TY - JOUR T1 - Cramér-Rao Bounds for SNR Estimation of Oversampled Linearly Modulated Signals JF - IEEE Trans. Signal Processing Y1 - 2015 A1 - R. López-Valcarce A1 - J. Villares A1 - J. Riba A1 - W. Gappmair A1 - C. Mosquera KW - adaptive signal processing KW - compass KW - Cramér-Rao bound (CRB) KW - dynacs KW - oversampling KW - Signal-to-noise ratio (SNR) AB -
Most Signal-to-noise ratio (SNR) estimators use the
receiver matched filter output sampled at the symbol rate, an
approach which does not preserve all information in the analog
waveform due to aliasing. Thus, it is relevant to ask whether
avoiding aliasing could improve SNR estimation. To this end, we
compute the corresponding data-aided (DA) and non-data-aided
(NDA) Cramér-Rao bounds (CRBs). We adopt a novel dual filter
framework, which is shown to be information-preserving under
suitable conditions and considerably simplifies the analysis. It is
shown that the CRB can be substantially reduced by exploiting
any available excess bandwidth, depending on the modulation
scheme, the SNR range, and the estimator (DA or NDA) type.
VL - 63 IS - 7 ER - TY - THES T1 - Estimation, Detection, and Learning for Dynamic Spectrum Access Y1 - 2015 A1 - Daniel Romero KW - cognitive radio KW - compass KW - dynacs KW - wsn PB - University of Vigo CY - Vigo, Spain VL - Ph.D. ER - TY - JOUR T1 - Active Interference Cancellation for OFDM Spectrum Sculpting: Linear Processing is Optimal JF - IEEE Communications Letters Y1 - 2014 A1 - Schmidt, J.F. A1 - Daniel Romero A1 - R. López-Valcarce KW - cognitive radio KW - compass KW - dynacs KW - spectrum shaping AB -

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.

 

VL - 18 IS - 9 ER - TY - CONF T1 - Antenna competition to boost Active Interference Cancellation in cognitive MIMO-OFDM T2 - IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM) Y1 - 2014 A1 - Schmidt, J.F. A1 - R. López-Valcarce KW - cognitive radio KW - dynacs KW - spectrum shaping AB - 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. JF - IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM) CY - A Coruña, Spain ER - TY - CONF T1 - Balancing Closed and Open Loop CSI in Mobile Satellite Link Adaptation T2 - Proc. ASMS & SPSC Y1 - 2014 A1 - Alberto Rico-Alvariño A1 - Arnau, Jesus A1 - Carlos Mosquera KW - dynacs KW - satcom JF - Proc. ASMS & SPSC CY - Livorno, Italy U1 -

Best paper award

ER - TY - CONF T1 - Dissection of multibeam satellite communications with a large-scale antenna system toolbox T2 - European Wireless 2014 (EW2014) Y1 - 2014 A1 - Arnau, Jesus A1 - Carlos Mosquera KW - dynacs KW - large-scale analysis KW - Massive MIMO KW - multibeam satellites KW - Multiuser detection KW - satcom AB -

Current multibeam satellite systems consist of a very large number of spot beams. In this paper, we analyze them from the large scale MIMO perspective, and establish a comparison with massive MIMO systems. It will be shown that the large number of beams has important operational implications, and that it simplifies the analysis because it allows using asymptotic results. However, it will also be shown that multibeam satellite systems cannot be considered massive MIMO systems.

JF - European Wireless 2014 (EW2014) CY - Barcelona, Spain ER - TY - CONF T1 - Distributed Total Least Squares Estimation over Networks T2 - IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP) Y1 - 2014 A1 - R. López-Valcarce A1 - Silvana Silva Pereira A1 - Alba Pagès-Zamora KW - dynacs KW - wsn AB -

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.

JF - IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP) CY - Florence, Italy ER - TY - CONF T1 - FER prediction with variable codeword length T2 - ICASSP2014 - Signal Processing for Communications and Networking (ICASSP2014 - SPCOM) Y1 - 2014 A1 - Alberto Rico-Alvariño A1 - Robert W. Heath Jr. A1 - Carlos Mosquera KW - adaptive signal processing KW - compass KW - dynacs KW - Effective SNR KW - FER prediction KW - PHY abstraction AB -

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.

JF - ICASSP2014 - Signal Processing for Communications and Networking (ICASSP2014 - SPCOM) CY - Florence, Italy ER - TY - CONF T1 - Flat Fading Channel Estimation Based on Dirty Paper Coding T2 - IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP) Y1 - 2014 A1 - Gabriel Domínguez-Conde A1 - Pedro Comesaña A1 - Fernando Pérez-González KW - channel estimation KW - dirty paper coding KW - dynacs KW - superimposed pilots AB -

A novel complex flat fading channel estimation scheme is proposed. Contrarily to previous schemes in the literature, this new approach is not based on introducing pilot sequences, but on reducing the  interference caused by the information-bearing signal on the estimation-aiding signal by using Dirty Paper Coding.  We show through simulations that our method outperforms the  Partially-Data Dependent scheme, which is a state-of-the-art technique based on superimposed pilots. 

JF - IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP) CY - Florence, Italy ER - TY - CONF T1 - How to Implement Doubly-Stochastic Matrices for Consensus-Based Distributed Algorithms T2 - IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM) Y1 - 2014 A1 - S. Valcárcel-Macua A1 - C. Moreno-León A1 - J. S. Romero A1 - Silvana Silva Pereira A1 - Javier Zazo A1 - Alba Pagès-Zamora A1 - R. López-Valcarce A1 - S. Zazo KW - compass KW - dynacs KW - wsn AB -
Doubly-stochastic matrices are usually required by
consensus-based distributed algorithms. We propose a simple
and efficient protocol and present some guidelines for implementing
doubly-stochastic combination matrices even in noisy,
asynchronous and changing topology scenarios. The proposed
ideas are validated with the deployment of a wireless sensor
network, in which nodes run a distributed algorithm for robust
estimation in the presence of nodes with faulty sensors.
JF - IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM) CY - A Coruña, Spain ER - TY - JOUR T1 - Learning-Based Adaptive Transmission for Limited Feedback Multiuser MIMO-OFDM JF - IEEE Transactions on Wireless Communications Y1 - 2014 A1 - Alberto Rico-Alvariño A1 - Robert W. Heath Jr. KW - adaptive signal processing KW - dynacs ER - TY - CONF T1 - Nearly-Optimal Compression Matrices for Signal Power Estimation T2 - IEEE Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC) Y1 - 2014 A1 - Daniel Romero A1 - R. López-Valcarce KW - cognitive radio KW - dynacs JF - IEEE Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC) CY - Toronto, Canada ER - TY - CONF T1 - OFDM spectrum sculpting with active interference cancellation: Keeping spectral spurs at bay T2 - IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP) Y1 - 2014 A1 - Schmidt, J.F. A1 - R. López-Valcarce KW - cognitive radio KW - dynacs KW - spectrum shaping JF - IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP) PB - IEEE CY - Florence, Italy ER - TY - JOUR T1 - Performance of the Multibeam Satellite Return Link with Correlated Rain Attenuation JF - IEEE Transactions on Wireless Communications Y1 - 2014 A1 - Arnau, Jesus A1 - Christopoulos, D. A1 - Chatzinotas, S. A1 - C. Mosquera A1 - Ottersten, B. KW - Antennas KW - Approximation methods KW - Attenuation KW - Correlation KW - dynacs KW - Rain KW - satcom KW - Satellites KW - Signal to noise ratio AB -

Rain attenuation is among the major impairments for satellite systems operating in the K band and above. In this paper, we investigate the impact of spatially correlated rain attenuation on the performance of a multibeam satellite return link. For a comprehensive assessment, an analytical model for the antenna pattern that generates the beams is also proposed. We focus on the outage capacity of the link, and obtain analytical approximations at high and low SNR. The derived approximations provide insights on the effect of key system parameters – like the inter-user distance, the satellite beam radius, or the rain intensity– and simulation results show that it fits tightly to the Monte Carlo results. Additionally, the derived expressions can be easily particularized for the single-user case, providing some novel insights.

ER - TY - CONF T1 - Power spectrum blind sampling using optimal multicoset sampling patterns in the MSE sense T2 - IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) Y1 - 2014 A1 - Bamrung TauSiesakul A1 - Nuria González-Prelcic KW - cognitive radio KW - dynacs JF - IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) ER - TY - CONF T1 - Sensitivity of compressive sensing architectures based on time interleaved analog-to-digital converters to channel mismatches T2 - IEEE International New Circuits and Systems Conference (NEWCAS) Y1 - 2014 A1 - Roi Méndez-Rial A1 - J.M. Caurel-Carrera A1 - Nuria González-Prelcic KW - dynacs JF - IEEE International New Circuits and Systems Conference (NEWCAS) ER - TY - JOUR T1 - Spectrum Sensing for Wireless Microphone Signals using Multiple Antennas JF - IEEE Trans. on Vehicular Technology Y1 - 2014 A1 - Daniel Romero A1 - R. López-Valcarce KW - cognitive radio KW - dynacs AB - 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. VL - 63 IS - 9 ER - TY - CONF T1 - Adaptive Self-interference Cancellation in Wideband Full-Duplex Decode-and-Forward MIMO Relays T2 - IEEE 14th Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC) Y1 - 2013 A1 - Emilio Antonio-Rodríguez A1 - R. López-Valcarce A1 - Taneli Riihonen A1 - Stefan Werner A1 - Risto Wichman KW - adaptive signal processing KW - dynacs KW - full duplex JF - IEEE 14th Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC) CY - Darmstadt, Germany ER - TY - CONF T1 - Analytical Characterization of the Single Frequency Network Gain Using Effective SNR Metrics T2 - The Tenth International Symposium on Wireless Communication Systems 2013 (ISWCS 2013) Y1 - 2013 A1 - Alberto Rico-Alvariño A1 - C. Mosquera KW - broadcasting KW - dynacs KW - Effective SNR metrics KW - Single Frequency Network AB -

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.

JF - The Tenth International Symposium on Wireless Communication Systems 2013 (ISWCS 2013) CY - Ilmenau, Germany ER - TY - CONF T1 - Autocorrelation-based adaptation rule for feedback equalization in Wideband Full-Duplex Amplify-and-Forward MIMO relays T2 - Int. Conf. Acoust., Speech, Signal Process. (ICASSP) Y1 - 2013 A1 - Emilio Antonio-Rodríguez A1 - R. López-Valcarce A1 - Taneli Riihonen A1 - Stefan Werner A1 - Risto Wichman KW - adaptive signal processing KW - dynacs KW - full duplex AB -
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.
JF - Int. Conf. Acoust., Speech, Signal Process. (ICASSP) ER - TY - CONF T1 - Cancelling self-interference in full-duplex relays without Angle-of-Arrival information T2 - Int. Conf. Acoust., Speech, Signal Process. (ICASSP) Y1 - 2013 A1 - Emilio Antonio-Rodríguez A1 - R. López-Valcarce KW - adaptive signal processing KW - dynacs KW - full duplex AB -
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.
JF - Int. Conf. Acoust., Speech, Signal Process. (ICASSP) ER - TY - JOUR T1 - Choose Your Subcarriers Wisely: Active Interference Cancellation for Cognitive OFDM JF - IEEE Journal on Emerging and Selected Topics in Circuits and Systems Y1 - 2013 A1 - Schmidt, J.F. A1 - Costas-Sanz, S. A1 - R. López-Valcarce KW - cognitive radio KW - dynacs KW - spectrum shaping VL - 3 IS - 4 ER - TY - CONF T1 - A Class of Circular Sparse Rulers for Compressive Power Spectrum Estimation T2 - European Signal Processing Conf. (EUSIPCO), Marrakech (Morocco) Y1 - 2013 A1 - M. Elena Domínguez-Jiménez A1 - Nuria González-Prelcic KW - cognitive radio KW - dynacs JF - European Signal Processing Conf. (EUSIPCO), Marrakech (Morocco) ER - TY - JOUR T1 - A Cognitive Mobile BTS Solution with Software-Defined Radioelectric Sensing JF - Sensors Y1 - 2013 A1 - J. Muñoz A1 - J. Vales-Alonso A1 - F. Quiñoy-García A1 - Costas-Sanz, S. A1 - M. Pillado A1 - F.J. González-Castaño A1 - M. García-Sanchez A1 - R. López-Valcarce A1 - C. López-Bravo KW - cognitive radio KW - dynacs KW - mobile communications KW - SDR KW - vehicular communications AB -

 Private communications inside large vehicles such as ships may be effectively provided using standard cellular systems. In this paper we propose a new solution based on software-defined radio with electromagnetic sensing support. Software-defined radio allows low-cost developments and, potentially, added-value services not available in commercial cellular networks. The platform of reference, OpenBTS, only supports single-channel cells. Our proposal, however, has the ability of changing BTS channel frequency without disrupting ongoing communications. This ability should be mandatory in vehicular environments, where neighbouring cell configurations may change rapidly, so a moving cell must be reconfigured in real-time to avoid interferences. Full details about frequency occupancy sensing and the channel reselection procedure are provided in this paper. Moreover, a procedure for fast terminal detection is proposed. This may be decisive in emergency situations, e.g., if someone falls overboard. Different tests confirm the feasibility of our proposal and its compatibility with commercial GSM terminals.

VL - 13 IS - 2 ER - TY - CONF T1 - Compressive Angular and Frequency Periodogram Reconstruction for Multiband Signals T2 - IEEE Int. Workshop Comput. Advances Multi-Sensor Adaptive Process (CAMSAP) Y1 - 2013 A1 - Ariananda, D. D. A1 - Daniel Romero A1 - Geert Leus KW - cognitive radio KW - dynacs JF - IEEE Int. Workshop Comput. Advances Multi-Sensor Adaptive Process (CAMSAP) CY - San Martin ER - TY - CONF T1 - Compressive Covariance Sampling T2 - Inform. Theory Appl. Workshop Y1 - 2013 A1 - Daniel Romero A1 - Geert Leus KW - cognitive radio KW - dynacs JF - Inform. Theory Appl. Workshop ER - TY - CONF T1 - Compressive wideband spectrum sensing with spectral prior information T2 - Int. Conf. Acoust., Speech, Signal Process. (ICASSP) Y1 - 2013 A1 - Daniel Romero A1 - R. López-Valcarce A1 - Geert Leus KW - cognitive radio KW - dynacs KW - spectrum sensing AB -
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.
JF - Int. Conf. Acoust., Speech, Signal Process. (ICASSP) ER - TY - Generic T1 - Cross Layer Link Adaptation in Time Varying Mobile Satellite Channels with Statistical and Outdated CSIT T2 - Asilomar Conference on Signals Systems and Computers Y1 - 2013 A1 - Alberto Rico-Alvariño A1 - J. Arnau A1 - Carlos Mosquera KW - dynacs KW - satcom JF - Asilomar Conference on Signals Systems and Computers ER - TY - JOUR T1 - On the design of a novel two-objective harmony search approach for distance- and connectivity-based localization in wireless sensor networks JF - Engineering Applications of Artificial Intelligence Y1 - 2013 A1 - Diana Manjarres A1 - Javier Del Ser A1 - Sergio Gil-Lopez A1 - Massimo Vecchio A1 - Itziar Landa-Torres A1 - Sancho Salcedo-Sanz A1 - R. López-Valcarce KW - dynacs KW - wsn VL - 26 IS - 2 ER - TY - CONF T1 - A Diffusion-based distributed EM algorithm for density estimation in wireless sensor networks T2 - Int. Conf. Acoust., Speech, Signal Process. (ICASSP) Y1 - 2013 A1 - Silvana Silva Pereira A1 - Alba Pagès-Zamora A1 - R. López-Valcarce KW - dynacs KW - wsn AB -
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.
JF - Int. Conf. Acoust., Speech, Signal Process. (ICASSP) ER - TY - JOUR T1 - A Diffusion-Based EM Algorithm for Distributed Estimation in Unreliable Sensor Networks JF - IEEE Signal Processing Letters Y1 - 2013 A1 - Silvana Silva Pereira A1 - R. López-Valcarce A1 - Alba Pagès-Zamora KW - dynacs KW - wsn AB -

We address the problem of distributed estimation of a parameter from a set of noisy observations collected by a sensor network, assuming that some sensors may be subject to data failures and report only noise. In such scenario, simple schemes such as the Best Linear Unbiased Estimator result in an error floor in moderate and high signal-to-noise ratio (SNR), whereas previously proposed methods based on hard decisions on data failure events degrade as the SNR decreases. Aiming at optimal performance within the whole range of SNRs, we adopt a Maximum Likelihood framework based on the Expectation-Maximization (EM) algorithm. The statistical model and the iterative nature of the EM method allow for a diffusion-based distributed implementation, whereby the information propagation is embedded in the iterative update of the parameters. Numerical examples show that the proposed algorithm practically attains the Cramer–Rao Lower Bound at all SNR values and compares favorably with other approaches.

VL - 20 IS - 6 ER - TY - CONF T1 - Learning Based Link Adaptation in Multiuser MIMO-OFDM T2 - 21st European Signal Processing Conference 2013 (EUSIPCO 2013) Y1 - 2013 A1 - Alberto Rico-Alvariño A1 - Robert W. Heath Jr. KW - dynacs KW - link adaptation KW - Machine Learning KW - Multiuser MIMO-OFDM AB -

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.

JF - 21st European Signal Processing Conference 2013 (EUSIPCO 2013) CY - Marrakech, Morocco ER - TY - CONF T1 - Link Adaptation in MIMO-OFDM with Practical Impairments T2 - Asilomar Conference on Signals Systems and Computers Y1 - 2013 A1 - Alberto Rico-Alvariño A1 - Robert W. Heath Jr. KW - dynacs KW - link adaptation KW - MIMO-OFDM JF - Asilomar Conference on Signals Systems and Computers ER - TY - CONF T1 - Low Complexity Primary User Protection for Cognitive OFDM T2 - European Signal Processing Conf. (EUSIPCO), Marrakech (Morocco) Y1 - 2013 A1 - Schmidt, J.F. A1 - R. López-Valcarce KW - cognitive radio KW - dynacs KW - spectrum shaping JF - European Signal Processing Conf. (EUSIPCO), Marrakech (Morocco) ER - TY - JOUR T1 - MMSE Performance Analysis of Generalized Multibeam Satellite Channels JF - Communications Letters, IEEE Y1 - 2013 A1 - Christopoulos, D. A1 - J. Arnau A1 - Chatzinotas, S. A1 - C. Mosquera A1 - Ottersten, B. KW - dynacs KW - linear minimum mean square error receivers KW - multibeam satellites KW - Multiuser detection KW - return link KW - satcom ER - TY - JOUR T1 - A novel heuristic approach for distance- and connectivity-based multihop node localization in wireless sensor networks JF - Soft Computing Y1 - 2013 A1 - Diana Manjarres A1 - Javier Del Ser A1 - Sergio Gil-Lopez A1 - Massimo Vecchio A1 - Itziar Landa-Torres A1 - R. López-Valcarce KW - dynacs KW - wsn VL - 17 IS - 1 ER - TY - CONF T1 - Open Loop Adaptive Coding and Modulation for Mobile Satellite Return Links T2 - 31st AIAA International Communications Satellite Systems Conference Y1 - 2013 A1 - Arnau, Jesus A1 - Carlos Mosquera KW - dynacs KW - link adaptation KW - satcom JF - 31st AIAA International Communications Satellite Systems Conference PB - American Institute of Aeronautics and Astronautics CY - Florence, Italy U1 -

http://dx.doi.org/10.2514/6.2013-5704

ER - TY - CONF T1 - Power Spectrum Blind Sampling Using Minimum Mean Square Error and Weighted Least Squares T2 - Asilomar Conference on Signals, Systems and Computers Y1 - 2013 A1 - Bamrung TauSiesakul A1 - Nuria González-Prelcic KW - cognitive radio KW - dynacs JF - Asilomar Conference on Signals, Systems and Computers ER - TY - CONF T1 - Spectrum Sensing in Time-Varying Channels Using Multiple Antennas T2 - IEEE 14th Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC), Darmstadt (Germany) Y1 - 2013 A1 - Daniel Romero A1 - R. López-Valcarce KW - cognitive radio KW - dynacs KW - spectrum sensing JF - IEEE 14th Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC), Darmstadt (Germany) ER - TY - CONF T1 - Statistical Cross Layer Adaptation in Fast Fading Mobile Satellite Channels T2 - Globecom 2013 - Symposium on Selected Areas in Communications (GC13 SAC) Y1 - 2013 A1 - Alberto Rico-Alvariño A1 - J. Arnau A1 - C. Mosquera KW - dynacs KW - fast fading channels KW - link adaptation KW - mobile satellite KW - satcom AB -

Link 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.

JF - Globecom 2013 - Symposium on Selected Areas in Communications (GC13 SAC) CY - Atlanta, USA ER - TY - JOUR T1 - Wideband Spectrum Sensing From Compressed Measurements Using Spectral Prior Information JF - IEEE Trans. Signal Process. Y1 - 2013 A1 - Daniel Romero A1 - Geert Leus KW - cognitive radio KW - compressed sensing KW - dynacs KW - spectrum sensing VL - 61 ER - TY - JOUR T1 - An Adaptive Feedback Canceller for Full-Duplex Relays Based on Spectrum Shaping JF - IEEE J. Selected Areas in Communications Y1 - 2012 A1 - R. López-Valcarce A1 - Emilio Antonio-Rodríguez A1 - C. Mosquera A1 - Fernando Pérez-González KW - adaptive signal processing KW - dynacs KW - full duplex AB -
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.
VL - 30 IS - 8 ER - TY - CONF T1 - Adaptive self-interference suppression for full-duplex relays with multiple receive antennas T2 - IEEE 13th Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC 2012) Y1 - 2012 A1 - Emilio Antonio-Rodríguez A1 - R. López-Valcarce KW - adaptive signal processing KW - dynacs KW - full duplex AB -
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.
JF - IEEE 13th Int. Workshop on Signal Processing Advances in Wireless Communications (SPAWC 2012) PB - IEEE CY - Çesme, Turkey ER - TY - CONF T1 - Adaptive Transmission Techniques for Mobile Satellite Links T2 - 30th AIAA International Communications Satellite Systems Conference (ICSSC) Y1 - 2012 A1 - Arnau, Jesus A1 - Alberto Rico-Alvariño A1 - C. Mosquera KW - dynacs KW - satcom JF - 30th AIAA International Communications Satellite Systems Conference (ICSSC) CY - Ottawa, Canada U1 -
Best Proffesional Paper Award
ER - TY - CONF T1 - Detection of Gaussian signals in unknown time-varying channels T2 - IEEE Statistical Signal Processing Workshop (SSP 2012) Y1 - 2012 A1 - Daniel Romero A1 - Javier Vía A1 - R. López-Valcarce A1 - Ignacio Santamaría KW - cognitive radio KW - dynacs KW - spectrum sensing AB -
Detecting the presence of a white Gaussian signal distorted by a noisy time-varying channel is addressed by means of three different detectors. First, the generalized likelihood ratio test (GLRT) is found for the case where the channel has no temporal structure, resulting in the well-known Bartlett’s test. Then it is shown that, under the transformation group given by scaling factors, a locally most powerful invariant test (LMPIT) does not exist. Two alternative approaches are explored in the low signal-to-noise ratio (SNR) regime: the first assigns a prior probability density function (pdf) to the channel (hence modeled as random), whereas the second assumes an underlying basis expansion model (BEM) for the (now deterministic) channel and obtains the maximum likelihood (ML) estimates of the parameters relevant for the detection problem. The performance of these detectors is evaluated via Monte Carlo simulation.
JF - IEEE Statistical Signal Processing Workshop (SSP 2012) PB - IEEE CY - Ann Arbor, MI ER - TY - CONF T1 - Detection of unknown constant magnitude signals in time-varying channels T2 - 3rd Int. Workshop on Cognitive Information Processing (CIP 2012) Y1 - 2012 A1 - Daniel Romero A1 - R. López-Valcarce KW - cognitive radio KW - dynacs KW - spectrum sensing AB -

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.

JF - 3rd Int. Workshop on Cognitive Information Processing (CIP 2012) CY - Baiona, Spain ER - TY - CONF T1 - On the Effect of Echoes in Hybrid Terrestrial-Satellite Single Frequency Networks: Analysis and Countermeasures T2 - 2012 6th Advanced Satellite Multimedia Systems Conference (ASMS) and 12th Signal Processing for Space Communications Workshop (SPSC) (ASMS/SPSC 2012) Y1 - 2012 A1 - Alberto Rico-Alvariño A1 - C. Mosquera KW - dynacs KW - Effective SNR KW - Hybrid Terrestrial- Satellite KW - satcom KW - Satellite OFDM KW - Single Frequency Network KW - Space-Time Coding AB -

Hybrid 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.

JF - 2012 6th Advanced Satellite Multimedia Systems Conference (ASMS) and 12th Signal Processing for Space Communications Workshop (SPSC) (ASMS/SPSC 2012) CY - Baiona, Spain ER - TY - CONF T1 - Generalized matched filter detector for fast fading channels T2 - IEEE Int. Conf. on Acoustics, Speech and Signal Processing (ICASSP 2012) Y1 - 2012 A1 - Daniel Romero A1 - R. López-Valcarce A1 - Geert Leus KW - cognitive radio KW - dynacs KW - spectrum sensing AB -
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.
JF - IEEE Int. Conf. on Acoustics, Speech and Signal Processing (ICASSP 2012) PB - IEEE CY - Kyoto, Japan ER - TY - JOUR T1 - Multiantenna GLR detection of rank-one signals with known power spectrum in white noise with unknown spatial correlation JF - IEEE Trans. on Signal Processing Y1 - 2012 A1 - Josep Sala A1 - Gonzalo Vázquez-Vilar A1 - R. López-Valcarce KW - cognitive radio KW - dynacs AB -
Multiple-antenna detection of a Gaussian signal with spatial rank one in temporally white Gaussian noise with arbitrary and  unknown spatial covariance is considered. This is motivated by spectrum sensing problems in the context of Dynamic Spectrum Access in which several secondary networks coexist but do not cooperate, creating a background of spatially correlated broadband interference. When the temporal correlation of the signal of interest is assumed known up to a scale factor, the corresponding Generalized Likelihood Ratio Test is shown to yield a scalar optimization problem. Closed-form expressions of the test are obtained for the general signal spectrum case in the low signal-to-noise ratio (SNR) regime, as well as for signals with binary-valued power spectrum in arbitrary SNR. The two resulting detectors turn out to be equivalent. An asymptotic approximation to the test distribution for the low-SNR regime is derived, closely matching empirical results from spectrum sensing simulation experiments.
VL - 60 IS - 6 ER - TY - CONF T1 - Multiuser Detection Performance in Multibeam Satellite Links under Imperfect CSI T2 - ASILOMAR 2012 Y1 - 2012 A1 - Arnau, Jesus A1 - C. Mosquera KW - dynacs KW - satcom JF - ASILOMAR 2012 CY - Pacific Grove, CA U1 -
Accepted for publication
ER - TY - CONF T1 - Optimum Training for CSI Acquisition in Cognitive Radio Channels T2 - Asilomar Conference on Signals, Systems, and Computers Y1 - 2012 A1 - Alberto Rico-Alvariño A1 - C. Mosquera KW - adaptive signal processing KW - cognitive radio KW - dynacs JF - Asilomar Conference on Signals, Systems, and Computers CY - Pacific Grove, CA ER - TY - JOUR T1 - Overlay Cognitive Transmission in a Multicarrier Broadcast Network with Dominant Line of Sight Reception JF - IEEE Transactions on Wireless Communications Y1 - 2012 A1 - Alberto Rico-Alvariño A1 - C. Mosquera A1 - Fernando Pérez-González KW - cognitive radio KW - dynacs KW - satcom ER - TY - CONF T1 - Overlay cognitive transmission in OFDM point to point systems exploiting primary feedback T2 - 3rd International Workshop on Cognitive Information Processing (CIP) Y1 - 2012 A1 - Alberto Rico-Alvariño A1 - C. Mosquera KW - cognitive radio KW - dynacs AB -

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.

JF - 3rd International Workshop on Cognitive Information Processing (CIP) CY - Baiona, Galicia, Spain ER - TY - Generic T1 - Overlay Spectrum Reuse in a Broadcast Network: Covering the Whole Grayscale of Spaces T2 - IEEE Symposium on New Frontiers in Dynamic Spectrum Access Networks (DySPAN 2012) Y1 - 2012 A1 - Alberto Rico-Alvariño A1 - C. Mosquera KW - cognitive radio KW - dynacs JF - IEEE Symposium on New Frontiers in Dynamic Spectrum Access Networks (DySPAN 2012) CY - Bellevue, WA ER - TY - CONF T1 - Overlay Spectrum Reuse in a Multicarrier Broadcast Network: Coverage Analysis T2 - The 13th IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC 2012) Y1 - 2012 A1 - Alberto Rico-Alvariño A1 - C. Mosquera A1 - Fernando Pérez-González KW - cognitive radio KW - dynacs AB -

A 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.

JF - The 13th IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC 2012) CY - Cesme, Turkey ER - TY - CONF T1 - Overlay Spectrum Reuse in a Multicarrier Broadcast Network: Single Receiver Analysis T2 - The 13th IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC 2012) Y1 - 2012 A1 - Alberto Rico-Alvariño A1 - C. Mosquera A1 - Fernando Pérez-González KW - cognitive radio KW - dynacs AB -

The 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.

JF - The 13th IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC 2012) CY - Cesme, Turkey ER - TY - CONF T1 - Performance Analysis of Multiuser Detection for Multibeam Satellites Under Rain Fading T2 - 2012 6th Advanced Satellite Multimedia Systems Conference (ASMS) and 12th Signal Processing for Space Communications Workshop (SPSC) (ASMS/SPSC 2012) Y1 - 2012 A1 - Arnau, Jesus A1 - C. Mosquera KW - dynacs KW - hybrid beamforming KW - multibeam satellites. KW - Multiuser detection KW - rain fading KW - satcom AB -

Multibeam satellite systems are nowadays widely employed, and their use is expected to grow in the next decades. This has raised the interest for signal processing techniques able to mitigate the interference among beams, since they could enable a much more aggressive spectrum reuse. From an engineering point of view, the design of the system must be no longer based on the capabilities provided by the usual physical layer; it should take into account the presence of these interference canceling techniques, predict their performance as accurately as possible -even under a number of impairments and non-idealities- and design accordingly in order to fully exploit them. In this paper, we investigate the effect of a practical impairment of great importance, namely, the attenuation due to the rain, on the performance of a return link which performs MMSE interference canceling. Analytical expressions are derived for a number of performance measures based on the statistical characterization of the rain attenuation.

JF - 2012 6th Advanced Satellite Multimedia Systems Conference (ASMS) and 12th Signal Processing for Space Communications Workshop (SPSC) (ASMS/SPSC 2012) CY - Baiona, Spain ER - TY - JOUR T1 - Detection of Rank-P Signals in Cognitive Radio Networks With Uncalibrated Multiple Antennas JF - IEEE Trans. on Signal Processing Y1 - 2011 A1 - David Ramírez A1 - Gonzalo Vázquez-Vilar A1 - R. López-Valcarce A1 - Javier Vía A1 - Ignacio Santamaría KW - cognitive radio KW - dynacs KW - spectrum sensing AB -
Spectrum sensing is a key component of the Cognitive Radio paradigm. Typically, primary signals have to be detected with uncalibrated receivers at signal-to-noise ratios (SNRs) well below decodability levels. Multiantenna detectors exploit spatial independence of receiver thermal noise to boost detection performance and robustness. We study the problem
of detecting a Gaussian signal with rank-P unknown spatial
covariance matrix in spatially uncorrelated Gaussian noise with
unknown covariance using multiple antennas. The generalized
likelihood ratio test (GLRT) is derived for two scenarios. In the
first one, the noises at all antennas are assumed to have the same (unknown) variance, whereas in the second, a generic diagonal noise covariance matrix is allowed in order to accommodate calibration uncertainties in the different antenna frontends. In the latter case, the GLRT statistic must be obtained numerically, for which an efficient method is presented. Furthermore, for asymptotically low SNR, it is shown that the GLRT does admit a closed form, and the resulting detector performs well in practice. Extensions are presented in order to account for unknown temporal correlation in both signal and noise, as well as frequency-selective channels.
VL - 59 IS - 8 ER - TY - JOUR T1 - Gain-Invariant Dirty Paper Coding for Hierarchical OFDM JF - IEEE Transactions on Communications Y1 - 2011 A1 - Scagliola, Michele A1 - Fernando Pérez-González A1 - Guccione, Pietro KW - dirty paper KW - dynacs KW - Hierarchical OFDM KW - watermarking AB -

A novel approach is here presented to superimpose a low-priority data stream on a high-priority data stream for OFDM systems. The main improvement with respect to conventional hierarchical modulation, which is included with the same purpose in various wireless technologies, is that the low-priority data stream can be decoded from the received subcarrier symbols without any previous equalization for multipath fading channels. As a consequence, the expected performance is nearly invariant of the channel estimation method used to equalize the channel. The low-priority stream is inserted adopting a gain-invariant dirty paper coding based on Rational Dither Modulation, which was proposed for data hiding applications. In this paper an analysis of the developed system is presented and several simulations have been carried out using DVB-T system parameters to verify the validity of the proposed approach. The experimental results show the better performance of the proposed method with respect to that of a conventional hierarchical modulation, particularly when the accuracy of the estimated channel response decreases.

VL - 59 ER - TY - JOUR T1 - Multiantenna Spectrum Sensing Exploiting Spectral a priori Information JF - IEEE Trans. on Wireless Communications Y1 - 2011 A1 - Gonzalo Vázquez-Vilar A1 - R. López-Valcarce A1 - Josep Sala KW - cognitive radio KW - dynacs KW - spectrum sensing VL - 10 IS - 12 ER - TY - JOUR T1 - Spectrum Sensing Exploiting Guard Bands and Weak Channels JF - IEEE Trans. on Signal Processing Y1 - 2011 A1 - Gonzalo Vázquez-Vilar A1 - R. López-Valcarce KW - cognitive radio KW - dynacs KW - spectrum sensing AB -
We address the problem of primary user detection in Cognitive Radio from a wideband signal comprising multiple primary channels, exploiting a priori knowledge about the primary network: channelization and spectral shape of primary transmissions. Using this second-order statistical information, a multichannel Gaussian model is formulated. In order to obtain a Generalized Likelihood Ratio Test, we first address Maximum Likelihood (ML) estimation of the power levels at the different channels, as well as of the noise variance. The ML conditions suggest a suboptimal closed-form estimate, which takes the form of a constrained Least Squares estimator whose asymptotic efficiency is shown for flat bandpass spectra in white noise, a case of practical importance. The resulting detectors exploit those frequency bins corresponding to guard bands and to primary channels perceived as weak to improve noise variance estimation. Analytical expressions for the probabilities of detection and false alarm are presented. Performance is evaluated via simulations in the setting of a terrestrial TV primary network with realistic channelization parameters.
VL - 59 IS - 12 ER - TY - JOUR T1 - A two-objective evolutionary approach based on topological constraints for node localization in wireless sensor networks JF - Applied Soft Computing Y1 - 2011 A1 - Massimo Vecchio A1 - R. López-Valcarce A1 - Francesco Marcelloni KW - dynacs KW - Multiobjective evolutionary algorithms KW - Node localization KW - Range measurements KW - Stochastic optimization KW - wsn AB -

To know the location of nodes plays an important role in many current and envisioned wireless sensor network applications. In this framework, we consider the problem of estimating the locations of all the nodes of a network, based on noisy distance measurements for those pairs of nodes in range of each other, and on a small fraction of anchor nodes whose actual positions are known a priori. The methods proposed so far in the literature for tackling this non-convex problem do not generally provide accurate estimates. The difficulty of the localization task is exacerbated by the fact that the network is not generally uniquely localizable when its connectivity is not sufficiently high. In order to alleviate this drawback, we propose a two-objective evolutionary algorithm which takes concurrently into account during the evolutionary process both the localization accuracy and certain topological constraints induced by connectivity considerations. The proposed method is tested with different network configurations and sensor setups, and compared in terms of normalized localization error with another metaheuristic approach, namely SAL, based on simulated annealing. The results show that, in all the experiments, our approach achieves considerable accuracies and significantly outperforms SAL, thus manifesting its effectiveness and stability.

VL - 12 IS - 7 ER -