Dissertations / Theses on the topic 'Galileo satellite navigation system'

In 1999 Europe, through the European Commission and the European Space Agency, began detailed definition of a second generation Global Navigation Satellite System (GNSS). This GNSS development programme, known as “Galileo”, was intended to both complement and compete against the existing US Global Positioning System (GPS). Unlike GPS, Galileo is intended to be privately financed, following the initial development investment from the EC and ESA, which implies that Galileo should provide some revenue-earning services. From its earliest inception, the basis of these services has been assumed to be through the provision of Signal Integrity through an Integrity Flag broadcast through the Galileo system– a service which GPS cannot provide without some external system augmentation. This thesis undertakes a critical evaluation of the value of this integrity system in Galileo. This thesis has two parts. The first demonstrates that the conditions required to attract adequate private finance to the Galileo programme are incompatible with the system architecture derived from the early Galileo system studies and taken forward into the system early deployment phase, which includes an Integrity system within Galileo. The second part of this thesis aims to demonstrate that receivers which can combine the signals from GPS and Galileo may offer a free Integrity service which meet the needs of the majority of users, possibly up to the standards required for aviation precision approach. A novel Receiver Autonomous Integrity Monitoring (RAIM) technique is described, using an Errors in Variables/Total Least Squares approach to the detection of inconsistencies in an over-determined set of GNSS signal measurements. The mathematical basis for this technique is presented, along with results which compare the simulated performance of receivers using this algorithm against the expected performance of Galileo’s internal integrity determination system.

The work focuses on the application of satellite navigation systems in the different transport fields. It describes the general principle of operation of navigation systems, as well as its history and development. The following section describes the current navigation systems, the principle of operation, architecture and services. A separate chapter is devoted to being the European Galileo system and its services. Practical work deals with the applications according to the navigation systems across different transport sectors. In addition to the transport sector are given applications in other areas of human activity. The main part is devoted to the application in the monitoring and management of the company's fleet. Part of the analysis is the calculation of the efficiency of this investment.

La propagation des ondes électromagnétiques dans l’ionosphère est influencée par le nombre d’électrons libres présent le long du trajet de propagation, représenté par le contenu électronique total (CET). La conception des signaux GPS, basée sur l’utilisation de deux fréquences porteuses, permet de corriger l’erreur ionosphérique au premier ordre, ce qui conduit à une élimination de plus de 99% du retard ionosphérique. Dans une première partie de ce travail on montre que pour des applications où une précision plus importante est attendue, l’élimination des ordres supérieurs s’avère nécessaire, car ils peuvent induire une erreur de plusieurs centimètres sur l’estimation de la distance satellite-récepteur. Pour diminuer cette erreur, on propose un modèle de correction, applicable aux systèmes bi-fréquence actuels ainsi qu’aux futurs systèmes tri-fréquence. Dans une deuxième partie du travail, on analyse l’utilisation de trois fréquences pour le système GPS et le futur système Galileo, ainsi que la précision des codes de ce dernier. Les premiers résultats obtenus à partir des mesures des signaux Giove-A montrent que le bruit de mesure d’un système tri-fréquence ne permet pas l’estimation en temps réel de l’effet des termes d’ordre supérieur. La correction de ces termes doit donc s’effectuer par l’utilisation d’un modèle. Finalement, on réalise une évaluation des effets de la correction du terme ionosphérique du deuxième ordre en suivant une stratégie basée sur le Positionnement Ponctuel Précis (PPP) en configuration mono-station ainsi qu’une autre stratégie basée sur le traitement GPS en réseau. Les différences observées sur l’estimation de la position et sur le retard troposphérique sont abordées de façon approfondie lors de perturbations ionosphériques présentant de forts CET. Une interprétation des résultats est présentée en fonction de la stratégie utilisée pour l’obtention de la solution en réseau<br>Electromagnetic wave propagation in the ionosphere is influenced by the number of free electrons present along the propagation path and represented by the Total Electron Content (TEC). GPS signals based on the use of two carrier frequencies enable one to reduce the ionospheric error to the first order, which implies an elimination of more than 99% of the ionospheric delay. Firstly we show in this work that for applications in which better precision is awaited, the elimination of higher order; proves to be necessary, because they can induce an error of several centimeters. To mitigate this error, we propose a correction model, applicable to current dual frequency systems as well as to triple frequency systems. Secondly, we analyze the use of three frequencies for the future GPS and Galileo systems, as well as the precision of the codes of the last one. First results obtained from Giove-A signals measurements show that the estimate of higher ionospheric terms is not possible in real time in a triple-frequency system due to the measurement noise. The model correction of the higher order terms is thus still appropriate. Finally, we evaluate the effects of the second-order term correction considering both Precise Point Positioning (PPP) in a single-station configuration and in the processing of data from a network of GPS receivers. In all cases we have taken into consideration ionospheric storm situations presenting very strong TEC values. Observed differences on position and tropospheric delay are carefully analyzed and the results are interpreted according to the strategy adopted for the processing of network data

Master’s thesis deals with global navigation satellite systems. It gathers information about operation principles of individual systems and evaluates their applicability for Air transportation through own measures.

Les systèmes de navigation par satellite (GNSS) font partie de notre quotidien. On peut présentement les trouver dans un ensemble d’applications. Avec les nouveaux besoins, des nouveaux enjeux sont aussi apparus : le traitement du signal dans les environnements urbains est extrêmement complexe. Dans cette thèse, le traitement des signaux GNSS à faible puissance est abordé, en particulier dans la première phase du traitement, nommé acquisition de signal. Le premier axe de rechercheporte sur l’analyse et la compensation de l’effet Doppler dans l’acquisition. Le décalage Doppler perçu par l’utilisateur est un des paramètres principaux pour la configuration du module d’acquisition. Dans cette étude, des solutions sont proposées pour trouver le meilleur compromis sensibilité-complexité propre à l’acquisition. En deuxième axe, la caractérisation des détecteurs différentiels est abordée, en particulier la quantification de sa sensibilité. Pour l’acquisition des signaux faibles, après une première phase d’intégration cohérente, il faut passer par une intégration «postcohérente» (noncohérente ou différentielle.) L’analyse exécutée ici permet de meilleur identifier le meilleur choix entre les deux possibilités. Le troisième axe de recherche est consacré à la méthode de Détection Collective (CD), une innovation qui fait l’acquisition simultanée de tous les signaux visible par le récepteur. Plusieurs analyses sont réalisées incluant l’amélioration de la procédure de recherche de la CD, et l’hybridisation avec l’acquisition standard. Enfin on effectuel’analyse de la CD dans un contexte multi-constellation, en utilisant simultanément des vrais signaux GPS et Galileo<br>Satellite navigation (GNSS) is a constant in our days. The number of applications that depend on it is already remarkable and is constantly increasing. With new applications, new challenges have also risen: much of the new demand for signals comes from urban areas where GNSS signal processing is highly complex. In this thesis the issue of weak GNSS signal processing is addressed, in particular at the first phase of the receiver processing, known as signal acquisition. The first axe of research pursued deals with the analysis and compensation of the Doppler effect in acquisition. The Doppler shift that is experienced by a user is one of the main design drivers for the acquisitionmodule and solutions are proposed to improve the sensitivity-complexity trade-off typical of the acquisition process. The second axe of research deals with the characterization of differential GNSS detectors. After a first step of coherent integration, transition to post coherent (noncoherent or differential) integration is required for acquiring weak signals. The quantification of the sensitivity of differential detectors was not found in literature and is the objective of this part of the research. Finally, the third axe of research is devoted to multi-constellation Collective Detection (CD). CD is an innovative approach for the simultaneous processing of all signals in view. Severalissues related to CD are addressed, including the improvement of the CD search process and the hybridization with standard acquisition. Finally, the application of this methodology in the context of a multi-constellation receiver is also addressed, by processing simultaneously real GPS and Galileo signals

Thèse qui propose d'analyser le processus de construction de la politique spatiale européenne. La question au coeur de la recherche est de comprendre pourquoi, alors qu’il fut initialement décidé de ne pas s’en remettre au cadre offert pas la Communauté pour européaniser les efforts naissants de coopération spatiale, put-on assister, à la fin des années 1980, à une implication grandissante de la Communauté européenne, qui se traduisit progressivement par une nouvelle européanisation du spatial ?La thèse défendue est que, loin de résulter uniquement de la confrontation et du choc des intérêts portés par les différents Etats, la politique spatiale européenne a été progressivement construite au travers d’un parcours historique dans lequel ont été impliqués différents espaces sociaux régis par des référentiels et des normes qui leur sont propres.<br>Doctorat en Sciences politiques et sociales<br>info:eu-repo/semantics/nonPublished

L’orbite d’un satellite autour de la terre est perturbée en permanence par différents facteurs, tels que la variation du champ gravitationnel et la pression du vent solaire. La dérive de la position du satellite peut compromettre la mission, voire mener à une collision ou à une chute dans l’atmosphère. Les opérations de maintien à poste consistent donc à effectuer une mesure précise de la trajectoire du satellite puis à utiliser ses propulseurs pour corriger sa dérive. La solution classique de mesure de position est basée sur des radars au sol. Ce dispositif est couteux et ne permet pas d’avoir la position du satellite en permanence : les corrections de trajectoires se font donc de façon espacées dans le temps.Un système de positionnement et de navigation autonome utilisant les constellations de satellites de navigation, appelées Global Navigation Satellite System (GNSS), permettrait une réduction importante des coûts de conception et de maintenance opérationnelle. Plusieurs études ont été menées en ce sens et les premiers systèmes de navigation, basés sur des récepteurs GPS, voient le jour. Un récepteur en mesure de traiter plusieurs systèmes de navigation, tel que GPS et Galileo, permettrait d’obtenir une meilleure disponibilité de service. En effet, le système Galileo est conçu pour être compatible avec le système GPS,tant en terme de signaux émis que de données de navigation. La connaissance permanente de la position permettrait alors de réaliser un contrôle asservit du maintien à poste.Dans un premier temps, nous avons défini quelles seront les spécifications d’un récepteur spatial multi-mission.En effet, les contraintes pesant sur un tel récepteur sont différentes de celles d’un récepteur situé à la surface de la Terre. L’analyse de ces contraintes, ainsi que des performances demandées à un système de positionnement, est donc nécessaire afin de déterminer les spécifications du futur récepteur. Il existe peu d’études sur le sujet. Certaines d’entre elles sont classées secret industriel, d’autres présentent, à notre avis,un biais d’analyse qui fausse la détermination des spécifications.Nous avons donc modélisé le système : orbites des satellites GNSS et des satellites récepteurs, liaison radiofréquence. Certains paramètres de cette liaison ne sont pas donnés dans les documents de spécifications ou les documents constructeurs. De plus, les données théoriques disponibles ne sont pas toujours pertinentes pour une modélisation réaliste. Nous avons donc dû estimer ces paramètres en utilisant des données disponibles.Le modèle a été ensuite utilisé afin de simuler divers scenarii représentatifs de futures missions. Après avoir défini des critères d’analyse, les spécifications ont été déterminées à partir des résultats des simulations.Le calcul d’une position par un système de navigation par satellite se déroule en trois phases principales.Pour chacune de ces phases, il existe plusieurs algorithmes possibles, présentant des caractéristiques différentes de performance, de taille de circuit ou de charge de calcul. L’essor de nouvelles applications basées sur la navigation entraine également le développement de nouveaux algorithmes adaptés.Nous présentons le principe permettant la détermination d’une position, puis les signaux de navigation GPS et Galileo. A partir de la structure des signaux, nous expliquons les phases de la démodulation et de la localisation. Grâce à l’utilisation des constellations GPS et Galileo, les algorithmes standards permettent d’atteindre les performances nécessaires pour des applications spatiales. Ces algorithmes nécessitent néanmoins d’être adaptés ; ainsi certaines parties ont été conçues spécifiquement. Afin de valider les choix d’algorithmes, et les paramètres liés aux spécifications, nous avons simulés les différentes phases de fonctionnement du récepteur en utilisant des signaux GPS réels.Pour terminer, les retombées et perspectives sont exposées dans la conclusion<br>The orbit of a satellite around the earth is constantly disturbed by various factors, such as variations in the gravitational field and the solar wind pressure. The drift of the satellite position can compromise the mission, and even lead to a crash or a fall in the atmosphere. The station-keeping operations therefore consist in performing an accurate measurement of the satellite trajectory and then in using its thrusters to correct the drift. The conventional solution is to measure the position with the help of a ground based radar. This solution is expensive and does not allow to have the satellite position permanently: the trajectory corrections are therefore in frequent. A positioning and autonomous navigation system using constellations of navigation satellites, called Global Navigation Satellite System (GNSS), allows a significant reduction in design and operational maintenance costs. Several studies have been conducted in this direction and the first navigation systems based on GPS receivers, are emerging. A receiver capable of processing multiple navigation systems, such as GPS and Galileo, would provide a better service availability. Indeed, Galileo is designed to be compatible with GPS, both in terms of signals and navigation data. Continuous knowledge of the position would then allow a closed loop control of the station keeping. Initially, we defined what the specifications of a multi-mission space receiver are. Indeed, the constraints on such a receiver are different from those for a receiver located on the surface of the Earth. The analysis of these constraints, and the performance required of a positioning system, is necessary to determine the specifications of the future receiver. There are few studies on the subject. Some of them are classified; others have, in our view, an analytical bias that distorts the determination of specifications. So we modeled the system: GNSS and receivers satellite orbits, radio frequency link. Some parameters of this link are not given in the specification or manufacturers documents. Moreover, the available theoretical data are not always relevant for realistic modeling. So we had to assess those parameters using the available data. The model was then used to simulate various scenarios representing future missions. After defining analysis criteria, specifications were determined from the simulation results. Calculating a position of a satellite navigation system involves three main phases. For each phase, there are several possible algorithms, with different performance characteristics, the circuit size or the computation load. The development of new applications based on navigation also drives the development of new adapted algorithms. We present the principle for determining a position, as well as GPS and Galileo navigation signals. From the signal structure, we explain the phases of the demodulation and localization. Through the use of GPS and Galileo constellations, standard algorithms achieve the performance required for space applications. However, these algorithms need to be adapted, thus some parts were specifically designed. In order to validate the choice of algorithms and parameters, we have simulated the various operating phases of the receiver using real GPS signals. Finally, impact and prospects are discussed in the conclusion

This paper deals with study of inertial navigation, global navigation satellite system, and their fusion into the one navigation solution. The first part of the work is to calculate the trajectory from accelerometers and gyroscopes measurements. Navigation equations calculate rotation with quaternions and remove gravity sensed by accelerometers. The equation’s output is in earth centred fixed navigation frame. Then, inertial navigation errors are discussed and focused to the bias correction. Theory about INS/GNSS inte- gration compares different integration architecture. The Kalman filter is used to obtain navigation solution for attitude, velocity and position with advantages of both systems.

Per migliaia di anni i navigatori hanno osservato il cielo per orientarsi, affidandosi al proprio senso di orientamento, a mappe e segnali. Con il passare dei secoli differenti tecniche di navigazione sono andate evolvendosi fra le varie culture, ma tutte si fondavano sullo stesso principio base: la comparazione della propria posizione con punti noti o schemi prestabiliti. Oggigiorno la navigazione è cambiata, dall’utilizzo di oggetti naturali si è passati all’impiego di satelliti artificiali. L’idea di servirsi di satelliti per scopi di navigazione è nata dall’esperienza sulla propagazione delle onde elettromagnetiche nello spazio acquisita con la missione Sputnik 1, avvenuta nell’Ottobre del 1957. Da allora in poi, numerosi passi in avanti sono stati fatti. Sistemi Satellitari di Navigazione Globale (Global Navigation Satellite Systems – GNSS), quali il GPS e il GLONASS, e relativi sistemi di Augmentation sono attualmente operativi, mentre, nei prossimi anni, Sistemi Satellitari di Navigazione Globale di Seconda Generazione (GNSS-2), principalmente caratterizzati dai sistemi GALILEO e GPS III, saranno dispiegati. Sia il GPS che il GLONASS sono stati sviluppati nel corso della guerra fredda fra USA e URSS e quindi originariamente ideati per scopi prettamente militari. Nel corso degli anni, questi sistemi, in particolare il GPS, si sono evoluti ben oltre le loro origini, fornendo servizi di navigazione sia per utenti di tipo militare che civile. In particolare, il notevole miglioramento della accuratezza, ottenuto nel 2000 in seguito alla decisione di rimuovere la Disponibilità Selettiva (Selective Availability – SA), ha incoraggiato il favore e l’integrazione del GPS verso applicazioni pacifiche ed ha stimolato, al tempo stesso, il settore privato ad investire ed utilizzare tecnologie e servizi GPS. L’aspetto più affascinante della navigazione satellitare è rappresentato dalla sua versatilità di applicazione, ovvero dalla capacità di supportare una vasta gamma di possibili applicazioni. Di conseguenza, i sistemi GNSS hanno trovato applicazione in molti campi civili, scientifici e commerciali ed un numero ancor maggiore è atteso per gli anni a venire. Infatti, i futuri sistemi GNSS-2 consentiranno l’implementazione di innovativi servizi ed applicazioni, sempre più vicini ai bisogni dell’utente. I sistemi GNSS-2, quindi, contribuiranno significativamente ad incrementare la presenza di servizi/sistemi basati sulla navigazione satellitare in molti campi della vita dell’uomo, aree safety-critical comprese. In un tale contesto, la presente Tesi di Dottorato studia l’evoluzione dei sistemi GNSS e ne esplora ambiziose ed innovative applicazioni in contesti terrestri, aerei e spaziali. L’obiettivo principale è quello di evidenziare il crescente e strategico ruolo che rivestirà la navigazione satellitare nella Società futura. Particolare enfasi è posta sulle applicazioni aeree, in particolare sul settore dell’aviazione civile, in cui i continui miglioramenti nei sistemi GNSS, in particolare in termini di accuratezza, hanno aperto nuove importanti prospettive ed opportunità per l’uso di queste tecnologie.<br>Navigators have looked to the sky for direction for thousands of years, relying on human sense of direction, maps and signs. Different navigational techniques have evolved over the ages in different cultures, but all involve locating one's position compared to known locations or patterns. Today, celestial navigation has switched from natural objects to artificial satellites. The idea of using satellites for navigation began with the launch of Sputnik 1 on October 4, 1957. From then on, several steps ahead have been performed. Global Navigation Satellite Systems (GNSS) constellations, i.e. GPS and GLONASS, and related augmentation systems are presently operational, while in the next few years, the so-called Global Navigation Satellite Systems of Second Generation (GNSS-2), mainly characterised by the European GALILEO and the American GPS III, will be deployed. Both GPS and GLONASS were developed during the cold war between USA and USSR and, thereby, originally thought for military purposes. Over the years, these systems, especially the GPS, have evolved far beyond their military origins, providing navigation services to both military and civilian users. In particular, the significant accuracy improvement resulted from the removal of the Selective Availability (SA) in 2000 has encouraged acceptance and integration of GPS into peaceful applications and has stimulated, at the same time, the private sector in investing and using GPS technologies and services. The most fascinating feature of satellite navigation is its potential to cover a wide range of applications. As a consequence, GNSS have found application in a wide range of civil, scientific, and commercial fields and even more are expected in the future. Future GNSS-2 and related advanced capabilities, in fact, will enable the implementation of innovative services and applications more and more close to the user needs. Therefore, GNSS-2 will significantly contribute to increase the penetration of the GNSS services in most fields of the human life, including safety-critical areas. In this framework, this Ph.D. dissertation studies GNSS evolution and explores challenging and innovative applications of satellite navigation in Ground, Air and Space contexts. The overall aim is to provide evidence of the growing and strategic role that satellite navigation will play in the World Community in the coming years. Special emphasis is put on air segment, specifically on the civil aviation sector, where, in order to address the future traffic demand, the continuous improvements in satellite navigation systems, especially in terms of accuracy performance, have been opening new perspectives and opportunities for the use of these technologies in the Air Traffic Management (ATM) system.

The research described by this thesis was undertaken at a very timely moment in the development of global navigation satellite systems (GNSS). During the course of this work the signal structure of an entirely new generation of GNSS signals was been defined. The first satellites producing a new range of different coding and modulation schemes have been launched, initiating the modernisation of the American GPS and the introduction of the European Galileo system. An important aspect of the new signal structure for both GPS modernisation and Galileo is an entirely new kind of modulation called BOC (Binary Offset Carrier). Despite certain advantages this modulation comes with the notorious characteristic of a multi-peaked correlation function. In our view all known receivers, or receiver principles, have problems with this: either because the receiver is not fail safe and is potentially unreliable (the so-called bump-jumping receiver); or the multi-peaks are eliminated at the very substantial cost in much degraded accuracy. During my research under Dr Hodgart what seems to be an entirely new and original method has been developed which entirely solves the problem of tracking BOC. The problem of multi-peaks goes away and there is no loss of potential accuracy. This thesis describes in detail this invention and the first experimental results. This research was carried out at the University of Surrey under the joint supervision of Surrey Space Centre and Surrey Satellite Technology Ltd. Shortly before this work began SSTL achieved a contract to design and build the first ever test satellite (Giove- A) of the Galileo signals and technology. This research contributed to the design and manufacture of a Galileo signal generator which was flown on-board the satellite (launched December 2005). Expanding upon SSTL's existing designs this work enabled the design and creation appropriate receivers to monitor the transmissions both in ground based emulations and real live tests after launch. These designs are intended to be the core of future SSTL space receivers. This thesis describes in detail the creation of both transmitter and receiver architectures for the testing and evaluation of GNSS signals.

This thesis describes an Intelligent Differential GPS Navigation System developed for a PhD research project. The first part of the work was to apply differential technology to Global Positioning System to locate the current position of the user with an improved positioning accuracy. The essential part of this Differential GPS system is a Differential GPS Reference Station. This DGPS Reference Station includes a DGPS mathematical model and the corresponding algorithms, which calculates the differential correction messages. These messages are then transmitted to a mobile GPS receiver by a radio data link. By using these corrections, the mobile GPS receiver's positioning accuracy can be improved from about 100 m to 4 m. This DGPS Reference station has been used to implement system software for this research. Differential correction algorithms were modified, characteristics of system components were changed, and different digital filters were also applied at different locations to investigate the impact on system performance. Besides all these capabilities which are needed for the research purpose, this DGPS Reference Station has all the standard functions, and can be used as a standard DGPS Reference Station. The second part of the work was to combine this Differential GPS system with a suitable digital map to form a navigation system. A suitable digital map database was chosen and modified, and the content of the map was then reproduced on the mobile GPS receiver's host PC screen. This digital map, combined with the current location of the user, provides the basic navigational information for the user to reach a desired destination. To help the user further and demonstrate the potential use of the system, an intelligent route-planing algorithm that can produce the optimum route automatically was also designed. The system integration was achieved by the design of the mobile navigation unit and the combination of this mobile navigation unit with the constructed DGPS Reference Station. The final system consists of a DGPS Reference Station, a UHF radio data transmitter, a mobile GPS receiver, a digital map system, a route searching and planing algorithm and a UHF radio data receiver. Field trials were carried out to test the system static and dynamic performances. Repeated experiments showed that both the static and dynamic positioning accuracies were within the range of 4 meters. The constructed system is a prototype navigation system which incorporates the basic navigational functions. It is envisaged that this system can be directly used, or further developed to suit a special need, as required. A typical application of the system would be to guide a user to a desired destination. Other examples include: aircraft autolanding control system, car self-driving, taxi fleet control, criminal tracing and personal navigation systems.

The Global Satellite Navigation System (GNSS), the core of the International Civil Aviation Organization (ICAO) Communication, Navigation, Surveillance/Air Traffic Management concept is capable of supporting future aviation needs. The implementation of this revolutionary technology however remains overshadowed by a series of complex institutional and legal issues. The extraterritorial control and ownership of existing GNSS systems coupled with the dual character of this technology poses a serious threat to the concept of national sovereignty as traditionally understood. This is further aggravated by the fact that there exists only one de facto GNSS signal provider, thus placed in a position to impose its own conditions without reference to the requirements of the rest of the world.<br>In an attempt to secure both European political independence and a fair share in the global GNSS market Europe has decided to play an active role by launching Galileo, an autonomous global constellation under the control of civil authorities scheduled to be operational by 2008.<br>The present thesis analyses the desirability of a suitable legal and institutional GNSS framework to achieve universal acceptance of the GNSS. However, in the context of the present status quo it is unrealistic to expect that the only GNSS signal provider surrender its nationally procured system under the umbrella of an international instrument. National security concerns and industrial policy goals underlie this tendency. The present situation may turn different when the incumbent GPS faces the competition of Galileo, an alternative civil system willing to offer firm legal guarantees of service performance albeit in exchange for a fee. The entire viability of this theory remains however dependent upon the European capability of defining a successful business case for Galileo.

The precise positioning applications have long been carried out using dual frequency carrier phase and code observables from the Global Positioning System (GPS). The carrier phase observables are very precise in comparison to the code ones, the reason phase observables play an important role in precise geodetic applications. The carrier phase observables can have precision of about 3 millimeters. However the precision of the estimated parameter of interest, say the receiver position, depends upon the correct resolution of integer ambiguities present in the carrier phase observables. Significant contributions have been made in the last couple of decades towards integer ambiguity estimation to make precise positioning applications possible, using GPS carrier phase and code data from geodetic receivers.Precise positioning applications have been successful in the past, but at the cost of time taken to correctly resolve the integer ambiguities. This delay in integer ambiguity estimation is caused due to the presence of various propagation and hardware related effects present in the observables of GPS or in that case, any other Global Navigation System. The propagation errors related to the atmosphere are significant for medium to long baseline lengths. Among the atmospheric errors, the ionosphere is found to have profound effect on the process of integer ambiguity estimation. With the aid of permanent reference networks, corrections for ionosphere could be interpolated and further transferred to the user with an aim to enhance users ambiguity resolution and fulfill the aim of an efficient and reliable precise positioning.With the advancement of Global Navigation Satellite Systems (GNSS) several of the limiting factors which degrade users ambiguity resolution are seen to be met. The relatively poor precision of the code data in comparison to the phase data, is foreseen to improve for third GPS frequency, also called as GPS L5. Also most of the frequencies on Galileo system would have improved code precision.The ionosphere which has been a major blockade in fast integer ambiguity resolution, for long baseline lengths, would also benefit in a multi-frequency, multi-GNSS scenario. Since a GNSS model, in which the ionosphere is considered unknown and estimated, gains strength with addition of a frequency. The addition of L5 on GPS and availability of up to four frequencies on Galileo system would strengthen the GNSS model which would be beneficial when ionosphere is parameterized for estimation. This study aims at understanding the above mentioned and other possible benefits of the future GPS and Galileo system.The benefits that the future GPS and Galileo can bring to precise applications can be evaluated in terms of correct resolution of integer ambiguities present in the carrier phase data and further by understanding the contribution of the ambiguity resolution towards improvement of fixed-precision of the parameters of interest. The correct resolution of ambiguities was judged by computing the probability of correct integer bootstrap along with LAMBDA decorrelation method. The decorrelation of the ambiguity Variance Covariance matrix resulted the probability of Integer Bootstrap to correspond to lower bounds for the probability of Integer Least Square. The ambiguities were considered to be successfully resolved only after a minimum of 0.999 probability could be obtained from Integer Bootstrap. While all the ambiguities collectively contributed to give 0.999 Ambiguity Success Rate (ASR) it was termed as full Ambiguity Resolution (AR). In scenarios when full AR took large number of epochs to give 0.999 ASR, only a subset of ambiguities were fixed which met the 0.999 ASR criteria. This approach is known as Partial AR (PAR). PAR solution was accepted only when the resolved subset of ambiguities could contribute to give a minimum value of fixed-precision for the parameters of interest. Since this research involves future GPS and Galileo system, GNSS observables, real or simulated were not used. Instead simulations were done based on model assumptions, that is the functional and the stochastic model.This research work focuses on understanding the benefits of multi-frequency GPS and Galileo to its core. This was done by planning multiple scenarios of GNSS frequencies, GNSS combinations, atmospheric considerations, latitudinal variations and baseline orientations. With the aid of this multiple scenario simulation, an estimate for time taken for successful AR and the fixed-precision of parameters of interest obtained after successful AR could be computed for a range of possible situations. When a multi-GNSS scenario consisting of future GPS and Galileo was considered, there have been challenges while a mathematical model for multi-GNSS was being formed. The design of the multi-GNSS mathematical model accounted for the Inter System Biases (ISB’s) which surface while different GNSS systems use the same reference satellite. While a rank defect between the ISB’s and the ionosphere was detected, it was mitigated by choosing an appropriate S-Basis. To make the simulation software robust and realistic, accounting for setting and rising satellites and change of reference satellite was implemented. With the above considerations a multi-GNSS, multi-frequency simulation software was developed in MATLAB programming language. The results have been obtained based on assumption in the functional and stochastic models. In real practice unmodelled errors have an impact on ASR and time to fix the integer ambiguities to its correct solution due to multipath , insufficient knowledge of the stochastic model, etcetera.Presented below are some of the important findings of this study.The Geometry Free model does not gain strength with the addition of satellites. Since with addition of a satellite a receiver-satellite range is added to the unknowns. Also for a combined GPS and Galileo system, the Geometry Free model does not have a coupling parameter in the unknowns, say troposphere or receiver coordinates. Hence while the mathematical model is formed, from a single system to a combined system, the model does not gain strength. Hence a multi-GNSS constellation would not help to reduce the time-to-fix integer ambiguities for a Geometry Free model.The permanent reference networks can benefit from an integrated GPS and Galileo system. The precision of the ionospheric estimates with a permanent network could reach 2cm instantaneously, almost any time of the day by using quadruple frequency (L1pE1q, L5pE5aq, L2,E5b) GPS and Galileo combined system with the aid of PAR.While the user aims at performing relative positioning using a permanent network, the benefits from a combined GPS and Galileo system are immense. For a user with low-end single frequency receiver, for short baseline lengths ( 10Km), obtaining its receiver positions with 2cm precision for north- and east-components and 6cm precision for the up-component would be possible instantaneously using a combined GPS and Galileo. While the user is equipped with ionospheric corrections from the network, all the ambiguities could be resolved in a short time with a combined GPS and Galileo quadruple frequency system (L1pE1q, L5pE5aq, L2,E5b). The findings from this simulation study shows that, while ionosphere corrections are given to the user, all the ambiguities could be successfully resolved (full AR) within 20 epochs (1 second sampling) by using quadruple frequency from an integrated GPS and Galileo system.

Les systèmes de navigation par satellite sont connus pour être sensibles aux interférences. Cette thèse étudie les techniques d'antennes adaptatives comme une solution au problème du brouillage des signaux militaires (GPS et Galileo) par des interférences de forte puissance et à grande occupation spectrale. L'objectif est de réaliser, à terme, une antenne réseau indépendante du récepteur de radionavigation, ce qui nous a rapidement conduit à privilégier les systèmes MISO.<br />Divers algorithmes de traitement ont été évalués sur plusieurs géométries de réseau. Nous avons mis en évidence que le SINR moyen de sortie du réseau n'est pas représentatif des performances d'un récepteur de radionavigation. Un critère de sélection des méthodes, basé sur la précision finale de localisation, a donc été défini. Nous avons montré que, selon ce critère, la connaissance a priori des DOA ne permet pas forcément de gain de traitement avec un système MISO. La stabilité de la réponse des réseaux a également été étudiée, nous conduisant finalement à restreindre notre étude aux méthodes aveugles de minimisation de puissance sous contrainte linéaire. <br />Nous avons ensuite caractérisé les principaux défauts de la chaîne RF (dus aux dispersions de fabrication des capteurs et des filtres analogiques, et au couplage inter-capteurs) et en avons évalué l'impact sur les performances des filtres spatiaux. Physiquement, comme l'effet large bande, les défauts du réseau se traduisent par une augmentation du nombre de degrés de liberté consommés par un signal de forte puissance. Le traitement Spatio-Temporel (STAP) constitue une solution possible à cette augmentation du rang du sous-espace interférent car il permet d'accroitre le nombre de degrés de liberté disponibles, sans augmenter la taille du réseau. Cependant, la composante fréquentielle du filtrage STAP peut dégrader les performances du corrélateur d'un récepteur GNSS générique. Aussi, avons-nous défini un nouveau critère de performance, adapté au traitement des signaux GNSS. Nous avons ainsi pu écrire le filtre STAP optimal et nous en avons déduit une version simplifiée qui constitue un bon compromis performances - complexité.<br /> Globalement, le réseau STAP ne permet pas de gain de traitement sur la puissance utile transmise au récepteur mais il permet de mieux rejeter les signaux interférents de forte puissance en présence de défauts linéaires de chaîne.

The use of Global Navigation Satellite System (GNSS) for air navigation brings important advantages to aviation since it is able to reduce routes, save fuel and diminish greenhouse gas emissions. It is also a more flexible and precise navigational aid that improves flight operations at critical moments such approach, landing and take-off. However, the GNSS signal may fail; and depending on the moment of this failure, its failure could cause an accident. Therefore, air navigation service providers' liability in using GNSS is a concern. Since there is no international treaty that responds to the liability of the GNSS and of air navigation service providers, national solutions appear as a practical and necessary answer to liability claims. Brazil has already started using GNSS in air navigation, and it has a Ground Based Augmentation System (GBAS) that is being tested at Rio de Janeiro International Airport. Therefore, it is important to study the Brazilian liability regime in order to determine if its general liability rules, especially its governmental liability system could apply to the civil liability of the air navigation service providers using GNSS in case of an accident caused by a signal failure. These claims are mostly governed by government liability in Brazil and the legal system in place is able to respond to them. However, since there is much controversy regarding government liability under the Brazilian doctrine, a specific legislation that would be able to balance the different interests at stake seems a reasonable option.<br>L'utilisation du Système de positionnement par satellites (GNSS) pour la navigation aérienne offre de nombreux avantages à l'aviation puisqu'il est en mesure de réduire les itinéraires, d'économiser de l'essence et de diminuer les émissions de gaz à effet de serre. Il constitue également une aide à la navigation plus flexible et plus précise qui améliore les opérations de vol à des moments critiques tels que l'approche, l'atterrissage, et le décollage. Cependant, le signal GNSS pourrait être défectueux. Dépendamment du moment de la défaillance du signal, celle-là pourrait causer un accident. Ainsi donc, la responsabilité des fournisseurs de services de navigation aérienne est sujette à préoccupation. Puisqu'aucun traité international ne se penche sur la question de la responsabilité du GNSS et des fournisseurs de services de navigation aérienne, des solutions nationales apparaissent comme des réponses pratiques et nécessaires aux revendications de responsabilité. Le Brésil a déjà commencé à utiliser la GNSS en navigation aérienne, et a un Ground Based Augmentation System (GBAS) qui est en train d'être testé à l'aéroport international de Rio de Janeiro. Ainsi donc, il est important d'étudier le régime de responsabilité brésilien pour déterminer si ses règles générales de responsabilité – et plus particulièrement son système de responsabilité gouvernemental – pourraient également s'appliquer à la responsabilité civile des fournisseurs de services de navigation aérienne utilisant le GNSS dans le cas d'un accident causé par une défaillance de signal. Ces revendications sont en grande partie gouvernées par la responsabilité gouvernementale au Brésil et le système légal en place pour y répondre. Cependant, puisqu'il y a beaucoup de controverse entourant la responsabilité du gouvernement sous la doctrine brésilienne, une législation spécifique qui serait en mesure d'équilibrer les différents intérêts en jeu semble être une alternative raisonnable.

The objective of this thesis is to design a model for a multi global navigation satellite system using Simulink. It explains a design procedure which includes the models for transmitter and receiver for two different navigation systems. To overcome the problem, where less number of satellites are visible to determine location degrades the performance of any positioning system significantly, this research has done to make use of multi GNSS satellite signals in one navigation receiver.

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<br>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

The purpose of this study was to evaluate the accuracy in real time measurements acquired from GPS and GLONASS satellite observations using RTK techniques in an urban and forested environment. To determine this accuracy, 2 data sets of 3-dimensional coordinates were created and compared at 14 stations situated at East Tennessee State University. One data set included coordinates determined by conventional land survey methods; the second was solved by RTK GPS/GLONASS. Once the magnitude of any deviation in the coordinate positions was determined, the contributions to the accuracies from cycle slips, multipath, satellite availability, PDOP, and fixed or float solutions were evaluated. Three points in the urban environment varied from the conventional data set. Multipath was assumed to be the major bias in these points. Seven points in the forested environment varied from the conventional data set. The use of float solutions and high PDOP may have caused this bias.

1. S. Beauregard and H. Haas, “Pedestrian dead reckoning: A basis for personal positioning,” in Proceedings of the 3rd Workshop on Positioning, Navigation and Communication, March 2006, pp. 27–35. 2. A. R. Jimenez, F. Seco, C. Prieto, and J. Guevara, “A comparison of pedestrian dead-reckoning algorithms using a low-cost MEMS IMU,” in 2009 IEEE International Symposium on Intelligent Signal Processing, August 2009, pp. 37–42. 3. P. Kasebzadeh, C. Fritsche, G. Hendeby, F. Gunnarsson, and F. Gustafsson, “Improved pedestrian dead reckoning positioning with gait parameter learning” in 2016 19th International Conference on Information Fusion (FUSION), July 2016, pp. 379–385. 4. A. Brajdic, R. Harle, “Walk detection and step counting on unconstrained smartphones,” in Proceedings of the 2013 ACM international joint conference on Pervasive and ubiquitous computing, September, 2013, pp. 225–234. https://doi.org/10.1145/2493432.2493449<br>The problem of pedestrian dead reckoning (PDR) is referred to the class of individual navigation problems. The common solution in mobile phones is the use of satellite navigation (GPS, GLONASS, Galileo, etc.). But satellite signal sometimes can be jammed intentionally or lost due to obstacles in urban area. Also, the problem of PDR is interesting in the user localization in indoor environment such as large garages, city molls, etc. Instrumentation of smartphones is now based on Micro-Electro-Mechanical Sensors (MEMS) technology and includes standard set of Inertial Measurement Unit (IMU): accelerometers, gyroscopes, magnetometers and pressure sensor (optionally). Accelerometers can be used to detect step events and further to calculate lengths. But it is sensitive to walking speed, slope of the road, etc., which leads to inaccurate results of calculating the stride length. Also, as any dead reckoning technique PDR suffers from the cumulative error. Since the location estimate is always calculated based on the previous result, the error accumulates rapidly over time. This means that correction updates are necessary on regular basis.<br>Проблема обліку загибелі пішоходів (ОЗП) відноситься до класу індивідуальних проблем навігації. Загальним рішенням у мобільних телефонах є використання супутникової навігації (GPS, ГЛОНАСС, Galileo тощо). Але супутниковий сигнал іноді може бути заклинений навмисно або втрачений через перешкоди в міській місцевості. Крім того, проблема ОЗП цікава в локалізації користувачів у приміщенні, наприклад, у великих гаражах, міських торгових центрах тощо. Зараз прилади для смартфонів засновані на технології мікро-електромеханічні датчики (MEМД) і включають стандартний набір інерційних вимірювальних приладів (IВП): акселерометри, гіроскопи, магнітометри та датчик тиску (за бажанням). Акселерометри можна використовувати для виявлення крокових подій та подальшого обчислення довжин. Але він чутливий до швидкості ходьби, нахилу дороги тощо, що призводить до неточних результатів розрахунку довжини кроку. Крім того, як і будь-яка техніка розрахунок критичних випадків, ОЗП залежить від сукупної помилки. Оскільки оцінювання місця розташування завжди обчислюється на основі попереднього результату, помилка швидко накопичується з часом. Це означає, що необхідні регулярні оновлення виправлень.

GPS has become very popular in recent years. It is used in wide range of applications including aircraft navigation, search and rescue, space borne attitude and position determination and cellular network synchronization. Each application places demands on GPS for various levels of accuracy, integrity, system availability and continuity of service. Radio frequency interference (RFI) which results from many sources such as TV/FM harmonics, radar or mobile satellite systems, presents a challenge to the use of GPS. It can affect all the service performance indices mentioned above. To improve the accuracy of GPS positioning, a continuously operating reference station (CORS) network can be used. A CORS network provides all the enabled GPS users in an area with corrections to the fundamental measurements, producing more precise positioning. A threat to these networks is a threat to all high-accuracy GPS users. It is therefore necessary to monitor the quality of the received signal with the objective of promptly detecting the presence of RFI and providing a timely warning of the degradation of system accuracy, thereby boosting the integrity of GPS. This research was focused on four main tasks: a) Detection. The focus here is on a power spectral density fluctuation detection technique, in which statistical inference is used to detect narrowband continuous-wave (CW) interference in the GPS signal band after being captured by the RF front-end. An optimal detector algorithm is proposed. At this optimal point, for a fixed Detection Threshold (DT), probability of false alarm becomes minimal and for a fixed probability of false alarm, we can achieve the minimum value for the detection threshold. Experiments show that at this point we have the minimum computational load. This theoretical result is supported by real experiments. Finally this algorithm is employed to detect a real GPS interference signal generated by a TV transmitter in Sydney. b) Characterization. In the characterization section, using the GNSS signal structure and the baseband signal processing inside the GNSS receiver, a closed formula is derived for the received signal quality in terms of effective carrier to noise ratio ( ). This formula is tested and proved by calculating the C/No using the I and Q data from a software GPS receiver. For pulsed CW, a similar analysis is done to characterize the effect of parameters such as pulse repetition period (PRP) and also duty cycle on the received signal quality. Considering this characterization and the commonality between the GPS C/A code and Galileo signal as a basis to build up a common term for satellite availability, the probability of satellite availability in the presence of CW interference is defined and for the two currently available satellite navigation systems (GPS L1 signal and Galileo signal (GIOVE-A BOC(1, 1) in the E1/L1 band)) it is shown that they can be considered as alternatives to each other in the presence of different RFI frequencies as their availability in the presence of CW RFI is different in terms of RFI frequency. c) Mitigation. The last section of the research presents a new concept of ?Satellite Exclusion Zone?. In this technique, using our previously developed characterization techniques, and considering the fact that RFI has different effects on different satellite signals at different times depending on satellite Doppler frequency, the idea of excluding the most vulnerable satellite signal from positioning calculations is proposed. Using real data and real interference, the effectiveness of this technique is proven and its performance analyzed. d) Hardware implementation. The above detection technique is implemented using the UNSW FPGA receiver board called NAMURU.

In addition to the emergence of smartphones and tablets in recent years, the rise of Global Navigation Satellite Systems (GNSS) has allowed mobile tracking applications to become popular and be put into many uses. Analyzing tracking records to identify points of interest (POIs) is useful for both prediction applications and research such as human behavior analysis, transportation planning, and especially travel surveys. Past research in travel surveys has shown that a GPS mobile phone-based survey is a useful tool for collecting information about individuals. Moreover, a passive travel survey collection is preferred to an active travel survey method by the respondents and the analysts because it is proven to be less error prone. However, passive collection remains a challenge due to a lack of high accuracy algorithms to automatically identify trip starts and trip ends. While travel surveys need a POI identification algorithm to carry out passive information collection, mobile tracking applications must be careful not to affect the user's battery life, which limits the number of GPS coordinates that can be recorded and therefore affects the accuracies of existing POI identification algorithms. This thesis presents Automatic Spatial Temporal Identification of Points of Interest (ASTIPI), an unsupervised spatial temporal algorithm to identify POIs. ASTIPI utilizes the temporal and spatial properties of the dataset to obtain a high accuracy of POI identification, even on a reduced GPS dataset that uses techniques to conserve battery life on mobile devices. While reducing outliers within POIs, ASTIPI also has a linear running time and maintains the temporal orders of the location data so that arrival and departure information can be easily extracted and thus, users' trips can be quickly identified. Using data from real mobile devices, evaluations of ASTIPI and other existing algorithms are performed, showing that ASTIPI obtains the highest accuracy of POI identification with an average accuracy of 88% when performing on full datasets generated using the GPS Auto-Sleep module and an average accuracy of 59% when performing on a reduced dataset generated using both the GPS Auto-Sleep module and the Critical Points algorithm.

This thesis describes the definition, implementation, and in-orbit testing of an autonomous navigation unit based upon a GPS receiver for use on board a small satellite in low Earth orbit. It explains the motivation for the use of GPS to provide this function, and describes the practical application and integration of this technology into an existing microsatellite system. Until now, the technology for any satellite to track itself has not existed. Space agencies spend significant funds supporting a network of tracking stations around the world for orbit determination. With the recent realisation of the Global Positioning System and the availability of inexpensive receiver hardware, it has become a practical proposition to include a GPS receiver within the demanding constraints of a small satellite. A GPS receiver on-board a satellite can eliminate the necessity for ground-based tracking by providing an autonomous orbit determination capability. During the course of these studies, the requirements and constraints of a small satellite were identified by the author and matched with the capabilities of a GPS receiver. A GPS Navigation Unit was defined to provide autonomous services available oil demand for the satellite platform and payloads; position and velocity; time synchronisation; orbital elements; payload triggering and GPS data logging (for experimental and research purposes). The GPS Navigation Unit includes a processing facility capable of command and initialisation of the GPS receiver, and data processing to give orbit determination capability. When used on a microsatellite, the additional constraints of low power consumption necessitate the intermittent operation of the GPS receiver. To test the concept of the GPS Navigation Unit, a commercial Trimble TANS II GPS receiver system that had been modified for orbital velocities was integrated into the PoSAT-1 microsatellite which was launched into low Earth orbit in September 1993. A method for orbit determination was developed for use with the output from the GPS receiver, and the GPS Navigation Unit was implemented in software according to the constraints of the PoSAT-1 mission. The significant results from these studies include: The first use of a GPS receiver on a microsatellite, PoSAT-1. The implementation, test and validation of a GPS Navigation Unit in low Earth orbit. The first satellite mission to demonstrate the capability for autonomous orbit determination through the GPS Navigation Unit. The definition of the general-purpose interfaces between a small satellite and a satellite- borne GPS Navigation Unit.

Aquesta tesi gira al voltant del disseny de receptors per a sistemes globals de navegació per satèl·lit (Global Navigation Satellite Systems, GNSS). El terme GNSS fa referència a tots aquells sistemes de navegació basats en una constel·lació de satèl·lits que emeten senyals de navegació útils per a posicionament. El més popular és l'americà GPS, emprat globalment. Els esforços d'Europa per a tenir un sistema similar veuran el seu fruit en un futur proper, el sistema s'anomena Galileo. Altres sistemes globals i regionals existeixen dissenyats per al mateix objectiu: calcular la posició dels receptors. Inicialment la tesi presenta l'estat de l'art en GNSS, a nivell de l'estructura dels actuals senyals de navegació i pel que fa a l'arquitectura dels receptors.<br/><br/>El disseny d'un receptor per a GNSS consta d'un seguit de blocs funcionals. Començant per l'antena receptora fins al càlcul final de la posició del receptor, el disseny proporciona una gran motivació per a la recerca en diversos àmbits. Tot i que la cadena de Radiofreqüència del receptor també és comentada a la tesis, l'objectiu principal de la recerca realitzada recau en els algorismes de processament de senyal emprats un cop realitzada la digitalització del senyal rebut. En un receptor per a GNSS, aquests algorismes es poden dividir en dues classes: els de sincronisme i els de posicionament. Aquesta classificació correspon als dos grans processos que típicament realitza el receptor. Primer, s'estima la distancia relativa entre el receptor i el conjunt de satèl·lits visibles. Aquestes distancies es calculen estimant el retard patit pel senyal des de que és emès pel corresponent satèl·lit fins que és rebut pel receptor. De l'estimació i seguiment del retard se n'encarrega l'algorisme de sincronisme. Un cop calculades la distancies relatives als satèl·lits, multiplicant per la velocitat de la llum el retards estimats, l'algorisme de posicionament pot operar. El posicionament es realitza típicament pel procés de trilateralització: intersecció del conjunt d'esferes centrades als satèl·lits visibles i de radi les distancies estimades relatives al receptor GNSS. Així doncs, sincronització i posicionament es realitzen de forma seqüencial i ininterrompudament. La tesi fa contribucions a ambdues parts, com explicita el subtítol del document.<br/><br/>Per una banda, la tesi investiga l'ús del filtrat Bayesià en el seguiment dels paràmetres de sincronisme (retards, desviaments Doppler i phases de portadora) del senyal rebut. Una de les fonts de degradació de la precisió en receptors GNSS és la presència de repliques del senyal directe, degudes a rebots en obstacles propers. És per això que els algorismes proposats en aquesta part de la tesi tenen com a objectiu la mitigació de l'efecte multicamí. La dissertació realitza una introducció dels fonaments teòrics del filtrat Bayesià, incloent un recull dels algorismes més populars. En particular, el Filtrat de Partícules (Particle Filter, PF) s'estudia com una de les alternatives més interessants actualment per a enfrontar-se a sistemes no-lineals i/o no-Gaussians. Els PF són mètodes basats en el mètode de Monte Carlo que realitzen una caracterització discreta de la funció de probabilitat a posteriori del sistema. Al contrari d'altres mètodes basats en simulacions, els PF tenen resultats de convergència que els fan especialment atractius en casos on la solució òptima no es pot trobar. En aquest sentit es proposa un PF que incorpora un seguit de característiques que el fan assolir millors prestacions i robustesa que altres algorismes, amb un nombre de partícules reduït. Per una banda, es fa un seguiment dels estats lineals del sistema mitjançant un Filtre de Kalman (KF), procediment conegut com a Rao-Blackwellization. Aquest fet provoca que la variància de les partícules decreixi i que un menor nombre d'elles siguin necessàries per a assolir una certa precisió en l'estimació de la distribució a posteriori. D'altra banda, un dels punts crítics en el disseny de PF és el disseny d'una funció d'importància (emprada per a generar les partícules) similar a l'òptima, que resulta ésser el posterior. Aquesta funció òptima no està disponible en general. En aquesta tesi, es proposa una aproximació de la funció d'importància òptima basada en el mètode de Laplace. Paral·lelament es proposen algorismes com l'Extended Kalman Filter (EKF) i l'Unscented Kalman Filter (UKF), comparant-los amb el PF proposat mitjançant simulacions numèriques.<br/><br/>Per altra banda, la presentació d'un nou enfocament al problema del posicionament és una de les aportacions originals de la tesi. Si habitualment els receptors operen en dos passos (sincronització i posicionament), la proposta de la tesi rau en l'Estimació Directa de la Posició (Direct Position Estimation, DPE) a partir del senyal digital. Tenint en compte la novetat del mètode, es proporcionen motivacions qualitatives i quantitatives per a l'ús de DPE enfront al mètode convencional de posicionament. Se n'ha estudiat l'estimador de màxima versemblança (Maximum Likelihood, ML) i un algorisme per a la seva implementació pràctica basat en l'algorisme Accelerated Random Search (ARS). Els resultats de les simulacions numèriques mostren la robustesa de DPE a escenaris on el mètode convencional es veu degradat, com per exemple el cas d'escenaris rics en multicamí. Una de les reflexions fruit dels resultats és que l'ús conjunt dels senyals provinents dels satèl·lits visibles proporciona millores en l'estimació de la posició, doncs cada senyal està afectada per un canal de propagació independent. La tesi també presenta l'extensió de DPE dins el marc Bayesià: Bayesian DPE (BDPE). BDPE manté la filosofia de DPE, tot incloent-hi possibles fonts d'informació a priori referents al moviment del receptor. Es comenten algunes de les opcions com l'ús de sistemes de navegació inercials o la inclusió d'informació atmosfèrica. Tot i així, cal tenir en compte que la llista només està limitada per la imaginació i l'aplicació concreta on el marc BDPE s'implementi.<br/><br/>Finalment, la tesi els límits teòrics en la precisió dels receptors GNSS. Alguns d'aquests límits teòrics eren ja coneguts, d'altres veuen ara la llum. El límit de Cramér-Rao (Cramér-Rao Bound, CRB) ens prediu la mínima variància que es pot obtenir en estimar un paràmetre mitjançant un estimador no esbiaixat. La tesi recorda el CRB dels paràmetres de sincronisme, resultat ja conegut. Una de les aportacions és la derivació del CRB de l'estimador de la posició pel cas convencional i seguint la metodologia DPE. Aquests resultats proporcionen una comparativa asimptòtica dels dos procediments pel posicionament de receptors GNSS. D'aquesta manera, el CRB de sincronisme pel cas Bayesià (Posterior Cramér-Rao Bound, PCRB) es presenta, com a límit teòric dels filtres Bayesians proposats en la tesi.<br>This dissertation deals with the design of satellite-based navigation receivers. The term Global Navigation Satellite Systems (GNSS) refers to those navigation systems based on a constellation of satellites, which emit ranging signals useful for positioning. Although the american GPS is probably the most popular, the european contribution (Galileo) will be operative soon. Other global and regional systems exist, all with the same objective: aid user's positioning. Initially, the thesis provides the state-of-the-art in GNSS: navigation signals structure and receiver architecture. The design of a GNSS receiver consists of a number of functional blocks. From the antenna to the final position calculation, the design poses challenges in many research areas. Although the Radio Frequency chain of the receiver is commented in the thesis, the main objective of the dissertation is on the signal processing algorithms applied after signal digitation. These algorithms can be divided into two: synchronization and positioning. This classification corresponds to the two main processes typically performed by a GNSS receiver. First, the relative distance between the receiver and the set of visible satellites is estimated. These distances are calculated after estimating the delay suffered by the signal traveling from its emission at the corresponding satellite to its reception at the receiver's antenna. Estimation and tracking of these parameters is performed by the synchronization algorithm. After the relative distances to the satellites are estimated, the positioning algorithm starts its operation. Positioning is typically performed by a process referred to as trilateration: intersection of a set of spheres centered at the visible satellites and with radii the corresponding relative distances. Therefore, synchronization and positioning are processes performed sequentially and in parallel. The thesis contributes to both topics, as expressed by the subtitle of the dissertation.<br/><br/>On the one hand, the thesis delves into the use of Bayesian filtering for the tracking of synchronization parameters (time-delays, Doppler-shifts and carrier-phases) of the received signal. One of the main sources of error in high precision GNSS receivers is the presence of multipath replicas apart from the line-of-sight signal (LOSS). Wherefore the algorithms proposed in this part of the thesis aim at mitigating the multipath effect on synchronization estimates. The dissertation provides an introduction to the basics of Bayesian filtering, including a compendium of the most popular algorithms. Particularly, Particle Filters (PF) are studied as one of the promising alternatives to deal with nonlinear/nonGaussian systems. PF are a set of simulation-based algorithms, based on Monte-Carlo methods. PF provide a discrete characterization of the posterior distribution of the system. Conversely to other simulation-based methods, PF are supported by convergence results which make them attractive in cases where the optimal solution cannot be analytically found. In that vein, a PF that incorporates a set of features to enhance its performance and robustness with a reduced number of particles is proposed. First, the linear part of the system is optimally handled by a Kalman Filter (KF), procedure referred to as Rao-Blackwellization. The latter causes a reduction on the variance of the particles and, thus, a reduction on the number of required particles to attain a given accuracy when characterizing the posterior distribution. A second feature is the design of an importance density function (from which particles are generated) close to the optimal, not available in general. The selection of this function is typically a key issue in PF designs. The dissertation proposes an approximation of the optimal importance function using Laplace's method. In parallel, Extended Kalman Filter (EKF) and Unscented Kalman Filter (UKF) algorithms are considered, comparing these algorithms with the proposed PF by computer simulations.<br/><br/>On the other hand, a novel point of view in the positioning problem constitutes one of the original contributions of the thesis. Whereas conventional receivers operate in a two-steps procedure (synchronization and positioning), the proposal of the thesis is a Direct Position Estimation (DPE) from the digitized signal. Considering the novelty of the approach, the dissertation provides both qualitative and quantitative motivations for the use of DPE instead of the conventional two-steps approach. DPE is studied following the Maximum Likelihood (ML) principle and an algorithm based on the Accelerated Random Search (ARS) is considered for a practical implementation of the derived estimator. Computer simulation results carried show the robustness of DPE in scenarios where the conventional approach fails, for instance in multipath-rich scenarios. One of the conclusions of the thesis is that joint processing of satellite's signals provides enhance positioning performances, due to the independent propagation channels between satellite links. The dissertation also presents the extension of DPE to the Bayesian framework: Bayesian DPE (BDPE). BDPE maintains DPE's philosophy, including the possibility of accounting for sources of side/prior information. Some examples are given, such as the use of Inertial Measurement Systems and atmospheric models. Nevertheless, we have to keep in mind that the list is only limited by imagination and the particular applications were BDPE is implemented. Finally, the dissertation studied the theoretical lower bounds of accuracy of GNSS receivers. Some of those limits were already known, others see the light as a result of the research reported in the dissertation. The Cramér-Rao Bound (CRB) is the theoretical lower bound of accuracy of any unbiased estimator of a parameter. The dissertation recalls the CRB of synchronization parameters, result already known. A novel contribution of<br/>the thesis is the derivation of the CRB of the position estimator for either conventional and DPE approaches. These results provide an asymptotical comparison of both GNSS positioning approaches. Similarly, the CRB of synchronization parameters for the Bayesian case (Posterior Cramér-Rao Bound, PCRB) is given, used as a fundamental limit of the Bayesian filters proposed in the thesis.

The goal of this thesis is to improve the understanding of the performance of Global Navigation Satellite System (GNSS) receivers that use assistance data provided by cellular networks. A typical example of such a receiver is a mobile phone including a Global Positioning System (GPS) receiver. Using assistance data such as an accurate estimate of the GPS system time is known to improve the availability and the time-tofirst- fix performance of a GNSS receiver. However, the performance depends on the architecture of the cellular network and may vary significantly across networks. This thesis presents three new contributions to the performance analysis of assisted-GNSS receivers in cellular networks. I first introduce a mathematical framework that can be used to calculate a theoretical lower bound of the time-to-first-fix (TTFF) in an assisted-GNSS receiver. Existing methods, for example the flow-graph method, generally focus on calculating the theoretical mean acquisition time of a pseudo-noise signal for one satellite only. I extend these methods to calculate the full probability distribution of the joint acquisition of several satellites, as well as the sequential acquisition of satellites, which is commonly performed in assisted receivers. The method is applied to real measurements made in a multipath fading channel. I next consider time assistance in unsynchronised cellular networks. It is often argued that unsynchronised networks can not provide fine-time aiding since they do not have a common clock, although few experimental results have been reported in the existing literature. I carried out experiments on a GSM network, a second-generation cellular network, in Cambridge, UK, in order to measure the time stability of the synchronisation signals. The results showed a large variability in the time stabilities across different base stations and I evaluated the performance of an ensemble filter that combines the measurements into a single, more accurate, estimate of the universal time. The main contribution is to show that the performance of such a filter is adequate to provide fine-time assistance to a satellite navigation receiver. Finally, I address the positioning performance of an assisted receiver in synchronised cellular networks. Cellular positioning has been often investigated in the literature, but few results on real networks have been presented. Many positioning methods are proprietary and little information about their performance in real networks haven been published publicly. A CDMA2000 cellular network in Calgary, Canada, was used to collect experimental data. The time stability and the synchronisation of the CDMA2000 pilot signals were excellent and were used to evaluate the performance of CDMA2000-based cellular positioning system. I then developed a method to combine the pseudo-range measurements from the GPS signals and the CDMA2000 base stations. I evaluated the performance of positioning in both outdoor and indoor environments, and I analysed the effects and the possible mitigation of non-line-of-sight signals. The main contribution is to show that additional satellite navigation signals can improve the accuracy of cellular positioning beyond what is theoretically expected from the improvement in the geometry.