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.

%B IEEE Int. Conf. Acoustics, Speech and Signal Processing (ICASSP) %I IEEE %C Brighton, UK %P 4794-4798 %8 04/2019 %G eng %R 10.1109/ICASSP.2019.8683831 %0 Conference Paper %B 36th International Communications Satellite Systems Conference (ICSSC) %D 2018 %T Adjacent Beams Resource Sharing to Serve Hot Spots : A Rate Splitting Approach %A Tomás Ramírez %A Carlos Mosquera %A Màrius Caus %A Adriano Pastore %A Nader Alagha %A Nele Noels %XThis work addresses the uneven traffic demand scenario in multi-beam satellite systems, in which a hot-spot beam

is surrounded by cold beams. After partitioning the hotspot beam in different sectors, resource pulling from cold

neighbouring beams is allowed following an aggressive frequency-reuse scheme. As a consequence, the level of

the co-channel interference within the hot-spot beam increases. A scheme known as Non-Coherent Rate-Splitting (NCRS)

is employed to cope with this interference, based on the exclusive use of magnitude channel state information at the transmitter (CSIT).

The receiver complexity is increased with respect to full CSIT precoding schemes, which are considered for benchmarking purposes. Different NCRS strategies are analyzed and compared with several partial and full CSIT schemes. The proposed solution not only shows an improvement with respect to partial CSIT benchmarks, but also displays a competitive performance against full CSIT precoders.

%B 36th International Communications Satellite Systems Conference (ICSSC)
%C Niagara Falls, Canada
%8 10/2018
%G eng
%0 Journal Article
%J IEEE Transactions on Wireless Communication
%D 2018
%T Distributed Precoding Systems in Multi-Gateway Multibeam Satellites: Regularization and Coarse Beamforming
%A Carlos Mosquera
%A R. López-Valcarce
%A Tomás Ramírez
%A Vahid Joroughi
%B IEEE Transactions on Wireless Communication
%G eng
%0 Conference Paper
%B 15th International Symposium on Wireless Communication Systems (ISWCS)
%D 2018
%T Exploratory Analysis of Superposition Coding and Rate Splitting for Multibeam Satellite Systems
%A Màrius Caus
%A Adriano Pastore
%A Mònica Navarro
%A Tomás Ramírez
%A Carlos Mosquera
%A Nele Noels
%A Nader Alagha
%A Ana I. Perez-Neira
%B 15th International Symposium on Wireless Communication Systems (ISWCS)
%C Lisbon, Portugal
%G eng
%0 Conference Paper
%B IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP)
%D 2018
%T Locally optimal invariant detector for testing equality of two power spectral densities
%A David Ramírez
%A Daniel Romero
%A Javier Vía
%A R. López-Valcarce
%A Ignacio Santamaría
%K cognitive radio
%K winter
%X This work addresses the problem of determining whether two multivariate random time series have the same power spectral density

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

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

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

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

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

previously proposed approaches, as computer simulations show.

%B IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP)
%C Calgary, Canada
%G eng
%0 Conference Paper
%B 9th Advanced Satellite Multimedia Systems Conference (ASMS) and 15th Signal Processing for Space Communications Workshop (SPSC)
%D 2018
%T Message-Splitting for Interference Cancellation in Multibeam Satellite Systems
%A Tomás Ramírez
%A Carlos Mosquera
%A Màrius Caus
%A Adriano Pastore
%A Mònica Navarro
%A Nele Noels
%B 9th Advanced Satellite Multimedia Systems Conference (ASMS) and 15th Signal Processing for Space Communications Workshop (SPSC)
%C Berlin, Germany
%G eng
%0 Conference Paper
%B 6th IEEE Global Conference on Signal and Information Processing
%D 2018
%T Symbol-Asynchronous Transmission In Multibeam Satellite User Down-Link: Rate Regions For Novel Superposition Coding Schemes
%A Nele Noels
%A Marc Moeneclaey
%A Tomás Ramírez
%A Carlos Mosquera
%A Màrius Caus
%A Adriano Pastore
%X We consider the forward link of a multibeam satellite system with high spectral reuse and the novel low-complexity transmission and detection strategies from ["“Exploratory analysis of superposition coding and rate splitting for multibeam satellite systems", ISWCS 2018]. More specifically, we study the impact of a time offset between the antenna beams that cooperate to simultaneously serve a given user. Assuming Gaussian signaling, we provide closed-form expressions for the achievable rate region. It is demonstrated that, in the absence of timing information at the gateway, this region is not affected by a time offset. Our numerical results further show that, in case timing is known at the gateway, an offset of half a symbol period at both user terminals is optimal in terms of spectral efficiency.

%B 6th IEEE Global Conference on Signal and Information Processing %G eng %0 Journal Article %J IEEE Trans. Signal Processing %D 2018 %T Testing equality of multiple power spectral density matrices %A David Ramírez %A Daniel Romero %A Javier Vía %A R. López-Valcarce %A Ignacio Santamaría %K winter %B IEEE Trans. Signal Processing %V 66 %P 6268-6280 %8 12/2018 %G eng %N 23 %R 10.1109/TSP.2018.2875884 %0 Conference Paper %B 22nd International Workshop on Smart Antennas (WSA) %D 2018 %T Two-Level Precoding for High Throughput Satellites with non-Cooperative Gateways %A Tomás Ramírez %A Carlos Mosquera %A Roberto López-Valcarce %B 22nd International Workshop on Smart Antennas (WSA) %G eng %0 Conference Paper %B European Signal Processing Conference (EUSIPCO) %D 2017 %T Defending Surveillance Sensor Networks Against Data-Injection Attacks via Trusted Nodes %A R. López-Valcarce %A Daniel Romero %K winter %K wsn %XBy injecting false data through compromised sensors, an adversary can drive the probability of detection in a sensor network-based spatial field surveillance system to arbitrarily low values. As a countermeasure, a small subset of sensors may be secured. Leveraging the theory of Matched Subspace Detection, we propose and evaluate several detectors that add robustness to attacks when such trusted nodes are available. Our results reveal the performance-security tradeoff of these schemes and can be used to determine the number of trusted nodes required for a given performance target.

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

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

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

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

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

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

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

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

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

%B IEEE Transactions on Signal Processing
%V 65
%P 2547-2560
%8 05/2017
%G eng
%N 10
%R 10.1109/TSP.2017.2666775
%0 Journal Article
%J Signal Processing
%D 2017
%T Wideband full-duplex MIMO relays with blind adaptive self-interference cancellation
%A Emilio Antonio-Rodríguez
%A Stefan Werner
%A R. López-Valcarce
%A Taneli Riihonen
%A Risto Wichman
%K adaptive signal processing
%K compass
%K full duplex
%K winter
%X 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.

%B Signal Processing
%V 130
%P 74-85
%8 01/2017
%G eng
%& 74
%R 10.1016/j.sigpro.2016.06.010
%0 Conference Paper
%B IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP)
%D 2016
%T Array thinnig for antenna selection in millimeter wave MIMO systems
%A C. Rusu
%A Nuria González-Prelcic
%A R. W. Heath Jr
%K compass
%K mmWave
%B IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP)
%8 2016
%G eng
%0 Journal Article
%J IEEE Signal Processing Magazine
%D 2016
%T Compressive Covariance Sensing: Structure-Based Compressive Sensing Beyond Sparsity
%A Daniel Romero
%A Dyonisius D Ariananda
%A Zhi Tian
%A Geert Leus
%K compass
%K compressed sensing
%X 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.

%B IEEE Signal Processing Magazine
%V 33
%P 78--93
%8 01/2016
%G eng
%N 1
%0 Conference Paper
%B IEEE Workshop on Statistical Signal Processing (SSP)
%D 2016
%T Design of data-injection adversarial attacks against spatial field detectors
%A R. López-Valcarce
%A Daniel Romero
%K adversarial signal processing
%K compass
%K wsn
%X Data-injection attacks on spatial field detection corrupt a subset of measurements to cause erroneous decisions. We consider a centralized decision scheme exploiting spatial field smoothness to overcome lack of knowledge on system parameters such as noise variance. We obtain closed-form expressions for system performance and investigate strategies for an intruder injecting false data in a fraction of the sensors in order to reduce the probability of detection. The problem of determining the most vulnerable subset of sensors is also analyzed.

%B IEEE Workshop on Statistical Signal Processing (SSP) %C Palma de Mallorca, Spain %8 06/2016 %G eng %0 Journal Article %J IEEE Transactions on Signal Processing %D 2016 %T Designing incoherent frames through convex techniques for optimized compressed sensing %A Cristian Rusu %A Nuria González-Prelcic %K compass %K compressed sensing %B IEEE Transactions on Signal Processing %V 64 %P 2334-2344 %8 May/2016 %G eng %N 9 %& 2334 %0 Conference Paper %B IEEE Workshop on Statistical Signal Processing (SSP) %D 2016 %T Distributed multivariate regression with unknown noise covariance in the presence of outliers: a minimum description length approach %A R. López-Valcarce %A Daniel Romero %A Josep Sala %A Alba Pagès-Zamora %K compass %K wsn %XWe consider the problem of estimating the coefficients in a multivariable linear model by means of a wireless sensor network

which may be affected by anomalous measurements. The noise covariance matrices at the different sensors are assumed

unknown. Treating outlying samples, and their support, as additional nuisance parameters, the Maximum Likelihood

estimate is investigated, with the number of outliers being estimated according to the Minimum Description Length

principle. A distributed implementation based on iterative consensus techniques is then proposed, and it is shown effective

for managing outliers in the data.

%B IEEE Workshop on Statistical Signal Processing (SSP)
%C Palma de Mallorca, Spain
%G eng
%0 Journal Article
%J IEEE Transactions on Signal Processing
%D 2016
%T Fast orthonormal sparsifying transforms based on Householder reflectors
%A C. Rusu
%A Nuria González-Prelcic
%A R.W. Heath Jr.
%K compass
%K compressed sensing
%B IEEE Transactions on Signal Processing
%V 64
%P 6589-6599
%8 12/2016
%G eng
%N 24
%R 10.1109/TSP.2016.2612168
%0 Conference Paper
%B 8th Advanced Satellite Multimedia Systems Conference and 14th Signal Processing for Space Communications Workshop
%D 2016
%T Full-duplex operation in two-way broadcast service for maritime applications
%A Tomás Ramírez
%A Carlos Mosquera
%K compass
%K full duplex
%K satcom
%B 8th Advanced Satellite Multimedia Systems Conference and 14th Signal Processing for Space Communications Workshop
%8 09/2016
%G eng
%0 Journal Article
%J IEEE Access
%D 2016
%T Hybrid MIMO Architectures for Millimeter Wave Communications: Phase Shifters or Switches?
%A Mendez-Rial, Roi
%A Rusu, Cristian
%A Nuria González-Prelcic
%A Alkhateeb, A.
%A Heath Jr, Robert W.
%B IEEE Access
%V 4
%P 247-267
%8 January, 2016
%G eng
%U http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=7370753
%R 10.1109/ACCESS.2015.2514261
%0 Conference Paper
%B IEEE Global Telecommunications Conf. (GLOBECOM)
%D 2016
%T Hybrid precoders and combiners for mmWave MIMO systems with per-antenna power constraints
%A R. López-Valcarce
%A Nuria González-Prelcic
%A Cristian Rusu
%A R. W. Heath, Jr
%K compass
%K mmWave
%X This paper considers the design of hybrid precoders

and combiners for mmWave MIMO systems with per-antenna

power constraints and the additional limitations introduced by

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

hybrid designs were obtained using a total power constraint,

but in practical implementations per-antenna constraints are

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

power amplifiers used in the transmit array. Assuming perfect

channel knowledge, we obtain first an approximation to the alldigital

solution for the precoder and the combiner given the

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

design of the hybrid precoder and combiner which attempts to

match such all-digital approximation. Simulation results show

the effectiveness of the proposed approach, which performs close

to the all-digital solution.

%B IEEE Global Telecommunications Conf. (GLOBECOM)
%G eng
%0 Journal Article
%J International Journal of Satellite Communications and Networking
%D 2016
%T Link adaptation in mobile satellite links: schemes for different degrees of CSI knowledge
%A Alberto Rico-Alvariño
%A Jesus Arnau
%A Carlos Mosquera
%K compass
%K satcom
%B International Journal of Satellite Communications and Networking
%V 34
%P 679-694
%8 09/2016
%G eng
%N 5
%0 Journal Article
%J IEEE Trans. Wireless Communications
%D 2016
%T Low complexity hybrid precoding strategies for millimeter wave communication systems
%A Cristian Rusu
%A Roi Méndez-Rial
%A Nuria González-Prelcic
%A Robert W. Heath Jr.
%K compass
%K mmWave
%X Millimeter communication systems use large antenna arrays to provide good average received power and to take advantage of multi-stream MIMO communication. Unfortunately, due to power consumption in the analog front-end, it is impractical to perform beamforming and fully digital precoding at baseband. Hybrid precoding/combining architectures have been proposed to overcome this limitation. The hybrid structure splits the MIMO processing between the digital and analog domains, while keeping the performance close to that of the fully digital solution. In this paper, we introduce and analyze several algorithms that efficiently design hybrid precoders and combiners starting from the known optimum digital precoder/combiner, which can be computed when perfect channel state information is available. We propose several low complexity solutions which provide different trade-offs between performance and complexity. We show that the proposed iterative solutions perform better in terms of spectral efficiency and/or are faster than previous methods in the literature. All of them provide designs which perform close to the known optimal digital solution. Finally, we study the effects of quantizing the analog component of the hybrid design and show that even with coarse quantization, the average rate performance is good.

%B IEEE Trans. Wireless Communications %V 15 %P 8380 - 8393 %8 12/2016 %G eng %N 12 %R 10.1109/TWC.2016.2614495 %0 Journal Article %J IEEE J. Selected Topics in Signal Processing. Special issue on Signal Processing for Millimeter Wave Wireless Communications %D 2016 %T An overview of signal processing techniques for millimeter wave MIMO systems %A Robert W. Heath Jr. %A Nuria González-Prelcic %A Sundeep Rangan %A Wonil Roh %A Akbar M. Sayeed %K compass %K mmWave %XCommunication at millimeter wave (mmWave) frequencies is defining a new era of wireless communication. The mmWave band offers higher bandwidth communication channels versus those presently used in commercial wireless systems. The applications of mmWave are immense: wireless local and personal area networks in the unlicensed band, 5G cellular systems, not to mention vehicular area networks, ad hoc networks, and wearables. Signal processing is critical for enabling the next generation of mmWave communication. Due to the use of large antenna arrays at the transmitter and receiver, combined with radio frequency and mixed signal power constraints, new multiple-input multiple-output (MIMO) communication signal processing techniques are needed. Because of the wide bandwidths, low complexity transceiver algorithms become important. There are opportunities to exploit techniques like compressed sensing for channel estimation and beamforming. This article provides an overview of signal processing challenges in mmWave wireless systems, with an emphasis on those faced by using MIMO communication at higher carrier frequencies.

%B IEEE J. Selected Topics in Signal Processing. Special issue on Signal Processing for Millimeter Wave Wireless Communications %V 10 %P 436 - 453 %8 04/2016 %G eng %N 3 %R 10.1109/JSTSP.2016.2523924 %0 Journal Article %J Linear Algebra and its Applications %D 2016 %T Properties of real and complex ETFs and their application to the design of low coherence frames %A Cristian Rusu %A Nuria González-Prelcic %A Robert W. Heath Jr. %B Linear Algebra and its Applications %V 508 %P 81-90 %8 November, 2016 %G eng %U http://www.sciencedirect.com/science/article/pii/S0024379516302555 %0 Conference Paper %B IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP) %D 2016 %T The use of unit norm tight measurement matrices for one-bit compressed sensing %A C. Rusu %A Nuria González-Prelcic %A R. W. Heath Jr. %K compass %K compressed sensing %XIn this paper we analyze the mean squared error (MSE) for one-bit compressed sensing schemes based on measurement matrices that correspond to unit norm tight frames. We show that, as in the unquantized case, sensing with unit norm tight frames improves the MSE in the reconstruction of sparse vectors from one-bit measurements using l1 and thresholding algorithms. From our analytical and experimental results we conclude that when implementing one-bit compressed sensing schemes with fixed measurement matrices unit norm tight frames are the measurements of choice

%B IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP) %8 2016 %G eng %0 Conference Paper %B IEEE Global Telecommunications Conf. (GLOBECOM), %D 2015 %T Adaptive one-bit compressive sensing with application to low-precision receivers at mmWave %A C. Rusu %A R. Méndez-Rial %A Nuria González-Prelcic %A R. W. Heath, Jr %K compass %K mmWave %B IEEE Global Telecommunications Conf. (GLOBECOM), %8 December, 2015 %G eng %0 Conference Paper %B European Signal Processing Conf. (EUSIPCO) %D 2015 %T Attack detectors for data aggregation in clustered sensor networks %A R. López-Valcarce %A Daniel Romero %K adversarial signal processing %K compass %K wsn %XAmong many security threats to sensor networks, compromised sensing is particularly challenging due to the fact that it cannot be addressed by standard authentication approaches. We consider a clustered scenario for data aggregation in which an attacker injects a disturbance in sensor readings. Casting the problem in an estimation framework, we systematically apply the Generalized Likelihood Ratio approach to derive attack detectors. The analysis under different attacks reveals that detectors based on similarity of means across

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

%B European Signal Processing Conf. (EUSIPCO)
%I EURASIP
%C Nice, France
%P 2098-2102
%8 accepted
%G eng
%0 Conference Paper
%B IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP)
%D 2015
%T An attack on antenna subset modulation for millimeter-wave communication
%A Cristian Rusu
%A Nuria González-Prelcic
%A Robert W. Heath Jr.
%K adversarial signal processing
%K compass
%K mmWave
%X Antenna subset modulation (ASM) is a physical layer security technique that is well suited for millimeter wave communication systems. The key idea is to vary the radiation pattern at the symbol rate by selecting one from a subset of patterns with a similar main lobe and different side lobes. This paper shows that ASM is not robust to an eavesdropper that makes multiple simultaneous measurements at multiple angles. The measurements are combined and used to formulate an estimation problem to undo the effects of the side lobe randomization. Simulations show the performance of the estimation algorithms and how the eavesdropper can effectively recover the information if the signal-to-noise ratio exceeds a certain threshold. Using fewer active radio frequency chains makes it harder for the attacker to recover the transmit symbol, at the expense of more grating lobes.

%B IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP) %I IEEE %C Brisbane, Australia %P 2914-2918 %8 04/2015 %G eng %0 Journal Article %J IEEE Trans. Information Theory %D 2015 %T Compression Limits for Random Vectors with Linearly Parameterized Second-Order Statistics %A Daniel Romero %A R. López-Valcarce %A Geert Leus %K compass %K compressed sensing %XThe class of complex random vectors whose covariance

matrix is linearly parameterized by a basis of Hermitian

Toeplitz (HT) matrices is considered, and the maximum

compression ratios that preserve all second-order information

are derived — the statistics of the uncompressed vector must

be recoverable from a set of linearly compressed observations.

This kind of vectors arises naturally when sampling widesense

stationary random processes and features a number of

applications in signal and array processing.

Explicit guidelines to design optimal and nearly optimal

schemes operating both in a periodic and non-periodic fashion

are provided by considering two of the most common linear

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

is seen that the maximum compression ratios depend on the

structure of the HT subspace containing the covariance matrix of

the uncompressed observations. Compression patterns attaining

these maximum ratios are found for the case without structure as

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

samplers are also proposed to compress unknown HT subspaces.

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

receiver matched filter output sampled at the symbol rate, an

approach which does not preserve all information in the analog

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

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

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

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

framework, which is shown to be information-preserving under

suitable conditions and considerably simplifies the analysis. It is

shown that the CRB can be substantially reduced by exploiting

any available excess bandwidth, depending on the modulation

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

%B IEEE Trans. Signal Processing
%V 63
%P 1675-1683
%8 04/2015
%G eng
%N 7
%& 1675
%R 10.1109/TSP.2015.2396013
%0 Conference Paper
%B IEEE Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC)
%D 2015
%T Dictionary-free Hybrid Precoders and Combiners for mmWave MIMO Systems
%A Roi Méndez-Rial
%A Cristian Rusu
%A Nuria González-Prelcic
%A Robert W. Heath Jr.
%K compass
%K mmWave
%B IEEE Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC)
%I IEEE
%C Stockholm, Sweden
%8 06/2015
%G eng
%0 Thesis
%D 2015
%T Estimation, Detection, and Learning for Dynamic Spectrum Access
%A Daniel Romero
%K cognitive radio
%K compass
%K dynacs
%K wsn
%I University of Vigo
%C Vigo, Spain
%V Ph.D.
%8 05/2015
%G eng
%9 Ph.D. Thesis
%0 Conference Paper
%B IEEE Int. Conference on Communications (ICC)
%D 2015
%T Low Complexity Hybrid Sparse Precoding and Combining in Millimeter Wave MIMO Systems
%A Cristian Rusu
%A Roi Méndez-Rial
%A Nuria González-Prelcic
%A Robert W. Heath Jr.
%K compass
%K mmWave
%B IEEE Int. Conference on Communications (ICC)
%I IEEE
%C London, UK
%8 06/2015
%G eng
%0 Conference Paper
%B Asilomar Conf. on Signals, Systems, and Computers
%D 2015
%T Low Resolution Adaptive Compressed Sensing for mmWave MIMO receivers
%A C. Rusu
%A Nuria González-Prelcic
%A R.W. Heath Jr.
%K compass
%K mmWave
%B Asilomar Conf. on Signals, Systems, and Computers
%8 November, 2015
%G eng
%0 Conference Paper
%B IEEE International Workshop on Signal Processing Advances in Wireless Communications, SPAWC
%D 2015
%T Robust Adaptive Coding and Modulation Scheme for the Mobile Satellite Forward Link
%A Alberto Rico-Alvariño
%A Anxo Tato
%A Carlos Mosquera
%K compass
%K satcom
%B IEEE International Workshop on Signal Processing Advances in Wireless Communications, SPAWC
%G eng
%0 Conference Paper
%B IEEE Int. Conference on Acoustics, Speech and Signal Processing (ICASSP)
%D 2015
%T Spectrum Cartography using quantized observations
%A Daniel Romero
%A Seung-Jun Kim
%A R. López-Valcarce
%A Georgios Giannakis
%K cognitive radio
%K compass
%K compressed sensing
%K spectrum sensing
%X 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.

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

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

%B IEEE Communications Letters %V 18 %P 1543-1546 %8 09/2014 %G eng %N 9 %& 1543 %R 10.1109/LCOMM.2014.2338316 %0 Conference Paper %B Proc. ASMS & SPSC %D 2014 %T Balancing Closed and Open Loop CSI in Mobile Satellite Link Adaptation %A Alberto Rico-Alvariño %A Arnau, Jesus %A Carlos Mosquera %K dynacs %K satcom %B Proc. ASMS & SPSC %C Livorno, Italy %G eng %1

**Best paper award**

Frame error rate (FER) prediction in wireless communication systems is an important tool with applications to system level simulations and link adaptation, among others. Although in realistic communication scenarios it is expected to have codewords of different lengths, previous work on FER prediction marginally treated the dependency of the FER on the codeword length. In this paper, we present a method to estimate the FER using codewords of different length. We derive a low complexity FER estimator for frames of different length transmitted over a binary symmetric channel of unknown error probability. We extend this technique to coded systems by the use of effective SNR FER predictors. The proposed estimation scheme is shown to outperform other simpler estimation methods.

%B ICASSP2014 - Signal Processing for Communications and Networking (ICASSP2014 - SPCOM) %C Florence, Italy %G eng %R 10.1109/ICASSP.2014.6853935 %0 Conference Paper %B IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM) %D 2014 %T How to Implement Doubly-Stochastic Matrices for Consensus-Based Distributed Algorithms %A S. Valcárcel-Macua %A C. Moreno-León %A J. S. Romero %A Silvana Silva Pereira %A Javier Zazo %A Alba Pagès-Zamora %A R. López-Valcarce %A S. Zazo %K compass %K dynacs %K wsn %XDoubly-stochastic matrices are usually required by

consensus-based distributed algorithms. We propose a simple

and efficient protocol and present some guidelines for implementing

doubly-stochastic combination matrices even in noisy,

asynchronous and changing topology scenarios. The proposed

ideas are validated with the deployment of a wireless sensor

network, in which nodes run a distributed algorithm for robust

estimation in the presence of nodes with faulty sensors.

%B IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM)
%C A Coruña, Spain
%G eng
%R 10.1109/SAM.2014.6882409
%0 Journal Article
%J IEEE Transactions on Wireless Communications
%D 2014
%T Learning-Based Adaptive Transmission for Limited Feedback Multiuser MIMO-OFDM
%A Alberto Rico-Alvariño
%A Robert W. Heath Jr.
%K adaptive signal processing
%K dynacs
%B IEEE Transactions on Wireless Communications
%G eng
%R 10.1109/TWC.2014.2314104
%0 Conference Paper
%B European Signal Processing Conference (EUSIPCO)
%D 2014
%T Low-Power Active Interference Cancellation for OFDM Spectrum Sculpting
%A Schmidt, J.F.
%A Daniel Romero
%A R. López-Valcarce
%X We present a low-power design for Active Interference

Cancellation (AIC) sculpting of the OFDM spectrum, based

on sparse design concepts. Optimal AIC designs compute

cancellation weights based on contributions from all data subcarriers.

Thus, as the number of subcarriers grows, power

consumption becomes a concern, and suboptimal solutions

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

we present novel sparse AIC designs based on a zeronorm

minimization of the matrix defining the cancellation

weights. These designs drastically reduce the number of operations

per symbol, and thus the power consumption, while allowing

to tune the loss with respect the optimal design. They

can be efficiently obtained and significantly outperform usual

thresholding or sparsity-inducing l_1-norm minimization approaches.

%B European Signal Processing Conference (EUSIPCO)
%8 09/2014
%G eng
%U http://www.eurasip.org/Proceedings/Eusipco/Eusipco2014/HTML/papers/1569912103.pdf
%0 Conference Paper
%B IEEE Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC)
%D 2014
%T Nearly-Optimal Compression Matrices for Signal Power Estimation
%A Daniel Romero
%A R. López-Valcarce
%K cognitive radio
%K dynacs
%B IEEE Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC)
%C Toronto, Canada
%G eng
%R 10.1109/SPAWC.2014.6941849
%0 Conference Paper
%B IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM)
%D 2014
%T SINR Optimization in Wideband Full-Duplex MIMO Relays under Limited Dynamic Range
%A Emilio Antonio-Rodríguez
%A R. López-Valcarce
%A Taneli Riihonen
%A Stefan Werner
%A Risto Wichman
%K adaptive signal processing
%K compass
%K full duplex
%B IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM)
%C A Coruña, Spain
%G eng
%R 10.1109/SAM.2014.6882369
%0 Journal Article
%J IEEE Trans. on Vehicular Technology
%D 2014
%T Spectrum Sensing for Wireless Microphone Signals using Multiple Antennas
%A Daniel Romero
%A R. López-Valcarce
%K cognitive radio
%K dynacs
%X Spectrum sensors for cognitive radio are expected to deploy multiple antennas in order to overcome the noise uncertainty problem and minimize the effects of small-scale fading. Despite the requirement that these sensors must detect wireless microphone (WM) signals, works in the literature have focused either on general purpose multiantenna detectors, or single antenna WM detectors. We exploit the spatial structure and particular properties of WM waveforms to derive four multiantenna detectors for WM signals with different performance/ complexity tradeoffs. These detectors are based on the generalized likelihood ratio test, which is derived under several signal models exploiting either the fact that the bandwidth of a WM signal never exceeds 200 kHz, the property that these signals have a constant magnitude, or both. The proposed detectors do not require synchronization with the WM signal and are robust to the noise uncertainty problem as well as to small-scale fading. Using the simulation guidelines from the IEEE 802.22 standard, the novel multiantenna WM detectors are shown to outperform previous schemes, thus demonstrating the advantages of exploiting spatial correlation along with WM signal structure.
%B IEEE Trans. on Vehicular Technology
%V 63
%P 4395-4407
%8 11/2014
%G eng
%N 9
%& 4395
%R 10.1109/TVT.2014.2316513
%0 Conference Paper
%B IEEE 14th Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC)
%D 2013
%T Adaptive Self-interference Cancellation in Wideband Full-Duplex Decode-and-Forward MIMO Relays
%A Emilio Antonio-Rodríguez
%A R. López-Valcarce
%A Taneli Riihonen
%A Stefan Werner
%A Risto Wichman
%K adaptive signal processing
%K dynacs
%K full duplex
%B IEEE 14th Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC)
%C Darmstadt, Germany
%8 06/2013
%G eng
%R 10.1109/SPAWC.2013.6612074
%0 Conference Paper
%B The Tenth International Symposium on Wireless Communication Systems 2013 (ISWCS 2013)
%D 2013
%T Analytical Characterization of the Single Frequency Network Gain Using Effective SNR Metrics
%A Alberto Rico-Alvariño
%A C. Mosquera
%K broadcasting
%K dynacs
%K Effective SNR metrics
%K Single Frequency Network
%X The design of broadcasting networks operating in a single frequency way is challenging due to the difficulty of predicting the performance in a frequency selective channel, caused by natural multipath and echoes coming from different transmitters. In this paper we resort to the use of frame error rate prediction metrics (also known as effective SNR metrics) to characterize the performance gain (or loss) under different multipath and SNR regimes in a simplified scenario with two transmitters. The analysis shows clearly that receivers with a dominant line of sight reception and high SNR are more sensitive to the presence of echoes, while those users in low SNR or strong multipath conditions are easily enforced by the insertion of a second transmitter.

%B The Tenth International Symposium on Wireless Communication Systems 2013 (ISWCS 2013) %C Ilmenau, Germany %G eng %0 Conference Paper %B Int. Conf. Acoust., Speech, Signal Process. (ICASSP) %D 2013 %T Autocorrelation-based adaptation rule for feedback equalization in Wideband Full-Duplex Amplify-and-Forward MIMO relays %A Emilio Antonio-Rodríguez %A R. López-Valcarce %A Taneli Riihonen %A Stefan Werner %A Risto Wichman %K adaptive signal processing %K dynacs %K full duplex %XSimultaneous reception and transmission in the same frequency, so-called full-duplex operation, causes an infinite feedback loop in an amplify-and-forward relay. The unwanted echoes may result in oscillation at the relay, making it unstable, and distorting the spectrum. This paper presents an adaptive MIMO filtering method for full-duplex amplify-and-forward relays that aims at solving the joint problem of self-interference mitigation and equalization of the source-relay channel. The scheme exploits knowledge of the autocorrelation of the transmitted signal as the only side information while allowing the relay, in the best case, to implement precoding as if there was not any self-interference or frequency selectivity in the source-relay channel. Finally, the proposed adaptation algorithm is investigated by determining its stationary points and by performing simulations in a MIMO-OFDM framework.

%B Int. Conf. Acoust., Speech, Signal Process. (ICASSP)
%G eng
%R 10.1109/ICASSP.2013.6638606
%0 Conference Paper
%B IEEE Int. Workshop Comput. Advances Multi-Sensor Adaptive Process (CAMSAP)
%D 2013
%T Compressive Angular and Frequency Periodogram Reconstruction for Multiband Signals
%A Ariananda, D. D.
%A Daniel Romero
%A Geert Leus
%K cognitive radio
%K dynacs
%B IEEE Int. Workshop Comput. Advances Multi-Sensor Adaptive Process (CAMSAP)
%C San Martin
%G eng
%R 10.1109/CAMSAP.2013.6714102
%0 Conference Paper
%B Inform. Theory Appl. Workshop
%D 2013
%T Compressive Covariance Sampling
%A Daniel Romero
%A Geert Leus
%K cognitive radio
%K dynacs
%B Inform. Theory Appl. Workshop
%P 1-8
%8 Feb.
%G eng
%R 10.1109/ITA.2013.6502949
%0 Conference Paper
%B Int. Conf. Acoust., Speech, Signal Process. (ICASSP)
%D 2013
%T Compressive wideband spectrum sensing with spectral prior information
%A Daniel Romero
%A R. López-Valcarce
%A Geert Leus
%K cognitive radio
%K dynacs
%K spectrum sensing
%X 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.

%B Int. Conf. Acoust., Speech, Signal Process. (ICASSP)
%G eng
%R 10.1109/ICASSP.2013.6638505
%0 Conference Proceedings
%B Asilomar Conference on Signals Systems and Computers
%D 2013
%T Cross Layer Link Adaptation in Time Varying Mobile Satellite Channels with Statistical and Outdated CSIT
%A Alberto Rico-Alvariño
%A J. Arnau
%A Carlos Mosquera
%K dynacs
%K satcom
%B Asilomar Conference on Signals Systems and Computers
%G eng
%R 10.1109/ACSSC.2013.6810481
%0 Conference Paper
%B 21st European Signal Processing Conference 2013 (EUSIPCO 2013)
%D 2013
%T Learning Based Link Adaptation in Multiuser MIMO-OFDM
%A Alberto Rico-Alvariño
%A Robert W. Heath Jr.
%K dynacs
%K link adaptation
%K Machine Learning
%K Multiuser MIMO-OFDM
%X Link adaptation in multiple user multiple-input multiple-output orthogonal frequency division multiplexing communication systems is challenging because of the coupling between user selection, mode selection, precoding, and equalization. In this paper, we present a methodology to perform link adaptation under this multiuser setting, focusing on the capabilities of IEEE 802.11ac. We propose to use a machine learning classifier to solve the problem of selecting a proper modulation and coding scheme, combined with a greedy algorithm that performs user and spatial mode selection. We observe that our solution offers good performance in the case of perfect channel state information or high feedback rate, while those scenarios with less feedback suffer some degradation due to inter-user interference.

%B 21st European Signal Processing Conference 2013 (EUSIPCO 2013) %C Marrakech, Morocco %G eng %0 Conference Paper %B Asilomar Conference on Signals Systems and Computers %D 2013 %T Link Adaptation in MIMO-OFDM with Practical Impairments %A Alberto Rico-Alvariño %A Robert W. Heath Jr. %K dynacs %K link adaptation %K MIMO-OFDM %B Asilomar Conference on Signals Systems and Computers %G eng %R 10.1109/ACSSC.2013.6810579 %0 Conference Paper %B IEEE 14th Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC), Darmstadt (Germany) %D 2013 %T Spectrum Sensing in Time-Varying Channels Using Multiple Antennas %A Daniel Romero %A R. López-Valcarce %K cognitive radio %K dynacs %K spectrum sensing %B IEEE 14th Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC), Darmstadt (Germany) %8 06/2013 %G eng %R 10.1109/SPAWC.2013.6612027 %0 Conference Paper %B Globecom 2013 - Symposium on Selected Areas in Communications (GC13 SAC) %D 2013 %T Statistical Cross Layer Adaptation in Fast Fading Mobile Satellite Channels %A Alberto Rico-Alvariño %A J. Arnau %A C. Mosquera %K dynacs %K fast fading channels %K link adaptation %K mobile satellite %K satcom %XLink adaptation in mobile satellite channels is difficult because of the large propagation delays, the frequent signal blockage and the variation of the channel statistics. In this paper, we propose a cross-layer link adaptation strategy that exploits statistical, long-term CSI to increase the throughput when some retransmissions are available; this increase is obtained while meeting a target outage probability constraint. Our strategy takes as inputs the estimated packet error rates of the available modulation and coding schemes (MCS) and their rates; as an output, it returns the optimum sequence of MCS to be used. Results will also show that simple information acquisition strategies can still provide very good results.

%B Globecom 2013 - Symposium on Selected Areas in Communications (GC13 SAC) %C Atlanta, USA %G eng %R 10.1109/GLOCOM.2013.6831502 %0 Journal Article %J IEEE Trans. Signal Process. %D 2013 %T Wideband Spectrum Sensing From Compressed Measurements Using Spectral Prior Information %A Daniel Romero %A Geert Leus %K cognitive radio %K compressed sensing %K dynacs %K spectrum sensing %B IEEE Trans. Signal Process. %V 61 %P 6232-6246 %G eng %R 10.1109/TSP.2013.2283473 %0 Conference Paper %B 30th AIAA International Communications Satellite Systems Conference (ICSSC) %D 2012 %T Adaptive Transmission Techniques for Mobile Satellite Links %A Arnau, Jesus %A Alberto Rico-Alvariño %A C. Mosquera %K dynacs %K satcom %B 30th AIAA International Communications Satellite Systems Conference (ICSSC) %C Ottawa, Canada %G eng %1Detecting the presence of a white Gaussian signal distorted by a noisy time-varying channel is addressed by means of three different detectors. First, the generalized likelihood ratio test (GLRT) is found for the case where the channel has no temporal structure, resulting in the well-known Bartlett’s test. Then it is shown that, under the transformation group given by scaling factors, a locally most powerful invariant test (LMPIT) does not exist. Two alternative approaches are explored in the low signal-to-noise ratio (SNR) regime: the first assigns a prior probability density function (pdf) to the channel (hence modeled as random), whereas the second assumes an underlying basis expansion model (BEM) for the (now deterministic) channel and obtains the maximum likelihood (ML) estimates of the parameters relevant for the detection problem. The performance of these detectors is evaluated via Monte Carlo simulation.

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

%B 3rd Int. Workshop on Cognitive Information Processing (CIP 2012) %C Baiona, Spain %8 05/2012 %G eng %R 10.1109/CIP.2012.6232933 %0 Conference Paper %B 2012 6th Advanced Satellite Multimedia Systems Conference (ASMS) and 12th Signal Processing for Space Communications Workshop (SPSC) (ASMS/SPSC 2012) %D 2012 %T On the Effect of Echoes in Hybrid Terrestrial-Satellite Single Frequency Networks: Analysis and Countermeasures %A Alberto Rico-Alvariño %A C. Mosquera %K dynacs %K Effective SNR %K Hybrid Terrestrial- Satellite %K satcom %K Satellite OFDM %K Single Frequency Network %K Space-Time Coding %XHybrid Terrestrial Satellite Single Frequency Networks achieve large spectral efficiencies due to a higher frequency reuse, which is attained by transmitting the same waveform in the same frequency band from satellite and terrestrial transmitters. However, the presence of multiple transmitters propitiates the existence of the so-called SFN echoes, which can degrade the system performance even if they arrive within the OFDM guard interval. In this paper we characterize this effect by resorting to PER prediction metrics (or effective SNR metrics), and analyze two simple preprocessing schemes that mitigate this degradation: the use of Alamouti space-time codes, and a convenient prefiltering at the terrestrial transmitter.

%B 2012 6th Advanced Satellite Multimedia Systems Conference (ASMS) and 12th Signal Processing for Space Communications Workshop (SPSC) (ASMS/SPSC 2012) %C Baiona, Spain %G eng %R 10.1109/ASMS-SPSC.2012.6333071 %0 Conference Paper %B IEEE Int. Conf. on Acoustics, Speech and Signal Processing (ICASSP 2012) %D 2012 %T Generalized matched filter detector for fast fading channels %A Daniel Romero %A R. López-Valcarce %A Geert Leus %K cognitive radio %K dynacs %K spectrum sensing %XWe consider the problem of detecting a known signal with constant magnitude immersed in noise of unknown variance,

when the propagation channel is frequency-flat and randomly

time-varying within the observation window. A Basis Expansion

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

Matched Filter detector, to which it reduces for timeinvariant

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

%B IEEE Int. Conf. on Acoustics, Speech and Signal Processing (ICASSP 2012)
%I IEEE
%C Kyoto, Japan
%8 07/2012
%G eng
%R 10.1109/ICASSP.2012.6288587
%0 Conference Paper
%B Asilomar Conference on Signals, Systems, and Computers
%D 2012
%T Optimum Training for CSI Acquisition in Cognitive Radio Channels
%A Alberto Rico-Alvariño
%A C. Mosquera
%K adaptive signal processing
%K cognitive radio
%K dynacs
%B Asilomar Conference on Signals, Systems, and Computers
%C Pacific Grove, CA
%G eng
%R 10.1109/ACSSC.2012.6488973
%0 Journal Article
%J IEEE Transactions on Wireless Communications
%D 2012
%T Overlay Cognitive Transmission in a Multicarrier Broadcast Network with Dominant Line of Sight Reception
%A Alberto Rico-Alvariño
%A C. Mosquera
%A Fernando Pérez-González
%K cognitive radio
%K dynacs
%K satcom
%B IEEE Transactions on Wireless Communications
%G eng
%R 10.1109/TWC.2012.092112.120257
%0 Conference Paper
%B 3rd International Workshop on Cognitive Information Processing (CIP)
%D 2012
%T Overlay cognitive transmission in OFDM point to point systems exploiting primary feedback
%A Alberto Rico-Alvariño
%A C. Mosquera
%K cognitive radio
%K dynacs
%X A secondary user that tries to reuse the spectrum allocated to a primary user can exploit the knowledge of the primary message to perform this task. In particular, the overlay cognitive radio paradigm postulates the use of a fraction of the available power at the secondary transmitter to convey the primary message, so the spectral efficiency of the primary system is increased, and, therefore, some transmission resources (time slots or frequency bands) can be released to the secondary transmission while the primary user rate is kept constant. The fraction of released resources can be incremented if some channel state information is available at the secondary transmitter. In this paper, we present a scenario where the secondary transmitter maximizes the primary link quality (measured in terms of Effective SNR), and obtains its channel state information by exploiting the primary user SNR-based feedback.

%B 3rd International Workshop on Cognitive Information Processing (CIP) %C Baiona, Galicia, Spain %8 05/2012 %G eng %R 10.1109/CIP.2012.6232932 %0 Conference Proceedings %B IEEE Symposium on New Frontiers in Dynamic Spectrum Access Networks (DySPAN 2012) %D 2012 %T Overlay Spectrum Reuse in a Broadcast Network: Covering the Whole Grayscale of Spaces %A Alberto Rico-Alvariño %A C. Mosquera %K cognitive radio %K dynacs %B IEEE Symposium on New Frontiers in Dynamic Spectrum Access Networks (DySPAN 2012) %C Bellevue, WA %G eng %R 10.1109/DYSPAN.2012.6478172 %0 Conference Paper %B The 13th IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC 2012) %D 2012 %T Overlay Spectrum Reuse in a Multicarrier Broadcast Network: Coverage Analysis %A Alberto Rico-Alvariño %A C. Mosquera %A Fernando Pérez-González %K cognitive radio %K dynacs %XA secondary cognitive user overlaying its message in a broadcast multicarrier network is studied. The secondary user exploits the primary message knowledge to convey its own information while preserving the primary user coverage area, determined by a bound on the BER, and taking into account the degradation due to the insertion of an echo in a dominant line of sight environment. The results are compared with those obtained when the coverage area is defined in capacity terms, and regardless of the degradation caused by the secondary replica of the primary message.

%B The 13th IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC 2012) %C Cesme, Turkey %G eng %R 10.1109/SPAWC.2012.6292889 %0 Conference Paper %B The 13th IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC 2012) %D 2012 %T Overlay Spectrum Reuse in a Multicarrier Broadcast Network: Single Receiver Analysis %A Alberto Rico-Alvariño %A C. Mosquera %A Fernando Pérez-González %K cognitive radio %K dynacs %XThe overlay cognitive radio paradigm presents a framework where a secondary user exploits the knowledge of the primary user's message to improve spectrum utilization. A multicarrier broadcast network is one of the scenarios where this knowledge is possible: the secondary user could join a single frequency network and, therefore, gain access to the primary message. However, if the primary signal is received with a strong line of sight component, its relaying from the secondary transmitter does not suffice to ensure the primary user quality of service. In this paper we study the scenario where a secondary transmitter maximizes its own transmission rate, keeping the quality of a primary receiver over a given threshold. The analytical results, based on bit error rate bounds, are verified by means of software simulations and hardware tests.

%B The 13th IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC 2012) %C Cesme, Turkey %G eng %R 10.1109/SPAWC.2012.6292890 %0 Conference Paper %B International Workshop on Computational Advances in Multi-Sensor Adaptive Processing (CAMSAP) %D 2011 %T Bandlimited or Constant Envelope? Exploiting Waveform Properties in Wireless Microphone Detection %A Daniel Romero %A R. López-Valcarce %K Bandlimited signals. %K Constant Magnitude %K dynamic spectrum access %K Wireless Microphones %B International Workshop on Computational Advances in Multi-Sensor Adaptive Processing (CAMSAP) %C San Juan, Puerto Rico %P 17-20 %8 December %G eng %0 Conference Paper %B International Conference on Cognitive Radio and Advanced Spectrum Management %D 2011 %T On the Co-existence of Primary and Secondary Transmitters in a Broadcast Network %A Alberto Rico-Alvariño %A C. Mosquera %A Fernando Pérez-González %K Broadcast %K cognitive radio %K Overlay %K Single Frequency Network %B International Conference on Cognitive Radio and Advanced Spectrum Management %C Barcelona, Catalonia, Spain %G eng %0 Journal Article %J IEEE Trans. on Signal Processing %D 2011 %T Detection of Rank-P Signals in Cognitive Radio Networks With Uncalibrated Multiple Antennas %A David Ramírez %A Gonzalo Vázquez-Vilar %A R. López-Valcarce %A Javier Vía %A Ignacio Santamaría %K cognitive radio %K dynacs %K spectrum sensing %XSpectrum sensing is a key component of the Cognitive Radio paradigm. Typically, primary signals have to be detected with uncalibrated receivers at signal-to-noise ratios (SNRs) well below decodability levels. Multiantenna detectors exploit spatial independence of receiver thermal noise to boost detection performance and robustness. We study the problem

of detecting a Gaussian signal with rank-P unknown spatial

covariance matrix in spatially uncorrelated Gaussian noise with

unknown covariance using multiple antennas. The generalized

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

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

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

%B IEEE Workshop on Signal Processing Advances in Wireless Communications (SPAWC) %P 441 -445 %8 june %G eng %R 10.1109/SPAWC.2011.5990448 %0 Conference Paper %B International Conference on Cloud Computing and Services Science (CLOSER) %D 2011 %T Encrypted Domain Processing for Cloud Privacy: Concept and Practical Experience %A Daniel A. Rodríguez-Silva %A F. Javier González-Castaño %A Lilian Adkinson-Orellana %A Alexandre Fernández-Cordeiro %A Juan Ramón Troncoso-Pastoriza %A Daniel González-Martínez %K cloud %K privacy %K security %K watermarking %B International Conference on Cloud Computing and Services Science (CLOSER) %C Noordwijkerhout, The Netherlands %8 May %G eng %0 Conference Paper %B IEEE Workshop on Signal Processing Advances in Wireless Communications (SPAWC) %D 2011 %T Multiantenna detection of constant-envelope signals in noise of unknown variance %A Daniel Romero %A R. López-Valcarce %K cognitive radio %K multiantenna detection %K spectrum sensing %XDetection of unknown signals with constant modulus (CM) using multiple antennas in additive white Gaussian noise of unknown variance is considered. The channels from the source to each antenna are assumed frequency-flat and unknown. This problem is of interest for spectrum sensing in cognitive radio systems in which primary signals are known to have the CM property. Examples include analog frequency modulated signals such as those transmitted by wireless microphones in the TV bands and Gaussian Minimum Shift Keying modulated signals as in the GSM cellular standard. The proposed detector, derived from a Generalized Likelihood Ratio (GLR) approach, exploits both the CM property and the spatial independence of noise, outperforming the GLR test for Gaussian signals as shown by simulation.

%B IEEE Workshop on Signal Processing Advances in Wireless Communications (SPAWC) %P 446 -450 %8 june %G eng %R 10.1109/SPAWC.2011.5990449 %0 Conference Paper %B IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) %D 2011 %T Multiantenna detection under noise uncertainty and primary user's spatial structure %A David Ramírez %A Gonzalo Vázquez-Vilar %A R. López-Valcarce %A Javier Vía %A Ignacio Santamaría %K cognitive radio %K generalized likelihood ratio test (GLRT) %K spectrum sensing %B IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) %I IEEE %C Prage, Czech Republic %P 2948-2951 %8 May %G eng %0 Conference Paper %B Document Recognition and Retrieval %D 2011 %T A new method for perspective correction of document images %A José Rodríguez-Piñeiro %A Pedro Comesaña %A Fernando Pérez-González %A Alberto Malvido %K Document image %K perspective distortion correction %K watermarking %B Document Recognition and Retrieval %S Proc. of SPIE %I SPIE %C San Francisco, CA %V 7874 %P 787410 %8 January %G eng %0 Conference Paper %B IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) %D 2010 %T Multiantenna spectrum sensing: detection of spatial correlation among time-series with unknown spectra %A David Ramírez %A Javier Vía %A Ignacio Santamaría %A R. López-Valcarce %A L. L. Scharf %K cognitive radio %K coherence spectrum %K generalized likelihood ratio test %K Hadamard ratio %K multiple-channel signal detection %B IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) %C Dallas, TX %G eng %0 Conference Paper %B Advanced Satellite Multimedia Systems Conference (ASMA) %D 2010 %T Performance Analysis of Distributed Tracking with Consensus on Noisy Time-Varying Graphs %A Yongxiang Ruan %A Sudhaman K. Jayaweera %A C. Mosquera %K connectivity graph %K distributed local Kalman filtering %K distributed tracking %K distributed tracking with consensus %K graph topology %K network theory (graphs) %K noisy communications links %K noisy time-varying graphs %K performance analysis %K telecommunication links %K telecommunication network topology %K time-varying network topology %K time-varying systems %B Advanced Satellite Multimedia Systems Conference (ASMA) %C Cagliari, Italy %P 395-400 %G eng %0 Book Section %D 2007 %T Digital Satellite Communications %A A. A. Rontogiannis %A Marcos Álvarez-Díaz %A M. Casadei %A V. Dalakas %A A. Duverdier %A F. J. González-Serrano %A M. Iubatti %A T. Javornik %A L. Lapierre %A Neri, Massimo %A P. Salmi %I Springer %C New York %P - %8 April %G eng %& Distortion Countermeasures %0 Conference Paper %B AIAA International Communications Satellite Systems Conference (ICSSC) %D 2005 %T Aeronautical Channel Model for Broadband L-Band Satellite Communication %A Madhavendra Richharia %A Naveen Kaluvala %A Panos Fines %A Marcos Álvarez-Díaz %A Axel Jahn %K Digital Communications %K L-Band %K satellite communications %B AIAA International Communications Satellite Systems Conference (ICSSC) %C Rome, Italy %8 September 25-28 %G eng %0 Conference Paper %B International Workshop on Digital Watermarking (IWDW) %D 2003 %T Optimal Data-Hiding Strategies for Games with BER Payoffs %A Pedro Comesaña %A Fernando Pérez-González %A Félix Balado %E Ton Kalker %E Ingemar J. Cox %E Yong Man Ro %K data-hiding %K watermarking %B International Workshop on Digital Watermarking (IWDW) %S Lecture Notes in Computer Science %I Springer-Verlag Heidelberg %V 2939 / 2004 %P 101-116 %8 October %G eng %0 Journal Article %J Signal Processing %D 2000 %T Improving the Performance of Spatial Watermarking of Images Using Channel Coding %A Juan R. Hernández %A José M. Rodríguez %A Fernando Pérez-González %K data-hiding %K watermarking %B Signal Processing %V 80 %P 1261-1279 %8 July %G eng %0 Conference Paper %B COST #254 Int. Workshop on Intelligent Communications %D 1998 %T Coding and Synchronization: A Boost and a Bottleneck for the Development of Image Watermarking %A Juan R. Hernández %A Fernando Pérez-González %A José M. Rodríguez %K data-hiding %K watermarking %B COST #254 Int. Workshop on Intelligent Communications %I SSGRR %C L'Aquila, Italy %P 77–82 %8 June %G eng %0 Conference Paper %B IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) %D 1998 %T The Impact of Channel Coding on the Performance of Spatial Watermarking for Copyright Protection %A Juan R. Hernández %A Fernando Pérez-González %A José M. Rodríguez %K data-hiding %K watermarking %B IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) %C Seattle, Washington, USA %V 5 %P 2973–2976 %8 May %G eng %0 Journal Article %J IEEE Journal on Selected Areas in Communications %D 1998 %T Performance Analysis of a 2D-Multipulse Amplitude Modulation Scheme for Data Hiding and Watermarking of Still Images %A Juan R. Hernández %A Fernando Pérez-González %A José M. Rodríguez %A Gustavo Nieto %K data-hiding %K watermarking %B IEEE Journal on Selected Areas in Communications %V 16 %P 510–524 %8 May %G eng %0 Conference Paper %B Emerging Techniques for Communication Terminals %D 1997 %T Data Hiding for Copyright Protection of Still Images %A Juan R. Hernández %A Fernando Pérez-González %A José M. Rodríguez %K data-hiding %K watermarking %B Emerging Techniques for Communication Terminals %I ENSEEIHT %C Tolouse, France %P 285–289 %8 July %G eng