Microwave multiplexing networks are widely used in satellite communication systems. Their performances, such as the insertion loss and rejection between channels, are extremely critical. This research aims at effective design of multiplexing networks for applications in communication satellites exploring different design methodologies. First, the enhanced type of multiplexer has been proven to be able to significantly improve its performances by forming an extra pole in the pass-band of each channel using the existing manifold. For completeness of the design methodology, the design of the enhanced type of multiplexers with H-plane T-junctions is investigated in this thesis. Design equations are given. By changing the distance between the channel filters and the distance between manifold waveguide and channel filter, the resonances and the magnitude of coupling can be readily controlled to satisfy the design requirement. Examples are used to demonstrate the feasibility and effectiveness of the new design using H-plane T-junctions. Secondly, Artificial Neural Network (ANN) is applied in the spurious mode compensation in the multiplexer design. Channel filter tuning, circuit model simplification, and neural network training processes are detailed in the thesis. Space-Mapping optimization technology has been applied in the tuning of a channel filter. The artificial neural network is applied as the method to compensate disadvantages of both electromagnetic (EM) simulation, which is accurate but extremely time consuming, and circuit model, which is fast but with limited accuracy. The neural network model of a simplified circuit can rapidly and accurately simulate the spurious mode of a channel filter in its out-of-band. Design examples are used to demonstrate the modeling steps. Good agreements are observed between EM simulation and the results from the developed model. / UOIT

La collecte d’informations et leur transmission au travers d’un réseau de communications peut être effectuée par des réseaux de capteurs autonomes ainsi que par des satellites d’observation. L’utilisation conjointe de ces réseaux fournirait des données complémentaires et permettrait à l’Humanité de pérenniser son avenir en comprenant les mécanismes du monde qui l’entoure. Ces dernières années, le secteur spatial a montré une volonté d’unifier et de faciliter la réutilisation des développements réalisés avec la création de filières de plateformes multi-missions ainsi que la définition de protocoles applicables à différents contextes. L’objectif de cette thèse est d’étudier les caractéristiques des différentes technologies d’observation afin d’en exploiter les points communs. À ces fins, nous nous intéressons aux technologies et aux architectures utilisées dans de tels contextes. Nous proposons alors une architecture de réseau répondant aux contraintes des systèmes les plus communément utilisés dans un tel cadre. Les principales contraintes des scénarios d’observation sont liées à la forte intermittence des liens et donc au manque de connexité du réseau. Nous nous orientons donc vers une solution ayant recours au concept de réseaux tolérants au délai. Dans un tel contexte, l’existence d’une route entre la source et la destination n’est pas garantie. C’est pourquoi les protocoles de communication utilisés propagent généralement plusieurs exemplaires d’un même message vers plusieurs entités afin d’augmenter le taux de délivrance. Nous avons souhaité diminuer l’utilisation des ressources du réseau tout en conservant des performances similaires afin d’augmenter l’efficacité du réseau. Après avoir proposé une architecture commune, nous nous sommes focalisés sur les spécificités des différents segments de notre réseau afin de répondre localement à ces problèmes. Pour le segment satellite, nous nous sommes plus spécialement concentrés sur les techniques de gestion de mémoire. Nous considérons un satellite défilant avec une mémoire embarquée limitée, collectant des données en provenance de passerelles. Il s’agit alors de sélectionner les messages les plus urgents quitte à déposer sur une autre passerelle les messages moins contraints. Sur le réseau de capteurs terrestre, nous nous sommes focalisés sur la diminution de l’utilisation des ressources du réseau. Pour cela nous avons utilisé l’historique des rencontres entre les nœuds et analysé l’influence de la quantité de mémoire allouée aux accusés de réception sur les performances du réseau. Nous sommes parvenus à atteindre des performances supérieures aux solutions existantes à moindre frais. Les solutions proposées peuvent être mises en œuvre et appliquées dans différents contextes applicatifs. / Data gathering and transmission through a communicating network can be obtained thanks to wireless sensor networks and observation satellites. Using both these technologies will allow mankind to build a sustainable future by understanding the world around. In recent years, space actors have demonstrated a will to reuse the developed technologies by creating multiple programs platforms and defining context-agnostic protocols. The goal of this thesis is to study the characteristics of several observation technologies to exploit their similarities. We analyse the existing technologies and architectures in several contexts. Then, we propose a networking architecture handling constraints of most commonly used systems in such a context. The main constraints of observation scenarios are due to the links intermittence and lack of network connectivity. We focus on a solution using the delay tolerant networking concept. In such a context, a path between source and destination might not exist at all time. That is why most proposed protocols send multiple copies of a message to increase the delivery ratio. We wanted to decrease network resource use while keeping a similar performance to increase network efficiency. After having proposed a common architecture, we focused on particularities of each network segment to solve problems locally. Concerning the satellite part, we focused specifically on memory management techniques. We considered a low earth orbit satellite with a limited on-board buffer, gathering data from gateways. The goal is then to select the most urgent messages even though the least urgent ones are sent back to the ground. On the terrestrial sensor network part, we focused on the decrease of network resource use. We used the history of encounters between nodes and analysed the influence of the proportion of memory allocated to acknowledgements on network performance. We achieved better performance than existing solutions and at lower cost. The proposed solutions can be deployed and applied in several applications.

Made available in DSpace on 2014-06-11T19:24:13Z (GMT). No. of bitstreams: 0 Previous issue date: 2004-07Bitstream added on 2014-06-13T18:51:55Z : No. of bitstreams: 1 assis_sc_me_guara.pdf: 1352384 bytes, checksum: 82532e5fd71ac4103ee475d8432b8f1f (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Universidade Estadual Paulista (UNESP) / Um abordagem analítica para a propagação de atitude de satélites estabilizados por rotação em órbita circular é apresentada, incluindo o torque magnético residual (torque devido ao momento magnético ao longo do eixo de rotação do satélite). O modelo de quadripolo é utilizado para descrever o campo geomagnético. O método da média é aplicado para determinar o torque ao longo de um período orbital. Observa-se que Torque Magnético Residual Médio não possui componente ao longo do eixo de rotação, de modo que não afeta o módulo da velocidade de rotação do satélite. Para um período orbital uma solução analítica é apresentada. Esta solução mostra que o torque residual contribui para a deriva e precessão do eixo de rotação. Simulações são realizadas com os dados dos Satélites de Coleta de Dados Brasileiros (SCD1 e SCD2). / An analytical approach for the attitude motion of spin stabilized artificial satellite in circular orbit is presented, including residual torque. The quadripolo model is used to described the geomagnetic field. The averaged residual torque is computed for one orbital period. It is observed that the residual magnetic torque does not have a component along the spin axis. The inclusion of this torque on the rotational motion differential equations of spin stabilized spacecraft's yields the conditions to derive an analytical solution. The solution shows that residual torque does not affect the spin velocity magnitude, contributing only for the precession and the drift of the spin axis of the spacecraft. Applications are shown for the spin stabilized Brazilian satellites SCD1 and SCD2.

Plusieurs nouvelles missions spatiales exigent que le satellite puisse accomplir des manoeuvres de façon autonome. Ces missions nécessitent souvent des satellites plus volumineux pour intégrer tous les instruments de mesure nécessaires. L'utilisation de matériaux légers pour diminuer la masse ainsi que de panneaux solaires de grande envergure pour permettre de fournir à la demande électrique rendent le satellite très flexible. Cette flexibilité peut intéragir avec le système de commande et amener le système à être instable. Cette thèse a pour objectif de proposer des techniques de commande innovatrices permettant le positionnement précis de façon autonome d'un satellite flexible lors des manoeuvres en orientation. Afin de diminuer la masse du satellite et augmenter le volume disponible à l'intérieur de ce dernier, toutes les manoeuvres doivent se faire en utilisant uniquement des propulseurs chimiques de type tout-ou-rien. De plus, la puissance limitée de l'ordinateur de bord exige que les différents systèmes de commande soient suffisamment petits pour pouvoir être implantés à l'intérieur de celui-ci. Le candidat propose trois approches pour améliorer la commande d'un satellite flexible : une amélioration des techniques de modulation des actionneurs tout-ou-rien, une mise en forme des signaux de consigne, ou input shaping , afin d'éviter d'exciter les modes flexibles et une technique de découplage de la dynamique rigide qui permet d'atténuer simultanément l'excitation des modes flexibles. Chacune des contributions est présentée séparément et appliquée à des exemples simples afin de bien démontrer l'amélioration qui en découle. Par la suite, elles sont appliquées sur un modèle d'un satellite très flexible afin d'en démontrer l'efficacité.

International Telemetering Conference Proceedings / October 26-29, 1998 / Town & Country Resort Hotel and Convention Center, San Diego, California / The recent proliferation of Low Earth Orbiting (LEO) science, earth resources, and global communication satellites requires a significant number of ground stations for support. A network of satellite tracking ground stations with the ability to support multiple users and communicate with multiple satellites requires a robust scheduling and conflict resolution system. This paper describes an automated scheduling implementation for managing such a commercial, multi-user, multiple satellite, ground station network.

International Telemetering Conference Proceedings / October 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, Nevada / Prototyping an Internet Protocol (IP) compliant architecture will demonstrate a realistic basis for satellite communication design. The prototype IP architecture should prove seamless and secure communications between the satellites and ground stations. Using commercial off the shelf (COTS) equipment, design and development of satellite communications becomes easier and less expensive than developing specialized equipment. IP space applications will improve communications while minimizing development costs.

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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International Telemetering Conference Proceedings / October 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, Nevada / The usage of Internet is explosively growing. Satellite has become a choice solution breaking through the bandwidth bottleneck and the terrain limit. TCP, which is well suited to terrestrial networks, performs poorly on a satellite channel. The reduced efficiency and QoS(Quality of Service) mainly result from three characteristics of a satellite link: higher bit error rate, the high latency, asymmetry. For this issue, the paper presents connection-subsection network architecture, and brings forward S-TCP based on the architecture.