Estimating the unknown parameters of a statistical model based on the observations collected by a sensor network is an important problem with application in multiple fields. In this setting, distributed processing, by which computations are carried out within the network in order to avoid raw data transmission to a fusion centre, is a desirable feature resulting in improved robustness and energy savings. In the presence of incomplete data, the expectation-maximisation (EM) algorithm is a popular means to iteratively compute the maximum likelihood (ML) estimate. It has found application in diverse fields such as computational biology, anomaly detection, speech segmentation, reinforcement learning, and motion estimation, among others. In this chapter we will review the formulation of the centralised EM estimation algorithm as a starting point and then discuss distributed versions well suited for implementation in sensor networks. The first class of these distributed versions requires specialised routing through the network in terms of a linear or circular path visiting all nodes, whereas the second class does away with this requirement by using the concept of network consensus to diffuse information through the network. Our focus will be on a relevant sensor network application, in which the parameter of a linear model is to be estimated in the presence of an unknown number of randomly malfunctioning sensors.

%B Data Fusion in Wireless Sensor Networks: A statistical signal processing perspective %I The Institution of Engineering and Technology (IET) %C London, UK %P 201-230 %@ 978-1-78561-584-9 %G eng %& 9 %0 Conference Paper %B IEEE Int. Conf. Acoustics, Speech and Signal Processing (ICASSP) %D 2019 %T Flexible spectral precoding for sidelobe suppression in OFDM systems %A Khawar Hussain %A Ana Lojo %A R. López-Valcarce %K spectrum shaping %K winter %XSpectral precoding is a popular approach to reduce out-of-band radiation (OBR) in multicarrier systems in order to avoid adjacent channel interference. Since precoding will introduce signal distortion, appropriate decoding is required at the receiver side. We present a novel linear precoder design with flexibility to trade off OBR reduction, precoding/decoding complexity, and error rate at the receiver. The precoding matrices have low rank, which translates into significant computational savings. In this way, the requirements of different systems can be satisfied with varying complexity levels.

%B IEEE Int. Conf. Acoustics, Speech and Signal Processing (ICASSP) %I IEEE %C Brighton, UK %P 4789 - 4793 %8 04/2019 %G eng %R 10.1109/ICASSP.2019.8683162 %0 Conference Paper %B IEEE Int. Conf. Acoustics, Speech and Signal Processing (ICASSP) %D 2019 %T Frequency-selective hybrid precoding and combining for mmWave MIMO systems with per-antenna power constraints %A Javier Rodríguez-Fernández %A R. López-Valcarce %A Nuria González-Prelcic %K mmWave %K winter %XConfiguring hybrid precoders and combiners is the main challenge to be solved to operate at millimeter wave (mmWave) frequencies. The use of hybrid architectures imposse hardware constraints on the analog precoder that need to be carefully dealt with. In this paper, we develop hybrid precoders and combiners aiming at minimizing the Euclidean distance with respect to the approximate all-digital precoders and combiners maximizing the spectral efficiency under per-antenna power constraints. Numerical results demonstrate the effectiveness of the proposed design method, whose performance is close to that of the all-digital solution.

%B IEEE Int. Conf. Acoustics, Speech and Signal Processing (ICASSP) %I IEEE %C Brighton, UK %P 4794-4798 %8 04/2019 %G eng %R 10.1109/ICASSP.2019.8683831 %0 Journal Article %J Mechanical Systems and Signal Processing %D 2019 %T Maximally stationary window design for overlap-add based random vibration synthesis %A Damián González %A R. López-Valcarce %K random vibration %XThe accurate synthesis of realistic waveforms conforming to certain specica-

tions is a fundamental step in random vibration testing. Since real-time imple-

mentation of digital signal processing systems for random vibration and noise

synthesis necessarily operates frame by frame, the overlap-add (OLA) method,

by which frames are windowed and overlapped, is widely used in practice to

avoid artifacts at frame boundaries. When a wide-sense stationary random

signal is desired, however, the OLA method presents a shortcoming, because

the inherent periodicity of the frame-by-frame process unavoidably produces a

cyclostationary signal, i.e., its statistics present an undesired periodic behav-

ior. We analyze the impact of the window coecients in the cyclostationarity

properties of the synthetic process, and then present algorithms for window de-

sign with the goal of maximizing a measure of its stationarity, considering both

second- and fourth-order statistical properties. The proposed designs are shown

to signicantly improve the stationarity properties when compared to commonly

used windows.

%B Mechanical Systems and Signal Processing
%V 122
%P 642-657
%8 05/2019
%G eng
%R 10.1016/j.ymssp.2018.12.038
%0 Journal Article
%J Signal Processing
%D 2019
%T MMSE filter design for Full-Duplex filter-and-forward MIMO relays under limited dynamic range
%A Emilio Antonio-Rodríguez
%A Stefan Werner
%A R. López-Valcarce
%A Risto Wichman
%K full-duplex
%K winter
%X We study the problem of optimizing the end-to-end performance of a full-duplex filter-and-forward MIMO relay link, consisting

of a source, a relay, and a destination node, by employing linear filtering at each node. The system model accounts for multipath

propagation and self-interference at the relay, as well as transmitter impairments and limited dynamic range at every node. The

design accommodates signals with arbitrary spectra and includes the direct link between the source and destination nodes. Under

the minimum mean square error criterion, the resulting non-convex problem is approximated by a sequence of convex problems

and solved by means of an alternating minimization method. Linear constraints allocate some of the degrees of freedom in the relay

to guarantee a sufficiently small residual self-interference. Simulations quantify the impact of degrees of freedom, the dynamic

range, and the balance between direct and relay paths on the link performance.

%B Signal Processing
%V 156
%P 208-219
%8 03/2019
%G eng
%R doi.org/10.1016/j.sigpro.2018.11.001
%0 Journal Article
%J IEEE Transactions on Wireless Communications
%D 2019
%T Partial-Duplex Amplify-and-Forward Relaying: Spectral Efficiency Analysis under Self-Interference
%A R. López-Valcarce
%A C. Mosquera
%K full-duplex
%K myrada
%K winter
%X We propose a novel mode of operation for Amplify-and-

Forward relays in which the spectra of the relay input and

output signals partially overlap. This partial-duplex relaying mode

encompasses half- and full-duplex as particular cases. By viewing

the partial-duplex relay as a bandwidth-preserving Linear

Periodically Time-Varying system, a spectral efficiency analysis

under self-interference is developed. In contrast with previous

works, self-interference is regarded as a useful informationbearing

component rather than simply assimilated to noise. This

approach reveals that previous results regarding the impact of

self-interference on (full-duplex) relay performance are overly

pessimistic. Based on a frequency-domain interpretation of the

effect of self-interference, a number of suboptimal decoding

architectures at the destination node are also discussed. It is found

that the partial-duplex relaying mode may provide an attractive

tradeoff between spectral efficiency and receiver complexity.

%B IEEE Transactions on Wireless Communications
%V 18
%P 2271-2285
%8 04/2019
%G eng
%N 4
%R 10.1109/TWC.2019.2902390
%0 Journal Article
%J IEEE Transactions on Wireless Communication
%D 2018
%T Distributed Precoding Systems in Multi-Gateway Multibeam Satellites: Regularization and Coarse Beamforming
%A Carlos Mosquera
%A R. López-Valcarce
%A Tomás Ramírez
%A Vahid Joroughi
%B IEEE Transactions on Wireless Communication
%G eng
%0 Conference Paper
%B IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP)
%D 2018
%T Locally optimal invariant detector for testing equality of two power spectral densities
%A David Ramírez
%A Daniel Romero
%A Javier Vía
%A R. López-Valcarce
%A Ignacio Santamaría
%K cognitive radio
%K winter
%X 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.

%B IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP)
%C Calgary, Canada
%G eng
%0 Journal Article
%J Signal Processing
%D 2018
%T Parameter estimation in wireless sensor networks with faulty transducers: A distributed EM approach
%A Silvana Silva Pereira
%A R. López-Valcarce
%A Alba Pagès-Zamora
%K winter
%K wsn
%X We address the problem of distributed estimation of a vector-valued parameter performed by a wireless sensor network in the presence of noisy observations which may be unreliable due to faulty transducers. The proposed distributed estimator is based on the Expectation-Maximization (EM) algorithm and combines consensus and diffusion techniques: a term for information diffusion is gradually turned off, while a term for updated information averaging is turned on so that all nodes in the network approach the same value of the estimate. The proposed method requires only local exchanges of information among network nodes and, in contrast with previous approaches, it does not assume knowledge of the a priori probability of transducer failures or the noise variance. A convergence analysis is provided, showing that the convergent points of the centralized EM iteration are locally asymptotically convergent points of the proposed distributed scheme. Numerical examples show that the distributed algorithm asymptotically attains the performance of the centralized EM method.

%B Signal Processing %V 144 %P 226-237 %8 03/2018 %G eng %U https://authors.elsevier.com/a/1W90XbZX4rsob %R 10.1016/j.sigpro.2017.10.012 %0 Conference Paper %B Int. Conf. on Noise and Vibration Engineering, ISMA-USD 2018 %D 2018 %T Spectral and statistical evaluation of the properties of the vibration measured at the base of an automotive seat for non-Gaussian random noise synthesis %A Damián González %A R. López-Valcarce %K random vibration %XThe first step in the definition of the specifications for the vibration tests of any automotive component

is the recording and evaluation of the properties of the input vibration during field measurements. In this

paper, we explore the properties of the vibration measured at the base of the driver seat when driving

through different surfaces, with the purpose of defining a model for non-Gaussian random vibration

testing. The recorded acceleration signals are first transformed to a 6 Degree of Freedom (DOF) space,

and then segmented into stationary sections that are later analyzed. The non-Gaussian nature of the

recorded vibration is demonstrated through different Gaussianity hypothesis tests, and the distribution of

the third and fourth order moments, as well as the crest factor, are computed and analyzed. The second-order

spectral content reveals significant correlation at specific frequencies, while the significance of

third order polyspectra is checked through hypothesis testing. Based on our observations, a practical

definition of the random process is proposed based on second-order spectral content, univariate kurtosis

and crest factor levels.

%B Int. Conf. on Noise and Vibration Engineering, ISMA-USD 2018
%C Leuven, Belgium
%8 09/2018
%G eng
%0 Journal Article
%J IEEE Trans. Signal Processing
%D 2018
%T Testing equality of multiple power spectral density matrices
%A David Ramírez
%A Daniel Romero
%A Javier Vía
%A R. López-Valcarce
%A Ignacio Santamaría
%K winter
%B IEEE Trans. Signal Processing
%V 66
%P 6268-6280
%8 12/2018
%G eng
%N 23
%R 10.1109/TSP.2018.2875884
%0 Journal Article
%J Digital Signal Processing
%D 2017
%T CDMA-based Acoustic Local Positioning System for Portable Devices with Multipath Cancellation
%A Fernando J. Alvarez
%A Teodoro Aguilera
%A R. López-Valcarce
%K compass
%K wsn
%X This paper presents an acoustic local positioning system (ALPS) suitable for indoor positioning

of portable devices such as smartphones or tablets, based on the transmission of high frequency

CDMA-coded signals from a fixed network of beacons. The main novelty of the proposed ALPS is

its capability to mitigate the effects of multipath propagation by performing an accurate estimation

of the Line-of-Sight Time-of-Flights (LOS-TOF) through the Matching Pursuit algorithm. Signal

detection, multipath cancellation and positioning estimation all take place within the portable device,

which provides a graphical representation of the updated position in less than a second. The

performance of the Matching Pursuit algorithm is analyzed in a real scenario and the results show

that the proposed method is capable to retrieve the multipath-free System Availability under strong

multipath conditions with SNR levels as low as 0 dB.

%B Digital Signal Processing
%V 62
%P 38-51
%8 03/2017
%G eng
%R 10.1016/j.dsp.2016.11.001
%0 Conference Paper
%B European Signal Processing Conference (EUSIPCO)
%D 2017
%T Defending Surveillance Sensor Networks Against Data-Injection Attacks via Trusted Nodes
%A R. López-Valcarce
%A Daniel Romero
%K winter
%K wsn
%X By injecting false data through compromised sensors, an adversary can drive the probability of detection in a sensor network-based spatial field surveillance system to arbitrarily low values. As a countermeasure, a small subset of sensors may be secured. Leveraging the theory of Matched Subspace Detection, we propose and evaluate several detectors that add robustness to attacks when such trusted nodes are available. Our results reveal the performance-security tradeoff of these schemes and can be used to determine the number of trusted nodes required for a given performance target.

%B European Signal Processing Conference (EUSIPCO)
%C Kos Island, Greece
%8 08/2017
%G eng
%0 Conference Paper
%B 35th AIAA International Communications Satellite Systems Conference
%D 2017
%T Distributed Precoding Systems in Multi-Gateway Multibeam Satellites
%A Carlos Mosquera
%A R. López-Valcarce
%A Tomás Ramírez
%K precoding
%K satcom
%B 35th AIAA International Communications Satellite Systems Conference
%C Trieste,Italy
%8 10/2017
%G eng
%0 Journal Article
%J IEEE Transactions on Wireless Communications
%D 2017
%T FER Estimation in a Memoryless BSC with Variable Frame Length and Unreliable ACK/NAK Feedback
%A Alberto Rico-Alvariño
%A R. López-Valcarce
%A Carlos Mosquera
%A Robert W. Heath Jr.
%K adaptive signal processing
%K compass
%K Cramér-Rao bound (CRB)
%K frame error rate
%K myrada
%K winter
%X We consider the problem of estimating the frame error rate (FER) of a given memoryless binary symmetric channel by observing the success or failure of transmitted packets. Whereas FER estimation is relatively straightforward if all observations correspond to packets with equal length, the problem becomes considerably more complex when this is not the case. We develop FER estimators when

transmissions of different lengths are observed, together with the Cramer-Rao Lower Bound (CRLB). Although the main focus is on Maximum Likelihood (ML) estimation, we also obtain low complexity schemes performing close to optimal in some scenarios. In a second stage, we consider the case in which FER estimation is performed at a node different from the receiver, and incorporate the impairment of unreliable observations by considering noisy ACK/NAK feedback links. The impact of unreliable feedback is analyzed by means of the corresponding CRLB. In this setting, the ML estimator is obtained by applying the Expectation-Maximization algorithm to jointly estimate the error probabilities of the data and feedback links. Simulation results illustrate the benefits of the proposed estimators.

%B IEEE Transactions on Wireless Communications
%V 16
%P 3661 - 3673
%8 06/2017
%G eng
%N 6
%R 10.1109/TWC.2017.2686845
%0 Journal Article
%J IEEE Transactions on Signal Processing
%D 2017
%T Learning Power Spectrum Maps from Quantized Power Measurements
%A Daniel Romero
%A Seung-Jun Kim
%A Georgios Giannakis
%A R. López-Valcarce
%K cognitive radio
%K compass
%K compressed sensing
%K spectrum sensing
%K winter
%K wsn
%X Using power measurements collected by a network of low-cost sensors, power spectral density (PSD) maps are con-

structed to capture the distribution of RF power across space and frequency. Linearly compressed and quantized power measure-

ments enable wideband sensing at affordable implementation complexity using a small number of bits. Strengths of data- and model-

driven approaches are combined to develop estimators capable of incorporating multiple forms of spectral and propagation prior

information while fitting the rapid variations of shadow fading across space. To this end, novel nonparametric and semiparametric

formulations are investigated. It is shown that the desired PSD maps can be obtained using support vector machine-type solvers.

In addition to batch approaches, an online algorithm attuned to real-time operation is developed. Numerical tests assess the performance of the novel algorithms.

%B IEEE Transactions on Signal Processing
%V 65
%P 2547-2560
%8 05/2017
%G eng
%N 10
%R 10.1109/TSP.2017.2666775
%0 Conference Paper
%B IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP)
%D 2017
%T Robust clustering of data collected via crowdsourcing
%A Alba Pagès-Zamora
%A Georgios Giannakis
%A R. López-Valcarce
%A Pere Gimenez-Febrer
%K winter
%K wsn
%X Crowdsourcing approaches rely on the collection of multiple individuals to solve problems that require analysis of large data sets in a timely accurate manner. The inexperience of participants or annotators motivates well robust techniques. Focusing on clustering setups, the data provided by all annotators is suitably modeled here as a mixture of Gaussian components plus a uniformly distributed random variable to capture outliers. The proposed algorithm is based on the expectation-maximization algorithm and allows for soft assignments of data to clusters, to rate annotators according to their performance, and to estimate the number of Gaussian components in the non-Gaussian/Gaussian mixture model, in a jointly manner.

%B IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP) %C New Orleans %P 4014 - 4018 %8 03/2017 %G eng %R 10.1109/ICASSP.2017.7952910 %0 Journal Article %J Signal Processing %D 2017 %T Wideband full-duplex MIMO relays with blind adaptive self-interference cancellation %A Emilio Antonio-Rodríguez %A Stefan Werner %A R. López-Valcarce %A Taneli Riihonen %A Risto Wichman %K adaptive signal processing %K compass %K full duplex %K winter %XWe develop adaptive self-interference cancellation algorithms for both filter-and-forward and decode-and-forward

multiple-input multiple-output relays. The algorithms are blind in the sense that they only exploit the spectral properties

of the transmitted signal to identify the self-interference channel, while dealing with frequency-selective channels and

arbitrary signal spectra. Our approach is non-intrusive in the sense that the algorithms can successfully identify, track,

and cancel the self-interference distortion while the relay is operating in its normal mode. We study the stationary

points of the algorithms and analyze under which conditions they achieve perfect cancellation of the self-interference.

Simulation results show that the algorithms provide residual self-interference levels below the noise floor by using

the time samples of only a few OFDM symbols.

%B Signal Processing
%V 130
%P 74-85
%8 01/2017
%G eng
%& 74
%R 10.1016/j.sigpro.2016.06.010
%0 Conference Paper
%B The 17th IEEE International workshop on Signal Processing advances in Wireless Communications (SPAWC)
%D 2016
%T Bandwidth Allocation in Partial Duplex Relaying
%A Carlos Mosquera
%A R. López-Valcarce
%K compass
%K full duplex
%K relay
%B The 17th IEEE International workshop on Signal Processing advances in Wireless Communications (SPAWC)
%C Edinburgh, UK
%8 07/2016
%G eng
%0 Conference Paper
%B IEEE Workshop on Statistical Signal Processing (SSP)
%D 2016
%T Design of data-injection adversarial attacks against spatial field detectors
%A R. López-Valcarce
%A Daniel Romero
%K adversarial signal processing
%K compass
%K wsn
%X Data-injection attacks on spatial field detection corrupt a subset of measurements to cause erroneous decisions. We consider a centralized decision scheme exploiting spatial field smoothness to overcome lack of knowledge on system parameters such as noise variance. We obtain closed-form expressions for system performance and investigate strategies for an intruder injecting false data in a fraction of the sensors in order to reduce the probability of detection. The problem of determining the most vulnerable subset of sensors is also analyzed.

%B IEEE Workshop on Statistical Signal Processing (SSP) %C Palma de Mallorca, Spain %8 06/2016 %G eng %0 Conference Paper %B IEEE Workshop on Statistical Signal Processing (SSP) %D 2016 %T Distributed multivariate regression with unknown noise covariance in the presence of outliers: a minimum description length approach %A R. López-Valcarce %A Daniel Romero %A Josep Sala %A Alba Pagès-Zamora %K compass %K wsn %XWe 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.

%B IEEE Workshop on Statistical Signal Processing (SSP)
%C Palma de Mallorca, Spain
%G eng
%0 Conference Paper
%B IEEE Global Telecommunications Conf. (GLOBECOM)
%D 2016
%T Hybrid precoders and combiners for mmWave MIMO systems with per-antenna power constraints
%A R. López-Valcarce
%A Nuria González-Prelcic
%A Cristian Rusu
%A R. W. Heath, Jr
%K compass
%K mmWave
%X This paper considers the design of hybrid precoders

and combiners for mmWave MIMO systems with per-antenna

power constraints and the additional limitations introduced by

the phase-shifting network in the analog processing stage. Previous

hybrid designs were obtained using a total power constraint,

but in practical implementations per-antenna constraints are

more realistic, specially at mmWave, given the large number of

power amplifiers used in the transmit array. Assuming perfect

channel knowledge, we obtain first an approximation to the alldigital

solution for the precoder and the combiner given the

per-antenna constraints. Then, we develop a new method for the

design of the hybrid precoder and combiner which attempts to

match such all-digital approximation. Simulation results show

the effectiveness of the proposed approach, which performs close

to the all-digital solution.

%B IEEE Global Telecommunications Conf. (GLOBECOM)
%G eng
%0 Journal Article
%J IEEE Transactions on Signal Processing
%D 2016
%T Multiantenna GLR detection of rank-one signals with known power spectral shape under spatially uncorrelated noise
%A Josep Sala
%A Gonzalo Vázquez-Vilar
%A R. López-Valcarce
%A Saeid Sedighi
%A Abbas Taherpour
%K cognitive radio
%K compass
%X 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.

%B IEEE Transactions on Signal Processing %V 64 %P 6269-6283 %8 12/2016 %G eng %N 23 %& 6269 %R 10.1109/TSP.2016.2601290 %0 Conference Paper %B European Signal Processing Conference (EUSIPCO) %D 2016 %T Online EM-based distributed estimation in sensor networks with faulty nodes %A Pere Gimenez-Febrer %A Alba Pagès-Zamora %A R. López-Valcarce %K compass %K wsn %XThis paper focuses on the problem of the distributed estimation of a parameter vector based on noisy observations regularly acquired by the nodes of a wireless sensor network and assuming that some of the nodes have faulty sensors. We propose two online schemes, both centralized and distributed, based on the Expectation-Maximization (EM) algorithm. These algorithms are able to identify and disregard the faulty nodes, and provide a refined estimate of the parameters each time instant after a new set of observations is acquired. Simulation results demonstrate that the centralized versions of the proposed online algorithms attain the same estimation error as the centralized batch EM, whereas the distributed versions come very close to matching the batch EM.

%B European Signal Processing Conference (EUSIPCO)
%C Budapest, Hungary
%8 09/2016
%G eng
%0 Conference Paper
%B European Signal Processing Conf. (EUSIPCO)
%D 2015
%T Attack detectors for data aggregation in clustered sensor networks
%A R. López-Valcarce
%A Daniel Romero
%K adversarial signal processing
%K compass
%K wsn
%X Among many security threats to sensor networks, compromised sensing is particularly challenging due to the fact that it cannot be addressed by standard authentication approaches. We consider a clustered scenario for data aggregation in which an attacker injects a disturbance in sensor readings. Casting the problem in an estimation framework, we systematically apply the Generalized Likelihood Ratio approach to derive attack detectors. The analysis under different attacks reveals that detectors based on similarity of means across

clusters are suboptimal, with Bartlett’s test for homoscedasticity constituting a good candidate when lacking a priori knowledge of the variance of the underlying distribution.

%B European Signal Processing Conf. (EUSIPCO)
%I EURASIP
%C Nice, France
%P 2098-2102
%8 accepted
%G eng
%0 Journal Article
%J IEEE Trans. Information Theory
%D 2015
%T Compression Limits for Random Vectors with Linearly Parameterized Second-Order Statistics
%A Daniel Romero
%A R. López-Valcarce
%A Geert Leus
%K compass
%K compressed sensing
%X The class of complex random vectors whose covariance

matrix is linearly parameterized by a basis of Hermitian

Toeplitz (HT) matrices is considered, and the maximum

compression ratios that preserve all second-order information

are derived — the statistics of the uncompressed vector must

be recoverable from a set of linearly compressed observations.

This kind of vectors arises naturally when sampling widesense

stationary random processes and features a number of

applications in signal and array processing.

Explicit guidelines to design optimal and nearly optimal

schemes operating both in a periodic and non-periodic fashion

are provided by considering two of the most common linear

compression schemes, which we classify as dense or sparse. It

is seen that the maximum compression ratios depend on the

structure of the HT subspace containing the covariance matrix of

the uncompressed observations. Compression patterns attaining

these maximum ratios are found for the case without structure as

well as for the cases with circulant or banded structure. Universal

samplers are also proposed to compress unknown HT subspaces.

%B IEEE Trans. Information Theory
%V 61
%P 1410-1425
%8 03/2015
%G eng
%N 3
%& 1410
%R 10.1109/TIT.2015.2394784
%0 Journal Article
%J IEEE Trans. Signal Processing
%D 2015
%T Cramér-Rao Bounds for SNR Estimation of Oversampled Linearly Modulated Signals
%A R. López-Valcarce
%A J. Villares
%A J. Riba
%A W. Gappmair
%A C. Mosquera
%K adaptive signal processing
%K compass
%K Cramér-Rao bound (CRB)
%K dynacs
%K oversampling
%K Signal-to-noise ratio (SNR)
%X 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.

%B IEEE Trans. Signal Processing
%V 63
%P 1675-1683
%8 04/2015
%G eng
%N 7
%& 1675
%R 10.1109/TSP.2015.2396013
%0 Conference Paper
%B IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP)
%D 2015
%T Distributed AoA-based Source Positioning in NLOS with Sensor Networks
%A Pere Gimenez-Febrer
%A Alba Pagès-Zamora
%A Silvana Silva Pereira
%A R. López-Valcarce
%K compass
%K wsn
%X This paper focuses on the problem of positioning a source using angle-of-arrival measurements taken by a wireless sensor network in which some of the nodes experience non-line-of-sight (NLOS) propagation conditions. In order to mitigate the errors induced by the nodes in NLOS, we derive an algorithm that combines the expectation-maximization algorithm with a weighted least-squares 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.

%B IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP)
%I IEEE
%C Brisbane, Australia
%8 04/2015
%G eng
%0 Conference Paper
%B IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP)
%D 2015
%T Distributed TLS Estimation under Random Data Faults
%A Silvana Silva Pereira
%A Alba Pagès-Zamora
%A R. López-Valcarce
%K compass
%K wsn
%X This paper addresses the problem of distributed estimation of a parameter vector in the presence of noisy input and output data as well as data faults, performed by a wireless sensor network in which only local interactions among the nodes are allowed. In the presence of unreliable observations, standard estimators become biased and perform poorly in low signal-to-noise ratios. We propose two different distributed approaches based on the Expectation-Maximization algorithm: in the first one the regressors are estimated at each iteration,

whereas the second one does not require explicit regressor estimation. Numerical results show that the proposed methods approach the performance of a clairvoyant scheme with knowledge of the random data faults.

%B IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP)
%I IEEE
%C Brisbane, Australia
%8 04/2015
%G eng
%0 Journal Article
%J Information Processing Letters
%D 2015
%T A Greedy Topology Design to Accelerate Consensus in Broadcast Wireless Sensor Networks
%A Massimo Vecchio
%A R. López-Valcarce
%K compass
%K wsn
%X 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.

%B Information Processing Letters %V 115 %P 408-413 %8 03/2015 %G eng %N 3 %& 408 %R 10.1016/j.ipl.2014.11.009 %0 Journal Article %J Journal of Network and Computer Applications %D 2015 %T Improving Area Coverage of Wireless Sensor Networks Via Controllable Mobile Nodes: a Greedy Approach %A Massimo Vecchio %A R. López-Valcarce %K compass %K wsn %XReliable 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.

%B Journal of Network and Computer Applications
%V 48
%P 1-13
%8 02/2015
%G eng
%R 10.1016/j.jnca.2014.10.007
%0 Conference Paper
%B IEEE 9th International Symposium on Intelligent Signal Processing (WISP)
%D 2015
%T Multipath cancellation in broadband acoustic local positioning systems
%A Fernando J. Alvarez
%A R. López-Valcarce
%K compass
%K wsn
%X This work proposes a novel method to estimate the Line-of-Sight Time-of-Flights (LOS-TOFs) in a broadband acoustic local positioning system (ALPS) with strong multipath interference. The proposed method is based on the Matching Pursuit channel estimation algorithm that provides a low complexity approximation to the Maximum Likelihood solution for sparse channels. A multichannel version of this algorithm has been implemented to estimate a minimum of three coefficients in the channel responses of a particular ALPS, composed of four beacons that perform the simultaneous emission of BPSK modulated 255-bit Kasami codes. A statistical analysis of performance has been carried out by using a set of test signals synthetically generated to simulate different positions and reflection coefficients of the environment. The results of this analysis show the enhanced capability of the proposed method to estimate the LOS-TOFs under strong multipath interference, with respect to that of a classical system based on correlation + thresholding.

%B IEEE 9th International Symposium on Intelligent Signal Processing (WISP) %I IEEE %C Siena, Italy %8 05/2015 %G eng %R 10.1109/WISP.2015.7139174 %0 Conference Paper %B IEEE Int. Conference on Acoustics, Speech and Signal Processing (ICASSP) %D 2015 %T Spectrum Cartography using quantized observations %A Daniel Romero %A Seung-Jun Kim %A R. López-Valcarce %A Georgios Giannakis %K cognitive radio %K compass %K compressed sensing %K spectrum sensing %XThis work proposes a spectrum cartography algorithm used for learning the power spectrum distribution over a wide frequency band across a given geographic area. Motivated by low-complexity sensing hardware and stringent communication constraints, compressed and quantized measurements are considered. Setting out from a nonparametric regression framework, it is shown that a sensible approach leads to a support vector machine formulation. The simulated tests verify that accurate spectrum maps can be constructed using a simple sensing architecture with significant savings in the feedback.

%B IEEE Int. Conference on Acoustics, Speech and Signal Processing (ICASSP)
%I IEEE
%C Brisbane, Australia
%8 04/2015
%G eng
%0 Conference Paper
%B IEEE 16th Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC)
%D 2015
%T Subspace-constrained SINR optimization in MIMO full-duplex relays under limited dynamic range
%A Emilio Antonio-Rodríguez
%A R. López-Valcarce
%A Taneli Riihonen
%A Stefan Werner
%A Risto Wichman
%K adaptive signal processing
%K compass
%K full duplex
%X We propose a method for maximizing the signal-to-interference-plus-noise ratio (SINR) in a wideband full-duplex MIMO regenerative relay that accounts limited dynamic range of the receiver and transmitter impairments. Transmit and receive filters are designed at the relay, by means of an alternating minimization algorithm, to minimize the interference at the decoder input in the destination node. We impose channel shortening and subspace constraints to ensure that the received signal at the destination is not compromised. Simulation results show that the presented method significantly outperforms other constrained approaches.

%B IEEE 16th Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC)
%I IEEE
%C Stockholm, Sweden
%8 06/2015
%G eng
%0 Journal Article
%J IEEE Communications Letters
%D 2014
%T Active Interference Cancellation for OFDM Spectrum Sculpting: Linear Processing is Optimal
%A Schmidt, J.F.
%A Daniel Romero
%A R. López-Valcarce
%K cognitive radio
%K compass
%K dynacs
%K spectrum shaping
%X Active interference cancellation (AIC) is a multicarrier spectrum sculpting technique which reduces the power of undesired out-of-band emissions by adequately modulating a subset of reserved cancellation subcarriers. In most schemes online complexity is a concern, and thus cancellation subcarriers have traditionally been constrained to linear combinations of the data subcarriers. Recent AIC designs truly minimizing out-of-band emission shift complexity to the offline design stage, motivating the consideration of more general mappings to improve performance. We show that there is no loss in optimality incurred by constraining these mappings to the set of linear functions.

%B IEEE Communications Letters %V 18 %P 1543-1546 %8 09/2014 %G eng %N 9 %& 1543 %R 10.1109/LCOMM.2014.2338316 %0 Conference Paper %B IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM) %D 2014 %T Antenna competition to boost Active Interference Cancellation in cognitive MIMO-OFDM %A Schmidt, J.F. %A R. López-Valcarce %K cognitive radio %K dynacs %K spectrum shaping %X Active Interference Cancellation (AIC) techniques for OFDM spectrum sculpting have gained interest over the last years, and several extensions to the MIMO case have been recently proposed. However, these designs do not fully exploit the spatial diversity provided by the multiple transmit antennas, as canceler allocation is fixed. This paper proposes a more general mechanism for the allocation of the cancellation subcarriers across antennas in order to better exploit spatial diversity. In particular, we present a novel AIC design for cognitive MIMOOFDM systems, in which transmit antennas compete against each other for a fixed number of cancellation subcarriers. We show that this more general allocation approach results in significant performance improvements with respect to previous designs. %B IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM) %C A Coruña, Spain %G eng %R 10.1109/SAM.2014.6882392 %0 Conference Paper %B IEEE Workshop on Information Forensics and Security (WIFS) %D 2014 %T Detecting Misreporting Attacks to the Proportional Fair Scheduler %A Schmidt, J.F. %A R. López-Valcarce %K adversarial signal processing %K compass %X

The Proportional Fair Scheduler (PFS) has become

a popular channel-aware resource allocation method in wireless

networks, as it effectively exploits multiuser diversity while

providing fairness to users. PFS decisions on which mobile station

(MS) to schedule next are based on Channel Quality Indicator

(CQI) values. Since CQI values are reported by the MSs to the

scheduler, network performance can be severely degraded if some

malicious MSs report forged information. Previous approaches to

this security issue are based either on modifying PFS, which may

be undesirable in some contexts, or authenticating CQI reports

by periodic transmission of challenges, which increases overhead.

Instead, we propose to detect misreporting attackers, based on the

time correlation features of the wireless channel. Our approach

does not require scheduler modification, and it does not increase

overhead. Simulation results under realistic settings are provided

to show the effectiveness of the proposed test.

%B IEEE Workshop on Information Forensics and Security (WIFS)
%C Atlanta, USA
%8 12/2014
%G eng
%R 10.1109/WIFS.2014.7084310
%0 Conference Paper
%B IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP)
%D 2014
%T Distributed Total Least Squares Estimation over Networks
%A R. López-Valcarce
%A Silvana Silva Pereira
%A Alba Pagès-Zamora
%K dynacs
%K wsn
%X We consider Total Least Squares (TLS) estimation in a network in which each node has access to a subset of equations of an overdetermined linear system. Previous distributed approaches require that the number of equations at each node be larger than the dimension L of the unknown parameter. We present novel distributed TLS estimators which can handle as few as a single equation per node. In the first scheme, the network computes an extended correlation matrix via standard iterative average consensus techniques, and the TLS estimate is extracted afterwards by means of an eigenvalue decomposition (EVD). The second scheme is EVD-free, but requires that a linear system of size L be solved at each iteration by each node. Replacing this step by a single Gauss-Seidel subiteration is shown to be an effective means to reduce computational cost without sacrificing performance.

%B IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP) %C Florence, Italy %G eng %R 10.1109/ICASSP.2014.6855074 %0 Conference Paper %B IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM) %D 2014 %T How to Implement Doubly-Stochastic Matrices for Consensus-Based Distributed Algorithms %A S. Valcárcel-Macua %A C. Moreno-León %A J. S. Romero %A Silvana Silva Pereira %A Javier Zazo %A Alba Pagès-Zamora %A R. López-Valcarce %A S. Zazo %K compass %K dynacs %K wsn %XDoubly-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.

%B IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM)
%C A Coruña, Spain
%G eng
%R 10.1109/SAM.2014.6882409
%0 Conference Paper
%B European Signal Processing Conference (EUSIPCO)
%D 2014
%T Low-Power Active Interference Cancellation for OFDM Spectrum Sculpting
%A Schmidt, J.F.
%A Daniel Romero
%A R. López-Valcarce
%X We present a low-power design for Active Interference

Cancellation (AIC) sculpting of the OFDM spectrum, based

on sparse design concepts. Optimal AIC designs compute

cancellation weights based on contributions from all data subcarriers.

Thus, as the number of subcarriers grows, power

consumption becomes a concern, and suboptimal solutions

that avoid involving all subcarriers are of interest. In this context,

we present novel sparse AIC designs based on a zeronorm

minimization of the matrix defining the cancellation

weights. These designs drastically reduce the number of operations

per symbol, and thus the power consumption, while allowing

to tune the loss with respect the optimal design. They

can be efficiently obtained and significantly outperform usual

thresholding or sparsity-inducing l_1-norm minimization approaches.

%B European Signal Processing Conference (EUSIPCO)
%8 09/2014
%G eng
%U http://www.eurasip.org/Proceedings/Eusipco/Eusipco2014/HTML/papers/1569912103.pdf
%0 Conference Paper
%B IEEE Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC)
%D 2014
%T Nearly-Optimal Compression Matrices for Signal Power Estimation
%A Daniel Romero
%A R. López-Valcarce
%K cognitive radio
%K dynacs
%B IEEE Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC)
%C Toronto, Canada
%G eng
%R 10.1109/SPAWC.2014.6941849
%0 Conference Paper
%B IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP)
%D 2014
%T OFDM spectrum sculpting with active interference cancellation: Keeping spectral spurs at bay
%A Schmidt, J.F.
%A R. López-Valcarce
%K cognitive radio
%K dynacs
%K spectrum shaping
%B IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP)
%I IEEE
%C Florence, Italy
%P 1-5
%8 05/2014
%G eng
%R 10.1109/ICASSP.2014.6855169
%0 Conference Paper
%B IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM)
%D 2014
%T SINR Optimization in Wideband Full-Duplex MIMO Relays under Limited Dynamic Range
%A Emilio Antonio-Rodríguez
%A R. López-Valcarce
%A Taneli Riihonen
%A Stefan Werner
%A Risto Wichman
%K adaptive signal processing
%K compass
%K full duplex
%B IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM)
%C A Coruña, Spain
%G eng
%R 10.1109/SAM.2014.6882369
%0 Journal Article
%J IEEE Trans. on Vehicular Technology
%D 2014
%T Spectrum Sensing for Wireless Microphone Signals using Multiple Antennas
%A Daniel Romero
%A R. López-Valcarce
%K cognitive radio
%K dynacs
%X Spectrum sensors for cognitive radio are expected to deploy multiple antennas in order to overcome the noise uncertainty problem and minimize the effects of small-scale fading. Despite the requirement that these sensors must detect wireless microphone (WM) signals, works in the literature have focused either on general purpose multiantenna detectors, or single antenna WM detectors. We exploit the spatial structure and particular properties of WM waveforms to derive four multiantenna detectors for WM signals with different performance/ complexity tradeoffs. These detectors are based on the generalized likelihood ratio test, which is derived under several signal models exploiting either the fact that the bandwidth of a WM signal never exceeds 200 kHz, the property that these signals have a constant magnitude, or both. The proposed detectors do not require synchronization with the WM signal and are robust to the noise uncertainty problem as well as to small-scale fading. Using the simulation guidelines from the IEEE 802.22 standard, the novel multiantenna WM detectors are shown to outperform previous schemes, thus demonstrating the advantages of exploiting spatial correlation along with WM signal structure.
%B IEEE Trans. on Vehicular Technology
%V 63
%P 4395-4407
%8 11/2014
%G eng
%N 9
%& 4395
%R 10.1109/TVT.2014.2316513
%0 Conference Paper
%B IEEE 14th Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC)
%D 2013
%T Adaptive Self-interference Cancellation in Wideband Full-Duplex Decode-and-Forward MIMO Relays
%A Emilio Antonio-Rodríguez
%A R. López-Valcarce
%A Taneli Riihonen
%A Stefan Werner
%A Risto Wichman
%K adaptive signal processing
%K dynacs
%K full duplex
%B IEEE 14th Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC)
%C Darmstadt, Germany
%8 06/2013
%G eng
%R 10.1109/SPAWC.2013.6612074
%0 Conference Paper
%B Int. Conf. Acoust., Speech, Signal Process. (ICASSP)
%D 2013
%T Autocorrelation-based adaptation rule for feedback equalization in Wideband Full-Duplex Amplify-and-Forward MIMO relays
%A Emilio Antonio-Rodríguez
%A R. López-Valcarce
%A Taneli Riihonen
%A Stefan Werner
%A Risto Wichman
%K adaptive signal processing
%K dynacs
%K full duplex
%X Simultaneous reception and transmission in the same frequency, so-called full-duplex operation, causes an infinite feedback loop in an amplify-and-forward relay. The unwanted echoes may result in oscillation at the relay, making it unstable, and distorting the spectrum. This paper presents an adaptive MIMO filtering method for full-duplex amplify-and-forward relays that aims at solving the joint problem of self-interference mitigation and equalization of the source-relay channel. The scheme exploits knowledge of the autocorrelation of the transmitted signal as the only side information while allowing the relay, in the best case, to implement precoding as if there was not any self-interference or frequency selectivity in the source-relay channel. Finally, the proposed adaptation algorithm is investigated by determining its stationary points and by performing simulations in a MIMO-OFDM framework.

%B Int. Conf. Acoust., Speech, Signal Process. (ICASSP)
%G eng
%R 10.1109/ICASSP.2013.6638606
%0 Conference Paper
%B Int. Conf. Acoust., Speech, Signal Process. (ICASSP)
%D 2013
%T Cancelling self-interference in full-duplex relays without Angle-of-Arrival information
%A Emilio Antonio-Rodríguez
%A R. López-Valcarce
%K adaptive signal processing
%K dynacs
%K full duplex
%X With full-duplex relays, simultaneous reception and transmission in

the same frequency produce self-interference distortion and relay oscillation,

hampering reception at the receiver end unless properly

mitigated. Previous adaptive methods for self-interference cancellation

using multiple receive antennas require knowledge of the direction

of arrival of the source signal. We present a novel architecture

and adaptive scheme for Amplify-and-Forward relays allowing cancellation

without such knowledge. The temporal filter is updated

under the property restoral paradigm in order to match the power

spectrum of the retransmitted signal to that of the source signal.

%B Int. Conf. Acoust., Speech, Signal Process. (ICASSP)
%G eng
%R 10.1109/ICASSP.2013.6638558
%0 Journal Article
%J IEEE Journal on Emerging and Selected Topics in Circuits and Systems
%D 2013
%T Choose Your Subcarriers Wisely: Active Interference Cancellation for Cognitive OFDM
%A Schmidt, J.F.
%A Costas-Sanz, S.
%A R. López-Valcarce
%K cognitive radio
%K dynacs
%K spectrum shaping
%B IEEE Journal on Emerging and Selected Topics in Circuits and Systems
%V 3
%P 615-625
%8 12/2013
%G eng
%N 4
%& 615
%R 10.1109/JETCAS.2013.2280808
%0 Journal Article
%J Sensors
%D 2013
%T A Cognitive Mobile BTS Solution with Software-Defined Radioelectric Sensing
%A J. Muñoz
%A J. Vales-Alonso
%A F. Quiñoy-García
%A Costas-Sanz, S.
%A M. Pillado
%A F.J. González-Castaño
%A M. García-Sanchez
%A R. López-Valcarce
%A C. López-Bravo
%K cognitive radio
%K dynacs
%K mobile communications
%K SDR
%K vehicular communications
%X 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.

%B Sensors %V 13 %P 2051-2075 %8 02/2013 %G eng %N 2 %& 2051 %R 10.3390/s130202051 %0 Conference Paper %B Int. Conf. Acoust., Speech, Signal Process. (ICASSP) %D 2013 %T Compressive wideband spectrum sensing with spectral prior information %A Daniel Romero %A R. López-Valcarce %A Geert Leus %K cognitive radio %K dynacs %K spectrum sensing %XWideband spectrum sensing provides a means to determine

the occupancy of channels spanning a broad range of frequencies.

Practical limitations impose that the acquisition should

be accomplished at a low rate, much below the Nyquist lower

bound. Dramatic rate reductions can be obtained by the observation

that only a few parameters need to be estimated in

typical spectrum sensing applications. This paper discusses

the joint estimation of the power of a number of channels,

whose power spectral density (PSD) is known up to a scale

factor, using compressive measurements. First, relying on

a Gaussian assumption, an efficient approximate maximum

likelihood (ML) technique is presented. Next, a least-squares

estimator is applied for the general non-Gaussian case.

%B Int. Conf. Acoust., Speech, Signal Process. (ICASSP)
%G eng
%R 10.1109/ICASSP.2013.6638505
%0 Journal Article
%J Engineering Applications of Artificial Intelligence
%D 2013
%T On the design of a novel two-objective harmony search approach for distance- and connectivity-based localization in wireless sensor networks
%A Diana Manjarres
%A Javier Del Ser
%A Sergio Gil-Lopez
%A Massimo Vecchio
%A Itziar Landa-Torres
%A Sancho Salcedo-Sanz
%A R. López-Valcarce
%K dynacs
%K wsn
%B Engineering Applications of Artificial Intelligence
%V 26
%P 669-676
%8 02/2013
%G eng
%N 2
%& 669
%R 10.1016/j.engappai.2012.06.002
%0 Conference Paper
%B Int. Conf. Acoust., Speech, Signal Process. (ICASSP)
%D 2013
%T A Diffusion-based distributed EM algorithm for density estimation in wireless sensor networks
%A Silvana Silva Pereira
%A Alba Pagès-Zamora
%A R. López-Valcarce
%K dynacs
%K wsn
%X Distributed implementations of the Expectation-Maximization

(EM) algorithm reported in the literature have been proposed for

applications to solve specific problems. In general, a primary

requirement to derive a distributed solution is that the

structure of the centralized version enables the computation

involving global information in a distributed fashion. This

paper treats the problem of distributed estimation of Gaussian

densities by means of the EM algorithm in wireless sensor

networks using diffusion strategies, where the information

is gradually diffused across the network for the computation

of the global functions. The low-complexity implementation

presented here is based on a two time scale operation

for information averaging and diffusion. The convergence to

a fixed point of the centralized solution has been studied and

the appealing results motivates our choice for this model. Numerical

examples provided show that the performance of the

distributed EM is, in practice, equal to that of the centralized

scheme.

%B Int. Conf. Acoust., Speech, Signal Process. (ICASSP)
%G eng
%R 10.1109/ICASSP.2013.6638501
%0 Journal Article
%J IEEE Signal Processing Letters
%D 2013
%T A Diffusion-Based EM Algorithm for Distributed Estimation in Unreliable Sensor Networks
%A Silvana Silva Pereira
%A R. López-Valcarce
%A Alba Pagès-Zamora
%K dynacs
%K wsn
%X We address the problem of distributed estimation of a parameter from a set of noisy observations collected by a sensor network, assuming that some sensors may be subject to data failures and report only noise. In such scenario, simple schemes such as the Best Linear Unbiased Estimator result in an error floor in moderate and high signal-to-noise ratio (SNR), whereas previously proposed methods based on hard decisions on data failure events degrade as the SNR decreases. Aiming at optimal performance within the whole range of SNRs, we adopt a Maximum Likelihood framework based on the Expectation-Maximization (EM) algorithm. The statistical model and the iterative nature of the EM method allow for a diffusion-based distributed implementation, whereby the information propagation is embedded in the iterative update of the parameters. Numerical examples show that the proposed algorithm practically attains the Cramer–Rao Lower Bound at all SNR values and compares favorably with other approaches.

%B IEEE Signal Processing Letters %V 20 %P 595-598 %8 06/2013 %G eng %N 6 %& 595 %R 10.1109/LSP.2013.2260329 %0 Journal Article %J EURASIP Journal on Advances in Signal Processing %D 2013 %T Lattice implementation of adaptive channel shortening in multicarrier transmission over IIR channels %A E. Ben Salem %A S. Cherif %A H. Besbes %A R. López-Valcarce %B EURASIP Journal on Advances in Signal Processing %V 2013:174 %8 11/2013 %G eng %U http://asp.eurasipjournals.com/content/2013/1/174 %R 10.1186/1687-6180-2013-174 %0 Conference Paper %B European Signal Processing Conf. (EUSIPCO), Marrakech (Morocco) %D 2013 %T Low Complexity Primary User Protection for Cognitive OFDM %A Schmidt, J.F. %A R. López-Valcarce %K cognitive radio %K dynacs %K spectrum shaping %B European Signal Processing Conf. (EUSIPCO), Marrakech (Morocco) %8 09/2013 %G eng %0 Journal Article %J Soft Computing %D 2013 %T A novel heuristic approach for distance- and connectivity-based multihop node localization in wireless sensor networks %A Diana Manjarres %A Javier Del Ser %A Sergio Gil-Lopez %A Massimo Vecchio %A Itziar Landa-Torres %A R. López-Valcarce %K dynacs %K wsn %B Soft Computing %V 17 %P 17-28 %8 01/2013 %G eng %N 1 %& 17 %R 10.1007/s00500-012-0897-2 %0 Conference Paper %B IEEE 14th Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC), Darmstadt (Germany) %D 2013 %T Spectrum Sensing in Time-Varying Channels Using Multiple Antennas %A Daniel Romero %A R. López-Valcarce %K cognitive radio %K dynacs %K spectrum sensing %B IEEE 14th Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC), Darmstadt (Germany) %8 06/2013 %G eng %R 10.1109/SPAWC.2013.6612027 %0 Journal Article %J IEEE J. Selected Areas in Communications %D 2012 %T An Adaptive Feedback Canceller for Full-Duplex Relays Based on Spectrum Shaping %A R. López-Valcarce %A Emilio Antonio-Rodríguez %A C. Mosquera %A Fernando Pérez-González %K adaptive signal processing %K dynacs %K full duplex %XAlthough full-duplex relaying schemes are appealing in order to improve spectral efficiency, simultaneous reception and transmission in the same frequency results in selfinterference,

distorting the retransmitted signal and making the relay prone to oscillation. Current feedback cancellation techniques by means of adaptive filters are hampered by the fact that the useful and interference signals are highly correlated. We present a new adaptive algorithm which effectively and blindly

restores the spectral shape of the desired signal. In contrast

with previous schemes, the novel adaptive feedback canceller has low complexity, does not introduce additional delay in the relay station, and partly compensates for multipath propagation.

%B IEEE J. Selected Areas in Communications
%V 30
%P 1566 - 1577
%8 08/2012
%G eng
%N 8
%R 10.1109/JSAC.2012.120923
%0 Conference Paper
%B IEEE 13th Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC 2012)
%D 2012
%T Adaptive self-interference suppression for full-duplex relays with multiple receive antennas
%A Emilio Antonio-Rodríguez
%A R. López-Valcarce
%K adaptive signal processing
%K dynacs
%K full duplex
%X In full-duplex relays, simultaneous reception and transmission

in the same frequency results in self-interference which distorts the retransmitted signal and makes the relay prone to oscillation. We present an adaptive feedback canceller for multiple-input single-output (MISO) relays, efficiently combining spatial and temporal processing. The receive array is adaptively steered towards the minimum variance distortionless response (MVDR), whereas the temporal filter update is based on a novel low-complexity spectrum shaping scheme which avoids introducing additional delay in the relay station.

%B IEEE 13th Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC 2012)
%I IEEE
%C Çesme, Turkey
%8 07/2012
%G eng
%R 10.1109/SPAWC.2012.6292948
%0 Conference Paper
%B IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP)
%D 2012
%T Design of universal multicoset sampling patterns for compressed sensing of multiband sparse signals
%A M. Elena Domínguez-Jiménez
%A Nuria González-Prelcic
%A Gonzalo Vázquez-Vilar
%A R. López-Valcarce
%X 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.

%B IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) %C Kyoto (Japan) %P 3337 - 3340 %8 03/2012 %@ 978-1-4673-0044-5 %G eng %R 10.1109/ICASSP.2012.6288630 %0 Conference Paper %B IEEE Statistical Signal Processing Workshop (SSP 2012) %D 2012 %T Detection of Gaussian signals in unknown time-varying channels %A Daniel Romero %A Javier Vía %A R. López-Valcarce %A Ignacio Santamaría %K cognitive radio %K dynacs %K spectrum sensing %XDetecting 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.

%B IEEE Statistical Signal Processing Workshop (SSP 2012)
%I IEEE
%C Ann Arbor, MI
%8 08/2012
%G eng
%R 10.1109/SSP.2012.6319858
%0 Conference Paper
%B 3rd Int. Workshop on Cognitive Information Processing (CIP 2012)
%D 2012
%T Detection of unknown constant magnitude signals in time-varying channels
%A Daniel Romero
%A R. López-Valcarce
%K cognitive radio
%K dynacs
%K spectrum sensing
%X Spectrum sensing constitutes a key ingredient in many cognitive radio paradigms in order to detect and protect primary transmissions. Most sensing schemes in the literature assume a time-invariant channel. However, when operating in low Signal-to-Noise Ratio (SNR) conditions, observation times are necessarily long and may become larger than the coherence time of the channel. In this paper the problem of detecting an unknown constant-magnitude waveform in frequency-flat time-varying channels with noise background of unknown variance is considered. The channel is modeled using a basis expansion model (BEM) with random coefficients. Adopting a generalized likelihood ratio (GLR) approach in order to deal with nuisance parameters, a non-convex optimization problem results. We discuss different possibilities to circumvent this problem, including several low complexity approximations to the GLR test as well as an efficient fixed-point iterative method to obtain the true GLR statistic. The approximations exhibit a performance ceiling in terms of probability of detection as the SNR increases, whereas the true GLR test does not. Thus, the proposed fixed-point iteration constitutes the preferred choice in applications requiring a high probability of detection.

%B 3rd Int. Workshop on Cognitive Information Processing (CIP 2012) %C Baiona, Spain %8 05/2012 %G eng %R 10.1109/CIP.2012.6232933 %0 Conference Paper %B IEEE Int. Conf. on Acoustics, Speech and Signal Processing (ICASSP 2012) %D 2012 %T Generalized matched filter detector for fast fading channels %A Daniel Romero %A R. López-Valcarce %A Geert Leus %K cognitive radio %K dynacs %K spectrum sensing %XWe consider the problem of detecting a known signal with constant magnitude immersed in noise of unknown variance,

when the propagation channel is frequency-flat and randomly

time-varying within the observation window. A Basis Expansion

Model with random coefficients is used for the channel, and a Generalized Likelihood Ratio approach is adopted in order to cope with deterministic nuisance parameters. The resulting scheme can be seen as a generalization of the well-known

Matched Filter detector, to which it reduces for timeinvariant

channels. Closed-form analytical expressions are provided for the distribution of the test statistic under both hypotheses, which allow to assess the detection performance.

%B IEEE Int. Conf. on Acoustics, Speech and Signal Processing (ICASSP 2012)
%I IEEE
%C Kyoto, Japan
%8 07/2012
%G eng
%R 10.1109/ICASSP.2012.6288587
%0 Journal Article
%J IEEE Trans. on Signal Processing
%D 2012
%T Multiantenna GLR detection of rank-one signals with known power spectrum in white noise with unknown spatial correlation
%A Josep Sala
%A Gonzalo Vázquez-Vilar
%A R. López-Valcarce
%K cognitive radio
%K dynacs
%X 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.

%B IEEE Trans. on Signal Processing
%V 60
%P 3065 - 3078
%8 06/2012
%G eng
%N 6
%R 10.1109/TSP.2012.2189767
%0 Conference Paper
%B IEEE International Conference on Intelligent Systems Design and Applications (ISDA)
%D 2011
%T On the Application of a Hybrid Harmony Search Algorithm to Node Localization in Anchor-based Wireless Sensor Networks
%A Diana Manjarres
%A Javier Del Ser
%A Sergio Gil-Lopez
%A Massimo Vecchio
%A Itziar Landa-Torres
%A R. López-Valcarce
%B IEEE International Conference on Intelligent Systems Design and Applications (ISDA)
%G eng
%0 Conference Paper
%B International Workshop on Computational Advances in Multi-Sensor Adaptive Processing (CAMSAP)
%D 2011
%T Bandlimited or Constant Envelope? Exploiting Waveform Properties in Wireless Microphone Detection
%A Daniel Romero
%A R. López-Valcarce
%K Bandlimited signals.
%K Constant Magnitude
%K dynamic spectrum access
%K Wireless Microphones
%B International Workshop on Computational Advances in Multi-Sensor Adaptive Processing (CAMSAP)
%C San Juan, Puerto Rico
%P 17-20
%8 December
%G eng
%0 Conference Paper
%B IEEE Int. Conf. on Acoustics, Speech and Signal Processing (ICASSP 2011)
%D 2011
%T Detection diversity of multiantenna spectrum sensors
%A Gonzalo Vázquez-Vilar
%A R. López-Valcarce
%A Ashish Pandharipande
%K cognitive radio
%K detection diversity
%K spectrum sensing
%X 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.

%B IEEE Int. Conf. on Acoustics, Speech and Signal Processing (ICASSP 2011)
%I IEEE
%C Prague, Czech Republic
%P 2936-2939
%8 05/2011
%G eng
%0 Journal Article
%J IEEE Trans. on Signal Processing
%D 2011
%T Detection of Rank-P Signals in Cognitive Radio Networks With Uncalibrated Multiple Antennas
%A David Ramírez
%A Gonzalo Vázquez-Vilar
%A R. López-Valcarce
%A Javier Vía
%A Ignacio Santamaría
%K cognitive radio
%K dynacs
%K spectrum sensing
%X 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.

%B IEEE Trans. on Signal Processing
%V 59
%P 3764-3774
%8 08/2012
%G eng
%N 8
%R 10.1109/TSP.2011.2146779
%0 Conference Paper
%B IEEE Workshop on Signal Processing Advances in Wireless Communications (SPAWC)
%D 2011
%T Distributed spectrum sensing with multiantenna sensors under calibration errors
%A Daniel Romero
%A R. López-Valcarce
%K ad hoc detectors
%K antenna arrays
%K calibration
%K calibration errors
%K cognitive radio
%K energy detector
%K generalized likelihood ratio
%K log normal distribution
%K lognormal shadowing
%K multiantenna sensors
%K Ricean fading
%K spectrum sensing
%K wireless medium
%X Spectrum sensing design for Cognitive Radio systems is challenged by the nature of the wireless medium, which makes the detection requirements difficult to achieve by standalone sensors. To combat shadowing and fading, distributed strategies are usually proposed. However, most distributed approaches are based on the energy detector, which is not robust to noise uncertainty. This phenomenon can be overcome by multi-antenna sensors exploiting spatial independence of the noise process. We combine both ideas to develop distributed detectors for multiantenna sensors. Fusion rules are provided for sensors based on the Generalized Likelihood Ratio as well as for ad hoc detectors derived from geometric considerations. Simulation results are provided comparing the performance of the different strategies under lognormal shadowing and Ricean fading.

%B IEEE Workshop on Signal Processing Advances in Wireless Communications (SPAWC) %P 441 -445 %8 june %G eng %R 10.1109/SPAWC.2011.5990448 %0 Conference Paper %B IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS) %D 2011 %T An Effective Metaheuristic Approach to Node Localization in Wireless Sensor Networks %A Massimo Vecchio %A R. López-Valcarce %A Francesco Marcelloni %B IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS) %G eng %0 Conference Paper %B IEEE Workshop on Signal Processing Advances in Wireless Communications (SPAWC) %D 2011 %T Multiantenna detection of constant-envelope signals in noise of unknown variance %A Daniel Romero %A R. López-Valcarce %K cognitive radio %K multiantenna detection %K spectrum sensing %XDetection of unknown signals with constant modulus (CM) using multiple antennas in additive white Gaussian noise of unknown variance is considered. The channels from the source to each antenna are assumed frequency-flat and unknown. This problem is of interest for spectrum sensing in cognitive radio systems in which primary signals are known to have the CM property. Examples include analog frequency modulated signals such as those transmitted by wireless microphones in the TV bands and Gaussian Minimum Shift Keying modulated signals as in the GSM cellular standard. The proposed detector, derived from a Generalized Likelihood Ratio (GLR) approach, exploits both the CM property and the spatial independence of noise, outperforming the GLR test for Gaussian signals as shown by simulation.

%B IEEE Workshop on Signal Processing Advances in Wireless Communications (SPAWC) %P 446 -450 %8 june %G eng %R 10.1109/SPAWC.2011.5990449 %0 Conference Paper %B IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) %D 2011 %T Multiantenna detection under noise uncertainty and primary user's spatial structure %A David Ramírez %A Gonzalo Vázquez-Vilar %A R. López-Valcarce %A Javier Vía %A Ignacio Santamaría %K cognitive radio %K generalized likelihood ratio test (GLRT) %K spectrum sensing %B IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) %I IEEE %C Prage, Czech Republic %P 2948-2951 %8 May %G eng %0 Journal Article %J IEEE Trans. on Wireless Communications %D 2011 %T Multiantenna Spectrum Sensing Exploiting Spectral a priori Information %A Gonzalo Vázquez-Vilar %A R. López-Valcarce %A Josep Sala %K cognitive radio %K dynacs %K spectrum sensing %B IEEE Trans. on Wireless Communications %V 10 %P 4345 - 4355 %8 12/2011 %G eng %N 12 %R 10.1109/TWC.2011.101211.110665 %0 Conference Paper %B the 3-th IEEE World Congress on Nature and Biologically Inspired Computing (NaBIC 2011) %D 2011 %T Solving the Node Localization Problem in WSNs by a Two-objective Evolutionary Algorithm and Gradient Descent %A Massimo Vecchio %A R. López-Valcarce %A Francesco Marcelloni %B the 3-th IEEE World Congress on Nature and Biologically Inspired Computing (NaBIC 2011) %G eng %0 Journal Article %J IEEE Trans. on Signal Processing %D 2011 %T Spectrum Sensing Exploiting Guard Bands and Weak Channels %A Gonzalo Vázquez-Vilar %A R. López-Valcarce %K cognitive radio %K dynacs %K spectrum sensing %XWe 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.

%B IEEE Trans. on Signal Processing
%V 59
%P 6045-6057
%8 12/2011
%G eng
%N 12
%R 10.1109/TSP.2011.2167615
%0 Conference Paper
%B IEEE International Conference on Intelligent Systems Design and Applications (ISDA)
%D 2011
%T A study on the Application of Different Two-objective Evolutionary Algorithms to the Node Localization Problem in Wireless Sensor Networks
%A Massimo Vecchio
%A R. López-Valcarce
%A Francesco Marcelloni
%B IEEE International Conference on Intelligent Systems Design and Applications (ISDA)
%G eng
%0 Journal Article
%J Applied Soft Computing
%D 2011
%T A two-objective evolutionary approach based on topological constraints for node localization in wireless sensor networks
%A Massimo Vecchio
%A R. López-Valcarce
%A Francesco Marcelloni
%K dynacs
%K Multiobjective evolutionary algorithms
%K Node localization
%K Range measurements
%K Stochastic optimization
%K wsn
%X 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.

%B Applied Soft Computing %V 12 %P 1891-1901 %8 07/2012 %G eng %N 7 %R 10.1016/j.asoc.2011.03.012 %0 Journal Article %J Signal Processing %D 2010 %T Blind l_1-Norm-Based Phase Estimation for Cross-QAM Robust to Finite Precision Effects %A Marcos Álvarez-Díaz %A R. López-Valcarce %A Iago Gómez-Alonso %K blind phase estimation %K carrier offset %K cross-QAM constellations %K fixed point implementation %B Signal Processing %V 90 %P 2934-2948 %8 11/2010 %G eng %0 Journal Article %J Signal Processing %D 2010 %T Closed-form real single-tone frequency estimator based on a normalized IIR notch filter %A R. Elasmi-Ksibi %A S. Cherif %A R. López-Valcarce %A H. Besbes %K Frequency estimation %K IIR notchfilter %K Least squares %K Real sinusoid %K RPHD estimator %B Signal Processing %V 90 %P 1905-1915 %8 June %G eng %0 Conference Paper %B European Wireless %D 2010 %T A finite interval constant modulus criterion for multicarrier channel shortening %A E. Ben Salem %A R. López-Valcarce %A H. Besbes %A S. Cherif %B European Wireless %C Lucca, Italy %G eng %0 Journal Article %J Signal Processing %D 2010 %T Frequency estimation of real-valued single-tone in colored noise using multiple autocorrelation lags %A R. Elasmi-Ksibi %A H. Besbes %A R. López-Valcarce %A S. Cherif %K Autocorrelation %K Frequency estimation %K Single sinusoid %B Signal Processing %V 90 %P 2303-2307 %8 July %G eng %0 Journal Article %J IEEE Signal Processing Letters %D 2010 %T Joint NDA Estimation of Carrier Frequency/Phase and SNR for Linearly Modulated Signals %A Wilfried Gappmair %A R. López-Valcarce %A C. Mosquera %K Carrier offset estimation %K Cramer-Rao lower bound %K expectation-maximization algorithm %K SNR estimation %B IEEE Signal Processing Letters %V 17 %P 517-520 %8 05/2010 %G eng %0 Conference Paper %B IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) %D 2010 %T Multiantenna spectrum sensing: detection of spatial correlation among time-series with unknown spectra %A David Ramírez %A Javier Vía %A Ignacio Santamaría %A R. López-Valcarce %A L. L. Scharf %K cognitive radio %K coherence spectrum %K generalized likelihood ratio test %K Hadamard ratio %K multiple-channel signal detection %B IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) %C Dallas, TX %G eng %0 Conference Paper %B International Workshop on Cognitive Information Processing (CIP) %D 2010 %T Multiantenna spectrum sensing for Cognitive Radio: overcoming noise uncertainty %A R. López-Valcarce %A Gonzalo Vázquez-Vilar %A Josep Sala %B International Workshop on Cognitive Information Processing (CIP) %C Elba Island, Italy %G eng %0 Journal Article %J IEEE Transactions on Signal Processing %D 2010 %T SNR Estimation for Multilevel Constellations Using Higher-Order Moments %A Marcos Álvarez-Díaz %A R. López-Valcarce %A C. Mosquera %K Blind estimation %K higher-order statistics %K Moments-based estimation %K SNR estimation %B IEEE Transactions on Signal Processing %V 58 %P 1515–1526 %8 March %G eng %0 Journal Article %J IEEE Signal Processing Letters %D 2010 %T Stepsize Sequence Design for Distributed Average Consensus %A C. Mosquera %A R. López-Valcarce %A Sudhaman K. Jayaweera %B IEEE Signal Processing Letters %V 17 %P 169-172 %8 Feb %G eng %0 Conference Paper %B IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) %D 2010 %T Wideband Spectral Estimation from Compressed Measurements Exploiting Spectral a priori Information in Cognitive Radio Systems %A Gonzalo Vázquez-Vilar %A R. López-Valcarce %A C. Mosquera %A Nuria González-Prelcic %K cognitive radio %K compressive sampling %K Spectral estimation %B IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) %C Dallas, U.S.A. %8 March 14-19 %G eng %0 Journal Article %J IEEE Transactions on Communications %D 2009 %T Cramer-Rao Lower Bound and EM Algorithm for Envelope-Based SNR Estimation of Nonconstant Modulus Constellations %A Wilfried Gappmair %A R. López-Valcarce %A C. Mosquera %B IEEE Transactions on Communications %V 57 %P 1622 - 1627 %8 june %G eng %0 Conference Paper %B International Conference on Cognitive Radio Oriented Wireless Networks and Communications (Crowncom) %D 2009 %T Multiantenna detection of multicarrier primary signals exploiting spectral a priori information %A R. López-Valcarce %A Gonzalo Vázquez-Vilar %A Marcos Álvarez-Díaz %B International Conference on Cognitive Radio Oriented Wireless Networks and Communications (Crowncom) %C Hannover, Germany %8 June 22-24 %G eng %0 Conference Paper %B IEEE Workshop on Signal Processing Advances in Wireless Communications (SPAWC) %D 2009 %T Wideband Spectrum Sensing in Cognitive Radio: Joint Estimation of Noise Variance and Multiple Signal Levels %A R. López-Valcarce %A Gonzalo Vázquez-Vilar %B IEEE Workshop on Signal Processing Advances in Wireless Communications (SPAWC) %C Perugia, Italy %8 June 21-24 %G eng %0 Conference Paper %B IEEE International Workshop on Signal Processing Advances in Wireless Communications %D 2008 %T Distributed Estimation with Noisy Exchanges %A C. Mosquera %A R. López-Valcarce %A Sudhaman K. Jayaweera %K distributed estimation %K sensor network %B IEEE International Workshop on Signal Processing Advances in Wireless Communications %C Recife, Brazil %G eng %0 Conference Paper %B European Signal Processing Conference (EUSIPCO) %D 2008 %T A family of frequency estimators using higher-order sample covariance lags for real sinusoid detection %A R. Elasmi-Ksibi %A R. López-Valcarce %A H. Besbes %A S. Cherif %A M. Jaidane %K Frequency estimator %K Sinusoid detection %B European Signal Processing Conference (EUSIPCO) %C Lausanne, Switzerland %8 August %G eng %0 Conference Paper %B European Signal Processing Conference (EUSIPCO) %D 2008 %T Lattice implementation of Sum-squared Auto-correlation Minimization (SAM) channel shortener %A E. Ben Salem %A R. López-Valcarce %A S. Cherif %A H. Besbes %K Blind Adaptation %K Lattice %K SAM %B European Signal Processing Conference (EUSIPCO) %C Lausanne, Switzerland %8 August %G eng %0 Conference Paper %B IEEE International Workshop on Signal Processing Advances in Wireless Communications %D 2008 %T Maximum Likelihood SNR Estimation for Asynchronously Oversampled OFDM Signals %A R. López-Valcarce %A C. Mosquera %K estimation %K ML %K OFDM %K SNR %B IEEE International Workshop on Signal Processing Advances in Wireless Communications %C Recife, Brazil %G eng %0 Conference Paper %B International Symposium on Communication Systems, Networks and Signal Processing (CNSDSP) %D 2008 %T ML and EM Algorithm for non-data-aided SNR Estimation of Linearly Modulated Signals %A Wilfried Gappmair %A R. López-Valcarce %A C. Mosquera %K EM %K ML %K SNR estimation %B International Symposium on Communication Systems, Networks and Signal Processing (CNSDSP) %P 530-534 %G eng %0 Journal Article %J IEEE Transactions on Signal Processing %D 2008 %T Non-Data-Aided Symbol Rate Estimation of Linearly Modulated Signals %A C. Mosquera %A Sandro Scalise %A R. López-Valcarce %B IEEE Transactions on Signal Processing %8 February %G eng %0 Conference Paper %B Advanced Satellite Mobile Systems Conference %D 2008 %T SNR Estimation with Heterogeneous Frames %A Marcos Álvarez-Díaz %A R. López-Valcarce %A C. Mosquera %B Advanced Satellite Mobile Systems Conference %C Bologna, Italy %8 August 26-28 %G eng %0 Book %D 2007 %T Comunicaciones Digitales %A Antonio Artés-Rodríguez %A Fernando Pérez-González %A Jesús Cid-Sueiro %A R. López-Valcarce %A C. Mosquera %A Fernando Pérez-Cruz %I Pearson - Prentice Hall %8 May %G eng %0 Conference Paper %B IEEE Workshop on Signal Processing Advances in Wireless Communications (SPAWC) %D 2007 %T Iterative Envelope-Based SNR Estimation for Non-Constant Modulus Constellations %A R. López-Valcarce %A C. Mosquera %A Wilfried Gappmair %K EM %K SNR %K synchronization %B IEEE Workshop on Signal Processing Advances in Wireless Communications (SPAWC) %G eng %0 Journal Article %J IEEE Communications Letters %D 2007 %T Sixth-Order Statistics-Based Non-Data-Aided SNR Estimation %A R. López-Valcarce %A C. Mosquera %B IEEE Communications Letters %V 11 %P 351-353 %8 April %G eng %0 Conference Paper %B International Symposium on Image/Video Communications (ISIVC) %D 2006 %T Analysis of non-data-aided magnitude gain estimators %A R. López-Valcarce %K Digital Communications %K gain estimation %K synchronization %B International Symposium on Image/Video Communications (ISIVC) %C Hammamet, Tunisia %G eng %0 Conference Paper %B IEEE Workshop on Signal Processing Advances in Wireless Communications (SPAWC) %D 2006 %T Blind carrier phase estimation for non-equiprobable constellations %A R. López-Valcarce %A C. Mosquera %K Digital Communications %K phase estimation %K signal shaping %K synchronization %K Tomlinson-Harashima precoding %B IEEE Workshop on Signal Processing Advances in Wireless Communications (SPAWC) %C Cannes, France %G eng %0 Journal Article %J International Journal of Adaptive Control and Signal Processing %D 2006 %T Second-order blind algorithms for adaptive recursive linear equalizers: Analysis and lattice implementation %A R. López-Valcarce %K adaptive IIR filters %K blind equalization %K Digital Communications %K lattice filters %B International Journal of Adaptive Control and Signal Processing %V 20 %P 265–289 %8 August %G eng %0 Conference Paper %B International Workshop on Signal Processing for Space Communications (SPSC) %D 2006 %T Symbol-Rate Estimation for DVB-S2 Broadcasting %A C. Mosquera %A Sandro Scalise %A R. López-Valcarce %K DVB %K symbol rate %K synchronization %B International Workshop on Signal Processing for Space Communications (SPSC) %G eng %0 Conference Paper %B IEEE Workshop on Signal Processing Advances in Wireless Communications (SPAWC) %D 2006 %T Toward a theory of multirate nonlinear systems %A R. López-Valcarce %A Soura Dasgupta %K multirate systems %K nonlinear filters %K polyphase filters %B IEEE Workshop on Signal Processing Advances in Wireless Communications (SPAWC) %C Cannes, France %G eng %0 Conference Paper %B IEEE Conference on Decision and Control / European Control Conference (CDC/ECC) %D 2005 %T Analysis of a first-order adaptive recursive predictor %A R. López-Valcarce %K adaptive signal processing %K equalization %K second-order statistics %B IEEE Conference on Decision and Control / European Control Conference (CDC/ECC) %C Seville, Spain %G eng %R 10.1109/CDC.2005.1582919 %0 Conference Paper %B IEEE Workshop on Statistical Signal Processing (SSP) %D 2005 %T Diamond contour-based phase recovery for (cross-)QAM constellations %A Marcos Álvarez-Díaz %A R. López-Valcarce %K adaptive signal processing %K synchronization %B IEEE Workshop on Statistical Signal Processing (SSP) %C Bordeaux, France %G eng %R 10.1109/SSP.2005.1628678 %0 Journal Article %J IEEE Transactions on Signal Processing %D 2005 %T Realizable minimum mean-squared error channel shorteners %A R. López-Valcarce %K adaptive signal processing %K Channel shortening %B IEEE Transactions on Signal Processing %V 53 %P 4354–4362 %8 November %G eng %R 10.1109/TSP.2005.857050 %0 Conference Paper %B European Signal Processing Conference (EUSIPCO) %D 2004 %T Bias analysis and removal of a microphone array based road traffic speed estimator %A R. López-Valcarce %A D. Hurtado %A C. Mosquera %A Fernando Pérez-González %K microphone arrays %K speed estimation %K traffic monitoring %B European Signal Processing Conference (EUSIPCO) %C Vienna, Austria %G eng %0 Journal Article %J IEEE Transactions on Signal Processing %D 2004 %T Blind input, initial state, and system identification of SIMO Laguerre systems %A Jacob H. Gunther %A R. López-Valcarce %K blind identification %K blind input estimation %K Laguerre systems %K system identification %B IEEE Transactions on Signal Processing %V 52 %P 3357–3369 %8 December %G eng %R 10.1109/TSP.2004.837438 %0 Conference Paper %B IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM) %D 2004 %T Broadband analysis of a microphone array based road traffic speed estimator %A R. López-Valcarce %K microphone arrays %K speed estimation %K traffic monitoring %B IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM) %C Sitges, Barcelona, Spain %G eng %R 10.1109/SAM.2004.1503005 %0 Journal Article %J IEE Electronics Letters %D 2004 %T Cost minimisation interpretation of fourth power phase estimator and links to multimodulus algorithm %A R. López-Valcarce %K constant modulus %K Digital Communications %K equalization %K multimodulus %K phase estimation %B IEE Electronics Letters %V 40 %P 278–279 %8 19 February %G eng %0 Journal Article %J EURASIP Journal of Applied Signal Processing %D 2004 %T Estimation of road vehicle speed using two omnidirectional microphones: a maximum likelihood approach %A R. López-Valcarce %A C. Mosquera %A Fernando Pérez-González %K microphone arrays %K speed estimation %K traffic monitoring %B EURASIP Journal of Applied Signal Processing %V 2004 %P 1059–1077 %8 August %G eng %0 Journal Article %J IEEE Signal Processing Letters %D 2004 %T Minimum delay spread TEQ design in multicarrier systems %A R. López-Valcarce %K channel shortener %K cyclic prefix %K delay spread %K Digital Communications %K multicarrier communications %K time domain equalizer %B IEEE Signal Processing Letters %V 11 %P 682–685 %8 August %G eng %R 10.1109/LSP.2004.831676 %0 Journal Article %J IEEE Transactions on Signal Processing %D 2004 %T Realizable linear and decision feedback equalizers: properties and connections %A R. López-Valcarce %K adaptive signal processing %K channel equalization %B IEEE Transactions on Signal Processing %V 52 %P 757–773 %8 March %G eng %1**Best Paper Award** of the IEEE Signal Processing Society (Signal Processing for Communications), 2005