Papers by Fernando Cruz-roldán
2017 25th European Signal Processing Conference (EUSIPCO), 2017
The analysis of finite wordlength effects in linear digital networks requires specifying the exac... more The analysis of finite wordlength effects in linear digital networks requires specifying the exact order in which all the internal computations are performed, as well as the type and resolution of all the quantizers. Popular digital filter descriptions (difference equations, transfer function, state space representation, etc.) are unable to provide a bit-true description valid for any filter structure, thus preventing most of the results in the literature from being truly reproducible. Furthermore, the quantizers are often not properly described. In this work, we introduce a novel and compact framework to describe unambiguously any single-input single-output (SISO) linear digital network. The proposed approach is simple, efficient and guarantees the reproducibility of the results obtained for any network by allowing us to describe in detail the data flow as well as the quantization of all the coefficients and operations performed. An example of a third order Butterworth filter with four different implementations is provided to show the descriptive power and flexibility of the proposed approach.
Publication in the conference proceedings of EUSIPCO, Lisbon, Portugal, 2014
2019 27th European Signal Processing Conference (EUSIPCO), 2019
This work quantifies, for the first time, intersymbol and intercarrier interferences induced by v... more This work quantifies, for the first time, intersymbol and intercarrier interferences induced by very dispersive channels in OFDM systems. The resulting achievable data rate for suboptimal OFDM transmissions is derived based on the computation of signal-to-interference-plus-noise ratio for arbitrary length finite duration channel impulse responses. Simulation results point to significant differences between data rates obtained via conventional formulations, for which interferences are supposed to be limited to two or three blocks, versus the data rates considering the actual channel dispersion.
2018 IEEE Statistical Signal Processing Workshop (SSP), 2018
In this work, we address the problem of channel estimation in multicarrier communications by mean... more In this work, we address the problem of channel estimation in multicarrier communications by means of the Type-III even discrete cosine transform (DCT3e). We present a novel efficient procedure based on using the DCT3e both at the transmitter and the receiver. The proposed approach does not require adding any redundancy or knowing the exact length of the channel's impulse response. It suffices to use any symmetric training sequence at the transmitter with enough leading and tail zeros. We demonstrate that an accurate estimation of the channel's impulse response can be attained, and illustrate the good behavior of the proposed scheme using ITU-T pedestrian channel B.
This paper introduces a novel approach for designing critically sampled cosine-modulated transcei... more This paper introduces a novel approach for designing critically sampled cosine-modulated transceivers (CMTs) for communications applications. The key idea in this approach is to design the prototype filter in such a manner that it provides a properly optimized tradeoff between the inter-symbol and inter-channel interferences for CMTs without directly concentrating on designing the prototype filter according to any predetermined criteria. In order to generate a very fast technique for testing this approach, the windowing technique is used for optimizing the prototype filter and the window function is a generalized Blackman window in the sense that this window function has the fourth additional term. Using this windowing approach results in a very fast unconstrained optimization problem with only three unknowns involved for optimally determining the above-mentioned tradeoff for a CMT, independently of the order of the prototype filter and the number of channel of the CMT. Several exam...
Wireless Communications and Mobile Computing, 2018
Multicarrier modulation based on discrete cosine transform (DCT-MCM) is a candidate technique for... more Multicarrier modulation based on discrete cosine transform (DCT-MCM) is a candidate technique for future wireless communication. DCT-MCM provides a better usage of the spectrum, allowing for much lower out-of-band radiation than conventional OFDM. In this paper, we address the problem of correcting the symbol timing offset in DCT-MCM. Two sliding window-based correlation algorithms are proposed. The new approaches consider a prefix and a suffix that are inserted into each data symbol, which are the replica of part of the useful data. The performance of the proposed approaches is verified and tested, and their usefulness and effectiveness are illustrated by computer simulations.
IEEE Transactions on Wireless Communications, 2019
This paper aims at studying the achievable data rate of discrete cosine transform (DCT)-based mul... more This paper aims at studying the achievable data rate of discrete cosine transform (DCT)-based multicarrier modulation (MCM) systems. To this end, a general formulation is presented for the full transmission/reception process of data in Type−II even DCT and Type−IV even DCT-based systems. The paper focuses on the use of symmetric extension (SE) and zero padding (ZP) as redundancy methods. Furthermore, three cases related to the channel order and the length of the redundancy are studied. In the first case, the channel order is less than or equal to the length of the redundancy. In the second and third cases, the channel order is greater than the length of the redundancy; the interference caused by the channel impulse response is calculated, and theoretical expressions for their powers are derived. These expressions allow studying the achievable data rate of DCT-based MCM systems, besides enabling the comparison with the conventional MCM based on the discrete Fourier Transform. Index Terms-Multicarrier modulation (MCM), single carrier modulation (SCM), orthogonal frequency-division multiplexing (OFDM), discrete multi-tone modulation (DMT), cyclic prefix (CP), symmetric extension (SE), zero padding (ZP), discrete Fourier transform (DFT), discrete cosine transform (DCT).
Circuits, Systems, and Signal Processing, 2018
The electrocardiogram (ECG) is relevant for several medical purposes. In this work, a novel analy... more The electrocardiogram (ECG) is relevant for several medical purposes. In this work, a novel analysis-by-synthesis method to process ECG signals is presented. It is based on the matching pursuit algorithm, which is employed here to decompose the ECG in the time domain. The main features of the ECG are extracted through a dictionary of triangular functions, due to their good correlation with the typical electrocardiographic waveforms, especially the R wave. The individual elements of this signal representation can be further employed for different processing tasks, such as ECG compression and QRS detection. Compression is required to store and transmit signals in situations related to massive acquisitions, frequent monitoring, high-resolution data, real-time needs or narrow bandwidths. QRS detection is not only essential to study the heart rate variability, but also the basis of automatic systems for ECG applications such as heartbeat classification or anomaly identification. In this study, it is shown how to employ the proposed processing approach to perform ECG compression and beat detection jointly. The resulting algorithm is tested over the whole MIT-BIH Arrhyth-This work has been partially supported by the Spanish Ministry of Economy and Competitiveness through Project TEC2015-64835-C3-1-R and by CNPq (Brazil) through Project 302829/2017-2.
Physiological Measurement, 2015
The aim of electrocardiogram (ECG) compression is to reduce the amount of data as much as possibl... more The aim of electrocardiogram (ECG) compression is to reduce the amount of data as much as possible while preserving the significant information for diagnosis. Objective metrics that are derived directly from the signal are suitable for controlling the quality of the compressed ECGs in practical applications. Many approaches have employed figures of merit based on the percentage root mean square difference (PRD) for this purpose. The benefits and drawbacks of the PRD measures, along with other metrics for quality assessment in ECG compression, are analysed in this work. We propose the use of the root mean square error (RMSE) for quality control because it provides a clearer and more stable idea about how much the retrieved ECG waveform, which is the reference signal for establishing diagnosis, separates from the original. For this reason, the RMSE is applied here as the target metric in a thresholding algorithm that relies on the retained energy. A state of the art compressor based on this approach, and its PRD-based counterpart, are implemented to test the actual capabilities of the proposed technique. Both compression schemes are employed in several experiments with the whole MIT-BIH Arrhythmia Database to assess both global and local signal distortion. The results show that, using the RMSE for quality control, the distortion of the reconstructed signal is better controlled without reducing the compression ratio.
ISPA 2005. Proceedings of the 4th International Symposium on Image and Signal Processing and Analysis, 2005., 2005
This paper introduces a novel approach for designing critically sampled cosine-modulated transcei... more This paper introduces a novel approach for designing critically sampled cosine-modulated transceivers (CMTs) for communications applications. The key idea in this approach is to design the prototype filter in such a manner that it provides a properly optimized tradeoff between the inter-symbol and inter-channel interferences for CMTs without directly concentrating on designing the prototype filter according to any predetermined criteria.
Proceedings of the 2014 IEEE Emerging Technology and Factory Automation (ETFA), 2014
Authors propose with the real-time implementation of a transmultiplexer based on an embedded filt... more Authors propose with the real-time implementation of a transmultiplexer based on an embedded filter bank as a medium access technique for multicarrier communications, such as in broadband PLC (power-line communications). For that purpose, the signal processing algorithms have been analyzed, not only to determine the corresponding requirements, but also to optimize them for a suitable implementation. The definition of an efficient SoC-based architecture to achieve real-time performance has been carried out. The proposed architecture has been optimized in terms of datawidth, data rates and frequencies, as well as resource consumption.
Signal Processing, 2011
... 1, pp.53-60, Jan./Feb. 2008. [12] GH Jajamovich and CG Galarza, Multicarrier demodulation for... more ... 1, pp.53-60, Jan./Feb. 2008. [12] GH Jajamovich and CG Galarza, Multicarrier demodulation for frequency selective channels subject to narrow band interferences, Digital Signal Processing, vol. 18, no. 4, pp. 598-611, Jul. 2008. ...
Medical Engineering & Physics, 2012
The recent use of long-term records in electroencephalography is becoming more frequent due to it... more The recent use of long-term records in electroencephalography is becoming more frequent due to its diagnostic potential and the growth of novel signal processing methods that deal with these types of recordings. In these cases, the considerable volume of data to be managed makes compression necessary to reduce the bit rate for transmission and storage applications. In this paper, a new compression algorithm specifically designed to encode electroencephalographic (EEG) signals is proposed. Cosine modulated filter banks are used to decompose the EEG signal into a set of subbands well adapted to the frequency bands characteristic of the EEG. Given that no regular pattern may be easily extracted from the signal in time domain, a thresholding-based method is applied for quantizing samples. The method of retained energy is designed for efficiently computing the threshold in the decomposition domain which, at the same time, allows the quality of the reconstructed EEG to be controlled. The experiments are conducted over a large set of signals taken from two public databases available at Physionet and the results show that the compression scheme yields better compression than other reported methods.
IEEE Transactions on Wireless Communications, 2013
Multicarrier and single-carrier communications can be performed by using different orthogonal tra... more Multicarrier and single-carrier communications can be performed by using different orthogonal transforms. In this work, we derive the conditions to use discrete cosine transform type-IV even (DCT4e) in these contexts. Basically, these conditions are the two following: 1) The channel impulse response has to be symmetric. 2) Redundancy (a prefix and also a suffix guard sequence) must be appended into each data symbol to be transmitted. To satisfy the former, a front-end prefilter must be incorporated at the receiver. With regard to the second condition, we use a matrix formulation to demonstrate how the global transmission channel matrix can be diagonalized when symmetric extension or zero padding are used as redundancy. The use of zero padding requires an additional block at the receiver, whose structure is also shown. Moreover, a new expression based on the DCT4e to obtain the value of the per-subcarrier coefficients of the frequency-domain equalizer is derived. Finally, the proposed transceivers are compared to the DFT-based standardized systems in different communication scenarios under the presence of carrier frequency offset. Index Terms-Multicarrier transceiver, multicarrier modulation (MCM), discrete Fourier transform (DFT), discrete cosine transform (DCT), single-carrier frequency domain equalization (SC-FDE), single-carrier frequency domain multiple access (SC-FDMA), orthogonal frequency-division multiplexing (OFDM), carrier-frequency offset (CFO).
IEEE Transactions on Circuits and Systems II: Analog and Digital Signal Processing, 2003
A digital quadrature demodulator is proposed that gives the complex components of the received si... more A digital quadrature demodulator is proposed that gives the complex components of the received signal. The adoption of a modulated local oscillator (LO) with four periodic phase states synchronized with the sampling avoids the use of two mixing paths, simplifying the radio-frequency (RF) circuits and allowing an effective VLSI integration. This receiver minimizes the in-phase/quadrature (I/Q) mismatch and, with an adequate choice of the periodic modulating sequence, avoids the direct current (dc) offset of the direct conversion receivers.
I Jornadas científicas …, 2010
Información del artículo Análisis de esquemas de comprensión de EEG basados en bancos de filtros ... more Información del artículo Análisis de esquemas de comprensión de EEG basados en bancos de filtros modulados y transformada Wavelet.
Sensors, 2021
The aim of this paper is to formulate the physical layer of the broadband and narrowband power li... more The aim of this paper is to formulate the physical layer of the broadband and narrowband power line communication (PLC) systems described in standards IEEE 1901 and IEEE 1901.2, which address new communication technologies over electrical networks for Smart Grid and Internet of Things applications. Specifically, this paper presents a mathematical formulation by means of matrices of a transmitter and receiver system based on windowed OFDM. The proposed formulation is essential for obtaining the input–output relation, as well as an analysis of the interference present in the system. It is very useful for simulating PLC systems using software designed to operate primarily on whole matrices and arrays, such as Matlab. In addition, it eases the analysis and design of different receiver configurations, simply by modifying or adding a matrix. Since the relevant standards only describe the blocks corresponding to the transmitter, and leave the set-up of the receiver open to the manufacturer...
Digital Signal Processing, 2000
Alternating Analysis and Synthesis Filters: A New Pseudo-QMF Bank, Digital Signal Processing 11 (... more Alternating Analysis and Synthesis Filters: A New Pseudo-QMF Bank, Digital Signal Processing 11 (2001) 329-345.
2001 Conference Proceedings of the 23rd Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2001
An electrocardiogram (ECG) compression technique based on subband coding has been developed in th... more An electrocardiogram (ECG) compression technique based on subband coding has been developed in this paper to compare with compression techniques based on Wavelet Packets (WP). The filter bank designed is a cosine-modulated pseudo-QMF bank using the Kaiser Window Approach (KWA) method that does not have the perfect reconstruction (PR) property, as opposed to WP that are implemented by means of a PR filter bank. In both schemes, the coding process is the same to be able to compare the results. This is carried out using a very easy algorithm based on a thresholding technique, which provides good compression rate. Its main application is to encode long-term registers of digitized electrocardiogram signal, in order to reduce the bit rate. To preserve the reconstructed signal accuracy, the percentage root-mean-square difference (PRD) is used as an objective measurement parameter, which is selected before compression. The tests have been done for the twelve principal cardiac leads, and the compression degree measurement is evaluated by means of the mean number of bits per sample (MBPS) and the compression ratio (CR).
2004 IEEE International Symposium on Circuits and Systems (IEEE Cat. No.04CH37512), 2004
Abstract Recently, the authors of this paper studied the performance of a simple design scheme fo... more Abstract Recently, the authors of this paper studied the performance of a simple design scheme for synthesizing nearly perfect-reconstruction critically sampled cosine-modulated M-channel filter bank and transmultiplexer systems without nonlinear optimizations. In this ...
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Papers by Fernando Cruz-roldán