Ponències/Comunicacions de congressos
http://hdl.handle.net/2117/1257
20200930T00:28:01Z

Source enumeration via Toeplitz matrix completion
http://hdl.handle.net/2117/191913
Source enumeration via Toeplitz matrix completion
Vaibhav, Garg; Giménez Febrer, Pedro Juan; Pagès Zamora, Alba Maria; Santamaria Caballero, Ignacio
This paper addresses the problem of source enumeration by an array of sensors in the presence of noise whose spatial covariance structure is a diagonal matrix with possibly different variances, referred to noniid noise hereafter, when the sources are uncorrelated. The diagonal terms of the sample covariance matrix are removed and, after applying Toeplitz rectification as a denoising step, the signal covariance matrix is reconstructed by using a lowrank matrix completion method adapted to enforce the Toeplitz structure of the sought solution. The proposed source enumeration criterion is based on the Frobenius norm of the reconstructed signal covariance matrix obtained for increasing rank values. As illustrated by simulation examples, the proposed method performs robustly for both small and largescale arrays with few snapshots, i.e. smallsample regime.
© 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.
20200629T13:51:26Z
Vaibhav, Garg
Giménez Febrer, Pedro Juan
Pagès Zamora, Alba Maria
Santamaria Caballero, Ignacio
This paper addresses the problem of source enumeration by an array of sensors in the presence of noise whose spatial covariance structure is a diagonal matrix with possibly different variances, referred to noniid noise hereafter, when the sources are uncorrelated. The diagonal terms of the sample covariance matrix are removed and, after applying Toeplitz rectification as a denoising step, the signal covariance matrix is reconstructed by using a lowrank matrix completion method adapted to enforce the Toeplitz structure of the sought solution. The proposed source enumeration criterion is based on the Frobenius norm of the reconstructed signal covariance matrix obtained for increasing rank values. As illustrated by simulation examples, the proposed method performs robustly for both small and largescale arrays with few snapshots, i.e. smallsample regime.

A novel formulation of independence detection based on the sample characteristic function
http://hdl.handle.net/2117/186732
A novel formulation of independence detection based on the sample characteristic function
Cabrera Estanyol, Ferran de; Riba Sagarra, Jaume
A novel independence test for continuous random sequences is proposed in this paper. The test is based on seeking for coherence in a particular fixeddimension feature space based on a uniform sampling of the sample characteristic function of the data, providing significant computational advantages over kernel methods. This feature space relates uncorrelation and independence, allowing to analyze the second order statistics as it is encountered in traditional signal processing. As a result, the possibility of utilizing well known correlation tools arises, motivating the usage of Canonical Correlation Analysis as the main tool for detecting independence. Comparative simulation results are provided using a model based on fading AWGN channels.
20200508T06:20:07Z
Cabrera Estanyol, Ferran de
Riba Sagarra, Jaume
A novel independence test for continuous random sequences is proposed in this paper. The test is based on seeking for coherence in a particular fixeddimension feature space based on a uniform sampling of the sample characteristic function of the data, providing significant computational advantages over kernel methods. This feature space relates uncorrelation and independence, allowing to analyze the second order statistics as it is encountered in traditional signal processing. As a result, the possibility of utilizing well known correlation tools arises, motivating the usage of Canonical Correlation Analysis as the main tool for detecting independence. Comparative simulation results are provided using a model based on fading AWGN channels.

Squaredloss mutual information via highdimension coherence matrix estimation
http://hdl.handle.net/2117/185713
Squaredloss mutual information via highdimension coherence matrix estimation
Cabrera Estanyol, Ferran de; Riba Sagarra, Jaume
Squaredloss mutual information (SMI) is a surro gate of Shannon mutual information that is more advantageous for estimation. On the other hand, the coherence matrix of a pair of random vectors, a powernormalized version of the sample crosscovariance matrix, is a wellknown secondorder statistic found in the core of fundamental signal processing problems, such as canonical correlation analysis (CCA). This paper shows that SMI can be estimated from a pair of independent and identically distributed (i.i.d.) samples as a squared Frobenius norm of a coherence matrix estimated after mapping the data onto some fixed feature space. Moreover, low computation complexity is achieved through the fast Fourier transform (FFT) by exploiting the Toeplitz structure of the involved autocorrelation matrices in that space. The performance of the method is analyzed via computer simulations using Gaussian mixture models.
20200429T09:36:09Z
Cabrera Estanyol, Ferran de
Riba Sagarra, Jaume
Squaredloss mutual information (SMI) is a surro gate of Shannon mutual information that is more advantageous for estimation. On the other hand, the coherence matrix of a pair of random vectors, a powernormalized version of the sample crosscovariance matrix, is a wellknown secondorder statistic found in the core of fundamental signal processing problems, such as canonical correlation analysis (CCA). This paper shows that SMI can be estimated from a pair of independent and identically distributed (i.i.d.) samples as a squared Frobenius norm of a coherence matrix estimated after mapping the data onto some fixed feature space. Moreover, low computation complexity is achieved through the fast Fourier transform (FFT) by exploiting the Toeplitz structure of the involved autocorrelation matrices in that space. The performance of the method is analyzed via computer simulations using Gaussian mixture models.

Interference mitigation under degreesoffreedom sensing uncertainties in opportunistic transmission
http://hdl.handle.net/2117/185624
Interference mitigation under degreesoffreedom sensing uncertainties in opportunistic transmission
Borràs Pino, Jordi; Vázquez Grau, Gregorio
Intersystem interference may limit the performance of coexisting systems in dense heterogeneous wireless networks. Contextaware waveform design can profitably overcome this limitation. However, the latter substantially depends on degreesoffreedom (DoF) sensing mechanisms. In this work, we show that total leastsquares (TLS)based waveform design is robust against sensing uncertainties. Given the equivalence of minimum norm and TLS, the latter exhibits the good properties of linear predictors, which are of paramount importance to guarantee minimum intersystem interference and detectability by neighboring nodes. Additionally, since derived solution relies on orthogonal projector onto the so called noise subspace, we can efficiently and iteratively construct an orthogonal waveformbook enabling the presented transmission scheme in multicarrier scenarios. Simulation results are presented to support our theoretical contributions, and to highlight any potential advantage of proposed solution in crowded heterogenous wireless networks.
© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.
20200429T04:39:54Z
Borràs Pino, Jordi
Vázquez Grau, Gregorio
Intersystem interference may limit the performance of coexisting systems in dense heterogeneous wireless networks. Contextaware waveform design can profitably overcome this limitation. However, the latter substantially depends on degreesoffreedom (DoF) sensing mechanisms. In this work, we show that total leastsquares (TLS)based waveform design is robust against sensing uncertainties. Given the equivalence of minimum norm and TLS, the latter exhibits the good properties of linear predictors, which are of paramount importance to guarantee minimum intersystem interference and detectability by neighboring nodes. Additionally, since derived solution relies on orthogonal projector onto the so called noise subspace, we can efficiently and iteratively construct an orthogonal waveformbook enabling the presented transmission scheme in multicarrier scenarios. Simulation results are presented to support our theoretical contributions, and to highlight any potential advantage of proposed solution in crowded heterogenous wireless networks.

A nonlinear channel code for covert communications
http://hdl.handle.net/2117/178482
A nonlinear channel code for covert communications
Lamarca Orozco, M. Meritxell; Matas Navarro, David
This paper presents an explicit channel code design for covert communications in the Binary Symmetric Channel. The proposed architecture is composed of the serial concatenation of a linear code and a graphbased nonlinear code baptized as moderatedensity nonlinear code. This nonlinear code encompasses pulse position modulation as a particular case. In order to guarantee covertness, a scrambling sequence that is not known to the warden is employed.
20200224T15:20:45Z
Lamarca Orozco, M. Meritxell
Matas Navarro, David
This paper presents an explicit channel code design for covert communications in the Binary Symmetric Channel. The proposed architecture is composed of the serial concatenation of a linear code and a graphbased nonlinear code baptized as moderatedensity nonlinear code. This nonlinear code encompasses pulse position modulation as a particular case. In order to guarantee covertness, a scrambling sequence that is not known to the warden is employed.

Joint energy and rate allocation for successive interference cancellation in the finite blocklength regime
http://hdl.handle.net/2117/177796
Joint energy and rate allocation for successive interference cancellation in the finite blocklength regime
Molina Oliveras, Francesc; Sala Álvarez, José; Villares Piera, Nemesio Javier; Rey Micolau, Francesc
This work addresses the optimization of the network spectral efficiency (SE) under successive interference cancellation (SIC) at a given blocklength n. We adopt a proofofconcept satellite scenario where network users can vary their transmission power and select their transmission rate from a set of encoders, for which decoding is characterized by a known packet error rate (PER) function. In the largesystem limit, we apply variational calculus (VC) to obtain the userenergy distribution, the assigned peruser rate and the SIC decoding order maximizing the network SE under a sumpower constraint at the SIC input. We analyze two encoder sets: (i) an infinite set of encoders achieving informationtheoretic finite blocklength PER results over a continuum of code rates, where the largen second order expansion of the maximal channel coding rate is used; (ii) a feasible finite set of encoders. Simulations quantify the
performance gap between the two schemes.
© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.
20200214T19:39:38Z
Molina Oliveras, Francesc
Sala Álvarez, José
Villares Piera, Nemesio Javier
Rey Micolau, Francesc
This work addresses the optimization of the network spectral efficiency (SE) under successive interference cancellation (SIC) at a given blocklength n. We adopt a proofofconcept satellite scenario where network users can vary their transmission power and select their transmission rate from a set of encoders, for which decoding is characterized by a known packet error rate (PER) function. In the largesystem limit, we apply variational calculus (VC) to obtain the userenergy distribution, the assigned peruser rate and the SIC decoding order maximizing the network SE under a sumpower constraint at the SIC input. We analyze two encoder sets: (i) an infinite set of encoders achieving informationtheoretic finite blocklength PER results over a continuum of code rates, where the largen second order expansion of the maximal channel coding rate is used; (ii) a feasible finite set of encoders. Simulations quantify the
performance gap between the two schemes.

Decentralized shaping for pilot generation and detection in opportunistic communications
http://hdl.handle.net/2117/173994
Decentralized shaping for pilot generation and detection in opportunistic communications
Borràs Pino, Jordi; Vázquez Grau, Gregorio
The uncoordinated design of pulse shaping filters for opportunistic communications is addressed. We show that under degreesoffreedom sensing uncertainties the waveform design problem can be cast as a minimumnorm optimization, admitting hence a closedform expression. Because designed waveforms are adapted to scenario working conditions, proposed design scheme may be considered in pilot reference signals design to achieve orthogonality, regardless the traditionally considered pilot symbols orthogonality. Hence, the effect of interferences such as pilot contamination is diminished. However, a crucial aspect relies on their detectability. Since each node uses only local observations from the wireless network, the sensed degreesoffreedom may slightly differ from one node to others. In this paper we prove that, thanks to the existence of some invariances, designed waveforms can be detected by neighboring nodes. Even though degreesoffreedom sensing uncertainties may incur in a performance loss, we propose a leastsquares constrained basis pursuit algorithm to reduce the effect of uncertainties by considering only the degreesoffreedom subspace intersection.
© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.
20191216T14:28:29Z
Borràs Pino, Jordi
Vázquez Grau, Gregorio
The uncoordinated design of pulse shaping filters for opportunistic communications is addressed. We show that under degreesoffreedom sensing uncertainties the waveform design problem can be cast as a minimumnorm optimization, admitting hence a closedform expression. Because designed waveforms are adapted to scenario working conditions, proposed design scheme may be considered in pilot reference signals design to achieve orthogonality, regardless the traditionally considered pilot symbols orthogonality. Hence, the effect of interferences such as pilot contamination is diminished. However, a crucial aspect relies on their detectability. Since each node uses only local observations from the wireless network, the sensed degreesoffreedom may slightly differ from one node to others. In this paper we prove that, thanks to the existence of some invariances, designed waveforms can be detected by neighboring nodes. Even though degreesoffreedom sensing uncertainties may incur in a performance loss, we propose a leastsquares constrained basis pursuit algorithm to reduce the effect of uncertainties by considering only the degreesoffreedom subspace intersection.

Distributed feedbackaided subspace concurrent opportunistic communications
http://hdl.handle.net/2117/173930
Distributed feedbackaided subspace concurrent opportunistic communications
Borràs Pino, Jordi; Vázquez Grau, Gregorio
This paper deals with the distributed subspace agreement problem for opportunistic communications in time division duplex (TDD) distributed networks. Since scenarioadapted opportunistic transmission schemes rely on locally sampled observations from the wireless environment, degreesoffreedom (DoF) sensed as available at any node may differ. Transmitting information without agreeing the common active subspace may incur in a performance loss due to noise enhancement, energy loss and intersystem interference. In this context, we propose two subspace concurrence schemes with and without side information about neighboring user's DoF.
© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.
20191213T18:47:30Z
Borràs Pino, Jordi
Vázquez Grau, Gregorio
This paper deals with the distributed subspace agreement problem for opportunistic communications in time division duplex (TDD) distributed networks. Since scenarioadapted opportunistic transmission schemes rely on locally sampled observations from the wireless environment, degreesoffreedom (DoF) sensed as available at any node may differ. Transmitting information without agreeing the common active subspace may incur in a performance loss due to noise enhancement, energy loss and intersystem interference. In this context, we propose two subspace concurrence schemes with and without side information about neighboring user's DoF.

Lowcomplexity switching network design for hybrid precoding in mmWave MIMO systems
http://hdl.handle.net/2117/173929
Lowcomplexity switching network design for hybrid precoding in mmWave MIMO systems
Molina Oliveras, Francesc; Borràs Pino, Jordi
This paper deals with the design of a hybrid precoder for millimeterwave MIMO systems. For the sake of concreteness, we consider an analog processing stage composed of a switching network with analog combining. The main contribution of this work consists on the proposal and evaluation of an optimization procedure based on a smart relaxation. The optimal hybrid precoder under a transmit power constraint is derived, after which, the analog precoding matrix is binarized. After an intuitive reasoning, we note that multiple solutions exist. Nevertheless, the (very) reduced computational complexity of the proposed optimization scheme makes it feasible for realistic implementations. Numerical results are reported to assess the performance of proposed hybrid precoder design.
© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.
20191213T18:44:28Z
Molina Oliveras, Francesc
Borràs Pino, Jordi
This paper deals with the design of a hybrid precoder for millimeterwave MIMO systems. For the sake of concreteness, we consider an analog processing stage composed of a switching network with analog combining. The main contribution of this work consists on the proposal and evaluation of an optimization procedure based on a smart relaxation. The optimal hybrid precoder under a transmit power constraint is derived, after which, the analog precoding matrix is binarized. After an intuitive reasoning, we note that multiple solutions exist. Nevertheless, the (very) reduced computational complexity of the proposed optimization scheme makes it feasible for realistic implementations. Numerical results are reported to assess the performance of proposed hybrid precoder design.

Energy efficient transmitreceive spatial modulation for uplinkdownlink largescale MIMO systems
http://hdl.handle.net/2117/173154
Energy efficient transmitreceive spatial modulation for uplinkdownlink largescale MIMO systems
Raafat Hosny Mohamed Fahm, Ahmed; Yüzgeçcioglu, Merve; Zahid Aslam, Mohammed; Agustín de Dios, Adrián; Vidal Manzano, José; Jorswieck, Eduard Axel; Corre, Yoann
Energy efficient spatial modulationaided uplink and downlink designs for future millimeterwave (mmWave) largescale multipleinput multipleoutput (MIMO) systems are considered. Two novel uplink transceivers are proposed with the aim of considerably reducing the energy consumption at the user terminal, while achieving high spectral efficiency both in uplink and downlink transmissions. System performance is investigated using both stochastic and deterministic channels emulating real world urban scenarios.
© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.
20191127T13:54:59Z
Raafat Hosny Mohamed Fahm, Ahmed
Yüzgeçcioglu, Merve
Zahid Aslam, Mohammed
Agustín de Dios, Adrián
Vidal Manzano, José
Jorswieck, Eduard Axel
Corre, Yoann
Energy efficient spatial modulationaided uplink and downlink designs for future millimeterwave (mmWave) largescale multipleinput multipleoutput (MIMO) systems are considered. Two novel uplink transceivers are proposed with the aim of considerably reducing the energy consumption at the user terminal, while achieving high spectral efficiency both in uplink and downlink transmissions. System performance is investigated using both stochastic and deterministic channels emulating real world urban scenarios.