936 research outputs found

    Distributed multivariate regression with unknown noise covariance in the presence of outliers: an MDL approach

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    We consider the problem of estimating the coefficients in a multivariable linear model by means of a wireless sensor network which may be affected by anomalous measurements. The noise covariance matrices at the different sensors are assumed unknown. Treating outlying samples, and their support, as additional nuisance parameters, the Maximum Likelihood estimate is investigated, with the number of outliers being estimated according to the Minimum Description Length principle. A distributed implementation based on iterative consensus techniques is then proposed, and it is shown effective for managing outliers in the data.Peer ReviewedPostprint (author's final draft

    Separation of digital communication signals through joint space-time decorrelation

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    In this paper we derive the optimum linear algorithm for the separation by an array of a given number of cyclostationary signals of the type encountered in digital communications. Spatially and temporally uncorrelated noise is considered at the input to each sensor. It is proved that the optimum signal separator can be expressed as a matrix transfer function in the z-domain. It is intended that this algorithm be used as a benchmark to test the performance of adaptive schemes. Therefore, bounds on the noise estimation covariance are obtained assuming perfect knowledge of the number of sources as well as of their timing and DOA.Peer ReviewedPostprint (published version

    Average PER performance metrics of iterative successive interference cancellation

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    © 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.The average packet error rate (PER) and user-PER profiles of iterative successive interference cancellation (I-SIC) are analyzed for a proof-of-concept scenario where asymptotically many code-division-multiple-access users share the same channel encoder. To characterize the iterative decoding receiver, we propose a novel multivariate PER function evaluated over the consecutive signal-to-interference-plus-noise ratios (SINRs) experienced by each undecoded user. Analytic expressions for the user-energy and user-SINR profiles at every iteration are derived via warping operators on the user ordering that relate the asymptotic distribution of undecoded users at different iterations. Monte Carlo simulations using a chip-level I-SIC implementation assess the accuracy of the proposed user-limit analysis.Peer ReviewedPostprint (author's final draft

    Epidemiological and pathogenic relationship between sleep apnea and ischemic heart disease

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    Obstructive sleep apnea is recognized as having high prevalence and causing remarkable cardiovascular risk. Coronary artery disease has been associated with obstructive sleep apnea in many reports. The pathophysiology of coronary artery disease in obstructive sleep apnea patients probably includes the activation of multiple mechanisms, as the sympathetic activity, endothelial dysfunction, atherosclerosis, and systemic hypertension. Moreover, chronic intermittent hypoxia and oxidative stress have an important role in the pathogenesis of coronary disease and are also fundamental to the development of atherosclerosis and other comorbidities present in coronary artery diseases such as lipid metabolic disorders. Interestingly, the prognosis of patients with coronary artery disease has been associated with obstructive sleep apnea and the severity of sleep disordered breathing may have a direct relationship with the morbidity and mortality of patients with coronary diseases. Nevertheless, treatment with CPAP may have important effects, and recent reports have described the benefits of obstructive sleep apnea treatment on the recurrence of acute heart ischaemic events in patients with coronary artery diseas

    Regions de decisió i cota de la unió

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    Presentació Docent: Regions de Decisió i Cota de la Unió. Assignatura: ICOM - ETSETB (UPC) El document constitueix una còpia per l'estudiant de la presentació de diversos conceptes teòrics relacionats amb la determinació de regions de decisió en el pla IQ per sistemes de comunicacions pas banda. Es presenta de forma gràfica com es determinen les regions de decisió, com es calcula la probabilitat d'error de símbol i com s'estableix una cota superior utilitzant la cota de la unió. Es fa èmfasi en la utilització de raonaments gràficsm utilitzant segons conveniència, propietats bàsiques de teoria de conjunts. El document s'organitza en base a 2 transparències per pàgina.Aquest document presenta de forma gràfica: - La determinació de la regió de decisió R associada a un símbol complexe s = I + jQ . - La determinació de la seva probabilitat d’error i la d’una cot a superior (Cota de la Unió). - Exemples d’aplicació: 8-PSK, QPSK, 3-PSK+0Preprin

    Multiantenna GLR detection of a gaussian signal in spatially uncorrelated noise

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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.Peer ReviewedPostprint (published version

    Hábitos de lectura y consumo de información de los adolescentes en el ámbito digital

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    The present work tries to echo how the communicative metamorphoses occurred in the last years, inferring in the reading habits and in the consumption of information in a general way and more specifically in adolescents. The analysis will start from the report prepared by the writers' guild 2018 (2019), since it allows us to monitor the state of reading habits and book purchases in a generalized way in Spain. Then, apply what has been poured out to young people extensively and, finally, materializing by extrapolating all the data analyzed to the geographical area of Cadiz adolescents and their position in relation to the rest of Spanish adolescents. Gender variables will also be taken into account in a very special way, to see if there is a certain preference depending on the sex of the reader in the choice of medium (digital or analogue) and if within the digital medium there are discrepancies in the type of text read. We will also check whether digital reading by young people is reduced exclusively to short texts and whether this choice can be derived from the very nature of digital. In the same way, we will pay special attention to the preferences of analogical reading versus digital reading, when we talk about long texts, again due to the personal nature of paper reading. We will analyze the reading frequency of the different digital media, as well as the choice of other shorter texts, categorized within the taxonomy of digital reading. Finally, we will take into account what types of readers with respect to reading frequency become from digital media. The idea is to draw up a panorama that shows how reading occurs among adolescents in the digital world, by definition, closer to their thoughts and feelings

    Efficient bit-level design of an on-board digital TV demultiplexer

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    A bit-level description of the signal processing stage of an on-board integrated VLSI multi-carrier demodulator is presented in this paper, along with a description of the optimization procedure that has been developed for the signal processing functions1. The demultiplexer is capable of handling a varying number of carriers in a 36 MHz bandwidth on the satellite up-link. Its architecture has been optimized at bit-level in a way dependent on the known input signal statistics and carrier distributions allowed by the frequency plan.Peer ReviewedPostprint (published version

    SINR profile for spectral efficiency optimization of SIC receivers in the many-user regime

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    © 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.In dense wireless scenarios, and particularly under high traffic loads, the design of efficient random access protocols is necessary. Some candidate solutions are based on Direct- Sequence Spread Spectrum (DS-SS) combined with a Successive Interference Cancellation (SIC) demodulator, but the perfor- mance of these techniques is highly related to the distribution of the users received power. In that context, this paper presents a theoretical analysis to calculate the optimum user SINR profile at the decoder maximizing the spectral efficiency in bps/Hz for a specific modulation and practical Forward Error Correction (FEC) code. This solution is achieved by means of Variational Calculus operating in the asymptotic large-user case. Although a constant SINR function has been typically assumed in the literature (the one maximizing capacity), the theoretical results evidence that the optimum SINR profile must be an increasing function of the users received power. Its performance is compared with that of the uniform profile for two representative scenarios with different channel codes in a slightly overloaded system. The numerical results show that the optimum solution regulates the network load preventing the aggregate throughput from collapsing when the system is overloaded. In scenarios with a large number of transmitters, this optimum solution can be implemented in an uncoordinated manner with the knowledge of a few public system parameters.Peer ReviewedPostprint (published version

    Average performance analysis of circular and hyperbolic geolocation

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    A comparative performance analysis of four geolocation methods in terms of their theoretical root mean square positioning errors is provided. Comparison is established in two different ways: strict and average. In the strict type, methods are examined for a particular geometric configuration of base stations(BSs) with respect to mobile position, which determines a given noise profile affecting the respective time-of-arrival (TOA) or timedifference- of-arrival (TDOA) estimates. In the average type, methods are evaluated in terms of the expected covariance matrix of the position error over an ensemble of random geometries, so that comparison is geometry independent. Exact semianalytical equations and associated lower bounds (depending solely on the noise profile) are obtained for the average covariance matrix of the position error in terms of the so-called information matrix specific to each geolocation method. Statistical channel models inferred from field trials are used to define realistic prior probabilities for the random geometries. A final evaluation provides extensive results relating the expected position error to channel model parameters and the number of base stations.Peer Reviewe
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