Design of communication systems based on broadband sources for fiber and free space optical links

[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/10251/172542TESI

Structural behaviour of concrete filled hollow steel sections exposed to parametric fire

This article analyzes steel-concrete composite columns subjected to natural fire scenarios in order to verify that the possibility of structural collapse during or after the cooling phase is real. The main objectives of this study are: first, to highlight the phenomenon of delayed collapse of this type of columns during or after the cooling phase of a fire, and then analyze the influence of some determinant parameters, such as section size, tube thickness, reinforcement (ratio), concrete cover and column length. The results show that critical conditions with respect to delayed failure arise for massive sections, small values of the steel tube thickness and for columns with massive section

Corporate Social Responsibility during COVID-19 crisis: Implementing CSR in the new normal phase

Purpose: This article takes a critical look at the reality of corporate social responsibility (CSR( in time of crisis and tries to set the features of the future of CSR post Covid-19 crisis by indicating its potentials and limitations and how evolving post-Covid corporate practices may lead towards a new approach to set the new normal phase. Findings: The crisis has shown that CSR has played a leading role, and the dramatic consequences of the crisis could have been more drastic if companies had confined themselves to their classic role of profit-making producer. In our conceptual model, for implementing the new CSR approach, we focused on a number of repercussions in terms of organizational management in order to implement a post-Covid CSR behavior. Theoretical Implications: Grounded on the review of the literature published during the pandemic, a critical look at the positioning of CSR in times of crisis has been by indicating the importance of a number of factors supporting companies’ organizational management. Practical Implications: the article reflects the importance of delimitating the major factors that help companies for overcoming new challenges such as resilience, supply chains, public health and corporate responsibility in the digital juncture.   Originality/Value: This study provides a comprehensive framework of CSR practices in times of crisis, as a lever of corporate governance, by tracing the new components of CSR approach and the new definition of CSR as a business model. Research Limitations/Future Research: This paper offers important implications for future empirical research in order to investigate the dimensions highlighted in our model as “CSR approach in the new normal phase”. Researches exploring how businesses can use CSR to positively influence public health are at the top of priorities for scholars to give evidence of the importance of Public health as a new dimension of CSR named “Corporate Public Health Responsibility”

Annie Ernaux et l'autosociobiographie

This study seeks to understand the principal elements of the autosociobiography, a term which is not widely recognized in the literary world. This term is usually associated with the author Annie Ernaux and her book La place (1983). The main search question is to try identifying the criteria to determine if a given literally work can be classified as an autosociobiography. The study is drawn upon the theory of the autobiobiographical pact of Phillipe Leujeune and Pierre Bourdieu’s social theory The Distinction (1979). To identify the elements of the autosociobiography, this work explores the recent dialogues of Frédéric-Yves Jeannet around the works of Annie Ernaux in 2003 and it will involve several studies on the same subject. The result shows five different elements; the first one is the flat writing characterized by its simplicity and avoids the subjectivity and feelings. The second one is the class defector or the class mobility. The third one promotes the total reject of the fiction or autofiction. The fourth is the impersonal “I” which is a technique that uses an individual narrative way with an intention to reach the collective audience. The last one is the unique style of writing the life and living the writing. Moreover, the study confirms the results mentioned above with a projection of the identified elements on the work La place (1983) to deepen the understanding of the subject

Corporate Social Responsibility during COVID-19 crisis: Implementing CSR in the new normal phase

Purpose: This article takes a critical look at the reality of corporate social responsibility (CSR( in time of crisis and tries to set the features of the future of CSR post Covid-19 crisis by indicating its potentials and limitations and how evolving post-Covid corporate practices may lead towards a new approach to set the new normal phase. Findings: The crisis has shown that CSR has played a leading role, and the dramatic consequences of the crisis could have been more drastic if companies had confined themselves to their classic role of profit-making producer. In our conceptual model, for implementing the new CSR approach, we focused on a number of repercussions in terms of organizational management in order to implement a post-Covid CSR behavior. Theoretical Implications: Grounded on the review of the literature published during the pandemic, a critical look at the positioning of CSR in times of crisis has been by indicating the importance of a number of factors supporting companies’ organizational management. Practical Implications: the article reflects the importance of delimitating the major factors that help companies for overcoming new challenges such as resilience, supply chains, public health and corporate responsibility in the digital juncture.   Originality/Value: This study provides a comprehensive framework of CSR practices in times of crisis, as a lever of corporate governance, by tracing the new components of CSR approach and the new definition of CSR as a business model. Research Limitations/Future Research: This paper offers important implications for future empirical research in order to investigate the dimensions highlighted in our model as “CSR approach in the new normal phase”. Researches exploring how businesses can use CSR to positively influence public health are at the top of priorities for scholars to give evidence of the importance of Public health as a new dimension of CSR named “Corporate Public Health Responsibility” &nbsp

Практики корпоративної соціальної відповідальності під час кризи COVID-19: критичний огляд

Purpose: This article aims to identify CSR activities undertaken by companies during Covid-19 in terms of environmental, social, and economic dimensions as well as the responsibility toward employees and customers, using a “systematic literature review method” in order to outline the perceived challenges in terms of companies’ organizational practices. Findings: This study shows that the Covid-19 pandemic has forced a redefinition of the norms of social responsibility and created significant challenges to companies that required difficult decisions to be made regarding the safety of employees, the economic viability of the company, and its dedication to CSR efforts. Materially, the pandemic directs researchers towards different ways of conceptualizing CSR, yet the existing literature on CSR and the Covid-19 pandemic has focused on the social responsibility without taking into account the challenges faced by companies during this transition in terms of companies’ organizational practices. Theoretical Implications: This study provides a comprehensive framework of CSR practices in times of the crisis and underlines the changes in companies’ organizational practices in order to implement a sustainable business model not only to tackle this ongoing crisis but also to resist future crises by balancing economic performance and social responsibility. Practical Implications: The article reflects the importance of delimitating the major factors that help companies overcome new challenges such as resilience, supply chains, public health and corporate responsibility at a new juncture. Originality/Value: The relevance of this study is the discussion of CSR during the Covid-19 pandemic and its Impact on the organizational practices that have been changed and which should exist to ensure future effective CSR practices. Research Limitations/Future Research: As in all studies, this research has some limitations. The most important one is that it addresses the topic by referring to a defined literature base. It would be more useful for future comparative research to use other literature bases to assess the robustness of our results. In addition, this paper offers important implications for future empirical researches in order to investigate the impact of each factor highlighted in our study and to explore how CSR can help to address challenges such as public health, supply chains, corporate governance, and corporate responsibility at a new juncture.Мета роботи: Ця стаття має на меті визначити діяльність компаній у сфері корпоративної соціальної відповідальності (КСВ) під час Covid-19 з точки зору екологічних, соціальних та економічних аспектів, а також відповідальності перед працівниками та клієнтами, використовуючи «метод систематичного огляду літератури» для того, щоб окреслити виклики, які сприймаються компаніями з точки зору організаційних практик. Результати дослідження: Результати дослідження показують, що пандемія Covid-19 змусила переосмислити норми соціальної відповідальності та створила значні виклики для компаній, які вимагали прийняття складних рішень щодо безпеки працівників, економічної життєздатності компанії та її відданості зусиллям з КСВ. По суті, пандемія спрямовує дослідників до різних способів концептуалізації КСВ, проте існуюча література про КСВ та пандемію Covid-19 зосереджується на соціальній відповідальності, не беручи до уваги виклики, з якими стикаються компанії під час цього переходу з точки зору організаційних практик компаній. Теоретична цінність дослідження: Це дослідження надає комплексну картину практик КСВ під час кризи та підкреслює зміни в організаційних практиках компаній з метою впровадження стійкої бізнес-моделі не лише для подолання поточної кризи, але й для протистояння майбутнім кризам шляхом збалансування економічних показників та соціальної відповідальності. Практична цінність дослідження: Стаття відображає важливість розмежування основних факторів, які допомагають компаніям долати нові виклики, такі як стійкість, ланцюги поставок, громадське здоров'я та корпоративна відповідальність на новому етапі. Оригінальність / Цінність дослідження: Актуальність цього дослідження полягає в обговоренні КСВ під час пандемії Covid-19 та її впливу на організаційні практики, які були змінені і які повинні існувати для забезпечення ефективних практик КСВ у майбутньому. Обмеження дослідження / Майбутні дослідження: Як і всі дослідження, це дослідження має певні обмеження. Найважливішим з них є те, що воно розглядає тему, посилаючись на визначену літературну базу. Для майбутніх порівняльних досліджень було б корисніше використовувати інші літературні джерела, щоб оцінити надійність наших результатів.  Крім того, ця стаття пропонує важливі висновки для майбутніх емпіричних досліджень з метою вивчення впливу кожного фактору, виокремленого в нашому дослідженні, та вивчення того, як КСВ може допомогти у вирішенні таких проблем, як громадське здоров'я, ланцюги поставок, корпоративне управління та корпоративна відповідальність на новому етапі

Thermo-Mechanical Behavior of Steel-Concrete Composite Columns under Natural Fire Including Heating and Cooling Phases

International audienceThe fire behavior of concrete filled hollow steel sections has been studied extensively in various countries. Almost all essential parameters influencing their resistance have been identified section shape and dimensions, concrete filling, reinforcement ratio, steel tube thickness, column slenderness, thermal and mechanical properties of steel and concrete, and even the contact problem at the steel-concrete interface. Most of these works were done under standard fire conditions (ISO), which are represented by a continuously increasing temperature over time. It is thus not really a curve reflecting a natural fire which includes not only a heating phase but also a cooling phase during which the temperature of the fire is decreasing back to ambient temperature. In this paper, the behavior of axially loaded concrete filled square hollow section columns subjected to natural fire conditions has been studied. The main objectives of this study are first, to demonstrate the phenomenon of delayed collapse of this type of columns during or after the cooling phase of a fire, and then study the influence of certain determinant parameters, such as section size, tube thickness, reinforcement ratio, concrete cover and column length. The results show that delayed failures occur for massive sections, small values of the thickness of the steel tube and for the low-slendernes

Bidirectional WDM-OOFDM access network based on a sliceable optical transceiver with colorless ONUs

[EN] A WDM OOFDM access network using a centralized optical transceiver based on a single optical broadband sliced source at the Central Office is presented as a low cost solution. Such network offers downlink and uplink signal transmission by using double sideband modulation and optical carrier re-use, as well as dynamic bandwidth allocation, multiple band selection and tunable OFDM band selection in reconfigurable networks at moderate bitrates.The authors acknowledge the Research Excellence Award Programme GVA PROMETEO 2017/103 Future Microwave Photonic Technologies and Applications.Sekkiou, I.; Chicharro López, FI.; Ortega Tamarit, B.; Mora Almerich, J. (2018). Bidirectional WDM-OOFDM access network based on a sliceable optical transceiver with colorless ONUs. Optical Fiber Technology. 45:98-105. https://doi.org/10.1016/j.yofte.2018.04.015S981054