In on-board processing satellite systems in which FDMA/SCPC access schemes are employed. transmultiplexers are required for the frequency demultiplexing of the SCPC signals. Digital techniques for the implementation of the transmultiplexer for such application were examined in this project. The signal processing in the transmultiplexer operations involved many parameters which could be optimized in order to reduce the hardware complexity whilst satisfying the level of performance required of the system. An approach for the assessment of the relationship between the various parameters and the system performance was devised. which allowed hardware requirement of practical system specifications to be estimated. For systems involving signals of different bandwidths a more flexible implementation of the trans multiplexer is required and two computationally efficient methods. the DFT convolution and analysis/synthesis filter bank. were investigated. These methods gave greater flexibility to the input frequency plan of the transmultiplexer. at the expense of increased computational requirements. Filters were then designed to exploit specific properties of the flexible transmultiplexer methods. resulting in considerable improvement in their efficiencies. Hardware implementation of the flexible transmultiplexer was considered and an efficient multi-processor architecture in combination with parallel processing software algorithms for the signal processing operations were designed. Finally. an experimental model of the payload for a land-mobile satellite system proposal. T -SAT. was constructed using general-purpose digital signal processors and the merits of the on-board processing architecture was demonstrated.

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This thesis examines a new market for satellite communication serving small fixed-station business systems. This market requires transmission between a large number of smaller and cheaper earth terminals. The traffic requirements for satellite business services in Europe by the year 2000 have been reviewed. An advanced regenerative on-board processing business satellite with 13 spot-beams for the European coverage was then proposed to meet the expected traffic growth. This satellite system is designed to meet the needs of the user rather than, as traditionally, the user fitting in with the satellite. SCPC/FDMA and R-TDMA (reservation-TDMA) multiple access schemes were found to be most suitable for the proposed system serving many small users whose traffic was mixed voice, data and video. The architecture of the satellite payload has been studied and two main functional blocks, transmultiplexer and baseband switch were identified. The use of the transmultiplexer is to transform the EDM channels into TDM and the baseband switch is to provide full connectivity between all the stations so that the revolutionary idea of having a "switchboard in the sky" can be realised. The development work for the baseband switch is reported in detail in this thesis together with a comparison of different architectures for the baseband switch. A proof-of-concept model for the baseband switch was designed, built and tested. From the test results, the feasibility of implementing the baseband switch using the chosen architecture was proved. Another main area studied in this thesis was device technology. The present and future capability of bipolar, CMOS and GaAs technology has been investigated concentrating mainly on digital devices and semi-custom technology. Since the satellite is operating in an hostile environment, it has been necessary to study the effects of radiation on semiconductor devices. The outcome of these studies indicate that it is very promising to launch such advanced satellite payloads in the late 1990's.

京都大学 / 0048 / 新制・課程博士 / 博士(情報学) / 甲第22585号 / 情博第722号 / 新制||情||124(附属図書館) / 京都大学大学院情報学研究科数理工学専攻 / (主査)教授 梅野 健, 教授 山下 信雄, 教授 守倉 正博 / 学位規則第4条第1項該当 / Doctor of Informatics / Kyoto University / DFAM

Les systèmes de communication prennent de nos jours une importance de plus en plus prépondérante dans tous les aspects de la vie courante et les exigences de connectivité se retrouvent dorénavant dans de très nombreux projets. Ces besoins de connexion exigent des débits de communication ainsi que des taux de couverture de plus en plus importants, poussant de ce fait vers l’utilisation de systèmes de communication par satellite (SATCOM). Les applications envisagées n’étant pas limitées à des installations fixes, celles-ci demandent de pouvoir assurer une communication par satellite depuis un porteur en mouvement. Il est donc nécessaire d’utiliser des servomécanismes de positionnement de l’antenne de façon à assurer un pointage correct de l’antenne vers le satellite. Ces positionneurs sont donc asservis de façon à orienter la ligne de visée de l’antenne vers le satellite, avec une erreur angulaire de l’ordre du dixième de degré. Cette précision a pour conséquences certaines exigences fortes sur la conception. Ces contraintes imposent l’utilisation de composants de qualité supérieure, des études mécaniques poussées ainsi que des réglages propres à chaque positionneur après assemblage. Dans le cadre de ces travaux de thèse, une stratégie de pointage différente de l’état de l’art a été conçue. Cette stratégie, nommée Helios (Hybrid Estimator of Line Of Sight), permet de lever certains verrous scientifiques spécifiques. Notamment, elle permet une diminution des performances requises de l’asservissement en position de l’antenne en fournissant une trajectoire plus facile à suivre. Cela permet une diminution des contraintes de conception, notamment mécaniques (frottements, raideurs …). Cela est rendu possible par une meilleure estimation de la direction à pointer, utilisant un plus grand nombre de mesures, sans introduire de retard dans l’estimation. Les moyens d’essais de Thales ont permis d’effectuer des essais expérimentaux sur des prototypes industriels. Ainsi, la stratégie est testée en simulation et en expérimentation sur un hexapode simulant un porteur, permettant un recalage du modèle de simulation à partir de données expérimentales. C’est ainsi que la stratégie est validée en conditions opérationnelles. Afin de réaliser ces tests expérimentaux, une étape de mise en place du moyen d’essais a été réalisée. Notamment, les outils de communication ont été mis au point (bus de terrains, liaisons série …). L’asservissement en position de la station a été réalisé à partir d’une identification non-paramétrique en boucle fermée du mécanisme. L’intégration de la station complète a été réalisée, permettant ainsi les tests en extérieur, sur un hexapode. / In military and civil application, satellite communications (SACTOM) are often needed on moving vehicles (drones, planes, land vehicles, vessels…) in order to transfer all kind of data (pictures, videos, internet …). These types of stations are called SATCOM On The Move (SOTM). In order insure high data rates, the antenna must be directional, which means that they direct electro-magnetic waves in a particular direction of space, called line of sight. The line of sight must be steered in order to be aligned with the satellite to insure a strong communication link with the highest data rate possible. Stabilized platforms, called Antenna Positioning System, aim to steer the antenna’s line of sight in the satellite direction. The pointing requirements are the source of conception constraints that reduce the cost efficiency of the overall station. This PhD report focus on the development and the study of a new pointing strategy called Helios (“Hybrid Estimator of LIne Of Sight”). This algorithm uses least squares to found the antenna pattern in real time, using an observation window. Among others, it allows to reduce the bandwidth of the control loops by generating a trajectory easier to follow. Therefore, it decreases the conception constraints (friction, backlash, field bus data rate …). Helios is tested through experimentation, using Thales industrial prototypes. The vehicle is emulated by a hexapod. Simulation is carried out in order to fit the measured experimental behavior. To do so, parametrical and non-parametrical identification has been done on the SOTM prototype. This way, Helios is validated and studied in operational conditions.