The Variation of Prediction Footprint (VPF), formerly used in video forensics for double compression detection and GOP size estimation, is comprehensively investigated to improve its acquisition capabilities and extend its use to video sequences that contain bi-directional frames (B-frames). By relying on a universal rate-distortion analysis applied to a generic double compression scheme, we first explain the rationale behind the presence of the VPF in double compressed videos and then justify the need of exploiting a new source of information such as the motion vectors, to enhance the VPF acquisition process. Finally, we describe the shifted VPF induced by the presence of B-frames and detail how to compensate the shift to avoid misguided GOP size estimations. The experimental results show that the proposed Generalized VPF (G-VPF) technique outperforms the state of the art, not only in terms of double compression detection and GOP size estimation, but also in reducing computational time.

VL - 15 IS - 1 ER - TY - CONF T1 - Prediction Residue Analysis in MPEG-2 Double Compressed Video Sequences T2 - EUSIPCO Y1 - 2019 A1 - David Vázquez-Padín A1 - Fernando Pérez-González KW - double compression detection KW - GOP size estimation KW - MPEG-2 KW - prediction residue analysis KW - video forensics AB -In video forensics, the study of the prediction residue across successive frames is key to verify the integrity of digital videos. Focusing on an MPEG-2 double compression scheme, we analyze how the variance of the prediction residue evolves during the second compression depending on the type of frame (either I or P) employed in the first encoding and exploring different compression strengths and deadzone widths for quantization. This analysis reveals that the width of the quantizer deadzones actually affects the performance of existing methods based on the Variation of Prediction Footprint (VPF) for double compression detection and Group Of Pictures (GOP) size estimation. The predicted behavior from the theoretical characterization of the prediction residue is confirmed through experimental results with real video sequences.

JF - EUSIPCO CY - A Coruña, Spain ER - TY - RPRT T1 - Technical Report: MPEG-2 Prediction Residue Analysis Y1 - 2019 A1 - David Vázquez-Padín A1 - Fernando Pérez-González PB - University of Vigo ER - TY - CONF T1 - Locally optimal invariant detector for testing equality of two power spectral densities T2 - IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP) Y1 - 2018 A1 - David Ramírez A1 - Daniel Romero A1 - Javier Vía A1 - R. López-Valcarce A1 - Ignacio Santamaría KW - cognitive radio KW - winter AB -This work addresses the problem of determining whether two multivariate random time series have the same power spectral density

(PSD), which has applications, for instance, in physical-layer security and cognitive radio. Remarkably, existing detectors for this

problem do not usually provide any kind of optimality. Thus, we study here the existence under the Gaussian assumption of optimal

invariant detectors for this problem, proving that the uniformly most powerful invariant test (UMPIT) does not exist. Thus, focusing on

close hypotheses, we show that the locally most powerful invariant test (LMPIT) only exists for univariate time series. In the multivariate

case, we prove that the LMPIT does not exist. However, this proof suggests two LMPIT-inspired detectors, one of which outperforms

previously proposed approaches, as computer simulations show.

JF - IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP)
CY - Calgary, Canada
ER -
TY - JOUR
T1 - Testing equality of multiple power spectral density matrices
JF - IEEE Trans. Signal Processing
Y1 - 2018
A1 - David Ramírez
A1 - Daniel Romero
A1 - Javier Vía
A1 - R. López-Valcarce
A1 - Ignacio Santamaría
KW - cognitive radio
KW - winter
VL - 66
IS - 23
ER -
TY - JOUR
T1 - A Random Matrix Approach to the Forensic Analysis of Upscaled Images
JF - IEEE Transactions on Information Forensics and Security
Y1 - 2017
A1 - David Vázquez-Padín
A1 - Fernando Pérez-González
A1 - Pedro Comesaña
KW - Multimedia security
KW - winter
VL - 12
IS - 9
ER -
TY - CONF
T1 - Random Matrix Theory for Modeling the Eigenvalue Distribution of Images under Upscaling
T2 - International Tyrrhenian Workshop on Digital Communication 2017
Y1 - 2017
A1 - David Vázquez-Padín
A1 - Fernando Pérez-González
A1 - Pedro Comesaña
KW - Multimedia security
KW - winter
AB - The stochastic representation of digital images through a two-dimensional autoregressive (2D-AR) model offers a proper way to approximate the empirical distribution of the eigenvalues coming from genuine images. By considering this model, we apply random matrix theory to analytically derive the asymptotic eigenvalue distribution of causal 2D-AR random fields that have undergone an upscaling operation with a particular interpolation kernel. This eigenvalue characterization is useful in developing new forensic techniques for image resampling detection since we can use theoretical bounds to drive the decision of detectors based on subspace decomposition. Moreover, experimental results with real images show that the obtained asymptotic limits turn out to be excellent approximations, even when working with images of small size.

JF - International Tyrrhenian Workshop on Digital Communication 2017 PB - Springer International Publishing CY - Palermo, Italy ER - TY - RPRT T1 - Technical Report UV-TSC-DVP-19042017: Derivation of the Asymptotic Eigenvalue Distribution for Causal 2D-AR Models under Upscaling Y1 - 2017 A1 - David Vázquez-Padín A1 - Fernando Pérez-González A1 - Pedro Comesaña PB - University of Vigo ER - TY - CONF T1 - Time-domain channel estimation for wideband millimeter wave systems with hybrid architecture T2 - IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) Y1 - 2017 A1 - Kiran Venugopal A1 - Ahmed Alkhateeb A1 - Robert W. Heath Jr. A1 - Nuria González-Prelcic KW - compass KW - mmWave KW - myrada AB -Millimeter wave (mm Wave) systems will likely employ large antennas at both the transmitter and receiver for directional beamforming. Hybrid analog/digital MIMO architectures have been proposed previously for leveraging both array gain and multiplexing gain, while reducing the power consumption in analog-to-digital converters. Channel knowledge is needed to design the hybrid precoders/combiners, which is difficult to obtain due to the large antenna arrays and the frequency selective nature of the channel. In this paper, we propose a sparse recovery based time-domain channel estimation technique for hybrid architecture based frequency selective mmWave systems. The proposed compressed sensing channel estimation algorithm is shown to provide good estimation error performance, while requiring small training overhead. The simulation results show that using multiple RF chains at the receiver and the transmitter further reduces the training overhead.

JF - IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) ER - TY - CONF T1 - Co-creating Security-and-Privacy-by-Design Systems T2 - International Conference on Availability, Reliability and Security (ARES) Y1 - 2016 A1 - Sauro Vicini A1 - Francesco Alberti A1 - Nicolás Notario A1 - Alberto Crespo A1 - Juan Ramón Troncoso-Pastoriza A1 - Alberto Sanna JF - International Conference on Availability, Reliability and Security (ARES) CY - Salzburg, Germany ER - TY - THES T1 - Detection of Image Resampling and Video Encoding Footprints for Forensic Applications Y1 - 2016 A1 - David Vázquez-Padín PB - University of Vigo CY - Vigo ER - TY - JOUR T1 - Multiantenna GLR detection of rank-one signals with known power spectral shape under spatially uncorrelated noise JF - IEEE Transactions on Signal Processing Y1 - 2016 A1 - Josep Sala A1 - Gonzalo Vázquez-Vilar A1 - R. López-Valcarce A1 - Saeid Sedighi A1 - Abbas Taherpour KW - cognitive radio KW - compass AB -We establish the generalized likelihood ratio (GLR) test for a Gaussian signal of known power spectral shape and unknown rank-one spatial signature in additive white Gaussian noise with an unknown diagonal spatial correlation matrix. This is motivated by spectrum sensing problems in dynamic spectrum access (DSA), in which the temporal correlation of the primary signal can be assumed known up to a scaling, and where the noise is due to an uncalibrated receive array. For spatially independent identically distributed (i.i.d.) noise, the corresponding GLR test reduces to a scalar optimization problem, whereas the GLR detector in the general non-i.i.d. case yields a more involved expression, which can be computed via alternating optimization methods. Low signal-to-noise ratio (SNR) approximations to the detectors are given, together with an asymptotic analysis showing the influence on detection performance of the signal power spectrum and SNR distribution across antennas. Under spatial rank-P conditions, we show that the rank-one GLR detectors are consistent with a statistical criterion that maximizes the output energy of a beamformer operating on filtered data. Simulation results support our theoretical findings in that exploiting prior knowledge on the signal power spectrum can result in significant performance improvement.

VL - 64 IS - 23 ER - TY - JOUR T1 - Cramér-Rao Bounds for SNR Estimation of Oversampled Linearly Modulated Signals JF - IEEE Trans. Signal Processing Y1 - 2015 A1 - R. López-Valcarce A1 - J. Villares A1 - J. Riba A1 - W. Gappmair A1 - C. Mosquera KW - adaptive signal processing KW - compass KW - Cramér-Rao bound (CRB) KW - dynacs KW - oversampling KW - Signal-to-noise ratio (SNR) AB -Most Signal-to-noise ratio (SNR) estimators use the

receiver matched filter output sampled at the symbol rate, an

approach which does not preserve all information in the analog

waveform due to aliasing. Thus, it is relevant to ask whether

avoiding aliasing could improve SNR estimation. To this end, we

compute the corresponding data-aided (DA) and non-data-aided

(NDA) Cramér-Rao bounds (CRBs). We adopt a novel dual filter

framework, which is shown to be information-preserving under

suitable conditions and considerably simplifies the analysis. It is

shown that the CRB can be substantially reduced by exploiting

any available excess bandwidth, depending on the modulation

scheme, the SNR range, and the estimator (DA or NDA) type.

VL - 63
IS - 7
ER -
TY - JOUR
T1 - A Greedy Topology Design to Accelerate Consensus in Broadcast Wireless Sensor Networks
JF - Information Processing Letters
Y1 - 2015
A1 - Massimo Vecchio
A1 - R. López-Valcarce
KW - compass
KW - wsn
AB - We present techniques to improve convergence speed of distributed average consensus algorithms in wireless sensor networks by means of topology design. A broadcast network is assumed, so that only the transmit power of each node can be independently controlled, rather than each individual link. Starting with a maximally connected configuration in which all nodes transmit at full power, the proposed methods successively reduce the transmit power of a chosen node in order to remove one and only one link; nodes are greedily selected either in order to yield fastest convergence at each step, or if they have the largest degree in the network. These greedy schemes provide a good complexity-performance tradeoff with respect to full-blown global search methods. As a side benefit, improving the convergence speed also results in savings in energy consumption with respect to the maximally connected setting.

VL - 115 IS - 3 ER - TY - JOUR T1 - Improving Area Coverage of Wireless Sensor Networks Via Controllable Mobile Nodes: a Greedy Approach JF - Journal of Network and Computer Applications Y1 - 2015 A1 - Massimo Vecchio A1 - R. López-Valcarce KW - compass KW - wsn AB -Reliable wide-area monitoring with Wireless Sensor Networks (WSNs) remains a problem of

interest: simply deploying more nodes to cover wider areas is generally not a viable solution, due to

deployment and maintenance costs and the increase in radio interference. One possible solution

gaining popularity is based on the use of a reduced number of mobile nodes with controllable

trajectories in the monitored field. In this framework, we present a distributed technique for iteratively

computing the trajectories of the mobile nodes in a greedy fashion. The static sensor nodes actively

assist the mobile nodes in this task by means of a bidding protocol, thus participating towards the goal

of maximizing the area coverage of the monitored field. The performance of the proposed technique is

evaluated on various simulation scenarios with different number of mobile and static nodes in terms of

achieved coverage and mean time to achieve X% coverage. Comparison with previous state-of-the-art

techniques reveals the effectiveness and stability of the proposed method.

VL - 48
ER -
TY - CONF
T1 - Pushing for higher rates and efficiency in Satcom: the different perspectives within SatNExIV
T2 - Twelfth International Symposium on Wireless Communication Systems (ISWCS)
Y1 - 2015
A1 - Miguel Ángel Vázquez
A1 - Ana Pérez Neira
A1 - Carlos Mosquera
A1 - Bhavani Shankar
A1 - Pol Henarejos
A1 - Athanasios Panagopoulos
A1 - Giovanni Giambene
A1 - Vasilios Siris
A1 - George Polyzos
A1 - Nader Alagha
KW - satcom
JF - Twelfth International Symposium on Wireless Communication Systems (ISWCS)
CY - Brussels
ER -
TY - CONF
T1 - An SVD Approach to Forensic Image Resampling Detection
T2 - EUSIPCO
Y1 - 2015
A1 - David Vázquez-Padín
A1 - Pedro Comesaña
A1 - Fernando Pérez-González
KW - compass
KW - digital image forensics
KW - resampling detection
KW - SVD
KW - tampering detection
AB - This paper describes a new strategy for image resampling detection whenever the applied resampling factor is larger than one. Delving into the linear dependencies induced in an image after the application of an upsampling operation, we show that interpolated images belong to a subspace defined by the interpolation kernel. Within this framework, by computing the SVD of a given image block and a measure of its degree of saturated pixels per row/column, we derive a simple detector capable of discriminating between upsampled images and genuine images. Furthermore, the proposed detector shows remarkable results with blocks of small size and outperforms state-of-the-art methods.

JF - EUSIPCO
ER -
TY - CONF
T1 - How to Implement Doubly-Stochastic Matrices for Consensus-Based Distributed Algorithms
T2 - IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM)
Y1 - 2014
A1 - S. Valcárcel-Macua
A1 - C. Moreno-León
A1 - J. S. Romero
A1 - Silvana Silva Pereira
A1 - Javier Zazo
A1 - Alba Pagès-Zamora
A1 - R. López-Valcarce
A1 - S. Zazo
KW - compass
KW - dynacs
KW - wsn
AB - Doubly-stochastic matrices are usually required by

consensus-based distributed algorithms. We propose a simple

and efficient protocol and present some guidelines for implementing

doubly-stochastic combination matrices even in noisy,

asynchronous and changing topology scenarios. The proposed

ideas are validated with the deployment of a wireless sensor

network, in which nodes run a distributed algorithm for robust

estimation in the presence of nodes with faulty sensors.

JF - IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM)
CY - A Coruña, Spain
ER -
TY - JOUR
T1 - A Cognitive Mobile BTS Solution with Software-Defined Radioelectric Sensing
JF - Sensors
Y1 - 2013
A1 - J. Muñoz
A1 - J. Vales-Alonso
A1 - F. Quiñoy-García
A1 - Costas-Sanz, S.
A1 - M. Pillado
A1 - F.J. González-Castaño
A1 - M. García-Sanchez
A1 - R. López-Valcarce
A1 - C. López-Bravo
KW - cognitive radio
KW - dynacs
KW - mobile communications
KW - SDR
KW - vehicular communications
AB - Private communications inside large vehicles such as ships may be effectively provided using standard cellular systems. In this paper we propose a new solution based on software-defined radio with electromagnetic sensing support. Software-defined radio allows low-cost developments and, potentially, added-value services not available in commercial cellular networks. The platform of reference, OpenBTS, only supports single-channel cells. Our proposal, however, has the ability of changing BTS channel frequency without disrupting ongoing communications. This ability should be mandatory in vehicular environments, where neighbouring cell configurations may change rapidly, so a moving cell must be reconfigured in real-time to avoid interferences. Full details about frequency occupancy sensing and the channel reselection procedure are provided in this paper. Moreover, a procedure for fast terminal detection is proposed. This may be decisive in emergency situations, e.g., if someone falls overboard. Different tests confirm the feasibility of our proposal and its compatibility with commercial GSM terminals.

VL - 13 IS - 2 ER - TY - JOUR T1 - On the design of a novel two-objective harmony search approach for distance- and connectivity-based localization in wireless sensor networks JF - Engineering Applications of Artificial Intelligence Y1 - 2013 A1 - Diana Manjarres A1 - Javier Del Ser A1 - Sergio Gil-Lopez A1 - Massimo Vecchio A1 - Itziar Landa-Torres A1 - Sancho Salcedo-Sanz A1 - R. López-Valcarce KW - dynacs KW - wsn VL - 26 IS - 2 ER - TY - CONF T1 - Localization of Forgeries in MPEG-2 Video through GOP Size and DQ analysis T2 - IEEE International Workshop on Multimedia Signal Processing (MMSP) Y1 - 2013 A1 - Daniele Labartino A1 - Tiziano Bianchi A1 - Alessia De Rosa A1 - Marco Fontani A1 - David Vázquez-Padín A1 - Alessandro Piva A1 - Mauro Barni AB -This work addresses forgery localization in MPEG-2 compressed videos. The proposed method is based on the analysis of Double Quantization (DQ) traces in frames that were encoded twice as intra (i.e., I-frames). Employing a state-of-the-art method, such frames are located in the video under analysis by estimating the size of the Group Of Pictures (GOP) that was used in the first compression; then, the DQ analysis is devised for the MPEG-2 encoding scheme and applied to frames that were intra-coded in both the first and second compression. In such a way, regions that were manipulated between the two encodings are detected. Compared to existing methods based on double quantization analysis, the proposed scheme makes forgery localization possible on a wider range of settings.

**Top 10% Award**

The problem of resampling factor estimation as a means for tampering detection has been largely investigated. Most of the existing techniques rely on the analysis of cyclic correlations induced in the resampled signal. However, in this paper, a new direction is explored by addressing the same problem in terms of the set-membership estimation theory. The proposed technique constructs a model of the problem using available a priori knowledge and in consonance with a finite number of observations that comes from the resampled signal under study. With this information, the proposed technique is able to provide an estimate of the resampling factor applied to the original signal and, if required, an estimate of such signal and an estimate of the interpolation filter. The performance in terms of accuracy and MSE of the proposed approach is evaluated and comparative results with state-of-the-art methods are reported.

Many problems in digital communications involve wideband radio signals. As the most recent example, the impressive advances in Cognitive Radio systems make even more necessary the development of sampling schemes for wideband radio signals with spectral holes. This is equivalent to considering a sparse multiband signal in the framework of Compressive Sampling theory. Starting from previous results on multicoset sampling and recent advances in compressive sampling, we analyze the matrix involved in the corresponding reconstruction equation and define a new method for the design of universal multicoset codes, that is, codes guaranteeing perfect reconstruction of the sparse multiband signal.

JF - IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) CY - Kyoto (Japan) SN - 978-1-4673-0044-5 ER - TY - CONF T1 - Detection of Gaussian signals in unknown time-varying channels T2 - IEEE Statistical Signal Processing Workshop (SSP 2012) Y1 - 2012 A1 - Daniel Romero A1 - Javier Vía A1 - R. López-Valcarce A1 - Ignacio Santamaría KW - cognitive radio KW - dynacs KW - spectrum sensing AB -Detecting the presence of a white Gaussian signal distorted by a noisy time-varying channel is addressed by means of three different detectors. First, the generalized likelihood ratio test (GLRT) is found for the case where the channel has no temporal structure, resulting in the well-known Bartlett’s test. Then it is shown that, under the transformation group given by scaling factors, a locally most powerful invariant test (LMPIT) does not exist. Two alternative approaches are explored in the low signal-to-noise ratio (SNR) regime: the first assigns a prior probability density function (pdf) to the channel (hence modeled as random), whereas the second assumes an underlying basis expansion model (BEM) for the (now deterministic) channel and obtains the maximum likelihood (ML) estimates of the parameters relevant for the detection problem. The performance of these detectors is evaluated via Monte Carlo simulation.

JF - IEEE Statistical Signal Processing Workshop (SSP 2012)
PB - IEEE
CY - Ann Arbor, MI
ER -
TY - CONF
T1 - Detection of video double encoding with GOP size estimation
T2 - IEEE International Workshop on Information Forensics and Security (WIFS)
Y1 - 2012
A1 - David Vázquez-Padín
A1 - Marco Fontani
A1 - Tiziano Bianchi
A1 - Pedro Comesaña
A1 - Alessandro Piva
A1 - Mauro Barni
AB - Video forensics is an emerging discipline, that aims at inferring information about the processing history undergone by a digital video in a blind fashion. In this work we introduce a new forensic footprint and, based on it, propose a method for detecting whether a video has been encoded twice; if this is the case, we also estimate the size of the Group Of Pictures (GOP) employed during the first encoding. As shown in the experiments, the footprint proves to be very robust even in realistic settings (i.e., when encoding is carried out using typical compression rates), that are rarely addressed by existing techniques.

JF - IEEE International Workshop on Information Forensics and Security (WIFS) PB - IEEE CY - Tenerife, Spain ER - TY - CONF T1 - ML Estimation of the Resampling Factor T2 - IEEE International Workshop on Information Forensics and Security (WIFS) Y1 - 2012 A1 - David Vázquez-Padín A1 - Pedro Comesaña AB -In this work, the problem of resampling factor estimation for tampering detection is addressed following the maximum likelihood criterion. By relying on the rounding operation applied after resampling, an approximation of the likelihood function of the quantized resampled signal is obtained. From the underlying statistical model, the maximum likelihood estimate is derived for one-dimensional signals and a piecewise linear interpolation. The performance of the obtained estimator is evaluated, showing that it outperforms state-of-the-art methods.

JF - IEEE International Workshop on Information Forensics and Security (WIFS) PB - IEEE CY - Tenerife, Spain ER - TY - JOUR T1 - Multiantenna GLR detection of rank-one signals with known power spectrum in white noise with unknown spatial correlation JF - IEEE Trans. on Signal Processing Y1 - 2012 A1 - Josep Sala A1 - Gonzalo Vázquez-Vilar A1 - R. López-Valcarce KW - cognitive radio KW - dynacs AB -Multiple-antenna detection of a Gaussian signal with spatial rank one in temporally white Gaussian noise with arbitrary and unknown spatial covariance is considered. This is motivated by spectrum sensing problems in the context of Dynamic Spectrum Access in which several secondary networks coexist but do not cooperate, creating a background of spatially correlated broadband interference. When the temporal correlation of the signal of interest is assumed known up to a scale factor, the corresponding Generalized Likelihood Ratio Test is shown to yield a scalar optimization problem. Closed-form expressions of the test are obtained for the general signal spectrum case in the low signal-to-noise ratio (SNR) regime, as well as for signals with binary-valued power spectrum in arbitrary SNR. The two resulting detectors turn out to be equivalent. An asymptotic approximation to the test distribution for the low-SNR regime is derived, closely matching empirical results from spectrum sensing simulation experiments.

VL - 60
IS - 6
ER -
TY - CONF
T1 - On the Application of a Hybrid Harmony Search Algorithm to Node Localization in Anchor-based Wireless Sensor Networks
T2 - IEEE International Conference on Intelligent Systems Design and Applications (ISDA)
Y1 - 2011
A1 - Diana Manjarres
A1 - Javier Del Ser
A1 - Sergio Gil-Lopez
A1 - Massimo Vecchio
A1 - Itziar Landa-Torres
A1 - R. López-Valcarce
JF - IEEE International Conference on Intelligent Systems Design and Applications (ISDA)
ER -
TY - CONF
T1 - Detection diversity of multiantenna spectrum sensors
T2 - IEEE Int. Conf. on Acoustics, Speech and Signal Processing (ICASSP 2011)
Y1 - 2011
A1 - Gonzalo Vázquez-Vilar
A1 - R. López-Valcarce
A1 - Ashish Pandharipande
KW - cognitive radio
KW - detection diversity
KW - spectrum sensing
AB - In the context of spectrum sensing, we investigate the performance of detectors equipped with M antennas (co-located or distributed) under Rayleigh fading, in terms of detection diversity. Rather than the high-SNR concept of diversity order common in the communications literature, we adopt the notion recently advocated by Daher and Adve in the radar community: the slope of the average probability of detection (\bar{P}_D) vs. SNR curve at \bar{P}_D = 0.5. This definition is well suited to spectrum sensing, which invariably deals with low SNR levels. It is shown that the diversity order grows as M for an optimal centralized detector having access to all observations, whereas for the two distributed schemes considered (the multiantenna energy detector and the OR detector) it grows no faster than √M.

JF - IEEE Int. Conf. on Acoustics, Speech and Signal Processing (ICASSP 2011)
PB - IEEE
CY - Prague, Czech Republic
ER -
TY - JOUR
T1 - Detection of Rank-P Signals in Cognitive Radio Networks With Uncalibrated Multiple Antennas
JF - IEEE Trans. on Signal Processing
Y1 - 2011
A1 - David Ramírez
A1 - Gonzalo Vázquez-Vilar
A1 - R. López-Valcarce
A1 - Javier Vía
A1 - Ignacio Santamaría
KW - cognitive radio
KW - dynacs
KW - spectrum sensing
AB - Spectrum sensing is a key component of the Cognitive Radio paradigm. Typically, primary signals have to be detected with uncalibrated receivers at signal-to-noise ratios (SNRs) well below decodability levels. Multiantenna detectors exploit spatial independence of receiver thermal noise to boost detection performance and robustness. We study the problem

of detecting a Gaussian signal with rank-P unknown spatial

covariance matrix in spatially uncorrelated Gaussian noise with

unknown covariance using multiple antennas. The generalized

likelihood ratio test (GLRT) is derived for two scenarios. In the

first one, the noises at all antennas are assumed to have the same (unknown) variance, whereas in the second, a generic diagonal noise covariance matrix is allowed in order to accommodate calibration uncertainties in the different antenna frontends. In the latter case, the GLRT statistic must be obtained numerically, for which an efficient method is presented. Furthermore, for asymptotically low SNR, it is shown that the GLRT does admit a closed form, and the resulting detector performs well in practice. Extensions are presented in order to account for unknown temporal correlation in both signal and noise, as well as frequency-selective channels.

VL - 59
IS - 8
ER -
TY - CONF
T1 - An Effective Metaheuristic Approach to Node Localization in Wireless Sensor Networks
T2 - IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS)
Y1 - 2011
A1 - Massimo Vecchio
A1 - R. López-Valcarce
A1 - Francesco Marcelloni
JF - IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS)
ER -
TY - CONF
T1 - Exposing original and duplicated regions using SIFT features and resampling traces
T2 - International Workshop on Digital Watermarking (IWDW)
Y1 - 2011
A1 - David Vázquez-Padín
A1 - Fernando Pérez-González
KW - Image forensics
KW - region duplication
KW - resampling estimation
KW - SIFT
AB - A common type of digital image forgery is the duplication of a region in the same image to conceal something in a captured scene. The detection of region duplication forgeries has been recently addressed using methods based on SIFT features that provide points of the regions involved in the tampering and also the parameters of the geometric transformation between both regions. However, considering this output, there is not yet any information about which of the regions are originals and which are the duplicated ones. A reliable image forensic analysis must provide this information. In this paper, we propose to use a resampling-based method to provide an accurate way to distinguish the original and the tampered regions by analizing the resampling factor of each area. Comparative results are presented to evaluate the performance of the combination of both methods.

JF - International Workshop on Digital Watermarking (IWDW) PB - Springer Berlin Heidelberg CY - Atlantic City, USA ER - TY - CONF T1 - Hybrid Space-Ground Processing for High-Capacity Multi-beam Satellite Systems T2 - IEEE GLOBECOM Y1 - 2011 A1 - Arnau, Jesus A1 - Michael Bergmann A1 - Enzo Alberto Candreva A1 - Giovanni Emanuele Corazza A1 - Riccardo {De Gaudenzi} A1 - Bertrand Devillers A1 - Wilfried Gappmair A1 - Francesco Lombardo A1 - C. Mosquera A1 - Ana Pérez-Neira A1 - Ilaria Thibault A1 - Alessandro Vanelli-Coralli JF - IEEE GLOBECOM CY - Houston, Texas, USA N1 - Selected Areas in Communications Symposium - Satellite & Space Communications Track (GC'11 - SAC - SSC) ER - TY - THES T1 - Interference and Network Management in Cognitive Communication Systems Y1 - 2011 A1 - Gonzalo Vázquez-Vilar KW - cognitive radio KW - spectrum sensing PB - University of Vigo CY - Vigo, Spain VL - Ph.D. ER - TY - CONF T1 - Multiantenna detection under noise uncertainty and primary user's spatial structure T2 - IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) Y1 - 2011 A1 - David Ramírez A1 - Gonzalo Vázquez-Vilar A1 - R. López-Valcarce A1 - Javier Vía A1 - Ignacio Santamaría KW - cognitive radio KW - generalized likelihood ratio test (GLRT) KW - spectrum sensing JF - IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) PB - IEEE CY - Prage, Czech Republic ER - TY - JOUR T1 - Multiantenna Spectrum Sensing Exploiting Spectral a priori Information JF - IEEE Trans. on Wireless Communications Y1 - 2011 A1 - Gonzalo Vázquez-Vilar A1 - R. López-Valcarce A1 - Josep Sala KW - cognitive radio KW - dynacs KW - spectrum sensing VL - 10 IS - 12 ER - TY - CONF T1 - Prefilter Design for Forensic Resampling Estimation T2 - IEEE International Workshop on Information Forensics and Security (WIFS) Y1 - 2011 A1 - David Vázquez-Padín A1 - Fernando Pérez-González AB -

Starting from a theoretical analysis of the resampling estimation problem for image tampering detection, this work presents a study, based on cyclostationarity theory, about the use of prefilters to improve the estimation accuracy of the resampling factor. Considering the methods that perform the estimation by analyzing the spectrum of the covariance of a resampled region, we propose an analytical framework that allows the definition of a cost function that measures the degree of detectability of the spectral peaks. Based on this measure, the design of the optimum prefilters for a particular resampling factor can be solved numerically. Experimental results validate the developed analysis and illustrate the enhancement of the performance in a real scenario.

JF - IEEE International Workshop on Information Forensics and Security (WIFS) PB - IEEE CY - Foz do Iguaçu, Brazil ER - TY - CONF T1 - Solving the Node Localization Problem in WSNs by a Two-objective Evolutionary Algorithm and Gradient Descent T2 - the 3-th IEEE World Congress on Nature and Biologically Inspired Computing (NaBIC 2011) Y1 - 2011 A1 - Massimo Vecchio A1 - R. López-Valcarce A1 - Francesco Marcelloni JF - the 3-th IEEE World Congress on Nature and Biologically Inspired Computing (NaBIC 2011) ER - TY - JOUR T1 - Spectrum Sensing Exploiting Guard Bands and Weak Channels JF - IEEE Trans. on Signal Processing Y1 - 2011 A1 - Gonzalo Vázquez-Vilar A1 - R. López-Valcarce KW - cognitive radio KW - dynacs KW - spectrum sensing AB -We address the problem of primary user detection in Cognitive Radio from a wideband signal comprising multiple primary channels, exploiting a priori knowledge about the primary network: channelization and spectral shape of primary transmissions. Using this second-order statistical information, a multichannel Gaussian model is formulated. In order to obtain a Generalized Likelihood Ratio Test, we first address Maximum Likelihood (ML) estimation of the power levels at the different channels, as well as of the noise variance. The ML conditions suggest a suboptimal closed-form estimate, which takes the form of a constrained Least Squares estimator whose asymptotic efficiency is shown for flat bandpass spectra in white noise, a case of practical importance. The resulting detectors exploit those frequency bins corresponding to guard bands and to primary channels perceived as weak to improve noise variance estimation. Analytical expressions for the probabilities of detection and false alarm are presented. Performance is evaluated via simulations in the setting of a terrestrial TV primary network with realistic channelization parameters.

VL - 59
IS - 12
ER -
TY - CONF
T1 - A study on the Application of Different Two-objective Evolutionary Algorithms to the Node Localization Problem in Wireless Sensor Networks
T2 - IEEE International Conference on Intelligent Systems Design and Applications (ISDA)
Y1 - 2011
A1 - Massimo Vecchio
A1 - R. López-Valcarce
A1 - Francesco Marcelloni
JF - IEEE International Conference on Intelligent Systems Design and Applications (ISDA)
ER -
TY - JOUR
T1 - A two-objective evolutionary approach based on topological constraints for node localization in wireless sensor networks
JF - Applied Soft Computing
Y1 - 2011
A1 - Massimo Vecchio
A1 - R. López-Valcarce
A1 - Francesco Marcelloni
KW - dynacs
KW - Multiobjective evolutionary algorithms
KW - Node localization
KW - Range measurements
KW - Stochastic optimization
KW - wsn
AB - To know the location of nodes plays an important role in many current and envisioned wireless sensor network applications. In this framework, we consider the problem of estimating the locations of all the nodes of a network, based on noisy distance measurements for those pairs of nodes in range of each other, and on a small fraction of anchor nodes whose actual positions are known a priori. The methods proposed so far in the literature for tackling this non-convex problem do not generally provide accurate estimates. The difficulty of the localization task is exacerbated by the fact that the network is not generally uniquely localizable when its connectivity is not sufficiently high. In order to alleviate this drawback, we propose a two-objective evolutionary algorithm which takes concurrently into account during the evolutionary process both the localization accuracy and certain topological constraints induced by connectivity considerations. The proposed method is tested with different network configurations and sensor setups, and compared in terms of normalized localization error with another metaheuristic approach, namely SAL, based on simulated annealing. The results show that, in all the experiments, our approach achieves considerable accuracies and significantly outperforms SAL, thus manifesting its effectiveness and stability.

VL - 12 IS - 7 ER - TY - JOUR T1 - Dynamic spectrum leasing (DSL): A new paradigm for spectrum sharing in cognitive radio networks JF - IEEE Transactions on Vehicular Technology Y1 - 2010 A1 - Sudhaman K. Jayaweera A1 - Gonzalo Vázquez-Vilar A1 - C. Mosquera KW - cognitive radio KW - DSL KW - dynamic spectrum access KW - dynamic spectrum leasing KW - dynamic spectrum sharing KW - game theory KW - power control VL - 59 ER - TY - CONF T1 - Dynamic Spectrum Leasing (DSL) in Dynamic Channels T2 - ICC Workshop on Cognitive Radio Interfaces and Signal Processing (ICC CRISP) Y1 - 2010 A1 - Georges El-Howayek A1 - Sudhaman K. Jayaweera A1 - Kamrul Hakim A1 - Gonzalo Vázquez-Vilar A1 - C. Mosquera KW - cognitive radio KW - DSL KW - dynamic spectrum leasing KW - game theory KW - Rayleigh fading KW - time-varying channels KW - time-varying secondary system JF - ICC Workshop on Cognitive Radio Interfaces and Signal Processing (ICC CRISP) CY - Cape Town, South Africa ER - TY - CONF T1 - Multiantenna spectrum sensing: detection of spatial correlation among time-series with unknown spectra T2 - IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) Y1 - 2010 A1 - David Ramírez A1 - Javier Vía A1 - Ignacio Santamaría A1 - R. López-Valcarce A1 - L. L. Scharf KW - cognitive radio KW - coherence spectrum KW - generalized likelihood ratio test KW - Hadamard ratio KW - multiple-channel signal detection JF - IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) CY - Dallas, TX ER - TY - CONF T1 - Multiantenna spectrum sensing for Cognitive Radio: overcoming noise uncertainty T2 - International Workshop on Cognitive Information Processing (CIP) Y1 - 2010 A1 - R. López-Valcarce A1 - Gonzalo Vázquez-Vilar A1 - Josep Sala JF - International Workshop on Cognitive Information Processing (CIP) CY - Elba Island, Italy ER - TY - JOUR T1 - Primary User Enters the Game: Performance of Dynamic Spectrum Leasing in Cognitive Radio Networks JF - IEEE Transactions on Wireless Communications Y1 - 2010 A1 - Gonzalo Vázquez-Vilar A1 - C. Mosquera A1 - Sudhaman K. Jayaweera ER - TY - CONF T1 - Two-dimensional Statistical Test for the Presence of Almost Cyclostationarity on Images T2 - IEEE International Conference on Image Processing (ICIP) Y1 - 2010 A1 - David Vázquez-Padín A1 - C. Mosquera A1 - Fernando Pérez-González KW - cyclostationarity KW - Image forensics KW - interpolation KW - resampling factor estimation KW - spatial transformation KW - watermarking AB -In this work, we study the presence of almost cyclostationary fields in images for the detection and estimation of digital forgeries. The almost periodically correlated fields in the two-dimensional space are introduced by the necessary interpolation operation associated with the applied spatial transformation. In this theoretical context, we extend a statistical time-domain test for presence of cyclostationarity to the two-dimensional space. The proposed method allows us to estimate the scaling factor and the rotation angle of resized and rotated images, respectively. Examples of the output of our method are shown and comparative results are presented to evaluate the performance of the two-dimensional extension.

JF - IEEE International Conference on Image Processing (ICIP) PB - IEEE CY - Hong Kong, China ER - TY - CONF T1 - Wideband Spectral Estimation from Compressed Measurements Exploiting Spectral a priori Information in Cognitive Radio Systems T2 - IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) Y1 - 2010 A1 - Gonzalo Vázquez-Vilar A1 - R. López-Valcarce A1 - C. Mosquera A1 - Nuria González-Prelcic KW - cognitive radio KW - compressive sampling KW - Spectral estimation JF - IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) CY - Dallas, U.S.A. ER - TY - CONF T1 - Multiantenna detection of multicarrier primary signals exploiting spectral a priori information T2 - International Conference on Cognitive Radio Oriented Wireless Networks and Communications (Crowncom) Y1 - 2009 A1 - R. López-Valcarce A1 - Gonzalo Vázquez-Vilar A1 - Marcos Álvarez-Díaz JF - International Conference on Cognitive Radio Oriented Wireless Networks and Communications (Crowncom) CY - Hannover, Germany ER - TY - CONF T1 - Wideband Spectrum Sensing in Cognitive Radio: Joint Estimation of Noise Variance and Multiple Signal Levels T2 - IEEE Workshop on Signal Processing Advances in Wireless Communications (SPAWC) Y1 - 2009 A1 - R. López-Valcarce A1 - Gonzalo Vázquez-Vilar JF - IEEE Workshop on Signal Processing Advances in Wireless Communications (SPAWC) CY - Perugia, Italy ER - TY - JOUR T1 - Quantization-Based Methods: Additive Attacks Performance Analysis JF - Transactions on Data Hiding and Multimedia Security III Y1 - 2008 A1 - Jose Emilio Vila-Forcén A1 - Sviatoslav Voloshynovskiy A1 - Oleksiy Koval A1 - Fernando Pérez-González A1 - Thierry Pun KW - data-hiding KW - watermarking VL - 4920 ER - TY - CHAP T1 - Digital Satellite Communications Y1 - 2007 A1 - C. Mosquera A1 - M. L. Boucheret A1 - M. Bousquet A1 - S. Cioni A1 - Wilfried Gappmair A1 - R. Pedone A1 - Sandro Scalise A1 - P. Skoutaridis A1 - M. Villanti PB - Springer ER - TY - CHAP T1 - Digital Satellite Communications Y1 - 2007 A1 - R. Pedone A1 - G. Albertazzi A1 - P.T. Mathiopoulos A1 - C. Mosquera A1 - N. Sagias A1 - M. Villanti PB - Springer ER - TY - CHAP T1 - Digital Satellite Communications Y1 - 2007 A1 - Sandro Scalise A1 - L. Castanet A1 - M. Luglio A1 - Neri, Massimo A1 - Marcos Álvarez-Díaz A1 - J. Bito A1 - M. Bousquet A1 - I. Frigyes A1 - P. Horvath A1 - Axel Jahn A1 - M. Krejcarek A1 - J. Lemorton A1 - S. Morosi A1 - M. A. Vázquez-Castro PB - Springer CY - New York ER - TY - CONF T1 - Satellite Communications: Research Trends and Open Issues T2 - International Workshop on Satellite and Space Communications (IWSSC) Y1 - 2007 A1 - Alessandro Vanelli-Coralli A1 - Giovanni Emanuele Corazza A1 - G.K. Karagiannidis A1 - P.T. Mathiopoulos A1 - D.S. Michalopoulos A1 - C. Mosquera A1 - S. Papaharalabos A1 - Sandro Scalise KW - satellite communications JF - International Workshop on Satellite and Space Communications (IWSSC) ER - TY - JOUR T1 - An accurate analysis of scalar quantization-based data-hiding JF - IEEE Transactions on Information Forensics and Security Y1 - 2006 A1 - Luis Pérez-Freire A1 - Fernando Pérez-González A1 - Sviatoslav Voloshynovskiy KW - data-hiding KW - security KW - watermarking VL - 1 ER - TY - JOUR T1 - Robustness Improvement of Known-Host-State Watermarking Using Host Statistics JF - Signal Processing Y1 - 2006 A1 - Oleksiy Koval A1 - Sviatoslav Voloshynovskiy A1 - Jose Emilio Vila-Forcén A1 - Fernando Pérez-González A1 - Frederic Deguillaume A1 - Thierry Pun KW - data-hiding KW - watermarking VL - 86 ER - TY - CONF T1 - On reversibility of random binning techniques: multimedia perspectives T2 - Conference on Communications and Multimedia Security (CMS) Y1 - 2005 A1 - Sviatoslav Voloshynovskiy A1 - Oleksiy Koval A1 - E. Topak A1 - Jose Emilio Vila-Forcén A1 - Pedro Comesaña A1 - Thierry Pun KW - data-hiding KW - watermarking JF - Conference on Communications and Multimedia Security (CMS) T3 - Lecture Notes in Computer Science PB - Springer-Verlag Heidelberg CY - Salzburg, Austria ER - TY - CONF T1 - Robustness Improvement of Known-Host-State Watermarking Using Host Statistics T2 - Security, Steganography, and Watermarking of Multimedia Contents Y1 - 2005 A1 - Oleksiy Koval A1 - Sviatoslav Voloshynovskiy A1 - Frederic Deguillaume A1 - Fernando Pérez-González A1 - Thierry Pun ED - Edward J. Delp ED - Ping W. Wong KW - data-hiding KW - watermarking JF - Security, Steganography, and Watermarking of Multimedia Contents T3 - Proc. of SPIE PB - SPIE CY - San Jose, California, USA VL - 5306 ER - TY - CONF T1 - Worst case additive attack against quantization-based data-hiding methods T2 - Security, Steganography, and Watermarking of Multimedia Contents Y1 - 2005 A1 - Jose Emilio Vila-Forcén A1 - Sviatoslav Voloshynovskiy A1 - Oleksiy Koval A1 - Fernando Pérez-González A1 - Thierry Pun ED - Edward J. Delp ED - Ping W. Wong KW - data-hiding KW - watermarking JF - Security, Steganography, and Watermarking of Multimedia Contents T3 - Proc. of SPIE PB - SPIE CY - San Jose, California, USA VL - 5306 ER - TY - CONF T1 - Quantization-based watermarking performance improvement using host statistics: additive noise attack T2 - ACM Workshop on Multimedia and Security (MMSEC) Y1 - 2004 A1 - Oleksiy Koval A1 - Sviatoslav Voloshynovskiy A1 - Fernando Pérez-González A1 - Frederic Deguillaume A1 - Thierry Pun JF - ACM Workshop on Multimedia and Security (MMSEC) CY - Magdeburg, Germany ER - TY - CONF T1 - Revealing the true achievable rates of Scalar Costa Scheme T2 - IEEE International Workshop on Multimedia Signal Processing Y1 - 2004 A1 - Luis Pérez-Freire A1 - Fernando Pérez-González A1 - Sviatoslav Voloshynovskiy KW - data-hiding KW - watermarking JF - IEEE International Workshop on Multimedia Signal Processing CY - Siena, Italy ER - TY - CONF T1 - Spread Spectrum Watermarking for Real Images: Is Everything So Hopeless? T2 - European Signal Processing Conference (EUSIPCO) Y1 - 2004 A1 - Oleksiy Koval A1 - Sviatoslav Voloshynovskiy A1 - Fernando Pérez-González A1 - Frederic Deguillaume A1 - Thierry Pun JF - European Signal Processing Conference (EUSIPCO) CY - Vienna, Austria ER - TY - CONF T1 - Worst case additive attack against quantization-based watermarking techniques T2 - IEEE International Workshop on Multimedia Signal Processing Y1 - 2004 A1 - Jose Emilio Vila-Forcén A1 - Sviatoslav Voloshynovskiy A1 - Oleksiy Koval A1 - Thierry Pun A1 - Fernando Pérez-González JF - IEEE International Workshop on Multimedia Signal Processing CY - Siena, Italy ER - TY - JOUR T1 - ArboX, a Contribution to Digital Library JF - Computer Applications in Engineering Education Y1 - 2000 A1 - O.W. Márquez A1 - Félix Balado A1 - M. Vázquez A1 - D. Docampo VL - 8 ER - TY - CONF T1 - ArboX, a Contribution to Digital Library T2 - International Conference on Engineering and Computer Education (ICECE) Y1 - 1999 A1 - O.W. Márquez A1 - Félix Balado A1 - M. Vázquez A1 - D. Docampo JF - International Conference on Engineering and Computer Education (ICECE) PB - IEEE Education Society CY - Rio de Janeiro, Brazil ER -