Ponències/Comunicacions de congressos
http://hdl.handle.net/2117/1257
Mon, 23 Jan 2017 15:18:10 GMT
20170123T15:18:10Z

Impact of noisy annotators’ reliability in a crowdsourcing system performance
http://hdl.handle.net/2117/99747
Impact of noisy annotators’ reliability in a crowdsourcing system performance
Cabrera Beán, Margarita Asuncion; Diaz Vilor, Carles; Vidal Manzano, José
Crowdsourcing is a powerful tool to harness citizen assessments in some complex decision tasks. When multiple annotators provide their individual labels a more reliable collective decision is obtained if the individual reliability parameters are incorporated in the decision making procedure. The wellknown Maximum A Posteriori (MAP) rule weights the individual labels in proportion to the annotators’ reliability. In this work we analyze how the crowdsourcing system performance is degraded with the use of noisy annotators’ reliability parameters and we derive an alternative MAP based rule to be applied when these parameters are neither known nor even estimated by the decision system. We also derive analytical expected error rates and their upper bounds obtained by each rule as a useful tool to estimate the number of necessary annotators in the collective decision system depending on the level of noise present in the estimated reliability parameters.
Fri, 20 Jan 2017 11:04:43 GMT
http://hdl.handle.net/2117/99747
20170120T11:04:43Z
Cabrera Beán, Margarita Asuncion
Diaz Vilor, Carles
Vidal Manzano, José
Crowdsourcing is a powerful tool to harness citizen assessments in some complex decision tasks. When multiple annotators provide their individual labels a more reliable collective decision is obtained if the individual reliability parameters are incorporated in the decision making procedure. The wellknown Maximum A Posteriori (MAP) rule weights the individual labels in proportion to the annotators’ reliability. In this work we analyze how the crowdsourcing system performance is degraded with the use of noisy annotators’ reliability parameters and we derive an alternative MAP based rule to be applied when these parameters are neither known nor even estimated by the decision system. We also derive analytical expected error rates and their upper bounds obtained by each rule as a useful tool to estimate the number of necessary annotators in the collective decision system depending on the level of noise present in the estimated reliability parameters.

Equalization of nonminimum phase channels with a nonlinear architecture
http://hdl.handle.net/2117/99335
Equalization of nonminimum phase channels with a nonlinear architecture
Pagès Zamora, Alba Maria; Lagunas Hernandez, Miguel A.
The equalization of nonminimum phase channels by means of a transversal filter becomes quite complicated when the real conditions are different from the ideal ones. The optimum delay that must be applied to the reference signal in order to make the equalization of the channel with a linear filter possible, is usually not known. Even if
it is known, the channel can be nonstationary and w to find a linear equalizer optimum for all the possible situations may be difficult. On the other hand, the solution of increasing the length of the transversal filter can not be afforded when the signaltonoise ratio is low.
In this context, a nonlinear filter called the Kfilter is introduced as a good altemative to classical linear equalizers. As it will be seen below, the Kfllter is built on a strong theoretical approach and this fact gives the certainty that good results will be obtained if the Kfilter
is considered whenever a nonlinear fllter is required.
Mon, 16 Jan 2017 16:06:57 GMT
http://hdl.handle.net/2117/99335
20170116T16:06:57Z
Pagès Zamora, Alba Maria
Lagunas Hernandez, Miguel A.
The equalization of nonminimum phase channels by means of a transversal filter becomes quite complicated when the real conditions are different from the ideal ones. The optimum delay that must be applied to the reference signal in order to make the equalization of the channel with a linear filter possible, is usually not known. Even if
it is known, the channel can be nonstationary and w to find a linear equalizer optimum for all the possible situations may be difficult. On the other hand, the solution of increasing the length of the transversal filter can not be afforded when the signaltonoise ratio is low.
In this context, a nonlinear filter called the Kfilter is introduced as a good altemative to classical linear equalizers. As it will be seen below, the Kfllter is built on a strong theoretical approach and this fact gives the certainty that good results will be obtained if the Kfilter
is considered whenever a nonlinear fllter is required.

Asymptotic MAP upper bounds for LDPC codes
http://hdl.handle.net/2117/98937
Asymptotic MAP upper bounds for LDPC codes
Matas Navarro, David; Lamarca Orozco, M. Meritxell
This paper aims at computing tight upper bounds for the maximum a posteriori threshold of lowdensity parity check codes in the asymptotic blocklength regime for the transmission over binaryinput memoryless symmetricoutput channels. While these bounds are already known, we propose a novel derivation based on a completely different approach: based solely on the concept of the chain rule and the conditional entropy, resorting to the concentration theorem for the code ensemble to compute the syndrome entropy with low complexity employing density
evolution.
Tue, 10 Jan 2017 10:49:48 GMT
http://hdl.handle.net/2117/98937
20170110T10:49:48Z
Matas Navarro, David
Lamarca Orozco, M. Meritxell
This paper aims at computing tight upper bounds for the maximum a posteriori threshold of lowdensity parity check codes in the asymptotic blocklength regime for the transmission over binaryinput memoryless symmetricoutput channels. While these bounds are already known, we propose a novel derivation based on a completely different approach: based solely on the concept of the chain rule and the conditional entropy, resorting to the concentration theorem for the code ensemble to compute the syndrome entropy with low complexity employing density
evolution.

Optimum watermark detection in color images
http://hdl.handle.net/2117/98440
Optimum watermark detection in color images
Sayrol Clols, Elisa; Vidal Manzano, José; Cabanillas, Silvia; Santamaria, Sonia
This work concentrates on the problem of watermarking embedding and optimum detection in color images through the use of spread spectrum techniques both in space (Direct Sequence Spread Spectrum or DSSS) and frequency (Frequency Hopping). It is applied to RGB and opponent color component representations Perceptive information is considered in both color systems. Some tests are performed in order to ensure imperceptibility and to assess detection quality of the optimum color detectors.
Fri, 16 Dec 2016 10:08:03 GMT
http://hdl.handle.net/2117/98440
20161216T10:08:03Z
Sayrol Clols, Elisa
Vidal Manzano, José
Cabanillas, Silvia
Santamaria, Sonia
This work concentrates on the problem of watermarking embedding and optimum detection in color images through the use of spread spectrum techniques both in space (Direct Sequence Spread Spectrum or DSSS) and frequency (Frequency Hopping). It is applied to RGB and opponent color component representations Perceptive information is considered in both color systems. Some tests are performed in order to ensure imperceptibility and to assess detection quality of the optimum color detectors.

Uplink beamforming for the FDD mode of UTRA
http://hdl.handle.net/2117/98437
Uplink beamforming for the FDD mode of UTRA
Mestre Pons, Francesc X.; Rodríguez Fonollosa, Javier; Vázquez Grau, Gregorio
This paper presents some link level simulation results for the evaluation of adaptive antennas in the uplink of the FDD mode of UTRA (UMTS terrestrial radio access). Two families of algorithms were initially considered, the basic difference between them being their ability/disability to suppress the contribution from WCDMA directional interfering sources. Two distinct schemes were established as representatives for each family and their performance was evaluated in presence of some illustrative interfering scenarios. In the light of the results it is shown that timereference beamforming algorithms suffer from severe beam pattern distortion effects when applied as such. This in turn causes harsh performance degradation in terms of raw BER, especially at high SINR levels. It is shown that these shortcomings are essentially caused by the uplink multiplexing of the traffic channel, which is seen by the base station as a powerful interfering source coming from the direction of arrival of the desired user.
Fri, 16 Dec 2016 09:57:16 GMT
http://hdl.handle.net/2117/98437
20161216T09:57:16Z
Mestre Pons, Francesc X.
Rodríguez Fonollosa, Javier
Vázquez Grau, Gregorio
This paper presents some link level simulation results for the evaluation of adaptive antennas in the uplink of the FDD mode of UTRA (UMTS terrestrial radio access). Two families of algorithms were initially considered, the basic difference between them being their ability/disability to suppress the contribution from WCDMA directional interfering sources. Two distinct schemes were established as representatives for each family and their performance was evaluated in presence of some illustrative interfering scenarios. In the light of the results it is shown that timereference beamforming algorithms suffer from severe beam pattern distortion effects when applied as such. This in turn causes harsh performance degradation in terms of raw BER, especially at high SINR levels. It is shown that these shortcomings are essentially caused by the uplink multiplexing of the traffic channel, which is seen by the base station as a powerful interfering source coming from the direction of arrival of the desired user.

Blind channel equalization using weighted subspace methods
http://hdl.handle.net/2117/98431
Blind channel equalization using weighted subspace methods
Ruiz Feliu, Rafael; Cabrera Beán, Margarita Asuncion
This paper addresses the problems of blind channel estimation and symbol detection with second order statistics methods from the received data. It can be shown that this problem is similar to direction of arrival (DOA) estimation, where many solutions like the MUSIC algorithm or
Fri, 16 Dec 2016 09:38:52 GMT
http://hdl.handle.net/2117/98431
20161216T09:38:52Z
Ruiz Feliu, Rafael
Cabrera Beán, Margarita Asuncion
This paper addresses the problems of blind channel estimation and symbol detection with second order statistics methods from the received data. It can be shown that this problem is similar to direction of arrival (DOA) estimation, where many solutions like the MUSIC algorithm or

Sphericity minimum description length: asymptotic performance under unknown noise variance
http://hdl.handle.net/2117/98254
Sphericity minimum description length: asymptotic performance under unknown noise variance
Font Segura, Josep; Riba Sagarra, Jaume; Vázquez Grau, Gregorio
This paper revisits the model order selection problem in the context of secondorder spectrum sensing in cognitive radio. Taking advantage of the recent interest on the generalized likelihood ratio (GLR), the asymptotic performance of the minimum description length (MDL) rule under unknown noise variance is addressed. In particular, by exploiting the asymptotically Chisquared distribution of the GLR, a complete characterization of the error probability is reported, instead of approximating only the misseddetection probability as done in the literature.
Wed, 14 Dec 2016 15:20:54 GMT
http://hdl.handle.net/2117/98254
20161214T15:20:54Z
Font Segura, Josep
Riba Sagarra, Jaume
Vázquez Grau, Gregorio
This paper revisits the model order selection problem in the context of secondorder spectrum sensing in cognitive radio. Taking advantage of the recent interest on the generalized likelihood ratio (GLR), the asymptotic performance of the minimum description length (MDL) rule under unknown noise variance is addressed. In particular, by exploiting the asymptotically Chisquared distribution of the GLR, a complete characterization of the error probability is reported, instead of approximating only the misseddetection probability as done in the literature.

Distributed multivariate regression with unknown noise covariance in the presence of outliers: an MDL approach
http://hdl.handle.net/2117/97423
Distributed multivariate regression with unknown noise covariance in the presence of outliers: an MDL approach
López Valcarce, Roberto; Romero Gonzalez, Daniel; Sala Álvarez, José; Pagès Zamora, Alba Maria
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.
Tue, 29 Nov 2016 13:31:08 GMT
http://hdl.handle.net/2117/97423
20161129T13:31:08Z
López Valcarce, Roberto
Romero Gonzalez, Daniel
Sala Álvarez, José
Pagès Zamora, Alba Maria
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.

Distributed AOAbased source positioning in NLOS with sensor networks
http://hdl.handle.net/2117/97377
Distributed AOAbased source positioning in NLOS with sensor networks
Giménez Febrer, Pedro Juan; Pagès Zamora, Alba Maria; Silva Pereira, Silvana; López Valcarce, Roberto
This paper focuses on the problem of positioning a
source using angleofarrival measurements taken by a wireless
sensor network in which some of the nodes experience non lineofsight
(LOS) propagation conditions. In order to mitigate the
errors induced by the nodes in NLOS, we derive an algorithm
that combines the expectationmaximization algorithm with a
weighted leastsquares estimation of the source position so that
the nodes in NLOS are eventually identified and discarded.
Moreover, a distributed version of this algorithm based on a
diffusion strategy that iteratively refines the position estimate
while driving the network to a consensus is presented.
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Tue, 29 Nov 2016 08:59:43 GMT
http://hdl.handle.net/2117/97377
20161129T08:59:43Z
Giménez Febrer, Pedro Juan
Pagès Zamora, Alba Maria
Silva Pereira, Silvana
López Valcarce, Roberto
This paper focuses on the problem of positioning a
source using angleofarrival measurements taken by a wireless
sensor network in which some of the nodes experience non lineofsight
(LOS) propagation conditions. In order to mitigate the
errors induced by the nodes in NLOS, we derive an algorithm
that combines the expectationmaximization algorithm with a
weighted leastsquares estimation of the source position so that
the nodes in NLOS are eventually identified and discarded.
Moreover, a distributed version of this algorithm based on a
diffusion strategy that iteratively refines the position estimate
while driving the network to a consensus is presented.

Analysis of LDPC code syndrome entropy based on subgraphs
http://hdl.handle.net/2117/96486
Analysis of LDPC code syndrome entropy based on subgraphs
Matas Navarro, David; Lamarca Orozco, M. Meritxell
We propose a method to bound the syndrome entropy of linear block codes from their factor graph representation. It is specially suited for sparse graphs such as those of low density parity check codes. It is based on the chain rule decomposition of the entropy and the confinement of dependencies within code subgraphs. After
forcing or assuming the subgraphs to have a tree structure, the computation is done by means of density evolution as for a belief propagation analysis. We employ this method to compute upper bounds of the LDPC code syndrome entropy, which allows us to obtain asymptotic MAP upper bounds that match the ones obtained by the generalized area theorem.
Thu, 10 Nov 2016 13:54:08 GMT
http://hdl.handle.net/2117/96486
20161110T13:54:08Z
Matas Navarro, David
Lamarca Orozco, M. Meritxell
We propose a method to bound the syndrome entropy of linear block codes from their factor graph representation. It is specially suited for sparse graphs such as those of low density parity check codes. It is based on the chain rule decomposition of the entropy and the confinement of dependencies within code subgraphs. After
forcing or assuming the subgraphs to have a tree structure, the computation is done by means of density evolution as for a belief propagation analysis. We employ this method to compute upper bounds of the LDPC code syndrome entropy, which allows us to obtain asymptotic MAP upper bounds that match the ones obtained by the generalized area theorem.