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Jupiter's aurorae put on a permanent, ever-changing light show more than a thousand times brighter than the Earth's own aurorae. At ultraviolet wavelengths these aurorae are dominated by the ME: discontinuous ovals of curtain-like light partially encircling each of the planet's magnetic poles. The properties of these aurorae are a reflection of processes in Jupiter's magnetosphere, as the two are coupled together by currents flowing along magnetic field lines. By understanding auroral features in the ME, the vast Jovian magnetosphere's complex interactions with the planet can thus be better understood. The evolution of this energetic system has implications for Jupiter's present and past, as well as its place within the Solar System. While Jupiter's large-scale aurorae have been extensively studied, the properties, particularly motions, of small-scale auroral features represent a comparatively unexplored route to gain deeper understanding of this system. Here, the motions of these auroral features are characterized and related back to the physical processes in Jupiter's magnetosphere and ionosphere. First, a survey of auroral feature motions in Jupiter's ME is created based on Hubble Space Telescope observations. A dichotomy in auroral motion is found: features near dawn remain fixed in local time significantly more than features elsewhere. This finding gives context for Jupiter's dawn storms-- rare, enigmatic auroral phenomena noted for their fixedness, brightness, and appearance only at local dawn. Next, the ME is measured on smaller scales and compared with in-situ measurements of magnetospheric plasma flow from the Galileo spacecraft to estimate the magnetospheric and ionospheric properties associated with fixed auroral features. Finally, these properties are used to inform a self-consistent model of the currents generating the ME. Ionospheric conductance-- the ease with which currents flow through the ionosphere-- is varied to generate models which best match the auroral observations. Altogether, a coherent description of ME auroral features and their associated physical processes emerges. Increased conductance is found to correspond with both auroral emissions and the acceleration of magnetospheric plasma. The conductance, which is spatially variable but fixed in local time on average, is proposed to explain the motions of small-scale ultraviolet Jovian auroral forms.

Global Navigation Satellite System (GNSS) är ett system för global satellitpositionering och navigering och innefattar bland annat Global Positioning System (GPS) och Globalnaya Navigatsionnaya Sputnikovaya Sistema (GLONASS), dessa två system är de enda fullt globala operativa systemen i dagsläget. Galileo är ett europeiskt satellitsystem under utveckling och erbjuder för närvarande 14 satelliter, men ska bestå av totalt 30 satelliter när systemet beräknas vara fullt fungerande 2020. Den mätmetod med GNSS som har lägst osäkerhet är statisk mätning. Det är en relativ metod vilket innebär att minst två mottagare samlar observationer samtidigt, vanligtvis i flera timmar. Snabb statisk mätning är en vidareutveckling av statisk mätning och erbjuder mycket kortare observationstider, däremot innebär det en begränsning på baslinjelängden. Syftet med denna studie var att undersöka Galileos påverkan vid snabb statisk mätning och se huruvida Galileo kan bidra med lägre osäkerheter, avvikelser och observationstider i olika konstellationer tillsammans med GPS och GLONASS. Mätningarna utfördes under två dagar i fyra respektive två timmar. Två baslinjer mättes; ena baslinjen hade en längd på 0,4 km och den andra på drygt 2 km. I ett bearbetningsprogram delades därefter konstellationerna upp i tio tidsfönster (epoker) och varje tidsfönster delades i sin tur upp i tre sessioner (1, 5 och 10 minuter). Fyra typer av konstellationer testades: GPS, GPS och GLONASS, GPS och Galileo och sist alla tre tillsammans. Resultatet i studien visar på låga osäkerheter när fler än en konstellation används. Lägst osäkerhet uppnås generellt när mätning med alla konstellationer görs. Mätning med endast GPS ger högst osäkerhet i samtliga fall, men detta är framförallt kännbart vid den kortaste sessionen (1 minut). Likheten i osäkerheterna vid den korta och långa baslinjen är tydlig, men osäkerheterna är större för den långa baslinjen. Avvikelserna är lägst med alla konstellationer, men baslinjelängden är i nästan alla fall för kort mot sin referens. Slutsatsen från studien är att Galileo kan användas för att minska observationstider och osäkerheter vid snabb statisk mätning. Detta är dock försumbart ifall GPS och GLONASS redan används, åtminstone för de två baslinjerna i detta test. Låga osäkerheter uppnås antingen med multi-konstellation eller längre observationstider. / Global Navigation Satellite System (GNSS) is a global system for satellite positioning and navigation and consists, amongst other, of Global Positioning System (GPS) and Globalnaya Navigatsionnaya Sputnikovaya Sistema (GLONASS). Currently, these systems are the only fully global operative satellite systems for positioning. Galileo is an upcoming satellite system and offers at the present time 14 active satellites, but will consist of 30 satellites once it is fully operational by 2020. The survey method with GNSS that has lowest uncertainties is static survey. It is a relative method which means that a minimum of two receivers observe simultaneously, usually for several hours. Rapid static surveying is a further development of static surveying and offers much shorter observation times, but it imposes a restriction of the baseline length. The purpose of this study is to evaluate Galileo’s contribution on rapid static surveying and see whether Galileo can decrease uncertainties, deviations and observation times in different constellations with GPS and GLONASS. Measurements were conducted during two days for two and four hours respectively. Two baselines were measured; the first baseline had a length of 0.4 km and the second nearly 2 km. Later in a software, each constellation was divided in ten time windows (epochs) and each time window was then divided in three sessions (1, 5 and 10 minutes). Four types of constellations were tried: GPS, GPS and GLONASS, GPS and Galileo and lastly all three combined. Results show that low uncertainties are obtained when more than one constellation is used. Lowest uncertainties can be obtained with all constellations active. Surveying with only GPS gives the highest uncertainties in all cases, but this is especially true for the shortest session (1 minute). Similarities in uncertainties between the short and long baseline is clear, but uncertainties are higher for the long baseline. Deviations are lower with all constellations active, but the baseline length is in almost all cases too short. The conclusion from the study is that Galileo can be used to lower observation time and uncertainties. However this is negligible when used with GPS and GLONASS, at least for the two baselines in this test. Low uncertainties can be achieved with multi constellation or longer observation time.

Location-based services have grown in importance as smartphones, and location-based applications have become an integral part of everyday life. While Global Navigation Satellite Systems (GNSSs) provide the most accurate position determination, open service GNSS signals remain unprotected and susceptible to spoofing attacks. Previous work within the domain highlighted this issue, with many smartphone receivers shown susceptible to GPS L1 spoofing, suggesting that their resilience experiments should be extended to include other GNSS signals in the future. Given that multi-GNSS receivers now have become the norm in smartphones, this thesis investigates whether smartphone GNSS receiver spoofing resilience depends on the type of signal; by conducting a series of comparative spoofing experiments involving GPS L1 and Galileo E1-B/C signals. To conduct the experiments, we developed a Galileo E1-B/C signal simulator that, together with the open-source GPS-SDR-SIM signal simulator, was the basis for conducting a series of experiments designed to identify the potential presence of anti-spoofing measures. The result of our experiments indicates that smartphone multi-GNSS receivers were significantly more resilient towards Galileo E1-B/C spoofing attacks, often accepting GPS L1 signals with significant position, time, and data errors, while refusing to accept corresponding Galileo E1-B/C signals. While we never observed cases of E1-B/C signals being accepted while rejecting GPS L1 signals, external factors limited the scope of the investigation and do not allow a generalized conclusion. As such, to deepen our understanding of these issues and how they relate to the development of anti-spoofing measures and trust in different signals, it is essential to extend this research to include more devices and other GNSS signals. / Positionstjänster har växt i betydelse allteftersom smarttelefoner och positionsapplikationer har blivit en integral del av våran vardag. Även om satellitpositionering utger det mest precisa och vedertagna positionsbestämningen av tillgängliga positionstjänser så är de publika satellitnavigeringssignalarna oskyddade och sårbara för förfalskningsattacker. Tidigare forskning inom området har evaluerat dessa sårbarheter och visat att ett betydande antal smarttelefoner var sårbara för GPS-L1 förfalskningsattacker och att denna forskning borde utökas i framtiden allteftersom satellitnavigeringsmottagare med förmåga att mottaga olika satellitsignaler integreras i smarttelefoner. Givet att en majoritet av nya smarttelefoner nu integrerar denna typ av mottagare så utvärderar detta arbete hur sårbarheten mot förfalskningsattacker beror på typ av satellitsignal genom en komparativ jämförelse av sårbarhet mellan GPS-L1 och den nyare Galileo E1-B/C signalen. För att genomföra utvärderingen så utvecklade vi en Galileo E1-B/C signalsimulator som tillsammans med GPS-L1 signalsimulatorn (GPS-SDR-SIM) utgjorde grunden för en serie av experiment designade för att identifiera och utvärdera sårbarheter och potentiella motåtgärder i smarttelefoner. Våra resultat indikerar att smarttelefoner är betydligt mer sårbara for GPS-L1 forfalskningsattacker då de accepterade GPS-L1 signaler med betydande position, tid, och datafel medans motsvarande Galileo E1-B/C signaler ej accepterades. Trots resultaten så är det viktigt att inte dra för starka slutsatser då underlaget var kraftigt begränsat givet rådande omständigheter (Covid), som gjorde det svårt/omöjligt att på ett säkert sätt samla volontärer med olika smarttelefoner för våra experiment. Därav så är det viktigt att i framtiden utöka arbetet med ett större underlag och fler signaltyper.

Scintillation of Global Positioning Systems (GPS) signals have been extensively studied at low and high latitude regions of the Earth. It has been shown in past studies that amplitude scintillation is severe at low latitudes and phase scintillation is severe at high latitudes. Unlike low and high latitude regions, mid-latitude scintillation has not been extensively studied. Further, it has been suggested that mid-latitude scintillation is negligible. The purpose of this research is to challenge this belief. A multi-constellation and multi-frequency receiver, that tracks American, Russian, and European satellites, was used to monitor scintillation activity at the Virginia Tech Space Center. Analysis was performed on collected data from various days and compared to past research done at high, mid, and low latitudes. The results are discussed in this thesis. / Master of Science / Earth’s atmosphere disrupts signals transmitted by Global Navigation Satellite Systems (GNSS). In certain regions of the Earth, these signals can be severely degraded. Not much research has been done on what could potentially happen to GNSS signals at mid-latitude regions of the Earth. It is important to gain a better understanding of the impacts mid-latitude regions can have on GNSS signals, in preparation for potential future outages across the system. The United States and Russia have had Global Positioning Systems (GPS) technology for decades. Today, China and Europe are expanding their global positioning systems. In the future there may be up to one hundred or more satellites available for public usage. This study was done to determine if outages could potentially occur at mid-latitudes, and to gain more knowledge on which of these satellite constellations have the best service.

To be able to receive a position from a smartphone user is very valuable. Wit- hout this many applications would not work at all. For many applications the existing position libraries are not good enough, for example augmented reality applications which requires millimeter precision for a good experience. The goal of this report is to study if GNSS positioning can be improved for smartphones.The study focuses mostly on Android and has the goal of using the method “trilateration” to combine multiple satellites position and their distance to a receiver in order to calculate a real position. The projekt consists of two parts: and Android application and a Java Tomcat server. The android applica- tion uses the programming library “Location” to access raw GNSS-data for cal- culating the distance between the receiver and the satellites, which is called “pseudorange”, and the server functions as a REST API which provides GALI- LEO satellites current position. The project tries to combine these parameters in the Application to create a position. Although the report did not succeed in com- bining these parameters to calculate a position, it does describe of it is still pos- sible; which applications has succeeded before and what others ought to think about when starting similar studies. This project would require a bit more time to reach its end goal, but the fact that raw GNSS-data has become available to all developers on Android is a promising development since others may conti- nue or do their own research. This project focuses solely on GALILEO satelli- tes, mostly to time constraints. In future works all available satellite constella- tions should be used for better results. / Att få en position av en smartphoneanvändare är mycket användbart, utan detta skulle många applikationer inte fungera alls. För många applikationer är den givna positionerings biblioteken inte tillräckligt bra dock, som t.ex. för augmen- ted reality applikationer som kräver millimeter-säker precision för en bra an- vändarupplevelse. Målet med denna rapport är att undersöka om GNSS-positio- nering kan förbättras inom smartphones. Undersökningen fokuserar mest på Android och har som målsättning att använda metoden “trilateration” för att kombinera satelliternas position och dess distans till en mottagare för att sedan räkna ut en verklig position. Projektet består av två delar: en Android applika- tion och en Java TomCat server. Android applikationen använder programme- rings biblioteket “Location” för att få tag på rå GNSS-data för att räkna ut di- stansen mellan satelliter och mottagaren, vilket kallas för “pseudorange”, och servern fungerar som ett REST API som returnerar GALILEO-satelliters nuva- rande position. Applikationen försöker kombinera pseudorange och satelliter- nas position med trilateration för at få ut mottagarens position. Rapporten lyck- as inte uppnå detta mål dock, men den beskriver hur det ändå är möjligt, vilka andra applikationer som lyckats och vad andra bör tänka på om de vill göra lik- nande studier. Det skulle behövas lite mer tid för att avsluta detta projekt, men faktumet att råa GNSS-data har blivit tillgänglig för alla Android-utvecklare, från att ha varit helt gömd, är en lovande utveckling då det låter andra forska på egen hand. Detta projekt fokuserar enbart på GALILEO satelliter, mestadels för tidsbegränsningar.

Although air pollution is one of the largest threats to human health, the data available to the public is often sparse and not very accurate nor updated. For example, there exists only about 5-10 air quality measuring points across the city of Stockholm. This means that the available data is good in close proximity of the sensing equipment but can differentiate much only a couple of blocks away. In order for individuals to receive up to date information around a larger city, stationary measurements are not sufficient enough to get a clear picture of how the current state of the air quality stands. Instead, other methods of collecting this data is needed, for instance by making the measurements mobile. GOEASY is a project financed by the European Commission where Galileo, Europe’s new navigational service, is used to enable more location-based service applications. As part of the GOEASY project is the evaluation of the potential of collaborative applications where users are engaged to help individuals affected by breathing-related diseases such as asthma. This thesis presents the choice of architecture and the implementation of a mobile platform serving this purpose. Using sensors mounted on a range of objects real time air quality data is collected and made available. The result is a mobile platform and connected Android application which by utilizing air quality sensors, reports pollution measurements together with positional coordinates to a central server. Thanks to the features of the underlying systems used, this provides a platform which is accurate and more resilient to exploits compared to traditional location-based services available today. The result allows individuals with respiratory conditions to receive much more accurate and up to date information in a larger resolution. It also serves the purpose of demonstrating the potential of the supporting technology as part of the GOEASY project. / Trots att föroreningar i luften är bland de största hoten mot mänsklig hälsa är den information som finns tillgänglig för allmänheten ofta både gles och inte tillräckligt noggrann eller uppdaterad. Till exempel finns det i hela Storstockholm endast mellan 5–10 luftkvalitetstationer som mäter föroreningar. Detta innebär att den data som finns tillgänglig är bra i närheten av mätutrustningen men kan skilja sig mycket enbart ett par kvarter bort. För att öka mängden information som är tillgänglig till allmänheten räcker inte längre enbart de stationära lösningarna som finns idag för att visa hur de rådande halterna av föroreningar står sig. Andra metoder måste införas, exempelvis genom att nyttja mobila mätningar från en plattform som kan röra sig fritt. GOEASY är ett projekt finansierat av den Europeiska Kommissionen, där Galileo, Europas nya navigationssystem används för att tillåta fler platsbaserade tjänster att äntra marknaden. Som en del av GOEASY projektet ingår evalueringen av potentialen i en applikation där användare samlar in data för att hjälpa individer med andningssvårigheter som astma. Denna avhandling presenterar valen till arkitekturen samt implementationen av en mobil plattform som en del av GOEASY. Lösningen använder sig av mobila luftkvalitetsensorer som kan monteras på en rad olika objekt som samlar data i realtid som görs tillgänglig för allmänheten. Resultatet är en mobil plattform och tillhörande Android applikation som med hjälp av luftkvalitetsensorer rapporterar halten av olika skadliga föroreningar tillsammans med platsinformation till en central server. Tack vare egenskaperna av de underliggande systemen som används, skapas en plattform som är mycket mer precis när det gäller positionering jämfört med liknande system som finns tillgängligt. Det resulterande systemet gör det möjligt för individer med andningssvårigheter att få tillgång till noggrannare samt mer uppdaterad information i större utsträckning än vad som för närvarande är tillgängligt. Systemet fyller även syftet med att demonstrera potentialen i den bakomliggande teknologin som en del av GOEASY.

La navigation par satellite, Global Navigation Satellite System, a été reconnue comme une solution prometteuse afin de fournir des services de navigation aux utilisateurs de l'Aviation Civile. Ces dernières années, le GNSS est devenu l'un des moyens de navigation de référence, son principal avantage étant sa couverture mondiale. Cette tendance globale est visible à bord des avions civils puisqu'une majorité d'entre eux est désormais équipée de récepteurs GNSS. Cependant, les exigences de l'Aviation Civile sont suffisamment rigoureuses et contraignantes en termes de précision de continuité, de disponibilité et d'intégrité pour que les récepteurs GPS seuls ne puissent être utilisés comme unique moyen de navigation. Cette réalité a mené à la définition de plusieurs architectures visant à augmenter les constellations GNSS. Nous pouvons distinguer les SBAS (Satellite Based Augmentation Systems), les GBAS (Ground Based Augmentation Systems), et les ABAS (Aircraft Based Augmentation Systems). Cette thèse étudie le comportement de l'erreur de position en sortie d'architectures de récepteur qui ont été identifiées comme étant très prometteuses pour les applications liées à l'Aviation Civile. / Since many years, civil aviation has identified GNSS as an attractive mean to provide navigation services for every phase of flight due to its wide coverage area. However, to do so, GNSS has to meet relevant requirements in terms of accuracy, integrity, availability and continuity. To achieve this performance, augmentation systems have been developed to correct the GNSS signals and to monitor the quality of the received Signal-In-Space (SIS). We can distinguish GBAS (Ground Based Augmentation Systems), ABAS (Airborne Based Augmentation Systems) SBAS (Satellite Based Augmentation Systems). In this context, the aim of this study is to characterize and evaluate the GNSS position error of various positioning solutions which may fulfil applicable civil aviation requirements for GNSS approaches. In particular, this study focuses on two particular solutions which are: • Combined GPS/GALILEO receivers augmented by RAIM where RAIM is a type of ABAS augmentation. This solution is a candidate to provide a mean to conduct approaches with vertical guidance (APV I, APV II and LPV 200). • GPS L1 C/A receivers augmented by GBAS. This solution should allow to conduct precision approaches down to CAT II/III, thus providing an alternative to classical radio navigation solutions such as ILS. This study deals with the characterization of the statistics of the position error at the output of these GNSS receivers. It is organised as following. First a review of civil aviation requirements is presented. Then, the different GNSS signals structure and the associated signal processing selected are described. We only considered GPS and GALILEO constellations and concentrated on signals suitable for civil aviation receivers. The next section details the GNSS measurement models used to model the measurements made by civil aviation receivers using the previous GNSS signals. The following chapter presents the GPS/GALILEO and RAIM combination model developed as well as our conclusions on the statistics of the resulting position error. The last part depicts the GBAS NSE (Navigation System Error) model proposed in this report as well as the rationales for this model.

Cette thèse étudie l'intérêt des architectures SDR à échantillonnage direct pour des récepteurs Galileo dans le contexte particulier de l'Aviation Civile, caractérisé notamment par une exigence de robustesse à des interférences bien spécifiées, principalement les interférences causées par les signaux DME ou CW. Le concept de Software Defined Radio traduit la migration toujours plus grande, au sein des récepteurs, des procédés de démodulation d'une technologie analogique à du traitement numérique, donc de façon logicielle. La quasi généralisation de ce choix de conception dans les architectures nouvelles nous a conduit à le considérer comme acquis dans notre travail. La méthode d'échantillonnage direct, ou Direct Sampling, quant à elle consiste à numériser les signaux le plus près possible de l'antenne, typiquement derrière le LNA et les filtres RF associés. Cette technique s'affranchit donc de toute conversion en fréquence intermédiaire, utilisant autant que possible le principe de l'échantillonnage passe-bande afin de minimiser la fréquence d'échantillonnage et en conséquence les coûts calculatoires ultérieurs. De plus cette thèse s'est proposée de pousser jusqu'au bout la simplification analogique en renonçant également à l'utilisation de l'AGC analogique qui équipe les récepteurs de conception traditionnelle. Seuls des amplificateurs à gain fixe précéderont l'ADC. Ce mémoire rend compte des travaux menés pour déterminer si ces choix peuvent s'appliquer aux récepteurs Galileo multifréquences (signaux E5a et E1) destinés à l'Aviation Civile. La structure du document reflète la démarche qui a été la notre durant cette thèse et qui a consisté à partir de l'antenne pour, d'étape en étape, aboutir au signal numérique traité par la partie SDR. Après une introduction détaillant le problème posé et le contexte dans lequel il s'inscrit, le deuxième chapitre étudie les exigences de robustesse aux interférences auquel doit se soumettre un récepteur de navigation par satellites destiné à l'Aviation Civile. Il s'agit de la base qui conditionne toute la démarche à suivre. Le troisième chapitre est consacré au calcul des fréquences d'échantillonnage. Deux architectures d'échantillonnage sont proposées. La première met en oeuvre un échantillonnage cohérent des deux bandes E5a et E1 tandis que la seconde implémente un échantillonnage séparé. Dans les deux cas, la nécessité de filtres RF supplémentaires précédant l'échantillonnage est mise en évidence. L'atténuation minimale que doivent apporter ces filtres est spécifiée. Ces spécifications sont suffisamment dures pour qu'il ait été jugé indispensable d'effectuer une étude de faisabilité. C'est l'objet du chapitre quatre où une approche expérimentale à base d'un composant disponible sur étagère a été menée. La problématique de la gigue de l'horloge d'échantillonnage, incontournable ici eu égard à la haute fréquence des signaux à numériser, est étudiée dans le chapitre cinq. Des résultats de simulation sont présentés et un dimensionnement de la qualité de l'horloge d'échantillonnage est proposé. Dans le chapitre six, la quantification, second volet de la numérisation, est détaillée. Il s'agit très précisément du calcul du nombre minimum de bits de quantification que doit exhiber l'ADC pour représenter toute la dynamique, non seulement du signal utile mais aussi des interférences potentielles. Au vu des débits de données conséquents mis en évidence dans les chapitres trois et six, le chapitre sept évalue la possibilité de réduire la dynamique de codage du signal à l'aide de fonctions de compression. Le dernier chapitre est focalisé sur la séparation numérique des bandes E5a et E1 dans l'architecture à échantillonnage cohérent introduite au chapitre deux. Ici aussi l'atténuation minimale que doivent apporter les filtres requis est spécifiée. / This thesis studies the relevance of DS SDR architectures applied to Galileo receivers in the specific context of Civil Aviation, characterized in particular by strict requirements of robustness to interference, in particular, interference caused by DME or CW signals. The Software Defined Radio concept renders the major tendency, inside the receiver, to move the demodulation part from an analog technology to digital signal processing, that is software. The choice of this kind of design is nearly generalized in new receiver architectures so it was considered the case in this work. The Direct Sampling method consists in digitizing the signal as close as possible to the antenna, typically after the LNA and the associated RF bandpass filter. So this technique does not use any conversion to an intermediate frequency, using as much as possible the bandpass sampling principle in order to minimize the sampling frequency and consequently the downstream computational costs. What is more, this thesis aiming at the greatest simplification of the analog part of the receiver, the decision was made to suppress the analog AGC which equips the receivers of classical architecture. Only fixed gained amplifiers should precede the ADC. This document exposes the work done to determine if these choices can apply to a multifrequency (E5a and E1 signals) Galileo receiver intended for a Civil Aviation use. The structure of the document reflects the approach used during this thesis. It progresses step by step from the antenna down to the digital signal, to be processed then by the SDR part. After an introduction detailing the problem to study and its context, the second chapter investigates the Civil Aviation requirements of robustness to interference a satellite navigation receiver must comply with. It is the basis which completely conditions the design process. The third chapter is devoted to the determination of the sampling frequency. Two sampling architectures are proposed: the first implements coherent sampling of the two E5a and E1 bands while the second uses separate sampling. In both cases the necessity to use extra RF filters is shown. The minimum attenuation to be provided by these filters is also specified. These requirements are strong enough to justify a feasibility investigation. It is the subject of chapter four where an experimental study, based on a SAW filter chip available on the shelf, is related. The issue of the sampling clock jitter, of concern with the Direct Sampling technique because of the high frequency of the signal to digitize, is investigated in chapter five. Some simulation results are presented and a dimensioning of the quality of the sampling clock is proposed. In chapter six, quantization, a byproduct of digitization, is detailed. Precisely it is the calculation of the number of bits the ADC must have to digitally represent the whole dynamic of, not only the useful signal, but also of the potential interference. Considering the high binary throughput highlighted in chapters three and six, chapter seven evaluates the possibility to reduce the coding dynamic of the digital signal at the output of the ADC by means of compression functions. The last chapter is focused on the digital separation of the two E5a and E1 bands in the coherent sampling architecture presented in chapter two. Here also specifications of minimum attenuation are given. Lastly the conclusions synthesize the contributions of this thesis and proposes ideas for future work to enrich them and more generally the subject of DS-SDR Galileo receivers for Civil Aviation.

Made available in DSpace on 2014-06-11T19:25:31Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-12-22Bitstream added on 2014-06-13T18:53:36Z : No. of bitstreams: 1 merguizosanchez_d_me_rcla.pdf: 2937684 bytes, checksum: 8831a2baec961b9a95e300124d0b3a90 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A estabilidade dos membros das constelações Galileo e GPS é investigada. Devido à ressonância 2:1 entre w e W, ocorre um aumento significativo da excentricidade. Este aumento causa riscos de colisão entre os satélites descartáveis e os ativos. Como a ressonância não depende do semi–eixo do satélite, estratégias usuais de aumentar a altitude não resolvem o problema. Então, condições iniciais especiais são achadas tais que os satélites descartáveis permanecem estáveis, com baixa excentricidade por pelo menos 250 anos. Outra estratégia de atacar o problema é mover o objeto descartável para uma órbita particular, acelerando o crescimento da excentricidade. Este estudo é brevemente apresentado. A dinâmica de satélites heliossíncronos é também estudada. Devido o arrasto atmosférico, a altitude do satélite sempre decai e portanto ele cruza o valor ressonante do semi-eixo. Sempre que isso ocorre, um salto na inclinação é observado e em alguns casos, há alguns cruzamentos tais que a inclinação permanece aprisionada (durante algum tempo) no centro de libração. Este evento é importante, pois isso pode ser explorado para realizar manobras de baixo custo para controlar o satélite numa determinada inclinação. Através do sistema exato, investigamos estas quasecapturas e seu aproveitamento em manobras de manutenção de inclinação. / The stability of the disposed members of the Galileo and GPS constellations is investigated. Due to the 2:1 resonance between w and W, a significant increase of the eccentricity occurs. These increase cause risk of collisions between the operational and disposed satellites. As the resonance does not depend on the semi-major axis of the satellite, usual strategies of raising the altitude do not solve the problem. Therefore, special initial conditions are found such that the disposed satellites remain stable with small eccentricity, for at least 250 years. Another strategy to attack the problem is to move the disposed object to a particular orbit, accelerating the growth of the eccentricity. This study is briefly presented. The dynamics of the sun-synchronous satellite is also studied. Due to the atmospheric drag, the altitude of the satellite always decays and therefore it crosses the resonant value of the semi-major axis. Whenever this happens, a jump in the inclination is observed and in some cases, there are some crossing such that the inclination remains locked (during some time) in the center of the libration. This event is interesting since it can be exploited to perform inexpensive maneuvers to control the satellite at desired inclination.