The Gaussian assumption in second-order estimation problems in digital communications

This paper deals with the goodness of the Gaussian assumption when designing second-order blind estimationmethods in the context of digital communications. The low- andhigh-signal-to-noise ratio (SNR) asymptotic performance of the maximum likelihood estimator—derived assuming Gaussiantransmitted symbols—is compared with the performance of the optimal second-order estimator, which exploits the actualdistribution of the discrete constellation. The asymptotic study concludes that the Gaussian assumption leads to the optimalsecond-order solution if the SNR is very low or if the symbols belong to a multilevel constellation such as quadrature-amplitudemodulation (QAM) or amplitude-phase-shift keying (APSK). On the other hand, the Gaussian assumption can yield importantlosses at high SNR if the transmitted symbols are drawn from a constant modulus constellation such as phase-shift keying (PSK)or continuous-phase modulations (CPM). These conclusions are illustrated for the problem of direction-of-arrival (DOA) estimation of multiple digitally-modulated signals.

Statistical reference criteria for adaptive signal processing in digital communications

A general criterion for the design of adaptive systemsin digital communications called the statistical reference criterionis proposed. The criterion is based on imposition of the probabilitydensity function of the signal of interest at the outputof the adaptive system, with its application to the scenario ofhighly powerful interferers being the main focus of this paper.The knowledge of the pdf of the wanted signal is used as adiscriminator between signals so that interferers with differingdistributions are rejected by the algorithm. Its performance isstudied over a range of scenarios. Equations for gradient-basedcoefficient updates are derived, and the relationship with otherexisting algorithms like the minimum variance and the Wienercriterion are examined.

Hemerotecas de prensa digital: evolución y tendencias

Se analizan las hemerotecas digitales de los diarios españoles de mayor audiencia y difusión. Es un estudio evaluativo basado en 27 indicadores divididos en 4 grandes secciones: aspectos generales, contenidos, sistema de consulta y presentación de resultados. Se muestran los resultados de un análisis realizado en 2010, y se relacionan con los obtenidos anteriormente en 2007. Se señalan los aspectos mejores y peores de las hemerotecas de prensa digital, se establece un ranking de diarios en el que ocupan las primeras posiciones El mundo, Abc, El país y La vanguardia, y se destacan 5 grandes tendencias observadas: ampliación del fondo temporal online, hemerotecas gratuitas versus hemerotecas de pago, simplificación (y empobrecimiento) de la búsqueda, filtros en la presentación de resultados y productos documentales en la sección Hemeroteca

La sostenibilitat econòmica i tècnica dels repositoris de preservació digital

A partir d"una anàlisi de la bibliografia especialitzada, es presenten els aspectes institucionals, econòmics i tècnics que cal tenir en compte per assegurar la sostenibilitat dels repositoris de preservació digital. En els aspectes institucionals s"assenyala la importància de la cooperació entre institucions. En l"apartat tècnic, l"anàlisi dels costos mostra que les despeses d"emmagatzematge tenen menys pes que no pas es pensa i també es destaca la interrelació entre les dificultats de finançament i les decisions tècniques que afecten el disseny dels repositoris. Finalment s"explica la utilitat de l"aplicació dels sistemes d"auditoria (ISO 27000, Esquema Nacional de Seguretat, DRAMBORA, TRAC) per comprovar la fiabilitat dels sistemes de preservació.

Review of the concept of digital literacy and its implications on the study of the gender digital divide

El concepte d'alfabetització digital ha evolucionat per diverses vies al llarg del temps pel que fa a l'enfocament teòric emprat per a investigar les seves implicacions en l'estudi de la divisió digital de gènere en diversos contextos de la vida real. L'objectiu principal d'aquest document consisteix a fer servir un enfocament interdisciplinari per a analitzar algunes de les llacunes teòriques i empíriques presents en l'estudi de la divisió digital de gènere. S'analitzen alguns dels estudis empírics existents sobre aquesta qüestió i es proposen futures línies de recerca, amb l'objectiu de cobrir algunes de les llacunes en la recerca relacionada amb les implicacions de l'alfabetització digital en l'anàlisi de la divisió digital de gènere.

WiBed, A Platform for Commodity Wireless Testbeds

Testbeds are a stage between the simulation and the production stages. To this end they must be as close as possible to production environments (i.e. real hardware, on the field deployments) while also keeping the traits of experimentation facilities (i.e. fault tolerance, ease of deployment, testing and data collection). This paper presents WiBed, a FOSS platform for WiFi testbeds based on OpenWRT Linux made to run oncommodity IEEE802.11 WiFi routers part of the Community-lab.net project, a global testbed for Community networks. WiBedhas been designed to support realistic low layer network exper-iments (according to the OSI model). This work recolects thedetails of the architecture, design and implementation of WiBed consolidated during its operation as a testbed. In addition to a set of routing experimentation results obtained during the Wireless Battlemesh v7 where WiBed was used as testbed platform.

Modelado, simulación y control digital de autogiros

Este proyecto consiste en diseñar el algoritmo de control de un autogiro no tripulado. Su aplicación principal es llevar a cabo tareas rutinarias o peligrosas para el piloto como, por ejemplo, extinción de incendios, evaluación de riesgo químico o vigilancia de lugares de acceso restringido. Se realiza un estudio del movimiento del vehículo para obtener su modelo dinámico. A partir de las ecuaciones que describen su movimiento, se realiza una simulación numérica del vehículo. Se incorpora el controlador diseñado y se evalúa su funcionamiento. Finalmente, se implementa el sistema en un microcontrolador.

La situación de la venta de contenidos on line en España: un estudio del lector de prensa digital

Actualmente es una realidad la dificultad del cobro por servicios on line. Sobre todo si estos servicios son de carácter generalista y se reproducen en muchos sitios web. Las actuales iniciativas de algunos periódicos para cobrar no tienen todavía el suficiente valor añadido para que los usuarios paguen. Muchas veces el tráfico que pierden, y por lo tanto los ingresos de publicidad on line que dejan de ingresar, representan una mayor cantidad económica que el dinero que les suponen las nuevas suscripciones. En el presente trabajo se pretende estudiar el comportamiento de los lectores de diarios on line, identificando cuales son los principales elementos que este tipo de lectores valoran para posteriormente realizar una buena estrategia de contenidos de pago.

Guia de contingut digital accessible

La guia de contingut digital accessible està dissenyada per donar informació pas a pas sobre com estructurar, formatar i escriure un document realitzat amb Microsoft Word, OpenOffice Writer o Microsoft PowerPoint perquè siguin accessibles. Es descriu com transformar aquests documents a format PDF i mantenir, alhora, les seves propietats d’accessibilitat. També es descriuen aspectes d’accessibilitat que cal tenir en compte a l’hora d’introduir contingut web mitjançant les Sakai i OpenCMS.

Building a usable and accessible semantic web interaction platform

Semantic Web applications take off is being slower than expected, at least with respect to “real-world” applications and users. One of the main reasons for this lack of adoption is that most Semantic Web user interfaces are still immature from the usability and accessibility points of view. This is due to the novelty of these technologies, but this also motivates the exploration of alternative interaction paradigms, different from the “traditional” Web or Desktop applications ones. Our proposal is realized in the Rhizomer platform, which explores the possibilities of the object–action interaction paradigm at the Web scale. This paradigm is well suited for heterogeneous resource spaces such as those common in the Semantic Web. Resources, described by metadata, correspond to the objects in the paradigm. Semantic web services, which are dynamically associated to these objects, correspond to the actions. The platform is being put into practice in the context of a research project in order to build an open application for media distribution based on Semantic Web technologies. Moreover, its usability and accessibility have been evaluated in this real setting and compared to similar systems.

A web ontologies framework for digital rights management

In order to improve the management of copyright in the Internet, known as Digital Rights Management, there is the need for a shared language for copyright representation. Current approaches are based on purely syntactic solutions, i.e. a grammar that defines a rights expression language. These languages are difficult to put into practise due to the lack of explicit semantics that facilitate its implementation. Moreover, they are simple from the legal point of view because they are intended just to model the usage licenses granted by content providers to end-users. Thus, they ignore the copyright framework that lies behind and the whole value chain from creators to end-users. Our proposal is to use a semantic approach based on semantic web ontologies. We detail the development of a copyright ontology in order to put this approach into practice. It models the copyright core concepts for creation, rights and the basic kinds of actions that operate on content. Altogether, it allows building a copyright framework for the complete value chain. The set of actions operating on content are our smaller building blocks in order to cope with the complexity of copyright value chains and statements and, at the same time, guarantee a high level of interoperability and evolvability. The resulting copyright modelling framework is flexible and complete enough to model many copyright scenarios, not just those related to the economic exploitation of content. The ontology also includes moral rights, so it is possible to model this kind of situations as it is shown in the included example model for a withdrawal scenario. Finally, the ontology design and the selection of tools result in a straightforward implementation. Description Logic reasoners are used for license checking and retrieval. Rights are modelled as classes of actions, action patterns are modelled also as classes and the same is done for concrete actions. Then, to check if some right or license grants an action is reduced to check for class subsumption, which is a direct functionality of these reasoners.

Guia de contingut digital accessible: vídeo

La guia consta d’un conjunt de documents en format pdf i d’una web (http://www.videoaccessible.udl.cat) que es complementen per donar pautes, recomanacions i exemples necessaris per poder mostrar informació en format vídeo digital accessible per a les persones amb diferents discapacitats.

WiBed, a platform for commodity wireless testbeds

This paper presents WiBed, a FOSS platform for WiFi testbeds based on OpenWRT Linux made to run on commodity IEEE802.11 WiFi routers part of the Community-lab.net project, a global testbed for Community networks. WiBed has been designed to support realistic low layer network experiments (according to the OSI model). This work recolects the details of the architecture, design and implementation of WiBed consolidated during its operation as a testbed.

Estudi digital per a guitarra

El treball de fi de carrera "Estudi digital per a guitarra" fa una anàlisi d'un tipus de programari dedicat a la música, i més concretament a l'instrument de la guitarra. En ell s'analitzen programes per gravar àudio, editors de partitures, estudis d'àudio digital, efectes, emuladors, etc., tot muntat sobre un sistema GNU/Linux.

Televisión digital: aspectos generales

Análisis sobre la televisión digital, sus ventajas e inconvenientes. La Recomendación 601 del CCIRR (conversión analógica-digital). Cronología de los acontecimientos más interesantes ocurridos entre 1862 a 1988 que contribuyeron al desarrollo e implantación de la televisión.