@conference {1075, title = {Radio Maps for Beam Alignment in mmWave Communications with Location Uncertainty}, booktitle = {IEEE 99th Vehicular Technology Conference: VTC2024-Spring. Workshop "Radio Map for 6G Communications"}, year = {2024}, month = {accepted}, address = {Singapore}, abstract = {
Abstract{\textemdash}Next generation communication systems require
accurate beam alignment to counteract the impairments that
characterize propagation in high-frequency bands. The overhead
of the pilot sequences required to select the best beam pair is
prohibitive when codebooks contain a large number of beams, as
is the case in practice. To remedy this issue, some schemes exploit
information about the user location to predict the best beam pair.
However, these schemes (i) involve no measurements whatsoever,
which generally results in a highly suboptimal predicted beam,
and (ii) are not robust to localization errors. To address these
limitations, this paper builds upon the notion of radio map to
develop two algorithms that attain a balance between the quality
of the obtained beam pair and measurement overhead. The
proposed algorithms predict the received power corresponding to
each pair and measure just the Q pairs with highest prediction.
While the first algorithm targets simplicity, the second one
relies on a Bayesian approach to endow the prediction process
with robustness to localization error. The performance of both
algorithms is shown to widely outperform existing methods using
ray-tracing data.
}, keywords = {mayte, mmWave, radio maps}, author = {Tien, Ngoc-Ha and Daniel Romero and R. L{\'o}pez-Valcarce} } @article {1066, title = {Sidelobe Suppression for Multicarrier Signals via Structured Spectral Precoding}, journal = {IEEE Transactions on Communications}, year = {2024}, month = {accepted}, abstract = {
Reducing the large sidelobes of multicarrier signals
is crucial to prevent adjacent channel interference. Spectral
precoding is an effective approach toward this goal, at the
expense of throughput loss due to precoder redundancy; thus,
it is of interest to explore alternative precoder designs with
improved performance at lower redundancies. We present a
novel precoder which minimizes radiated power within a userselectable
frequency region. The structure of the precoding
matrix is chosen to allow efficient mitigation of in-band distortion
at the receiver by means of iterative and successive interference
cancellation, while completely avoiding distortion to protected
and pilot subcarriers. By exploiting the low-rank properties of
constituent blocks, computational complexity can be significantly
reduced with little impact on sidelobe reduction. Simulation
results show the benefits of the proposed design, which is
particularly effective in redundancy-limited settings targeting
high spectral efficiency.
}, keywords = {mayte, multicarrier communications, OFDM, spectrum shaping}, doi = {10.1109/TCOMM.2024.3357429}, author = {Khawar Hussain and R. L{\'o}pez-Valcarce and Francesc Rey and Josep Sala and Javier Villares} } @conference {1054, title = {Frequency-selective hybrid beamforming for mmWave full-duplex}, booktitle = {IEEE Int. Conf. Acoustics, Speech and Signal Processing (ICASSP)}, year = {2023}, address = {Rhodes, Greece}, abstract = {
We study beamforming cancellation for a full-duplex (FD) wideband millimeter wave (mmWave) point-to-point bidirectional link in which both multicarrier-based nodes transmit and receive simultaneously and on the same frequency. The focus is on hybrid architectures in which the analog subblock of the beamformer, common to all subcarriers, is fully-connected and based on phase shifters with finite resolution, to avoid frontend saturation by mitigating FD-induced self-interference in the analog domain.
}, keywords = {full-duplex, mmWave, rodin}, doi = {10.1109/ICASSP49357.2023.10094826}, author = {Andrea Guamo-Morocho and R. L{\'o}pez-Valcarce} } @conference {1063, title = {Introducing the TRUMPET project: TRUstworthy Multi-site Privacy Enhancing Technologies}, booktitle = {IEEE International Conference on Cyber Security and Resilience (CSR)}, year = {2023}, pages = {604-611}, publisher = {IEEE}, organization = {IEEE}, address = {Venice, Italy}, isbn = {979-8-3503-1170-9}, doi = {https://doi.org/10.1109/CSR57506.2023.10224961}, author = {Alberto Pedrouzo-Ulloa and Jan Ramon and Fernando P{\'e}rez-Gonz{\'a}lez and Siyanna Lilova and Patrick Duflot and Zakaria Chihani and Nicola Gentili and Paola Ulivi and Mohammad Ashadul Hoque and Twaha Mukammel and Zeev Pritzker and Augustin Lemesle and Jaime Loureiro-Acu{\~n}a and Xavier Mart{\'\i}nez and Gonzalo Jim{\'e}nez-Balsa} } @conference {1058, title = {Overview of Use Cases in Single Channel Full Duplex Techniques for Satellite Communication}, booktitle = {40th International Communications Satellite Systems Conference (ICSSC)}, year = {2023}, author = {V{\'\i}ctor Monz{\'o}n Baeza and Carlos Mosquera and Roberto L{\'o}pez-Valcarce and JL Gonz{\'a}lez-R{\'\i}os and JA Vasquez-Peralvo and Tom{\'a}s Ram{\'\i}rez and P Losada and JC Merlano and S Chatzinotas and Steven Kisseleff} } @article {1024, title = {Full-duplex mmWave MIMO with finite-resolution phase shifters}, journal = {IEEE Trans. Wireless Communications}, volume = {21}, year = {2022}, month = {11/2022}, pages = {8979-8994}, abstract = {
Enabling simultaneous transmission and reception on the same carrier frequency, i.e., full-duplex (FD) communication, critically requires that the self-interference (SI) be sufficiently suppressed. We investigate the design of precoders and combiners for an FD millimeter wave point-to-point bidirectional link, where dense antenna arrays provide an opportunity for SI suppression via beamforming cancellation. In practice the precoders and combiners are usually implemented in a hybrid digital/analog fashion with a reduced number of radio frequency (RF) chains, and it becomes necessary to overcome a number of limitations imposed by this structure. We focus on a hybrid architecture with a phase shifter-based fully-connected analog stage, assuming finite-resolution phase shifters. To avoid analog-to-digital converter saturation at the receiver, the proposed design aims at cancelling SI at the analog combiner output. Although accurate SI suppression is difficult with low-resolution phase shifters, our design is able to provide reasonable performance, significantly improving upon previous approaches, and allowing to efficiently exploit the availability of RF chains to partially compensate for coarse phase quantization effects.
}, keywords = {full-duplex, mmWave, rodin}, issn = {1536-1276}, doi = {10.1109/TWC.2022.3171664}, author = {R. L{\'o}pez-Valcarce and M. Mart{\'\i}nez-Cotelo} } @article {1028, title = {General Form of the Power Spectral Density of Multicarrier Signals}, journal = {IEEE Communications Letters}, volume = {26}, year = {2022}, month = {08/2022}, pages = {1755-1759}, chapter = {1755}, abstract = {
Multicarrier modulation has been adopted in many modern communication systems because of its many appealing\ 
properties. Its relatively high out-of-band radiation has spurred many techniques to shape the power spectral density (PSD)\ 
of multicarrier signals, including spectral precoding and pulse shaping. We derive a general expression for the PSD which is\ 
valid for subcarrier-specific pulses and for spectral precoders operating over multiple blocks. The only statistical assumptions\ 
on the vector-valued sequence modulating the active subcarriers are wide-sense cyclostationarity and properness. The applicability\ 
of the result to a number of popular multicarrier formats is discussed.
}, keywords = {rodin, spectrum shaping}, doi = {10.1109/LCOMM.2022.3181728}, author = {R. L{\'o}pez-Valcarce} } @article {1009, title = {Hybrid Beamforming Designs for Frequency-Selective mmWave MIMO Systems with Per-RF chain or Per-antenna Power Constraints}, journal = {IEEE Trans. Wireless Communications}, volume = {21}, year = {2022}, month = {08/2022}, pages = {5770-5784}, chapter = {5770}, abstract = {
Configuring precoders and combiners is a major
challenge to deploy practical multiple-input multiple-output
(MIMO) millimeter wave (mmWave) communication systems
with large antenna arrays. Most prior work addresses the problem
focusing on a total transmit power constraint. In practical
transmitters, however, power amplifiers must operate within their
linear range, so that a power constraint applies to each one
of the input signals to these devices. Therefore, precoder and
combiner designs should incorporate per-antenna or per-radio
frequency (RF) chain transmit power constraints. We focus on
such problem for frequency-selective channels with multicarrier
modulation, and assuming hybrid analog/digital architectures
based on fully connected analog blocks implemented with finite resolution
phase shifters. We first derive an all-digital solution
which aims to maximize spectral efficiency. Then, we develop
hybrid precoders and combiners by approximately matching
the corresponding all-digital matrices while still enforcing the
power constraints. Numerical results show that the proposed
all-digital design performs close to the upper bound given
by the standard waterfilling-based solution with a total power
constraint. Additionally, the hybrid designs exhibit a moderate
loss even when low-resolution phase shifters are considered.
}, keywords = {mmWave, rodin}, doi = {10.1109/TWC.2022.3142959}, author = {R. L{\'o}pez-Valcarce and Nuria Gonz{\'a}lez-Prelcic} } @article {1030, title = {Joint Precoder and Window Design for OFDM Sidelobe Suppression}, journal = {IEEE Communications Letters}, volume = {26}, year = {2022}, month = {12/2022}, pages = {3044-3048}, abstract = {

Spectral precoding and windowing are two effective approaches to reduce out-of-band radiation (OBR) in multicarrier systems. Their performance comes at the price of reduced throughput and additional computational complexity, so there is strong motivation for simultaneously using both techniques. We present a novel design that jointly optimizes the precoder and window coefficients to minimize radiated power within a user-selectable frequency region. Results show that the proposed design achieves a better OBR/throughput/complexity tradeoff than either of these individual techniques separately.

}, keywords = {rodin, spectrum shaping}, doi = {10.1109/LCOMM.2022.3203521}, author = {Khawar Hussain and R. L{\'o}pez-Valcarce} } @conference {1025, title = {Orthogonal precoding with memory for sidelobe suppression in OFDM}, booktitle = {European Signal Processing Conference (EUSIPCO)}, year = {2022}, abstract = {
Orthogonal precoding is a very effective approach to reduce out-of-band radiation (OBR) in multicarrier systems in order to avoid adjacent channel interference. This is achieved at the cost of introducing precoder redundancy, which results in throughput loss. Introducing memory in the precoding operation has the potential to improve performance without sacrificing additional spectral efficiency, in exchange for extra computational complexity. We present a novel orthogonal memory precoder which minimizes OBR within a user-selectable frequency region and allows for controlling spectral overshoot. Decision-feedback decoding avoids symbol error rate degradation at the receiver.
}, keywords = {rodin, spectrum shaping}, author = {Khawar Hussain and R. L{\'o}pez-Valcarce} } @conference {996, title = {Analog beamforming for full-duplex mmWave communication with low-resolution phase shifters}, booktitle = {IEEE International Conference on Communications (ICC)}, year = {2021}, month = {06/2021}, address = {Montreal, Canada (Virtual event)}, abstract = {
Full-Duplex (FD) communication has been the object of recent attention, particularly in sub-6 GHz bands. By enabling in-band simultaneous transmission and reception, these techniques present great potential in terms of spectral efficiency, latency, and medium access flexibility, and their extension to millimeter wave (mmWave) bands can be expected to benefit similarly. The dense antenna arrays available in mmWave offer a large number of degrees of freedom which could be exploited towards self-interference (SI) mitigation in FD. However, analog beamforming architectures based on practical phase shifters make this task quite challenging due to the lack of amplitude
control and finite phase resolution. In this context, we consider a single-stream bidirectional point-to-point mmWave FD link, and develop a new analog beamforming design requiring a single radio frequency chain in each direction, explicitly taking into account such hardware-related constraints. Simulation results show that the proposed scheme significantly outperforms previous methods for practical phase shifter resolution values of a few bits.
}, keywords = {full-duplex, mmWave, rodin}, author = {R. L{\'o}pez-Valcarce and M. Mart{\'\i}nez-Cotelo} } @conference {1002, title = {Homomorphic SVM Inference for Fraud Detection}, booktitle = {VI Jornadas Nacionales de Investigaci{\'o}n en Ciberseguridad (JNIC)}, year = {2021}, publisher = {Ediciones de la Universidad de Castilla-La Mancha}, organization = {Ediciones de la Universidad de Castilla-La Mancha}, author = {Adri{\'a}n V{\'a}zquez-Saavedra and Gonzalo Jim{\'e}nez-Balsa and Jaime Loureiro-Acu{\~n}a and Manuel Fern{\'a}ndez-Veiga and Alberto Pedrouzo-Ulloa} } @article {995, title = {Mask-Compliant Orthogonal Precoding for Spectrally Efficient OFDM}, journal = {IEEE Transactions on Communications}, volume = {69}, year = {2021}, month = {03/2021}, pages = {1990-2001}, abstract = {
Orthogonal precoding constitutes a powerful technique to reduce spectrum sidelobes of multicarrier signals. This reduction is bought at the cost of introducing precoder redundancy, which results in some throughput loss and additional precoding/decoding complexity. When the goal is to meet some spectral emission mask constraints, it is desirable to avoid unnecessary sidelobe suppression in order to keep precoder redundancy at a minimum. In this context, we introduce a general framework under which we develop a novel Lagrange multiplier-based mask-compliant orthogonal precoder design targeting minimal redundancy. We also adapt to this framework two previously proposed
designs based on spectral notches and minimum out-of-band emission, respectively, to explicitly incorporate mask constraints. Simulation results are provided to show the effectiveness of the proposed designs under different practical masks for multicarrier wireless systems.
}, keywords = {rodin, spectrum shaping, winter}, doi = {10.1109/TCOMM.2020.3041351}, author = {Ravinder Kumar and Khawar Hussain and R. L{\'o}pez-Valcarce} } @conference {1003, title = {Memory Tricks: Improving Active Interference Cancellation for Out-of-Band power reduction in OFDM}, booktitle = {IEEE Int. Workshop Signal Process. Adv. Wireless Commun. (SPAWC)}, year = {2021}, address = {Lucca, Italy (Virtual event)}, abstract = {

Although active interference cancellation (AIC) is an appealing approach to reduce out-of-band radiation (OBR) in multicarrier systems without distorting data subcarriers, it usually requires a large number of reserved subcarriers to be effective. Introducing memory in AIC precoding may help alleviate this drawback in exchange for some increase in computational complexity. We propose a novel memory AIC precoder which, in contrast to previous schemes, minimizes OBR within a user-selectable frequency region and allows for controlling spectral overshoot.

}, keywords = {rodin, spectrum shaping}, author = {Khawar Hussain and R. L{\'o}pez-Valcarce} } @conference {990, title = {Energy-efficient analog beamforming with short packets in millimeter-wave MIMO systems}, booktitle = {2020 54th Asilomar Conference on Signals, Systems, and Computers, California, 2020}, year = {2020}, address = {Virtual event}, abstract = {
The energy-aware design of fully analog precoders and combiners is investigated in this paper. To that aim, we consider a millimeter-wave short-packet communication scenario where power consumption and hardware complexity constitute relevant factors. User terminals employ a single channel encoder and, at hardware level, they implement analog architectures that combine phase shifters and switches. Additionally, transmitting terminals also leverage a power control system. An energy efficiency figure of merit is considered, and its optimization subject to finite packet-length constraints is tackled cyclically over disconnected feasible sets. Numerical results are reported
firstly, to illustrate the advantages of the proposed short-packet fully analog design, secondly, to compare its performance to that of on-off beamforming, and finally, to discuss the optimality of the proposed optimization algorithm.
}, keywords = {mmWave, rodin}, author = {Jordi Borr{\`a}s and Francesc Molina and R. L{\'o}pez-Valcarce and Josep Sala} } @conference {989, title = {Full-Duplex mmWave Communication with Hybrid Precoding and Combining}, booktitle = {European Signal Processing Conference (EUSIPCO)}, year = {2020}, month = {08/2020}, address = {Amsterdam (Netherlands)}, abstract = {
We investigate the design of hybrid precoders and combiners for a millimeter wave (mmWave) point-to-point bidirectional link in which both nodes transmit and receive simultaneously and on the same carrier frequency. In such full-duplex configuration, mitigation of self-interference (SI) becomes critical. Large antenna arrays provide an opportunity for spatial SI suppression in mmWave. We assume a phase-shifter based, fully connected architecture for the analog part of the precoder and combiner. The proposed design, which aims at cancelling SI in the analog domain to avoid frontend saturation, significantly improves on the performance of previous approaches.
}, keywords = {full-duplex, mmWave, rodin, winter}, author = {R. L{\'o}pez-Valcarce and M. Mart{\'\i}nez-Cotelo} } @article {985, title = {Link Adaptation and SINR errors in Practical Multicast Multibeam Satellite Systems with Linear Precoding}, journal = {International Journal of Satellite Communications and Networking}, year = {2020}, keywords = {link adaptation, multi-beam satellite, precoding, satellite communications}, author = {Anxo Tato and Stefano Andrenacci and Eva Lagunas and Symeon Chatzinotas and Carlos Mosquera} } @conference {981, title = {Optimal window design for W-OFDM}, booktitle = {IEEE Int. Conf. Acoustics, Speech and Signal Processing (ICASSP)}, year = {2020}, month = {05/2020}, abstract = {
Windowing is an effective approach to reduce out-of-band radiation (OBR) in multicarrier systems in order to avoid adjacent channel interference. However, commonly used window functions are chosen in an ad hoc manner and fixed. We present an optimal window design for windowed-OFDM minimizing OBR within a given frequency region. The proposed technique is flexible in that it allows to specify the range of frequencies involved in the minimization and to apply spectral weighting. The optimal window can be computed offline.
}, keywords = {spectrum shaping, winter}, author = {Khawar Hussain and R. L{\'o}pez-Valcarce} } @conference {991, title = {Robustness analysis of beamforming based designs for mmWave Full-Duplex Amplify-and-Forward relays}, booktitle = {2020 14th International Conference on Signal Processing and Communication Systems (ICSPCS)}, year = {2020}, month = {12/2020}, abstract = {
We consider the robust design of a millimeter wave MIMO two-hop system in which source, relay and destination are
equipped with large antenna arrays. The relay implements the amplify-and-forward protocol and operates in full-duplex mode,
thus being subjected to self-interference (SI). Imperfect channel state information (CSI) is assumed in all involved links, including
the SI channel, with a deterministic isotropic bounded model on CSI errors. The proposed robust design seeks to maximize
the worst-case spectral efficiency, accommodates both digital and phase shifter-based analog beamforming, and is computationally
simple; moreover, it does not require knowledge of the size of the CSI uncertainty regions.
}, keywords = {full-duplex, mmWave, rodin}, author = {R. L{\'o}pez-Valcarce and M. Mart{\'\i}nez-Cotelo} } @article {988, title = {Two-Level Frame Precoding with non-Cooperative Gateways}, journal = {EURASIP Journal on Wireless Communications and Networking}, year = {2020}, keywords = {myrada, satcom, winter}, doi = {https://doi.org/10.1186/s13638-020-01757-7}, url = {https://rdcu.be/b5KB3}, author = {Tom{\'a}s Ram{\'\i}rez and Carlos Mosquera and R. L{\'o}pez-Valcarce} } @conference {961, title = {Analog beamforming for full-duplex millimeter wave communication}, booktitle = {16th International Symposium on Wireless Communication Systems (ISWCS)}, year = {2019}, month = {08/2019}, address = {Oulu, Finland}, abstract = {

Full-duplex (FD) communication has the potential for significant improvements in spectral efficiency, as long as the problem of self-interference (SI) can be overcome. For millimeter wave (mmWave) systems with large antenna arrays, beamforming based SI mitigation is attractive because of the large number of degrees of freedom available. Previously proposed precoder-combiner designs, however, suffer from a large performance loss under the hardware-constrained architectures required for operation at mmWave. In this context, we develop a new algorithm for the design of constant-amplitude analog precoders and combiners of an FD mmWave single-stream bidirectional link, significantly reducing the aforementioned performance loss.

}, keywords = {full-duplex, mmWave, winter}, author = {R. L{\'o}pez-Valcarce and Nuria Gonz{\'a}lez-Prelcic} } @conference {962, title = {Beamformer design for full-duplex amplify-and-forward millimeter wave relays}, booktitle = {16th International Symposium on Wireless Communication Systems (ISWCS)}, year = {2019}, month = {08/2019}, address = {Oulu, Finland}, abstract = {

We consider the design of Amplify \& Forward Full-Duplex (FD) relay-assisted communication systems. The FD mode has potential for significant improvements in spectral efficiency, but it suffers from large self-interference (SI) levels.

Beamforming-based SI mitigation is attractive for millimeter wave (mmWave) systems due to the large number of degrees of freedom available with large antenna arrays. We first develop an all-digital beamformer design by imposing a zero-forcing constraint on SI, performing quasi-optimally in terms of spectral efficiency. The design is then modified to fit the hardware-related constraints usually found when operating at mmWave, so that the beamformers can be implemented in the analog domain by using phase shifters, with an acceptable performance loss.

}, keywords = {full-duplex, mmWave, winter}, author = {R. L{\'o}pez-Valcarce and Nuria Gonz{\'a}lez-Prelcic} } @inbook {956, title = {Expectation{\textendash}maximisation based distributed estimation in sensor networks}, booktitle = {Data Fusion in Wireless Sensor Networks: A statistical signal processing perspective}, year = {2019}, pages = {201-230}, publisher = {The Institution of Engineering and Technology (IET)}, organization = {The Institution of Engineering and Technology (IET)}, chapter = {9}, address = {London, UK}, abstract = {

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.

}, keywords = {winter, wsn}, isbn = {978-1-78561-584-9}, author = {R. L{\'o}pez-Valcarce and Alba Pag{\`e}s-Zamora} } @conference {969, title = {Flexible spectral precoding for OFDM systems}, booktitle = {2nd XoveTIC Conference}, year = {2019}, month = {09/2019}, address = {A Coru{\~n}a (Spain)}, abstract = {
Spectral precoding is a popular approach to reduce out-of-band radiation (OBR) in
multicarrier systems in order to avoid adjacent channel interference. However, it introduces
distortion in the data, appropriate decoding is required at the receiver side. Thus, trading off
between implementation complexity, OBR reduction and error rate is important. We present a novel
linear precoder design with flexibility to trade off OBR reduction, precoding/decoding complexity,
and error rate at the receiver. Moreover, the constraint can be imposed on each subcarrier individually
to provide more flexibility. 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
}, keywords = {spectrum shaping, winter}, doi = {10.3390/proceedings2019021024}, author = {Khawar Hussain and R. L{\'o}pez-Valcarce} } @conference {958, title = {Flexible spectral precoding for sidelobe suppression in OFDM systems}, booktitle = {IEEE Int. Conf. Acoustics, Speech and Signal Processing (ICASSP)}, year = {2019}, month = {04/2019}, pages = {4789 - 4793}, publisher = {IEEE}, organization = {IEEE}, address = {Brighton, UK}, abstract = {

Spectral 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.

}, keywords = {spectrum shaping, winter}, doi = {10.1109/ICASSP.2019.8683162}, author = {Khawar Hussain and Ana Lojo and R. L{\'o}pez-Valcarce} } @conference {957, title = {Frequency-selective hybrid precoding and combining for mmWave MIMO systems with per-antenna power constraints}, booktitle = {IEEE Int. Conf. Acoustics, Speech and Signal Processing (ICASSP)}, year = {2019}, month = {04/2019}, pages = {4794-4798}, publisher = {IEEE}, organization = {IEEE}, address = {Brighton, UK}, abstract = {

Configuring 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.

}, keywords = {mmWave, winter}, doi = {10.1109/ICASSP.2019.8683831}, author = {Javier Rodr{\'\i}guez-Fern{\'a}ndez and R. L{\'o}pez-Valcarce and Nuria Gonz{\'a}lez-Prelcic} } @conference {960, title = {Low-rank data matrix recovery with missing values and faulty sensors}, booktitle = {European Signal Processing Conference (EUSIPCO)}, year = {2019}, month = {09/2019}, address = {A Coru{\~n}a, Spain}, abstract = {

In practice, data gathered by wireless sensor networks often belongs in a low-dimensional subspace, but it can present missing as well as corrupted values due to sensor malfunctioning and/or malicious attacks. We study the problem of Maximum Likelihood estimation of the low-rank factors of the underlying structure in such situation, and develop an Expectation-Maximization algorithm to this purpose, together with an effective initialization scheme. The proposed method outperforms previous schemes based on an initial faulty sensor identification stage, and is competitive in terms of complexity and performance with convex optimization-based matrix completion approaches.

}, keywords = {winter, wsn}, author = {R. L{\'o}pez-Valcarce and Josep Sala} } @article {948, title = {Maximally stationary window design for overlap-add based random vibration synthesis}, journal = {Mechanical Systems and Signal Processing}, volume = {122}, year = {2019}, month = {05/2019}, pages = {642-657}, abstract = {
The accurate synthesis of realistic waveforms conforming to certain speci ca-
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 signi cantly improve the stationarity properties when compared to commonly
used windows.
}, keywords = {random vibration}, doi = {10.1016/j.ymssp.2018.12.038}, author = {Dami{\'a}n Gonz{\'a}lez and R. L{\'o}pez-Valcarce} } @article {947, title = {MMSE filter design for Full-Duplex filter-and-forward MIMO relays under limited dynamic range}, journal = {Signal Processing}, volume = {156}, year = {2019}, month = {03/2019}, pages = {208-219}, abstract = {
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.
}, keywords = {adaptive signal processing, full-duplex, winter}, doi = {doi.org/10.1016/j.sigpro.2018.11.001}, author = {Emilio Antonio-Rodr{\'\i}guez and Stefan Werner and R. L{\'o}pez-Valcarce and Risto Wichman} } @conference {959, title = {OFDM spectral precoding with per-subcarrier distortion constraints}, booktitle = {European Signal Processing Conference (EUSIPCO)}, year = {2019}, month = {09/2019}, address = {A Coru{\~n}a, Spain}, abstract = {
Spectral precoding is effective in reducing out-of-band radiation
(OBR) in multicarrier systems, but it introduces distortion
in the data, requiring a suitable decoder at the receiver.
Thus, trading off OBR reduction, implementation complexity,
and error rate is of paramount importance. We present a precoder
design which minimizes OBR under constraints on the
distortion at each individual data subcarrier. By judiciously
choosing the distortion profile, the decoding task can be significantly
alleviated, with a sizable improvement in terms of
implementation complexity with respect to previous designs.
}, keywords = {spectrum shaping, winter}, author = {Khawar Hussain and R. L{\'o}pez-Valcarce} } @article {952, title = {Partial-Duplex Amplify-and-Forward Relaying: Spectral Efficiency Analysis under Self-Interference}, journal = {IEEE Transactions on Wireless Communications}, volume = {18}, year = {2019}, month = {04/2019}, pages = { 2271-2285}, abstract = {
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.
}, keywords = {full-duplex, myrada, winter}, doi = {10.1109/TWC.2019.2902390}, author = {R. L{\'o}pez-Valcarce and C. Mosquera} } @proceedings {968, title = {Solving self-interference issues in a Full-Duplex radio transceiver}, journal = {2nd XoveTIC Conference}, year = {2019}, month = {09/2019}, address = {A Coru{\~n}a (Spain)}, abstract = {
Most wireless devices transmit and receive at different spectrum frequency bands. This
approach is no longer optimal due to increasing electromagnetic exhaustion. Besides, interference
among all present and future working services should be negligible. A full-duplex scheme using
the same band for simultaneous uplink and downlink is a huge step towards solving this issue.
However, sharing the same frequency band involves a large interference of transmitted signal over
received signal. To fix this problem, we propose the usage of a hybrid multistage cancellation system,
consisting of an analog cancellation setup at RF frequencies and a baseband digital cancellation stage.
}, keywords = {adaptive signal processing, full-duplex, winter}, doi = {10.3390/proceedings2019021035}, author = {Miguel Franco-Martinez and Francisco-Javier Martinez-Alonso and R. L{\'o}pez-Valcarce} } @article {935, title = {Distributed Precoding Systems in Multi-Gateway Multibeam Satellites: Regularization and Coarse Beamforming}, journal = {IEEE Transactions on Wireless Communication}, year = {2018}, author = {Carlos Mosquera and R. L{\'o}pez-Valcarce and Tom{\'a}s Ram{\'\i}rez and Vahid Joroughi} } @conference {921, title = {Locally optimal invariant detector for testing equality of two power spectral densities}, booktitle = { IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP)}, year = {2018}, address = {Calgary, Canada}, abstract = {
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.
}, keywords = {cognitive radio, winter}, author = {David Ram{\'\i}rez and Daniel Romero and Javier V{\'\i}a and R. L{\'o}pez-Valcarce and Ignacio Santamar{\'\i}a} } @article {913, title = {Parameter estimation in wireless sensor networks with faulty transducers: A distributed EM approach}, journal = {Signal Processing}, volume = {144}, year = {2018}, month = {03/2018}, pages = {226-237}, abstract = {

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.

}, keywords = {winter, wsn}, doi = {10.1016/j.sigpro.2017.10.012}, url = {https://authors.elsevier.com/a/1W90XbZX4rsob}, author = {Silvana Silva Pereira and R. L{\'o}pez-Valcarce and Alba Pag{\`e}s-Zamora} } @conference {931, title = {Spectral and statistical evaluation of the properties of the vibration measured at the base of an automotive seat for non-Gaussian random noise synthesis}, booktitle = {Int. Conf. on Noise and Vibration Engineering, ISMA-USD 2018}, year = {2018}, month = {09/2018}, address = {Leuven, Belgium}, abstract = {
The 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.
}, keywords = {random vibration}, author = {Dami{\'a}n Gonz{\'a}lez and R. L{\'o}pez-Valcarce} } @article {941, title = {Testing equality of multiple power spectral density matrices}, journal = {IEEE Trans. Signal Processing}, volume = {66}, year = {2018}, month = {12/2018}, pages = {6268-6280}, keywords = {cognitive radio, winter}, doi = { 10.1109/TSP.2018.2875884}, author = {David Ram{\'\i}rez and Daniel Romero and Javier V{\'\i}a and R. L{\'o}pez-Valcarce and Ignacio Santamar{\'\i}a} } @conference {930, title = {Two-Level Precoding for High Throughput Satellites with non-Cooperative Gateways}, booktitle = {22nd International Workshop on Smart Antennas (WSA)}, year = {2018}, author = {Tom{\'a}s Ram{\'\i}rez and Carlos Mosquera and Roberto L{\'o}pez-Valcarce} } @article {871, title = {CDMA-based Acoustic Local Positioning System for Portable Devices with Multipath Cancellation}, journal = {Digital Signal Processing}, volume = {62}, year = {2017}, month = {03/2017}, pages = {38-51}, abstract = {
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.
}, keywords = {compass, wsn}, issn = {1051-2004}, doi = {10.1016/j.dsp.2016.11.001}, author = {Fernando J. Alvarez and Teodoro Aguilera and R. L{\'o}pez-Valcarce} } @conference {903, title = {Defending Surveillance Sensor Networks Against Data-Injection Attacks via Trusted Nodes}, booktitle = {European Signal Processing Conference (EUSIPCO)}, year = {2017}, month = {08/2017}, address = {Kos Island, Greece}, abstract = {
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.
}, keywords = {winter, wsn}, author = {R. L{\'o}pez-Valcarce and Daniel Romero} } @conference {912, title = {Distributed Precoding Systems in Multi-Gateway Multibeam Satellites}, booktitle = {35th AIAA International Communications Satellite Systems Conference}, year = {2017}, month = {10/2017}, address = {Trieste,Italy}, keywords = {precoding, satcom}, author = {Carlos Mosquera and R. L{\'o}pez-Valcarce and Tom{\'a}s Ram{\'\i}rez} } @article {880, title = {FER Estimation in a Memoryless BSC with Variable Frame Length and Unreliable ACK/NAK Feedback}, journal = {IEEE Transactions on Wireless Communications}, volume = {16}, year = {2017}, month = {06/2017}, pages = {3661 - 3673}, abstract = {
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.
}, keywords = {adaptive signal processing, compass, Cram{\'e}r-Rao bound (CRB), frame error rate, myrada, winter}, doi = {10.1109/TWC.2017.2686845}, author = {Alberto Rico-Alvari{\~n}o and R. L{\'o}pez-Valcarce and Carlos Mosquera and Robert W. Heath Jr.} } @article {878, title = {Learning Power Spectrum Maps from Quantized Power Measurements}, journal = {IEEE Transactions on Signal Processing}, volume = {65}, year = {2017}, month = {05/2017}, pages = {2547-2560}, abstract = {
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.\ 
}, keywords = {cognitive radio, compass, compressed sensing, spectrum sensing, winter, wsn}, doi = {10.1109/TSP.2017.2666775}, author = {Daniel Romero and Seung-Jun Kim and Georgios Giannakis and R. L{\'o}pez-Valcarce} } @conference {876, title = {Robust clustering of data collected via crowdsourcing}, booktitle = {IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP)}, year = {2017}, month = {03/2017}, pages = {4014 - 4018}, address = {New Orleans}, abstract = {

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.

}, keywords = {winter, wsn}, doi = {10.1109/ICASSP.2017.7952910}, author = {Alba Pag{\`e}s-Zamora and Georgios Giannakis and R. L{\'o}pez-Valcarce and Pere Gimenez-Febrer} } @article {838, title = {Wideband full-duplex MIMO relays with blind adaptive self-interference cancellation}, journal = {Signal Processing}, volume = {130}, year = {2017}, month = {01/2017}, pages = {74-85}, chapter = {74}, abstract = {
We 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.
}, keywords = {adaptive signal processing, compass, full duplex, winter}, issn = {0165-1684}, doi = {10.1016/j.sigpro.2016.06.010}, author = {Emilio Antonio-Rodr{\'\i}guez and Stefan Werner and R. L{\'o}pez-Valcarce and Taneli Riihonen and Risto Wichman} } @conference {840, title = {Bandwidth Allocation in Partial Duplex Relaying}, booktitle = {The 17th IEEE International workshop on Signal Processing advances in Wireless Communications (SPAWC)}, year = {2016}, month = {07/2016}, address = {Edinburgh, UK}, keywords = {compass, full duplex, relay}, author = {Carlos Mosquera and R. L{\'o}pez-Valcarce} } @article {825, title = {Compressive Covariance Sensing: Structure-Based Compressive Sensing Beyond Sparsity}, journal = {IEEE Signal Processing Magazine}, volume = {33}, year = {2016}, month = {01/2016}, pages = {78--93}, abstract = {
Compressed sensing deals with the reconstruction of signals
from sub-Nyquist samples by exploiting the sparsity of their
projections onto known subspaces. In contrast, the present
article is concerned with the reconstruction of second-order
statistics, such as covariance and power spectrum, even in
the absence of sparsity priors. The framework described here
leverages the statistical structure of random processes to
enable signal compression and offers an alternative perspective
at sparsity-agnostic inference. Capitalizing on parsimonious
representations, we illustrate how compression and reconstruction
tasks can be addressed in popular applications such
as power spectrum estimation, incoherent imaging, direction
of arrival estimation, frequency estimation, and wideband
spectrum sensing.
}, keywords = {compass, compressed sensing}, author = {Daniel Romero and Dyonisius D Ariananda and Zhi Tian and Geert Leus} } @conference {846, title = {Design of data-injection adversarial attacks against spatial field detectors}, booktitle = {IEEE Workshop on Statistical Signal Processing (SSP)}, year = {2016}, month = {06/2016}, address = {Palma de Mallorca, Spain}, abstract = {

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.

}, keywords = {adversarial signal processing, compass, wsn}, author = {R. L{\'o}pez-Valcarce and Daniel Romero} } @conference {845, title = {Distributed multivariate regression with unknown noise covariance in the presence of outliers: a minimum description length approach}, booktitle = {IEEE Workshop on Statistical Signal Processing (SSP)}, year = {2016}, address = {Palma de Mallorca, Spain}, abstract = {
We consider the problem of estimating the coefficients in a multivariable linear model by means of a wireless sensor network
which may be affected by anomalous measurements. The noise covariance matrices at the different sensors are assumed
unknown. Treating outlying samples, and their support, as additional nuisance parameters, the Maximum Likelihood
estimate is investigated, with the number of outliers being estimated according to the Minimum Description Length
principle. A distributed implementation based on iterative consensus techniques is then proposed, and it is shown effective
for managing outliers in the data.
}, keywords = {compass, wsn}, author = {R. L{\'o}pez-Valcarce and Daniel Romero and Josep Sala and Alba Pag{\`e}s-Zamora} } @conference {870, title = {Hybrid precoders and combiners for mmWave MIMO systems with per-antenna power constraints}, booktitle = { IEEE Global Telecommunications Conf. (GLOBECOM)}, year = {2016}, abstract = {
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.
}, keywords = {compass, mmWave}, author = {R. L{\'o}pez-Valcarce and Nuria Gonz{\'a}lez-Prelcic and Cristian Rusu and R. W. Heath, Jr} } @article {866, title = {Multiantenna GLR detection of rank-one signals with known power spectral shape under spatially uncorrelated noise}, journal = {IEEE Transactions on Signal Processing}, volume = {64}, year = {2016}, month = {12/2016}, pages = {6269-6283}, chapter = {6269}, abstract = {

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.

}, keywords = {cognitive radio, compass}, issn = {1053-587X}, doi = {10.1109/TSP.2016.2601290}, author = {Josep Sala and Gonzalo V{\'a}zquez-Vilar and R. L{\'o}pez-Valcarce and Saeid Sedighi and Abbas Taherpour} } @conference {847, title = {Online EM-based distributed estimation in sensor networks with faulty nodes}, booktitle = {European Signal Processing Conference (EUSIPCO)}, year = {2016}, month = {09/2016}, address = {Budapest, Hungary}, abstract = {
This 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.
}, keywords = {compass, wsn}, author = {Pere Gimenez-Febrer and Alba Pag{\`e}s-Zamora and R. L{\'o}pez-Valcarce} } @article {1045, title = {On the analysis of scheduling in dynamic duplex multi-hop mmWave cellular systems}, journal = {IEEE Transactions on Wireless Communications}, volume = {14}, year = {2015}, month = {jun}, pages = {6028 {\textendash} 6042}, author = {Garc{\'\i}a-Rois, Juan and Gomez-Cuba, Felipe and Akdeniz, Mustafa Riza and Gonz{\'a}lez-Casta{\~n}o, Francisco Javier and Burguillo-Rial, Juan Carlos and Rangan, Sundeep and Lorenzo, Beatriz} } @conference {815, title = {Attack detectors for data aggregation in clustered sensor networks}, booktitle = {European Signal Processing Conf. (EUSIPCO)}, year = {2015}, month = {accepted}, pages = {2098-2102}, publisher = {EURASIP}, organization = {EURASIP}, address = {Nice, France}, abstract = {
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{\textquoteright}s test for homoscedasticity constituting a good candidate when lacking a priori knowledge of the variance of the underlying distribution.
}, keywords = {adversarial signal processing, compass, wsn}, author = {R. L{\'o}pez-Valcarce and Daniel Romero} } @article {770, title = {Compression Limits for Random Vectors with Linearly Parameterized Second-Order Statistics}, journal = {IEEE Trans. Information Theory}, volume = {61}, year = {2015}, month = {03/2015}, pages = {1410-1425}, chapter = {1410}, abstract = {
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 {\textemdash} 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.
}, keywords = {compass, compressed sensing}, doi = {10.1109/TIT.2015.2394784}, author = {Daniel Romero and R. L{\'o}pez-Valcarce and Geert Leus} } @article {769, title = {Cram{\'e}r-Rao Bounds for SNR Estimation of Oversampled Linearly Modulated Signals}, journal = {IEEE Trans. Signal Processing}, volume = {63}, year = {2015}, month = {04/2015}, pages = {1675-1683}, chapter = {1675}, abstract = {
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) Cram{\'e}r-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.
}, keywords = {adaptive signal processing, compass, Cram{\'e}r-Rao bound (CRB), dynacs, oversampling, Signal-to-noise ratio (SNR)}, doi = {10.1109/TSP.2015.2396013}, author = {R. L{\'o}pez-Valcarce and J. Villares and J. Riba and W. Gappmair and C. Mosquera} } @conference {812, title = {Distributed AoA-based Source Positioning in NLOS with Sensor Networks}, booktitle = {IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP)}, year = {2015}, month = {04/2015}, publisher = {IEEE}, organization = {IEEE}, address = {Brisbane, Australia}, abstract = {
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.
}, keywords = {compass, wsn}, author = {Pere Gimenez-Febrer and Alba Pag{\`e}s-Zamora and Silvana Silva Pereira and R. L{\'o}pez-Valcarce} } @conference {811, title = {Distributed TLS Estimation under Random Data Faults}, booktitle = {IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP)}, year = {2015}, month = {04/2015}, publisher = {IEEE}, organization = {IEEE}, address = {Brisbane, Australia}, abstract = {
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.
}, keywords = {compass, wsn}, author = {Silvana Silva Pereira and Alba Pag{\`e}s-Zamora and R. L{\'o}pez-Valcarce} } @article {767, title = {A Greedy Topology Design to Accelerate Consensus in Broadcast Wireless Sensor Networks}, journal = {Information Processing Letters}, volume = {115}, year = {2015}, month = {03/2015}, pages = {408-413}, chapter = {408}, abstract = {

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.

}, keywords = {compass, wsn}, doi = {10.1016/j.ipl.2014.11.009}, author = {Massimo Vecchio and R. L{\'o}pez-Valcarce} } @article {756, title = {Improving Area Coverage of Wireless Sensor Networks Via Controllable Mobile Nodes: a Greedy Approach}, journal = {Journal of Network and Computer Applications}, volume = {48}, year = {2015}, month = {02/2015}, pages = {1-13}, abstract = {
Reliable wide-area monitoring with Wireless Sensor Networks (WSNs) remains a problem of
interest: simply deploying more nodes to cover wider areas is generally not a viable solution, due to
deployment and maintenance costs and the increase in radio interference. One possible solution
gaining popularity is based on the use of a reduced number of mobile nodes with controllable
trajectories in the monitored field. In this framework, we present a distributed technique for iteratively
computing the trajectories of the mobile nodes in a greedy fashion. The static sensor nodes actively
assist the mobile nodes in this task by means of a bidding protocol, thus participating towards the goal
of maximizing the area coverage of the monitored field. The performance of the proposed technique is
evaluated on various simulation scenarios with different number of mobile and static nodes in terms of
achieved coverage and mean time to achieve X\% coverage. Comparison with previous state-of-the-art
techniques reveals the effectiveness and stability of the proposed method.
}, keywords = {compass, wsn}, doi = {10.1016/j.jnca.2014.10.007}, author = {Massimo Vecchio and R. L{\'o}pez-Valcarce} } @conference {1038, title = {A Microeconomic Approach to Data Trading in User Provided Networks}, booktitle = {IEEE Globecom Workshops}, year = {2015}, pages = {1{\textendash}7}, author = {Lorenzo, B and Gomez-Cuba, F and Garcia-Rois, J and Gonzalez-Castano, F J and Burguillo, J C} } @conference {809, title = {Multipath cancellation in broadband acoustic local positioning systems}, booktitle = {IEEE 9th International Symposium on Intelligent Signal Processing (WISP)}, year = {2015}, month = {05/2015}, publisher = {IEEE}, organization = {IEEE}, address = {Siena, Italy}, abstract = {

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.

}, keywords = {compass, wsn}, doi = {10.1109/WISP.2015.7139174}, author = {Fernando J. Alvarez and R. L{\'o}pez-Valcarce} } @conference {810, title = {Spectrum Cartography using quantized observations}, booktitle = {IEEE Int. Conference on Acoustics, Speech and Signal Processing (ICASSP)}, year = {2015}, month = {04/2015}, publisher = {IEEE}, organization = {IEEE}, address = {Brisbane, Australia}, abstract = {
This 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.
}, keywords = {cognitive radio, compass, compressed sensing, spectrum sensing}, author = {Daniel Romero and Seung-Jun Kim and R. L{\'o}pez-Valcarce and Georgios Giannakis} } @conference {808, title = {Subspace-constrained SINR optimization in MIMO full-duplex relays under limited dynamic range}, booktitle = {IEEE 16th Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC)}, year = {2015}, month = {06/2015}, publisher = {IEEE}, organization = {IEEE}, address = {Stockholm, Sweden}, abstract = {
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.
}, keywords = {adaptive signal processing, compass, full duplex}, author = {Emilio Antonio-Rodr{\'\i}guez and R. L{\'o}pez-Valcarce and Taneli Riihonen and Stefan Werner and Risto Wichman} } @article {748, title = {Active Interference Cancellation for OFDM Spectrum Sculpting: Linear Processing is Optimal}, journal = {IEEE Communications Letters}, volume = {18}, year = {2014}, month = {09/2014}, pages = {1543-1546}, chapter = {1543}, abstract = {

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.

}, keywords = {cognitive radio, compass, dynacs, spectrum shaping}, doi = {10.1109/LCOMM.2014.2338316}, author = {Schmidt, J.F. and Daniel Romero and R. L{\'o}pez-Valcarce} } @conference {734, title = {Antenna competition to boost Active Interference Cancellation in cognitive MIMO-OFDM}, booktitle = {IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM)}, year = {2014}, address = {A Coru{\~n}a, Spain}, abstract = {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.}, keywords = {cognitive radio, dynacs, spectrum shaping}, doi = {10.1109/SAM.2014.6882392}, author = {Schmidt, J.F. and R. L{\'o}pez-Valcarce} } @conference {762, title = {Cooperative compressive power spectrum estimation}, booktitle = {IEEE Sensor Array Multichannel Signal Process. Workshop (SAM)}, year = {2014}, keywords = {cognitive radio, wsn}, author = {Dyonisius D Ariananda and Daniel Romero and Geert Leus} } @conference {753, title = {Detecting Misreporting Attacks to the Proportional Fair Scheduler}, booktitle = {IEEE Workshop on Information Forensics and Security (WIFS)}, year = {2014}, month = {12/2014}, address = {Atlanta, USA}, abstract = {
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.
}, keywords = {adversarial signal processing, compass}, doi = {10.1109/WIFS.2014.7084310}, author = {Schmidt, J.F. and R. L{\'o}pez-Valcarce} } @conference {731, title = {Distributed Total Least Squares Estimation over Networks}, booktitle = {IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP)}, year = {2014}, address = {Florence, Italy}, abstract = {

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.

}, keywords = {dynacs, wsn}, doi = {10.1109/ICASSP.2014.6855074}, author = {R. L{\'o}pez-Valcarce and Silvana Silva Pereira and Alba Pag{\`e}s-Zamora} } @conference {733, title = {How to Implement Doubly-Stochastic Matrices for Consensus-Based Distributed Algorithms}, booktitle = {IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM)}, year = {2014}, address = {A Coru{\~n}a, Spain}, abstract = {
Doubly-stochastic matrices are usually required by
consensus-based distributed algorithms. We propose a simple
and efficient protocol and present some guidelines for implementing
doubly-stochastic combination matrices even in noisy,
asynchronous and changing topology scenarios. The proposed
ideas are validated with the deployment of a wireless sensor
network, in which nodes run a distributed algorithm for robust
estimation in the presence of nodes with faulty sensors.
}, keywords = {compass, dynacs, wsn}, doi = {10.1109/SAM.2014.6882409}, author = {S. Valc{\'a}rcel-Macua and C. Moreno-Le{\'o}n and J. S. Romero and Silvana Silva Pereira and Javier Zazo and Alba Pag{\`e}s-Zamora and R. L{\'o}pez-Valcarce and S. Zazo} } @conference {751, title = {Low-Power Active Interference Cancellation for OFDM Spectrum Sculpting}, booktitle = {European Signal Processing Conference (EUSIPCO)}, year = {2014}, month = {09/2014}, abstract = {
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.
}, url = {http://www.eurasip.org/Proceedings/Eusipco/Eusipco2014/HTML/papers/1569912103.pdf}, author = {Schmidt, J.F. and Daniel Romero and R. L{\'o}pez-Valcarce} } @conference {740, title = {Nearly-Optimal Compression Matrices for Signal Power Estimation}, booktitle = {IEEE Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC)}, year = {2014}, address = {Toronto, Canada}, keywords = {cognitive radio, dynacs}, doi = {10.1109/SPAWC.2014.6941849}, author = {Daniel Romero and R. L{\'o}pez-Valcarce} } @conference {727, title = {OFDM spectrum sculpting with active interference cancellation: Keeping spectral spurs at bay}, booktitle = {IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP)}, year = {2014}, month = {05/2014}, pages = {1-5}, publisher = {IEEE}, organization = {IEEE}, address = {Florence, Italy}, keywords = {cognitive radio, dynacs, spectrum shaping}, doi = {10.1109/ICASSP.2014.6855169}, author = {Schmidt, J.F. and R. L{\'o}pez-Valcarce} } @conference {732, title = {SINR Optimization in Wideband Full-Duplex MIMO Relays under Limited Dynamic Range}, booktitle = {IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM)}, year = {2014}, address = {A Coru{\~n}a, Spain}, keywords = {adaptive signal processing, compass, full duplex}, doi = {10.1109/SAM.2014.6882369}, author = {Emilio Antonio-Rodr{\'\i}guez and R. L{\'o}pez-Valcarce and Taneli Riihonen and Stefan Werner and Risto Wichman} } @article {735, title = {Spectrum Sensing for Wireless Microphone Signals using Multiple Antennas}, journal = {IEEE Trans. on Vehicular Technology}, volume = {63}, year = {2014}, month = {11/2014}, pages = {4395-4407}, chapter = {4395}, abstract = {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.}, keywords = {cognitive radio, dynacs}, doi = {10.1109/TVT.2014.2316513}, author = {Daniel Romero and R. L{\'o}pez-Valcarce} } @conference {693, title = {Adaptive Self-interference Cancellation in Wideband Full-Duplex Decode-and-Forward MIMO Relays}, booktitle = {IEEE 14th Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC)}, year = {2013}, month = {06/2013}, address = {Darmstadt, Germany}, keywords = {adaptive signal processing, dynacs, full duplex}, doi = {10.1109/SPAWC.2013.6612074}, author = {Emilio Antonio-Rodr{\'\i}guez and R. L{\'o}pez-Valcarce and Taneli Riihonen and Stefan Werner and Risto Wichman} } @conference {687, title = {Autocorrelation-based adaptation rule for feedback equalization in Wideband Full-Duplex Amplify-and-Forward MIMO relays}, booktitle = {Int. Conf. Acoust., Speech, Signal Process. (ICASSP)}, year = {2013}, abstract = {
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.
}, keywords = {adaptive signal processing, dynacs, full duplex}, doi = {10.1109/ICASSP.2013.6638606}, author = {Emilio Antonio-Rodr{\'\i}guez and R. L{\'o}pez-Valcarce and Taneli Riihonen and Stefan Werner and Risto Wichman} } @conference {686, title = {Cancelling self-interference in full-duplex relays without Angle-of-Arrival information}, booktitle = {Int. Conf. Acoust., Speech, Signal Process. (ICASSP)}, year = {2013}, abstract = {
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.
}, keywords = {adaptive signal processing, dynacs, full duplex}, doi = {10.1109/ICASSP.2013.6638558}, author = {Emilio Antonio-Rodr{\'\i}guez and R. L{\'o}pez-Valcarce} } @article {711, title = {Choose Your Subcarriers Wisely: Active Interference Cancellation for Cognitive OFDM}, journal = {IEEE Journal on Emerging and Selected Topics in Circuits and Systems}, volume = {3}, year = {2013}, month = {12/2013}, pages = {615-625}, chapter = {615}, keywords = {cognitive radio, dynacs, spectrum shaping}, doi = {10.1109/JETCAS.2013.2280808}, author = {Schmidt, J.F. and Costas-Sanz, S. and R. L{\'o}pez-Valcarce} } @article {678, title = {A Cognitive Mobile BTS Solution with Software-Defined Radioelectric Sensing}, journal = {Sensors}, volume = {13}, year = {2013}, month = {02/2013}, pages = { 2051-2075}, chapter = { 2051}, abstract = {

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.

}, keywords = {cognitive radio, dynacs, mobile communications, SDR, vehicular communications}, doi = {10.3390/s130202051}, author = {J. Mu{\~n}oz and J. Vales-Alonso and F. Qui{\~n}oy-Garc{\'\i}a and Costas-Sanz, S. and M. Pillado and F.J. Gonz{\'a}lez-Casta{\~n}o and M. Garc{\'\i}a-Sanchez and R. L{\'o}pez-Valcarce and C. L{\'o}pez-Bravo} } @conference {725, title = {Compressive Angular and Frequency Periodogram Reconstruction for Multiband Signals}, booktitle = {IEEE Int. Workshop Comput. Advances Multi-Sensor Adaptive Process (CAMSAP)}, year = {2013}, address = {San Martin}, keywords = {cognitive radio, dynacs}, doi = {10.1109/CAMSAP.2013.6714102}, author = {Ariananda, D. D. and Daniel Romero and Geert Leus} } @conference {681, title = {Compressive Covariance Sampling}, booktitle = {Inform. Theory Appl. Workshop}, year = {2013}, month = {Feb.}, pages = {1-8}, keywords = {cognitive radio, dynacs}, doi = {10.1109/ITA.2013.6502949}, author = {Daniel Romero and Geert Leus} } @conference {685, title = {Compressive wideband spectrum sensing with spectral prior information}, booktitle = {Int. Conf. Acoust., Speech, Signal Process. (ICASSP)}, year = {2013}, abstract = {
Wideband 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.
}, keywords = {cognitive radio, dynacs, spectrum sensing}, doi = {10.1109/ICASSP.2013.6638505}, author = {Daniel Romero and R. L{\'o}pez-Valcarce and Geert Leus} } @article {676, title = {On the design of a novel two-objective harmony search approach for distance- and connectivity-based localization in wireless sensor networks}, journal = {Engineering Applications of Artificial Intelligence}, volume = {26}, year = {2013}, month = {02/2013}, pages = {669-676}, chapter = {669}, keywords = {dynacs, wsn}, doi = {10.1016/j.engappai.2012.06.002}, author = {Diana Manjarres and Javier Del Ser and Sergio Gil-Lopez and Massimo Vecchio and Itziar Landa-Torres and Sancho Salcedo-Sanz and R. L{\'o}pez-Valcarce} } @conference {684, title = {A Diffusion-based distributed EM algorithm for density estimation in wireless sensor networks}, booktitle = {Int. Conf. Acoust., Speech, Signal Process. (ICASSP)}, year = {2013}, abstract = {
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.
}, keywords = {dynacs, wsn}, doi = {10.1109/ICASSP.2013.6638501}, author = {Silvana Silva Pereira and Alba Pag{\`e}s-Zamora and R. L{\'o}pez-Valcarce} } @article {682, title = {A Diffusion-Based EM Algorithm for Distributed Estimation in Unreliable Sensor Networks}, journal = {IEEE Signal Processing Letters}, volume = {20}, year = {2013}, month = {06/2013}, pages = {595-598}, chapter = {595}, abstract = {

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{\textendash}Rao Lower Bound at all SNR values and compares favorably with other approaches.

}, keywords = {dynacs, wsn}, doi = {10.1109/LSP.2013.2260329}, author = {Silvana Silva Pereira and R. L{\'o}pez-Valcarce and Alba Pag{\`e}s-Zamora} } @article {712, title = {Lattice implementation of adaptive channel shortening in multicarrier transmission over IIR channels}, journal = {EURASIP Journal on Advances in Signal Processing}, volume = {2013:174}, year = {2013}, month = {11/2013}, doi = {10.1186/1687-6180-2013-174}, url = {http://asp.eurasipjournals.com/content/2013/1/174}, author = {E. Ben Salem and S. Cherif and H. Besbes and R. L{\'o}pez-Valcarce} } @conference {688, title = {Localization of Forgeries in MPEG-2 Video through GOP Size and DQ analysis}, booktitle = {IEEE International Workshop on Multimedia Signal Processing (MMSP)}, year = {2013}, pages = {494-499}, address = {Pula (Sardinia), Italy}, abstract = {

This work addresses forgery localization in MPEG-2 compressed videos. The proposed method is based on the analysis of Double Quantization (DQ) traces in frames that were encoded twice as intra (i.e., I-frames). \ Employing a state-of-the-art method, such frames are located in the video under analysis by estimating the size of the Group Of Pictures (GOP) that was used in the first compression; then, the DQ analysis is devised for the MPEG-2 encoding scheme and applied to frames that were intra-coded in both the first and second compression. In such a way, regions that were manipulated between the two encodings are detected. Compared to existing methods based on double quantization analysis, the proposed scheme makes forgery localization possible on a wider range of settings.

}, author = {Daniele Labartino and Tiziano Bianchi and Alessia De Rosa and Marco Fontani and David V{\'a}zquez-Pad{\'\i}n and Alessandro Piva and Mauro Barni} } @conference {692, title = {Low Complexity Primary User Protection for Cognitive OFDM}, booktitle = {European Signal Processing Conf. (EUSIPCO), Marrakech (Morocco)}, year = {2013}, month = {09/2013}, keywords = {cognitive radio, dynacs, spectrum shaping}, author = {Schmidt, J.F. and R. L{\'o}pez-Valcarce} } @article {677, title = {A novel heuristic approach for distance- and connectivity-based multihop node localization in wireless sensor networks}, journal = {Soft Computing}, volume = {17}, year = {2013}, month = {01/2013}, pages = {17-28}, chapter = {17}, keywords = {dynacs, wsn}, doi = {10.1007/s00500-012-0897-2}, author = {Diana Manjarres and Javier Del Ser and Sergio Gil-Lopez and Massimo Vecchio and Itziar Landa-Torres and R. L{\'o}pez-Valcarce} } @article {647, title = {Privacy-Preserving Data Aggregation in Smart Metering Systems: An Overview}, journal = {IEEE Signal Processing Magazine}, volume = {30}, year = {2013}, month = {03/2013}, pages = {75-86}, keywords = {SPED}, author = {Zekeriya Erkin and Juan Ram{\'o}n Troncoso-Pastoriza and Reginald Lagendijk and Fernando P{\'e}rez-Gonz{\'a}lez} } @conference {703, title = {Quantization lattice estimation for multimedia forensics}, booktitle = {IEEE International Conference on Image Processing}, year = {2013}, pages = {4452-4456}, address = {Melbourne, Australia}, keywords = {Dual lattice, lattice estimation, multimedia forensics, noisy estimation}, author = {Pedro Comesa{\~n}a and Fernando P{\'e}rez-Gonz{\'a}lez and Noelia Liste} } @conference {694, title = {Spectrum Sensing in Time-Varying Channels Using Multiple Antennas}, booktitle = {IEEE 14th Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC), Darmstadt (Germany)}, year = {2013}, month = {06/2013}, keywords = {cognitive radio, dynacs, spectrum sensing}, doi = {10.1109/SPAWC.2013.6612027}, author = {Daniel Romero and R. L{\'o}pez-Valcarce} } @article {724, title = {Wideband Spectrum Sensing From Compressed Measurements Using Spectral Prior Information}, journal = {IEEE Trans. Signal Process.}, volume = {61}, year = {2013}, pages = {6232-6246}, keywords = {cognitive radio, compressed sensing, dynacs, spectrum sensing}, issn = {1053-587X}, doi = {10.1109/TSP.2013.2283473}, author = {Daniel Romero and Geert Leus} } @article {651, title = {An Adaptive Feedback Canceller for Full-Duplex Relays Based on Spectrum Shaping}, journal = {IEEE J. Selected Areas in Communications}, volume = {30}, year = {2012}, month = {08/2012}, pages = {1566 - 1577}, abstract = {
Although 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.
}, keywords = {adaptive signal processing, dynacs, full duplex}, doi = {10.1109/JSAC.2012.120923}, author = {R. L{\'o}pez-Valcarce and Emilio Antonio-Rodr{\'\i}guez and C. Mosquera and Fernando P{\'e}rez-Gonz{\'a}lez} } @conference {652, title = {Adaptive self-interference suppression for full-duplex relays with multiple receive antennas}, booktitle = {IEEE 13th Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC 2012)}, year = {2012}, month = {07/2012}, publisher = {IEEE}, organization = {IEEE}, address = {{\c C}esme, Turkey}, abstract = {
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.
}, keywords = {adaptive signal processing, dynacs, full duplex}, doi = {10.1109/SPAWC.2012.6292948}, author = {Emilio Antonio-Rodr{\'\i}guez and R. L{\'o}pez-Valcarce} } @conference {679, title = {Design of universal multicoset sampling patterns for compressed sensing of multiband sparse signals}, booktitle = { IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP)}, year = {2012}, month = {03/2012}, pages = {3337 - 3340}, address = {Kyoto (Japan)}, abstract = {

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.

}, isbn = {978-1-4673-0044-5}, doi = {10.1109/ICASSP.2012.6288630}, author = {M. Elena Dom{\'\i}nguez-Jim{\'e}nez and Nuria Gonz{\'a}lez-Prelcic and Gonzalo V{\'a}zquez-Vilar and R. L{\'o}pez-Valcarce} } @conference {654, title = {Detection of Gaussian signals in unknown time-varying channels}, booktitle = {IEEE Statistical Signal Processing Workshop (SSP 2012)}, year = {2012}, month = {08/2012}, publisher = {IEEE}, organization = {IEEE}, address = {Ann Arbor, MI}, abstract = {
Detecting the presence of a white Gaussian signal distorted by a\ noisy time-varying channel is addressed by means of three different\ detectors. First, the generalized likelihood ratio test (GLRT) is\ found for the case where the channel has no temporal structure, resulting\ in the well-known Bartlett{\textquoteright}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.
}, keywords = {cognitive radio, dynacs, spectrum sensing}, doi = {10.1109/SSP.2012.6319858}, author = {Daniel Romero and Javier V{\'\i}a and R. L{\'o}pez-Valcarce and Ignacio Santamar{\'\i}a} } @conference {637, title = {Detection of unknown constant magnitude signals in time-varying channels}, booktitle = {3rd Int. Workshop on Cognitive Information Processing (CIP 2012) }, year = {2012}, month = {05/2012}, address = {Baiona, Spain}, abstract = {

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.

}, keywords = {cognitive radio, dynacs, spectrum sensing}, doi = {10.1109/CIP.2012.6232933}, author = {Daniel Romero and R. L{\'o}pez-Valcarce} } @conference {653, title = {Generalized matched filter detector for fast fading channels}, booktitle = {IEEE Int. Conf. on Acoustics, Speech and Signal Processing (ICASSP 2012) }, year = {2012}, month = {07/2012}, publisher = {IEEE}, organization = {IEEE}, address = {Kyoto, Japan}, abstract = {
We 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.
}, keywords = {cognitive radio, dynacs, spectrum sensing}, doi = {10.1109/ICASSP.2012.6288587}, author = {Daniel Romero and R. L{\'o}pez-Valcarce and Geert Leus} } @article {648, title = {Multiantenna GLR detection of rank-one signals with known power spectrum in white noise with unknown spatial correlation}, journal = {IEEE Trans. on Signal Processing}, volume = {60}, year = {2012}, month = {06/2012}, pages = {3065 - 3078}, abstract = {
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.
}, keywords = {cognitive radio, dynacs}, doi = {10.1109/TSP.2012.2189767}, author = {Josep Sala and Gonzalo V{\'a}zquez-Vilar and R. L{\'o}pez-Valcarce} } @conference {656, title = {On the Application of a Hybrid Harmony Search Algorithm to Node Localization in Anchor-based Wireless Sensor Networks}, booktitle = {IEEE International Conference on Intelligent Systems Design and Applications (ISDA)}, year = {2011}, author = {Diana Manjarres and Javier Del Ser and Sergio Gil-Lopez and Massimo Vecchio and Itziar Landa-Torres and R. L{\'o}pez-Valcarce} } @conference {romero2011bandlimited, title = {Bandlimited or Constant Envelope? Exploiting Waveform Properties in Wireless Microphone Detection}, booktitle = {International Workshop on Computational Advances in Multi-Sensor Adaptive Processing (CAMSAP)}, year = {2011}, month = {December}, pages = {17-20}, address = {San Juan, Puerto Rico}, keywords = {Bandlimited signals., Constant Magnitude, dynamic spectrum access, Wireless Microphones}, author = {Daniel Romero and R. L{\'o}pez-Valcarce} } @conference {VazquezValcarceICASSP11, title = {Detection diversity of multiantenna spectrum sensors}, booktitle = {IEEE Int. Conf. on Acoustics, Speech and Signal Processing (ICASSP 2011)}, year = {2011}, month = {05/2011}, pages = {2936-2939}, publisher = {IEEE}, organization = {IEEE}, address = {Prague, Czech Republic}, abstract = {
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.
}, keywords = {cognitive radio, detection diversity, spectrum sensing}, author = {Gonzalo V{\'a}zquez-Vilar and R. L{\'o}pez-Valcarce and Ashish Pandharipande} } @article {RamirezVazquezTSP11, title = {Detection of Rank-{P} Signals in Cognitive Radio Networks With Uncalibrated Multiple Antennas}, journal = {IEEE Trans. on Signal Processing}, volume = {59}, number = {8}, year = {2011}, month = {08/2012}, pages = {3764-3774}, abstract = {
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.
}, keywords = {cognitive radio, dynacs, spectrum sensing}, doi = {10.1109/TSP.2011.2146779}, author = {David Ram{\'\i}rez and Gonzalo V{\'a}zquez-Vilar and R. L{\'o}pez-Valcarce and Javier V{\'\i}a and Ignacio Santamar{\'\i}a} } @conference {5990448, title = {Distributed spectrum sensing with multiantenna sensors under calibration errors}, booktitle = {IEEE Workshop on Signal Processing Advances in Wireless Communications (SPAWC)}, year = {2011}, month = {june}, pages = {441 -445}, abstract = {

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.

}, keywords = {ad hoc detectors, antenna arrays, calibration, calibration errors, cognitive radio, energy detector, generalized likelihood ratio, log normal distribution, lognormal shadowing, multiantenna sensors, Ricean fading, spectrum sensing, wireless medium}, issn = {1948-3244}, doi = {10.1109/SPAWC.2011.5990448}, author = {Daniel Romero and R. L{\'o}pez-Valcarce} } @conference {MASS2011, title = {An Effective Metaheuristic Approach to Node Localization in Wireless Sensor Networks}, booktitle = {IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS)}, year = {2011}, author = {Massimo Vecchio and R. L{\'o}pez-Valcarce and Francesco Marcelloni} } @conference {Arna1112:Hybrid, title = {Hybrid Space-Ground Processing for High-Capacity Multi-beam Satellite Systems}, booktitle = {IEEE GLOBECOM}, year = {2011}, note = {Selected Areas in Communications Symposium - Satellite \& Space Communications Track (GC{\textquoteright}11 - SAC - SSC)}, month = {dec}, address = {Houston, Texas, USA}, author = {Arnau, Jesus and Michael Bergmann and Enzo Alberto Candreva and Giovanni Emanuele Corazza and Riccardo {De Gaudenzi} and Bertrand Devillers and Wilfried Gappmair and Francesco Lombardo and C. Mosquera and Ana P{\'e}rez-Neira and Ilaria Thibault and Alessandro Vanelli-Coralli} } @conference {5990449, title = {Multiantenna detection of constant-envelope signals in noise of unknown variance}, booktitle = {IEEE Workshop on Signal Processing Advances in Wireless Communications (SPAWC)}, year = {2011}, month = {june}, pages = {446 -450}, abstract = {

Detection 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.

}, keywords = {cognitive radio, multiantenna detection, spectrum sensing}, issn = {1948-3244}, doi = {10.1109/SPAWC.2011.5990449}, author = {Daniel Romero and R. L{\'o}pez-Valcarce} } @conference {RamirezVazquezICASSP11, title = {Multiantenna detection under noise uncertainty and primary user{\textquoteright}s spatial structure}, booktitle = {IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP)}, year = {2011}, month = {May}, pages = {2948-2951}, publisher = {IEEE}, organization = {IEEE}, address = {Prage, Czech Republic}, keywords = {cognitive radio, generalized likelihood ratio test (GLRT), spectrum sensing}, author = {David Ram{\'\i}rez and Gonzalo V{\'a}zquez-Vilar and R. L{\'o}pez-Valcarce and Javier V{\'\i}a and Ignacio Santamar{\'\i}a} } @article {649, title = {Multiantenna Spectrum Sensing Exploiting Spectral a priori Information}, journal = {IEEE Trans. on Wireless Communications}, volume = {10}, year = {2011}, month = {12/2011}, pages = {4345 - 4355}, keywords = {cognitive radio, dynacs, spectrum sensing}, doi = {10.1109/TWC.2011.101211.110665}, author = {Gonzalo V{\'a}zquez-Vilar and R. L{\'o}pez-Valcarce and Josep Sala} } @conference {NaBIC2011, title = {Solving the Node Localization Problem in WSNs by a Two-objective Evolutionary Algorithm and Gradient Descent}, booktitle = {the 3-th IEEE World Congress on Nature and Biologically Inspired Computing (NaBIC 2011)}, year = {2011}, author = {Massimo Vecchio and R. L{\'o}pez-Valcarce and Francesco Marcelloni} } @article {VazquezValcarceTSP11, title = {Spectrum Sensing Exploiting Guard Bands and Weak Channels}, journal = {IEEE Trans. on Signal Processing}, volume = {59}, number = {12}, year = {2011}, month = {12/2011}, pages = {6045-6057}, abstract = {
We address the problem of primary user detection\ in Cognitive Radio from a wideband signal comprising multiple\ primary channels, exploiting a priori knowledge about the\ primary network: channelization and spectral shape of primary\ transmissions. Using this second-order statistical information, a\ multichannel Gaussian model is formulated. In order to obtain\ a Generalized Likelihood Ratio Test, we first address Maximum\ Likelihood (ML) estimation of the power levels at the different\ channels, as well as of the noise variance. The ML conditions\ suggest a suboptimal closed-form estimate, which takes the form\ of a constrained Least Squares estimator whose asymptotic\ efficiency is shown for flat bandpass spectra in white noise, a\ case of practical importance. The resulting detectors exploit those\ frequency bins corresponding to guard bands and to primary\ channels perceived as weak to improve noise variance estimation.\ Analytical expressions for the probabilities of detection and false\ alarm are presented. Performance is evaluated via simulations\ in the setting of a terrestrial TV primary network with realistic\ channelization parameters.
}, keywords = {cognitive radio, dynacs, spectrum sensing}, doi = {10.1109/TSP.2011.2167615}, author = {Gonzalo V{\'a}zquez-Vilar and R. L{\'o}pez-Valcarce} } @conference {ISDA2011_1, title = {A study on the Application of Different Two-objective Evolutionary Algorithms to the Node Localization Problem in Wireless Sensor Networks}, booktitle = {IEEE International Conference on Intelligent Systems Design and Applications (ISDA)}, year = {2011}, author = {Massimo Vecchio and R. L{\'o}pez-Valcarce and Francesco Marcelloni} } @article {Vecchio2011, title = {A two-objective evolutionary approach based on topological constraints for node localization in wireless sensor networks}, journal = {Applied Soft Computing}, volume = {12}, year = {2011}, month = {07/2012}, pages = {1891-1901}, abstract = {

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.

}, keywords = {dynacs, Multiobjective evolutionary algorithms, Node localization, Range measurements, Stochastic optimization, wsn}, issn = {1568-4946}, doi = {10.1016/j.asoc.2011.03.012}, author = {Massimo Vecchio and R. L{\'o}pez-Valcarce and Francesco Marcelloni} } @article {Alvarez-Diaz-SigPro-10, title = {Blind l_1-Norm-Based Phase Estimation for Cross-QAM Robust to Finite Precision Effects}, journal = {Signal Processing}, volume = {90}, year = {2010}, note = {Accepted for publication}, month = {11/2010}, pages = {2934-2948}, keywords = {blind phase estimation, carrier offset, cross-QAM constellations, fixed point implementation}, author = {Marcos {\'A}lvarez-D{\'\i}az and R. L{\'o}pez-Valcarce and Iago G{\'o}mez-Alonso} } @article {KsibiCherif10, title = {Closed-form real single-tone frequency estimator based on a normalized IIR notch filter}, journal = {Signal Processing}, volume = {90}, number = {6}, year = {2010}, month = {June}, pages = {1905-1915}, keywords = {Frequency estimation, IIR notchfilter, Least squares, Real sinusoid, RPHD estimator}, author = {R. Elasmi-Ksibi and S. Cherif and R. L{\'o}pez-Valcarce and H. Besbes} } @conference {SalemValcarce10, title = {A finite interval constant modulus criterion for multicarrier channel shortening}, booktitle = {European Wireless}, year = {2010}, address = {Lucca, Italy}, author = {E. Ben Salem and R. L{\'o}pez-Valcarce and H. Besbes and S. Cherif} } @article {KsibiBesbesSP10, title = {Frequency estimation of real-valued single-tone in colored noise using multiple autocorrelation lags}, journal = {Signal Processing}, volume = {90}, number = {7}, year = {2010}, month = {July}, pages = {2303-2307}, keywords = {Autocorrelation, Frequency estimation, Single sinusoid}, author = {R. Elasmi-Ksibi and H. Besbes and R. L{\'o}pez-Valcarce and S. Cherif} } @article {MosqueraValcarceJayaweera2010, title = {Joint NDA Estimation of Carrier Frequency/Phase and SNR for Linearly Modulated Signals}, journal = {IEEE Signal Processing Letters}, volume = {17}, number = {5}, year = {2010}, month = {05/2010}, pages = {517-520}, keywords = {Carrier offset estimation, Cramer-Rao lower bound, expectation-maximization algorithm, SNR estimation}, author = {Wilfried Gappmair and R. L{\'o}pez-Valcarce and C. Mosquera} } @conference {RamirezValcarceICASSP10, title = {Multiantenna spectrum sensing: detection of spatial correlation among time-series with unknown spectra}, booktitle = {IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP)}, year = {2010}, address = {Dallas, TX}, keywords = {cognitive radio, coherence spectrum, generalized likelihood ratio test, Hadamard ratio, multiple-channel signal detection}, author = {David Ram{\'\i}rez and Javier V{\'\i}a and Ignacio Santamar{\'\i}a and R. L{\'o}pez-Valcarce and L. L. Scharf} } @conference {ValcarceVazquez10, title = {Multiantenna spectrum sensing for Cognitive Radio: overcoming noise uncertainty}, booktitle = {International Workshop on Cognitive Information Processing (CIP)}, year = {2010}, address = {Elba Island, Italy}, author = {R. L{\'o}pez-Valcarce and Gonzalo V{\'a}zquez-Vilar and Josep Sala} } @article {Alvarez-Diaz-TSP-10, title = {SNR Estimation for Multilevel Constellations Using Higher-Order Moments}, journal = {IEEE Transactions on Signal Processing}, volume = {58}, number = {3, Part 2}, year = {2010}, month = {March}, pages = {1515{\textendash}1526}, keywords = {Blind estimation, higher-order statistics, Moments-based estimation, SNR estimation}, author = {Marcos {\'A}lvarez-D{\'\i}az and R. L{\'o}pez-Valcarce and C. Mosquera} } @article {MosqueraValcarceJayaweera2009, title = {Stepsize Sequence Design for Distributed Average Consensus}, journal = {IEEE Signal Processing Letters}, volume = {17}, number = {2}, year = {2010}, month = {Feb}, pages = {169-172}, author = {C. Mosquera and R. L{\'o}pez-Valcarce and Sudhaman K. Jayaweera} } @conference {VazquezValcarceMosqueraPrelcic2010, title = {Wideband Spectral Estimation from Compressed Measurements Exploiting Spectral a priori Information in Cognitive Radio Systems}, booktitle = {IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP)}, year = {2010}, month = {March 14-19}, address = {Dallas, U.S.A.}, keywords = {cognitive radio, compressive sampling, Spectral estimation}, author = {Gonzalo V{\'a}zquez-Vilar and R. L{\'o}pez-Valcarce and C. Mosquera and Nuria Gonz{\'a}lez-Prelcic} } @article {ValcarceMosqueraTCOM08, title = {Cramer-Rao Lower Bound and EM Algorithm for Envelope-Based SNR Estimation of Nonconstant Modulus Constellations}, journal = {IEEE Transactions on Communications}, volume = {57}, number = {6}, year = {2009}, month = {june}, pages = {1622 - 1627}, author = {Wilfried Gappmair and R. L{\'o}pez-Valcarce and C. Mosquera} } @conference {ValcarceVazquezAlvarez2009, title = {Multiantenna detection of multicarrier primary signals exploiting spectral a priori information}, booktitle = {International Conference on Cognitive Radio Oriented Wireless Networks and Communications (Crowncom)}, year = {2009}, month = {June 22-24}, address = {Hannover, Germany}, author = {R. L{\'o}pez-Valcarce and Gonzalo V{\'a}zquez-Vilar and Marcos {\'A}lvarez-D{\'\i}az} } @conference {ValcarceVazquez2009, title = {Wideband Spectrum Sensing in Cognitive Radio: Joint Estimation of Noise Variance and Multiple Signal Levels}, booktitle = {IEEE Workshop on Signal Processing Advances in Wireless Communications (SPAWC)}, year = {2009}, month = {June 21-24}, address = {Perugia, Italy}, author = {R. L{\'o}pez-Valcarce and Gonzalo V{\'a}zquez-Vilar} } @conference {Mosquera08c, title = {Distributed Estimation with Noisy Exchanges}, booktitle = {IEEE International Workshop on Signal Processing Advances in Wireless Communications}, year = {2008}, address = {Recife, Brazil}, keywords = {distributed estimation, sensor network}, author = {C. Mosquera and R. L{\'o}pez-Valcarce and Sudhaman K. Jayaweera} } @conference {ElasmiEUSIPCO08, title = {A family of frequency estimators using higher-order sample covariance lags for real sinusoid detection}, booktitle = {European Signal Processing Conference (EUSIPCO)}, year = {2008}, month = {August}, address = {Lausanne, Switzerland}, keywords = {Frequency estimator, Sinusoid detection}, author = {R. Elasmi-Ksibi and R. L{\'o}pez-Valcarce and H. Besbes and S. Cherif and M. Jaidane} } @conference {SalemEUSIPCO08, title = {Lattice implementation of Sum-squared Auto-correlation Minimization (SAM) channel shortener}, booktitle = {European Signal Processing Conference (EUSIPCO)}, year = {2008}, month = {August}, address = {Lausanne, Switzerland}, keywords = {Blind Adaptation, Lattice, SAM}, author = {E. Ben Salem and R. L{\'o}pez-Valcarce and S. Cherif and H. Besbes} } @conference {ValcarceMosquera08a, title = {Maximum Likelihood SNR Estimation for Asynchronously Oversampled OFDM Signals}, booktitle = {IEEE International Workshop on Signal Processing Advances in Wireless Communications}, year = {2008}, address = {Recife, Brazil}, keywords = {estimation, ML, OFDM, SNR}, author = {R. L{\'o}pez-Valcarce and C. Mosquera} } @conference {GappmairCNSDSP08, title = {ML and EM Algorithm for non-data-aided SNR Estimation of Linearly Modulated Signals}, booktitle = {International Symposium on Communication Systems, Networks and Signal Processing (CNSDSP)}, year = {2008}, pages = {530-534}, keywords = {EM, ML, SNR estimation}, author = {Wilfried Gappmair and R. L{\'o}pez-Valcarce and C. Mosquera} } @article {MosqueraTSP07, title = {Non-Data-Aided Symbol Rate Estimation of Linearly Modulated Signals}, journal = {IEEE Transactions on Signal Processing}, year = {2008}, month = {February}, author = {C. Mosquera and Sandro Scalise and R. L{\'o}pez-Valcarce} } @conference {ASMS08, title = {SNR Estimation with Heterogeneous Frames}, booktitle = {Advanced Satellite Mobile Systems Conference}, year = {2008}, month = {August 26-28}, address = {Bologna, Italy}, author = {Marcos {\'A}lvarez-D{\'\i}az and R. L{\'o}pez-Valcarce and C. Mosquera} } @book {Artes07book, title = {Comunicaciones Digitales}, year = {2007}, month = {May}, publisher = {Pearson - Prentice Hall}, organization = {Pearson - Prentice Hall}, author = {Antonio Art{\'e}s-Rodr{\'\i}guez and Fernando P{\'e}rez-Gonz{\'a}lez and Jes{\'u}s Cid-Sueiro and R. L{\'o}pez-Valcarce and C. Mosquera and Fernando P{\'e}rez-Cruz} } @inbook {Chap8_Book_Corazza07, title = {Digital Satellite Communications}, year = {2007}, month = {April}, pages = {-}, publisher = {Springer}, organization = {Springer}, chapter = {Distortion Countermeasures}, address = {New York}, author = {A. A. Rontogiannis and Marcos {\'A}lvarez-D{\'\i}az and M. Casadei and V. Dalakas and A. Duverdier and F. J. Gonz{\'a}lez-Serrano and M. Iubatti and T. Javornik and L. Lapierre and Neri, Massimo and P. Salmi} } @inbook {Chap4_Book_Corazza07, title = {Digital Satellite Communications}, year = {2007}, month = {April}, pages = {-}, publisher = {Springer}, organization = {Springer}, chapter = {Satellite Channel Impairments}, address = {New York}, author = {Sandro Scalise and L. Castanet and M. Luglio and Neri, Massimo and Marcos {\'A}lvarez-D{\'\i}az and J. Bito and M. Bousquet and I. Frigyes and P. Horvath and Axel Jahn and M. Krejcarek and J. Lemorton and S. Morosi and M. A. V{\'a}zquez-Castro} } @conference {ValcarceSPAWC07, title = {Iterative Envelope-Based SNR Estimation for Non-Constant Modulus Constellations}, booktitle = {IEEE Workshop on Signal Processing Advances in Wireless Communications (SPAWC)}, year = {2007}, keywords = {EM, SNR, synchronization}, author = {R. L{\'o}pez-Valcarce and C. Mosquera and Wilfried Gappmair} } @conference {IWSSC07, title = {Non-Linear Interference Mitigation for Broadband Multimedia Satellite Systems}, booktitle = {International Workshop on Satellite and Space Communications (IWSSC)}, year = {2007}, month = {September 13-14}, address = {Salzburg, Austria}, author = {Marcos {\'A}lvarez-D{\'\i}az and Nicolas Courville and C. Mosquera and Gianluigi Liva and Giovanni Emanuele Corazza} } @conference {mmsec07-spedpoint, title = {A Secure Multidimensional Point Inclusion Protocol}, booktitle = {ACM Workshop on Multimedia and Security (MMSEC)}, year = {2007}, month = {September}, pages = {109{\textendash}120}, address = {Dallas, Texas, USA}, keywords = {multiparty computation, privacy, security, watermarking}, author = {Juan Ram{\'o}n Troncoso-Pastoriza and Stefan Katzenbeisser and Mehmet Celik and Aweke Lemma} } @article {ValcarceCL07, title = {Sixth-Order Statistics-Based Non-Data-Aided SNR Estimation}, journal = {IEEE Communications Letters}, volume = {11}, number = {4}, year = {2007}, month = {April}, pages = {351-353}, author = {R. L{\'o}pez-Valcarce and C. Mosquera} } @conference {uvigo:gainestimation, title = {Analysis of non-data-aided magnitude gain estimators}, booktitle = {International Symposium on Image/Video Communications (ISIVC)}, year = {2006}, address = {Hammamet, Tunisia}, keywords = {Digital Communications, gain estimation, synchronization}, author = {R. L{\'o}pez-Valcarce} } @conference {uvigo:gaussphase, title = {Blind carrier phase estimation for non-equiprobable constellations}, booktitle = {IEEE Workshop on Signal Processing Advances in Wireless Communications (SPAWC)}, year = {2006}, address = {Cannes, France}, keywords = {Digital Communications, phase estimation, signal shaping, synchronization, Tomlinson-Harashima precoding}, author = {R. L{\'o}pez-Valcarce and C. Mosquera} } @conference {spie05:dftrdm, title = {High-rate quantization data hiding robust to arbitrary linear filtering attacks}, booktitle = {Security, Steganography, and Watermarking of Multimedia Contents}, series = {Proc. of SPIE}, volume = {5306}, year = {2006}, month = {January}, pages = {592-601}, publisher = {SPIE}, organization = {SPIE}, address = {San Jose, California, USA}, keywords = {data-hiding, watermarking}, author = {Fernando P{\'e}rez-Gonz{\'a}lez and C. Mosquera and Marcos {\'A}lvarez-D{\'\i}az and Reginald Lagendijk}, editor = {Edward J. Delp and Ping W. Wong} } @article {uvigo:sosblind, title = {Second-order blind algorithms for adaptive recursive linear equalizers: Analysis and lattice implementation}, journal = {International Journal of Adaptive Control and Signal Processing}, volume = {20}, number = {6}, year = {2006}, month = {August}, pages = {265{\textendash}289}, keywords = {adaptive IIR filters, blind equalization, Digital Communications, lattice filters}, author = {R. L{\'o}pez-Valcarce} } @conference {Mosquera06, title = {Symbol-Rate Estimation for DVB-S2 Broadcasting}, booktitle = {International Workshop on Signal Processing for Space Communications (SPSC)}, year = {2006}, keywords = {DVB, symbol rate, synchronization}, author = {C. Mosquera and Sandro Scalise and R. L{\'o}pez-Valcarce} } @conference {uvigo:nlpoly, title = {Toward a theory of multirate nonlinear systems}, booktitle = {IEEE Workshop on Signal Processing Advances in Wireless Communications (SPAWC)}, year = {2006}, address = {Cannes, France}, keywords = {multirate systems, nonlinear filters, polyphase filters}, author = {R. L{\'o}pez-Valcarce and Soura Dasgupta} } @conference {uvigo:firstorder, title = {Analysis of a first-order adaptive recursive predictor}, booktitle = {IEEE Conference on Decision and Control / European Control Conference (CDC/ECC)}, year = {2005}, address = {Seville, Spain}, keywords = {adaptive signal processing, equalization, second-order statistics}, doi = {10.1109/CDC.2005.1582919}, author = {R. L{\'o}pez-Valcarce} } @conference {uvigo:diamond, title = {Diamond contour-based phase recovery for (cross-)QAM constellations}, booktitle = {IEEE Workshop on Statistical Signal Processing (SSP)}, year = {2005}, address = {Bordeaux, France}, keywords = {adaptive signal processing, synchronization}, doi = {10.1109/SSP.2005.1628678}, author = {Marcos {\'A}lvarez-D{\'\i}az and R. L{\'o}pez-Valcarce} } @article {uvigo:shorteners, title = {Realizable minimum mean-squared error channel shorteners}, journal = {IEEE Transactions on Signal Processing}, volume = {53}, number = {11}, year = {2005}, month = {November}, pages = {4354{\textendash}4362}, keywords = {adaptive signal processing, Channel shortening}, doi = {10.1109/TSP.2005.857050}, author = {R. L{\'o}pez-Valcarce} } @conference {uvigo:bias, title = {Bias analysis and removal of a microphone array based road traffic speed estimator}, booktitle = {European Signal Processing Conference (EUSIPCO)}, year = {2004}, address = {Vienna, Austria}, keywords = {microphone arrays, speed estimation, traffic monitoring}, author = {R. L{\'o}pez-Valcarce and D. Hurtado and C. Mosquera and Fernando P{\'e}rez-Gonz{\'a}lez} } @article {uvigo:laguerre, title = {Blind input, initial state, and system identification of SIMO Laguerre systems}, journal = {IEEE Transactions on Signal Processing}, volume = {52}, number = {12}, year = {2004}, month = {December}, pages = {3357{\textendash}3369}, keywords = {blind identification, blind input estimation, Laguerre systems, system identification}, doi = {10.1109/TSP.2004.837438}, author = {Jacob H. Gunther and R. L{\'o}pez-Valcarce} } @conference {uvigo:broadband, title = {Broadband analysis of a microphone array based road traffic speed estimator}, booktitle = {IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM)}, year = {2004}, address = {Sitges, Barcelona, Spain}, keywords = {microphone arrays, speed estimation, traffic monitoring}, doi = {10.1109/SAM.2004.1503005}, author = {R. L{\'o}pez-Valcarce} } @article {uvigo:fourthpower, title = {Cost minimisation interpretation of fourth power phase estimator and links to multimodulus algorithm}, journal = {IEE Electronics Letters}, volume = {40}, number = {4}, year = {2004}, month = {19 February}, pages = {278{\textendash}279}, keywords = {constant modulus, Digital Communications, equalization, multimodulus, phase estimation}, author = {R. L{\'o}pez-Valcarce} } @article {uvigo:speedestjnl, title = {Estimation of road vehicle speed using two omnidirectional microphones: a maximum likelihood approach}, journal = {EURASIP Journal of Applied Signal Processing}, volume = {2004}, number = {8}, year = {2004}, month = {August}, pages = {1059{\textendash}1077}, keywords = {microphone arrays, speed estimation, traffic monitoring}, author = {R. L{\'o}pez-Valcarce and C. Mosquera and Fernando P{\'e}rez-Gonz{\'a}lez} } @article {uvigo:teq, title = {Minimum delay spread TEQ design in multicarrier systems}, journal = {IEEE Signal Processing Letters}, volume = {11}, number = {8}, year = {2004}, month = {August}, pages = {682{\textendash}685}, keywords = {channel shortener, cyclic prefix, delay spread, Digital Communications, multicarrier communications, time domain equalizer}, doi = {10.1109/LSP.2004.831676}, author = {R. L{\'o}pez-Valcarce} } @article {uvigo:realizable, title = {Realizable linear and decision feedback equalizers: properties and connections}, journal = {IEEE Transactions on Signal Processing}, volume = {52}, number = {3}, year = {2004}, note = {Recipient of a 2005 Best Paper Award of the IEEE Signal Processing Society}, month = {March}, pages = {757{\textendash}773}, keywords = {adaptive signal processing, channel equalization}, doi = {10.1109/TSP.2003.822360}, author = {R. L{\'o}pez-Valcarce} } @article {uvigo:multipliers, title = {An algorithm for unit-norm equation-error system identification based on the method of multipliers}, journal = {IEEE Transactions on Signal Processing}, volume = {51}, number = {12}, year = {2003}, month = {December}, pages = {3080{\textendash}3085}, keywords = {adaptive IIR filters, equation error, system identification, unit-norm}, author = {R. L{\'o}pez-Valcarce} } @conference {uvigo:applicability, title = {On the applicability to correlated sources of a blind channel equalization method robust to order overestimation}, booktitle = {IFAC Symposium on System Identification}, year = {2003}, address = {Rotterdam, the Netherlands}, keywords = {correlated sources, Digital Communications, equalization, order overestimation, second-order statistics}, author = {R. L{\'o}pez-Valcarce} } @conference {uvigo:iterative, title = {Blind iterative decision feedback equalizers for block QAM transmission systems}, booktitle = {Baiona Workshop on Signal Processing in Communications}, year = {2003}, pages = {57{\textendash}62}, address = {Baiona, Pontevedra, Spain}, keywords = {blind equalization, decision feedback equalization, iterative equalization}, author = {R. L{\'o}pez-Valcarce} } @article {uvigo:nlpsk, title = {Second order statistical properties of nonlinearly distorted PSK signals}, journal = {IEEE Communications Letters}, volume = {7}, number = {7}, year = {2003}, month = {July}, pages = {323{\textendash}325}, keywords = {Digital Communications, equalization, nonlinear channels, PSK modulation, second-order statistics}, author = {R. L{\'o}pez-Valcarce and Soura Dasgupta} } @article {uvigo:subband, title = {Subband hyperstable adaptive IIR filters}, journal = {IEEE Transactions on Circuits and Systems II: Analog and Digital Signal Processing}, volume = {50}, number = {7}, year = {2003}, month = {July}, pages = {383{\textendash}389}, keywords = {adaptive IIR filters, subband adaptive filters, system identification}, author = {R. L{\'o}pez-Valcarce and Fernando P{\'e}rez-Gonz{\'a}lez} } @conference {uvigo:prewhitened, title = {Analysis of the prewhitened constant modulus cost function}, booktitle = {IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP)}, volume = {3}, year = {2002}, pages = {2641-2644}, address = {Orlando, FL, USA}, keywords = {constant modulus, Digital Communications, equalization}, author = {R. L{\'o}pez-Valcarce and Fernando P{\'e}rez-Gonz{\'a}lez} } @conference {uvigo:eigenvector, title = {Automatic delay selection in blind channel equalization: a prewhitening + eigenvector approach}, booktitle = {Asilomar Conference on Signals, Systems and Computers}, year = {2002}, address = {Pacific Grove, CA, USA}, keywords = {Digital Communications, equalization, higher-order statistics}, author = {R. L{\'o}pez-Valcarce and Fernando P{\'e}rez-Gonz{\'a}lez} } @conference {uvigo:staggered, title = {Channel equalization with staggered modulation formats}, booktitle = {IEEE International Conference on Digital Signal Processing (DSP)}, year = {2002}, pages = {769{\textendash}772}, address = {Santorini, Greece}, keywords = {Digital Communications, equalization, staggered modulation}, author = {R. L{\'o}pez-Valcarce} } @conference {uvigo:speedest, title = {Road vehicle speed estimation from a two-microphone array}, booktitle = {IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP)}, volume = {2}, year = {2002}, pages = {1321{\textendash}1324}, address = {Orlando, FL, USA}, keywords = {microphone arrays, speed estimation, traffic monitoring}, author = {Fernando P{\'e}rez-Gonz{\'a}lez and R. L{\'o}pez-Valcarce and C. Mosquera} } @mastersthesis {801, title = {Adaptive algorithms for identification and equalization using recursive filters}, volume = {Ph.D.}, year = {2001}, month = {11/2001}, school = {University of Vigo}, type = {Ph.D. thesis}, address = {Vigo, Spain}, keywords = {adaptive signal processing}, author = {R. L{\'o}pez-Valcarce} } @article {uvigo:revisited, title = {Adaptive lattice IIR filtering revisited: convergence issues and new algorithms with improved stability properties}, journal = {IEEE Transactions on Signal Processing}, volume = {49}, number = {4}, year = {2001}, month = {April}, pages = {811{\textendash}821}, keywords = {adaptive IIR filters, lattice filters, system identification}, author = {R. L{\'o}pez-Valcarce and Fernando P{\'e}rez-Gonz{\'a}lez} } @article {uvigo:coloredjnl, title = {Blind channel equalization with colored sources based on second-order statistics: a linear prediction approach}, journal = {IEEE Transactions on Signal Processing}, volume = {49}, number = {9}, year = {2001}, month = {September}, pages = {2050{\textendash}2059}, keywords = {correlated sources, Digital Communications, equalization, second-order statistics}, author = {R. L{\'o}pez-Valcarce and Soura Dasgupta} } @conference {uvigo:precoding, title = {Blind equalization of nonlinear channels from second order statistics using precoding and channel diversity}, booktitle = {IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP)}, volume = {4}, year = {2001}, pages = {2073{\textendash}2076}, address = {Salt Lake City, UT, USA}, keywords = {Digital Communications, equalization, nonlinear channels}, author = {R. L{\'o}pez-Valcarce and Xuejie Song and Soura Dasgupta} } @article {uvigo:nonlinear01, title = {Blind Equalization of Nonlinear Channels from Second-Order Statistics}, journal = {IEEE Transactions on Signal Processing}, volume = {49}, number = {12}, year = {2001}, month = {December}, pages = {3084{\textendash}3097}, keywords = {Digital Communications, equalization, nonlinear channels, second-order statistics}, author = {R. L{\'o}pez-Valcarce and Soura Dasgupta} } @conference {uvigo:psk, title = {Blind equalization of nonlinear digital satellite links with PSK modulation}, booktitle = {IEEE International Symposium on Circuits and Systems (ISCAS)}, volume = {2}, year = {2001}, pages = {409{\textendash}412}, address = {Sydney, Australia}, keywords = {Digital Communications, equalization, nonlinear channels, second-order statistics}, author = {R. L{\'o}pez-Valcarce and Soura Dasgupta} } @conference {uvigo:deficient, title = {On blind equalization of rank deficient nonlinear channels}, booktitle = {IEEE Workshop on Statistical Signal Processing (SSP)}, year = {2001}, pages = {269{\textendash}272}, address = {Singapore}, keywords = {Digital Communications, equalization, nonlinear channels}, author = {R. L{\'o}pez-Valcarce and Soura Dasgupta} } @article {uvigo:reinit01, title = {Efficient Reinitialization of the Prewhitened Constant Modulus Algorithm}, journal = {IEEE Communications Letters}, volume = {5}, number = {12}, year = {2001}, month = {December}, pages = {488{\textendash}490}, keywords = {constant modulus, Digital Communications, equalization}, author = {R. L{\'o}pez-Valcarce and Fernando P{\'e}rez-Gonz{\'a}lez} } @article {uvigo:cancellation, title = {Equalization and interference cancellation in linear multiuser systems based on second-order statistics}, journal = {IEEE Transactions on Signal Processing}, volume = {49}, number = {9}, year = {2001}, month = {September}, pages = {2042{\textendash}2049}, keywords = {Digital Communications, equalization, second-order statistics}, author = {R. L{\'o}pez-Valcarce and Zhi Ding and Soura Dasgupta} } @conference {uvigo:coloredcnf, title = {Second order statistics based blind channel equalization with correlated sources}, booktitle = {IEEE International Symposium on Circuits and Systems (ISCAS)}, volume = {4}, year = {2001}, pages = {366{\textendash}369}, address = {Sydney, Australia}, keywords = {correlated sources, Digital Communications, equalization, second-order statistics}, author = {R. L{\'o}pez-Valcarce and Soura Dasgupta} } @article {uvigo:someproperties, title = {Some properties of the matrix exponential}, journal = {IEEE Transactions on Circuits and Systems II: Analog and Digital Signal Processing}, volume = {48}, number = {2}, year = {2001}, month = {February}, pages = {213{\textendash}215}, keywords = {exponential matrix, linear algebra}, author = {R. L{\'o}pez-Valcarce and Soura Dasgupta} } @conference {icc00, title = {Analytical Bounds on the Error Performance of the DVB-T System in Time-Invariant Channels}, booktitle = {IEEE International Conference on Communications (ICC)}, year = {2000}, month = {June}, address = {New Orleans, LA, USA}, keywords = {Digital Communications, Digital Television, Rayleigh, Rice, Terrestrial}, author = {Jos{\'e} M. Lago and Fernando P{\'e}rez-Gonz{\'a}lez} } @conference {uvigo:blindadaptive, title = {On blind adaptive algorithms for IIR equalizers}, booktitle = {IEEE Digital Signal Processing Workshop (DSP)}, year = {2000}, address = {Hunt, TX, USA}, keywords = {adaptive IIR filters, Digital Communications, equalization, second-order statistics}, author = {R. L{\'o}pez-Valcarce and Fernando P{\'e}rez-Gonz{\'a}lez} } @conference {uvigo:identifiability, title = {Blind channel identifiability/equalizability of single input multiple output nonlinear channels from second order statistics}, booktitle = {IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP)}, volume = {5}, year = {2000}, pages = {2769{\textendash}2772}, address = {Istanbul, Turkey}, keywords = {Digital Communications, equalization, nonlinear channels, second-order statistics}, author = {R. L{\'o}pez-Valcarce and Soura Dasgupta} } @mastersthesis {802, title = {Blind equalization of linear and nonlinear digital communication channels from second-order statistics}, volume = {Ph.D.}, year = {2000}, month = {12/2000}, school = {University of Iowa}, type = {Ph.D. thesis}, address = {Iowa City, USA}, keywords = {adaptive signal processing, channel equalization}, author = {R. L{\'o}pez-Valcarce} } @article {uvigo:eas, title = {Exponential asymptotic stability of time-varying inverse prediction error filters}, journal = {IEEE Transactions on Signal Processing}, volume = {48}, number = {7}, year = {2000}, month = {July}, pages = {1928{\textendash}1936}, keywords = {nonstationary processes, prediction error filters, stability}, author = {R. L{\'o}pez-Valcarce and Soura Dasgupta and Roberto Tempo and Minyue Fu} } @conference {uvigo:interference, title = {Interference cancellation and blind equalization for linear multi-user systems}, booktitle = {IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP)}, volume = {1}, year = {2000}, pages = {145{\textendash}148}, address = {Istanbul, Turkey}, keywords = {Digital Communications, equalization, second-order statistics}, author = {Zhi Ding and Soura Dasgupta and R. L{\'o}pez-Valcarce} } @conference {uvigo:misconvergence, title = {Misconvergence and stabilization of adaptive IIR lattice filters}, booktitle = {IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP)}, volume = {1}, year = {2000}, pages = {65{\textendash}68}, address = {Istanbul, Turkey}, keywords = {adaptive IIR filters, lattice filters, system identification}, author = {Fernando P{\'e}rez-Gonz{\'a}lez and R. L{\'o}pez-Valcarce} } @conference {uvigo:role, title = {The role of second-order statistics in blind equalization of nonlinear channels}, booktitle = {IEEE Workshop on Statistical Signal Processing (SSP)}, year = {2000}, pages = {211{\textendash}215}, address = {Pocono Manor, PA, USA}, keywords = {Digital Communications, equalization, nonlinear channels, second-order statistics}, author = {R. L{\'o}pez-Valcarce and Soura Dasgupta} } @conference {bayona99, title = {BER Performance of the DVB-T System in Time-Invariant Channels}, booktitle = {Baiona Workshop on Emerging Technologies in Communications}, year = {1999}, month = {September}, pages = {230-235}, address = {Baiona-Vigo, Spain}, keywords = {Digital Communications, Digital Television, Rayleigh, Rice, Terrestrial}, author = {Jos{\'e} M. Lago and Fernando P{\'e}rez-Gonz{\'a}lez} } @article {uvigo:polyjnl, title = {Hyperstable adaptive IIR algorithms with polyphase structures: analysis and design}, journal = {IEEE Transactions on Signal Processing}, volume = {47}, number = {7}, year = {1999}, month = {July}, pages = {2043{\textendash}2046}, keywords = {adaptive IIR filters, system identification}, author = {R. L{\'o}pez-Valcarce and C. Mosquera and Fernando P{\'e}rez-Gonz{\'a}lez} } @conference {uvigo:polycnf, title = {Hyperstable polyphase adaptive IIR filters}, booktitle = {IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP)}, volume = {4}, year = {1999}, pages = {1841{\textendash}1844}, address = {Phoenix, AZ, USA}, keywords = {adaptive IIR filters, system identification}, author = {C. Mosquera and Fernando P{\'e}rez-Gonz{\'a}lez and R. L{\'o}pez-Valcarce} } @article {uvigo:newproof, title = {A new proof for the stability of equation-error models}, journal = {IEEE Signal Processing Letters}, volume = {6}, number = {6}, year = {1999}, month = {June}, pages = {148{\textendash}150}, keywords = {adaptive IIR filters, system identification}, author = {R. L{\'o}pez-Valcarce and Soura Dasgupta} } @article {Mosquera99, title = {The robust SPR problem: design algorithms and new applications}, journal = {Signal Processing}, volume = {76}, year = {1999}, pages = {269-283}, keywords = {robust, SPR}, author = {C. Mosquera and L. Leyra and Fernando P{\'e}rez-Gonz{\'a}lez} } @article {uvigo:remarks, title = {Some remarks on the lattice form of the Steiglitz-McBride iteration}, journal = {IEEE Signal Processing Letters}, volume = {6}, number = {11}, year = {1999}, month = {November}, pages = {290{\textendash}292}, keywords = {adaptive IIR filters, lattice filters, system identification}, author = {R. L{\'o}pez-Valcarce and Fernando P{\'e}rez-Gonz{\'a}lez} } @conference {uvigo:rwls, title = {On the stability of the inverse time-varying prediction error filter obtained with the RWLS algorithm}, booktitle = {IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP)}, volume = {3}, year = {1999}, pages = {1673{\textendash}1676}, address = {Phoenix, AZ, USA}, keywords = {nonstationary processes, prediction error filters, stability}, author = {R. L{\'o}pez-Valcarce and Soura Dasgupta} } @inbook {700, title = {Stable estimates in equation-error identification: an open problem}, booktitle = {Open Problems in Mathematical Systems and Control Theory}, year = {1999}, publisher = {Springer-Verlag}, organization = {Springer-Verlag}, chapter = {28}, isbn = { 1-85233-044-9}, url = {http://perso.uclouvain.be/vincent.blondel/books/openprobs/}, author = {R. L{\'o}pez-Valcarce and S. Dasgupta} } @article {uvigo:autoregressive, title = {An adaptive recursive filter for autoregressive inputs}, journal = {International Journal of Adaptive Control and Signal Processing}, volume = {12}, year = {1998}, month = {September}, pages = {467{\textendash}494}, keywords = {adaptive IIR filters, lattice filters, system identification}, author = {R. L{\'o}pez-Valcarce and Fernando P{\'e}rez-Gonz{\'a}lez} } @article {uvigo:notebias, title = {On the bias of the modified output error algorithm}, journal = {IEEE Transactions on Automatic Control}, volume = {43}, number = {9}, year = {1998}, month = {September}, pages = {1261{\textendash}1262}, keywords = {adaptive IIR filters, system identification}, author = {C. Mosquera and R. L{\'o}pez-Valcarce and Fernando P{\'e}rez-Gonz{\'a}lez} } @conference {uvigo:conditions, title = {Stability conditions for the time-varying linear predictor}, booktitle = {IEEE Conference on Decision and Control (CDC)}, year = {1998}, month = {December}, pages = {1840{\textendash}1845}, address = {Tampa, FL, USA}, keywords = {nonstationary processes, prediction error filters, stability}, author = {R. L{\'o}pez-Valcarce and Soura Dasgupta and Minyue Fu and Roberto Tempo} } @article {uvigo:allpole, title = {On the stability of equation-error estimates of all-pole systems}, journal = {IEEE Signal Processing Letters}, volume = {5}, number = {10}, year = {1998}, month = {October}, pages = {268{\textendash}270}, keywords = {adaptive IIR filters, system identification}, author = {R. L{\'o}pez-Valcarce and Soura Dasgupta} } @article {uvigo:newresults, title = {New results and theoretical analysis of the Master-Slave family of recursive identification algorithms}, journal = {Signal Processing}, volume = {58}, number = {1}, year = {1997}, month = {April}, pages = {79-94}, keywords = {adaptive IIR filters, lattice filters, system identification}, author = {R. L{\'o}pez-Valcarce and Fernando P{\'e}rez-Gonz{\'a}lez} } @conference {uvigo:stable, title = {Stable estimates in equation error identification}, booktitle = {IEEE Conference on Decision and Control (CDC)}, volume = {2}, year = {1997}, month = {December}, pages = {1678{\textendash}1679}, address = {San Diego, CA, USA}, keywords = {adaptive IIR filters, system identification}, author = {R. L{\'o}pez-Valcarce and Soura Dasgupta} } @conference {uvigo:masterslave, title = {The Master-Slave family of system identification algorithms: theoretical results and new structures}, booktitle = {IFAC World Congress}, volume = {J}, year = {1996}, month = {June}, pages = {185{\textendash}190}, publisher = {IFAC}, organization = {IFAC}, address = {San Francisco, CA, USA}, keywords = {adaptive IIR filters, lattice filters, system identification}, author = {R. L{\'o}pez-Valcarce and Fernando P{\'e}rez-Gonz{\'a}lez} }