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Interference Management in Wireless LAN Mesh Networks Using Free-Space Optical LinksRajakumar, Valavan January 2007 (has links)
<p> Wireless LAN mesh networks (WMNs) are a cost effective way of deploying wireless LAN (WLAN) coverage over extended areas. As WMNs become more populated, scalability issues may arise due to the co-channel interference which is inherent in publicly available RF (radio frequency) channels. This co-channel interference can severely degrade network capacity and link reliability and may eventually make it impossible to operate with the frequency channels for which the network was originally designed. In this thesis, this problem is addressed by selectively installing supplementary free-space optical (FSO) links when RF link performance has deteriorated. The frequency assignment problem is solved using a heuristic technique based on a genetic algorithm. In order to determine the quality of the results, the proposed algorithm is compared with a lower bound solution obtained using an Integer Linear Programming (ILP) formulation.</p> <p> Another advantage of FSO links is that they may reduce node power consumption compared with conventional RF links. This may be an important consideration in cases where power consumption at the nodes is important, such as in solar powered mesh networks. Power consumption estimates of RF and FSO links are obtained and compared for different data rates. This data is then used along with historical solar insolation data to estimate the solar panel and battery sizes required to guarantee a
given node outage probability. The results show that no extra provisioning is required for replacing the deployed wireless nodes with new FSO links.</p> / Thesis / Master of Applied Science (MASc)
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[en] SIMULATION AND DEVELOPMENT OF A FREE-SPACE OPTICS IN RIO DE JANEIRO AND RELATIONSHIP WITH ITU-T G.826 / [pt] SIMULAÇÃO E DESENVOLVIMENTO DE UM ENLACE DE FREE-SPACE OPTICS NO RIO DE JANEIRO E A RELAÇÃO COM A ITU-T G.826JOSE ALBERTO HUANACHIN OSORIO 17 January 2006 (has links)
[pt] Os sistemas de comunicações ópticas no espaço livre
(Free
Space Optics -
FSO) tem sido desenvolvidos nos últimos anos no Brasil,
contudo ha poucas
referencias de estudos realizadas em território
nacional.
Neste tipo de sistema, um
feixe de laser pode carregar informação de um ponto para
outro através de uma
distância curta (3-4 km), evitando-se o uso das fibras
ópticas. Por tanto, FSO
tornou-se uma alternativa rápida e muito econômica,
principalmente nas áreas
urbanas. Este trabalho apresenta um procedimento para a
análise, modelamento, e
um teste experimental do Free-Space Optics (FSO) é
apresentado; sendo realizado
dentro do perímetro urbano da cidade do Rio de Janeiro,
em
2002. Inicialmente, as
características do transmissor e do receptor foram
consideradas. Adicionam-se três
parâmetros: a perda atmosférica, a perda geométrica e a
cintilação.
Subseqüentemente, todas as perdas, incluindo outros
parâmetros que tratam das
perdas adicionais foram expressas em dB e inseridas em
uma
equação de balanço
de potência. A disponibilidade do sistema de FSO é
exibida, usando os dados de
visibilidade de dois aeroportos, e conduzindo a uma
predição sistemática da
disponibilidade. Uma atenção especial é focalizada no
parâmetro da taxa de erro de
bits (BER), que está relacionada com a Recomendação ITU-
T
G.826. Dentro esta
última recomendação, é possível realizar uma análise do
FSO com relação à
variação climática. A experiência abrangeu períodos
curtos
em que o Rio de
Janeiro apresentou uma névoa forte da manhã. Mostra-se,
finalmente, que FSO é
uma tecnologia competitiva e confiável na transmissão,
desde que seja usada de
forma correta e apropriada. / [en] Very few works had been developed in Brazil, dealing with
Free-Space
Optics (FSO). In this arrangement, a laser beam carries
information for a short
range (up to 3-4 km), avoiding the use of optical fiber.
FSO is a rapidly-improved
solution and very economical, specifically in urban areas.
In this work a FSO
system operating in Rio is described. This work presents a
procedure for the
analysis, modeling, and a practical trial of a Free-Space
Optics (FSO) system is
presented. The procedure has been conducted in the urban
area of Rio de Janeiro,
in 2002. Firstly, the transmitter and receiver
characteristics are considered. Next,
three additional parameters are introduced: atmospheric
loss, geometric loss and
scintillation. In this last parameter, a few ways how
scintillation might be
expressed in dB and translated into a power balance
equation, it presents. Other
fixed parameters, dealing with additional losses, are
subsequently inserted. The
FSO system availability is exhibited, using airports
visibility data, leading to a
prediction of the systemic availability. Attention is then
focused on the Bit Error
Rate, BER, which relates with the Recommendation ITU- T
G.826. Within this last
Recommendation, it shows how to perform a FSO analysis
with respect to the
climatic variation. The experiment has encompassed some
short periods in which
this city presents a strong morning fog. It is finally
shown that FSO is a
competitive and reliable transmission technology, provided
proper and correct use.
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Transmission multi-standards sur lien optique bas-coût / Multi-standard low-cost optical link transmissionBouhamri, Zine-Abidine 03 October 2013 (has links)
Dans ce travail, nous avons étudié un système complet d'antennes distribuées par voie optique pour déport de signaux radio suivant le principe de la radio sur fibre. La caractérisation du lien optique servant de base au système radio sur fibre, d'un point de vue composant et système via la transmission de standards radio a d'abord été effectuée. Nous avons montré par une nouvelle technique de caractérisation que l'élément non linéaire de notre chaîne de transmission pouvait se comporter de manière plus linéaire qu'attendue et faiblement impacter les standards radio transmis. Les standards choisis sont à enveloppe constante (GSM) et à enveloppe non constante (WLAN) pour mieux mettre en évidence les non-linéarités de la chaîne de transmission. Il est ainsi montré que les signaux à enveloppe non constante sont les signaux limitants et qu'en leur adjoignant un signal à enveloppe constante à faible puissance, la qualité de leur transmission n'est pas impactée. A partir de ces résultats expérimentaux, un algorithme de calcul de couvertures radio a été développé et appliqué à plusieurs scénarios de couverture intra-bâtiment. Notre étude montre que dans tous les cas, c'est la liaison montante, de l'utilisateur à la station centrale, qui est limitante puisque bien plus impactée par le bruit ajouté par la chaîne de transmission optique. Par suite, nous avons proposé une architecture de déploiement réseau originale de type bus pour laquelle nous montrons que malgré un coût de déploiement faible, il est possible d'atteindre des performances suffisantes pour assurer des couvertures au sein d'un réseau domestique. Enfin, ces résultats de simulation sur architecture bus sont confirmés par la réalisation d'un banc de test de type industriel permettant de confirmer par la mesure les résultats obtenus précédemment. Nous réalisons aussi un circuit radio passif permettant la séparation et recombination de plusieurs signaux (GSM et WLAN étudiés précédemment) de sorte que tous les éléments prouvant la réalisation et les mesures sur le système complet d'antennes distribuées sont à disposition et fonctionnels. / In this manuscript, we study a complete distributed antenna system through optical ways, to extend radio signals coverage, thanks to the radio over fiber principle. The optical link characterization is done first as the system basic building block. The characterization is done both through component and system analysis, thanks to different radio standards transmission. We develop a new characterization technique that allows us to confirm that the most non-linear element of the optical link behaves much more linearly than expected so that it has a low effect on transmission quality. Chosen standards are both constant and non-constant envelop to highlight the link non-linearities. This shows that non-constant envelop signals are the limiting signals for our system. This also allows to demonstrate that adding a low power constant envelop signal to a non-constant envelop one does not impact its transmission performance. From these experimental results, we develop an in-building coverage distance calculation algorithm for our system. Those simulations confirm that the uplink, from the user to the central station, is the most limiting section of our system because of the noise quantity added by the optical link. To follow this, we propose a new low-cost bus network in-building topology for our system that proves to be performing as wanted for personal homes. Finally, these bus topology simulation results are confirmed with the production of an industrial type test bench. We also produce a passive radio front-end that permits the separation and recombination of several radio signals (GSM and WLAN as previously studied) so that all the elements proving the production and the results of the complete distributed antenna system through optical ways are available and functional.
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[en] STATISTICAL SPECIFICATION OF THE POLARIZATION MODE DISPERSION IN OPTICAL LINKS / [pt] ESPECIFICAÇÃO ESTATÍSTICA DA DISPERSÃO DOS MODOS DE POLARIZAÇÃO EM ENLACES ÓPTICOSJOAO ARLINDO BRITO JUNIOR 17 December 2003 (has links)
[pt] Projetistas de sistemas de comunicações ópticas necessitam
estimar o coeficiente de PMD dos enlaces ópticos visando
determinar a correspondente penalidade de potência do
enlace. Os valores de PMD nas fibras variam aleatoriamente,
conseqüentemente a determinação da PMD dos enlaces deverá
ser calculada através de metodologias estatísticas.
Esta dissertação contém um estudo sistemático da estimação
do coeficiente de PMD das seções amplificadas de 02
backbones. Três 03 técnicas estatísticas: Técnica de Monte
Carlo, Modelo Gama e Teorema do Limite Central
Generalizado, recomendadas pelo Método 1 da norma TIA/EIA
TSB 107 foram usadas e os resultados comparados com os
valores medidos em campo destas seções. Os resultados das
avaliações realizadas mostraram que a metodologia
apresentada por esta recomendação induz a uma
superestimação do coeficiente de PMD do enlace devido a
limitação dos equipamentos de medição e conseqüentemente a
uma superestimação da penalidade prevista. Esta
superestimação deve-se ao fato da PMD das fibras estar
abaixo do limite de sensibilidade dos equipamentos de
medida comercialmente disponíveis. A estimação do
coeficiente de PMD de enlaces requer então a utilização de
equipamentos de medida mais precisos (ainda não
disponíveis) ou corrigir esta metodologia de cálculo para a
estimação da PMD dos enlaces ópticos com a utilização de
fibras/cabos de maior comprimento. / [en] Optical system designers need to estimate the expected PMD
coefficient of the links in order to calculate the
corresponding power penalty. Fiber PMD values varies
randomly, therefore the link PMD estimation shall be
calculated by statistical methodologies.
This thesis presents a systematic study of PMD estimation
of the amplified spans of two backbones. Three statistical
techniques: Monte Carlo Technique, Gamma Model and
Generalized Central Limit Theorem, recommended by
Method 1 from TIA/EIA TSB 107 Guideline were used and the
results compared with the field measurement values of these
spans. Evaluation results showed that this methodology
cause an overestimation of the link PMD coefficient due to
a limitation of the measurement eqquipments and
consequently an overestimation of the power penalty. This
overestimation is due to the fact that fiber PMD is bellow
of the resolution limit of the commercially available
measurement equipments. Link PMD coefficient estimation
needs the use of more precise measurement equipment (Not
available yet) or to correct this calculus methodology for
the optical link PMD estimation with the use of longer
fibers/cables.
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Optický spoj pro vnitřní bezkabelovou síť / Optical link intended for indoor networkHrbáčková, Petra January 2010 (has links)
This thesis deals with the structure of the optical wireless link intended for indoor applications. Optical transmitters and optical receivers as the basic elements of optical links and their characteristics and parameters are described. The characteristics of lenses used in the transmitter and receiver are presented. The special chapter is devoted to the directional reflectance properties of surfaces. The last part of the thesis is focused on a specific proposal of the wireless optical links and its power level diagram.
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Adaptive optical interconnects: The ADDAPT projectHenker, Ronny, Pliva, Jan, Khafaji, Mahdi, Ellinger, Frank, Toifl, Thomas, Offrein, Bert, Cevrero, Alessandro, Oezkaya, Ilter, Seifried, Marc, Ledentsov, Nikolay, Kropp, Joerg-R., Shchukin, Vitaly, Zoldak, Martin, Halmo, Leos, Turkiewicz, Jaroslaw, Meredith, Wyn, Eddie, Iain, Georgiades, Michael, Charalambides, Savvas, Duis, Jeroen, van Leeuwen, Pieter 05 August 2019 (has links)
Existing optical networks are driven by dynamic user and application demands but operate statically at their maximum performance. Thus, optical links do not offer much adaptability and are not very energy-effcient. In this paper a novel approach of implementing performance and power adaptivity from system down to optical device, electrical circuit and transistor level is proposed. Depending on the actual data load, the number of activated link paths and individual device parameters like bandwidth, clock rate, modulation format and gain are adapted to enable lowering the components supply power. This enables exible energy-efficient optical transmission links which pave the way for massive reductions of CO2 emission and operating costs in data center and high performance computing applications. Within the FP7 research project Adaptive Data and Power Aware Transceivers for Optical Communications (ADDAPT) dynamic high-speed energy-efficent transceiver subsystems are developed for short-range optical interconnects taking up new adaptive technologies and methods. The research of eight partners from industry, research and education spanning seven European countries includes the investigation of several adaptive control types and algorithms, the development of a full transceiver system, the design and fabrication of optical components and integrated circuits as well as the development of high-speed, low-loss packaging solutions. This paper describes and discusses the idea of ADDAPT and provides an overview about the latest research results in this field.
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Exploitation des effets électro-optiques pour la sécurité en IRM : applications des liaisons optiques pour des capteurs RF endoluminaux et des sondes de mesure du TAS / Electro-optical effects for safety in MRI : optical methods for endoluminal RF coils and TAS measurement probesSaniour, Isabelle 18 December 2017 (has links)
Le développement de systèmes IRM à plus haut champ magnétique statique s'est accompagné d'une interrogation légitime concernant l'effet des champs électromagnétiques RF sur les patients. L'effet peut être renforcé par l'introduction d'éléments conducteurs à l'intérieur de la bobine RF comme c'est le cas pour les capteurs endoluminaux utilisés pour l'analyse des parois digestives. Ces capteurs entraînent des risques d'échauffements locaux élevés pour le patient en raison du TAS local induit par le champ électrique RF en présence d'un fil conducteur. Ces capteurs ayant le potentiel de présenter un bénéfice pour le patient, il est nécessaire de s'affranchir de ces limitations. Le premier objectif de la thèse est le développement d'un capteur endoluminal à liaisons optiques. Un dispositif de découplage actif optique a été développé et caractérisé. Les images RMN in vitro montrent une distribution du RSB comparable au découplage classique, validant ainsi l'efficacité du découplage optique. Concernant la transmission optique du signal RMN, des travaux ont été réalisés afin de s'affranchir des contraintes liées à l'utilisation d'un guide d'onde pour la conversion électro-optique par effet Pockels. Le capteur a été rendu plus compact. En revanche, l'importance de contrôler le TAS local dans des conditions expérimentales données demeure un besoin ne s'arrêtant pas à ceux des capteurs endoluminaux. Le second objectif est donc la validation expérimentale d'une sonde électro-optique pour la mesure du champ électrique RF durant un examen IRM. Cette sonde a permis d'effectuer des mesures du champ électrique dans l'air et dans différents milieux biologiques à 3 T et 4,7 T et estimer le TAS local / The recent advancement in MRI systems and the increase of the static magnetic field strength were accompanied by a strong concern about the effect of RF electromagnetic fields on patients. The effect can be increased by the use of conductive elements inside the volume coil as in the case of endoluminal coils used to analyze digestive walls. These coils lead to an increase of the local SAR which is induced by RF electric field in the presence of the coaxial cable connecting the coil to the MR system, resulting in strong local heating. Giving that these coils have the potential to present a real benefit to the patient, it worth to overcome these limitations. Accordingly, the first objective of the thesis is the development of a fully optical endoluminal receiver coil. An optical active detuning system has been developed and characterized. The NMR images show a signal-to-noise ratio distribution similar to that obtained with conventional detuning techniques, thus validating the efficiency of the optical detuning. Concerning the electro-optical conversion and the optical transmission of the NMR signal, experiments were performed to overcome constraints related to the use of waveguide for electro-optical conversion by Pockels effect. Moreover, the importance of monitoring global and local SAR during MRI exams remains a need which is not limited only to the endoluminal coils. The second objective of the thesis is then the experimental validation of an electro-optical probe for real-time measurements of RF electric field. This probe can measure the RF electric field in air and in biological media at 3 T and 4.7 T MRI systems and allows the estimation of the local SAR
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Model atmosférického prostředí pro optické bezkabelové spoje / Model of atmospheric transmission media for free space opticsPřikryl, Petr January 2013 (has links)
The aim of this thesis is to study the methods of a free space optical link design and its application in the communication technologies. The thesis describes possible intrusive influences on the transmitted optical signal, which are the signal noise, atmospheric attenuation and atmospheric turbulences. The thesis is particulary focused on the influence of the atmospheric turbulences and atmospheric attenuation on the optical beam.
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