@article {300,
	title = {Variability of moisture in coarse woody debris from several ecologically important tree species of the Temperate Zone of Europe},
	journal = {Ecohydrology},
	volume = {5},
	year = {2012},
	month = {July},
	pages = {424{\textendash}434},
	abstract = {Deadwood moisture affects multiple functions of downed logs in forest ecosystems. They include provision of habitats for xylobionts, additional water stores and organic carbon stocks. In contrast to Northern American forests, little is known about moisture variability in downed logs of important tree species within the Temperate Zone of Europe. Therefore, our study aimed at elucidating this variability according to species, site and decay class (DC). Measurements were taken by TDR during two vegetation periods in eight Carpathian natural forests representing distinct site conditions, ranging from xerothermophilous to subalpine. Downed logs of Quercus spp., Abies alba Mill., Fagus sylvatica L., and Picea abies L., belonging to various DCs, were selected and instrumented with TDR probes. Species and DC-specific TDR calibration showed the importance of intrinsic wood porosity. The course of deadwood moisture consisted of drying during the early decay stage, except for A. alba and F. sylvatica, and an intense water reabsorption at later decay stages. Average moisture for all species and sites displayed seasonal trends, reflecting the occurrence of precipitation clusters and dry periods, as well as short-term fluctuations. Cross-spectral analysis revealed that both sapwood and heartwood participated in wetting and drying processes, but only after reaching an advanced stage of decay. New findings can be applied in interpreting, modelling and predicting deadwood water stores, habitat properties and respiration.},
	doi = {10.1002/eco.235},
	url = {http://onlinelibrary.wiley.com/doi/10.1002/eco.235/abstract},
	author = {Pichler, Viliam and Homol{\'a}k, Mari{\'a}n and Skierucha, Wojciech and Pichlerov{\'a}, Magdal{\'e}na and Ram{\'\i}rez, David and Gregor, Juraj and Jaloviar, Peter}
}
@article {637,
	title = {Union Bound Minimization Approach for Designing Grassmannian Constellations},
	journal = {IEEE Transactions on Communications},
	volume = {71},
	year = {2023},
	month = {April},
	pages = {1940-1952},
	doi = {10.1109/TCOMM.2023.3244965},
	author = {Cuevas, Diego and Alvarez-Vizoso, Javier and Beltr{\'a}n, Carlos and Santamar{\'\i}a, Ignacio and Tucek, V{\'\i}t and Peters, Gunnar}
}
@article {Trans_Wireless_Comm_2007,
	title = {Tight closed-form approximation for the ergodic capacity of orthogonal {STBC}},
	journal = {IEEE Transactions on Wireless Communications},
	volume = {6},
	number = {2},
	year = {2007},
	month = {February},
	pages = {452{\textendash}457},
	author = {P{\'e}rez, Jes{\'u}s and Ib{\'a}{\~n}ez, Jes{\'u}s and Vielva, Luis and P{\'e}rez-Blanco, David J. and Santamar{\'\i}a, Ignacio}
}
@article {532,
	title = {Testing Equality of Multiple Power Spectral Densities},
	journal = {IEEE Transactions on Signal Processing},
	volume = {66},
	year = {2018},
	month = {December},
	pages = {6268-6280},
	abstract = {This work studies the existence of optimal invariant detectors for determining whether P multivariate processes have the same power spectral density (PSD). This problem finds application in multiple fields, including physical layer security and cognitive radio. For Gaussian observations, we prove that
the optimal invariant detector, i.e., the uniformly most powerful invariant test (UMPIT), does not exist. Additionally, we consider the challenging case of close hypotheses, where we study the
existence of the locally most powerful invariant test (LMPIT). The LMPIT is obtained in closed form only for univariate signals. In the multivariate case, it is shown that the LMPIT does not exist.
However, the corresponding proof naturally suggests one LMPITinspired detector, which outperforms previously proposed detectors.},
	issn = {1053-587X},
	doi = {10.1109/TSP.2018.2875884},
	author = {Ram{\'\i}rez, David and Romero, Daniel and V{\'\i}a, Javier and L{\'o}pez-Valcarce, Roberto and Santamar{\'\i}a, Ignacio}
}
@article {367,
	title = {Testing blind separability of complex Gaussian mixtures},
	journal = {Signal Processing},
	volume = {95},
	year = {2014},
	month = {February},
	pages = {49{\textendash}57},
	abstract = {The separation of a complex mixture based solely on second-order statistics can be achieved using the Strong Uncorrelating Transform (SUT) if and only if all sources have distinct circularity coefficients. However, in most problems we do not know the circularity coefficients, and they must be estimated from observed data. In this work, we propose a detector, based on the generalized likelihood ratio test (GLRT), to test the separability of a complex Gaussian mixture using the SUT. For the separable case (distinct circularity coefficients), the maximum likelihood (ML) estimates are straightforward. On the other hand, for the non-separable case (at least one circularity coefficient has multiplicity greater than one), the ML estimates are much more difficult to obtain. To set the threshold, we exploit Wilks{\textquoteright} theorem, which gives the asymptotic distribution of the GLRT under the null hypothesis. Finally, numerical simulations show the good performance of the proposed detector and the accuracy of Wilks{\textquoteright} approximation.},
	doi = {10.1016/j.sigpro.2013.08.010},
	author = {Ram{\'\i}rez, David and Schreier, Peter J. and V{\'\i}a, Javier and Santamar{\'\i}a, Ignacio}
}
@article {Neurocomputing_2005_a,
	title = {Support vector regression for the simultaneous learning of a multivariate function and its derivatives},
	journal = {Neurocomputing},
	volume = {69},
	year = {2005},
	pages = {42{\textendash}61},
	author = {L{\'a}zaro, Marcelino and Santamar{\'\i}a, Ignacio and P{\'e}rez-Cruz, Fernando and Art{\'e}s, Antonio}
}
@article {549,
	title = {Subspace Averaging and Order Determination for Source Enumeration},
	journal = {IEEE Transactions on Signal Processing},
	volume = {67},
	year = {2019},
	month = {June},
	pages = {3028-3041},
	abstract = {In this paper we address the problem of subspace averaging, with special emphasis placed on the question of estimating the dimension of the average. The results suggest that the enumeration of sources in a multi-sensor array, which is a problem of estimating the dimension of the array manifold, and as a consequence the number of radiating sources, may be cast as a problem of averaging subspaces. This point of view stands in contrast to conventional approaches, which cast the problem as one of identifiying covariance models in a factor model. We present a robust formulation of the proposed order fitting rule based on majorization-minimization algorithms. A key element of the proposed method is to construct a bootstrap procedure, based on a newly proposed discrete distribution on the manifold of projection matrices, for stochastically generating subspaces from a function of experimentally-determined eigenvalues. In this way, the proposed subspace averaging (SA) technique determines the order based on the eigenvalues of an average projection matrix, rather than on the likelihood of a covariance model, penalized by functions of the model order. By means of simulation examples, we show that the proposed SA criterion is especially effective in high-dimensional scenarios with low sample support.},
	doi = {10.1109/TSP.2019.2912151},
	author = {Garg, Vaibhav and Santamar{\'\i}a, Ignacio and Ram{\'\i}rez, David and Louis L. Scharf}
}
@article {Trans_Signal_Proc_2005,
	title = {Stochastic blind equalization based on pdf fitting using {Parzen} estimator},
	journal = {IEEE Transactions on Signal Processing},
	volume = {53},
	number = {2},
	year = {2005},
	month = {February},
	pages = {696{\textendash}704},
	author = {L{\'a}zaro, Marcelino and Santamar{\'\i}a, Ignacio and Erdogmus, Deniz and Hild II, K. E. and Pantale{\'o}n, Carlos and Pr{\'\i}ncipe, Jos{\'e} C.}
}
@article {655,
	title = {Statistical Characterization of the Chordal Product Determinant of Grassmannian Codes},
	journal = {Information and Inference: A journal of the IMA},
	volume = {12},
	year = {2023},
	month = {September},
	doi = {10.1093/imaiai/iaad035},
	author = {Alvarez-Vizoso, Javier and Beltr{\'a}n, Carlos and Cuevas, Diego and Santamar{\'\i}a, Ignacio and Tucek, V{\'\i}t and Peters, Gunnar}
}
@article {Trans_Ant_Prop_2001,
	title = {Stationary phase method application for the analysis of radiation of complex {3-D} conducting structures},
	journal = {IEEE Transactions on Antennas and Propagation},
	volume = {49},
	number = {5},
	year = {2001},
	month = {May},
	pages = {724-731},
	author = {Conde, O. and P{\'e}rez, Jes{\'u}s and C{\'a}tedra, M. F.}
}
@article {Trans_Neural_Networks_2006,
	title = {A spectral clustering approach to underdetermined post-nonlinear blind source separation of sparse sources},
	journal = {IEEE Transactions on Neural Networks},
	volume = {17},
	number = {3},
	year = {2006},
	month = {May},
	pages = {811{\textendash}814},
	abstract = {This letter proposes a clustering-based approach for solving the underdetermined (i.e., fewer mixtures than sources) postnonlinear blind source separation (PNL BSS) problem when the sources are sparse. Although various algorithms exist for the underdetermined BSS problem for sparse sources, as well as for the PNL BSS problem with as many mixtures as sources, the nonlinear problem in an underdetermined scenario has not been satisfactorily solved yet. The method proposed in this letter aims at inverting the different nonlinearities, thus reducing the problem to linear underdetermined BSS. To this end, first a spectral clustering technique is applied that clusters the mixture samples into different sets corresponding to the different sources. Then, the inverse nonlinearities are estimated using a set of multilayer perceptrons (MLPs) that are trained by minimizing a specifically designed cost function. Finally, transforming each mixture by its corresponding inverse nonlinearity results in a linear underdetermined BSS problem, which can be solved using any of the existing methods.},
	author = {Van Vaerenbergh, Steven and Santamar{\'\i}a, Ignacio}
}
@article {651,
	title = {Spectral and Energy Efficiency Maximization of MISO STAR-RIS-Assisted URLLC Systems},
	journal = {IEEE Access},
	volume = {1},
	year = {2023},
	month = {July},
	pages = {70833-70852},
	doi = {10.1109/ACCESS.2023.3294092},
	author = {Mohammad Soleymani and Santamar{\'\i}a, Ignacio and Jorswieck, Eduard}
}
@article {484,
	title = {Spatial interference shaping for underlay MIMO cognitive networks},
	journal = {Signal Processing},
	volume = {134},
	year = {2017},
	pages = {174-184},
	doi = {j.sigpro.2016.12.012},
	author = {Lameiro, Christian and Utschick, Wolfgang and Santamar{\'\i}a, Ignacio}
}
@article {406,
	title = {Sparse Multivariate Gaussian Mixture Regression},
	journal = {IEEE Transactions on Neural Networks and Learning Systems},
	volume = {26},
	year = {2015},
	month = {May},
	pages = {1098-1108},
	doi = {10.1109/TNNLS.2014.2334596},
	author = {Luis Weruaga and V{\'\i}a, Javier}
}
@article {Eurasip_Signal_Proc_1996_a,
	title = {Sparse Deconvolution Using Adaptive Mixed-Gaussian Models},
	journal = {Signal Processing (EURASIP)},
	volume = {54},
	year = {1996},
	pages = {161{\textendash}172},
	author = {Santamar{\'\i}a, Ignacio and Pantale{\'o}n, Carlos and Art{\'e}s, Antonio}
}
@article {653,
	title = {SNR Maximization in Beyond Diagonal RIS-assisted Single and Multiple Antenna Links},
	journal = {IEEE Signal Processing Letters},
	volume = {30},
	year = {2023},
	month = {August},
	pages = {923-926},
	doi = {10.1109/LSP.2023.3296902},
	author = {Santamar{\'\i}a, Ignacio and Mohammad Soleymani and Jorswieck, Eduard and Guti{\'e}rrez, Jes{\'u}s}
}
@article {Trans_Cir_Sys_2001,
	title = {Smoothing the Canonical Piecewise-Linear Model: An Efficient and Derivable Large-Signal Model for {MESFET/HEMT} Transistors},
	journal = {IEEE Transactions on Circuits and Systems I: Fundamental Theory and Applications},
	volume = {48},
	number = {2},
	year = {2001},
	month = {February},
	pages = {184{\textendash}192},
	author = {L{\'a}zaro, Marcelino and Santamar{\'\i}a, Ignacio and Pantale{\'o}n, Carlos and Mediavilla, A. and Taz{\'o}n, A. and Navarro, C.}
}
@article {Trans_Comm_2004,
	title = {A Simple Expression for the Optimization of Spread-Spectrum Code Acquisition Detectors Operating in the Presence of Carrier-Frequency Offset},
	journal = {IEEE Transactions on Communications},
	volume = {52},
	number = {4},
	year = {2004},
	month = {April},
	pages = {550{\textendash}552},
	author = {D{\'\i}ez, J. and Pantale{\'o}n, Carlos and Vielva, Luis and Santamar{\'\i}a, Ignacio and Ib{\'a}{\~n}ez, Jes{\'u}s}
}
@article {352,
	title = {Semi-Supervised Object Recognition Based on Connected Image Transformations},
	journal = {Expert Systems with Applications},
	volume = {40},
	year = {2013},
	month = {December},
	pages = {7069--7079},
	abstract = {We present a novel semi-supervised classifier model based on paths between unlabeled and labeled data through a sequence of local pattern transformations. A reliable measure of path-length is proposed that combines a local dissimilarity measure between consecutive patters along a path with a global, connectivity-based metric. We apply this model to problems of object recognition, for which we propose a practical classification algorithm based on sequences of "Connected Image Transformations" (CIT). Experimental results on four popular image benchmarks demonstrate how the proposed CIT classifier outperforms state-of-the-art semi-supervised techniques. The results are particularly significant when only a very small number of labeled patterns is available: the proposed algorithm obtains a generalization error of 4.57\% on the MNIST data set trained on 2000 randomly chosen patterns with only 10 labeled patterns per digit class.},
	issn = {0957-4174},
	doi = {10.1016/j.eswa.2013.06.029},
	author = {Van Vaerenbergh, Steven and Santamar{\'\i}a, Ignacio and Barbano, Paolo Emilio}
}
@article {596,
	title = {Scale-Invariant Subspace Detectors based on First and Second-Order Statistical Models},
	journal = {IEEE Transactions on Signal Processing},
	volume = {68},
	year = {2020},
	pages = {6432-6443},
	doi = {10.1109/TSP.2020.3036725},
	author = {Santamar{\'\i}a, Ignacio and Louis L. Scharf and Ram{\'\i}rez, David}
}
@article {547,
	title = {Robust Improper Signaling for Two-user SISO Interference Channels},
	journal = {IEEE Transactions on Communications},
	volume = {67},
	year = {2019},
	month = {July},
	pages = {4709-4723},
	abstract = {It has been shown that improper Gaussian signaling (IGS) can improve the performance of wireless interference limited systems when perfect channel state information (CSI) is available. In this paper, we investigate the robustness of IGS against imperfect CSI on the transmitter side in a two-user single-input single-output (SISO) interference channel (IC) as well as in a SISO Z-IC, when interference is treated as noise. We assume that the true channel coefficients belong to a known region around the channel estimates, which we call the uncertainty region. Following a worst-case robustness approach, we study the rate-region boundary of the IC for the worst channel in the uncertainty region. For the two-user IC, we derive a robust design in closed-form, which is independent of the phase of the channels by allowing only one of the users to transmit IGS. For the Z-IC, we provide a closed-form design for the transmission parameters by considering an enlarged uncertainty region and allowing both users to employ IGS. In both cases, the IGS-based designs are ensured to perform no worse than proper Gaussian signaling. Furthermore, we show, through numerical examples, that the proposed robust designs significantly outperform non-robust solutions.},
	keywords = {Achievable rate region, imperfect CSI, improper Gaussian signaling, two-user interference channel, worst-case robustness.},
	doi = {10.1109/TCOMM.2019.2910549},
	author = {Mohammad Soleymani and Lameiro, Christian and Santamar{\'\i}a, Ignacio and Schreier, Peter J.}
}
@article {Trans_Signal_Proc_2007_b,
	title = {Robust array beamforming with sidelobe control using support vector machines},
	journal = {IEEE Transactions on Signal Processing},
	volume = {55},
	number = {2},
	year = {2007},
	month = {February},
	pages = {574{\textendash}584},
	author = {Gaudes, C. C. and Santamar{\'\i}a, Ignacio and V{\'\i}a, Javier and Masgrau, Enrique and Sese, T.}
}
@article {Eurasip_Signal_Proc_2003_a,
	title = {A regularized technique for the simultaneous reconstruction of a function and its derivatives with application to nonlinear transistor modeling},
	journal = {Signal Processing},
	volume = {83},
	year = {2003},
	pages = {1859{\textendash}1870},
	author = {L{\'a}zaro, Marcelino and Santamar{\'\i}a, Ignacio and Pantale{\'o}n, Carlos and Ib{\'a}{\~n}ez, Jes{\'u}s and Vielva, Luis}
}
@article {Electronic_Letters_2006,
	title = {Regularised approach to detection of constant modulus signals in {MIMO} channels},
	journal = {Electronic Letters},
	volume = {42},
	number = {3},
	year = {2006},
	month = {February},
	pages = {184{\textendash}186},
	author = {Ram{\'\i}rez, David and Santamar{\'\i}a, Ignacio}
}
@article {Electronic_Letters_1992,
	title = {{RCS} of electrically large targets modelled with {NURBS} surfaces},
	journal = {Electronic Letters},
	volume = {28},
	number = {12},
	year = {1992},
	month = {June},
	pages = {1119{\textendash}1121},
	author = {P{\'e}rez, Jes{\'u}s and C{\'a}tedra, M. F.}
}
@article {Aces_Journal_2000,
	title = {Ray-tracing techniques for mobile communications},
	journal = {Applied Computacional Electromagnetics Society (ACES) Journal},
	volume = {15},
	number = {3},
	year = {2000},
	month = {November},
	pages = {209{\textendash}231},
	author = {Guti{\'e}rrez, O. and Saez de Adana, F. and Gonz{\'a}lez, I. and P{\'e}rez, Jes{\'u}s and C{\'a}tedra, M. F.}
}
@article {631,
	title = {Rate Splitting in MIMO RIS-assisted Systems with Hardware Impairments and Improper Signaling},
	journal = {IEEE Transactions on Vehicular Technology},
	volume = {72},
	year = {2023},
	month = {April},
	pages = {4580-4597},
	doi = {10.1109/TVT.2022.3222633},
	author = {Mohammad Soleymani and Santamar{\'\i}a, Ignacio and Jorswieck, Eduard}
}
@article {487,
	title = {Rate Region Boundary of the SISO Z-interference Channel with Improper Signaling},
	journal = {IEEE Transactions on Communications},
	volume = {65},
	year = {2017},
	month = {March},
	pages = {1022-1024},
	abstract = {This paper provides a complete characterization of the boundary of an achievable rate region, called the Pareto boundary, of the single-antenna Z interference channel (Z-IC), when interference is treated as noise and users transmit complex Gaussian signals that are allowed to be improper. By considering the augmented complex formulation, we derive a necessary and sufficient condition for improper signaling to be optimal. This condition is stated as a threshold on the interference channel coefficient, which is a function of the interfered user rate and which allows insightful interpretations into the behavior of the achievable rates in terms of the circularity coefficient (i.e., degree of impropriety). Furthermore, the optimal circularity coefficient is provided in closed form. The simplicity of the obtained characterization permits interesting insights into when and how improper signaling outperforms proper signaling in the singleantenna Z-IC. We also provide an in-depth discussion on the
optimal strategies and the properties of the Pareto boundary.},
	issn = {0090-6778},
	doi = {10.1109/TCOMM.2016.2641948},
	author = {Lameiro, Christian and Santamar{\'\i}a, Ignacio and Schreier, Peter J.}
}
@article {Via_QICA_TSP2011,
	title = {Quaternion {ICA} From Second-Order Statistics},
	journal = {IEEE Transactions on Signal Processing},
	volume = {59},
	number = {4},
	year = {2011},
	month = {April},
	pages = {1586{\textendash}1600},
	author = {V{\'\i}a, Javier and Palomar, Daniel P. and Vielva, Luis and Santamar{\'\i}a, Ignacio}
}
@article {407,
	title = {A Quadratically Convergent Method for Interference Alignment in MIMO Interference Channels},
	journal = {IEEE Signal Processing Letters},
	volume = {21},
	year = {2014},
	month = {November},
	pages = {1423-1427},
	keywords = {alternating minimization, Gauss-Newton, interference alignment, interference channel, steepest descent},
	doi = {10.1109/LSP.2014.2338132},
	author = {Gonz{\'a}lez, {\'O}scar and Lameiro, Christian and Santamar{\'\i}a, Ignacio}
}
@article {Trans_Info_Theory_2010_QuaternionWL,
	title = {Properness and Widely Linear Processing of Quaternion Random Vectors},
	journal = {IEEE Transactions on Information Theory},
	volume = {56},
	number = {7},
	year = {2010},
	month = {July},
	pages = {3502{\textendash}3515},
	author = {V{\'\i}a, Javier and Ram{\'\i}rez, David and Santamar{\'\i}a, Ignacio}
}
@article {Trans_Veh_Tech_2000,
	title = {Propagation model based on ray-tracing for the design of personal communication systems in indoor environments},
	journal = {IEEE Transactions on Vehicular Technology},
	volume = {49},
	number = {6},
	year = {2000},
	month = {November},
	pages = {2105{\textendash}2112},
	author = {Saez de Adana, F. and Guti{\'e}rrez, O. and Gonz{\'a}lez, I. and P{\'e}rez, Jes{\'u}s and C{\'a}tedra, M. F.}
}
@article {Eurasip_JWCN_2009,
	title = {Performance Analysis of {SNR}-Based Scheduling Policies in Asymmetric Broadcast Ergodic Fading Channel},
	journal = {EURASIP Journal on Wireless Communications and Networking},
	year = {2009},
	author = {P{\'e}rez, Jes{\'u}s and Ib{\'a}{\~n}ez, Jes{\'u}s and V{\'\i}a, Javier and Santamar{\'\i}a, Ignacio}
}
@article {625,
	title = {Passive sampling in reproducing kernel Hilbert spaces using leverage scores},
	journal = {Signal Processing},
	volume = {199},
	year = {2022},
	month = {May},
	abstract = {This paper deals with the selection of the training dataset in kernel-based methods for function reconstruction, with a focus on kernel ridge regression. A functional analysis is performed which, in the absence of noise, links the optimal sampling distribution to the one minimizing the difference between the kernel matrix and its low-rank Nystr{\"o}m approximation. From this standpoint, a statistical passive sampling approach is derived which uses the leverage scores of the columns of the kernel matrix to design a sampling distribution that minimizes an upper bound of the risk function. The proposed approach constitutes a passive method, able to select the optimal subset of training samples using only information provided by the input set and the kernel, but without needing to know the values of the function to be approximated. Furthermore, the proposed approach is backed up by numerical tests on real datasets.},
	doi = {https://doi.org/10.1016/j.sigpro.2022.108603},
	author = {Gimenez-Febrer, Pere and Pages-Zamora, Alba and Santamar{\'\i}a, Ignacio}
}
@article {494,
	title = {Passive Detection of Correlated Subspace Signals in Two MIMO Channels},
	journal = {IEEE Transactions on Signal Processing},
	volume = {65},
	year = {2017},
	month = {October},
	pages = {5266-5280},
	doi = {10.1109/TSP.2017.2723340},
	author = {Santamar{\'\i}a, Ignacio and Louis L. Scharf and V{\'\i}a, Javier and Wang, Yuan and Wang, Haonan}
}
@article {omgp_pr,
	title = {Overlapping Mixtures of Gaussian Processes for the Data Association Problem},
	journal = {Pattern Recognition},
	volume = {45},
	number = {4},
	year = {2012},
	month = {April},
	pages = {1386{\textendash}1395},
	abstract = {In this work we introduce a mixture of GPs to address the data association problem, i.e. to label a group of observations according to the sources that generated them. Unlike several previously proposed GP mixtures, the novel mixture has the distinct characteristic of using no gating function to determine the association of samples and mixture components. Instead, all the GPs in the mixture are global and samples are clustered following {\textquotedblleft}trajectories{\textquotedblright} across input space. We use a non-standard variational Bayesian algorithm to efficiently recover sample labels and learn the hyperparameters. We show how multi-object tracking problems can be disambiguated and also explore the characteristics of the model in traditional regression settings.},
	issn = {0031-3203},
	author = {L{\'a}zaro-Gredilla, Miguel and Van Vaerenbergh, Steven and Lawrence, Neil D.}
}
@article {611,
	title = {Order Estimation via Matrix Completion for Multi-Switch Antenna Selection},
	journal = {IEEE Signal Processing Letters},
	volume = {28},
	year = {2021},
	pages = {2063-2067},
	abstract = {This letter addresses the problem of order estimation for uniform linear arrays (ULAs) with multi-switch antenna
selection in the small-sample regime. Multi-switch antenna selection results in a data matrix with missing entries, a scenario for which existing order estimation methods that build on the eigenvalues of the sample covariance matrix do not perform well. A direct application of the Davis-Kahan theorem allows us to
show that the signal subspace is quite robust in the presence of missing entries. Based on this finding, this letter proposes a matrix completion (MC) subspace-based order estimation criterion that exploits the shift-invariance property of ULAs. A recently proposed shift-invariant matrix completion (SIMC) method is used for reconstructing the data matrix, and the proposed order estimation criterion is based on the chordal subspace distance between two submatrices extracted from the reconstructed matrix for increasing values of the dimension of
the signal subspace. Our simulation results show that the method provides accurate order estimates with percentages of missing entries higher than 50\%.},
	doi = {10.1109/LSP.2021.3116525},
	author = {Garg, Vaibhav and Pages-Zamora, Alba and Santamar{\'\i}a, Ignacio}
}
@article {660,
	title = {Optimization of Rate-Splitting Multiple Access in Beyond Diagonal RIS-assisted URLLC Systems},
	journal = {IEEE Transactions on Wireless Communications},
	year = {2023},
	doi = {10.1109/TWC.2023.3324190},
	author = {Mohammad Soleymani and Santamar{\'\i}a, Ignacio and Jorswieck, Eduard and Clerckx,Bruno}
}
@article {Signal_Proc_Letters_2000,
	title = {Optimal Estimation of Chaotic Signals Generated by Piecewise-Linear Maps"},
	journal = {IEEE Signal Processing Letters},
	volume = {7},
	number = {8},
	year = {2000},
	month = {August},
	pages = {235{\textendash}237},
	author = {Pantale{\'o}n, Carlos and Luengo, David and Santamar{\'\i}a, Ignacio}
}
@article {Jour_Int_Mat_1999,
	title = {Optical Sensors and Their Fusion in a Quasi-Smart Structure for Real-Time Monitoring and Predictive Maintenance of Large Power Electric Power Generators},
	journal = {Journal of Intelligent Material Systems and Structures},
	volume = {9},
	number = {11},
	year = {1999},
	month = {November},
	pages = {938{\textendash}946},
	author = {L{\'o}pez-Higuera, J. M. and Cobo, A. and Morante, M. A. and Madruga, F. J. and Santamar{\'\i}a, Ignacio and Pantale{\'o}n, Carlos and Ib{\'a}{\~n}ez, Jes{\'u}s}
}
@article {621,
	title = {Online detection and SNR estimation in cooperative spectrum sensing},
	journal = {IEEE Transactions on Wireless Communications},
	volume = {21},
	year = {2022},
	month = {April},
	pages = {2521-2533},
	doi = {10.1109/TWC.2021.3113089},
	author = {P{\'e}rez, Jes{\'u}s and V{\'\i}a, Javier and Vielva, Luis and Ram{\'\i}rez, David}
}
@article {http://onlinelibrary.wiley.com/doi/10.1002/bies.200900164/pdf,
	title = {Numbers on the edges: A simplified and scalable method for quantifying the Gene Regulation Function},
	journal = {BioEssays},
	volume = {32},
	number = {4},
	year = {2010},
	month = {April},
	pages = {346{\textendash}355},
	url = {http://onlinelibrary.wiley.com/doi/10.1002/bies.200900164/pdf},
	author = {Fern{\'a}ndez-L{\'o}pez, R. and del Campo, I. and Ruiz, R. and Lanza, V. and Vielva, Luis and de la Cruz, Fernando}
}
@article {335,
	title = {On the Number of Interference Alignment Solutions for the K-User MIMO Channel with Constant Coefficients},
	journal = {IEEE Transaction on Information Theory},
	volume = {61},
	year = {2015},
	month = {November},
	pages = {6028-6048},
	abstract = {In this paper, we study the number of different interference alignment (IA) solutions that exists for the K-user multiple-input multiple-output (MIMO) interference channels with constant coefficients, when the alignment is performed via beamforming and without symbol extensions. When counting the number of IA solutions for a given problem, the most interesting case happens when the number of equations and variables of the polynomial system of equations are the same and the system is feasible. In this situation, the number of IA solutions is finite and, as we show in this paper, is given by an integral formula that can be numerically approximated using Monte Carlo integration methods. More precisely, the number of solutions is the scaled average over a subset of the solution variety (formed by all triplets of channels, precoders and decoders satisfying the IA polynomial equations) of the determinant of a certain Hermitian matrix related to the geometry of the problem. Interestingly, while the value of this determinant at an arbitrary point can be used to check the feasibility of the IA problem, the average of the determinant (properly scaled) gives us the number of solutions. Our results can be applied to arbitrary interference MIMO networks, with any number of users, antennas and streams per user.},
	doi = {10.1109/TIT.2015.2482493},
	author = {Gonz{\'a}lez, {\'O}scar and Beltr{\'a}n, Carlos and Santamar{\'\i}a, Ignacio}
}
@article {Trans_Inst_Meas_2001_b,
	title = {Nonlinearity Estimation in Power Amplifiers Based on Subsampled Temporal Data},
	journal = {IEEE Transactions on Instrumentation and Measurement},
	volume = {50},
	number = {4},
	year = {2001},
	month = {August},
	pages = {882{\textendash}887},
	author = {Ib{\'a}{\~n}ez, Jes{\'u}s and Pantale{\'o}n, Carlos and Santamar{\'\i}a, Ignacio and T. Fern{\'a}ndez and D. Mart{\'\i}nez}
}
@article {JOC_Kernel_RLS_2007,
	title = {Nonlinear System Identification using a New Sliding-Window Kernel {RLS} Algorithm},
	journal = {Journal of Communications},
	volume = {2},
	number = {3},
	year = {2007},
	month = {May},
	pages = {1{\textendash}8},
	abstract = {In this paper we discuss in detail a recently proposed kernel-based version of the recursive least-squares (RLS) algorithm for fast adaptive nonlinear filtering. Unlike other previous approaches, the studied method combines a sliding-window approach (to fix the dimensions of the kernel matrix) with conventional ridge regression (to improve generalization). The resulting kernel RLS algorithm is applied to several nonlinear system identification problems. Experiments show that the proposed algorithm is able to operate in a time-varying environment and to adjust to abrupt changes in either the linear filter or the nonlinearity.},
	keywords = {kernel adaptive filtering, KRLS},
	author = {Van Vaerenbergh, Steven and V{\'\i}a, Javier and Santamar{\'\i}a, Ignacio}
}
@article {Neurocomputing_1999,
	title = {A Nonlinear {MESFET} Model for Intermodulation Analysis Using a Generalized Radial Basis Function Network},
	journal = {Neurocomputing},
	volume = {25},
	year = {1999},
	pages = {1{\textendash}18},
	author = {Santamar{\'\i}a, Ignacio and L{\'a}zaro, Marcelino and Pantale{\'o}n, Carlos and Garc{\'\i}a, J. A. and Taz{\'o}n, A. and Mediavilla, A.}
}
@article {645,
	title = {NOMA-based Improper Signaling for Multicell MISO RIS-assisted Broadcast Channels},
	journal = {IEEE Transactions on Signal Processing},
	volume = {71},
	year = {2023},
	pages = {963-978},
	doi = {10.1109/TSP.2023.3259145},
	author = {Mohammad Soleymani and Santamar{\'\i}a, Ignacio and Jorswieck, Eduard and Rezvani, Sepehr}
}
@article {WCMC_Blind_Sel_MIMO_STBC,
	title = {A New Subspace Method for Blind Estimation of Selective {MIMO-STBC} Channels},
	journal = {Wireless Communications and Mobile Computing},
	volume = {10},
	number = {11},
	year = {2010},
	month = {November},
	pages = {1478{\textendash}1492},
	author = {V{\'\i}a, Javier and Santamar{\'\i}a, Ignacio and P{\'e}rez, Jes{\'u}s and Vielva, Luis}
}
@article {Neural_Networks_2003,
	title = {A New {EM}-Based Training Algorithm for {RBF} Networks},
	journal = {Neural Networks},
	volume = {16},
	number = {1},
	year = {2003},
	pages = {69{\textendash}77},
	author = {L{\'a}zaro, Marcelino and Santamar{\'\i}a, Ignacio and Pantale{\'o}n, Carlos}
}
@article {Trans_Inst_Meas_2001_a,
	title = {Neural Networks for Large and Small-Signal Modeling of {MESFET/HEMT} Transistors},
	journal = {IEEE Transactions on Instrumentation and Measurement},
	volume = {50},
	number = {6},
	year = {2001},
	month = {December},
	pages = {1587{\textendash}1593},
	author = {L{\'a}zaro, Marcelino and Santamar{\'\i}a, Ignacio and Pantale{\'o}n, Carlos}
}
@article {602,
	title = {Multiple Importance Sampling for Symbol Error Rate Estimation of Maximum-Likelihood Detectors in MIMO Channels},
	journal = {IEEE Transactions on Signal Processing},
	volume = {69},
	year = {2021},
	month = {March},
	pages = {1200-1212},
	abstract = {In this paper we propose a multiple importance sampling (MIS) method for the efficient symbol error rate (SER)
estimation of maximum likelihood (ML) multiple-input multipleoutput (MIMO) detectors. Given a transmitted symbol from the input lattice, obtaining the SER requires the computation of an integral outside its Voronoi region in a high-dimensional space, for which a closed-form solution does not exist. Hence, the SER must be approximated through crude or naive Monte Carlo (MC) simulations. This practice is widely used in the literature despite its inefficiency, particularly severe at high signal-to-noise-ratio (SNR) or for systems with stringent SER requirements. It is well-known
that more sophisticated MC-based techniques such as MIS, when carefully designed, can reduce the variance of the estimators in several orders of magnitude with respect to naive Monte Carlo in rare-event estimation, or equivalently, they need significantly less samples for attaining a desired performance. The proposed MIS method provides unbiased SER estimates by sampling from a mixture of components that are carefully chosen and parametrized.
The number of components, the parameters of the components, and their weights in the mixture, are automatically chosen by the proposed method. As a result, the proposed method is flexible, easy-to-use, theoretically sound, and presents a high performance in a variety of scenarios. We show in our simulations that SERs lower than 1e-8 can be accurately estimated with just 1e4 random samples.},
	author = {Elvira, Victor and Santamar{\'\i}a, Ignacio}
}
@article {538,
	title = {Multiple Importance Sampling for Efficient Symbol Error Rate Estimation},
	journal = {IEEE Signal Processing Letters},
	volume = {26},
	year = {2019},
	month = {March},
	pages = {420-424},
	abstract = {Digital constellations formed by hexagonal or other non-square two-dimensional lattices are often used in advanced
digital communication systems. The integrals required to evaluate the symbol error rate (SER) of these constellations in the presence of Gaussian noise are in general difficult to compute in closed form, and therefore Monte Carlo simulation is typically used to estimate the SER. However, naive Monte Carlo simulation can be very inefficient and requires very long simulation runs, especially at high signal-to-noise ratios. In this letter, we adapt a recently proposed multiple importance sampling (MIS) technique, called ALOE (for {\textquotedblleft}At Least One rare Event{\textquotedblright}), to this problem. Conditioned to a transmitted symbol, an error (or rare event) occurs when the observation falls in a union of half-spaces or, equivalently, outside a given polytope. The proposal distribution for ALOE samples the system conditionally on an error taking place, which makes it more efficient than other importance sampling techniques. ALOE provides unbiased SER estimates with simulation times orders of magnitude shorter than conventional Monte Carlo.},
	keywords = {Improper constellations, lattices, Monte Carlo, multiple importance sampling, symbol error rate},
	author = {Elvira, Victor and Santamar{\'\i}a, Ignacio}
}
@article {JLVSI_Signal_Proc_2004,
	title = {Multiple Composite Hypotheses Testing: A Competitive Approach},
	journal = {Journal of VLSI Signal Processing-Systems for Signal, Image, and Video Technology, (Ed. Kluwer)},
	volume = {37},
	year = {2004},
	month = {June},
	pages = {319{\textendash}331},
	author = {Luengo, David and Pantale{\'o}n, Carlos and Santamar{\'\i}a, Ignacio and Vielva, Luis and Ib{\'a}{\~n}ez, Jes{\'u}s}
}
@article {568,
	title = {Multi-Channel Factor Analysis with Common and Unique Factors},
	journal = {IEEE Transactions on Signal Processing},
	volume = {68},
	year = {2020},
	pages = {113-126},
	abstract = {This work presents a generalization of classical factor analysis (FA). Each of M channels carries measurements that share factors with all other channels, but also contains factors that are unique to the channel. Furthermore, each channel carries an additive noise whose covariance is diagonal, as is usual in factor analysis, but is otherwise unknown. This leads to a problem of multi-channel factor analysis with a specially structured covariance model consisting of shared low-rank components, unique low-rank components, and diagonal components. Under a multivariate normal model for the factors and the noises, a maximum likelihood (ML) method is presented for identifying the covariance model, thereby recovering the loading matrices and factors for the shared and unique components in each of the M multiple-input multiple-output (MIMO) channels. The method consists of a three-step cyclic alternating optimization, which can be framed as a block minorization-maximization (BMM) algorithm. Interestingly, the three steps have closed-form solutions and the convergence of the algorithm to a stationary point is ensured. Numerical results demonstrate the performance of the proposed algorithm and its application to passive radar.},
	issn = {1053-587X},
	doi = {10.1109/TSP.2019.2955829},
	author = {Ram{\'\i}rez, David and Santamar{\'\i}a, Ignacio and Louis L. Scharf and Van Vaerenbergh, Steven}
}
@article {Eurasip_Journal_App_Signal_Proc_2003,
	title = {Modeling nonlinear power amplifiers in {OFDM} systems form subsampled data: A comparative study using real measurements},
	journal = {EURASIP Journal on Applied Signal Processing,},
	volume = {12},
	year = {2003},
	month = {November},
	pages = {1219{\textendash}1228},
	author = {Santamar{\'\i}a, Ignacio and Ib{\'a}{\~n}ez, Jes{\'u}s and L{\'a}zaro, Marcelino and Pantale{\'o}n, Carlos and Vielva, Luis}
}
@article {Int_Journal_RF_1999,
	title = {Modeling {MESFETs} and {HEMTs} Intermodulation Distortion Behavior Using a {GRBF} Network},
	journal = {International Journal of RF and Microwave Computer-Aided Design},
	volume = {9},
	year = {1999},
	pages = {261{\textendash}276},
	author = {Garc{\'\i}a, J. A. and Taz{\'o}n, A. and Mediavilla, A. and Santamar{\'\i}a, Ignacio and L{\'a}zaro, Marcelino and Pantale{\'o}n, Carlos and Pedro, J. C.}
}
@article {351,
	title = {MIMO OTA Testing Based on Transmit Signal Processing},
	journal = {Hindawi International Journal of Antennas and Propagation},
	year = {2013},
	month = {May},
	abstract = {Usually,multiple-input-multiple-output (MIMO) testbeds are combined with channel emulators for testing devices and algorithms
under controlled channel conditions. In this work, we propose a simple methodology that allows over-the-air (OTA) MIMOtesting
using a MIMO testbed solely, avoiding the use of channel emulators. The MIMO channel is emulated by linearly combining the signals at the testbed transmitter.The method is fully flexible, so it is able to emulate any equivalent baseband narrowband MIMO channel by adequately selecting the weights of the linear combination. We derive closed-form expressions for the computation of such weights. To prove its feasibility, the method has been implemented and tested over a commercial MIMO testbed.},
	author = {Guti{\'e}rrez, Jes{\'u}s and Ib{\'a}{\~n}ez, Jes{\'u}s and P{\'e}rez, Jes{\'u}s}
}
@article {Eurasip_Signal_Proc_2003_b,
	title = {Maximum Margin Equalizers Trained with the Adatron Algorithm},
	journal = {Signal Processing},
	volume = {83},
	year = {2003},
	pages = {593{\textendash}602},
	author = {Santamar{\'\i}a, Ignacio and Gonz{\'a}lez, R. and Pantale{\'o}n, Carlos and Pr{\'\i}ncipe, Jos{\'e} C.}
}
@article {565,
	title = {Maximally improper signaling in underlay MIMO cognitive radio networks},
	journal = {IEEE Transactions on Signal Processing},
	year = {2019},
	abstract = {In this paper we address the problem of subspace averaging, with special emphasis placed on the question of estimating the dimension of the average. The results suggest that the enumeration of sources in a multi-sensor array, which is a problem of estimating the dimension of the array manifold, and as a consequence the number of radiating sources, may be cast as a problem of averaging subspaces. This point of view stands in contrast to conventional approaches, which cast the problem as one of identifiying covariance models in a factor model. We present a robust formulation of the proposed order fitting rule based on majorization-minimization algorithms. A key element of the proposed method is to construct a bootstrap procedure, based on a newly proposed discrete distribution on the manifold of projection matrices, for stochastically generating subspaces from a function of experimentally-determined eigenvalues. In this way, the proposed subspace averaging (SA) technique determines the order based on the eigenvalues of an average projection matrix, rather than on the likelihood of a covariance model, penalized by functions of the model order. By means of simulation examples, we show that the proposed SA criterion is especially effective in high-dimensional scenarios with low sample support.},
	doi = {10.1109/TSP.2019.2953665},
	author = {Lameiro, Christian and Santamar{\'\i}a, Ignacio and Schreier, Peter J. and Utschick, Wolfgang}
}
@article {JWCN_2011_RFMIMO,
	title = {MAC and Baseband Processors for RF-MIMO WLAN},
	journal = {EURASIP Journal on Wireless Communications and Networking},
	year = {2011},
	month = {December},
	author = {Stamenkovic, Z. and Tittelbach-Helmrich, K. and Krstic, M. and Ib{\'a}{\~n}ez, Jes{\'u}s and Elvira, Victor and Santamar{\'\i}a, Ignacio}
}
@article {Via_QLMPIT_TSP2012,
	title = {Locally Most Powerful Invariant Tests for the Properness of Quaternion Gaussian Vectors},
	journal = {IEEE Transactions on Signal Processing},
	volume = {60},
	number = {3},
	year = {2012},
	month = {March},
	pages = {997-1009},
	author = {V{\'\i}a, Javier and Vielva, Luis}
}
@article {340,
	title = {Locally Most Powerful Invariant Tests for Correlation and Sphericity of Gaussian Vectors},
	journal = {IEEE Transactions on Information Theory},
	volume = {59},
	year = {2013},
	month = {April},
	pages = {2128{\textendash}2141},
	abstract = {In this paper we study the existence of locally most powerful invariant tests (LMPIT) for the problem of testing the covariance structure of a set of Gaussian random vectors. The LMPIT is the optimal test for the case of close hypotheses, among those satisfying the invariances of the problem, and in practical scenarios can provide better performance than the typically used generalized likelihood ratio test (GLRT). The derivation of the LMPIT usually requires one to find the maximal invariant statistic for the detection problem and then derive its distribution under both hypotheses, which in general is a rather involved procedure. As an alternative, Wijsman{\textquoteright}s theorem provides the ratio of the maximal invariant densities without even finding an explicit expression for the maximal invariant. We first consider the problem of testing whether a set of N-dimensional Gaussian random vectors are uncorrelated or not, and show that the LMPIT is given by the Frobenius norm of the sample coherence matrix. Second, we study the case in which the vectors under the null hypothesis are uncorrelated and identically distributed, that is, the sphericity test for Gaussian vectors, for which we show that the LMPIT is given by the Frobenius norm of a normalized version of the sample covariance matrix. Finally, some numerical examples illustrate the performance of the proposed tests, which provide better results than their GLRT counterparts.},
	doi = {10.1109/TIT.2012.2232705},
	author = {Ram{\'\i}rez, David and V{\'\i}a, Javier and Santamar{\'\i}a, Ignacio and Louis L. Scharf}
}
@article {Neural_Networks_2007,
	title = {A learning algorithm for adaptive canonical correlation analysis of several data sets},
	journal = {Neural Networks},
	volume = {20},
	number = {1},
	year = {2007},
	month = {January},
	pages = {139{\textendash}152},
	author = {V{\'\i}a, Javier and Santamar{\'\i}a, Ignacio and P{\'e}rez, Jes{\'u}s}
}
@article {282,
	title = {Kernel Recursive Least-Squares Tracker for Time-Varying Regression},
	journal = {IEEE Transactions on Neural Networks and Learning Systems},
	volume = {23},
	year = {2012},
	month = {August},
	pages = {1313--1326},
	abstract = {In this paper, we introduce a kernel recursive least-squares (KRLS) algorithm that is able to track nonlinear, time-varying relationships in data. To this purpose, we first derive the standard KRLS equations from a Bayesian perspective (including a sensible approach to pruning) and then take advantage of this framework to incorporate forgetting in a consistent way, thus enabling the algorithm to perform tracking in nonstationary scenarios. The resulting method is the first kernel adaptive filtering algorithm that includes a forgetting factor in a principled and numerically stable manner. In addition to its tracking ability, it has a number of appealing properties. It is online, requires a fixed amount of memory and computation per time step, incorporates regularization in a natural manner and provides confidence intervals along with each prediction. We include experimental results that support the theory as well as illustrate the efficiency of the proposed algorithm.},
	keywords = {kernel adaptive filtering, KRLS},
	issn = {2162-237X},
	doi = {10.1109/TNNLS.2012.2200500},
	url = {http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6227361},
	author = {Van Vaerenbergh, Steven and L{\'a}zaro-Gredilla, Miguel and Santamar{\'\i}a, Ignacio}
}
@article {415,
	title = {Kernel Canonical Correlation Analysis for Robust Cooperative Spectrum Sensing in Cognitive Radio Networks},
	journal = {Transactions on Emerging Telecommunications Technologies},
	volume = {28},
	year = {2014},
	abstract = {Spectrum sensing is a key operation in Cognitive Radio (CR) systems, where secondary users (SUs) are able to exploit
spectrum opportunities by first detecting the presence of primary users (PUs). In a CR network composed of several
SUs, the detection accuracy can be much improved by cooperative spectrum sensing (CSS) strategies, which exploit the
spatial diversity among SUs. However, cooperative detection strategies, which are typically based on energy sensing, do
not perform satisfactorily under impairments such as non-Gaussian noise or interferences. In this paper, we propose a
scheme based on kernel canonical correlation analysis (KCCA), which is able to operate in non-ideal scenarios and in a
totally blind fashion. This technique is performed at the fusion center (FC) by exploiting the non-linear correlation among
the received signals of each SU. In this manner, statistical tests are extracted, allowing the SUs to make decisions either
autonomously at each SU or cooperatively at the FC. The performance of the KCCA-based detector is evaluated by means
of simulations and over-the-air experiments using a CR testbed composed of several Universal Radio Peripheral (USRP)
nodes. Both the simulations and the measurements show that the KCCA-based detector is able to obtain a significant
gain over a conventional energy detector, whose sensing performance is severely degraded by the presence of external
interferers.},
	keywords = {Cooperative Spectrum Sensing, Hardware Testbed, Kernel Canonical Correlation Analysis, USRP},
	issn = {2161-3915},
	doi = {10.1002/ett.2896},
	author = {Manco-V{\'a}squez, Julio and Van Vaerenbergh, Steven and V{\'\i}a, Javier and Santamar{\'\i}a, Ignacio}
}
@article {533,
	title = {Kafnets: Kernel-based non-parametric activation functions for neural networks},
	journal = {Neural Networks},
	volume = {110},
	year = {2019},
	month = {February},
	pages = {19-32},
	doi = {10.1016/j.neunet.2018.11.002},
	author = {Scardapane, Simone and Van Vaerenbergh, Steven and Totaro, Simone and Uncini, Aurelio}
}
@article {500,
	title = {Interference Alignment Testbeds},
	journal = {IEEE Communications Magazine},
	volume = {55},
	year = {2017},
	month = {October},
	pages = {120-126},
	author = {Yenk, Cenk and Fanjul, Jacobo and Garc{\'\i}a-Naya, J. A. and Moghadam, Nima and Farhadi, Hamed}
}
@article {IEEE_MMagazine_2010,
	title = {Integrated Adjustable Phase Shifters},
	journal = {IEEE Microwave Magazine},
	volume = {11},
	number = {6},
	year = {2010},
	month = {October},
	pages = {97{\textendash}108},
	author = {Ellinger, F. and Mayer, U. and Wickert, M. and Joram, N. and Wagner, J. and Eickhoff, R. and Santamar{\'\i}a, Ignacio and Scheytt, C. and Kramer, R.}
}
@article {506,
	title = {Information-Theoretic Analysis of a Family of Improper Discrete Constellations},
	journal = {Entropy},
	volume = {20},
	year = {2018},
	doi = { doi:10.3390/e20010045},
	url = {http://www.mdpi.com/1099-4300/20/1/45/pdf},
	author = {Santamar{\'\i}a, Ignacio and Crespo, P. and Lameiro, Christian and Schreier, Peter J.}
}
@article {Trans_Inst_Meas_1998,
	title = {Improved Procedures for Estimating Amplitudes and Phases of Harmonics with Application to Vibration Analysis},
	journal = {IEEE Transactions on Instrumentation and Measurement},
	volume = {47},
	number = {1},
	year = {1998},
	month = {February},
	pages = {209{\textendash}214},
	author = {Santamar{\'\i}a, Ignacio and Pantale{\'o}n, Carlos and Ib{\'a}{\~n}ez, Jes{\'u}s and G{\'o}mez, E.}
}
@article {559,
	title = {Improper Signaling for SISO Two-user Interference Channels with Additive Asymmetric Hardware Distortion},
	journal = {IEEE Transactions on Communications},
	volume = {67},
	year = {2019},
	month = {December},
	pages = {8624-8638},
	abstract = {Hardware non-idealities are among the main performance restrictions for upcoming wireless communication systems. Asymmetric hardware distortions (HWD) happen when the impairments of the I/Q branches are correlated or imbalanced, which in turn generate improper additive interference at the receiver side. When the interference is improper, as well as in other interference-limited scenarios, improper Gaussian signaling (IGS) has been shown to provide rate and/or power efficiency benefits. In this paper, we investigate the rate benefits of IGS in a two-user interference channel (IC) with additive asymmetric HWD when interference is treated as noise. We propose two iterative algorithms to optimize the parameters of the improper transmit signals. We first rewrite the rate region as an pseudo-signal-to-interference-plus-noiseratio (PSINR) region and employ majorization minimization and fractional programming to find a suboptimal solution for the achievable user rates. Then, we propose a simplified algorithm based on a separate optimization of the powers and complementary variances of the users, which exhibits lower computational complexity. We show that IGS can improve the performance of the two-user IC with additive HWD. Our proposed algorithms outperform proper Gaussian signaling and competing IGS algorithms in the literature that do not consider asymmetric HWD.},
	doi = {10.1109/TCOMM.2019.2939310},
	author = {Mohammad Soleymani and Lameiro, Christian and Santamar{\'\i}a, Ignacio and Schreier, Peter J.}
}
@article {620,
	title = {Improper Signaling for Multicell MIMO RIS-assisted Broadcast Channels with I/Q Imbalance},
	journal = {IEEE Transactions on Green Communications and Networking},
	volume = {6},
	year = {2022},
	month = {June},
	pages = {723-738},
	doi = {10.1109/TGCN.2021.3140150},
	author = {Mohammad Soleymani and Santamar{\'\i}a, Ignacio and Schreier, Peter J.}
}
@article {574,
	title = {Improper Gaussian Signaling for the K-user MIMO Interference Channels with Hardware Impairments},
	journal = {IEEE Transactions on Vehicular Technology},
	volume = {69},
	year = {2020},
	month = {October},
	pages = {11632-11645},
	doi = { 10.1109/TVT.2020.3015558},
	author = {Mohammad Soleymani and Santamar{\'\i}a, Ignacio and Schreier, Peter J.}
}
@article {543,
	title = {Improper Gaussian Signaling for Multiple-Access Channels in Underlay Cognitive Radio},
	journal = {IEEE Transactions on Communications},
	volume = {67},
	year = {2019},
	month = {March},
	pages = {1817-1830},
	abstract = {This  paper considers an unlicensed multiple-accesschannel (MAC) that coexists witha licensed point-to-point user,following  the  underlay  cognitive  radio  paradigm.  We  assumethat  every  transceiver  except  the  secondary  base  station  hasone  antenna  and  that  the  primary  user  (PU)  is  protected  bya   minimum   rate   constraint.  In   contrast   to   the  conventionalassumption of proper Gaussian signaling, we allow the secondaryusers  to  transmit  improper  Gaussian  signals,  which  are  corre-lated  with  their  complex  conjugate.  When  the  secondary  basestation  performs  zero-forcing,  we  show  that  improper  signalingis   optimal   if   the  sum   of   the   interference   channel  gains   (inan  equivalent  canonical  model)  is  above  a  certain  threshold.Additionally,  we  derive  an  efficient  algorithm  to  compute  thetransmission  parameters  that  attain  the  rate  region  boundaryfor  this  scenario.  The  proposed  algorithm  exploits  a  single-userrepresentation of the secondary MAC along with new results onthe optimality of improper signaling in the single-user case whenthe PU is corrupted  by an  improper noise.},
	issn = {1558-0857},
	doi = {10.1109/TCOMM.2018.2880765},
	author = {Lameiro, Christian and Santamar{\'\i}a, Ignacio and Schreier, Peter J.}
}
@article {482,
	title = {Homotopy Continuation for Spatial Interference Alignment in Arbitrary MIMO X Networks},
	journal = {IEEE Transactions on Signal Processing},
	volume = {65},
	year = {2017},
	month = {April},
	pages = {1752-1764},
	issn = {1053-587X},
	doi = {10.1109/TSP.2016.2637310},
	author = {Fanjul, Jacobo and Gonz{\'a}lez, {\'O}scar and Santamar{\'\i}a, Ignacio and Beltr{\'a}n, Carlos}
}
@article {Micro_Journal_2001,
	title = {High Speed Analysis and Optimization of Waveguide Band-Pass Filter Structures using Simple Neural Architectures},
	journal = {Microwave Journal},
	volume = {44},
	number = {6},
	year = {2001},
	month = {June},
	pages = {86{\textendash}98},
	author = {Mediavilla, A. and Taz{\'o}n, A. and Pereda, J. A. and L{\'a}zaro, Marcelino and Santamar{\'\i}a, Ignacio and Pantale{\'o}n, Carlos}
}
@article {Via_Q_GLRT_TSP2011,
	title = {Generalized Likelihood Ratios for Testing the Properness of Quaternion {Gaussian} Vectors},
	journal = {IEEE Transactions on Signal Processing},
	volume = {59},
	number = {4},
	year = {2011},
	month = {April},
	pages = {1356{\textendash}1370},
	author = {V{\'\i}a, Javier and Palomar, Daniel P. and Vielva, Luis}
}
@article {Trans_Signal_Proc_2006_b,
	title = {Generalized correlation function: definition, properties and application to blind equalization},
	journal = {IEEE Transactions on Signal Processing},
	volume = {54},
	number = {6},
	year = {2006},
	month = {June},
	pages = {2187{\textendash}2196},
	author = {Santamar{\'\i}a, Ignacio and Pokharel, Puskal P. and Pr{\'\i}ncipe, Jos{\'e} C.}
}
@article {Neurocomputing_2005_b,
	title = {A general solution to blind inverse problems for sparse input signals: deconvolution, equalization and source separation},
	journal = {Neurocomputing},
	volume = {69},
	year = {2005},
	pages = {198{\textendash}215},
	author = {Luengo, David and Santamar{\'\i}a, Ignacio and Vielva, Luis}
}
@article {Aces_Journal_2001,
	title = {A general method for the ray-tracing on convex bodies},
	journal = {Applied Computacional Electromagnetics Society (ACES) Journal},
	volume = {16},
	number = {1},
	year = {2001},
	month = {March},
	pages = {20{\textendash}26},
	author = {Saez de Adana, F. and Gonz{\'a}lez, I. and Guti{\'e}rrez, O. and P{\'e}rez, Jes{\'u}s and C{\'a}tedra, M. F.}
}
@article {Via - TxRx Analog Beamforming - TSP2010,
	title = {A General Criterion for Analog {Tx-Rx} Beamforming under {OFDM} Transmissions},
	journal = {IEEE Transactions on Signal Processing},
	volume = {58},
	number = {4},
	year = {2010},
	month = {April},
	pages = {2155-2167},
	author = {V{\'\i}a, Javier and Santamar{\'\i}a, Ignacio and Elvira, Victor and Eickhoff, R.}
}
@article {342,
	title = {Gaussian Processes for Nonlinear Signal Processing: An Overview of Recent Advances},
	journal = {IEEE Signal Processing Magazine},
	volume = {30},
	year = {2013},
	month = {July},
	pages = {40-50},
	abstract = {Gaussian processes (GPs) are versatile tools that have been successfully employed to solve nonlinear estimation problems in machine learning, but that are rarely used in signal processing. In this tutorial, we present GPs for regression as a natural nonlinear extension to optimal Wiener filtering. After establishing their basic formulation, we discuss several important aspects and extensions, including recursive and adaptive algorithms for dealing with non-stationarity, low-complexity solutions, non-Gaussian noise models and classification scenarios. Furthermore, we provide a selection of relevant applications to wireless digital communications.},
	keywords = {kernel adaptive filtering},
	issn = {1053-5888},
	doi = {10.1109/MSP.2013.2250352},
	url = {http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6530761},
	author = {P{\'e}rez-Cruz, Fernando and Van Vaerenbergh, Steven and Murillo-Fuentes, Juan Jos{\'e} and L{\'a}zaro-Gredilla, Miguel and Santamar{\'\i}a, Ignacio}
}
@article {378,
	title = {A Gaussian Process Model for Data Association and a Semi-Definite Programming Solution},
	journal = {IEEE Transactions on Neural Networks and Learning Systems},
	volume = {25},
	year = {2014},
	month = {November},
	pages = {1967-1979},
	abstract = {In this paper we propose a Bayesian model for the data association problem, in which trajectory smoothness is enforced through the use of Gaussian process priors. This model allows to score candidate associations by using the evidence framework, thus casting the data association problem into an optimization problem. Under some additional mild assumptions, this optimization problem is shown to be equivalent to a constrained Max K-Section problem. Furthermore, for K = 2, a MaxCut formulation is obtained, to which an approximate solution can be efficiently found using an SDP relaxation. Solving this MaxCut problem is equivalent to finding the optimal association out of the combinatorially many possibilities. The obtained clustering depends only on two hyperparameters, which can also be selected by maximum evidence.},
	issn = {2162-237X},
	doi = {10.1109/TNNLS.2014.2300701},
	author = {L{\'a}zaro-Gredilla, Miguel and Van Vaerenbergh, Steven}
}
@article {Trans_Inst_Meas_2011,
	title = {Frequency-Domain Methodology for Measuring {MIMO} Channels Using a Generic Test Bed},
	journal = {IEEE Transactions on Instrumentation and Measurement},
	volume = {60},
	number = {3},
	year = {2011},
	month = {March},
	pages = {827{\textendash}838},
	abstract = {A multiple-input multiple-output (MIMO) frequency-domain channel measurement methodology is presented. This methodology can be implemented in any transmit/receive hardware consisting of radio frequency modules and baseband digital processing units. It involves the transmission and reception of frequency and phase-optimized complex exponentials through antenna arrays, followed by an offline frequency estimation, which makes additional synchronization circuitry unnecessary. To test the feasibility of this method, a series of measurements is presented, employing a 4{\texttimes}4 dual-band (2.4/5 GHz) MIMO test bed.},
	author = {Guti{\'e}rrez, Jes{\'u}s and Gonz{\'a}lez, {\'O}scar and P{\'e}rez, Jes{\'u}s and Ram{\'\i}rez, David and Vielva, Luis and Ib{\'a}{\~n}ez, Jes{\'u}s and Santamar{\'\i}a, Ignacio}
}
@article {Signal_Proc_Letters_2004,
	title = {Frequency sampling design of prototype filters for nearly perfect reconstruction cosine-modulated filterbanks},
	journal = {IEEE Signal Processing Letters},
	volume = {11},
	number = {3},
	year = {2004},
	month = {March},
	pages = {397{\textendash}400},
	author = {Cruz-Rold{\'a}n, F. and Santamar{\'\i}a, Ignacio and Bravo, A. M.}
}
@article {336,
	title = {A Feasibility Test for Linear Interference Alignment in MIMO Channels with Constant Coefficients},
	journal = {IEEE Transactions on Information Theory.},
	volume = {60},
	year = {2014},
	month = {March},
	pages = {1840-1856},
	abstract = {In this paper, we consider the feasibility of linear interference alignment (IA) for multiple-input-multiple-output (MIMO) channels with constant coefficients for any number of users, antennas, and streams per user, and propose a polynomial-time test for this problem. Combining algebraic geometry techniques with differential topology ones, we first prove a result that generalizes those previously published on this topic. In particular, we consider the input set (complex projective space of MIMO interference channels), the output set (precoder and decoder Grassmannians), and the solution set (channels, decoders, and precoders satisfying the IA polynomial equations), not only as algebraic sets, but also as smooth compact manifolds. Using this mathematical framework, we prove that the linear alignment problem is feasible when the algebraic dimension of the solution variety is larger than or equal to the dimension of the input space and the linear mapping between the tangent spaces of both smooth manifolds given by the first projection is generically surjective. If that mapping is not surjective, then the solution variety projects into the input space in a singular way and the projection is a zero-measure set. This result naturally yields a simple feasibility test, which amounts to checking the rank of a matrix. We also provide an exact arithmetic version of the test, which proves that testing the feasibility of IA for generic MIMO channels belongs to the bounded-error probabilistic polynomial complexity class.},
	keywords = {algebraic geometry, differential topology, interference alignment, MIMO interference channel, polynomial equations},
	issn = {0018-9448},
	doi = {10.1109/TIT.2014.2301440},
	author = {Gonz{\'a}lez, {\'O}scar and Beltr{\'a}n, Carlos and Santamar{\'\i}a, Ignacio}
}
@article {Signal_Proc_Letters_2003,
	title = {A Fast Blind {SIMO} Channel Identification Algorithm for Sparse Sources},
	journal = {IEEE Signal Processing Letters},
	volume = {19},
	number = {5},
	year = {2003},
	month = {May},
	pages = {148{\textendash}151},
	author = {Luengo, David and Santamar{\'\i}a, Ignacio and Ib{\'a}{\~n}ez, Jes{\'u}s and Vielva, Luis and Pantale{\'o}n, Carlos}
}
@article {Ant_Prop_Magazine_1999,
	title = {{FASANT}: Fast Computer Tool for the Analysis of On-Board Antennas},
	journal = {IEEE Antennas and Propagation Magazine},
	volume = {41},
	number = {2},
	year = {1999},
	month = {April},
	pages = {94{\textendash}98},
	author = {P{\'e}rez, Jes{\'u}s and Saez de Adana, F. and Guti{\'e}rrez, O. and Gonz{\'a}lez, I. and C{\'a}tedra, M. F. and Montiel, I. and Guzm{\'a}n, J.}
}
@article {439,
	title = {Experimental Evaluation of Interference Alignment for Broadband WLAN Systems},
	journal = {EURASIP Journal on Wireless Communications and Networking},
	year = {2015},
	month = {June},
	abstract = {In this paper, we present an experimental study on the performance of spatial interference alignment (IA) in indoor wireless local area network scenarios that use orthogonal frequency division multiplexing (OFDM) according to the physical-layer specifications of the IEEE 802.11a standard. Experiments have been carried out using a wireless network testbed capable of implementing a 3-user MIMO interference channel. We have implemented IA decoding schemes that can be designed according to distinct criteria (e.g., zero-forcing or MaxSINR). The measurement methodology has been validated considering practical issues like the number of OFDM training symbols used for channel estimation or feedback time. In case of asynchronous users, a time-domain IA decoding filter is also compared to its frequency-domain counterpart. We also evaluated the performance of IA from bit error ratio measurement-based results in comparison to different time-division multiple access transmission schemes. The comparison includes single- and multiple-antenna systems transmitting over the dominant mode of the MIMO channel. Our results indicate that spatial IA is suitable for practical indoor scenarios in which wireless channels often exhibit relatively large coherence times.},
	doi = {10.1186/s13638-015-0409-z},
	author = {Lameiro, Christian and Gonz{\'a}lez, {\'O}scar and Garc{\'\i}a-Naya, J. A. and Santamar{\'\i}a, Ignacio and Castedo, Luis}
}
@article {593,
	title = {Experimental evaluation of flexible duplexing in multi-tier MIMO networks},
	journal = {EURASIP Journal onWireless Communications and Networking},
	year = {2020},
	month = {September},
	author = {Fanjul, Jacobo and Fern{\'a}ndez, Renzo D. and Ib{\'a}{\~n}ez, Jes{\'u}s and Garc{\'\i}a-Naya, J. A. and Santamar{\'\i}a, Ignacio}
}
@article {562,
	title = {Ergodic Rate for Fading  Interference Channels with Proper and Improper Gaussian Signaling},
	journal = {Entropy},
	volume = {21},
	year = {2019},
	month = {September},
	doi = {https://doi.org/10.3390/e21100922},
	author = {Mohammad Soleymani and Santamar{\'\i}a, Ignacio and Lameiro, Christian and Schreier, Peter J.}
}
@article {Trans_Signal_Proc_2002,
	title = {Entropy Minimization for Supervised Digital Communications Channel Equalization},
	journal = {IEEE Transactions on Signal Processing},
	volume = {50},
	number = {5},
	year = {2002},
	month = {May},
	pages = {1184{\textendash}1192},
	author = {Santamar{\'\i}a, Ignacio and Erdogmus, Deniz and Pr{\'\i}ncipe, Jos{\'e} C.}
}
@article {614,
	title = {An Efficient Sampling Scheme for the Eigenvalues of Dual Wishart Matrices},
	journal = {IEEE Signal Processing Letters},
	volume = {28},
	year = {2021},
	pages = {2177-2181},
	doi = {10.1109/LSP.2021.3121197},
	author = {Santamar{\'\i}a, Ignacio and Elvira, Victor}
}
@article {Ant_Prop_Magazine_1998,
	title = {Efficient Ray-Tracing Techniques for Three-Dimensional Analysis of Propagation in Mobile Communications: Appications to Picocell and Microcell Scenarios},
	journal = {IEEE Antennas and Propagation Magazine},
	volume = {40},
	number = {2},
	year = {1998},
	month = {April},
	pages = {15{\textendash}28},
	author = {C{\'a}tedra, M. F. and P{\'e}rez, Jes{\'u}s and Saez de Adana, F. and Guti{\'e}rrez, O.}
}
@article {Trans_Signal_Proc_2006_a,
	title = {Effective channel order estimation based on combined identification / equalization},
	journal = {IEEE Transactions on Signal Processing},
	volume = {54},
	number = {9},
	year = {2006},
	month = {september},
	pages = {3518{\textendash}3526},
	author = {V{\'\i}a, Javier and Santamar{\'\i}a, Ignacio and P{\'e}rez, Jes{\'u}s}
}
@article {FEMS_Micro_Rev_2006,
	title = {Dynamics of the {IncWgenetic} backbone implygeneral trends in conjugative plasmid evolution},
	journal = {FEMS Microbiol Rev.},
	volume = {30},
	year = {2006},
	pages = {942{\textendash}966},
	author = {Fern{\'a}ndez-L{\'o}pez, R. and Garcill{\'a}n-Barcia, M. P. and Revilla, C. and L{\'a}zaro, Marcelino and Vielva, Luis and de la Cruz, Fernando}
}
@article {601,
	title = {DOA Estimation via Shift-Invariant Matrix Completion},
	journal = {Signal Processing},
	volume = {183},
	year = {2021},
	abstract = {This paper presents a method to estimate the direction of arrival (DOA) of multiple sources received by a uniform linear array (ULA) with a reduced number of radio-frequency (RF) chains. The receiving array relies on antenna switching so that at every time instant only the signals received by a randomly selected subset of antennas are downconverted to baseband and sampled. Low-rank matrix completion (MC) techniques are then used to reconstruct the missing entries of the signal data matrix to keep the angular resolution of the original large-scale array. The proposed MC algorithm exploits not only the low- rank structure of the signal subspace, but also the shift-invariance property of ULAs, which results in a better estimation of the signal subspace. Further, the effect of MC on DOA estimation is discussed under the perturbation theory framework. The simulation results suggest that the proposed method provides accurate DOA estimates even in the small-sample regime with a significant reduction in the number of RF chains required for a given spatial resolution.},
	doi = {https://doi.org/10.1016/j.sigpro.2021.107993},
	author = {Garg, Vaibhav and Gimenez-Febrer, Pere and Pages-Zamora, Alba and Santamar{\'\i}a, Ignacio}
}
@article {609,
	title = {Distributed algorithms for spectral and energy-efficiency maximization of K-user interference channels},
	journal = {IEEE Access},
	volume = {9},
	year = {2021},
	month = {July},
	pages = {96948-96963},
	abstract = {In this paper, we propose a cooperative distributed framework to optimize a variety of rate and energy-efficiency (EE) utility functions, such as the minimum-weighted rate or the global EE, in the K-user interference channel. We focus on the single-input multiple-output (SIMO) case, where each user, based solely on local channel state information (CSI), optimizes its transmit power and receive beamformer, although the framework can also be extended to the multiple-output multiple-input (MIMO) case. The distributed framework combines an alternating optimization approach with majorization minimization (MM) techniques, thus ensuring convergence to a stationary point of the centralized cost function. Closed-form power update rules are obtained for some utility functions, thus obtaining very fast convergence algorithms. The receivers treat interference as noise (TIN) and apply the beamformers that maximize the signal-to-interference-plus-noise (SINR). The proposed cooperative distributed algorithms are robust against channel variations and network topology changes and, as our simulation results suggest, they perform close to the centralized solution. As a benchmark, we also study a non-cooperative distributed framework based on the so-called "signal-to-leakage-plus-noise ratio" (SNLR) that further reduces the overhead of the cooperative version.},
	doi = {10.1109/ACCESS.2021.3094976},
	author = {Mohammad Soleymani and Santamar{\'\i}a, Ignacio and Schreier, Peter J.}
}
@article {RF_MIMO_radios_IEEEVTMagazine_2009,
	title = {Developing Energy-Efficient MIMO Radios},
	journal = {IEEE Vehicular Technology Magazine},
	year = {2009},
	month = {March},
	pages = {34{\textendash}41},
	author = {Eickhoff, R. and Kraemer, R. and Santamar{\'\i}a, Ignacio and Gonz{\'a}lez, L.}
}
@article {Trans_Signal_Proc_2007_a,
	title = {Deterministic {CCA}-based algorithms for blind equalization of {FIR}-{MIMO} channels},
	journal = {IEEE Transactions on Signal Processing},
	volume = {55},
	number = {7},
	year = {2007},
	month = {July},
	pages = {3867{\textendash}3878},
	author = {V{\'\i}a, Javier and Santamar{\'\i}a, Ignacio and P{\'e}rez, Jes{\'u}s}
}
@article {413,
	title = {Determination of conjugation rates on solid surfaces},
	journal = {Plasmid},
	volume = {67},
	year = {2012},
	month = {March},
	pages = {174-182},
	abstract = {A cytometric method for the estimation of end-point conjugation rates is developed and adapted to surface conjugation. This method improves the through-put of conjugation assays based on replica-plating and results in less noisy experimental data. Although conjugation on solid surfaces deviates from ideal conditions in which cells are continuously mixed, results show that, within the limits of high initial population densities and short mating times, end-point estimates of the conjugation rates are robust measurements. They are independent of the donor/recipient ratios and, to some extent, of the sampling time. Remixing the mating population in the course of a conjugation experiment results in a boost in the frequency of transconjugants.},
	doi = {10.1016/j.plasmid.2012.01.008.},
	author = {del Campo, Irene and Ruiz, Raul and Cuevas, A and Revilla, C and Vielva, Luis and de la Cruz, Fernando}
}
@article {GLRT_GCS_Detection_Spatially_TrSP,
	title = {Detection of Spatially Correlated Gaussian Time Series},
	journal = {IEEE Transactions on Signal Processing},
	volume = {58},
	number = {10},
	year = {2010},
	month = {October},
	pages = {5006{\textendash}5015},
	author = {Ram{\'\i}rez, David and V{\'\i}a, Javier and Santamar{\'\i}a, Ignacio and Louis L. Scharf}
}
@article {rankPdetection_TrSP,
	title = {Detection of Rank-P signals in Cognitive Radio Networks with Uncalibrated Multiple Antennas},
	journal = {IEEE Transactions on Signal Processing},
	volume = {59},
	number = {8},
	year = {2011},
	month = {August},
	pages = {3764{\textendash}3774},
	author = {Ram{\'\i}rez, David and Vazquez-Vilar, G. and L{\'o}pez-Valcarce, Roberto and V{\'\i}a, Javier and Santamar{\'\i}a, Ignacio}
}
@article {453,
	title = {Detection of Multivariate Cyclostationarity},
	journal = {IEEE Transactions on Signal Processing},
	volume = {63},
	year = {2015},
	month = {October},
	pages = {5395-5408},
	abstract = {This paper derives an asymptotic generalized likelihood ratio test (GLRT) and an asymptotic locally most powerful invariant test (LMPIT) for two hypothesis testing problems: 1) Is a vector-valued random process cyclostationary (CS) or is it wide-sense stationary (WSS)? 2) Is a vector valued random process CS or is it nonstationary? Our approach uses the relationship between a scalar-valued CS time series and a vector-valued WSS time series for which the knowledge of the cycle period is required. This relationship allows us to formulate the problem as a test for the covariance structure of the observations. The covariance matrix of the observations has a block-Toeplitz structure for CS and WSS processes. By considering the asymptotic case where the covariance matrix becomes block-circulant we are able to derive its maximum likelihood (ML) estimate and thus an asymptotic GLRT. Moreover,
using Wijsman{\textquoteright}s theorem, we also obtain an asymptotic LMPIT.
These detectors may be expressed in terms of the Lo{\`e}ve spectrum, the cyclic spectrum, and the power spectral density, establishing how to fuse the information in these spectra for an asymptotic
GLRT and LMPIT. This goes beyond the state of-the-art, where it is common practice to build detectors of cyclostationarity from ad-hoc functions of these spectra.},
	author = {Ram{\'\i}rez, David and Schreier, Peter J. and V{\'\i}a, Javier and Santamar{\'\i}a, Ignacio and Louis L. Scharf}
}
@article {Trans_Cir_Sys_2000,
	title = {Design of Simultaneous Sampling Systems Based on Fractional Delay Lagrange Filters},
	journal = {IEEE Transactions on Circuits and Systems II: Analog and Digital Signal Processing},
	volume = {47},
	number = {5},
	year = {2000},
	month = {May},
	pages = {482{\textendash}485},
	author = {Luengo, David and Pantale{\'o}n, Carlos and Ib{\'a}{\~n}ez, Jes{\'u}s and Santamar{\'\i}a, Ignacio}
}
@article {Electronic_Letters_2003,
	title = {Design of linear-phase FIR filters using support vector regression approach},
	journal = {Electronic Letters},
	volume = {39},
	number = {19},
	year = {2003},
	month = {September},
	pages = {1422{\textendash}1423},
	author = {Santamar{\'\i}a, Ignacio}
}
@article {551,
	title = {Design of Asymptotically Optimal Improper Constellations with Hexagonal Packing},
	journal = {IEEE Transactions on Communications},
	volume = {67},
	year = {2019},
	month = {August},
	pages = {5445-5457},
	abstract = {This paper addresses the problem of designing asymptotically optimal improper constellations with a given circularity coefficient (correlation coefficient between the constellation and its complex conjugate). The designed constellations are optimal in the sense that, at high signal-to-noise-ratio (SNR) and for a large number of symbols, yield the lowest probability of error under an average power constraint for additive white Gaussian noise channels. As the number of symbols grows, the optimal constellation is the intersection of the hexagonal lattice with an ellipse whose eccentricity determines the circularity coefficient. Based on this asymptotic result, we propose an algorithm to design finite improper constellations. The proposed constellations provide significant SNR gains with respect to previous improper designs, which were generated through a widely linear transformation of a standard M-ary quadrature amplitude modulation constellation. As an application example, we study the use of these improper constellations by a secondary user in an underlay cognitive radio network.},
	doi = {10.1109/TCOMM.2019.2916857},
	author = {L{\'o}pez-Fern{\'a}ndez, Jes{\'u}s A. and Gonz{\'a}lez Ayestar{\'a}n, Rafael and Santamar{\'\i}a, Ignacio and Lameiro, Christian}
}
@article {Trans_Geo_Rem_Sen_1999,
	title = {Deconvolution of Seismic Data Using Adaptive Gaussian Mixtures},
	journal = {IEEE Transactions on Geoscience and Remote Sensing},
	volume = {37},
	number = {2},
	year = {1999},
	month = {March},
	pages = {855{\textendash}858},
	author = {Santamar{\'\i}a, Ignacio and Pantale{\'o}n, Carlos and Ib{\'a}{\~n}ez, Jes{\'u}s and Art{\'e}s, Antonio}
}
@article {Trans_Signal_Proc_2008_CM_OSTBC,
	title = {Correlation Matching Approaches for Blind {OSTBC} Channel Estimation},
	journal = {IEEE Transactions on Signal Processing},
	volume = {56},
	number = {12},
	year = {2008},
	month = {December},
	pages = {5950{\textendash}5961},
	author = {V{\'\i}a, Javier and Santamar{\'\i}a, Ignacio}
}
@article {639,
	title = {Constrained Riemannian Noncoherent Constellations for the MIMO Multiple Access Channel},
	journal = {IEEE Transactions on Information Theory},
	volume = {69},
	year = {2023},
	month = {July},
	pages = {4559-4578},
	abstract = {We consider the design of multiuser constellations for a multiple access channel (MAC) with $K$ users, with M antennas each, that transmit simultaneously to a receiver equipped with N antennas through a Rayleigh block-fading channel, when no channel state information (CSI) is available to either the transmitter or the receiver. In full-diversity scenarios where the coherence time is at least T >= (K+1)M, the proposed constellation design criterion is based on the asymptotic expression of the multiuser pairwise error probability (PEP) derived by Brehler and Varanasi (2001). In non-full diversity scenarios, for which the previous PEP expression is no longer valid, the proposed design criteria are based on proxies of the PEP recently proposed by Ngo and Yang (2021). Although both the PEP expression and its bounds or proxies were previously considered intractable for optimization, in this work we derive their respective unconstrained gradients. These gradients are in turn used in the optimization of the proposed cost functions in different Riemannian manifolds representing different power constraints. In particular, in addition to the standard unitary space-time modulation (USTM) leading to optimization on the Grassmann manifold, we consider a more relaxed per-codeword power constraint leading to optimization on the so-called oblique manifold, and an average power constraint leading to optimization on the so-called trace manifold. Equipped with these theoretical tools, we design multiuser constellations for the MIMO MAC in full-diversity and non-full-diversity scenarios with state-of-the-art performance in terms of symbol error rate (SER).},
	doi = {10.1109/TIT.2023.3249903},
	author = {Alvarez-Vizoso, Javier and Cuevas, Diego and Beltr{\'a}n, Carlos and Santamar{\'\i}a, Ignacio and Tucek, V{\'\i}t and Peters, Gunnar}
}
@article {650,
	title = {Constellations on the Sphere with Efficient Encoding-Decoding for Noncoherent Communications},
	journal = {IEEE Transactions on Wireless Communications},
	year = {2023},
	author = {Cuevas, Diego and Alvarez-Vizoso, Javier and Beltr{\'a}n, Carlos and Santamar{\'\i}a, Ignacio and Tucek, V{\'\i}t and Peters, Gunnar}
}
@article {Ant_Prop_Magazine_1995,
	title = {Computation of the {RCS} of complex bodies modeled using {NURBS} surfaces},
	journal = {IEEE Antennas and Propagation Magazine},
	volume = {37},
	number = {6},
	year = {1995},
	month = {December},
	pages = {36{\textendash}47},
	author = {Domingo, M. and Rivas, F. and P{\'e}rez, Jes{\'u}s and Torres, R. P. and C{\'a}tedra, M. F.}
}
@article {530,
	title = {Complex-valued Neural Networks with Non-parametric Activation Functions},
	journal = {IEEE Transactions on Emerging Topics in Computational Intelligence},
	volume = {3},
	year = {2018},
	abstract = {Complex-valued neural networks (CVNNs) are a powerful modeling tool for domains where data can be naturally interpreted in terms of complex numbers. However, several analytical properties of the complex domain (such as holomorphicity) make the design of CVNNs a more challenging task than their real counterpart. In this paper, we consider the problem of flexible activation functions (AFs) in the complex domain, i.e., AFs endowed with sufficient degrees of freedom to adapt their shape given the training data. While this problem has received considerable attention in the real case, very limited literature exists for CVNNs, where most activation functions are generally developed in a split fashion (i.e., by considering the real and imaginary parts of the activation separately) or with simple phase-amplitude techniques. Leveraging over the recently proposed kernel activation functions, and related advances in the design of complex-valued kernels, we propose the first fully complex, nonparametric activation function for CVNNs, which is based on a kernel expansion with a fixed dictionary that can be implemented efficiently on vectorized hardware. Several experiments on common use cases, including prediction and channel equalization, validate our proposal when compared to real-valued neural networks and CVNNs with fixed activation functions.},
	issn = {2471-285X},
	doi = {10.1109/TETCI.2018.2872600},
	url = {https://ieeexplore.ieee.org/document/8495012},
	author = {Scardapane, Simone and Van Vaerenbergh, Steven and Hussain, Amir and Uncini, Aurelio}
}
@article {Eurasip_Signal_Proc_1996_b,
	title = {Competitive Local Linear Modeling},
	journal = {Signal Processing (EURASIP)},
	volume = {49},
	year = {1996},
	pages = {73{\textendash}83},
	author = {Pantale{\'o}n, Carlos and Santamar{\'\i}a, Ignacio and Figueiras-Vidal, Anibal R.}
}
@article {Wireless_Communications_and_Mobile_Computing2008,
	title = {A comparative study of {STBC} transmissions at 2.4 {GHz} over indoor channels using a 2 {\texttimes} 2 {MIMO} testbed},
	journal = {Wireless Communications and Mobile Computing},
	volume = {8},
	number = {9},
	year = {2008},
	month = {November},
	pages = {1149{\textendash}1164},
	author = {Ram{\'\i}rez, David and Santamar{\'\i}a, Ignacio and P{\'e}rez, Jes{\'u}s and V{\'\i}a, Javier and Garc{\'\i}a-Naya, J. A. and Fern{\'a}ndez-Caram{\'e}s, T. M. and H{\'e}ctor J. P{\'e}rez Iglesias and Gonz{\'a}lez L{\'o}pez, M. and Castedo, Luis and Torres-Royo, J. M.}
}
@article {Mec_Sys_Signal_Proc_2000,
	title = {A Comparative Study of High-Accuracy Frequency Estimation Methods},
	journal = {Mechanical Systems and Signal Processing},
	volume = {14},
	number = {5},
	year = {2000},
	month = {September},
	pages = {819{\textendash}834},
	author = {Santamar{\'\i}a, Ignacio and Pantale{\'o}n, Carlos and Ib{\'a}{\~n}ez, Jes{\'u}s}
}
@article {Eurasip_JASP_Code_Combination_2009,
	title = {Code Combination for Blind Channel Estimation in General {MIMO-STBC} Systems},
	journal = {EURASIP Journal on Advances in Signal Processing},
	year = {2009},
	author = {V{\'\i}a, Javier and Santamar{\'\i}a, Ignacio and P{\'e}rez, Jes{\'u}s}
}
@article {Comm_Letter_2005,
	title = {Closed-form approximation for the outage capacity of orthogonal {STBC}},
	journal = {IEEE Communications Letters},
	volume = {9},
	number = {11},
	year = {2005},
	month = {November},
	pages = {961{\textendash}963},
	author = {P{\'e}rez, Jes{\'u}s and Ib{\'a}{\~n}ez, Jes{\'u}s and Vielva, Luis and Santamar{\'\i}a, Ignacio}
}
@article {341,
	title = {Blind Identification of SIMO Wiener Systems based on Kernel Canonical Correlation Analysis},
	journal = {IEEE Transactions on Signal Processing},
	volume = {61},
	year = {2013},
	month = {May},
	pages = {2219-2230},
	abstract = {We consider the problem of blind identification and equalization of single-input multiple-output (SIMO) nonlinear channels. Specifically, the nonlinear model consists of multiple single-channel Wiener systems that are excited by a common input signal. The proposed approach is based on a well-known blind identification technique for linear SIMO systems. By transforming the output signals into a reproducing kernel Hilbert space (RKHS), a linear identification problem is obtained, which we propose to solve through an iterative procedure that alternates between canonical correlation analysis (CCA) to estimate the linear parts, and kernel canonical correlation (KCCA) to estimate the memoryless nonlinearities. The proposed algorithm is able to operate on systems with as few as two output channels, on relatively small data sets and on colored signals. Simulations are included to demonstrate the effectiveness of the proposed technique. },
	issn = {1053-587X},
	doi = {10.1109/TSP.2013.2248004},
	author = {Van Vaerenbergh, Steven and V{\'\i}a, Javier and Santamar{\'\i}a, Ignacio}
}
@article {Trans_Info_Theory_OSTBC_Identifiability2008,
	title = {On the blind identifiability of orthogonal space-time block codes from second order statistics},
	journal = {IEEE Transactions on Information Theory},
	volume = {54},
	number = {2},
	year = {2008},
	month = {February},
	pages = {709-722},
	author = {V{\'\i}a, Javier and Santamar{\'\i}a, Ignacio}
}
@article {Trans_Signal_Proc_2004_a,
	title = {Blind equalization of constant modulus signals using support vector machines},
	journal = {IEEE Transactions on Signal Processing},
	volume = {52},
	number = {6},
	year = {2004},
	month = {June},
	pages = {1773{\textendash}1782},
	author = {Santamar{\'\i}a, Ignacio and Pantale{\'o}n, Carlos and Vielva, Luis and Ib{\'a}{\~n}ez, Jes{\'u}s}
}
@article {405,
	title = {Blind Analysis of Atrial Fibrillation Electrograms: A Sparsity-Aware Formulation},
	journal = {Integrated Computer-Aided Engineering},
	volume = {22},
	year = {2015},
	month = {January},
	pages = {71-85},
	doi = {10.3233/ICA-140471},
	author = {Luengo, David and Sandra Monz{\'o}n and Tom Trigano and V{\'\i}a, Javier and Antonio Art{\'e}s-Rodr{\'\i}guez}
}
@article {412,
	title = {Benefits of Improper Signaling for Underlay Cognitive Radio},
	journal = {IEEE Wireless Communications Letters},
	volume = {4},
	year = {2015},
	month = {Ferbuary},
	pages = {22-25},
	author = {Lameiro, Christian and Santamar{\'\i}a, Ignacio and Schreier, Peter J.}
}
@article {IEEE_TVT_2011_pub,
	title = {Beamforming Design for Simplified Analog Antenna Combining Architectures},
	journal = {IEEE Transactions on Vehicular Technology},
	volume = {60},
	number = {5},
	year = {2011},
	month = {June},
	pages = {2373-2378},
	author = {Gholam, Fouad and V{\'\i}a, Javier and Santamar{\'\i}a, Ignacio}
}
@article {Eurasip_Signal_Proc_2003_c,
	title = {Bayesian Estimation of Chaotic Signals Generated by Piecewise-Linear Maps},
	journal = {Signal Processing},
	volume = {84},
	year = {2003},
	pages = {659{\textendash}664},
	author = {Pantale{\'o}n, Carlos and Vielva, Luis and Luengo, David and Santamar{\'\i}a, Ignacio}
}
@article {375,
	title = {A Bayesian Approach for Adaptive Multiantenna Sensing in Cognitive Radio Networks},
	journal = {Signal Processing},
	volume = {96},
	year = {2014},
	month = {March},
	pages = {240},
	chapter = {228},
	abstract = {Recent work on multiantenna spectrum sensing in cognitive radio (CR) networks has been based on generalized likelihood ratio test (GLRT) detectors, which lack the ability to learn from past decisions and to adapt to the continuously changing environment. To overcome this limitation, in this paper we propose a Bayesian detector capable of learning in an efficient way the posterior distributions under both hypotheses. Our Bayesian model places priors directly on the spatial covariance matrices under both hypotheses, as well as on the probability of channel occupancy. Specifically, we use inverse-gamma and complex inverse-Wishart distributions as conjugate priors for the null and alternative hypothesis, respectively; and a binomial distribution as the prior for channel occupancy. At each sensing period, Bayesian inference is applied and the posterior for the channel occupancy is thresholded for detection. After a suitable approximation, the posteriors are employed as priors for the next sensing frame, which forms the basis of the proposed Bayesian learning procedure. The performance of the Bayesian detector is evaluated by simulations and by means of a CR testbed composed of universal radio peripheral (USRP) nodes. Both the simulations and experimental measurements show that the Bayesian detector outperforms the GLRT in a variety of scenarios.
},
	doi = {10.1016/j.sigpro.2013.10.005},
	author = {Manco-V{\'a}squez, Julio and L{\'a}zaro-Gredilla, Miguel and Ram{\'\i}rez, David and V{\'\i}a, Javier and Santamar{\'\i}a, Ignacio}
}
@article {Electronic_Letters_1998,
	title = {Asymptotic evaluation of physical optics for the analysis of on-board antennas},
	journal = {Electronic Letters},
	volume = {34},
	number = {5},
	year = {1998},
	month = {May},
	pages = {418{\textendash}419},
	author = {C{\'a}tedra, M. F. and Conde, O. and P{\'e}rez, Jes{\'u}s}
}
@article {Electronic_Letters_2004,
	title = {Approximate closed-form expression for the ergodic capacity of polarisation-diversity {MIMO} systems},
	journal = {Electronic Letters},
	volume = {40},
	number = {19},
	year = {2004},
	month = {September},
	pages = {1192{\textendash}1194},
	author = {P{\'e}rez, Jes{\'u}s and Ib{\'a}{\~n}ez, Jes{\'u}s and Vielva, Luis and Santamar{\'\i}a, Ignacio}
}
@article {Trans_Ant_Prop_1994,
	title = {Application of Physical Optics to the {RCS} computation of bodies modeled with {NURBS} surfaces},
	journal = {IEEE Transactions on Antennas and Propagation},
	volume = {42},
	number = {10},
	year = {1994},
	month = {October},
	pages = {1404{\textendash}1411},
	author = {P{\'e}rez, Jes{\'u}s and C{\'a}tedra, M. F.}
}
@article {Trans_Micro_Theory_Tech_2001,
	title = {Analyzing the stability of the {FDTD} technique by combining the von Neumann method with the Routh-Hurwitz criterion},
	journal = {IEEE Transactions on Microwave Theory and Techniques},
	volume = {49},
	number = {2},
	year = {2001},
	month = {February},
	pages = {377{\textendash}381},
	author = {Pereda, J. A. and Vielva, Luis and Vegas, A. and Prieto, A.}
}
@article {Trans_Ant_Prop_1997,
	title = {Analysis of antennas on board arbitrary structures modeled by {NURBS} surfaces},
	journal = {IEEE Transactions on Antennas and Propagation},
	volume = {45},
	number = {6},
	year = {1997},
	month = {June},
	pages = {1045{\textendash}1053},
	author = {P{\'e}rez, Jes{\'u}s and Sainz, J. A. and Conde, O. and Torres, R. P. and C{\'a}tedra, M. F.}
}
@article {Elvira_OBDM_SP2011,
	title = {Analog antenna combining in transmit correlated channels: {Transceiver} design and performance evaluation},
	journal = {Signal Processing},
	volume = {92},
	number = {3},
	year = {2012},
	month = {March},
	pages = {757-766},
	author = {Elvira, Victor and V{\'\i}a, Javier}
}
@article {285,
	title = {Amplify-and-Forward Strategies in the Two-Way Relay Channel with Analog Tx-Rx Beamforming},
	journal = {IEEE Transactions on Vehicular Technology},
	volume = {62},
	year = {2013},
	month = {February},
	pages = {642-654},
	author = {Lameiro, Christian and V{\'\i}a, Javier and Santamar{\'\i}a, Ignacio}
}
@article {JASP_2008_pub,
	title = {Adaptive kernel canonical correlation analysis algorithms for nonparametric identification of Wiener and Hammerstein systems},
	journal = {EURASIP Journal on Advances in Signal Processing},
	year = {2008},
	month = {April},
	abstract = {This paper treats the identification of nonlinear systems that consist of a cascade of a linear channel and a nonlinearity, such as the well-known Wiener and Hammerstein systems. In particular, we follow a supervised identification approach that simultaneously identifies both parts of the nonlinear system. Given the correct restrictions on the identification problem, we show how kernel canonical correlation analysis (KCCA) emerges as the logical solution to this problem.We then extend the proposed identification algorithm to an adaptive version allowing to deal with time-varying systems. In order to avoid overfitting problems, we discuss and compare three possible regularization techniques for both the batch and the adaptive versions of the proposed algorithm. Simulations are included to demonstrate the effectiveness of the presented algorithm.},
	author = {Van Vaerenbergh, Steven and V{\'\i}a, Javier and Santamar{\'\i}a, Ignacio}
}
@article {Trans_Signal_Proc_2004_b,
	title = {Adaptive blind deconvolution of linear channels using {Renyi} entropy with {Parzen} windowing estimation},
	journal = {IEEE Transactions on Signal Processing},
	volume = {52},
	number = {6},
	year = {2004},
	month = {June},
	pages = {1489{\textendash}1498},
	author = {Erdogmus, Deniz and Hild II, K. E. and Pr{\'\i}ncipe, Jos{\'e} C. and L{\'a}zaro, Marcelino and Santamar{\'\i}a, Ignacio}
}
@article {289,
	title = {Adaptive access and rate control of CSMA for energy, rate, and delay optimization},
	journal = {EURASIP Journal on Wireless Communications and Networking},
	year = {2012},
	month = {January},
	pages = {1-16},
	author = {M. Khodaian and P{\'e}rez, Jes{\'u}s and B.H. Khalaj and Crespo, P.}
}
