Distance learning offered to students by Swedish universities has continued to increase, which has led to an increase in the use of learning management system (LMS). Recently, due to the pandemic, many universities have temporarily made university classes compulsory as distance through remote learning, and the importance of LMS is also emerging. However, there is a problem that the dropout rate of remote students is significantly higher than that of on-campus students. Therefore, this qualitative study aims to propose various suggestions to enhance students' learning experience by understanding their perception and experience of using Moodle, one of the popular LMS platforms, for the distance students of Information system master program of Linnaeus university. When evaluating the system as a model for this study, David (1989)'s Technology acceptance model (TAM), which has already been verified in many studies, was considered first, but this model does not take into account the feelings of system users. After that, Hassenzhal's UX model was finally adopted as a model for this study. However, this study shows that Hedonic attributes, one of the elements of Apparent product character of this UX model, does not play any role for evaluating UX in LMS platforms such as Moodle. The reason for this is that users think of Moodle as a learning information tool only for their study purpose, and their identification and social communication are significantly poor in the platform. Also, Moodle does not provide any stimulation to their feeling. As the research method, semi-structured interviews were conducted through Skype or Zoom with 7 Moodle users from 5 different nationalities who voluntarily applied for the interviews. As a result, it was found that 8 issues (Usability and design of the main page and dashboard, information distributed across multiple platforms, notification and landing issue, lack of awareness of students about some features of Moodle, presence of unnecessary features, slow website speed, low use of mobile applications, non-standardized course page design) on Moodle through their past experiences that could be detrimental to the user experience. Based on the findings, this paper will discuss various suggestions to improve Moodle's UX for distance students’ better learning experience.

MCom / Department of Business Management / See the attached abstract below

Dans cette thèse nous nous sommes intéressés principalement, dans le cadre de l’e-learning, à mettre en oeuvre une méthodologie qui a pour mission d’assurer une interopérabilité entre la plate-forme de l’Université de Lubumbashi et les plates-formes des universités partenaires belges afin de permettre un transfert des contenus d’apprentissage. Notre démarche n’a pas voulu s’arrêter à l’échange des contenus, nous sommes allés jusqu’à proposer des moyens de permettre un suivi dynamique des étudiants via les outils de communication./ In this thesis we were mainly interested, within the framework of the e-learning, to implement(operate) a methodology which has for mission to assure(insure) an interoperability between the platform of the University of Lubumbashi and the platforms of the Belgian partner universities to allow a transfer of the contents of learning(apprenticeship). Our approach(initiative) did not want to stop(arrest) in the exchange of the contents, we went as far as suggesting means allowing a dynamic follow-up of the students via communications tools.<p> / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Webbasierte Lehr-Lernformen sind Gegenstand zahlreicher Forschungsprojekte, die häufig auf den technischen Hintergrund und den didaktischen Einsatz im Kontext der Ausbildung an Universitäten und Hochschulen fokussieren. In den Schulen befindet sich der Einsatz von E-Learning im Unterricht vorwiegend im Erprobungsstatus, da didaktische Szenarien, die Lehrer zu einem sinnvollen, lernzielorientierten Einsatz dieser Lehr-Lernmethode im Schulunterricht befähigen, erst noch zu entwickeln sind. Mit dem Übergang von der Schule zur Hochschule treffen die Abiturienten als Studienanfänger auf eine Hochschullandschaft, in der Lernumgebungen weitgehend etabliert sind. Selbstbestimmtes webbasiertes Lernen, das Organisieren des eigenen Studienablaufes via Webportal aber auch die im Vergleich zum Schulunterricht veränderte Methodik der Inhaltsvermittlung in den gewählten Studienfächern bedeuten für die jungen Studentinnen und Studenten neue Herausforderungen, denen sie teilweise unzureichend vorbereitet gegenüber stehen. Aus dem ESF-geförderten Projekt „Übergang Schule-Hochschule mit Unterstützung internetbasierter E-Learning-Tools (UnIbELT)“ sind Erfahrungen hervorgegangen, wie die Etablierung geeigneter, didaktisch aufbereiteter E-Learning-Szenarien in den Schulen einen Beitrag dazu leisten kann, künftige Studierende auf den Übergang zur Hochschule vorzubereiten und sie mit den Studienanforderungen vertraut zu machen. Diese Erfahrungen stützen sich auf mehr als 70 durchgeführte E-Learning-Kurse in 21 Gymnasien Sachsens, an denen seit 2009 mehr als 1100 Schüler der Sekundarstufe II teilgenommen haben.

Can adult learners of international English learn the language online? This thesis relates research in the domains of the English language learning paradigm, Second Language Acquisition theories, and online language learning findings to produce a model for an English Language Learning Online Network (ELLON) for usage from within an educational institution. This model is partially designable over Moodle. The main original features of this learning design are the reversal of the knowledge transmission system through learner-generated lessons and learning objects, a model designed towards an expanding network of users, knowledge conceptualization and reuse of generated language learning objects; personalization to the socio-economic context of learner needs in English; and its focus on the learning of “online international English” competences. Guidelines are given towards the building and testing of this “ELLON” model. ELLON is designed for learners of English with a B1 level onwards.

Radio astronomy is the science of observing the heavens at radio frequencies, from a few kHz to approximately 300 GHz. In recent years, radio astronomy has faced a growing interference problem as radio frequency (RF) bandwidth has become an increasingly scarce commodity. A programmable real-time DSP least-mean-square interference canceller was developed and demonstrated as a successful method of excising satellite down-link signals from both an experimental platform at BYU, and the Green Bank Telescope at the National Radio Astronomy Observatory in West Virginia. A performance analysis of this cancellation system in the radio astronomy radio frequency interference (RFI) mitigation regime constitutes the main contribution of this thesis. The real-time BYU test platform consists of small radio telescopes, low noise RF receivers, and a state-of-the-art DSP platform. This programmable real-time radio astronomy RFI mitigation tool is the first of its kind. Basic tools needed for radio astronomy observations and the analysis and implementation of interference mitigation algorithms were also implemented in the DSP platform, including a power spectral density estimator, a beamformer, and an array signal correlator.

在迴歸分析中，當資料中存在很多離群值時，偵測的工作變得非常不容易。 在此狀況下，我們無法使用傳統的殘差分析正確地偵測出其是否存在，此現象稱為遮蔽效應(The Masking Effect)。 而為了避免此效應的發生，我們利用最小中位數穩健迴歸估計值(Least Median Squares Estimator)正確地找出這些群集離群值，此估計值擁有最大即50﹪的容離值 (Breakdown point)。 在這篇論文中，用來求出最小中位數穩健迴歸估計值的演算法稱為步進搜尋演算法 (the Forward Search Algorithm)。 結果顯示，我們可以利用此演算法得到的穩健迴歸估計值，很快並有效率的找出資料中的群集離群值；另外，更進一步的結果顯示，我們只需從資料中隨機選取一百次子集，並進行步進搜尋，即可得到概似的穩健迴歸估計值並正確的找出那些群集離群值。 最後，我們利用鐘乳石圖(Stalactite Plot)列出所有被偵測到的離群值。 在多變量資料中，我們若使用Mahalanobis距離也會遭遇到同樣的屏蔽效應。 而此一問題，隨著另一高度穩健估計值的採用，亦可迎刃而解。 此估計值稱為最小體積橢圓體估計值 (Minimum Volume Ellipsoid)，其亦擁有最大即50﹪的容離值。 在此，我們也利用步進搜尋法求出此估計值，並利用鐘乳石圖列出所有被偵測到的離群值。 這篇論文的第二部分則利用變數轉換的技巧將迴歸資料中的殘差項常態化並且加強其等變異的特性以利後續的資料分析。 在步進搜尋進行的過程中，我們觀察分數統計量(Score Statistic)和其他相關診斷統計量的變化。 結果顯示，這些統計量一起提供了有關轉換參數選取豐富的資訊，並且我們亦可從步進搜尋進行的過程中觀察出某些離群值對參數選取的影響。 / Detecting regression outliers is not trivial when there are many of them. The methods of using classical diagnostic plots sometimes fail to detect them. This phenomenon is known as the masking effect. To avoid this, we propose to find out those multiple outliers by using a highly robust regression estimator called the least median squares (LMS) estimator which has maximal breakdown point. The algorithm in search of the LMS estimator is called the forward search algorithm. The estimator found by the forward search is shown to lead to the rapid detection of multiple outliers. Furthermore, the result reveals that 100 repeats of a simple forward search from a random starting subset are shown to provide sufficiently robust parameter estimators to reveal multiple outliers. Finally, those detected outliers are exhibited by the stalactite plot that shows greatly stable pattern of them. Referring to multivariate data, the Mahalanobis distance also suffers from the masking effect that can be remedied by using a highly robust estimator called the minimum volume ellipsoid (MVE) estimator. It can also be found by using the forward search algorithm and it also has maximal breakdown point. The detected outliers are then displayed in the stalactite plot. The second part of this dissertation is the transformation of regression data so that the approximate normality and the homogeneity of the residuals can be achieved. During the process of the forward search, we monitor the quantity of interest called score statistic and some other diagnostic plots. They jointly provide a wealth of information about transformation along with the effect of individual observation on this statistic.

Τα σύγχρονα πληροφοριακά συστήματα μάθησης τα οποία υποστηρίζουν εξ’ αποστάσεως εκπαίδευση, επιτρέπουν τη συστηματική διαχείριση του εκπαιδευτικού υλικού και υποστηρίζουν τις εκπαιδευτικές διαδικασίες των μαθημάτων. Τα συστήματα αυτά έχουν λειτουργικότητες όπως: η ανάρτηση ψηφιακού υλικού, η διεξαγωγή συζητήσεων, η ανάρτηση ασκήσεων-εργασιών, η πραγματοποίηση εξετάσεων και πολλές άλλες. Στόχος της συγκεκριμένης εργασίας είναι η διερεύνηση του χώρου των συστημάτων μάθησης τα οποία υποστηρίζουν εξ’ αποστάσεως εκπαίδευση καθώς επίσης και η παρουσίαση και η εφαρμογή μεθόδου αξιολόγησης τους, αξιολογώντας τα συστήματα σύμφωνα με μια λίστα λειτουργικών απαιτήσεων. Στο 1ο κεφάλαιο της διπλωματικής εργασίας γίνεται μια περιγραφή των βασικών εννοιών της εξ’αποστάσεως εκπαίδευσης καθώς επίσης και έννοιες που αφορούν τα συστήματα υποστήριξης μάθησης όπως:CBT, VLE, LMS, LCMS, CMS, Mobile Learning. Στο 2ο κεφάλαιο γίνεται μια επισκόπηση του χώρου των Συστημάτων Μάθησης Learning Course Management Systems (LCMS). Συγκεκριμένα γίνεται μία καταγραφή των χαρακτηριστικών των πιο δημοφιλών συστημάτων τόσο των εμπορικών όσο και των συστημάτων ανοικτού κώδικα με τη χρήση ενός κοινού template όπου καταγράφονται τα εξής στοιχεία: Κατασκευαστής, Σύντομη περιγραφή Λογισμικού, Πλεονεκτήματα (Δυνατά Σημεία ), Μειονεκτήματα (Αδυναμίες, Ελλείψεις), Πελατολόγιο, Τρέχουσα Έκδοση έτσι ώστε να μπορεί κάποιος εύκολα να τα συγκρίνει και να τα αξιολογήσει. Στο 3ο κεφάλαιο πραγματοποιείται ανάλυση απαιτήσεων ενός σύγχρονου συστήματος μάθησης έτσι ώστε να μπορεί να εφαρμοστεί η μεθοδολογία αξιολόγησης σε μια λίστα από χαρακτηριστικά-απαιτήσεις για τα συστήματα που παρουσιάζονται στο κεφάλαιο 2. Στο 4ο κεφάλαιο παρουσιάζεται η μεθοδολογία Αξιολόγησης των συστημάτων μάθησης η οποία στηρίζεται στη θεωρία της ασαφούς λογικής. Η συγκεκριμένη μεθοδολογία εφαρμόστηκε σαν μελέτη περίπτωσης για την αξιολόγηση συστημάτων εκπαιδευτικών δραστηριοτήτων προκειμένου να βρεθεί το πλέον κατάλληλο σύστημα για τις ανάγκες του Ελληνικού Ανοικτού Πανεπιστημίου. Τέλος στο κεφάλαιο 5 πραγματοποιείται η εφαρμογή της μεθοδολογίας αξιολόγησης μεταξύ των συστημάτων μάθησης και παρουσιάζονται τα αποτελέσματα- συμπεράσματα που εξάγονται από την εφαρμογή της μεθόδου ενώ στο τελευταίο κεφάλαιο (6ο ) παρουσιάζονται τα συμπεράσματα της εργασίας. / Modern learning information systems are designed to support distance education and have many features to support learning sequence such as: management of educational material, tools for uploading projects in several kinds (documents, multimedia files), many kinds of quizzes, grades management, forums, reports wiz and many others. The aim of this master thesis is the investigation of available learning course management systems(LCMS), requirements analysis for LCMS and presentation and implementation of an evaluation methodology for LCMS based on a requirements list. In the first chapter of this thesis, we describe the basic concepts and definitions of e-Learning, as well as concepts relating to learning support systems such as: CBT(Computer Based Training), VLE(Virtual Learning Environment), LMS(Learning Management Systems), LCMS(Learning Course Management Systems), CMS (Course Management Systems), Mobile Learning etc. The second chapter contains an investigation in the area of Learning Course Management Systems (LCMS). We used a common template in order to describe the features of the most popular LCMS (either Open Source or Commercial). The template contains features like: Small Description of any LCMS (Software Manufacturer and History, Active Users and Installations, Database Requirements, Web Server, Manufacturer Clients, Current Stable Version), Strengths of the Software, Weaknesses of the Software, Available Mobile Version. This features have been chosen in order to become easy the comparison and after that the evaluation of the systems. The third chapter contains requirements analysis of a modern learning course management system so that the evaluation methodology can be applied to a specified list of features-requirements for the systems presented in chapter 2. In the fourth chapter there is the presentation of the evaluation methodology which uses a multicriteria technical analysis which belongs to the field of methods of Multi-Criteria Group-based Decision Making Techniques, while uses methods of (intuitionistic) fuzzy logic. This method exports the results using a technique TOPSIS(Technique for Order Preference by Similarity to Ideal Solution). In this chapter there is the theoretical description of the methodology which has been implemented as a case study for evaluating learning management systems in order to find the most suitable system for the needs of the Hellenic Open University(HOU). In Chapter 5 we will find the implementation steps of the methodology in order to exclude the most suitable LCMS for HOU and the final results(list of Systems). We will also find the conclusions of the implementation of this method. Finally the last chapter (6th) presents the final conclusions of the whole thesis and the added value this thesis offers in this field of research .

La quinta generación de redes móviles (5G) se encuentra a la vuelta de la esquina. Se espera provea de beneficios extraordinarios a la población y que resuelva la mayoría de los problemas de las redes 4G actuales. El éxito de 5G, cuya primera fase de estandarización ha sido completada, depende de tres pilares: comunicaciones tipo-máquina masivas, banda ancha móvil mejorada y comunicaciones ultra fiables y de baja latencia (mMTC, eMBB y URLLC, respectivamente). En esta tesis nos enfocamos en el primer pilar de 5G, mMTC, pero también proveemos una solución para lograr eMBB en escenarios de distribución masiva de contenidos. Específicamente, las principales contribuciones son en las áreas de: 1) soporte eficiente de mMTC en redes celulares; 2) acceso aleatorio para el reporte de eventos en redes inalámbricas de sensores (WSNs); y 3) cooperación para la distribución masiva de contenidos en redes celulares. En el apartado de mMTC en redes celulares, esta tesis provee un análisis profundo del desempeño del procedimiento de acceso aleatorio, que es la forma mediante la cual los dispositivos móviles acceden a la red. Estos análisis fueron inicialmente llevados a cabo por simulaciones y, posteriormente, por medio de un modelo analítico. Ambos modelos fueron desarrollados específicamente para este propósito e incluyen uno de los esquemas de control de acceso más prometedores: access class barring (ACB). Nuestro modelo es uno de los más precisos que se pueden encontrar en la literatura y el único que incorpora el esquema de ACB. Los resultados obtenidos por medio de este modelo y por simulación son claros: los accesos altamente sincronizados que ocurren en aplicaciones de mMTC pueden causar congestión severa en el canal de acceso. Por otro lado, también son claros en que esta congestión se puede prevenir con una adecuada configuración del ACB. Sin embargo, los parámetros de configuración del ACB deben ser continuamente adaptados a la intensidad de accesos para poder obtener un desempeño óptimo. En la tesis se propone una solución práctica a este problema en la forma de un esquema de configuración automática para el ACB; lo llamamos ACBC. Los resultados muestran que nuestro esquema puede lograr un desempeño muy cercano al óptimo sin importar la intensidad de los accesos. Asimismo, puede ser directamente implementado en redes celulares para soportar el tráfico mMTC, ya que ha sido diseñado teniendo en cuenta los estándares del 3GPP. Además de los análisis descritos anteriormente para redes celulares, se realiza un análisis general para aplicaciones de contadores inteligentes. Es decir, estudiamos un escenario de mMTC desde la perspectiva de las WSNs. Específicamente, desarrollamos un modelo híbrido para el análisis de desempeño y la optimización de protocolos de WSNs de acceso aleatorio y basados en cluster. Los resultados muestran la utilidad de escuchar el medio inalámbrico para minimizar el número de transmisiones y también de modificar las probabilidades de transmisión después de una colisión. En lo que respecta a eMBB, nos enfocamos en un escenario de distribución masiva de contenidos, en el que un mismo contenido es enviado de forma simultánea a un gran número de usuarios móviles. Este escenario es problemático, ya que las estaciones base de la red celular no cuentan con mecanismos eficientes de multicast o broadcast. Por lo tanto, la solución que se adopta comúnmente es la de replicar e contenido para cada uno de los usuarios que lo soliciten; está claro que esto es altamente ineficiente. Para resolver este problema, proponemos el uso de esquemas de network coding y de arquitecturas cooperativas llamadas nubes móviles. En concreto, desarrollamos un protocolo para la distribución masiva de contenidos, junto con un modelo analítico para su optimización. Los resultados demuestran que el modelo propuesto es simple y preciso, y que el protocolo puede reducir el con / La cinquena generació de xarxes mòbils (5G) es troba molt a la vora. S'espera que proveïsca de beneficis extraordinaris a la població i que resolga la majoria dels problemes de les xarxes 4G actuals. L'èxit de 5G, per a la qual ja ha sigut completada la primera fase del qual d'estandardització, depén de tres pilars: comunicacions tipus-màquina massives, banda ampla mòbil millorada, i comunicacions ultra fiables i de baixa latència (mMTC, eMBB i URLLC, respectivament, per les seues sigles en anglés). En aquesta tesi ens enfoquem en el primer pilar de 5G, mMTC, però també proveïm una solució per a aconseguir eMBB en escenaris de distribució massiva de continguts. Específicament, les principals contribucions són en les àrees de: 1) suport eficient de mMTC en xarxes cel·lulars; 2) accés aleatori per al report d'esdeveniments en xarxes sense fils de sensors (WSNs); i 3) cooperació per a la distribució massiva de continguts en xarxes cel·lulars. En l'apartat de mMTC en xarxes cel·lulars, aquesta tesi realitza una anàlisi profunda de l'acompliment del procediment d'accés aleatori, que és la forma mitjançant la qual els dispositius mòbils accedeixen a la xarxa. Aquestes anàlisis van ser inicialment dutes per mitjà de simulacions i, posteriorment, per mitjà d'un model analític. Els models van ser desenvolupats específicament per a aquest propòsit i inclouen un dels esquemes de control d'accés més prometedors: el access class barring (ACB). El nostre model és un dels més precisos que es poden trobar i l'únic que incorpora l'esquema d'ACB. Els resultats obtinguts per mitjà d'aquest model i per simulació són clars: els accessos altament sincronitzats que ocorren en aplicacions de mMTC poden causar congestió severa en el canal d'accés. D'altra banda, també són clars en què aquesta congestió es pot previndre amb una adequada configuració de l'ACB. No obstant això, els paràmetres de configuració de l'ACB han de ser contínuament adaptats a la intensitat d'accessos per a poder obtindre unes prestacions òptimes. En la tesi es proposa una solució pràctica a aquest problema en la forma d'un esquema de configuració automàtica per a l'ACB; l'anomenem ACBC. Els resultats mostren que el nostre esquema pot aconseguir un acompliment molt proper a l'òptim sense importar la intensitat dels accessos. Així mateix, pot ser directament implementat en xarxes cel·lulars per a suportar el trànsit mMTC, ja que ha sigut dissenyat tenint en compte els estàndards del 3GPP. A més de les anàlisis descrites anteriorment per a xarxes cel·lulars, es realitza una anàlisi general per a aplicacions de comptadors intel·ligents. És a dir, estudiem un escenari de mMTC des de la perspectiva de les WSNs. Específicament, desenvolupem un model híbrid per a l'anàlisi de prestacions i l'optimització de protocols de WSNs d'accés aleatori i basats en clúster. Els resultats mostren la utilitat d'escoltar el mitjà sense fil per a minimitzar el nombre de transmissions i també de modificar les probabilitats de transmissió després d'una col·lisió. Pel que fa a eMBB, ens enfoquem en un escenari de distribució massiva de continguts, en el qual un mateix contingut és enviat de forma simultània a un gran nombre d'usuaris mòbils. Aquest escenari és problemàtic, ja que les estacions base de la xarxa cel·lular no compten amb mecanismes eficients de multicast o broadcast. Per tant, la solució que s'adopta comunament és la de replicar el contingut per a cadascun dels usuaris que ho sol·liciten; és clar que això és altament ineficient. Per a resoldre aquest problema, proposem l'ús d'esquemes de network coding i d'arquitectures cooperatives anomenades núvols mòbils. En concret, desenvolupem un protocol per a realitzar la distribució massiva de continguts de forma eficient, juntament amb un model analític per a la seua optimització. Els resultats demostren que el model proposat és simple i precís / The 5th generation (5G) of mobile networks is just around the corner. It is expected to bring extraordinary benefits to the population and to solve the majority of the problems of current 4th generation (4G) systems. The success of 5G, whose first phase of standardization has concluded, relies in three pillars that correspond to its main use cases: massive machine-type communication (mMTC), enhanced mobile broadband (eMBB), and ultra-reliable low latency communication (URLLC). This thesis mainly focuses on the first pillar of 5G: mMTC, but also provides a solution for the eMBB in massive content delivery scenarios. Specifically, its main contributions are in the areas of: 1) efficient support of mMTC in cellular networks; 2) random access (RA) event-reporting in wireless sensor networks (WSNs); and 3) cooperative massive content delivery in cellular networks. Regarding mMTC in cellular networks, this thesis provides a thorough performance analysis of the RA procedure (RAP), used by the mobile devices to switch from idle to connected mode. These analyses were first conducted by simulation and then by an analytical model; both of these were developed with this specific purpose and include one of the most promising access control schemes: the access class barring (ACB). To the best of our knowledge, this is one of the most accurate analytical models reported in the literature and the only one that incorporates the ACB scheme. Our results clearly show that the highly-synchronized accesses that occur in mMTC applications can lead to severe congestion. On the other hand, it is also clear that congestion can be prevented with an adequate configuration of the ACB scheme. However, the configuration parameters of the ACB scheme must be continuously adapted to the intensity of access attempts if an optimal performance is to be obtained. We developed a practical solution to this problem in the form of a scheme to automatically configure the ACB; we call it access class barring configuration (ACBC) scheme. The results show that our ACBC scheme leads to a near-optimal performance regardless of the intensity of access attempts. Furthermore, it can be directly implemented in 3rd Generation Partnership Project (3GPP) cellular systems to efficiently handle mMTC because it has been designed to comply with the 3GPP standards. In addition to the analyses described above for cellular networks, a general analysis for smart metering applications is performed. That is, we study an mMTC scenario from the perspective of event detection and reporting WSNs. Specifically, we provide a hybrid model for the performance analysis and optimization of cluster-based RA WSN protocols. Results showcase the utility of overhearing to minimize the number of packet transmissions, but also of the adaptation of transmission parameters after a collision occurs. Building on this, we are able to provide some guidelines that can drastically increase the performance of a wide range of RA protocols and systems in event reporting applications. Regarding eMBB, we focus on a massive content delivery scenario in which the exact same content is transmitted to a large number of mobile users simultaneously. Such a scenario may arise, for example, with video streaming services that offer a particularly popular content. This is a problematic scenario because cellular base stations have no efficient multicast or broadcast mechanisms. Hence, the traditional solution is to replicate the content for each requesting user, which is highly inefficient. To solve this problem, we propose the use of network coding (NC) schemes in combination with cooperative architectures named mobile clouds (MCs). Specifically, we develop a protocol for efficient massive content delivery, along with the analytical model for its optimization. Results show the proposed model is simple and accurate, and the protocol can lead to energy savings of up to 37 percent when compared to the traditional approach. / Leyva Mayorga, I. (2018). On reliable and energy efficient massive wireless communications: the road to 5G [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/115484 / TESIS

In automatic speech recognition systems (ASRs), training is a critical phase to the system?s success. Communication media, either analog (such as analog landline phones) or digital (VoIP) distort the speaker?s speech signal often in very complex ways: linear distortion occurs in all channels, either in the magnitude or phase spectrum. Non-linear but time-invariant distortion will always appear in all real systems. In digital systems we also have network effects which will produce packet losses and delays and repeated packets. Finally, one cannot really assert what path a signal will take, and so having error or distortion in between is almost a certainty. The channel introduces an acoustical mismatch between the speaker's signal and the trained data in the ASR, which results in poor recognition performance. The approach so far, has been to try to undo the havoc produced by the channels, i.e. compensate for the channel's behavior. In this thesis, we try to characterize the effects of different transmission media and use that as an inexpensive and repeatable way to train ASR systems.