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  • Spectrum sensing using correlated receiving multiple antennas in cognitive radios

     Sedighi, Saeid; Taherpour, Abbas; Sala Alvarez, Jose
    IEEE transactions on wireless communications
    Date of publication: 2013-11
    Journal article

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    In this paper, we address the problem of multiantenna spectrum sensing in Cognitive Radios (CRs) by considering the correlation between the received channels at different antennas. First, we derive the optimum genie-aided detector which assumes perfect knowledge of the antenna correlation coefficients, Primary User (PU) signal power and noise variance. This is used as a benchmark for comparing with more practical detectors when some or all of these parameters are unknown to the Secondary User (SU). Two scenarios are considered: 1) the antenna correlation coefficients and PU signal power are unknown to the SU; 2) the antenna correlation coefficients, PU signal power and noise variance are unknown to the SU. To derive sub-optimum detectors for these two scenarios, we apply the Rao test, an asymptotically equivalent test to the Generalized Likelihood Ratio Test (GLRT) that does not require the Maximum Likelihood (ML) estimates of unknown parameters. Additionally, we calculate analytical approximations to the detection and false-alarm probabilities of the proposed detectors and verify them with Monte-Carlo simulations. The simulation results show that these new detectors outperform several recently proposed detectors for CR using multiple antennas.

  • Asymptotically optimum energy profile for successive interference cancellation in DS-CDMA under a power unbalance constraint

     Sala Alvarez, Jose; Rey Micolau, Francesc; Villares Piera, N. Javier
    IEEE communications letters
    Date of publication: 2012-02
    Journal article

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  • Multiantenna GLR detection of rank-one signals with known power spectrum in white noise with unknown spatial correlation

     Sala Alvarez, Jose; Vázquez Vilar, Gonzalo; López Valcarce, Roberto
    IEEE transactions on signal processing
    Date of publication: 2012-06
    Journal article

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  • Multiantenna GLR detection of a gaussian signal in spatially uncorrelated noise

     Sala Alvarez, Jose
    European Signal Processing Conference
    Presentation's date: 2011-09-02
    Presentation of work at congresses

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    The exact all-SNR Generalized Log-likelihood Ratio Test (GLRT) of a Gaussian rank-one signal impinging on an - antenna receiver in unknown spatially uncorrelated white noise is derived and compared with some previous low-SNR approximations to this problem. It is confirmed that the coherence matrix used in the mentioned approximations is a sufficient statistic for the GLRT over the complete SNR range. In contrast, this exact, albeit more complex test, requires the unconstrained optimization of a highly nonlinear -variate complex function which can be addressed using classical optimization techniques. A maximum eigenvalue problem combined with a univariate optimization problem serves the purpose of initialization. Results validate the yet unproven close to optimum performance of previous detectors under the rank-one signal model for the tested SNR’s.

  • Multiantenna spectrum sensing exploiting spectral a priori information

     Vázquez Vilar, Gonzalo; López Valcarce, Roberto; Sala Alvarez, Jose
    IEEE transactions on wireless communications
    Date of publication: 2011-12
    Journal article

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    Dynamic Spectrum Access (DSA) is receiving considerable interest as a means to improve spectral usage in licensed bands. In order to avoid interference to licensed users, spectrum sensing has emerged as an enabling technology for DSA. The requirements for spectrum sensors are stringent, as licensed user detection must be performed reliably at low signal-to-noise ratios (SNR). Sensing performance can be improved by exploiting signal features not present in the background noise. These approaches result in tradeoffs among performance and robustness to departures from the signal model. We consider second-order signal features and develop detectors exploiting spatial (by using multiple antennas) as well as temporal signal correlation, taking advantage of the fact that the power spectrum of the primary signal at each antenna can be known up to a complex scalar representing the unknown propagation channel. A low-SNR Generalized Likelihood Ratio approach is adopted in order to overcome this uncertainty, resulting in different tests intimately related to familiar diversity combining techniques. The performance of the proposed detectors is analyzed and tested in different scenarios.

  • Asymptotic and finite user PER analysis of successive interference cancellation in DS-CDMA

     Sala Alvarez, Jose; Villares Piera, N. Javier; Rey Micolau, Francesc
    IEEE communications letters
    Date of publication: 2011-11
    Journal article

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    An expression is derived for the average Packet Error Rate (PER) of a Successive Interference Canceller (SIC) for DS-CDMA when the number of users asymptotically tends to infinity. The asymptotic probability density function of the interference power is governed by a Fokker-Planck differential equation with drift and (asymptotically vanishing) diffusion depending on the PER function of the adopted forward error-correcting code (FEC). In addition to the asymptotic solution for the PER, a particle-based algorithm is also developed for computing efficiently the PER in the finite user case.

  • ANTARES Project (Bridging Phase). Payload carrier synchronization : algorithms and simulations

     Font Segura, Josep; Matas Navarro, David; Ramirez Javega, Francisco; Rey Micolau, Francesc; Riba Sagarra, Jaume; Sala Alvarez, Jose; Vazquez Grau, Gregorio; Villares Piera, N. Javier
    Date: 2011-11-23
    Report

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    Informe final Bridging Phase. Versió 3.2

  • Access to the full text
    Multiantenna spectrum sensing for cognitive radio: overcoming noise uncertainty  Open access

     López Valcarce, Roberto; Vázquez Vilar, Gonzalo; Sala Alvarez, Jose
    International Workshop on Cognitive Information Processing
    Presentation's date: 2010-06-15
    Presentation of work at congresses

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    Spectrum sensing is a key ingredient of the dynamic spectrum access paradigm, but it needs powerful detectors operating at SNRs well below the decodability levels of primary signals. Noise uncertainty poses a significant challenge to the development of such schemes, requiring some degree of diversity (spatial, temporal, or in distribution) for identifiability of the noise level. Multiantenna detectors exploit spatial independence of receiver thermal noise. We review this class of schemes and propose a novel detector trading off performance and complexity. However, most of these methods assume that the noise power, though unknown, is the same at all antennas. As it turns out, calibration errors have a substantial impact on these detectors. Another novel detector is proposed, based on an approximation to the Generalized Likelihood Ratio, outperforming previous schemes for uncalibrated multiantenna receivers.

  • ANTARES Project (Phase B). Multiple acces scheme definition. Diverse trade-offs analysis for TDMA and CDMA

     Font Segura, Josep; Matas Navarro, David; Ramirez Javega, Francisco; Lamarca Orozco, M. Meritxell; Rey Micolau, Francesc; Riba Sagarra, Jaume; Sala Alvarez, Jose; Vazquez Grau, Gregorio; Villares Piera, N. Javier
    Date: 2010-03-01
    Report

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  • ANTARES Project (Phase B). Physical layer definition. Equalization detailed design

     Font Segura, Josep; Matas Navarro, David; Ramirez Javega, Francisco; Lamarca Orozco, M. Meritxell; Rey Micolau, Francesc; Riba Sagarra, Jaume; Sala Alvarez, Jose; Vazquez Grau, Gregorio; Villares Piera, N. Javier
    Date: 2010-08-01
    Report

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  • ANTARES Project (Phase B). Multiple access scheme definition. Impact of the aeronautical channel on the MAC techniques considered for the Antares forward and return links

     Font Segura, Josep; Lamarca Orozco, M. Meritxell; Matas Navarro, David; Ramirez Javega, Francisco; Rey Micolau, Francesc; Riba Sagarra, Jaume; Sala Alvarez, Jose; Vazquez Grau, Gregorio; Villares Piera, N. Javier
    Date: 2010-03-01
    Report

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  • Proyecto AVANT. Estudio de técnicas de sincronización para relaciones señal a ruido muy bajas. D12. Disseny i simulació dels algorismes de sincronització

     Lamarca Orozco, M. Meritxell; Ramirez Javega, Francisco; Rey Micolau, Francesc; Riba Sagarra, Jaume; Sala Alvarez, Jose; Vazquez Grau, Gregorio; Villares Piera, N. Javier
    Date: 2010-07-16
    Report

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    In this document, the synchronization algorithms developed during the project are presented and simulated. The studied algorithms are designed for a QS-CDMA system operating in the low SNR regime, i.e., at low Es/No values and/or with severe multiple access interference. Moreover, the proposed synchronization techniques must work correctly in the difficult mobility scenarios considered in the project (i.e., aeronautical, railroad and nautical scenarios).

  • ANTARES Project (Phase B). Multiple acces scheme definition. Spectral efficiency analysis of the MAC techniques considered for the Antares forward and return links

     Font Segura, Josep; Matas Navarro, David; Ramirez Javega, Francisco; Lamarca Orozco, M. Meritxell; Rey Micolau, Francesc; Riba Sagarra, Jaume; Sala Alvarez, Jose; Vazquez Grau, Gregorio; Villares Piera, N. Javier
    Date: 2010-07-01
    Report

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  • LDPC performance in presence of impulse noise

     Lamarca Orozco, M. Meritxell; Ramirez Javega, Francisco; Matas Navarro, David; Rey Micolau, Francesc; Riba Sagarra, Jaume; Sala Alvarez, Jose; Vazquez Grau, Gregorio; Villares Piera, N. Javier
    Date: 2010-11-02
    Report

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  • Proyecto AVANT. Estudio de técnicas de sincronización para relaciones señal a ruido muy bajas. D11: Disseny del codificador i descodificador del turbo-codi de l'estàndard DVB-RCS

     Lamarca Orozco, M. Meritxell; Ramirez Javega, Francisco; Rey Micolau, Francesc; Riba Sagarra, Jaume; Sala Alvarez, Jose; Vazquez Grau, Gregorio; Villares Piera, N. Javier
    Date: 2010-07-16
    Report

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    This document contains the instructions for the design of the DVB-RCS turbo-code. Both the algorithmic and implementation issues are addressed in the document.

  • ANTARES Project (Phase B). Multiple acces scheme definition. Successive interference cancellation for A-CDMA

     Font Segura, Josep; Matas Navarro, David; Ramirez Javega, Francisco; Lamarca Orozco, M. Meritxell; Rey Micolau, Francesc; Riba Sagarra, Jaume; Sala Alvarez, Jose; Vazquez Grau, Gregorio; Villares Piera, N. Javier
    Date: 2010-05-01
    Report

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  • ANTARES Project (Phase B). Physical layer definition. Payload carrier synchronization for the Antares TDMA return link

     Font Segura, Josep; Matas Navarro, David; Ramirez Javega, Francisco; Lamarca Orozco, M. Meritxell; Rey Micolau, Francesc; Riba Sagarra, Jaume; Sala Alvarez, Jose; Vazquez Grau, Gregorio; Villares Piera, N. Javier
    Date: 2010-08-01
    Report

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  • PROCESSAMENT DEL SENYAL EN COMUNICACIONS

     Rey Micolau, Francesc; Villares Piera, N. Javier; Vazquez Grau, Gregorio; Riba Sagarra, Jaume; Vidal Manzano, Jose; Cabrera Bean, Margarita Asuncion; Garcia Ordoñez, Luis; Rodriguez Fonollosa, Javier; Ramirez Javega, Francisco; Muñoz Medina, Olga; Matas Navarro, David; Font Segura, Josep; Silva Pereira, Silvana; Agustin de Dios, Adrian; Fernandez Rubio, Juan-antonio; Lamarca Orozco, M. Meritxell; Pages Zamora, Alba Maria; Sala Alvarez, Jose
    Participation in a competitive project

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  • A non-parametric method for the measurement of size diversity, with emphasis on data standardisation

     Quintana, X D; Brucet, S; Boix, D; López-Flores, R; Gascón, S; Badosa, A; Sala Alvarez, Jose; Moreno-Amich, R; Egozcue Rubi, Juan José
    Limnology and oceanography
    Date of publication: 2008-01
    Journal article

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  • Time-Varying Frequency-Selective MIMO Channel Estimation

     Nassar, Ali
    Defense's date: 2008-04-03
    Department of Signal Theory and Communications, Universitat Politècnica de Catalunya
    Theses

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  • Access to the full text
    A rain and scintillation Ka-band channel simulator  Open access

     Sala Alvarez, Jose; Lamarca Orozco, M. Meritxell; López, J. A.; Rey Micolau, Francesc; Riba Sagarra, Jaume; Vazquez Grau, Gregorio; Villares Piera, N. Javier; Jalón, A; Rodríguez, E
    International Workshop on Signal Processing for Space Communications
    Presentation's date: 2008-10-07
    Presentation of work at congresses

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    This paper describes the implementation of a Ka-band satellite channel simulator with emphasis on the synthesis of scintillation processes. The problem becomes one of generating a given probability density function, the Moulsley-Vilar distribution, with a specified power spectral density using aWiener model based on orthogonal Hermite polynomials for the nonlinearity. A numerical procedure is devised to calculate the filter and non-linearity coefficients of the Wiener model. The generation of rain processes conforms to the Maseng-Bakken model.

  • Foundations and Methodologies for Future Communication and Sensor Networks (COMONSENS)

     Pages Zamora, Alba Maria; Rodriguez Fonollosa, Javier; Muñoz Medina, Olga; Vidal Manzano, Jose; Cabrera Bean, Margarita Asuncion; Fernandez Rubio, Juan-antonio; Rey Micolau, Francesc; Villares Piera, N. Javier; Vazquez Grau, Gregorio; Lamarca Orozco, M. Meritxell; Sala Alvarez, Jose; Riba Sagarra, Jaume
    Participation in a competitive project

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  • Informe Número 1: Projecte SETRAM

     Sala Alvarez, Jose; Rey Micolau, Francesc; Riba Sagarra, Jaume; Villares Piera, N. Javier; Lamarca Orozco, M. Meritxell; Vazquez Grau, Gregorio
    Date: 2008-10-01
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  • Nota tècnica 1: projecte SETRAM

     Sala Alvarez, Jose; Riba Sagarra, Jaume; Rey Micolau, Francesc; Villares Piera, N. Javier; Vazquez Grau, Gregorio; Lamarca Orozco, M. Meritxell
    Date: 2008-02-26
    Report

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    Un dels aspectes més crítics per assolir una definició avançada i realista del sistema SETRAM és la identificació de les tecnologies més adequades per a la localització d’usuaris mòbils, des de les ja existents (aplicables tant a la localització individual com agregada) fins a les més el.laborades per a la seva aplicació específica i exclusiva en aquest sistema.

    Nota tècnica inici de projecte SETRAM (CIDEM)

  • Pulsar Navigation

     Josep, Sala; Sala Alvarez, Jose; Urruela, Andreu; Villares Piera, N. Javier; Romeu Robert, Jordi; Blanch Boris, Sebastian; Estalella Boadella, Robert; Paredes, Josep M
    ACT Workshop on Innovative Concepts 2008
    Presentation of work at congresses

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  • DA-GLRT burst detection and synchronization based on a chirp-like preamble

     Lamarca Orozco, M. Meritxell; Lopez Salcedo, Jose Antonio; Rey Micolau, Francesc; Riba Sagarra, Jaume; Sala Alvarez, Jose; Vazquez Grau, Gregorio; Villares Piera, N. Javier; Jalón, A; Rodríguez, E
    International Workshop on Signal Processing for Space Communications
    Presentation's date: 2008-10-08
    Presentation of work at congresses

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    A specific preamble for the tasks of signal detection and synchronization in burst digital communications is presented. The preamble resembles a chirp signal used in RADAR applications. Its main benefit is that it allows the application of the Generalized Likelihood Ratio Test in an efficient manner, as well as the derivation of closed-form estimators for the synchronization parameters, as shown in the paper. The proposal can be an alternative to turbo-synchronization in very low Eb/N0 scenarios.

  • Pulsar navigation

     Sala Alvarez, Jose; Urruela Planas, Andreu; Villares Piera, N. Javier; Romeu Robert, Jordi; Blanch Boris, Sebastian; Estalella Boadella, Robert; Paredes, J. M.
    Acta Futura
    Date of publication: 2008-12-31
    Journal article

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    This paper evaluates the fundamental performance bounds, signal processing and technological complexity associated with the synchronization to radio and X-ray pulsars as well as its impact on the positioning accuracy of an autonomous spacecraft navigation system. Performance analysis of synchronization and location algorithms builds on Maximum Likelihood (ML) estimation which provides, asymptotically, unbiased minimum variance estimates with mean square error strictly approaching the Cramer-Rao Lower Bound (CRLB).

  • Flat Fading Time-Variant MIMO Channel Estimation based on Raised Cosine Expansion under Orthogonal Codes Transmission

     Nassar, Ali; Josep, Sala; Sala Alvarez, Jose
    Mosharaka Multi-Conference on Communications, Computers and Applications
    Presentation of work at congresses

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  • Asymptotic ML Detection for the Photon Counting Channel

     Sala Alvarez, Jose
    IEEE International Conference on Acoustics, Speech, and Signal Processing
    Presentation of work at congresses

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  • Efficient 8-PSK/16-PSK Generation Using Distributed Arithmetic

     Sala Alvarez, Jose
    Date of publication: 2007-08-31
    Book chapter

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  • SPROACTIVE: Signal Processing Advanced techniques for CogniTIVE radio systems. Técnicas avanzadas de procesado de señal para sistemas de radio cognitive - II

     Villares Piera, N. Javier; Font Segura, Josep; Lamarca Orozco, M. Meritxell; Matas Navarro, David; Ramirez Javega, Francisco; Rey Micolau, Francesc; Riba Sagarra, Jaume; Sala Alvarez, Jose; Vazquez Grau, Gregorio
    Participation in a competitive project

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  • ADAPTIVE MULTICARRIER DEMODULATOR & DECODER DVB-RCS1 DESIGN DOCUMENT

     Lamarca Orozco, M. Meritxell; Rey Micolau, Francesc; Riba Sagarra, Jaume; Josep, Sala; Sala Alvarez, Jose; Vazquez Grau, Gregorio; Villares Piera, N. Javier
    Date: 2007-02
    Report

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  • IEEE Transactions on Signal Processing

     Sala Alvarez, Jose
    Collaboration in journals

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  • IEEE Communications Letters

     Sala Alvarez, Jose
    Collaboration in journals

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  • Simulation Results with Propagation, Non Linear and SS Modem Impairment Effects

     Lamarca Orozco, M. Meritxell; López-Salcedo, J A; Lopez Salcedo, Jose Antonio; Riba Sagarra, Jaume; Rey Micolau, Francesc; Sala Alvarez, Jose; Vazquez Grau, Gregorio; Villares Piera, N. Javier
    Date: 2006-06
    Report

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  • Simulations Results Document

     Lamarca Orozco, M. Meritxell; López-Salcedo, J A; Lopez Salcedo, Jose Antonio; Riba Sagarra, Jaume; Rey Micolau, Francesc; Sala Alvarez, Jose; Vazquez Grau, Gregorio; Villares Piera, N. Javier
    Date: 2006-04
    Report

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  • Requirements Revision and Design Inputs

     Lamarca Orozco, M. Meritxell; López-Salcedo, J A; Lopez Salcedo, Jose Antonio; Riba Sagarra, Jaume; Rey Micolau, Francesc; Sala Alvarez, Jose; Vazquez Grau, Gregorio; Villares Piera, N. Javier
    Date: 2006-03
    Report

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  • Average performance analysis of circular and hyperbolic geolocation

     Urruela, Planas A; Sala Alvarez, Jose; Riba Sagarra, Jaume
    IEEE transactions on vehicular technology
    Date of publication: 2006-01
    Journal article

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  • TEC2004-22641-E FOURTH-GENERATION INTELLIGENT TRANSPARENT NETWORKS ENHANCED THROUGH SPACE-TIME SYSTEM

     Lamarca Orozco, M. Meritxell; Lopez Salcedo, Jose Antonio; Rey Micolau, Francesc; Sala Alvarez, Jose; Vazquez Grau, Gregorio; Villares Piera, N. Javier
    Participation in a competitive project

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  • IEEE Transactions on Signal Processing

     Sala Alvarez, Jose
    Collaboration in journals

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  • Eurasip Signal Processing

     Sala Alvarez, Jose
    Collaboration in journals

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  • Channel Simulator Interface Document

     Sala Alvarez, Jose; Lamarca Orozco, M. Meritxell; Lopez Salcedo, Jose Antonio; Muntaner, Enric; Rey Micolau, Francesc; Riba Sagarra, Jaume; Vazquez Grau, Gregorio; Villares Piera, N. Javier; Bonet Domènech, Josep; Muntane Calvo, Enrique
    Date: 2005-09
    Report

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  • Adaptive Multicarrier Demodulator & Decoder DVB-RCS1 Definition

     Lamarca Orozco, M. Meritxell; López-Salcedo, J A; Lopez Salcedo, Jose Antonio; Muntaner, E; Rey Micolau, Francesc; Riba Sagarra, Jaume; Sala Alvarez, Jose; Vazquez Grau, Gregorio; Villares Piera, N. Javier; Muntane Calvo, Enrique
    Date: 2005-12
    Report

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  • UPC contrinution to ESA proposal Study of enhanced digital transmisión techniques for broadband satellite digital transmissions

     Sala Alvarez, Jose; Vazquez Grau, Gregorio; Lamarca Orozco, M. Meritxell; Lopez Salcedo, Jose Antonio; Riba Sagarra, Jaume; Villares Piera, N. Javier; Rey Micolau, Francesc; Muntaner, Enric; Bonet Domènech, Josep; Muntane Calvo, Enrique
    Date: 2005-07
    Report

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  • Advanced Decoding Algorithms for Reed-Solomon/Convolutional Concatenated Codes

     Lamarca Orozco, M. Meritxell; Sala Alvarez, Jose; MARTINEZ, A
    Annales des télecommunications. Annals of telecommunications
    Date of publication: 2005-01
    Journal article

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  • ADAPTIVE PRE-DISTORTION FOR NONLINEAR HIGH POWER AMPLIFIERS IN OFDM SYSTEMS  Open access

     Durney Wasaff, Hugo
    Defense's date: 2004-07-22
    Department of Signal Theory and Communications, Universitat Politècnica de Catalunya
    Theses

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    El acelerado crecimiento de las comunicaciones a través de plataformas de transmisión en banda ancha por vía alámbrica e inalámbrica, sumado al uso cada vez más extenso de modulaciones de amplitud no constante que, debido a su alta eficiencia espectral y bajo coste de implementación, han sido adoptadas en el marco de desarrollo de diversos estándares de transmisión, son aspectos que han servido de soporte y motivación fundamental para el presente trabajo de investigación en el campo de la compensación de distorsiones no lineales en sistemas de comunicación. El estudio de los efectos de la distorsión no lineal y su compensación ha sido desde hace ya muchos años objeto de atención para investigadores de diversas áreas. Hoy, en particular, este estudio sigue siendo fundamental ya que se encuentra directamente implicado en el desarrollo de tecnologías de última generación en el área de las comunicaciones. Los nuevos sistemas de transmisión digital, en especial aquellos basados en OFDM (Orthogonal Frequency Division Multiplexing), son capaces de ofrecer altos niveles de eficiencia espectral utilizando modulaciones lineales multinivel sobre un numeroso conjunto de subportadoras que, al ser (idealmente) ortogonales en frecuencia, pueden ser ubicadas en un ancho de banda muy reducido permitiendo así transmitir elevadas tasas de información por segundo y por ancho de banda. Sin embargo, y a consecuencia de esto, problemas como las interferencias por canal adyacente o la presencia de una distorsión no lineal en la cadena de transmisión afectan de manera crítica las prestaciones de estos sistemas imponiendo severos límites a su viabilidad. De hecho, en el campo de las comunicaciones móviles y satelitales, existen actualmente diversas aplicaciones donde estos esquemas de modulación y multicanalización están ya operativos. En estos casos, la eficiencia de potencia en transmisión resulta primordial para, entre otras razones, lograr una máxima autonomía del equipamiento. En este contexto, el comportamiento no lineal de los amplificadores de alta potencia utilizados en transmisión de radiofrecuencia, constituye el principal obstáculo (desde el punto de vista de la distorsión no lineal) para el buen funcionamiento de los sistemas de comunicación digital basados en OFDM. Afortunadamente, este nocivo efecto puede ser compensado mediante diversas técnicas clásicas de linealización cuyas variantes -ad-hoc' han sido propuestas y ampliamente investigadas, existiendo al día de hoy una nutrida literatura parte de la cual referimos a lo largo de este trabajo. Entre dichas técnicas, la pre-distorsión digital ofrece óptimas condiciones para el diseño de linealizadores adaptativos ya que puede ser implementada a muy bajo coste sobre la información discreta de las señales de banda base. El objetivo que se persigue, en general, es el de proveer las condiciones de linealidad necesarias para explotar las capacidades propias de las modulaciones de alta eficiencia espectral, y al mismo tiempo alcanzar un máximo aprovechamiento de la potencia disponible. En este trabajo de investigación, efectuamos inicialmente una revisión sintetizada de algunas importantes técnicas de linealización para luego dar paso a una revisión más detallada de dos modelos relevantes utilizados para caracterizar el comportamiento no lineal de los amplificadores de alta potencia (modelo se Series de Volterra y modelo de Saleh para amplificadores nolineales sin memoria). Junto con ello se examinan algunas interesantes propiedades estadísticas asociadas al fenómeno de la distorsión no lineal que han dado pie a considerar durante la investigación posibles nuevas aplicaciones en estrategias de pre-distorsión. Se ha querido también incluir la descripción, a nivel de sistema y modelo de señal, de un esquema de transmisión OFDM genérico incluyendo caracterizaciones analíticas detalladas del efecto no lineal a objeto de formalizar en propiedad un modelo discreto exacto que otorgue una visión más profunda para la comprensión del fenómeno estudiado. Finalmente se presenta el diseño y evaluación de un esquema de pre-distorsión basado en un algoritmo iterativo que considera, como principal aporte, la optimización bidimensional de un reducido número de coeficientes de interpolación que identifican de manera adaptativa la característica inversa de ganancia compleja de un amplificador, tanto en función de la particular morfología no lineal de dicha curva, como también de la distribución de probabilidad de las señales de entrada en banda base.

    The rapid growth of wired and wireless broad-band communications and the pervasive use of spectrally efficient non-constant amplitude modulations, adopted in the framework of several standardized transmission formats, motivates and supports the present research work in the field of non-linear distortion in communication systems. The compensation of nonlinearities has received a lot of attention in past and recent years, presenting direct implications on industrial development of last generation communication technologies. New digital transmission systems, particularly those based on Orthogonal Frequency Division Multiplexing (OFDM), feature high spectral efficiency as they exploit multilevel linear modulations to transmit at high information rates in combination with a dense allocation of a large number of (ideally) orthogonal sub-carriers in a relatively reduced bandwidth. As a result, problems such as adjacent channel interference and non-linear distortion become critical for system performance and, therefore, must be reduced to a minimum. Moreover, numerous applications of such transmission schemes are already operative in the field of satellite and mobile communications, where power efficiency is of primary concern due to, among other reasons, operation autonomy of the equipment and effective transmitted power. In this context, the non-linear behaviour of high power amplifiers (HPAs) constitutes a major impairment for OFDM-based digital communications systems. The compensation of these harmful effects can be achieved using a variety of techniques that have been proposed and widely dealt with in the literature. Among these techniques, digital pre-distortion, which can be carried out at a very low cost over the discrete base-band information, provides optimal features for the efficient implementation of adaptive linearization. Thence, in order to provide good conditions for the reliable use of high spectral efficiency modulations while taking the maximum advantage from the transmitting power budget, it is necessary to incorporate a suitable linearization technique.In the present work, we begin by reviewing some background on linearization techniques. This leads us to continue analyzing two relevant theoretical models typically used in characterizing memory and memoryless nonlinear HPAs (Volterra Series model and Saleh model for memoryless nonlinear HPAs). In addition to this a generic OFDM system and signal structure is described in detail by including the non-linear effect in the analytical model of the transmission chain. This is done in order to formalize an exact discrete OFDM model that help us in achieving a deeper understanding of the phenomenon under consideration. Then, some useful statistical properties and parameters associated to the nonlinear distortion are examined as well as the application of a CDF-based estimation of nonlinearities which is proposed as a new pre-distortion strategy. Finally, a new discrete adaptive pre-distortion scheme is formulated and then tested via simulation. The analysis and design of the main algorithm proposed considers the adaptive identification of the inverse complex gain characteristic of a nonlinear HPA. For this purpose, an iterative 2-D optimization of a reduced number of interpolation functions is formulated under a special two-fold criterion which accounts for the particular morphology of the HPA's nonlinear gain characteristic, as well as the probability distribution of the input base-band information.

  • Best Paper (Senior) Award of the IEEE Signal Processing Society

     Riba Sagarra, Jaume; Sala Alvarez, Jose; Vazquez Grau, Gregorio
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  • TEC2004-04526 TRANSMISION COOPERATIVA PARA SISTEMAS DE COMUNICACION INALAMBRICOS DE BANDA ANCHA

     Vidal Manzano, Jose; Fernandez Rubio, Juan-antonio; Sala Alvarez, Jose; Riba Sagarra, Jaume; Muñoz Medina, Olga; Villares Piera, N. Javier; madueño ruiz, maria isabel; Agustin de Dios, Adrian; Garcia Ordoñez, Luis; Huerta Guillén, Jose Manuel
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    Feasibility study for a spacecraft navigation system relying on pulsar timing information  Open access

     Sala Alvarez, Jose; Urruela Planas, Andreu; Villares Piera, N. Javier; Estalella Boadella, Robert; Paredes, J M
    Date: 2004-06
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    Estudi de fiabilitat per un sistema de navegacio d'espai profund basat en referencies de radio-estrelles pulsants (pulsar).