Design of serially-concatenated LDGM codes

[Resumen] Since Shannon demonstrated in 1948 the feasibility of achieving an arbitrarily low error probability in a communications system provided that the transmission rate was kept below a certain limit, one of the greatest challenges in the realm of digital communications and, more specifically, in the channel coding field, has been finding codes that are able to approach this limit as much as possible with a reasonable encoding and decoding complexity, However, it was not until 1993, when Berrou et al. presented the turbo codes, that a coding scheme capable of performing at less than 1dB from Shannon's limit with an extremely low error probability was found. The idea on which these codes are based is the iterative decoding of concatenated components that exchange information about the transmitted bits, which is known as the "turbo principle". The generalization of this idea led in 1995 to the rediscovery of LDPC (Low Density Parity Check) codes, proposed for the first time by Gallager in the 60s. LDPC codes are linear block codes with a sparse parity check matrix that are able to surpass the performance of turbo codes with a smaller decoding complexity. However, due to the fact that the generator matrix of general LDPC codes is not sparse, their encoding complexity can be excessively high. LDGM (Low Density Generator Matrix) codes, a particular case of LDPC codes, are codes with a sparse generator matrix, thanks to which they present a lower encoding complexity. However, except for the case of very high rate codes, LDGM codes are "bad", i.e., they have a non-zero error probability that is independent of the code block length. More recently, IRA (Irregular Repeat-Accumulated) codes, consisting of the serial concatenation of a LDGM code and an accumulator, have been proposed. IRA codes are able to get close to the performance of LDPC codes with an encoding complexity similar to that of LDGM codes. In this thesis we explore an alternative to IRA codes consisting in the serial concatenation of two LDGM codes, a scheme that we will denote SCLDGM (Serially-Concatenated Low-Density Generator Matrix). The basic premise of SCLDGM codes is that an inner code of rate close to the desired transmission rate fixes most of the errors, and an external code of rate close to one corrects the few errors that result from decoding the inner code. For any of these schemes to perform as close as possible to the capacity limit it is necessary to determine the code parameters that best fit the channel over which the transmission will be done. The two techniques most commonly used in the literature to optimize LDPC codes are Density Evolution (DE) and EXtrinsic Information Transfer (EXIT) charts, which have been employed to obtain optimized codes that perform at a few tenths of a decibel of the AWGN channel capacity. However, no optimization techniques have been presented for SCLDGM codes, which so far have been designed heuristically and therefore their performance is far from the performance achieved by IRA and LDPC codes. Other of the most important advances that have occurred in recent years is the utilization of multiple antennas at the trasmitter and the receiver, which is known as MIMO (Multiple-Input Multiple-Output) systems. Telatar showed that the channel capacity in these kind of systems scales linearly with the minimum number of transmit and receive antennas, which enables us to achieve spectral efficiencies far greater than with systems with a single transmit and receive antenna (or Single Input Single Output (SISO) systems). This important advantage has attracted a lot of attention from the research community, and has caused that many of the new standards, such as WiMax 802.16e or WiFi 802.11n, as well as future 4G systems are based on MIMO systems. The main problem of MIMO systems is the high complexity of optimum detection, which grows exponentially with the number of transmit antennas and the number of modulation levels. Several suboptimum algorithms have been proposed to reduce this complexity, most notably the SIC-MMSE (Soft-Interference Cancellation Minimum Mean Square Error) and spherical detectors. Another major issue is the high complexity of the channel estimation, due to the large number of coefficients which determine it. There are techniques, such as Maximum-Likelihood-Expectation-Maximization (ML-EM), that have been successfully applied to estimate MIMO channels but, as in the case of detection, they suffer from the problem of a very high complexity when the number of transmit antennas or the size of the constellation increase. The main objective of this work is the study and optimization of SCLDGM codes in SISO and MIMO channels. To this end, we propose an optimization method for SCLDGM codes based on EXIT charts that allow these codes to exceed the performance of IRA codes existing in the literature and get close to the performance of LDPC codes, with the advantage over the latter of a lower encoding complexity. We also propose optimized SCLDGM codes for both spherical and SIC-MMSE suboptimal MIMO detectors, constituting a system that is capable of approaching the capacity limits of MIMO channels with a low complexity encoding, detection and decoding. We analyze the BICM (Bit-Interleaved Coded Modulation) scheme and the concatenation of SCLDGM codes with Space-Time Codes (STC) in ergodic and quasi-static MIMO channels. Furthermore, we explore the combination of these codes with different channel estimation algorithms that will take advantage of the low complexity of the suboptimum detectors to reduce the complexity of the estimation process while keeping a low distance to the capacity limit. Finally, we propose coding schemes for low rates involving the serial concatenation of several LDGM codes, reducing the complexity of recently proposed schemes based on Hadamard codes

Avaliación 4.0: avaliación cooperativa en metodoloxías con aprendizaxe invertida

[Resumo] A palabra CAMBIO describe claramente a situación da Educación a todos os niveis (primaria, secundaria e superior) na nosa comunidade e fóra dela, polo que nos preguntamos se estamos preparados para este cambio. Vivimos na Sociedade da Información, unha sociedade en constante evolución que transforma tamén a Educación, de xeito que cómpre falar de Educación na Sociedade da Información. Este traballo xorde da vontade duns docentes por cambiar “algo” na súa docencia máis ou menos tradicional. Un dos aspectos máis críticos para os estudantes é, sen dúbida, a avaliación. A avaliación forma parte do proceso de aprendizaxe principalmente para determinar o grao de adquisición de competencias e adaptar o proceso educativo segundo as características do estudante ou grupo de estudantes. A responsabilidade da mesma é tradicionalmente do profesor, co que estamos a excluír o alumno deste elemento fundamental da educación. A demanda de roles de avaliación invertidos é crecente, polo que neste traballo propoñemos unha AVALIACION 4.0. Nela, estudantes e profesores comparten o rol de árbitros no proceso de aprendizaxe involucrando de xeito activo os primeiros, non só como deseñadores de probas ou instrumentos de avaliación, senón tamén como co-avaliadores, un rol innovador que, por analoxía coa aula invertida, leva a unha avaliación invertida.[Abstract] The word CHANGE clearly describes the state-of-the-art of Education at all levels (primary, secondary and higher) in our community and outside of it, so we are wondering if we are prepared for such a change. We live in the Information Society, which is continuously evolving and Education changes with it. Thus talking about Education in the Information Society is mandatory. This work arises from the willingness of some professors of higher education to change "something" in their more or less traditional teaching. The assessment is definitely the most critical aspect of the learning process from the point of view of students. The assessment determines the degree of acquisition of competences and adapts the educational process according to the characteristics of the student or group of students. The professor is traditionally responsible for that, so students are excluded from that task. The demand for flipping assessment roles is growing, and therefore in this work we propose what we denote 4.0 ASSESSMENT. Both students and teachers will share the role of referees in the learning process by actively involving students not only as designers of assessment tests and instruments but also as coevaluators, an innovative role that takes us by analogy with the flipped classroom to flipped assessmen

Incorporación de Trabajos Fin de Grado breves en la docencia

[Resumen] Los autores de esta ponencia participamos de forma activa tanto en la dirección de Trabajos Fin de Grado (TFG) como en los tribunales que los evalúan. Nuestra experiencia nos indica que, en general, los estudiantes demuestran haber adquirido las competencias de la titulación de forma satisfactoria, pero muestran carencias en competencias transversales, como la expresión oral y escrita. Esto nos ha llevado a plantear la incorporación de "TFG breves" en las asignaturas que impartimos en los últimos cursos de las titulaciones. La realización de los “TFG breves” sigue una metodología de Aprendizaje Basado en Proyectos (ABP) que se centra en la resolución de problemas o retos por parte del estudiante, dándole la oportunidad de trabajar de manera relativamente autónoma durante la mayor parte del tiempo y que culmina con la presentación de un producto final. Los “TFG breves” son elaborados por grupos de 2 o 3 estudiantes. El desarrollo es supervisado por el profesorado, permitiendo que gradualmente los estudiantes vayan responsabilizándose del trabajo. Además de desarrollar el proyecto, los estudiantes deben escribir una memoria y preparar una presentación oral de acuerdo con la normativa del TFG de su titulación. Un tribunal, formado por un profesor y por estudiantes, se encarga de revisar la memoria, realizar preguntas durante la presentación y emitir una calificación individual. El proceso termina con una reunión del profesorado con cada uno de los grupos para comentar los aspectos fuertes y débiles del proyecto desarrollado. Con esta metodología, intentamos contribuir a la adquisición de competencias transversales: la autonomía y el trabajo en grupo; la expresión oral y escrita; y la reflexión autocrítica. Además, buscamos que los estudiantes de los últimos cursos se familiaricen con las herramientas necesarias para la elaboración del TFG y con el procedimiento de defensa. AGRADECIMIENTOS: Los autores de este trabajo forman parte del Grupo de Innovación Educativa en Metodologías Activas y Tecnologías Emergentes en la Enseñanza Superior (MATEes), de la Universidade da Coruñ

New Computation of Resolving Connected Dominating Sets in Weighted Networks

[Abstract] In this paper we focus on the issue related to finding the resolving connected dominating sets (RCDSs) of a graph, denoted by G. The connected dominating set (CDS) is a connected subset of vertices of G selected to guarantee that all vertices in the graph are connected to vertices in the CDS. The connected dominating set with minimum cardinality, or minimum CDS (MCDS), is an adequate virtual backbone for information interchange in a network. When distinct vertices of G have also distinct representations with respect to a subset of vertices in the MCDS, it is said that the MCDS includes a resolving set (RS) of G. With this work, we explore different strategies to find the RCDS with minimum cardinality in complex networks where the vertices have different importances.Xunta de Galicia; ED431C 2016-045Xunta de Galicia; ED341D R2016/012Xunta de Galicia; ED431G/01Agencia Estatal de Investigación de España; TEC2013-47141-C4-1-RAgencia Estatal de Investigación de España; TEC2015-69648-REDCAgencia Estatal de Investigación de España; TEC2016-75067-C4-1-

Unha experiencia de aprendizaxe e servizo: tfg: unha ferramenta para o desenvolvemento de aplicacións móbiles de apoio á diversidade

Banco de experiencias de Aprendizaxe Servizo. Convocatoria 2021/202

Eye State Identification Based on Discrete Wavelet Transforms

[Abstract]: We present a prototype to identify eye states from electroencephalography signals captured from one or two channels. The hardware is based on the integration of low-cost components, while the signal processing algorithms combine discrete wavelet transform and linear discriminant analysis. We consider different parameters: nine different wavelets and two features extraction strategies. A set of experiments performed in real scenarios allows to compare the performance in order to determine a configuration with high accuracy and short response delay.Xunta de Galicia; ED431C 2020/15Xunta de Galicia; ED431G2019/01Xunta de Galicia; ED481A-2018/156This work has been funded by the Xunta de Galicia (by grant ED431C 2020/15 and grant ED431G2019/01 to support the Centro de Investigación de Galicia “CITIC”), the Agencia Estatal de Investigación of Spain (by grants RED2018-102668-T and PID2019-104958RB-C42) and ERDF funds of the EU (FEDER Galicia & AEI/FEDER, UE); and the predoctoral Grant No. ED481A-2018/156 (Francisco Laport)

A Comparative Study of Low Cost Open Source EEG Devices

[Abstract] A comparison of two open source electroencephalography devices designed to acquire signals associated to the brain activity is presented in this work. The experiments are developed considering the task of determining the user eye state i.e., open eyes or closed eyes, applying an algorithm based on computing the sliding Fourier Transform of the captured signals.Xunta de Galicia; ED481A-2018/15

Proposals and Comparisons from One-Sensor EEG and EOG Human-Machine Interfaces

[Abstract] Human-Machine Interfaces (HMI) allow users to interact with different devices such as computers or home elements. A key part in HMI is the design of simple non-invasive interfaces to capture the signals associated with the user’s intentions. In this work, we have designed two different approaches based on Electroencephalography (EEG) and Electrooculography (EOG). For both cases, signal acquisition is performed using only one electrode, which makes placement more comfortable compared to multi-channel systems. We have also developed a Graphical User Interface (GUI) that presents objects to the user using two paradigms—one-by-one objects or rows-columns of objects. Both interfaces and paradigms have been compared for several users considering interactions with home elements.Xunta de Galicia; ED431C 2020/15Xunta de Galicia; ED431G2019/01Agencia Estatal de Investigación de España; RED2018-102668-TAgencia Estatal de Investigación de España; PID2019-104958RB-C42Xunta de Galicia; ED481A-2018/156This work has been funded by the Xunta de Galicia (by grant ED431C 2020/15, and grant ED431G2019/01 to support the Centro de Investigación de Galicia “CITIC”), the Agencia Estatal de Investigación of Spain (by grants RED2018-102668-T and PID2019-104958RB-C42) and ERDF funds of the EU (FEDER Galicia & AEI/FEDER, UE); and the predoctoral Grant No. ED481A-2018/156 (Francisco Laport

A Prototype of EEG System for IoT

[Abstract] In this work, we develop open source hardware and software for eye state classification and integrate it with a protocol for the Internet of Things (IoT). We design and build the hardware using a reduced number of components and with a very low-cost. Moreover, we propose a method for the detection of open eyes (oE) and closed eyes (cE) states based on computing a power ratio between different frequency bands of the acquired signal. We compare several real- and complex-valued transformations combined with two decision strategies: a threshold-based method and a linear discriminant analysis. Simulation results show both classifier accuracies and their corresponding system delays.Xunta de Galicia; ED431G2019/01)Agencia Estatal de Investigación de España; TEC2016-75067-C4-1-RXunta de Galicia; ED481A-2018/156Xunta de Galicia; ED431G 2019/01This work has been funded by the Xunta de Galicia (ED431G2019/01), the Agencia Estatal de Investigacion of Spain (TEC2016-75067-C4-1-R) and ERDF funds of the EU (AEI/FEDER, UE), and the predoctoral Grant No. ED481A-2018/156 (Francisco Laport). CITIC as a Research Centre of the Galician University System is financed by the Conselleria de Educacion, Universidades e Formacion Profesional (Xunta de Galicia) through the ERDF (80%), Operational Programme ERDF Galicia 2014–2020 and the remaining 20% by the Secretaria Xeral de Universidades (Ref. ED431G 2019/01

Eye State Detection Using Frequency Features from 1 or 2-Channel EEG

© The Author(s) This is an Open Access article published by World Scientific Publishing Company. It is distributed under the terms of the Creative Commons Attribution 4.0 (CC BY) License which permits use, distribution and reproduction in any medium, provided the original work is properly cited.[Abstract]: Brain–computer interfaces (BCIs) establish a direct communication channel between the human brain and external devices. Among various methods, electroencephalography (EEG) stands out as the most popular choice for BCI design due to its non-invasiveness, ease of use, and cost-effectiveness. This paper aims to present and compare the accuracy and robustness of an EEG system employing one or two channels. We present both hardware and algorithms for the detection of open and closed eyes. Firstly, we utilize a low-cost hardware device to capture EEG activity from one or two channels. Next, we apply the discrete Fourier transform to analyze the signals in the frequency domain, extracting features from each channel. For classification, we test various well-known techniques, including Linear Discriminant Analysis (LDA), Support Vector Machine (SVM), Decision Tree (DT), or Logistic Regression (LR). To evaluate the system, we conduct experiments, acquiring signals associated with open and closed eyes, and compare the performance between one and two channels. The results demonstrate that employing a system with two channels and using SVM, DT, or LR classifiers enhances robustness compared to a single-channel setup and allows us to achieve an accuracy percentage greater than 95% for both eye states.This work has been supported by Grant No. ED431C 2020/15 funded by Xunta de Galicia and ERDF Galicia 2014–2020; by Grant No. PID2019-104958RB-C42 (ADELE) funded by MCIN/AEI/10.13039/501100 011033; and by project TED2021-130240B-I00 (IVRY) funded by MCIN/AEI/10.13039/501100011033 and by the European Union NextGeneration EU/PRTR and by the postdoctoral Grant No. ED481B 2022/012 funded by Xunta de Galicia.Xunta de Galicia; ED431C 2020/15Xunta de Galicia; ED481B 2022/01