Articles de revista
http://hdl.handle.net/2117/22108
2018-01-02T02:44:52ZSelf-reference spatial diversity processing for spread spectrum communications
http://hdl.handle.net/2117/98395
Self-reference spatial diversity processing for spread spectrum communications
Pérez Palomar, Daniel; Nájar Martón, Montserrat; Lagunas Hernandez, Miguel A.
n this paper, the application of three blind (or selfreference)
spatial diversity signal processing methods to Spread
Spectrum (SS) communications is described. These methods do
not require any kind of side information beyond knowledge of
the signal structure, in contraposition to methods that depend
on training sequences.
Each self-reference method is specifically designed for a particular
SS transmission scheme and uses a particular signal’s
structural information. All three methods, however, are derived
under the common goal of finding the optimum beamformer, in
the sense of maximum signal to interference-plus-noise ratio, in
a blind manner.
The Code Reference Beamformer for Frequency Hopping systems
is an approach based on the knowledge of the hopping
sequence or code structure of the signal. This method is the
best alternative for array signal processing on this particular
SS scheme. Two recently proposed beamforming methods,
which are based on the knowledge of the redundancy structure
of the desired signal, are described under the common
framework of efficiently using the inherent diversity – either
in frequency or time – of two signalling formats, namely, Frequency
Diversity (FD) SS and DS-CDMA. The former uses
frequency diversity, while the latter uses time diversity. The
diversity approach presented for FDSS seems to be the best
choice at the moment. Regarding DS-CDMA, for which many
beamforming algorithms have been developed in the literature,
the self-reference beamforming is simply an alternative blind
method that shows very good performance. These diversity approaches
were compared via simulations to the standard Time
Reference Beamformer (TRB) and showed a performance similar
to it (with 10% of the bits as a training sequence) even
without the need of any side information whatsoever.
2016-12-15T18:25:47ZPérez Palomar, DanielNájar Martón, MontserratLagunas Hernandez, Miguel A.n this paper, the application of three blind (or selfreference)
spatial diversity signal processing methods to Spread
Spectrum (SS) communications is described. These methods do
not require any kind of side information beyond knowledge of
the signal structure, in contraposition to methods that depend
on training sequences.
Each self-reference method is specifically designed for a particular
SS transmission scheme and uses a particular signal’s
structural information. All three methods, however, are derived
under the common goal of finding the optimum beamformer, in
the sense of maximum signal to interference-plus-noise ratio, in
a blind manner.
The Code Reference Beamformer for Frequency Hopping systems
is an approach based on the knowledge of the hopping
sequence or code structure of the signal. This method is the
best alternative for array signal processing on this particular
SS scheme. Two recently proposed beamforming methods,
which are based on the knowledge of the redundancy structure
of the desired signal, are described under the common
framework of efficiently using the inherent diversity – either
in frequency or time – of two signalling formats, namely, Frequency
Diversity (FD) SS and DS-CDMA. The former uses
frequency diversity, while the latter uses time diversity. The
diversity approach presented for FDSS seems to be the best
choice at the moment. Regarding DS-CDMA, for which many
beamforming algorithms have been developed in the literature,
the self-reference beamforming is simply an alternative blind
method that shows very good performance. These diversity approaches
were compared via simulations to the standard Time
Reference Beamformer (TRB) and showed a performance similar
to it (with 10% of the bits as a training sequence) even
without the need of any side information whatsoever.Fourier models for non linear signal processing
http://hdl.handle.net/2117/98266
Fourier models for non linear signal processing
Pagès Zamora, Alba Maria; Lagunas Hernandez, Miguel A.
This paper proposes a trigonometric functional extension, hereafter named the Fourier model, as an alternative framework to the Volterra approach for non-linear systems modelling. This work is focused on the general advantages that trigonometric functionals show in adaptive implementations and also on the possibility they provide to reuse well-known linear processing tools in a non-linear context. The performance of the Fourier model is compared in a set of simulations that cover companders for audio and radio frequency amplifiers, probability density function (PDF) whitening and PDF estimation.
2016-12-14T15:52:36ZPagès Zamora, Alba MariaLagunas Hernandez, Miguel A.This paper proposes a trigonometric functional extension, hereafter named the Fourier model, as an alternative framework to the Volterra approach for non-linear systems modelling. This work is focused on the general advantages that trigonometric functionals show in adaptive implementations and also on the possibility they provide to reuse well-known linear processing tools in a non-linear context. The performance of the Fourier model is compared in a set of simulations that cover companders for audio and radio frequency amplifiers, probability density function (PDF) whitening and PDF estimation.Cross-coupled doa trackers
http://hdl.handle.net/2117/97899
Cross-coupled doa trackers
Pérez Neira, Ana Isabel; Lagunas Hernandez, Miguel A.; Kirlin, R L
A new robust, low complexity algorithm for multiuser tracking is proposed, modifying the two-stage parallel architecture of the estimate-maximize (EM) algorithm. The algorithm copes with spatially colored noise, large differences in source powers, multipath, and crossing trajectories. Following a discussion on stability, the simulations demonstrate an asymptotic and tracking behavior that neither the EM nor a nonparallelized tracker can emulate.
2016-12-07T16:55:25ZPérez Neira, Ana IsabelLagunas Hernandez, Miguel A.Kirlin, R LA new robust, low complexity algorithm for multiuser tracking is proposed, modifying the two-stage parallel architecture of the estimate-maximize (EM) algorithm. The algorithm copes with spatially colored noise, large differences in source powers, multipath, and crossing trajectories. Following a discussion on stability, the simulations demonstrate an asymptotic and tracking behavior that neither the EM nor a nonparallelized tracker can emulate.Source reference in CIR beamforming
http://hdl.handle.net/2117/97269
Source reference in CIR beamforming
Lagunas Hernandez, Miguel A.; Nájar Martón, Montserrat
This paper presents a procedure for CIR beamforming that avoids SVD-like proceduresm and is derived from the classic CINR solution. The resulting nulls along the direction of the impinging interferers are of the same degree as those used in noise subspace procedures. The method is based on both the use of a temporal reference, available in the satellite payload, and on the spatial steered beamvector (the Applebaum solution). The resulting procedure is a valuable alternative to the classic covariance loading methods, as further matrix inversion is not required, and the noise estimate is derived from the existing hardware. Some results corresponding to a data relay satellite (DRS) scenario are reported.
2016-11-25T17:39:37ZLagunas Hernandez, Miguel A.Nájar Martón, MontserratThis paper presents a procedure for CIR beamforming that avoids SVD-like proceduresm and is derived from the classic CINR solution. The resulting nulls along the direction of the impinging interferers are of the same degree as those used in noise subspace procedures. The method is based on both the use of a temporal reference, available in the satellite payload, and on the spatial steered beamvector (the Applebaum solution). The resulting procedure is a valuable alternative to the classic covariance loading methods, as further matrix inversion is not required, and the noise estimate is derived from the existing hardware. Some results corresponding to a data relay satellite (DRS) scenario are reported.Eigendecomposition versus singular value decomposition in adaptive array signal processing
http://hdl.handle.net/2117/97154
Eigendecomposition versus singular value decomposition in adaptive array signal processing
Duarte Ortigueira, Manuel; Lagunas Hernandez, Miguel A.
Two important questions in array signal processing are addressed in this paper: the data matrix versus autocorrelation matrix alternative and the recursive implementation of subspace DOA methods. The discussion of the first question is done in face of the proposed class of recursive algorithms. These new algorithms are easily implementable and have a high degree of parallelism that is suitable for on-line implementations. Algorithms for recursive implementation of the eigendecomposition (ED) of the autocorrelation matrix and SVD of the data matrix are described. The ED/SVD trade-off is discussed.
2016-11-23T19:53:21ZDuarte Ortigueira, ManuelLagunas Hernandez, Miguel A.Two important questions in array signal processing are addressed in this paper: the data matrix versus autocorrelation matrix alternative and the recursive implementation of subspace DOA methods. The discussion of the first question is done in face of the proposed class of recursive algorithms. These new algorithms are easily implementable and have a high degree of parallelism that is suitable for on-line implementations. Algorithms for recursive implementation of the eigendecomposition (ED) of the autocorrelation matrix and SVD of the data matrix are described. The ED/SVD trade-off is discussed.Two-stage code reference beamformer for the reception of frequency hopping modulated signals
http://hdl.handle.net/2117/88140
Two-stage code reference beamformer for the reception of frequency hopping modulated signals
Nájar Martón, Montserrat; Mestre Pons, Francesc X.; Lagunas Hernandez, Miguel A.
This paper presents a beamforming technique for the reception of frequency hopping (FH) modulated signals, which takes advantage of their inherent frequency diversity. This technique, based on a code reference beamformer, requires neither temporal nor spatial a priori reference and allows continuous self-calibration of the array. The proposed framework is composed of two different stages. The first stage employs the inverse of the noise plus interference covariance matrix obtained by an anticipative processor. The second stage makes use of the steering vector of the signal of interest which is adaptively obtained by maximizing the output signal to interference plus noise ratio (SINR). Using this information, the first stage is in turn readjusted and, as a result, the scheme is able to track non-stationary scenarios following the channel variations with no previous references other than knowledge of the frequency hopping sequence. The two-stage code reference beamformer provides the convergence rate necessary to avoid the SINR reduction associated with frequency hops in existing methods.
2016-06-17T14:58:30ZNájar Martón, MontserratMestre Pons, Francesc X.Lagunas Hernandez, Miguel A.This paper presents a beamforming technique for the reception of frequency hopping (FH) modulated signals, which takes advantage of their inherent frequency diversity. This technique, based on a code reference beamformer, requires neither temporal nor spatial a priori reference and allows continuous self-calibration of the array. The proposed framework is composed of two different stages. The first stage employs the inverse of the noise plus interference covariance matrix obtained by an anticipative processor. The second stage makes use of the steering vector of the signal of interest which is adaptively obtained by maximizing the output signal to interference plus noise ratio (SINR). Using this information, the first stage is in turn readjusted and, as a result, the scheme is able to track non-stationary scenarios following the channel variations with no previous references other than knowledge of the frequency hopping sequence. The two-stage code reference beamformer provides the convergence rate necessary to avoid the SINR reduction associated with frequency hops in existing methods.Transceiver design framework for multiuser MIMO-OFDM broadcast systems with channel gram matrix feedback
http://hdl.handle.net/2117/87189
Transceiver design framework for multiuser MIMO-OFDM broadcast systems with channel gram matrix feedback
Sacristán Murga, Daniel; Payaró Llisterri, Miquel; Pascual Iserte, Antonio
This work considers a multiple-input multipleoutput
(MIMO) orthogonal frequency division multiplexing
based multiuser broadcast system with precoding at the transmitter
and feedback of channel state information. A general
framework is presented for the transceiver design, and also for
the design of the feedback link based on the quantization of the
users’ MIMO channel Gram matrices. The proposed design of
the feedback link exploits the correlation of the channel response
in the frequency domain due to the finite length of the channel
time impulse responses to outperform other schemes based on
feedback of the per carrier frequency responses. The transceiver
design framework is based on a unitary linear transformation
applied at the receivers which allows the computation of equivalent
triangular channel response matrices at the transmitter.
An analytic study of the error propagation due to the channel
quantization in the feedback link and the computation of the
equivalent triangular channel matrices is also performed. Based
on the previous concepts, all the usual transceiver design criteria
can be applied within this framework, and the particular case
of a space-frequency precoder for robust mean square error
minimization is derived as an example. Finally, the benefits
of the proposed strategy are evaluated by means of numerical
simulations and compared to other existing techniques.
2016-05-19T11:47:45ZSacristán Murga, DanielPayaró Llisterri, MiquelPascual Iserte, AntonioThis work considers a multiple-input multipleoutput
(MIMO) orthogonal frequency division multiplexing
based multiuser broadcast system with precoding at the transmitter
and feedback of channel state information. A general
framework is presented for the transceiver design, and also for
the design of the feedback link based on the quantization of the
users’ MIMO channel Gram matrices. The proposed design of
the feedback link exploits the correlation of the channel response
in the frequency domain due to the finite length of the channel
time impulse responses to outperform other schemes based on
feedback of the per carrier frequency responses. The transceiver
design framework is based on a unitary linear transformation
applied at the receivers which allows the computation of equivalent
triangular channel response matrices at the transmitter.
An analytic study of the error propagation due to the channel
quantization in the feedback link and the computation of the
equivalent triangular channel matrices is also performed. Based
on the previous concepts, all the usual transceiver design criteria
can be applied within this framework, and the particular case
of a space-frequency precoder for robust mean square error
minimization is derived as an example. Finally, the benefits
of the proposed strategy are evaluated by means of numerical
simulations and compared to other existing techniques.Differential Feedback of MIMO Channel Gram Matrices Based on Geodesic Curves
http://hdl.handle.net/2117/87108
Differential Feedback of MIMO Channel Gram Matrices Based on Geodesic Curves
Sacristán Murga, Daniel; Pascual Iserte, Antonio
This paper proposes a differential quantization
strategy to be used in the feedback link of a multiple-input
multiple-output (MIMO) communication system. This algorithm
is applied to the channel Gram matrix using geodesic curves and
exploiting the intrinsic geometry of positive definite Hermitian
matrices. It also exploits the temporal correlation of the channel,
and follows on average the gradient of the cost function associated
to the transmitter design criterion. A full description of the
algorithm, including the computational cost and a numerical
analysis of the effect of delays and errors in the feedback link is
presented. Simulation results show that the proposed algorithm
improves other techniques based on the direct quantization of
the channel response matrix or the quantization of the subspace
spanned by the strongest eigenmodes of the MIMO channel, i.e.,
Grassmannian based techniques. The main drawback of Grassmannian
based algorithms is that the transmitter is constrained
to apply a uniform power allocation among spatial transmission
modes, which is not forced in the algorithm proposed in this
paper.
2016-05-17T12:34:17ZSacristán Murga, DanielPascual Iserte, AntonioThis paper proposes a differential quantization
strategy to be used in the feedback link of a multiple-input
multiple-output (MIMO) communication system. This algorithm
is applied to the channel Gram matrix using geodesic curves and
exploiting the intrinsic geometry of positive definite Hermitian
matrices. It also exploits the temporal correlation of the channel,
and follows on average the gradient of the cost function associated
to the transmitter design criterion. A full description of the
algorithm, including the computational cost and a numerical
analysis of the effect of delays and errors in the feedback link is
presented. Simulation results show that the proposed algorithm
improves other techniques based on the direct quantization of
the channel response matrix or the quantization of the subspace
spanned by the strongest eigenmodes of the MIMO channel, i.e.,
Grassmannian based techniques. The main drawback of Grassmannian
based algorithms is that the transmitter is constrained
to apply a uniform power allocation among spatial transmission
modes, which is not forced in the algorithm proposed in this
paper.The effect of broadband matching in simultaneous information and power transfer
http://hdl.handle.net/2117/77900
The effect of broadband matching in simultaneous information and power transfer
Ho Yeung, Sai; Kumar Sarkar, Tapan; Salazar Palma, Magdalena; Lagunas Hernandez, Miguel A.; Pérez Neira, Ana Isabel
This paper presents the implementation and the effect of broadband matching in simultaneous information and power transfer. The narrowband characteristic of antennas limited the applications of simultaneous information and power transfer. The simplified real frequency technique (SRFT) and the non-foster matching technique have been presented to improve the performance in terms of channel capacity and power delivery. Electromagnetic simulation and multiobjective optimization are performed to analyze the tradeoff between the channel capacity and power delivery in different matching conditions. The performance gain using the matching networks have been demonstrated and analyzed
2015-10-19T14:53:58ZHo Yeung, SaiKumar Sarkar, TapanSalazar Palma, MagdalenaLagunas Hernandez, Miguel A.Pérez Neira, Ana IsabelThis paper presents the implementation and the effect of broadband matching in simultaneous information and power transfer. The narrowband characteristic of antennas limited the applications of simultaneous information and power transfer. The simplified real frequency technique (SRFT) and the non-foster matching technique have been presented to improve the performance in terms of channel capacity and power delivery. Electromagnetic simulation and multiobjective optimization are performed to analyze the tradeoff between the channel capacity and power delivery in different matching conditions. The performance gain using the matching networks have been demonstrated and analyzedLow-complexity interference variance estimation methods for coded multicarrier systems: application to SFN
http://hdl.handle.net/2117/21817
Low-complexity interference variance estimation methods for coded multicarrier systems: application to SFN
Caus López, Marius; Pérez Neira, Ana Isabel; Renfors, Markku
For single-frequency network (SFN) transmission, the echoes coming from different transmitters are superimposed at the reception, giving rise to a frequency selective channel. Although multicarrier modulations lower the dispersion, the demodulated signal is sensitive to be degraded by inter-symbol interference (ISI) and inter-carrier interference (ICI). In view of this, we use channel coding in conjunction either with filter bank multicarrier (FBMC) modulation or with orthogonal frequency division multiplexing (OFDM). To deal with the loss of orthogonality, we have devised an interference-aware receiver that carries out a soft detection under the assumption that the residual interference plus noise (IN) term is Gaussian-distributed. To keep the complexity low, we propose to estimate the variance of the IN term by resorting to data-aided algorithms. Experimental results show that regardless of the method, FBMC provides a slightly better performance in terms of coded bit error rate than OFDM, while the spectral efficiency is increased when FBMC is considered.
2014-02-28T17:08:36ZCaus López, MariusPérez Neira, Ana IsabelRenfors, MarkkuFor single-frequency network (SFN) transmission, the echoes coming from different transmitters are superimposed at the reception, giving rise to a frequency selective channel. Although multicarrier modulations lower the dispersion, the demodulated signal is sensitive to be degraded by inter-symbol interference (ISI) and inter-carrier interference (ICI). In view of this, we use channel coding in conjunction either with filter bank multicarrier (FBMC) modulation or with orthogonal frequency division multiplexing (OFDM). To deal with the loss of orthogonality, we have devised an interference-aware receiver that carries out a soft detection under the assumption that the residual interference plus noise (IN) term is Gaussian-distributed. To keep the complexity low, we propose to estimate the variance of the IN term by resorting to data-aided algorithms. Experimental results show that regardless of the method, FBMC provides a slightly better performance in terms of coded bit error rate than OFDM, while the spectral efficiency is increased when FBMC is considered.