Ponències/Comunicacions de congressos
http://hdl.handle.net/2117/1257
2017-06-27T10:51:21ZA new positive time-frequency distribution
http://hdl.handle.net/2117/104513
A new positive time-frequency distribution
Rodríguez Fonollosa, Javier; Nikias, C L
This article studies the formulation of new members of the Cohen-Posch (1985) class of positive time-frequency energy distributions. Members of this class are always positive functionals and satisfy the marginal constraints. Therefore, they can be properly interpreted as distributions. We considered the minimization of cross-entropy measures with respect to different priors or
2017-05-16T13:19:33ZRodríguez Fonollosa, JavierNikias, C LThis article studies the formulation of new members of the Cohen-Posch (1985) class of positive time-frequency energy distributions. Members of this class are always positive functionals and satisfy the marginal constraints. Therefore, they can be properly interpreted as distributions. We considered the minimization of cross-entropy measures with respect to different priors orDiversity mdir receiver for space-time dispersive channels
http://hdl.handle.net/2117/104070
Diversity mdir receiver for space-time dispersive channels
Vidal Manzano, José; Cabrera Beán, Margarita Asuncion; Agustin, Adrian; Lagunas Hernandez, Miguel A.
A particular property of the cellebrated MDIR receiver is introduced in this communication, namely, the fact that full exploitation of the diversity is obtained with multiple beamformers when the channel is spatially and timely dispersive. Therefore a new structure is developped which provides better performance. The hardware need for this new receiver may be obtained through reconfigurability of the RAKE architectures available at the base station. It will be tested in the FDD mode of UTRA.
2017-05-04T13:27:18ZVidal Manzano, JoséCabrera Beán, Margarita AsuncionAgustin, AdrianLagunas Hernandez, Miguel A.A particular property of the cellebrated MDIR receiver is introduced in this communication, namely, the fact that full exploitation of the diversity is obtained with multiple beamformers when the channel is spatially and timely dispersive. Therefore a new structure is developped which provides better performance. The hardware need for this new receiver may be obtained through reconfigurability of the RAKE architectures available at the base station. It will be tested in the FDD mode of UTRA.Joint beamforming and channel estimation for pilot-aided WCDMA systems
http://hdl.handle.net/2117/104001
Joint beamforming and channel estimation for pilot-aided WCDMA systems
Mestre Pons, Francesc X.; Nájar Martón, Montserrat; Rodríguez Fonollosa, Javier
The problem of joint beamforming and channel estimation for multi-rate multi-code systems is addressed. Usual schemes perform this filtering/estimation operation making use of a training sequence time-multiplexed with the transmitted data. However if pilot and traffic signals are transmitted simultaneously using distinct code allocation-as it is the case in recent standards such as cdma2000 or WCDMA-these schemes tend to fail. This paper proposes semi-blind techniques to overcome the uplink auto-interfering effects of such systems. It is shown that the semi-blind approach yields substantially better performance results thanks to the implicit modeling of the unknown traffic data.
2017-05-03T15:16:36ZMestre Pons, Francesc X.Nájar Martón, MontserratRodríguez Fonollosa, JavierThe problem of joint beamforming and channel estimation for multi-rate multi-code systems is addressed. Usual schemes perform this filtering/estimation operation making use of a training sequence time-multiplexed with the transmitted data. However if pilot and traffic signals are transmitted simultaneously using distinct code allocation-as it is the case in recent standards such as cdma2000 or WCDMA-these schemes tend to fail. This paper proposes semi-blind techniques to overcome the uplink auto-interfering effects of such systems. It is shown that the semi-blind approach yields substantially better performance results thanks to the implicit modeling of the unknown traffic data.Joint synchronization and symbol detection in asynchronous DS-CDMA systems
http://hdl.handle.net/2117/103983
Joint synchronization and symbol detection in asynchronous DS-CDMA systems
Rey Micolau, Francesc; Vázquez Grau, Gregorio; Riba Sagarra, Jaume
The design of accurate estimators which also consider the noise term in low SNR scenarios is paramount for achieving optimal solutions and obtaining precise symbol detectors. Particularly, this paper estimates the propagation delays focusing on asynchronous DS-CDMA systems. The proposed minimum conditioned variance (MCV) is the choice in noisy environments, implementing the best linear detector of the transmitted symbols under a minimum mean-square error criterion. The result is an estimator that improves the conditional ML (CML) solution when noise is not negligible, and attains the derived Gaussian unconditional Cramer-Rao bound (UCRB) in the whole EbNo range as classical Gaussian unconditional ML (UML) does. Consequently, the proposed MCV estimator, becomes an optimal quadratic solution achieving similar features than UML in a straightforward way, and with no assumptions on the signal statistics.
2017-05-03T13:54:09ZRey Micolau, FrancescVázquez Grau, GregorioRiba Sagarra, JaumeThe design of accurate estimators which also consider the noise term in low SNR scenarios is paramount for achieving optimal solutions and obtaining precise symbol detectors. Particularly, this paper estimates the propagation delays focusing on asynchronous DS-CDMA systems. The proposed minimum conditioned variance (MCV) is the choice in noisy environments, implementing the best linear detector of the transmitted symbols under a minimum mean-square error criterion. The result is an estimator that improves the conditional ML (CML) solution when noise is not negligible, and attains the derived Gaussian unconditional Cramer-Rao bound (UCRB) in the whole EbNo range as classical Gaussian unconditional ML (UML) does. Consequently, the proposed MCV estimator, becomes an optimal quadratic solution achieving similar features than UML in a straightforward way, and with no assumptions on the signal statistics.Space-time coding for UMTS. Performance evaluation in combination with convolutional and turbo coding
http://hdl.handle.net/2117/103917
Space-time coding for UMTS. Performance evaluation in combination with convolutional and turbo coding
Gaspa Maynou, Roger; Rodríguez Fonollosa, Javier
Space-time codes provide both diversity and coding gain when using multiple transmit antennas to increase spectral efficiency over wireless communications systems. Space-time block codes have already been included in the standardization process of UMTS in conjunction with conventional channel codes (convolutional and turbo codes). We discuss different encoding and decoding strategies when transmit diversity is combined with conventional channel codes, and present simulations results for the TDD and FDD modes of UTRA.
2017-05-02T14:57:33ZGaspa Maynou, RogerRodríguez Fonollosa, JavierSpace-time codes provide both diversity and coding gain when using multiple transmit antennas to increase spectral efficiency over wireless communications systems. Space-time block codes have already been included in the standardization process of UMTS in conjunction with conventional channel codes (convolutional and turbo codes). We discuss different encoding and decoding strategies when transmit diversity is combined with conventional channel codes, and present simulations results for the TDD and FDD modes of UTRA.A reduced-complexity and asymptotically efficient time-delay estimator
http://hdl.handle.net/2117/103912
A reduced-complexity and asymptotically efficient time-delay estimator
Seco Granados, Gonzalo; Swindlehurst, A L; Fernández Rubio, Juan Antonio; Astély, D
This paper considers the problem of estimating the time delays of multiple replicas of a known signal received by an array of antennas. Under the assumptions that the noise and co-channel interference (CCI) are spatially colored Gaussian processes and that the spatial signatures are arbitrary, the maximum likelihood (ML) solution to the general time delay estimation problem is derived. The resulting criterion for the delays yields consistent and asymptotically efficient estimates. However, the criterion is highly non-linear, and not conducive to simple minimization procedures. We propose a new cost function that is shown to provide asymptotically efficient delay estimates. We also outline a heuristic way of deriving this cost function. The form of this new estimator lends itself to minimization by the computationally attractive iterative quadratic maximum likelihood (IQML) algorithm. The existence of simple yet accurate initialization schemes based on ESPRIT and identity weightings makes the approach viable for practical implementation.
2017-05-02T13:39:30ZSeco Granados, GonzaloSwindlehurst, A LFernández Rubio, Juan AntonioAstély, DThis paper considers the problem of estimating the time delays of multiple replicas of a known signal received by an array of antennas. Under the assumptions that the noise and co-channel interference (CCI) are spatially colored Gaussian processes and that the spatial signatures are arbitrary, the maximum likelihood (ML) solution to the general time delay estimation problem is derived. The resulting criterion for the delays yields consistent and asymptotically efficient estimates. However, the criterion is highly non-linear, and not conducive to simple minimization procedures. We propose a new cost function that is shown to provide asymptotically efficient delay estimates. We also outline a heuristic way of deriving this cost function. The form of this new estimator lends itself to minimization by the computationally attractive iterative quadratic maximum likelihood (IQML) algorithm. The existence of simple yet accurate initialization schemes based on ESPRIT and identity weightings makes the approach viable for practical implementation.Time-delay estimation of the line-of-sight signal in a multipath environment
http://hdl.handle.net/2117/103911
Time-delay estimation of the line-of-sight signal in a multipath environment
Seco Granados, Gonzalo; Fernández Rubio, Juan Antonio
The problem of estimating the time-delay of the line-of-sight (LOSS) or direct signal received by an antenna array in a multipath scenario is addressed. This problem is essential in many communication, radar, sonar and navigation systems, since the signal that propagates through the direct path may be the only one that bears useful information for the operation of the receiver. In many of these systems, it is possible to have an approximate a priori knowledge about the direction-of-arrival (DOA) of the direct signal. We analyze several time-delay estimators that exploit this information. In order that they can operate in the presence of co-channel interference (CCI), it is assumed that the noise field has an arbitrary and unknown spatial correlation. We show that the maximum likelihood (ML) estimator is the only one that presents a sufficient robustness against calibration or modeling errors. Starting from the ML estimator, we derive a new method that takes the uncertainty about the steering vector of the LOSS into account.
2017-05-02T13:35:21ZSeco Granados, GonzaloFernández Rubio, Juan AntonioThe problem of estimating the time-delay of the line-of-sight (LOSS) or direct signal received by an antenna array in a multipath scenario is addressed. This problem is essential in many communication, radar, sonar and navigation systems, since the signal that propagates through the direct path may be the only one that bears useful information for the operation of the receiver. In many of these systems, it is possible to have an approximate a priori knowledge about the direction-of-arrival (DOA) of the direct signal. We analyze several time-delay estimators that exploit this information. In order that they can operate in the presence of co-channel interference (CCI), it is assumed that the noise field has an arbitrary and unknown spatial correlation. We show that the maximum likelihood (ML) estimator is the only one that presents a sufficient robustness against calibration or modeling errors. Starting from the ML estimator, we derive a new method that takes the uncertainty about the steering vector of the LOSS into account.Non-data-aided frequency offset and symbol timing estimation for binary CPM: performance bounds
http://hdl.handle.net/2117/103905
Non-data-aided frequency offset and symbol timing estimation for binary CPM: performance bounds
Riba Sagarra, Jaume; Vázquez Grau, Gregorio
The use of (spectrally efficient) CPM modulations may lead to a serious performance degradation of the classical non-data-aided (NDA) frequency and timing estimators due to the presence of self noise. The actual performance of these estimators is usually much worse than that predicted by the classical modified Cramer-Rao bound. We apply some well known results in the field of signal processing to these two important problems of synchronization. In particular we propose and explain the meaning of the unconditional CRB in the synchronization task. Simulation results for MSK and GMSK, along with the performance of some classical and previously proposed synchronizers, show that the proposed bound (along with the MCRB) is useful for a better prediction of the ultimate performance of the NDA estimators.
2017-05-02T13:14:13ZRiba Sagarra, JaumeVázquez Grau, GregorioThe use of (spectrally efficient) CPM modulations may lead to a serious performance degradation of the classical non-data-aided (NDA) frequency and timing estimators due to the presence of self noise. The actual performance of these estimators is usually much worse than that predicted by the classical modified Cramer-Rao bound. We apply some well known results in the field of signal processing to these two important problems of synchronization. In particular we propose and explain the meaning of the unconditional CRB in the synchronization task. Simulation results for MSK and GMSK, along with the performance of some classical and previously proposed synchronizers, show that the proposed bound (along with the MCRB) is useful for a better prediction of the ultimate performance of the NDA estimators.Pilot-aided ML schemes for joint beamforming and channel estimation in WCDMA systems
http://hdl.handle.net/2117/103869
Pilot-aided ML schemes for joint beamforming and channel estimation in WCDMA systems
Mestre Pons, Francesc X.; Rodríguez Fonollosa, Javier
This paper proposes semi-blind channel estimation and interference cancellation schemes for the reception of pilot-aided signals in WCDMA systems. It is shown that the performance of classical training-based schemes is severely degraded due to the code-multiplexing (as opposed to time-multiplexing) of traffic and pilot signals. The time-dispersivity of the channel destroys the orthogonality between the traffic signal and the pilot, and consequently the traffic signal appears as a new interfering signal for the channel estimation/beamforming algorithm. In order to avoid this effect, we propose techniques that exploit both the presence of the training sequence and the structure of the traffic signal in a semi-blind fashion.
2017-04-28T17:38:55ZMestre Pons, Francesc X.Rodríguez Fonollosa, JavierThis paper proposes semi-blind channel estimation and interference cancellation schemes for the reception of pilot-aided signals in WCDMA systems. It is shown that the performance of classical training-based schemes is severely degraded due to the code-multiplexing (as opposed to time-multiplexing) of traffic and pilot signals. The time-dispersivity of the channel destroys the orthogonality between the traffic signal and the pilot, and consequently the traffic signal appears as a new interfering signal for the channel estimation/beamforming algorithm. In order to avoid this effect, we propose techniques that exploit both the presence of the training sequence and the structure of the traffic signal in a semi-blind fashion.Data hidding in color images using perceptual models
http://hdl.handle.net/2117/103866
Data hidding in color images using perceptual models
Vidal Manzano, José; Sayrol Clols, Elisa; Madueño Ruíz, María Isabel
One of the problems arising from the use of digital media is the ease of identical copies of digital images or audio files, allowing manipulation and unauthorized use. Copyright is an effective tool for preserving intellectual
property of those documents but authors and publishers need effective techniques that prevent from copyright modification, due to the straightforward access to multimedia applications and the wider use of digital publications through the www. These techniques are generally called watermarking and allow the introduction of side information (i.e. author
identification, copyrights, dates, etc.). This work concentrates on the problem embedding and optimum blind detection of data 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.
2017-04-28T17:18:31ZVidal Manzano, JoséSayrol Clols, ElisaMadueño Ruíz, María IsabelOne of the problems arising from the use of digital media is the ease of identical copies of digital images or audio files, allowing manipulation and unauthorized use. Copyright is an effective tool for preserving intellectual
property of those documents but authors and publishers need effective techniques that prevent from copyright modification, due to the straightforward access to multimedia applications and the wider use of digital publications through the www. These techniques are generally called watermarking and allow the introduction of side information (i.e. author
identification, copyrights, dates, etc.). This work concentrates on the problem embedding and optimum blind detection of data 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.