Multitone tracking with coupled EKFs and high order learning

A multitone tracker is described using two basic principles in optimum frequency estimation: processing bandwidth depending on the distance from the estimate to the actual frequency values, and parallel estimates with inhibitory paths to ensure orthogonality between the enhanced tones. The first feature is provided by extended Kalman filters (EKFs), and the second one is achieved by a high-order rule for the learning of the inhibitory cells. It is shown that the independence between signals is linked to the high-order function of the learning process. The resulting multitone tracker seems to be a potential alternative to adaptive high-resolution methods or time-frequency tools.Peer ReviewedPostprint (published version

The K-filter: a new model of non-linear systems with memory

Peer ReviewedPostprint (published version

Joint probability density function estimation by spectral estimate methods

The estimation of probability density functions (PDFs) of a given random variable (r.v.) is involved in topics related to codification, speech or whenever a short record of data is available but a greater amount is needed. Existing methods go from the so-called minimum description-length method, up to others based on the maximisation of the differential entropy imposing constraints on the moments of the r.v. In this paper we propose to estimate a PDF function by means of spectral estimate methods, since the positiveness and the real character of any PDF function allow us to deal with it as a power spectrum density function. Particularly, the minimum variance method is focused on because it can be generalised to multidimensional problems, being used in this paper to estimate the joint-PDF function of a multidimensional r.vPeer ReviewedPostprint (published version

A novel architecture to model non-linear systems

This paper shows a new architecture specially thought to model non-linear systems (NLSs). At first, it was applied only to memoryless systems but then it developed to solve a more general problem, NLSs with memory. The result is a new filter, based on the Fourier transform, that the authors have named “K-filter”. Important features of the K-filter are its nonlinear behaviour and second, that it profits from a temporal diversity of the input signal in order to provide itself with memory. At the end of the paper, the K-filter is used to solve an identification problem of a communication system which behaves nonlinearly due to the response of the amplifiers and which also has memory introduced basically by the channel response. The simulation results will provide an evaluation of the K-filter.Peer ReviewedPostprint (published version

Memoryless predistortion of nonlinear amplifiers based on Fourier series based models

In order to maximise the efficiency of the RF amplifier located in a transmitter, for instance in both analog and digital terrestrial TV links, it is forced to work near saturation thus introducing an undesirable nonlinear effect. A common solution includes a predistortion system before the modulation that compensates as much as possible the posterior nonlinear distortion, in such a way that the overall performance of the transmitter results in a linear and efficient amplifier. Polynomial models usually implement the predistortion, but we propose an alternative model based on the Fourier-exponential series that shows better performance in the design stage without a significant increase of the complexity.Peer ReviewedPostprint (published version

The K-filter: design alternatives to model non-linear systems

This paper presents an architecture named K-filter able to model non-linear systems both memoryless and with memory. The most general version of the k-filter applies to any non linearity but sometimes at the cost of holding a considerable computational load, specially when the memory of the non-linear system increases. Thus, the paper is basically devoted to present how different simpler versions of the original k-filter can be obtained taking into account symmetrical properties of the input/output relation of the non-linear system to model. The theoretical points along with the simulation results will show how these symmetrical considerations simplify the k-filter without making worse the performance.Peer ReviewedPostprint (published version

Nonlinear system inversion applied to random variable generation

A method to design random variable (RV) generators with the same probability density function (PDF) as a given RV record is presented. The resulting RV generator is a nonlinear system that when driven by a uniformly distributed RV, provides an output RV with the desired PDF distribution. The analytical description of the desired PDF is not needed; in fact, only a data record of the desired RV is used. Inversion of nonlinear systems and nonlinear system adaptive design are used.Peer ReviewedPostprint (published version

Mechanical Isolation of Highly Stable Antimonene under Ambient Conditions

Using mechanical exfoliation combined with a controlled double step transfer procedure we demonstrate that single layers of antimony can be readily produced. These flakes are not significantly contaminated upon exposure to ambient conditions and they do not react with water. DFT calculations confirm our experimental observations and predict a band gap of 1.2-1.3 eV (ambient conditions) for single layer antimonene, which is smaller than that calculated under vacuum conditions at 0 K. Our work confirms antimonene as a highly stable 2D material with promising relevant applications in optoelectronics.Comment: main paper: 5 pages, 4 figures supporting: 9 pages, 7 figures, Advanced Materials, 201

Proceso adaptativo para la implantación de ABP en materias de sistemas embebidos

Una de las metodologías activas que más aceptación está teniendo es el Aprendizaje Basado en Proyectos (ABP), que presenta una adaptación perfecta en enseñanzas técnicas, ya que los futuros ingenieros tendrán que adoptar metodologías similares en el mundo laboral. El presente trabajo ofrece una guía de buenas prácticas y un marco perfecto de discusión sobre ABP, llevadas a cabo en dos asignaturas. En el artículo se explican los cambios hechos en las asignaturas objeto de estudio, hasta llegar al punto actual de implantación del ABP, y se describe la metodología seguida en el pasado curso. Los resultados de esta experiencia muestran las mejoras en las calificaciones, la calidad del aprendizaje y la mayor motivación del alumno. Finalmente, se discuten los principales inconvenientes y las cuestiones de mayor importancia que se han de considerar en un proceso adaptativo de esta índole.Los autores agradecen al Ministerio de Educación y Ciencia la financiación ofrecida dentro del programa FPU, con la beca AP2005-1437. Este trabajo ha sido llevado a cabo dentro del grupo de investigación de Sistemas Inteligentes, incluido dentro del Registro de Grupos de Excelencia de la Fundación Séneca-Agencia de Ciencia y Tecnología de la Región de Murcia, con la subvención 04552/GERM/06

The K-filter: a new architecture to model and design non-linear systems from Kolmogorov's theorem

A new architecture to model and design nonlinear transfer functions is presented using a new formulation for nonlinear systems. This approach follows the guidelines of the mapping theorem due to A. Kolmogorov and it is based on the direct Fourier transform of the transfer function. The resulting scheme is formed by two stages; the first stage contains phase modulators, which, based on random sampling concepts reported by I. Bilinskis, are duplicated with a small perturbation in the modulation factor. This stage depends on the number of diversity data and it is independent of the function. The second step reduces to Volterra systems and a direct combiner of the new diversity kernels. The reported architecture and design seem to be able to cope with both linear and nonlinear filtering problems, which can be considered as a formal framework for generalised signal processing.Peer ReviewedPostprint (published version