con una celda de Rowe. Para tal fin, se mezcla arena de Santo Tomás, Atlántico y una arcilla caolín en distintas proporciones. Con estos resultados, se evalúa la dependencia de la permeabilidad con respecto al porcentaje de finos. Se realizan además ensayos para cuantificar la migración de finos ante un gradiente hidráulico, y se realizan simulaciones numéricas en elementos finitos para medir la dependencia de la permeabilidad con la distribución espacial de los finos