Netzbasierte interkulturelle Zusammenarbeit gewinnt in verschiedensten Bereichen mehr und mehr an Bedeutung und wird dementsprechend auch in der Lehre - speziell in E-Learning-Settings immer häufiger thematisiert. Neben den technischen und organisatorischen Herausforderungen gibt es eine ganze Reihe didaktischer Aspekte die es bei der Konzeption und der Durchführung derartiger Arrangements zu beachten gilt. (...)

To achieve greater compression ratios new video and image CODECs like H.264 and JPEG 2000 take advantage of Context adaptive binary arithmetic coding. As it contains computationally heavy algorithms, fast implementations have to be made when they are performed on large amount of data such as compressing high resolution formats like HDTV. This document describes how entropy coding works in general with a focus on arithmetic coding and CABAC. Furthermore the document dicusses the demands of the different CABACs and propose different options to hardware and instruction level optimisation. Testing and benchmarking of these implementations are done to ease evaluation. The main contribution of the thesis is parallelising and unifying the CABACs which is discussed and partly implemented. The result of the ILA is improved program flow through a specialised branching operations. The result of the DHA is a two bit parallel accelerator with hardware sharing between JPEG 2000 and H.264 encoder with limited decoding support.

This diploma thesis is focused on design and prototyping of wireless optical link for an indoor usage. In the beginning of the thesis frequency spectrums of infrared, visible and ultraviolet light are described by its typical qualities such as values of attenuation or reflection capability. On the basis of this analysis, a proper wavelength has been chosen for usage at the engineered communication system. Next part is devoted to selection of suitable communication components on basis of its declared qualities. In the following chapter this qualities are in carefully measured and after that they are compared with values provided by its manufacturer. The following section is devoted to design schemes of transceiver modules. After completion of the design the manufacturing of PCB, mounting components and the analysis of their distribution was described. The last part of this thesis deals with testing of created prototype in terms of maximum transmission distances and operating frequencies. At the very end of this project, in one small section ways to improve system characteristics was discussed.

Integration of optical wireless communications (OWC) within switched-mode power supplies (SMPS) / Although visible light communication(VLC) systems can provide high density links for use with IoT devices, an energy efficient, high rate method of designing a VLC transmitter is still unclear. Present designs for transmitters such as the bias-T, designs with switch manipulation, and interleaved converters are not commercially viable due to costly and complex designs that sacrifice energy efficiency for data rate. A design allowing for efficient, high rate communications, while maintaining a low cost would allow for widespread adoption of this technology. In this thesis, a novel approach of integrating power converters and VLC systems is explored by replacing commutating diodes with LEDs. By leveraging switched-mode power supply(SMPS) structures, the power dissipated within the converter may be harnessed and used for communications. The result is a simple and energy efficient solution capable of high rate links. Simulation and experimental results demonstrate buck and boost SMPS topologies that simultaneously increase energy efficiency and provide communications at SMPS switching rate without increasing component count. / Thesis / Master of Applied Science (MASc)

O objetivo deste trabalho é propor um instrumento de medição de desempenho em Comunidades Virtuais de Aprendizagem (CVA). Para isso foram utilizadas as variáveis da teoria do capital social. Todo o trabalho está direcionado à construção de uma matriz composta pelas variáveis: (a) capital social estrutural, sob o enfoque econômico, aqui relacionado aos fatores de infra-estrutura tecnológica e utilização de ambientes virtuais, bem como às políticas de incentivo ao uso de recursos de Tecnologia da Informação; (b) capital social cognitivo, gerado por meio da criação da cultura virtual e (c) coesão social sob o enfoque ações coletivas, analisadas a partir da interação e colaboração entre seus participantes no tocante à promoção de tais ações. A pesquisa parte do pressuposto de que a geração de conhecimento em ambientes virtuais de aprendizagem está relacionada à alfabetização digital e à conseqüente utilização dos ambientes virtuais pelos participantes da comunidade em estudo. A metodologia está fundamentada na análise etnográfica do ambiente estudado, nas técnicas de coleta por meio de questionário, bem como na análise da construção de um discurso do sujeito coletivo. Uma visão estruturada dessas questões relativas ao desempenho de uma CVA está representada na Matriz do Capital Social resultante. Esta visão converge para os requisitos almejados nas análises de desempenho, ou seja para o estabelecimento de metas de gestão e a avaliação de seus resultados. / This paper has the objective of proposing a measuring tool for performances in Virtual Learning Communities (VLC). For this purpose, variables of the theory of social capital have been used. The whole work heads for the building of a matrix with the following variables: a) structural social capital under economic focus, here related to factors such as technological infra-structure and the use of virtual environments, as well as policies to encourage the use of resources of Information Technology (IT); b) cognitive social capital, generated through the creation of virtual culture, and c) social cohesion under the focus of social actions, analyzed from the point of view of the interaction and cooperation of their participants in respect to the promotion of such actions. The research starts from the presupposition that knowledge generation in virtual learning environments is related to digital literacy, and the use of virtual environments by the participants of the studied community is a consequence. The methodology is based on the ethnographic analysis of the environment under study, on the techniques of collecting data through questionnaires, as well as on the analysis of the construction of a discourse of a collective subject. A structured view of these questions related to the performance of a VLC is represented in the resulting Social Capital Matrix. This view converges to the requisites desired in the different performance analyses or, in other words, to the establishment of management goals and the assessment of their results.

Along with the rapidly increasing demand for wireless data while more and more crowded radio frequency (RF) spectrum, optical wireless communications (OWC) become a promising candidate to complement conventional RF communications, especially for indoor short and medium range data transmissions. Orthogonal frequency division multiplexing (OFDM) is considered for OWC due to its ability to boost data rates. However, the average emitted optical power and dynamic range of driving signals of LEDs are two major constraints in OWC. OFDM waveforms exhibits high upper and lower peak-to-average power ratios (PAPRs), which make OFDM signals optical power inefficient and easy to violate the dynamic range of LEDs, resulting clipping and nonlinear distortions. In this dissertation, we analyze and design optical power and dynamic range constrained OWC systems, for which OFDM is our major subject. We first derive distributions of upper PAPR and lower PAPR of OWC-OFDM signals. Then we analyze the clipped OFDM signals in term of error vector magnitude (EVM), signal-to-distortion ratio (SDR), and achievable data rates under both optical power and dynamic range constraints. The next part of this dissertation is the OFDM system design for visible light communications (VLC) considering illumination requirement. We investigate the illumination-to-communication efficiency (ICE) in VLC-OFDM, and design the brightness control and flickering mitigation schemes for VLC-OFDM. In the end, to reduce the complexity of driving circuits of LEDs , we propose using delta-sigma modulators in VLC-OFDM systems to convert continuous magnitude OFDM symbols into two-level LED driver signals without loss of the communication theory advantages of OFDM.

O objetivo deste trabalho é propor um instrumento de medição de desempenho em Comunidades Virtuais de Aprendizagem (CVA). Para isso foram utilizadas as variáveis da teoria do capital social. Todo o trabalho está direcionado à construção de uma matriz composta pelas variáveis: (a) capital social estrutural, sob o enfoque econômico, aqui relacionado aos fatores de infra-estrutura tecnológica e utilização de ambientes virtuais, bem como às políticas de incentivo ao uso de recursos de Tecnologia da Informação; (b) capital social cognitivo, gerado por meio da criação da cultura virtual e (c) coesão social sob o enfoque ações coletivas, analisadas a partir da interação e colaboração entre seus participantes no tocante à promoção de tais ações. A pesquisa parte do pressuposto de que a geração de conhecimento em ambientes virtuais de aprendizagem está relacionada à alfabetização digital e à conseqüente utilização dos ambientes virtuais pelos participantes da comunidade em estudo. A metodologia está fundamentada na análise etnográfica do ambiente estudado, nas técnicas de coleta por meio de questionário, bem como na análise da construção de um discurso do sujeito coletivo. Uma visão estruturada dessas questões relativas ao desempenho de uma CVA está representada na Matriz do Capital Social resultante. Esta visão converge para os requisitos almejados nas análises de desempenho, ou seja para o estabelecimento de metas de gestão e a avaliação de seus resultados. / This paper has the objective of proposing a measuring tool for performances in Virtual Learning Communities (VLC). For this purpose, variables of the theory of social capital have been used. The whole work heads for the building of a matrix with the following variables: a) structural social capital under economic focus, here related to factors such as technological infra-structure and the use of virtual environments, as well as policies to encourage the use of resources of Information Technology (IT); b) cognitive social capital, generated through the creation of virtual culture, and c) social cohesion under the focus of social actions, analyzed from the point of view of the interaction and cooperation of their participants in respect to the promotion of such actions. The research starts from the presupposition that knowledge generation in virtual learning environments is related to digital literacy, and the use of virtual environments by the participants of the studied community is a consequence. The methodology is based on the ethnographic analysis of the environment under study, on the techniques of collecting data through questionnaires, as well as on the analysis of the construction of a discourse of a collective subject. A structured view of these questions related to the performance of a VLC is represented in the resulting Social Capital Matrix. This view converges to the requisites desired in the different performance analyses or, in other words, to the establishment of management goals and the assessment of their results.

With rapid expansion of interest in multimedia and distributed computing applications across the Internet increases importance of optimized delivery of group traffic. According to current situation the best practice to achieve this goal is multicasting. This masters thesis summarizes multicasting methods and facts. Also it draws conclusions from practical application of presented information on commercial project.

Netzbasierte interkulturelle Zusammenarbeit gewinnt in verschiedensten Bereichen mehr und mehr an Bedeutung und wird dementsprechend auch in der Lehre - speziell in E-Learning-Settings immer häufiger thematisiert. Neben den technischen und organisatorischen Herausforderungen gibt es eine ganze Reihe didaktischer Aspekte die es bei der Konzeption und der Durchführung derartiger Arrangements zu beachten gilt. (...)

[ES] Las comunicaciones ópticas inalámbricas (OWC) constituyen una tecnología muy prometedora para el desarrollo de futuras comunicaciones inalámbricas. De hecho, ha despertado un interés creciente entre los investigadores y varias empresas de todo el mundo trabajan actualmente en el desarrollo de redes inalámbricas de muy alta velocidad. Las comunidades científica e industrial consideran la OWC como una tecnología complementaria en sus diversas formas: comunicaciones ópticas en el espacio libre (FSO), comunicaciones de luz visible (VLC) o fidelidad de la luz (Li-Fi). El espectro óptico ha sido considerado durante muchos años como una gran oportunidad para las comunicaciones inalámbricas, especialmente debido a la saturación del espectro de radiofrecuencia (RF). Esta disertación trata del uso de fuentes de banda ancha en sistemas de transmisión de luz visible (VLC), así como en sistemas de transmisión en el espectro infrarrojo por fibra óptica. En el trabajo de investigación realizado se pueden distinguir tres partes: En la primera parte, se considera el estudio y la simulación de componentes de Diodos Emisores de Luz (LED) con el software WIEN2k centrándose en las propiedades ópticas y eléctricas de los elementos II-VI. La segunda parte trata del diseño, la implementación y las pruebas de diferentes prototipos de comunicación VLC para la transmisión analógica y digital en modo simplex y semidúplex. Hemos demostrado un sistema OWC empleando una fuente de banda ancha (LED) para la transmisión no sólo de datos, sino también para la transmisión inalámbrica de energía. Además, se aborda el problema de la sincronización y la detección del nivel "1" o "0" de un bit en los sistemas de comunicación inalámbrica óptica implementados que surge como consecuencia de la atenuación de la luz a lo largo de la distancia y al problema de la pérdida de línea de visión (NLOS) entre el emisor y el receptor. Para hacer frente a este problema, se ha proporcionado un protocolo de comunicación que garantiza la transmisión fiable de datos digitales con un algoritmo de detección de nivel de bits adaptativo y se ha demostrado su eficacia mediante la transmisión de textos e imágenes. Además, esta tesis aporta una solución para la implementación de transmisores multiplexados en redes con división de longitud de onda (WDM) para formatos de modulación con multiplexación por división de frecuencia ortogonal (OFDM) basados en el uso de fuentes de banda ancha en el espectro infrarrojo para redes de fibra bidireccionales centralizadas. A pesar de las limitaciones impuestas por la dispersión cromática en el uso de este tipo de fuentes ópticas, la inclusión de ciertas estructuras antes de la detección permite la transmisión de señales OFDM en enlaces ópticos. En este trabajo se ha demostrado experimentalmente la reutilización de portadoras, la asignación dinámica de ancho de banda y la transmisión de señales OFDM multibanda mediante el uso de fuentes ópticas de banda ancha en redes WDM. Los principales resultados obtenidos en cada parte de esta tesis doctoral muestran los procedimientos de estudio, la eficacia de las soluciones propuestas y las limitaciones encontradas. / [CA] Les comunicacions òptiques sense fils (OWC) constitueixen una tecnologia molt prometedora per al desenvolupament de futures comunicacions sense fils. De fet, ha despertat un interés creixent entre els investigadors i diverses empreses de tot el món treballen actualment en el desenvolupament de xarxes sense fils de molt alta velocitat. Les comunitats científica i industrial consideren la OWC com una tecnologia complementària en les seues diverses formes: comunicacions òptiques en l'espai lliure (FSO), comunicacions de llum visible (VLC) o fidelitat de la llum (Li-Fi). L'espectre òptic ha sigut considerat durant molts anys com una gran oportunitat per a les comunicacions sense fils, especialment a causa de la saturació de l'espectre de radiofreqüència (RF). Aquesta dissertació tracta de l'ús de fonts de banda ampla en sistemes de transmissió de llum visible (VLC), així com en sistemes de transmissió en l'espectre infraroig per fibra òptica. En el treball de recerca realitzat es poden distingir tres parts: ¿ En la primera part, es considera l'estudi i la simulació de components de Díodes Emissors de Llum (LED) amb el software WIEN2k centrant-se en les propietats òptiques i elèctriques dels elements II-VI. ¿ La segona part tracta del disseny, la implementació i les proves de diferents prototips de comunicació VLC per a la transmissió analògica i digital de manera simplex i semidúplex. Hem demostrat un sistema OWC emprant una font de banda ampla (LED) per a la transmissió no sols de dades, sinó també per a la transmissió sense fil d'energia. A més, s'aborda el problema de la sincronització i la detecció del nivell "1" o "0" d'un bit en els sistemes de comunicació sense fil òptica implementats, que sorgeix a conseqüència de l'atenuació de la llum al llarg de la distància i al problema de la pèrdua de línia de visió (NLOS) entre l'emissor i el receptor. Per a fer front a aquest problema, s'ha proporcionat un protocol de comunicació que garanteix la transmissió fiable de dades digitals amb un algorisme de detecció de nivell de bits adaptatiu i s'ha demostrat la seua eficàcia mitjançant la transmissió de textos i imatges. ¿ A més, aquesta tesi aporta una solució per a la implementació de transmissors multiplexats en xarxes amb divisió de longitud d'ona (WDM) per a formats de modulació amb multiplexació per divisió de freqüència ortogonal (OFDM) basats en l'ús de fonts de banda ampla en l'espectre infraroig per a xarxes de fibra bidireccionals centralitzades. Malgrat les limitacions imposades per la dispersió cromàtica en l'ús d'aquest tipus de fonts òptiques, la inclusió d'unes certes estructures abans de la detecció permet la transmissió de senyals OFDM en enllaços òptics. En aquest treball s'ha demostrat experimentalment la reutilització de portadores, l'assignació dinàmica d'amplada de banda i la transmissió de senyals OFDM multibanda mitjançant l'ús de fonts òptiques de banda ampla en xarxes WDM. Els principals resultats obtinguts en cada part d'aquesta tesi doctoral mostren els procediments d'estudi, l'eficàcia de les solucions proposades i les limitacions trobades. / [EN] Optical wireless communication (OWC) is a very promising technology for future wireless communications developments. It has attracted increasing interest from researchers and several companies around the world are currently working on the development of very high-speed wireless networks. The scientific and industrial communities believe that OWC will be a complementary technology in its various forms: Free Space Optical communications (FSO), Visible Light Communications (VLC), Light Fidelity (Li-Fi). In fact, the optical spectrum has been considered for many years as a great opportunity for wireless communications especially due to the saturation of the radio frequency (RF) spectrum. This dissertation deals with the use of broadband sources in visible light transmission systems (VLC) as well as fiber optic systems. To carry out the research, three parts can be distinguished: In the first part, we consider the study and simulation of Light Emitting Diode (LED) components with the WIEN2k software by focusing on the optical and electrical properties of elements II-VI. The second part deals with the design, implementation and testing of different VLC communication prototypes for analog and digital transmission in simplex and half-duplex mode. We have demonstrated that an OWC system using a broadband source (i.e. an LED) can be used not only for data transmission, but also for wireless power transmission. Moreover, the synchronization problem and the detection of level "1" or "0" of a bit often arise in the optical wireless communication systems. This is a result of the attenuation nature of the light over the distance and the problem of Non Line-Of-Sight (NLOS) between the emitter and the receiver. To deal with this problem, a communication protocol ensuring reliable digital data transmission with an adaptive bit level detection algorithm has been provided and its effectiveness has been demonstrated by the transmission of texts and images. In addition, this thesis provides a solution for the implementation of wavelength division multiplexed - orthogonal frequency division multiplexed (WDM-OFDM) transmitters based on the use of broadband sources in the infrared spectrum for centralized bidirectional fiber networks. Despite the chromatic dispersion that avoids the use of this type of optical sources, the inclusion of certain structures before detection allows the transmission of OFDM signals in optical links. Carrier reuse, dynamic bandwidth allocation and multiband OFDM signals transmission will be experimentally demonstrated by using optical broadband sources in WDM networks. The main results obtained during this thesis work demonstrate the study procedures, for each part, the effectiveness of the proposed solutions as well as the constraints encountered. / Sekkiou, I. (2021). Design of communication systems based on broadband sources for fiber and free space optical links [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/172542