150 research outputs found

    Protocole de routage à chemins multiples pour des réseaux ad hoc

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    Ad hoc networks consist of a collection of wireless mobile nodes which dynamically exchange data without reliance on any fixed based station or a wired backbone network. They are by definition self-organized. The frequent topological changes make multi-hops routing a crucial issue for these networks. In this PhD thesis, we propose a multipath routing protocol named Multipath Optimized Link State Routing (MP-OLSR). It is a multipath extension of OLSR, and can be regarded as a hybrid routing scheme because it combines the proactive nature of topology sensing and reactive nature of multipath computation. The auxiliary functions as route recovery and loop detection are introduced to improve the performance of the network. The usage of queue length metric for link quality criteria is studied and the compatibility between single path and multipath routing is discussed to facilitate the deployment of the protocol. The simulations based on NS2 and Qualnet softwares are performed in different scenarios. A testbed is also set up in the campus of Polytech’Nantes. The results from the simulator and testbed reveal that MP-OLSR is particularly suitable for mobile, large and dense networks with heavy network load thanks to its ability to distribute the traffic into different paths and effective auxiliary functions. The H.264/SVC video service is applied to ad hoc networks with MP-OLSR. By exploiting the scalable characteristic of H.264/SVC, we propose to use Priority Forward Error Correction coding based on Finite Radon Transform (FRT) to improve the received video quality. An evaluation framework called SVCEval is built to simulate the SVC video transmission over different kinds of networks in Qualnet. This second study highlights the interest of multiple path routing to improve quality of experience over self-organized networks.Les réseaux ad hoc sont constitués d’un ensemble de nœuds mobiles qui échangent des données sans infrastructure de type point d’accès ou artère filaire. Ils sont par définition auto-organisés. Les changements fréquents de topologie des réseaux ad hoc rendent le routage multi-sauts très problématique. Dans cette thèse, nous proposons un protocole de routage à chemins multiples appelé Multipath Optimized Link State Routing (MP-OLSR). C’est une extension d’OLSR à chemins multiples qui peut être considérée comme une méthode de routage hybride. En effet, MP-OLSR combine la caractéristique proactive de la détection de topologie et la caractéristique réactive du calcul de chemins multiples qui est effectué à la demande. Les fonctions auxiliaires comme la récupération de routes ou la détection de boucles sont introduites pour améliorer la performance du réseau. L’utilisation de la longueur des files d’attente des nœuds intermédiaires comme critère de qualité de lien est étudiée et la compatibilité entre routage à chemins multiples et chemin unique est discutée pour faciliter le déploiement du protocole. Les simulations basées sur les logiciels NS2 et Qualnet sont effectuées pour tester le routage MP-OLSR dans des scénarios variés. Une mise en œuvre a également été réalisée au cours de cette thèse avec une expérimentation sur le campus de Polytech’Nantes. Les résultats de la simulation et de l’expérimentation révèlent que MP-OLSR est particulièrement adapté pour les réseaux mobiles et denses avec des trafics élevés grâce à sa capacité à distribuer le trafic dans des chemins différents et à des fonctions auxiliaires efficaces. Au niveau application, le service vidéo H.264/SVC est appliqué à des réseaux ad hoc MP-OLSR. En exploitant la hiérarchie naturelle délivrée par le format H.264/SVC, nous proposons d’utiliser un codage à protection inégale (PFEC) basé sur la Transformation de Radon Finie (FRT) pour améliorer la qualité de la vidéo à la réception. Un outil appelé SVCEval est développé pour simuler la transmission de vidéo SVC sur différents types de réseaux dans le logiciel Qualnet. Cette deuxième étude témoigne de l’intérêt du codage à protection inégale dans un routage à chemins multiples pour améliorer une qualité d’usage sur des réseaux auto-organisés

    Elimination of doubt : methods for a predictive design to direct and optimize the flow of visitors

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    Ympäristömme globaalistuu ja monimutkaistuu kaiken aikaa. Prosessi näkyy muun muassa kansainvälisen liikenteen solmukohdissa. Esimerkiksi lentokentät ovat kyseisiä eri kulttuurien keskinäisen vuorovaikutuksen kohtia. Eri kulttuureista tulevien ihmisten pitää osata orientoitua vieraassa ja usein sekavassa ympäristössä. Jotta toiminta olisi sujuvaa näissä solmukohdissa, on suunnistamiseen tarvittavan tiedon oltava nopeasti omaksuttavaa ja ymmärrettävää. Monet muotoilijat ja suunnittelijat ajattelevat, että opastejärjestelmät ovat reduktionistisia ja mekanistisia syy-seuraus systeemejä. On kuitenkin ilmeistä, että kansainvälisesti harmonisoimattomien piktogrammien kyky välittää informaatiota on epäonnistunutta. Nykyiset kognitiotieteen havainnot osoittavat, että visuaalisen havaitsemisen ja tilallisen orientaation aikaisemmat mallit ovat vain osittain toimivia. Siispä oli syytä kysyä ”onko mahdollista tuottaa ennakoiva malli jonka avulla voi kehittää, toteuttaa ja varmistaa suunnitteluratkaisuja, jotka ohjaavat ja optimoivat vierailijoiden virtaa laajoissa julkisissa tiloissa.“ Tutkimuksen keskiössä on tästä syystä tilallisessa orientoitumisessa tapahtuva kulttuurinen merkityksellistäminen ja paikkatietoisuuden lisääminen (situation awareness). Juuri tuo yksilöllinen merkityksen tuottaminen voi tarkoittaa laajaa kirjoa erilaisia tulkintoja. Paikkatietoisuuden syntymisen erilaiset mahdollisuudet yhdessä erilaisten menetelmien kanssa voivat tuottaa ratkaisuja suunnitteluprosessiin. Suunnitteluprosessissa voidaan ottaa huomioon myös havaintopsykologisia näkökulmia. Kaiken kaikkiaan tämä johtaa systeemis-holistiseen ja käyttäjäkeskeiseen ajatteluun julkisten tilojen opastejärjestelmien suunnittelun kehityksessä. Esitän myös käytännöllisen ratkaisun opastejärjestelmien suunnitteluun ja arviointiin tarkastelemalla olemassa olevien järjestelmien rakennetta ja parametreja sekä niiden kehitystyötä. Työ sisältää yhteensä yhdeksän tapaustarkastelua. Tutkimusmenetelminä käytin laadullista havainnointia ja kvantitatiivista analyysiä. Havainnoin ja tulkitsin etnisiä tottumuksia ja henkilökohtaisia näkemyksiä. Tekemäni kyselyjen perusteella näyttää siltä, että konstruoimaani mallia voitaisiin käyttää kehittämisen ja todentamisen välineenä.The rapid development of international traffic characterizes our increasingly globalized and ever more complex world. Nodal points (for example, airports) have formed where people from various cultural backgrounds and with differing levels of educational attainment need to reorient themselves in a unfamiliar and often confusing environment. A key condition to ensure everything works smoothly in such an international junction is the extremely fast reception and processing of information by everyone involved. The dominant school of thought among many designers and planners of guidance and routing systems is still a reductionist and mechanistic one (cause - effect). It has become apparent that the use of non-internationally harmonized pictograms as information carriers has failed completely. Recent findings in the field of cognitive science demonstrate convincingly that previous models of visual perception and spatial orientation can only highlight partial aspects. For these aspects, the question has arisen: “Is there a possibility to evolve a predictive system to develop, implement and verify design solutions to direct and optimize the flow of visitors in large public spaces?” Therefore, the moment of semiosis of the orientation seekers moved into the focus of the investigation. This moment of meaning-making, which is perceived by every individual differently, spans the entire spectrum of the perception of the designated item (the optical characteristic of the character substrate) between manifold interpretation or absolute certainty. The various viewing options of “situational awareness” with the help of various methodologies provide solutions for the design process. Taking the aspects of perceptual psychology into account leads to the development of a systemic/holistic and user-centred design of orientation systems in public spaces. Identifying and consulting the predictive parameters in a systematic process could show a practicable solution for the planning and evaluation of guidance and routing systems. In various national and international case studies, the process reliability and processing quality of this solution were demonstrated. Involving mixed research methodologies of qualitative observation and quantitative analysis, it was possible to develop a workable model. Through observation and interpretation, ethnic habits and personal views were taken into account to develop the methods. The use of questionnaires or surveys created statistics to prove or disprove the hypothetical model. The capacity of the presented model and the operationalization of the research demonstrated an effective method for overcoming barriers of age, language and culture. The publication satisfies, therefore, the criteria of the academic quality of a practice-based Ph.D

    The transmission of electricity in England and Wales; land use, and amenity aspects

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    Transmission of electricity is performed at 132, 275 and 400 kilovolts and is the responsibility of the Central Electricity Generating Board. The distribution of electricity at lower voltages is the responsibility of Area Boards. This thesis is solely concerned with the former. The first part deals with the historical development of the industry and the linking of many separate electricity undertakings, to provide economies from the reduction of spare generating plant, and security of supply. The factors determining the locations of coal, oil and nuclear power stations examined. The geographical pattern that results from the location of generating plant and of demand for electricity, determines the shape and size of the transmission network. Transmission is effected by overhead lines and underground cables, and the effects of both on the use of land and amenity are examined. Substations are required to switch electricity from one circuit to another and to transform it between voltages. Because of their size and the engineering considerations affecting their location they may also have a major effect on the land use and amenity of their surroundings. An overhead line and a substation that were both the subject of public inquiries are treated as case studies. The design of towers and insulators investigated to see whether engineering requirements arc considered or modified to take account of aesthetics. The screening of lines and substations by ground shaping and tree planting is frequently required by local Planning Authorities. The Board's attitude to this work, is evident from public inquiries and recent example of executed landscaping work. The thesis is illustrated with diagrams, maps and photographs

    Orbital construction demonstration study. Volume 2: Technical

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    The following items are discussed in reference to OCDA requirements; (1) flight mechanics and control, (2) effects of sun angle, (3) disturbance torques, (4) control system requirements, (5) OCDA orbit decay profile, and (6) aerodynamic drag forces. Structural design requirements are also given as well as basic design definition

    Book of short Abstracts of the 11th International Symposium on Digital Earth

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    The Booklet is a collection of accepted short abstracts of the ISDE11 Symposium

    Cellular Automata

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    Modelling and simulation are disciplines of major importance for science and engineering. There is no science without models, and simulation has nowadays become a very useful tool, sometimes unavoidable, for development of both science and engineering. The main attractive feature of cellular automata is that, in spite of their conceptual simplicity which allows an easiness of implementation for computer simulation, as a detailed and complete mathematical analysis in principle, they are able to exhibit a wide variety of amazingly complex behaviour. This feature of cellular automata has attracted the researchers' attention from a wide variety of divergent fields of the exact disciplines of science and engineering, but also of the social sciences, and sometimes beyond. The collective complex behaviour of numerous systems, which emerge from the interaction of a multitude of simple individuals, is being conveniently modelled and simulated with cellular automata for very different purposes. In this book, a number of innovative applications of cellular automata models in the fields of Quantum Computing, Materials Science, Cryptography and Coding, and Robotics and Image Processing are presented

    Satellite Communications

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    This study is motivated by the need to give the reader a broad view of the developments, key concepts, and technologies related to information society evolution, with a focus on the wireless communications and geoinformation technologies and their role in the environment. Giving perspective, it aims at assisting people active in the industry, the public sector, and Earth science fields as well, by providing a base for their continued work and thinking
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