Spectrum sensing via universal source coding

We consider nonparametric sequential hypothesis testing when the distribution under null hypothesis is fully known and the alternate hypothesis corresponds to some other unknown distribution. We use easily implementable universal lossless source codes to propose simple algorithms for such a setup. These algorithms are motivated from spectrum sensing application in Cognitive Radios. Universal sequential hypothesis testing using Lempel Ziv codes and Krichevsky-Trofimov estimator with Arithmetic Encoder are considered and compared for different distributions. Cooperative spectrum sensing with multiple Cognitive Radios using universal codes is also considered.

Optimal capacity relay node placement in a multi-hop network on a line

We use information theoretic achievable rate formulas for the multi-relay channel to study the problem of optimal placement of relay nodes along the straight line joining a source node and a destination node. The achievable rate formulas that we utilize are for full-duplex radios at the relays and decode-and-forward relaying. For the single relay case, and individual power constraints at the source node and the relay node, we provide explicit formulas for the optimal relay location and the optimal power allocation to the source-relay channel, for the exponential and the power-law path-loss channel models. For the multiple relay case, we consider exponential path-loss and a total power constraint over the source and the relays, and derive an optimization problem, the solution of which provides the optimal relay locations. Numerical results suggest that at low attenuation the relays are mostly clustered close to the source in order to be able to cooperate among themselves, whereas at high attenuation they are uniformly placed and work as repeaters. We also prove that a constant rate independent of the attenuation in the network can be achieved by placing a large enough number of relay nodes uniformly between the source and the destination, under the exponential path-loss model with total power constraint.

Modeling Time-Varying Aggregate Interference in Cognitive Radio Systems, and Application to Primary Exclusive Zone Design

Accurately characterizing the time-varying interference caused to the primary users is essential in ensuring a successful deployment of cognitive radios (CR). We show that the aggregate interference at the primary receiver (PU-Rx) from multiple, randomly located cognitive users (CUs) is well modeled as a shifted lognormal random process, which is more accurate than the lognormal and the Gaussian process models considered in the literature, even for a relatively dense deployment of CUs. It also compares favorably with the asymptotically exact stable and symmetric truncated stable distribution models, except at high CU densities. Our model accounts for the effect of imperfect spectrum sensing, which depends on path-loss, shadowing, and small-scale fading of the link from the primary transmitter to the CU; the interweave and underlay modes or CR operation, which determine the transmit powers of the CUs; and time-correlated shadowing and fading of the links from the CUs to the PU-Rx. It leads to expressions for the probability distribution function, level crossing rate, and average exceedance duration. The impact of cooperative spectrum sensing is also characterized. We validate the model by applying it to redesign the primary exclusive zone to account for the time-varying nature of interference.

Spectrum sensing using distributed sequential detection via noisy reporting MAC

This paper considers cooperative spectrum sensing algorithms for Cognitive Radios which focus on reducing the number of samples to make a reliable detection. We propose algorithms based on decentralized sequential hypothesis testing in which the Cognitive Radios sequentially collect the observations, make local decisions and send them to the fusion center for further processing to make a final decision on spectrum usage. The reporting channel between the Cognitive Radios and the fusion center is assumed more realistically as a Multiple Access Channel (MAC) with receiver noise. Furthermore the communication for reporting is limited, thereby reducing the communication cost. We start with an algorithm where the fusion center uses an SPRT-like (Sequential Probability Ratio Test) procedure and theoretically analyze its performance. Asymptotically, its performance is close to the optimal centralized test without fusion center noise. We further modify this algorithm to improve its performance at practical operating points. Later we generalize these algorithms to handle uncertainties in SNR and fading. (C) 2014 Elsevier B.V. All rights reserved.

Differential Multi-phase DLL for Reconfigurable Radio Frequency Synthesizer

A multi phase, delay-locked loop (DLL) based frequency synthesizer is designed for harmonic rejection mixing in reconfigurable radios. This frequency synthesizer uses a 1 GHz input reference frequency, and achieves <= 20ns settling time by utilizing a wide loop bandwidth. The circuit has been designed in 0.13-mu m CMOS technology. It is designed for a frequency range of 500 MHz to 3 GHz with stuck/harmonic lock removal assist. Index Terms-stuck lock, harmonic lock, delay-locked loops, multi phase, phase detector, frequency synthesis

A 0.5-2.0 GHz injection locked oscillator cascade for parallel wideband RF spectrum sensing

An area-efficient, wideband RF frequency synthesizer, which simultaneously generates multiple local oscillator (LO) signals, is designed. It is suitable for parallel wideband RF spectrum sensing in cognitive radios. The frequency synthesizer consists of an injection locked oscillator cascade (ILOC) where all the LO signals are derived from a single reference oscillator. The ILOC is implemented in a 130-nm technology with an active area of . It generates 4 uniformly spaced LO carrier frequencies from 500 MHz to 2 GHz. This design is the first known implementation of a CMOS based ILOC for wide-band RF spectrum sensing applications.

Near-Optimal Detection Thresholds for Bayesian Spectrum Sensing Under Fading

This paper considers the problem of energy-based, Bayesian spectrum sensing in cognitive radios under various fading environments. Under the well-known central limit theorem based model for energy detection, we derive analytically tractable expressions for near-optimal detection thresholds that minimize the probability of error under lognormal, Nakagami-m, and Weibull fading. For the Suzuki fading case, a generalized gamma approximation is provided, which saves on the computation of an integral. In each case, the accuracy of the theoretical expressions as compared to the optimal thresholds are illustrated through simulations.

Multi-dimensional Goodness-of-Fit Tests for Spectrum Sensing Based on Stochastic Distances

In this paper, we study two multi-dimensional Goodness-of-Fit tests for spectrum sensing in cognitive radios. The multi-dimensional scenario refers to multiple CR nodes, each with multiple antennas, that record multiple observations from multiple primary users for spectrum sensing. These tests, viz., the Interpoint Distance (ID) based test and the h, f distance based tests are constructed based on the properties of stochastic distances. The ID test is studied in detail for a single CR node case, and a possible extension to handle multiple nodes is discussed. On the other hand, the h, f test is applicable in a multi-node setup. A robustness feature of the KL distance based test is discussed, which has connections with Middleton's class A model. Through Monte-Carlo simulations, the proposed tests are shown to outperform the existing techniques such as the eigenvalue ratio based test, John's test, and the sphericity test, in several scenarios.

El cuento de la doncella sin manos : versiones hispánicas medievales y la tradición oral en América

Resumen: A partir de la primera versión literaria en lengua vernácula del “Cuento de la doncella sin manos”, escrita por Philippe de Remi en el siglo XIII, la literatura medieval no dejó de reelaborar el relato a lo largo y a lo ancho del Occidente europeo. Del periodo que abarca desde el siglo XIII hasta el XVII nos llegan, por lo menos, unas treinta y cuatro versiones escritas solo en los ámbitos románico y germánico. Existe asimismo una tradición arábiga del cuento, probablemente de origen semítico, que constituiría, según algunos autores, una rama narrativa independiente. En la tradición oral el relato ha pervivido hasta nuestros días, en diversos países del mundo, incluida América del Sur, particularmente Brasil, Chile y la Argentina. El legado folclórico en Europa, inicialmente recopilado y puesto por escrito por los hermanos Grimm en 1812, presenta, ciertamente, numerosos puntos de contacto con las versiones americanas. Sin embargo, se ha establecido un vínculo aún más estrecho entre estas y los Cuentos populares españoles recogidos por Aurelio Espinosa en 1923, por un lado, así como también con una de las tres versiones provenientes del ámbito árabe. Luego de trazar un panorama histórico del corpus y estudiar los puntos de contacto entre la tradición europea y la americana, nos centraremos en el análisis de las versiones sudamericanas, particularmente las recogidas en la Argentina

Los siete modos de amor de Beatriz de Nazareth : Caleidoscopio estético – místico del deseo de Dios

Los Siete grados de Amor de la poetisa y mística flamenca Beatriz de Nazareth conforma, junto con la obra de sus dos contemporáneas Hadewijch de Amberes y Matilde de Magdeburgo, un coro de voces femeninas que destacan dentro de la teología monástica del siglo XIII, por haber sido escritas en lengua vernácula y haber adoptado de modo creativo las formas poéticas del amor cortés para expresar su experiencia de Dios. En continuidad con la tradición patrística despliega Beatriz la via amoris, centrando su discurso en el deseo de Dios. El objetivo de este trabajo es demostrar la actualidad de esta obra medieval premoderna en el horizonte de una posmodernidad en la que deseo y alteridad se cruzan. La original concepción caleidoscópica del amor que presenta este texto abre horizontes desde los cuales plantear hoy la pregunta por lo absoluto a partir de la experiencia y el lenguaje de los místicos.

Peregrinación a la cibdat de gygantes : configuración del imaginario geográfico bíblico en La fazienda de Ultramar

Resumen: Dado que la imaginación medieval del mundo se nutre de ideas directamente heredadas de la Biblia, a menudo en contienda con la exploración empírica del globo terrestre, el estudio de los relatos de viajes en general, y de las guías de peregrinos a Tierra Santa en particular, nos permite comprender el modo en que el hombre de letras medieval se apropiaba del imaginario bíblico para darle forma a un mundo cuyos límites exóticos cobraban familiaridad por ser el escenario de las historias más apreciadas por los lectores de la época. Dentro del repertorio de literatura de viajes hispánica, La fazienda de Ultramar, cuya redacción se habría llevado a cabo a comienzos del siglo XIII, es un texto de singular importancia, por ser una de las más antiguas versiones en romance de la Biblia. No solo es un texto fundacional para una tradición que cambió la forma en que el hombre medieval se acercaba a las Sagradas Escrituras, sino que, debido a su carácter de itinerarium, nos permite conocer el modo en que la Biblia afectaba la imaginación del lector medieval acerca de la geografía de Tierra Santa. Es por ello que el propósito de esta comunicación será analizar el modo en que la estructura de itinerarium incide sobre el tratamiento del texto sagrado y la forma en que la lógica narrativa de los episodios bíblicos se subordina a la geográfica. De esta forma, se intentará echar luz sobre algunas cuestiones que han limitado el estudio de esta obra.

El tango en la obra de Juán José Castro

Resumen: Juan José Castro utilizó como material el tango para algunas de sus obras a lo largo de casi 20 años. Era ciertamente un conocedor del género, ya que lo había practicado en su juventud. Actualmente, es considerado un actor paradigmático cuando se aborda la cuestión del neoclasicismo y la utilización de materiales vernáculos en la música académica argentina. El propósito de este trabajo es señalar la presencia del tango en su obra y la articulación en la misma de los lenguajes culto y popular. A diferencia de otras incorporaciones del tango en la música académica, la de Castro es integradora y elabora a partir de la selección de determinados materiales “tanguísticos” un tango propio, reconocible a lo largo de su obra.

Transient Flows in Low Permeability Porous Media with Composite Start-Up Pressure Gradient

A new mathematical model for the transient flow in the composite low permeability is established. It is solved by FEM with different boundary conditions such as infinite, circular closed and constant pressure boundary conditions. The typical curves for transient wellbore pressure have been presented. It is shown that the pressure and pressure derivative curves with composite start-up pressure gradients have different slopes which are depended on the start-up pressure gradients and the mobility radios in different regions. The boundary effects are the same as the normal reservoirs without start-up pressure gradients. The study provides a new tool to analyze the transient pressure test data in the low permeability reservoir.

[R_Cornago_Castillo] Documentación Geométrica y Modelado Virtual del Castillo de Cornago (La Rioja)

[ES] El Castillo se encuentra coronando, junto a la iglesia de San Pedro, el cerro sobre el que se asienta el caserío de Cornago. Actualmente está formado por un patio interior de forma rectangular y rematado por cuatro torres en las esquinas, de las cuales tres son circulares de diferentes radios y una cuarta (NE) cuadrada, la superficie total ocupada es de unos 50 x 30 metros al exterior.