Dissertations / Theses on the topic 'GNSS'

The thesis deals with the analysis and the reception of the freely available signals of the navigation satellites in the L1 and E1 bands of the GPS and Galileo systems. The described signal reception sections include the process of the acquisition, the carrier frequency and phase synchronization and tracking, the spreading code phase tracking, the signal demodulation and the channel decoding. The simulation of the entire receiver is performed in MATLAB. The deeply analyzed signal reception component is the one responsible for the carrier phase and frequency synchronization and tracking. In that case, more methods and their comparison are usually listed. The signal reception component, which is responsible for the carrier phase and frequency tracking and the spreading code phase tracking, is also implemented in FPGA.

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Os modelos funcionais relacionados com as observações GNSS são mais conhecidos do que os modelos estocásticos, visto que o desenvolvimento destes últimos é mais complexo. Normalmente, utilizam-se modelos estocásticos numa forma simplificada, como o modelo padrão, o qual assume que todas as medidas das observações GNSS têm a mesma variância e são estatisticamente independentes, espacialmente e temporalmente. Porém, tal suposição não reflete a realidade. Desta forma, atualmente os modelos estocásticos vêm sendo pesquisados com maior profundidade, por exemplo, considerando correlação temporal, cintilação ionosférica, dentre outros. O Brasil, por estar numa região geomagnética equatorial, sofre forte influência de cintilação ionosférica e outros efeitos relacionados à ionosfera. Tendo em vista a recente tecnologia de receptores GNSS que proporciona a possibilidade de se obter parâmetros de cintilação ionosférica, este efeito é factível de ser considerado na modelagem estocástica. Mesmo com a realização de uma modelagem estocástica adequada no processamento de dados GNSS, ainda podem restar erros não-modelados (ruídos), os quais devem contaminar as séries temporais das coordenadas obtidas com as observáveis GNSS, em especial aqueles relacionados com fatores que extrapolam a duração de uma dia, que é o período em geral utilizado na modelagem e processamento dos dados. Desta forma, tais ruídos podem ser caracterizados a partir das componentes de variância dos ruídos das séries temporais. Sendo assim, essa pesquisa teve como objetivo expandir as investigações com relação à modelagem estocástica das observações GNSS considerando principalmente os efeitos de cintilação ionosférica na região brasileira...
Functional models related to GNSS observations are better known than the stochastic models because the development these last one is more complex. Generally, stochastic models are applied in a simplified form, as the standard model, which assumes that all GNSS measurements have the same variance and are statistically independent, spatially and temporally. However, this assumption does not reflect the reality. Therefore, currently the stochastic models have been investigated more deeply, for instance, considering time correlation, ionospheric scintillation, among others. Brazil is located in the equatorial geomagnetic region and because of this suffers strong influence of ionospheric scintillation and other effects related to the ionosphere. Considering the recent technology of the GNSS receivers, that provide ways to obtain parameters of ionospheric scintillation, this effect is feasible of being considered in the stochastic modeling. Even if an adequate stochastic modeling could be applied in the GNSS data processing, it still may remain non-modeled errors (noise) that can influence the coordinate’s time series, especially those related to factors that go beyond the duration of one day, which is in general the interval (one day) used in the modeling and data processing. Thus, such noise can be characterized from the noise variance components of the time series. Therefore, this research aimed to expand the investigations regarding the stochastic modeling of GNSS observations mainly considering the ionospheric scintillation effects in the Brazilian region. Furthermore, it also aims to perform investigations related to methodologies for the noise characterization in the GNSS coordinates time series and establish a methodology for building functional models of these series...

Orientador: João Francisco Galera Monico
Coorientador: Manoel Ivanildo Silvestre Bezerra
Banca: Silvio Rogério Correia de Freitas
Banca: Eunice Menezes de Souza
Banca: Vilma Mayumi Tachibana
Banca: Daniele Barroca Marra Alves
Resumo: Os modelos funcionais relacionados com as observações GNSS são mais conhecidos do que os modelos estocásticos, visto que o desenvolvimento destes últimos é mais complexo. Normalmente, utilizam-se modelos estocásticos numa forma simplificada, como o modelo padrão, o qual assume que todas as medidas das observações GNSS têm a mesma variância e são estatisticamente independentes, espacialmente e temporalmente. Porém, tal suposição não reflete a realidade. Desta forma, atualmente os modelos estocásticos vêm sendo pesquisados com maior profundidade, por exemplo, considerando correlação temporal, cintilação ionosférica, dentre outros. O Brasil, por estar numa região geomagnética equatorial, sofre forte influência de cintilação ionosférica e outros efeitos relacionados à ionosfera. Tendo em vista a recente tecnologia de receptores GNSS que proporciona a possibilidade de se obter parâmetros de cintilação ionosférica, este efeito é factível de ser considerado na modelagem estocástica. Mesmo com a realização de uma modelagem estocástica adequada no processamento de dados GNSS, ainda podem restar erros não-modelados (ruídos), os quais devem contaminar as séries temporais das coordenadas obtidas com as observáveis GNSS, em especial aqueles relacionados com fatores que extrapolam a duração de uma dia, que é o período em geral utilizado na modelagem e processamento dos dados. Desta forma, tais ruídos podem ser caracterizados a partir das componentes de variância dos ruídos das séries temporais. Sendo assim, essa pesquisa teve como objetivo expandir as investigações com relação à modelagem estocástica das observações GNSS considerando principalmente os efeitos de cintilação ionosférica na região brasileira...
Abstract: Functional models related to GNSS observations are better known than the stochastic models because the development these last one is more complex. Generally, stochastic models are applied in a simplified form, as the standard model, which assumes that all GNSS measurements have the same variance and are statistically independent, spatially and temporally. However, this assumption does not reflect the reality. Therefore, currently the stochastic models have been investigated more deeply, for instance, considering time correlation, ionospheric scintillation, among others. Brazil is located in the equatorial geomagnetic region and because of this suffers strong influence of ionospheric scintillation and other effects related to the ionosphere. Considering the recent technology of the GNSS receivers, that provide ways to obtain parameters of ionospheric scintillation, this effect is feasible of being considered in the stochastic modeling. Even if an adequate stochastic modeling could be applied in the GNSS data processing, it still may remain non-modeled errors (noise) that can influence the coordinate's time series, especially those related to factors that go beyond the duration of one day, which is in general the interval (one day) used in the modeling and data processing. Thus, such noise can be characterized from the noise variance components of the time series. Therefore, this research aimed to expand the investigations regarding the stochastic modeling of GNSS observations mainly considering the ionospheric scintillation effects in the Brazilian region. Furthermore, it also aims to perform investigations related to methodologies for the noise characterization in the GNSS coordinates time series and establish a methodology for building functional models of these series...
Doutor

Este trabalho investiga sistemas de navegação INS/GNSS auxiliado por medidas de baseline e ângulo GNSS. Os dados gerados para as simulações foram os dados IMU, dados GNSS e informações de baseline e ângulo GNSS. Estas informações, determinadas a partir de um sistema multiantenas para o posicionamento simples e relativo e no método direto, respectivamente, foram utilizadas como medidas auxiliares para a fusão INS/GNSS. Foi estudada a influência dessas medidas auxiliares nas estimativas de atitude do navegador, mais especificamente no ângulo de yaw, pois o acoplamento da dinâmica do sistema com este ângulo é fraco. Assim, a principal contribuição das medidas adicionais ocorre para este ângulo. Adicionalmente, foi feito um estudo da navegação INS/GNSS usando dados reais SIG-IMU/NAVCON para análise dos biase, baseado em um maior número de realizações, analisou-se a influência do valor de estimativa do erro de atitude do navegador INS/GNSS no erro máximo de posição. Uma interface gráfica foi aprimorada de modo a facilitar as mudanças nos parâmetros do sistema e as simulações dos vários casos, tais como navegação INS/GNSS sem auxílio e com auxílio de baseline e ângulo GNSS, falha do sinal GNSS e navegação INS/GNSS utilizando dados reais.

The United Kingdom utility services are facing the challenge of "mapping the underworld" over four million kilometres of buried pipes and cables (a combination of water, sewage, gas, electricity and drainage). Having accurately mapped pipes and cables increases the efficiency of street works projects, but many existing pipes and cables were only mapped relative to other topographic map features and to varying levels of accuracy. The aim of this thesis is to research various means of improving the positional accuracy of underground utilities in built-up areas through the use of Global Navigation Satellite System (GNSS), integrated with other positioning systems such as Inertial Navigation Systems (INS) and total stations. The reliability and accuracy of the integrated system is an underpinning issue and this thesis looks at testing both current and future GNSS constellations in a controlled environment at the University of Nottingham campus. GNSS integrated with an INS in the first instance, and integrated with a total-station in the second instance, are tested using a network of established points in urban canyon environments on the campus. Several, new technologies were developed by the author including: Urban Canyon GNSS Simulation (UCGS) - a GIS tool; Multiple Step Integration Technique (MSIT) - a methodology for GNSS/INS data collection and processing; and Continuous Updating Technique (CUPT) - a software for GNSS/total-station integration. The results of different simulations provide evidence that using more than one GNSS constellation will significantly increase the availability of GNSS positions in urban canyon environments. However, position availability using the criteria of 5 or more satellites with a Position Dilution Of Precision (PDOP) value of 6 or less for centimetre level is not guaranteed 100% of the time when using GNSS alone. Considering the results of the integrated GNSS/INS system, the position availability was guaranteed 100% of the time in all environments, but the accuracy is not enough to meet utility service requirements. The best results used GNSS integrated with a total-station and showed that, in this case, position availability to a centimetre level of accuracy can be guaranteed 100% of the time in all environments.

Goal of this thesis is to propose and realize a viable method to determine static a dynamic parameters of GNSS receivers. Thesis begins with research of GNSS, foremostly determining position and associated uncertainties of measurement. Following chapter contains research of GNSS receivers, data flow and methods of evaluating parameters of such measurements. Summary of obtained information is then used to schedule measurements, assemble experiment and create evaluating metrics. Main selected evaluating metric is weighted histogram of deviations with extended information. Aplication of proposed metrics onto measurements of GNSS receivers augments available information of GNSS receiver accuracy for whole range of values. This metrics also supplies additional statistical information about course of measurement.

The thesis deals with processing of epoch-wise GNSS measurements from local geodynamic network Sněžník. Its aim is to evaluate the geodynamics in the area of Králický Sněžník Massif and to assess the capabilities of epoch-wise GNSS measurements to detect the geodynamic movements. Within the thesis the comprehensive processing of all the GNSS measurements observed between years 1997 and 2011 is realized using the reprocessed products of first IGS reprocessing Repro1. Bernese GPS software version 5.0 is used for all the processing.

Signals broadcast by the Global Navigation Satellite Systems (GNSS) enable global, autonomous, geo-spatial positioning exploited in the areas such as geodesy, surveying, transportation and agriculture. The propagation of these signals is affected as they propagate through the Earth's upper atmosphere, the ionosphere, due to the ionic and electronic structure of the ionosphere. The ionosphere, a highly dynamic and spatially and temporally variable medium, can be the largest error source in Global Navigation Satellite System (Klobuchar 1991) in the absence of the Selective Availability. Propagation effects due to the ionosphere lead to errors in the range measurements, impact on receiver signal tracking performance and influence the GNSS positioning solution. The range error can vary from 1 to 100m depending on time of day, season, receiver location, conditions of the earth's magnetic field and solar activity (Hofmann-Wellenhof et al. 2001). This thesis focuses on modelling, monitoring and mitigating the ionospheric effects in GNSS within the scope of GNSS modernization, which introduces new signals, satellites and constellations. The ionosphere and its effects on GNSS signals, impact of the ionospheric effects at the receiver end, predicted error bounds of these effects under different solar, geomagnetic and ionospheric conditions, how these effects can be modelled and monitored with current and new (possible with GNSS modernization) correction approaches, degradation in the GNSS positioning solution and mitigation techniques to counter such degradation are investigated in this thesis. Field recorded and simulated data are considered for studying the refractive and diffractive effects of the ionosphere on GNSS signals, signal tracking performance and position solution. Data from mid-to-high latitudes is investigated for the refractive effects, which are due to dispersive nature of the ionosphere. With the use of multi-frequency, multi-constellation receivers, modelling of the refractive effects is discussed through elimination and estimation of these effects on the basis of dual and triple frequency approaches, concentrating on the benefit of the new GNSS signals. Data from the low latitudes is considered for studying the diffractive effects of the ionosphere, scintillation in particular, in GNSS positioning, and possible mitigation techniques to counter them. Scintillation can have a considerable impact on the performance of GNSS positioning by, for instance, increasing the probability of losing phase lock with a signal and reducing the accuracy of pseudoranges and phase measurements. In this sense, the impact of scintillation on signal tracking performance and position solution is discussed, where a novel approach is proposed for assessing the variance of the signal tracking error during scintillation. The proposed approach also contributes to the work related with scintillation mitigation, as discussed in this thesis. The timeliness of this PhD due to the recent and increasingly active period of the next Solar Cycle (predicted to reach a peak around 2013) and to the ongoing GNSS modernization give this research an opportunity to enhance the ionospheric knowledge, expertise and data archive at NGI, which is rewarding not only for this PhD but also for future research in this area.

Un récepteur GPS (Système de Positionnement Global par satellite) permet à son utilisateur de connaître sa position et sa vitesse à tout moment et à tout endroit du globe. Malheureusement, le GPS ne peut satisfaire à lui seul les exigences de l'OACI (Organisation de l'Aviation Civile Internationale) pour devenir un moyen unique de navigation. Il doit être amélioré pour cela. Une des principales limitations du GPS est son intégrité. Celle-ci peut être améliorée grâce à une augmentation du GPS ou par son hybridation avec un autre système de navigation. Au niveau du récepteur GPS, un module RAIM (Receiver Autonomous Integrity Monitoring) est proposé pour effectuer le contrôle autonome de l'intégrité du système. Ce module se sert de la redondance inhérente aux mesures GPS pour s'assurer qu'aucune panne n'affecte la solution GPS de navigation. En cas de panne, le RAIM doit aussi pouvoir rapidement détecter cette panne et exclure le satellite qui est en cause. Il existe deux sortes de RAIMs : le RAIM Snapshot n'utilise que les mesures GPS instantanées alors que le RAIM Séquentiel se sert de toutes les mesures passées et présentes pour décider de l'intégrité du système. La géométrie des satellites utilisée pour la solution de navigation peut nuire à la détection et/ou l'isolation d'une panne. Dans ces cas de figure, des tests sur mesures réelles et des simulations montrent que le RAIM Séquentiel est beaucoup plus performant que le RAIM Snapshot. De cette capacité à fonctionner sous des conditions adverses, la disponibilité du GPS lorsqu'il est contrôlé par un RAIM Séquentiel est naturellement améliorée. Beaucoup d'avions civils intègrent un Système de Navigation Inertielle (INS). Grâce à leur grande complémentarité, l'hybridation des systèmes GPS et INS peut devenir un moyen unique de navigation pour certaines phases de vol. Dans ce système, il faut s'assurer que la solution GPS utilisée pour recaler la solution INS soit intègre. C'est ce que permet le RAIM Séquentiel grâce à ses qualités théoriques (vérifiées par simulations). Un schéma d'hybridation exploitant ces qualités est présenté.

GNSS-Messungen werden neben systembedingten Fehlereinflüssen vor allem von den Auswirkungen der Mehrwegeausbreitung und Signalbeugung insbesondere in der Empfangsumgebung dominiert. Verschiedene Dienste z.B. der Landesvermessungsämter haben deshalb ein primäres Interesse daran, die Auswirkungen der Effekte möglichst gering zu halten oder aber genau bestimmen zu können, um Korrekturwerte zu generieren. Mehrwege- und Beugungseffekte lassen sich besonders innerhalb von Netzstrukturen gut bestimmen. Liegen Sollkoordinaten aller Beobachtungsstationen vor gelingt dies auch in Echtzeit. In der vorliegenden Arbeit werden neben einer detaillierten Beschreibung der jeweiligen Einflussgrößen auch Möglichkeiten aufgezeigt, die genannten Effekte zu erkennen und Maßnahmen zur Reduktion der Auswirkungen auf das Meßergebnis zu ergreifen. Kern der Untersuchungen ist ein zweistufiges Modell zur Reduzierung von Mehrwegeeffekten in Echtzeit innerhalb von (Referenz-) Stationsnetzen durch Bestimmung von Korrekturwerten für originale und abgeleitete Meßwerte pro Epoche, Station und Satellit.

There has been a significant growth in Location-Based Services (LBS) on mobileapplications. These applications provide service to users based on theirgeographical locations. Emergency services, tracking, navigation, advertisingand social networking are examples of them. As the majority of today’s mobilephones are equipped with GPS receivers, GPS positioning has become one ofthe primary methods for obtaining users’ location. Moreover, GPS providesaccurate time service and many applications specially for time synchronizationare relying on GPS. Despite the good accuracy it provides, security is notconsidered from scratch in civilian GPS and its signals are weak, vulnerable tospoofing and prone to jamming. As it has become a more and more valuableresource, malicious agents have also become keener to identify and abuse theweaknesses in order to interrupt users or commit fraud. That is why therehave been continuous alerts about insecurity in civilian GPS in scholarly andacademic publications. A considerable amount of research has been conductedto tackle the problem of insecurity in GPS, but proposed solutions need eitherfundamental changes in GPS signal structure or more sophisticated types ofreceivers. As changes in GPS signal structure need time, money and politicalwill, this work works on a method to detect spoofing of GPS signals based onthe current GPS signal structure and receivers on mobile phones. We crosscheckpositioning and time information by comparing it with other sourcesof information. GPS positioning data are compared with the user’s positionderived from Wi-Fi positioning and cell positioning and the distance betweenthose is shown to the user. The system also keeps the recent distances and ifthose positions are moving away from each other, it notifies the user about thissuspicious behaviour. Regarding verification of the GPS time, it is comparedwith a time server on the internet. An Android application was designed anddeveloped to implement this method. Then experimental evaluations wereperformed in the urban area of the city of Stockholm. Results show that thesystem can perform positioning with mean value of 50 meter accuracy anddetect simulated spoofing attack. Moreover, it detects the suspicious behaviourif the calculated position and GPS position are gradually moving away fromeach other.

Should civil aviation reach its promising full potential, it will inevitably be through the use and reliance upon Global Navigation Satellite Systems (GNSS) and its innovative technologies. At present only one option seems clearly and 'directly' operational for the civil aviation challenge, and that is a---USA owned and controlled---GPS based GNSS.
This thesis will critically discuss the legal and institutional issues of the GNSS. The issues considered will be based upon the discussions and conclusions recently reached within ICAO. The object of this thesis is to compare, contrast and criticise ICAO's international law-making propositions, related to GNSS, in the fight of the 'practical reality' varying from the users' demands and expectations, passing through the lack of practical experiences, to the USA monopoly as sole basic signal provider.
Whilst ICAO is undeniably a great contributor to global development of civil aviation, it seems that in the case of GNSS implementation, ICAO's role is limited by both its mandate, but equally a lack of political consensus upon potential 'solutions' to hypothetical problems.
The research is based on materials and documents available by the end of May 1997 and does not take into account the later developments in ICAO discussions.

In the next coming years global satellite navigation systems (GNSS) will make part of our daily life, as the world is becoming "GNSS-dependant in the same way that it has become Internet-dependant". Indeed, more than ten years folowing the opening up to civilians of satellite-based navigation systems initially designed for military purposes, civil satellite navigation applications are becoming more and more numerous. The potential benefits have proven enormous in terms of transport safety and efficiency as well as for non-transport-related industries.
Dans les toutes prochaines années, les systèmes globaux de navigation par satellite (GNSS) feront partie intégrante de notre vie quotidienne. En effet, un peu plus de dix ans après la libéralisation de l'accès des civils aux systèmes de navigation par satellite initialement conçus à des fins militaires, les applications civiles permises par la navigation par satellite sont de plus en plus nombreuses et les bénéfices potentiels sont énormes en matière de sécurité et d'efficacité des transports comme pour d'autres secteurs et industries. fr

Les systèmes de positionnement et de navigation par satellite (GNSS) ont connu un formidable essor au cours des deux dernières décennies au point d'être aujourd'hui un élément technologique universel. Le recours au positionnement précis par satellite est intégré à notre vie quotidienne: puces GPS intégrées dans les téléphones portables, systèmes de radionavigation utilisés pour le guidage d'engins agricoles, l'approche aérienne et maritime. Les stations GNSS déployées dans les réseaux géodésiques permanents participent au maintien des références géodésiques nationales et internationales et à la prévision météorologique. Ces applications scientifiques requièrent une mise en œuvre rigoureuse des équipements et un traitement sophistiqué des mesures. Une limitation de précision commune vient la présence d'erreurs dans les mesures dues à la traversée de l'atmosphère. L'amélioration des méthodes de correction de la propagation des signaux radiofréquence dans l'atmosphère a permis au cours des dix dernières années d'atteindre une précision sub-centimétrique en positionnement vertical et de faire des GNSS une technique de référence pour le sondage de la vapeur d'eau dans la troposphère. Ce manuscrit rassemble les résultats des recherches que j'ai développées au LATMOS et à l'IGN depuis une douzaine d'années dans le domaine du positionnement précis par GPS, de la télédétection de la vapeur d'eau atmosphérique par GPS et lidar Raman, et de l'étude du cycle de l'eau atmosphérique au moyen de systèmes d'observations et de modèles de prévision météorologique.

GNSS-Messungen werden neben systembedingten Fehlereinflüssen vor allem von den Auswirkungen der Mehrwegeausbreitung und Signalbeugung insbesondere in der Empfangsumgebung dominiert. Verschiedene Dienste z.B. der Landesvermessungsämter haben deshalb ein primäres Interesse daran, die Auswirkungen der Effekte möglichst gering zu halten oder aber genau bestimmen zu können, um Korrekturwerte zu generieren. Mehrwege- und Beugungseffekte lassen sich besonders innerhalb von Netzstrukturen gut bestimmen. Liegen Sollkoordinaten aller Beobachtungsstationen vor gelingt dies auch in Echtzeit. In der vorliegenden Arbeit werden neben einer detaillierten Beschreibung der jeweiligen Einflussgrößen auch Möglichkeiten aufgezeigt, die genannten Effekte zu erkennen und Maßnahmen zur Reduktion der Auswirkungen auf das Meßergebnis zu ergreifen. Kern der Untersuchungen ist ein zweistufiges Modell zur Reduzierung von Mehrwegeeffekten in Echtzeit innerhalb von (Referenz-) Stationsnetzen durch Bestimmung von Korrekturwerten für originale und abgeleitete Meßwerte pro Epoche, Station und Satellit.

Глобальные навигационные спутниковые системы все чаще используются для решения навигационной задачи в разных сферах экономики: картография, геодезия, управление наземным, воздушным, морським и космическим транспортом. Навигационные спутниковые системы предназначены для определения местоположения движущегося объекта в пространстве и его скорости в определенный момент времени, а также осуществляют координацию времени.
Національний авіаційний університет

There is an increasing demand for higher precision when using Global Navigation Satellite Systems, GNSS, for positioning. The measurement uncertainty depends on multiple factors and one of them is the ionosphere. Due to the ionosphere being ionized and contains free electrons, satellite signals that propagates the ionosphere will be affected by the total electron content, TEC. There is no way to reduce the errors caused by the ionosphere for single frequency measuring, but it can be done for dual frequencies. The objective for this study was to compare different websites modeling results for disturbance on ground and ionospheric turbulence. Three websites were used in the comparison: Swedish SWEPOS, Norwegian seSolstorm and German IMPC. Due to different content on the websites, SWEPOS was compared with seSolstorm and IMPC was compared to seSolstorm on five different dates. In total 10 comparisons were made. The websites were evaluated on four criteria, designed from the point of view of a land surveyor: user friendliness, graphical representation, knowledge requirement and mobile website adaptation. Each criterion was graded on a scale from 1–5, where 5 was considered the best. The study showed that the modeling results from the websites differed and that the difference can not only be explained by different graphical representation or scales for measure. The results for the evaluation and grading of the websites where as follows: SWEPOS 16, seSolstorm 13 and IMPC 12. This makes SWEPOS the best suited website to use for a land surveyor.
Vid positionsbestämning finns det ett behov av högre precision vid användandet av Global Navigation Satellite Systems, GNSS. Mätosäkerheten beror av ett flertal faktorer och en av dem är jonosfären. Tack vare att jonosfären är joniserad och innehåller fria elektroner kommer satellitsignaler som färdas genom jonosfären att påverkas av det totala elektroninnehållet, TEC. Det finns idag inget sätt för enkel frekvensmätning att eliminera den mätosäkerhet som uppstår till följd av jonosfäriska störningar, däremot är det möjligt att modellera för dessa störningar då två frekvenser används. Målet för denna studie var att jämföra olika webbplatsers modelleringsresultat för störningar på marknivå och för jonosfärisk turbulens. Tre webbplatser användes i jämförelsen: svenska SWEPOS, norska seSolstorm och tyska IMPC. På grund av att hemsidorna hade olika innehåll gällande modelleringar jämfördes SWEPOS med seSolstorm, medan IMPC jämfördes med seSolstorm. Totalt gjordes 10 jämförelser för fem olika datum. Webbplatserna utvärderades utifrån fyra kriterier vilka var utformade utifrån en mätteknikers synvinkel: användarvänlighet, grafisk representation, kunskapsbehov och mobil webbplatsanpassning. Varje kriterium betygsattes på en skala från 1–5, där 5 ansågs vara det bästa. Studien visade att modelleringsresultaten från webbplatserna skilde sig åt och att skillnaden inte kunde förklaras med olika grafiska framställningar eller skalstorlek. Resultaten för utvärdering och betygsättning av webbplatserna var följande: SWEPOS 16, seSolstorm 13 och IMPC 12. Detta gjorde SWEPOS till den bäst lämpade webbplatsen att använda för en mättekniker.

Today, GNSS measurements play an important role in the surveying industry, and their use is ever increasing. Many different GNSS receivers and antenna manufacturers are on the market with new ones appearing. The purpose of this study is to investigate the level of measurement uncertainty of three different GNSS receivers: Leica GS15, Sokkia GCX2 and Satlab SL300. The method in this study is based mainly on the method proposed by HMK - Geodatakvalitet 2015 (Manual in measurement and map issues – Geographic data quality 2015 [author’s translation]) by Swedish Lantmäteriet for "Evaluation of measurement uncertainty in Network RTK [author’s translation]”. Some corrections and additions are made to this method but the basis of the method is retrieved from there. Formulas are used to calculate radial deviation and limit requirements for these. Even standard deviations and radial mean deviations as well as tolerances for these are calculated. The field measurements are made on two RIX 95-points. This is done repeatedly to get up to 20 measurements. The GNSS receivers are mounted on a tripod with a tribrach that is centered over the known points. The main finding from this study is that all investigated receivers, apart from four overriding values ​​for the Leica GS15, perform better than specified by their manufacturers. However, Sokkia GCX2 and Satlab SL300 are approved with uncertainties within the calculated tolerances. The Leica GS15 instrument is very close to meeting the demands but does not reach all the way. A committed error during the performed measurements with the Satlab SL300 makes its evaluation based on 19 instead of 20 measurements. Still, calculations are performed on the collected data that resulted in low measurement uncertainties well below the manufacturer's specified uncertainty. The study was conducted during five weeks in May and June 2017.

The diploma thesis is focused on the topic of global satellite navigation of mobile robots. The paper describes the principle of currently available global satellite navigation systems. The main element of the thesis is the proposal of mobile robot navigation algorithm. An integral part is also the design of a mobile robot to verify the functionality of the navigation algorithm. The robot software program is described. At the end, everything is verified by real experiments.

Global Navigation Satellite Systems (GNSS) have found wide adoption in various applications, be they military, civilian or commercial. The susceptibility of GNSS to radio-frequency interference can, thus, be very disruptive, even for emergency services, therefore threatening people's lives. An early prototype of a system providing relatively cheap widescale GNSS jamming detection, called J911, is explored in this thesis. J911 is smartphone-based crowdsourcing of GNSS observations, most interesting of which are carrier-to-noise-density ratio () and Automatic Gain Control (AGC) voltage. To implement the prototype, an Android application to provide the measurements, a backend to parse and store the measurements, and a frontend to visualize the measurements were developed. In real-world use, the thesis argues, the J911 system would best be implemented over existing Enhanced 9-1-1 (E911) infrastructure, becoming a standardized part of the Public Switched Telephone Network (PSTN). The Android application, running on a smartphone, would periodically construct messages to be sent to the backend over an Internet connection. The messages would include: current location from all location providers available in Android OS, observed satellites from all supported constellations, the satellites' , and a timestamp. Once a message is received on the backend, the data would be extracted and stored in a database. The frontend would query the database and produce a map with the collected datapoints overlaid on top of it, whose color indicates received signal strength at that point. When a jammer gets close enough to a few smartphones, they will all be jammed, which is easily observed on the map. On top of that, if enough samples are gathered, a Power Difference of Arrival localization algorithm can be used to localize the jammer. The smartphones that the system was planned to be tested with did not support AGC level readings, therefore in order to obtain AGC levels over time, a few SiGe GN3S Samplers, which are radio-frequency frontends, were used. In eastern Idaho, United States, over three nights in July 2017, an exercise, named 2017 DHS JamX, was performed with the help of the US Department of Homeland Security. Sadly, the approval for the publication of the test results did not come in time to be included in this thesis.

As GPS signals are of low power, the receiving end is always highly susceptible to interference, both unintentional and deliberate. As such there is a need to develop practical ways of detecting and localizing interference sources. This paper evaluates different methods of localization, and also demonstrates a novel method of both practical and cheap localization.

This report shows the difference between today's geodetic measurementsand the one that comes withGalileo and Beidou included. As new GNSSequipment supporting Galileo and Beidou begins to be used, what are the differences and what can be expected by users in the future?This report addresses current theory of sources of error and satellite geometry to highlight the problems associated with GNSS. Based on the sources of error and satellite geometry, the results will be presentedand discussed at the end of the report.

Multipath effect is generated when a signal arrives at the antenna by multiple paths instead of one direct path. It is, to a large extent, dependent on the surrounding environment of the antenna and the satellite geometry. Despite all the efforts put into the mitigation of multipath errors, it remains the dominant error source that cannot be ignored for GNSS precise positioning and other GNSS applications. In this thesis report, two methods have been developed with Trimble Business Center and MATLAB to study the presence and performance of multipath effect. The first method – Trimble baseline analysis focuses on the height change pattern of the study station with regard to its reference station over time. The second method – RINEX analysis focuses on the change of the geometry-free combination of pseudorange codes and carrier phase measurements over time. These two methods have been firstly tested on station KTH and then applied on station Vidsel and station Botsmark. Various forms of results all indicate the existence of multipath effect on the three suspicious stations. The height value of the study station has a variation pattern on a daily basis because of multipath. Multipath errors also cause noise in the satellite signals, with pseudorange more affected than carrier phase. It is also worth-noted that satellite at low elevation angle is more susceptible to multipath errors than that at high elevation angle.
Flervägsfel genereras när en signal anländer till antennen genom flera olika vägar i stället för den direkta vägen från satelliten. Det är i stor utsträckning beroende på den omgivande miljön av antennen och satellitgeometrin. Trots olika metoder för att reducera flervägsfel, är det fortfarande en dominerande felkälla som inte kan ignoreras för precis positionering med GNSS och andra GNSS-tillämpningar. I denna rapport har två metoder utvecklats med Trimble Business Center och MATLAB för att studera närvaron och effekten av flervägsfelet. Den första metoden - Trimble baslinje analys fokuserar på förändring i höjden för studie stationen relativt till referensstationen över tid. Den andra metoden - RINEX analys fokuserar på förändring av den geometrifria kombination av pseudoavståndsmätningar () och fasmätningar () över tid. Dessa två metoder har först testats på KTH-stationen och sedan appliceras på stationen Vidsel och stationen Botsmark. Olika resultat indikerar förekomsten av flervägsfel på de tre stationer. Höjden för studiestationerna har ett dagligt variationsmönster på grund av flervägsfelet. Flervägsfel orsakar även buller i satellitsignalerna, var pseudoavstånd är mer drabbade än fasmätningarna. Det är också värt att noterade att satelliter med låg elevationsvinkel är mer mottagliga för flervägsfel än vid hög elevationsvinkel.

The purpose of this report is to provide a detailed assessment and investigation into the performance of the Real-Time Kinematic (RTK) network Nordic Construction Company (NCC) established, as part of its aim to better leverage technology within its business, to ensure the high quality and efficiency its clients have come to expect of NCC. Within the course of this investigation, extended RTK and raw data survey sessions were undertaken at each of four baselines significant to NCC (5, 15, 25, and 35 kilometers) from three of NCC’s five RTK base stations. Subsequent analysis resulted in hard documentation of the network performances and of the fidelity of the implementation itself. The research also resulted in deliverables consisting of statistics, computations, as well as utilities that will aid in decision making and allow users to better integrate and utilize the RTK network confidently within projects. It was found that NCC’s RTK performed essentially as expected in each circumstance and well within theory and empirical experience in terms of expected accuracies and best practices. This was concluded by comparison to accessible works by the U.S. Army Corps of Engineers and the NAVSTAR (GPS) development team. Of which are aggregated within document EM-110-1-1003 (NAVSTAR Global Positioning System Surveying) published by the U.S. Army Corps of Engineers. It is important to outline that this manual’s extensive use as a primary work throughout this report is due to authors’ trust in the publishing sources as well as the documents robust combination and illustration of theoretical and empirical content. The manual states that performance in the range of 1-3 centimeters in the horizontal and 3-10 centimeters in the vertical should be expected under the circumstances tested herein and to a majority were achieved. Some unique observations and patterns were identified as a result of discussion with NCC and analysis of the data. Patterns in the data pointed to a number of things in regards to the time and elevation mask influence. During the morning sessions the fifteen and thirty  five kilometer baselines exhibited better performance, while conversely the five and twenty five kilometer baselines performed best in the afternoon. In regards to elevation mask, little influence was found at the five kilometer baseline length, whoever the 10° displayed the best performance at the remaining baseline lengths.

This thesis aims to show that Global Navigation Satellite Systems (GNSS) positioning can play a significant role in the positioning systems of future automotive applications. This is through the adoption of state-of-the-art GNSS positioning technology and techniques, and the exploitation of the rapidly developing vehicle-to-vehicle concept. The merging together of these two developments creates greater performance than can be achieved separately. The original contribution of this thesis comes from this combination: Through the introduction of the Pseudo-VRS concept. Pseudo-VRS uses the princples of Network Real Time Kinematic (N-RTK) positioning to share GNSS information between vehicles, which enables absolute vehicle positioning. Pseudo-VRS is shown to improve the performance of high precision GNSS positioning for road vehicles, through the increased availability of GNSS correction messages and the rapid resolution of the N-RTK fixed solution. Positioning systems in the automotive sector are dominated by satellite-based solutions provided by GNSS. This has been the case since May 2001, when the United States Department of Defense switched off Selective Availability, enabling significantly improved positioning performance for civilian users. The average person most frequently encounters GNSS when using electronic personal navigation devices. The Sat Nav or GPS Navigator is ubiquitous in modern societies, where versions can be found on nomadic devices such as smartphones and dedicated personal navigation devices, or built in to the dashboards of vehicles. Such devices have been hugely successful due to their intrinsic ability to provide position information anywhere in the world with an accuracy of approximately 10 metres, which has proved ideal for general navigation applications. There are a few well known limitations of GNSS positioning, including anecdotal evidence of incorrect navigation advice for personal navigation devices, but these are minor compared to the overall positioning performance. Through steady development of GNSS positioning devices, including the integration of other low cost sensors (for instance, wheel speed or odometer sensors in vehicles), and the development of robust map matching algorithms, the performance of these devices for navigation applications is truly incredible. However, when tested for advanced automotive applications, the performance of GNSS positioning devices is found to be inadequate. In particular, in the most advanced fields of research such as autonomous vehicle technology, GNSS positioning devices are relegated to a secondary role, or often not used at all. They are replaced by terrestrial sensors that provide greater situational awareness, such as radar and lidar. This is due to the high performance demand of such applications, including high positioning accuracy (sub-decimetre), high availability and continuity of solutions (100%), and high integrity of the position information. Low-cost GNSS receivers generally do not meet such requirements. This could be considered an enormous oversight, as modern GNSS positioning technology and techniques have significantly improved satellite-based positioning performance. Other non-GNSS techniques also have their limitations that GNSS devices can minimise or eliminate. For instance, systems that rely on situational awareness require accurate digital maps of their surroundings as a reference. GNSS positioning can help to gather this data, provide an input, and act as a fail-safe in the event of digital map errors. It is apparent that in order to deliver advanced automotive applications - such as semi- or fully-autonomous vehicles - there must be an element of absolute positioning capability. Positioning systems will work alongside situational awareness systems to enable the autonomous vehicles to navigate through the real world. A strong candidate for the positioning system is GNSS positioning. This thesis builds on work already started by researchers at the University of Nottingham, to show that N-RTK positioning is one such technique. N-RTK can provide sub-decimetre accuracy absolute positioning solutions, with high availability, continuity, and integrity. A key component of N-RTK is the availability of real-time GNSS correction data. This is typically delivered to the GNSS receiver via mobile internet (for a roving receiver). This can be a significant limitation, as it relies on the performance of the mobile communications network, which can suffer from performance degradation during dynamic operation. Mobile communications systems are expected to improve significantly over the next few years, as consumers demand faster download speeds and wider availability. Mobile communications coverage already covers a high percentage of the population, but this does not translate into a high percentage of a country's geography. Pockets of poor coverage, often referred to as notspots, are widespread. Many of these notspots include the transportation infrastructure. The vehicle-to-vehicle concept has made significant forward steps in the last few years. Traditionally promoted as a key component of future automotive safety applications, it is now driven primarily by increased demand for in-vehicle infotainment. The concept, which shares similarities with the Internet of Things and Mobile Ad-hoc Networks, relies on communication between road vehicles and other road agents (such as pedestrians and road infrastructure). N-RTK positioning can take advantage of this communication link to minimise its own communications-related limitations. Sharing GNSS information between local GNSS receivers enables better performance of GNSS positioning, based on the principles of differential GNSS and N-RTK positioning techniques. This advanced concept is introduced and tested in this thesis. The Pseudo VRS concept follows the protocols and format of sharing GNSS data used in N-RTK positioning. The technique utilises the latest GNSS receiver design, including multiple frequency measurements and high quality antennas.

O principal objetivo dessa dissertação foi estudar a confiabilidade de redes GNSS. Em termos metodológicos foram analisadas redes obtidas pelos seguintes métodos: redes com inclusão de linhas-base repetidas, por posicionamento relativo e pelo Posicionamento por Ponto Preciso (PPP). A rede GNSS utilizada possui seis estações pertencentes a Rede Brasileira de Monitoramento Continuo (RBMC) do Instituto Brasileiro de Geografia e Estatística (IBGE). As estações se localizam no oeste do estado de São Paulo. Para atingir o objetivo do trabalho foram estruturadas as seguintes hipóteses: a inserção de novas linhas-base em uma estrutura de rede GNSS possibilita melhorar a eficiência na detecção de outliers e aumenta a confiabilidade da rede, bem como, existe um limiar de número de linhas-base que a partir dele não se verifica mais melhora na confiabilidade. E, a outra hipótese, é que redes GNSS podem ser formadas a partir do PPP e ter parâmetros de qualidade estimados (de precisão e de confiabilidade), requisito fundamental para o uso em aplicações geodésicas. Com relação a primeira hipótese foi gerado um artigo onde é aplicado o controle de qualidade por meio da teoria de confiabilidade convencional analisando a melhora da confiabilidade a partir da inclusão de linhas-base repetidas em rede GNSS. Primeiramente foi realizado o ajustamento por mínimos quadrados da rede GNSS e calculadas as medidas de confiabilidade: o número de redundância local, a confiabilidade interna, externa e razão tendência-ruído. As linhas-base repetida na rede foram selecionadas a partir da análise de qual observação possuía menor valor de número de redundância local. O ajustamento foi realizado novamente, bem como o cálculo das medidas de confiabilidade. Esse procedimento foi repetido cinco vezes, quando se verificou a estabilização dos resultados. A segunda hipótese resultou no artigo onde foi apresentada uma metodologia de desenvolvimento de rede utilizando dados GNSS processados pelo PPP. Nesse artigo foi aplicada a teoria convencional de confiabilidade para verificar a potencialidade da metodologia apresentada. Diferentes tempos de rastreio foram empregados nos experimentos. O serviço de processamento de PPP utilizado é o fornecido pelo IBGE. A partir dos resultados foram feitas análises para verificar a aplicabilidade da metodologia descrita em rede com dados GNSS de 24, 6 e 4 horas de rastreio. Após o ajustamento, os testes global e o data snooping foram aplicados. Também é analisada a confiabilidade da rede com o objetivo de avaliar o método proposto, além de verificar a influência do tempo de rastreio nos resultados.
The main goal of the present dissertation was to study the reliability of GNSS networks. In methodological terms networks obtained from the following methods were analyzed: networks with including repeated baselines, relative positioning and Precise Point positioning (PPP). The GNSS network used has six stations belonging to the Brazilian Network of Continuous Monitoring (RBMC) of the Brazilian Institute of Geography and Statistics (IBGE), located in the west part of São Paulo. In order to achieve the objective of the study the following hypotheses were structured: the insertion of the new baselines in a GNSS network structure enables to improve the efficiency in detecting outliers and increases network reliability, just like, there is a threshold in the number of baselines in which above these number there is no improvement in the reliability. The other hypothesis is that GNSS networks can be formed from the PPP and have its quality parameters estimated (accuracy and reliability), fundamental requirement for geodetic applications. An article was generated regarding the first hypothesis where the quality control trough the conventional reliability theory was applied to analyze the quality improvement from the inclusion of repeated baselines in GNSS network. First, the least squared adjustment was made and then the reliability measures were calculated, which are: local redundancy number, the internal and external reliability and bias to noise - ratio. The repeated base lines in the network were selected by choosing the observations with lowest number of local redundancy. The adjustment and the calculation of the reliability measures were performed again. When this procedure was repeated five times, the stabilization of the results was observed. The second hypothesis resulted in an article in which a methodology of network development using GNSS data processed by the PPP was presented. In this paper the conventional reliability theory was applied to verify the presented methodology capability. Different occupation times were used in the experiments. The PPP processing service used is provided by the IBGE. From the results, analyses were performed to verify the applicability of the methodology described in network with GNSS data of 24, 6 and 4 occupation. After the adjustment, the global and data snooping tests were applied. The network reliability is also analyzed with the objective of evaluating the proposed method. In addition was verifying the influence of occupation time in the results.

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.

The subject of this thesis is digitalization of bus transportation. The input is represented by a sequence of GNSS data which are transformed to the OpenStreetMap format. Doing so, it is enriched by the information OpenStreetMap format provides and it gains its positional advantages as well. Then this thesis deals with ways by which one can detect bus lines from this general sequence of GNSS coordinates. A bus line is recognized as a repeating trajectory, which satisfies criteria derived from its expectable or defined characteristics. A few clustering solutions are proposed and tested for their performance. On the basis of this testing, there is one solution chosen as the best performing one, to be the proposed solution of this thesis. The overall output will therefore be formed by automatic mapping of bus lines with no theoretical area limit and with minimum manual intervention needed. It lays the foundations for various intelligent real-time processes to be implemented as well as allowing for infrastructure to be processed for the statistics purposes or urban planning.

The topic of the master´s thesis is to verify Acquisition Engine and Tracking Engine in the Microcore GNSS Baseband digital circuit from Honeywell. Theoretical part contains a brief introduction into the satellite position determination, basic principles of the verified blocks is given and UVM methodology is introduced. Practical part contains requirements, test cases and test procedures. The verification environment is also described. In the last part of the thesis is the verification process and it´s results.

The diploma thesis deals with a testing of the real coordinates accuracy measured in favorable and unfavorable conditions, which are determined by method GNSS RTK. The work explores the real accuracy and reliability of heights measurement with the signal noise and multipath interference occurring, caused by surrounding vegetation, buildings, power lines, and also the accuracy under optimal conditions while measuring in a meadow. Influence of day time, observation length, correction provider to internal and external precision is watched. It also examines the issues of initialization in these conditions. For this purpose was collected set of statistics containing 960 measurements on 30 points. During survey was used apparatus Trimble R4. GNSS measurements were statistically processed and evaluated and finally the results were compared with the results of Bc. Klára Kordasová, who measured the same tested points with identical methodology using apparatus from Leica company. Results of the thesis can be used in praxis.

The aim of this thesis is to test the accuracy of the heights measured by GNSS RTK with service providers CZEPOS and Trimble VRS Now. The thesis deals with precise of height measurement with the influence of surrounded obstacles, such as multipath, fading with the tall buildings, presence of high-voltage lines, limited shadow horizons at the edge of the forest, and measurement under the ideal conditions. The work also deals with the comparison of the period initialization of these monitored conditions. In the locations mentioned a network of test points was built. For measuring GNSS Leica System 1200 apparatus was used. It was measured always five times in five-second epochs and three times twenty-second epochs for each provider in five locations and thirty points during the mornings and afternoons. For independent height comparison the technical levelling was used. The outcome can be applied in practical use.

he main subject of this thesis is accuracy testing of three GNSS RTK receivers – Trimble R4, Leica 1200, Topcon GRS-1. It is an outdoor research using different correction types provided by CZEPOS and Trimble.

Global Navigation Satellite Systems (GNSS) are used in a multitude of civilian as well as security related applications. GNSS-receivers are vulnerable to different types of spoofing attacks where the receiver is ``tricked'' to provide false position and time estimates. These attacks could have serious implications; hence, it is important to develop GNSS-receivers that are robust against spoofing attacks. This thesis investigates the use of multiple GNSS-receivers that exchange information such as pseudorange or carrier phase measurements in order to perform spoofing mitigation. It has previously been shown that carrier phase measurements from multiple receivers can be used to identify spoofing signals. The focus in this thesis is on investigating the possibility of using pseudorange measurements from two receivers to perform spoofing mitigation. The use of pseudoranges to perform spoofing mitigation is compared to the use of carrier phases. The spoofing attack is assumed to be performed using a single transmission antenna. This is exploited in order to identify the spoofing signals. The spoofing mitigation algorithms compute, for a pair of receivers, either pseudorange or carrier phase double differences. A double difference is the difference of two single differences for a satellite pair, where the single difference is the difference of pseudoranges or carrier phases measured from one satellite by a pair of receivers. The spoofing mitigation involves the identification of spoofing signals based on these calculated pseudorange or carrier phase double differences. The measurements obtained from identified spoofing signals are not used by the receivers in subsequent computations of position, velocity and time, thereby mitigating the effects of the spoofing attack. The spoofing mitigation algorithms were evaluated with the help of the software-defined GNSS-receiver GNSS-SDR, which was modified to acquire and track both authentic signals and spoofed signals. The spoofing mitigation algorithms were implemented and evaluated in MATLAB. Simulated meaconing attacks were created using a Spirent GNSS simulator. The evaluations indicate that spoofing mitigation is possible using pseudorange measurements from two receivers. However, the performance of the spoofing mitigation algorithms deteriorates for short distances between the receivers when pseudorange measurements are used. The use of carrier phase measurements for spoofing mitigation appears to be more appropriate for short distances between the receivers. The use of pseudoranges enabled quite fast identification of the spoofing signals for larger distances between the receivers. Most spoofing signals are identified within 30 seconds using pseudoranges and for distances larger than 20 meter between the receivers.

This thesis deals with a processing and evaluation of GNSS data measured during the years 2001 - 2012 in geodynamical network Sněžník. The aim of the thesis is a detection of possible horizontal and vertical displacements of points in this network. The thesis also deals with comparison of results determined by only GPS and both GPS and GLONASS measurements. Graphic interpretation of displacements’ evolution during the whole monitored period is one of the results of this thesis.

This diploma thesis deals with a positioning accuracy of global positioning system GPS and satellite augmentation system EGNOS. My thesis describes the procedure for investigation of the errors in previously mentioned global navigation satellite systems according to L10 regulation and further on an elaboration is worked out in more detail far beyond the requirements of this regulation. In the practical part, an assessment of errors on a real data sample is done, the errors are measured with using a static observation, and later a discussion is carried out on the achieved results.

The aim of this thesis is to graphically interpret navigation messages from a prototype of global navigation satellite system. The resulting application is implemented in Python programming language for Windows operating system and follows requests from researchers developing the prototype. Necessary terminology together with graphical user interface programming possibilities of object-oriented language Python is a base for theoretical background of this text. Practical part of this research describes a solution for receiving generated messages from the prototype as well as their storing and filtering into useful information. Further, the design of graphical user interface of the application for prototype interactions and other tools used for its configuration are included.

Quantum Communication (QC) is referred as all those protocols that deal with the faithful transportation of quantum states. The huge technological progress in the manipulation of the single quantum particles has led to the experimental tests of some of the most intriguing features of Quantum Mechanics (QM). The gedankenexperiments that were formulated by the fathers of QM in the last century, have become real. In the words of Schrödinger: “... we never experiment with just one electron or atom or (small) molecule.” This is no longer true. We can do experiments involving single atoms or molecules and even single photons, and thus it becomes possible to demonstrate that the “ridiculous consequences” alluded to by Schrödinger are, in fact, quite real. The possibility of preparing, manipulating and detecting single photons has paved the way for the field of QC . Many interesting applications related to the security of communication start taking shape, of which the most promising is the Quantum Key Distribution ( QKD ). The crucial step towards the establishment of these quantum technologies is the extension of the communication channel up to the possibility of connecting any two points around the Earth. To this aim, two main strategies are being pursued: the development of quantum repeaters in order to interconnect several fiber-based channels, each of which have limited extension due to the inherent losses of the fiber, and the progress of satellite-to-ground and satellite-to-satellite links that take advantage of the lower losses of the free-space channel. This thesis collects my research under the supervision of Prof. Giuseppe Vallone and Prof. Paolo Villoresi on a set of topics in the quantum communication science, the main objective being the extension of the satellite-to-ground channel towards MEO and its applications on the fundamental tests of QM . Particular attention have also been dedicated to the applications of weak measurements.
Il termine Comunicazione Quantistica si riferisce a tutti quei protocolli basati sulla trasmissione fedele di stati quantistici. L’enorme progresso tecnologico nella manipolazione delle singole particelle quantistiche ha portato alla realizzazione di test sperimentali su alcune delle più stravaganti predizioni della Meccanica Quantistica. I cosiddetti esperimenti mentali (gedankenexperiments) che sono stati formulati dai padri della Meccanica Quantistica nel secolo scorso, sono ora diventati realtà. Riportando le parole di Schrödinger: “... non sperimentiamo mai solo un elettrone o atomo o (piccola) molecola". Ciò non corrisponde più alla realtà dei fatti. Possiamo realizzare esperimenti che coinvolgono singoli atomi o molecole, e persino singoli fotoni; diventa quindi possibile dimostrare che le "conseguenze ridicole" a cui alludeva Schrödinger sono, in effetti, vere. La possibilità di preparare, manipolare e rilevare singoli fotoni ha aperto la strada al campo della comunicatione quantistica. Molte applicazioni interessanti legate alla sicurezza delle comunicazioni iniziano a prendere forma, fra cui la più promettente è la distribuzione di chiave quantistica. Il passaggio cruciale verso l’utilizzo di queste tecnologie quantistiche è l’estensione del canale quantistico in modo tale da poter mettere in comunicazione, in linea di principio, due punti qualsiasi sulla superficie terrestre. A tal fine, vengono perseguite principalmente due strategie: lo sviluppo di ripetitori quantistici per connettere diversi tratti realizzati in fibra ottica, i quali hanno un’estensione limitata a causa delle perdite intrinseche della fibra, e lo sviluppo di canali quantistici intersatellitari e satellite-terra che sfruttano le minori perdite della trasmissione in aria/vuoto. Questa tesi raccoglie i risultati del mio progetto di dottorato sotto la supervisione del Prof. Giuseppe Vallone e del Prof. Paolo Villoresi, relativi alla scienza della comunicazione quantistica. L’obiettivo principale del progetto è quello di estendere la comunicazione quantistica satellitare fino alle orbite MEO come base per la realizzazione di test fondamentali sulla Meccanica Quantistica. Particolare attenzione è stata dedicata anche alle applicazioni delle misure quantistiche deboli.

Le futur système de navigation par satellites GNSS devra satisfaire les exigences définies par l'OACI en termes de précision, d'intégrité, de disponibilité et de continuité de service. Le GPS ne permet pas de satisfaire pleinement ces exigences de manière autonome. En revanche son hybridation avec les systèmes de navigation inertielle tels que l'IRS est une solution candidate. Les mesures GPS sont utilisées comme observation pour l'estimation des erreurs inertielles, les données IRS corrigées forment la solution de navigation utilisée pour le positionnement. Lors de l'indisponibilité du signal GPS, l'IRS calibrée peut assurer la continuité de la navigation avec une bonne précision. Toutefois, de nombreuses perturbations peuvent affecter le signal reçu par le récepteur GPS et conduire à une mauvaise re-calibration de l'IRS. Les interférences sont les perturbations les plus redoutées par l'aviation civile: elles peuvent affecter au même instant plusieurs canaux de poursuite du signal. Cette étude débute par une caractérisation des systèmes GPS et IRS, ainsi que de leur hybridation serrée. Deux logiciels de génération des mesures GPS et IRS, et un logiciel d'intégration par filtrage de Kalman ont été réalisés et validés. Trois algorithmes de contrôle d'intégrité du signal GPS sont ensuite analysés. Un algorithme basé seulement sur la redondance des satellites poursuivis, de type RAIM instantané, a été implanté et ses performances en terme de disponibilité ont été caractérisées. Deux algorithmes AAIM classiques qui prennent en compte l'information inertielle et offrent de meilleures performances que le RAIM sont présentés. Ils sont construits sur l'hypothèse d'une défaillance de mesure unique. Nous avons choisi de développer l'étude de l'algorithme dit du maximum de séparation appliqué à l'hybridation GPS/IRS et développé par Honeywell. Par la suite, nous nous sommes intéressés à son adaptation dans le cas où plusieurs mesures GNSS peuvent être affectées instantanément.

Les travaux menés durant cette thèse ont pour objectif d’améliorer les performances des systèmes hybrides GNSS/MEMS. Ils se décomposent en deux parties distinctes : d’une part, le développement d’un ensemble de traitement capteurs cherchant à améliorer la mesure elle-même et d’autre part, l’optimisation des algorithmes d’hybridation pour les capteurs MEMS de Thales. Le traitement capteur consiste en l’estimation de l’accélération vraie (resp. la vitesse angulaire vraie) à partir de la sortie du capteur accélérométrique (resp. gyrométrique). Ce traitement a été réalisé en deux sous-étapes : 1) La calibration qui consiste en l’identification du système non-linéaire connaissant ses entrées et ses sorties. Les relations entrant en jeu dans le modèle étant linéaires vis-à-vis des paramètres, on peut alors résoudre cette partie du problème par l’estimateur des moindres carrés (après extension du vecteur comprenant les entrées afin qu’il comporte les non linéarités). 2) L’inversion du modèle qui a pour but d’estimer les entrées du modèle connaissant ses sorties et l’estimation des paramètres effectuée durant l’étape de calibration. Après formalisation de ce problème sous forme d’un modèle dynamique, la résolution se fera à l’aide d’algorithme type filtre de Kalman ou filtre particulaire. Les algorithmes d’hybridation ont pour but de localiser un mobile dans l’espace connaissant l’information issue des MEMS ainsi que celle apportée par le GPS. Cette partie peut également se décomposer en deux sous-problèmes : 1) Lorsque que les signaux GPS sont disponibles (cas nominal), le but est d’améliorer les méthodes de navigation hybride GPS/INS existantes (EKF, UKF, PF, …). Dans notre cas, la réflexion a portée sur une modélisation à l’ordre 2 des biais des capteurs MEMS et sur la fermeture de la boucle de navigation (correction de la centrale inertielle à l’aide des erreurs issues du filtre d’hybridation). 2) Dans des scénarii défavorables (multitrajet et masquage des signaux GPS), la qualité des capteurs MEMS ne permet pas d’obtenir des résultats de navigation satisfaisants. Un algorithme basé sur un réseau de neurones a donc été développé. Durant les phases où le GPS est disponible, cet algorithme permet d’apprendre l’erreur commise par la centrale inertielle en mode survie par rapport au résultat de navigation hybride. Le réseau de neurones ainsi appris fournira alors cet élément de correction en cas de perte de l’information GPS. Ces différentes méthodes ont permis d’accroître la précision de la navigation GNSS/MEMS aussi bien dans le cas nominal que lors de pertes du signal GPS
The goal of this thesis is to improve accuracy of GNSS/MEMS integrated navigation system. Two main parts can be distinguished in this thesis: first, sensor processing can be achieved to improve measurement accuracy and then, navigation algorithm can be optimized for the specific case of MEMS sensors. Sensor processing is the estimation of real acceleration (resp. real angular rate) from the one measured by accelerometer (resp. gyrometer). This processing have been realized in two steps: 1) Calibration: identification of the non-linear system describing sensors (resolved by Least Square method). 2) Model inversion: estimation of the input of the non-linear system, i.e. acceleration and/or angular rate (resolved by Kalman filtering). Navigation algorithm have then to locate an object in space from both GNSS and MEMS data. This part have been also realized in two steps: 1) If GNSS signals are available, the goal is to improve the existing GNSS/INS navigation schemes (2nd-order bias modeling of MEMS sensors). 2) If GNSS are not available (e.g. multipath or outage), a Neural Network based algorithm have been developped, which learn the error made by the inertial platform during the unavailability of GNSS signals. These different methods have allowed to improve accuracy of GNSS/MEMS inetgrated navigation system both for nominal case and degraded case

L’oggetto di studio di questa tesi consiste nel primo approccio di sperimentazione dell’utilizzo di tecnologia UAV (Unmanned aerial vehicle, cioè velivoli senza pilota), per fotogrammetria ai fini di una valutazione di eventuali danni ad edifici, a seguito di un evento straordinario o disastri naturali. Uno degli aspetti più onerosi in termini di tempo e costi di esecuzione, nel processamento di voli fotogrammetrici per usi cartografici è dovuto alla necessità di un appoggio topografico a terra. Nella presente tesi è stata valutata la possibilità di effettuare un posizionamento di precisione della camera da presa al momento dello scatto, in modo da ridurre significativamente la necessità di Punti Fotografici di Appoggio (PFA) rilevati per via topografica a terra. In particolare si è voluto sperimentare l’impiego di stazioni totali robotiche per l’inseguimento e il posizionamento del velivolo durante le acquisizioni, in modo da simulare la presenza di ricevitori geodetici RTK installati a bordo. Al tempo stesso tale metodologia permetterebbe il posizionamento di precisione del velivolo anche in condizioni “indoor” o di scarsa ricezione dei segnali satellitari, quali ad esempio quelle riscontrabili nelle attività di volo entro canyon urbani o nel rilievo dei prospetti di edifici. Nell’ambito della tesi è stata, quindi, effettuata una analisi di un blocco fotogrammetrico in presenza del posizionamento di precisione della camera all’istante dello scatto, confrontando poi i risultati ottenuti con quelli desumibili attraverso un tradizionale appoggio topografico a terra. È stato quindi possibile valutare le potenzialità del rilievo fotogrammetrico da drone in condizioni vicine a quelle tipiche della fotogrammetria diretta. In questo caso non sono stati misurati però gli angoli di assetto della camera all’istante dello scatto, ma si è proceduto alla loro stima per via fotogrammetrica.

Soil moisture and vegetation biomass are two essential parameters from a scienti c and economical point of view. On one hand, they are key for the understanding of the hydrological and carbon cycle. On the other hand, soil moisture is essential for agricultural applications and water management, and vegetation biomass is crucial for regional development programs. Several remote sensing techniques have been used to measure these two parameters. However, retrieving soil moisture and vegetation biomass with the required accuracy, and the appropriate spatial and temporal resolutions still remains a major challenge. The use of Global Navigation Satellite Systems (GNSS) reflected signals as sources of opportunity for measuring soil moisture and vegetation biomass is assessed in this PhD Thesis. This technique, commonly known as GNSS-Reflectometry (GNSS-R), has gained increasing interest among the scienti c community during the last two decades due to its unique characteristics. Previous experimental works have already shown the capabilities of GNSS-R to sense small reflectivity changes on the surface. The use of the co- and cross-polarized reflected signals was also proposed to mitigate nuisance parameters, such as soil surface roughness, in the determination of soil moisture. However, experimental evidence of the suitability of that technique could not be demonstrated. This work analyses from a theoretical and an experimental point of view the capabilities of polarimetric observations of GNSS reflected signals for monitoring soil moisture and vegetation biomass. The Thesis is structured in four main parts. The fi rst part examines the fundamental aspects of the technique and provides a detailed review of the GNSS-R state of the art for soil moisture and vegetation monitoring. The second part deals with the scattering models from land surfaces. A comprehensive description of the formation of scattered signals from rough surfaces is provided. Simulations with current state of the art models for bare and vegetated soils were performed in order to analyze the scattering components of GNSS reflected signals. A simpli ed scattering model was also developed in order to relate in a straightforward way experimental measurements to soil bio-geophysical parameters. The third part reviews the experimental work performed within this research. The development of a GNSS-R instrument for land applications is described, together with the three experimental campaigns carried out in the frame of this PhD Thesis. The analysis of the GNSS-R and ground truth data is also discussed within this part. As predicted by models, it was observed that GNSS scattered signals from natural surfaces are a combination of a coherent and an incoherent scattering components. A data analysis technique was proposed to separate both scattering contributions. The use of polarimetric observations for the determination of soil moisture was demonstrated to be useful under most soil conditions. It was also observed that forests with high levels of biomass could be observed with GNSS reflected signals. The fourth and last part of the Thesis provides an analysis of the technology perspectives. A GNSS-R End-to-End simulator was used to determine the capabilities of the technique to observe di erent soil reflectivity conditions from a low Earth orbiting satellite. It was determined that high accuracy in the estimation of reflectivity could be achieved within reasonable on-ground resolution, as the coherent scattering component is expected to be the predominant one in a spaceborne scenario. The results obtained in this PhD Thesis show the promising potential of GNSS-R measurements for land remote sensing applications, which could represent an excellent complementary observation for a wide range of Earth Observation missions such as SMOS, SMAP, and the recently approved ESA Earth Explorer Mission Biomass.
La humedad del suelo y la biomasa de la vegetaci on son dos parametros clave desde un punto de vista tanto cient co como econ omico. Por una parte son esenciales para el estudio del ciclo del agua y del carbono. Por otra parte, la humedad del suelo es esencial para la gesti on de las cosechas y los recursos h dricos, mientras que la biomasa es un par ametro fundamental para ciertos programas de desarrollo. Varias formas de teledetección se han utilizado para la observaci on remota de estos par ametros, sin embargo, su monitorizaci on con la precisi on y resoluci on necesarias es todav a un importante reto tecnol ogico. Esta Tesis evalua la capacidad de medir humedad del suelo y biomasa de la vegetaci on con señales de Sistemas Satelitales de Posicionamiento Global (GNSS, en sus siglas en ingl es) reflejadas sobre la Tierra. La t ecnica se conoce como Reflectometr í a GNSS (GNSS-R), la cual ha ganado un creciente inter es dentro de la comunidad científ ca durante las dos ultimas d ecadas. Experimentos previos a este trabajo ya demostraron la capacidad de observar cambios en la reflectividad del terreno con GNSS-R. El uso de la componente copolar y contrapolar de la señal reflejada fue propuesto para independizar la medida de humedad del suelo de otros par ametros como la rugosidad del terreno. Sin embargo, no se pudo demostrar una evidencia experimental de la viabilidad de la t ecnica. En este trabajo se analiza desde un punto de vista te orico y experimental el uso de la informaci on polarim etrica de la señales GNSS reflejadas sobre el suelo para la determinaci on de humedad y biomasa de la vegetaci on. La Tesis se estructura en cuatro partes principales. En la primera parte se eval uan los aspectos fundamentales de la t ecnica y se da una revisi on detallada del estado del arte para la observaci on de humedad y vegetaci on. En la segunda parte se discuten los modelos de dispersi on electromagn etica sobre el suelo. Simulaciones con estos modelos fueron realizadas para analizar las componentes coherente e incoherente de la dispersi on de la señal reflejada sobre distintos tipos de terreno. Durante este trabajo se desarroll o un modelo de reflexi on simpli cado para poder relacionar de forma directa las observaciones con los par ametros geof sicos del suelo. La tercera parte describe las campañas experimentales realizadas durante este trabajo y discute el an alisis y la comparaci on de los datos GNSS-R con las mediciones in-situ. Como se predice por los modelos, se comprob o experimentalmente que la señal reflejada est a formada por una componente coherente y otra incoherente. Una t ecnica de an alisis de datos se propuso para la separacióon de estas dos contribuciones. Con los datos de las campañas experimentales se demonstr o el bene cio del uso de la informaci on polarim etrica en las señales GNSS reflejadas para la medici on de humedad del suelo, para la mayor a de las condiciones de rugosidad observadas. Tambi en se demostr o la capacidad de este tipo de observaciones para medir zonas boscosas densamente pobladas. La cuarta parte de la tesis analiza la capacidad de la t ecnica para observar cambios en la reflectividad del suelo desde un sat elite en orbita baja. Los resultados obtenidos muestran que la reflectividad del terreno podr a medirse con gran precisi on ya que la componente coherente del scattering ser a la predominante en ese tipo de escenarios. En este trabajo de doctorado se muestran la potencialidades de la t ecnica GNSS-R para observar remotamente par ametros del suelo tan importantes como la humedad del suelo y la biomasa de la vegetaci on. Este tipo de medidas pueden complementar un amplio rango de misiones de observaci on de la Tierra como SMOS, SMAP, y Biomass, esta ultima recientemente aprobada para la siguiente misi on Earth Explorer de la ESA.

This Dissertation addresses the signal acquisition problem using antenna arrays in the general framework of Global Navigation Satellite Systems (GNSS) receivers. The term GNSS classi es those navigation systems based on a constellation of satellites, which emit ranging signals useful for positioning. Although the American GPS is already available, which coexists with the renewed Russian Glonass, the forthcoming European contribution (Galileo) along with the Chinese Compass will be operative soon. Therefore, a variety of satellite constellations and signals will be available in the next years. GNSSs provide the necessary infrastructures for a myriad of applications and services that demand a robust and accurate positioning service. The positioning availability must be guaranteed all the time, specially in safety-critical and mission-critical services. Examining the threats against the service availability, it is important to take into account that all the present and the forthcoming GNSSs make use of Code Division Multiple Access (CDMA) techniques. The ranging signals are received with very low precorrelation signal-to-noise ratio (in the order of 􀀀���22 dB for a receiver operating at the Earth surface). Despite that the GNSS CDMA processing gain o ers limited protection against Radio Frequency interferences (RFI), an interference with a interference-to-signal power ratio that exceeds the processing gain can easily degrade receivers' performance or even deny completely the GNSS service, specially conventional receivers equipped with minimal or basic level of protection towards RFIs. As a consequence, RFIs (either intentional or unintentional) remain as the most important cause of performance degradation. A growing concern of this problem has appeared in recent times. Focusing our attention on the GNSS receiver, it is known that signal acquisition has the lowest sensitivity of the whole receiver operation, and, consequently, it becomes the performance bottleneck in the presence of interfering signals. A single-antenna receiver can make use of time and frequency diversity to mitigate interferences, even though the performance of these techniques is compromised in low SNR scenarios or in the presence of wideband interferences. On the other hand, antenna arrays receivers can bene t from spatial-domain processing, and thus mitigate the e ects of interfering signals. Spatial diversity has been traditionally applied to the signal tracking operation of GNSS receivers. However, initial tracking conditions depend on signal acquisition, and there are a number of scenarios in which the acquisition process can fail as stated before. Surprisingly, to the best of our knowledge, the application of antenna arrays to GNSS signal acquisition has not received much attention. This Thesis pursues a twofold objective: on the one hand, it proposes novel arraybased acquisition algorithms using a well-established statistical detection theory framework, and on the other hand demonstrates both their real-time implementation feasibility and their performance in realistic scenarios. The Dissertation starts with a brief introduction to GNSS receivers fundamentals, providing some details about the navigation signals structure and the receiver's architecture of both GPS and Galileo systems. It follows with an analysis of GNSS signal acquisition as a detection problem, using the Neyman-Pearson (NP) detection theory framework and the single-antenna acquisition signal model. The NP approach is used here to derive both the optimum detector (known as clairvoyant detector ) and the sov called Generalized Likelihood Ratio Test (GLRT) detector, which is the basis of almost all of the current state-of-the-art acquisition algorithms. Going further, a novel detector test statistic intended to jointly acquire a set of GNSS satellites is obtained, thus reducing both the acquisition time and the required computational resources. The eff ects of the front-end bandwidth in the acquisition are also taken into account. Then, the GLRT is extended to the array signal model to obtain an original detector which is able to mitigate temporally uncorrelated interferences even if the array is unstructured and moderately uncalibrated, thus becoming one of the main contributions of this Dissertation. The key statistical feature is the assumption of an arbitrary and unknown covariance noise matrix, which attempts to capture the statistical behavior of the interferences and other non-desirable signals, while exploiting the spatial dimension provided by antenna arrays. Closed form expressions for the detection and false alarm probabilities are provided. Performance and interference rejection capability are modeled and compared both to their theoretical bound. The proposed array-based acquisition algorithm is also compared to conventional acquisition techniques performed after blind null-steering beamformer approaches, such as the power minimization algorithm. Furthermore, the detector is analyzed under realistic conditions, accounting for the presence of errors in the covariance matrix estimation, residual Doppler and delay errors, and signal quantization e ects. Theoretical results are supported by Monte Carlo simulations. As another main contribution of this Dissertation, the second part of the work deals with the design and the implementation of a novel Field Programmable Gate Array (FPGA)-based GNSS real-time antenna-array receiver platform. The platform is intended to be used as a research tool tightly coupled with software de ned GNSS receivers. A complete signal reception chain including the antenna array and the multichannel phase-coherent RF front-end for the GPS L1/ Galileo E1 was designed, implemented and tested. The details of the digital processing section of the platform, such as the array signal statistics extraction modules, are also provided. The design trade-o s and the implementation complexities were carefully analyzed and taken into account. As a proof-of-concept, the problem of GNSS vulnerability to interferences was addressed using the presented platform. The array-based acquisition algorithms introduced in this Dissertation were implemented and tested under realistic conditions. The performance of the algorithms were compared to single antenna acquisition techniques, measured under strong in-band interference scenarios, including narrow/wide band interferers and communication signals. The platform was designed to demonstrate the implementation feasibility of novel array-based acquisition algorithms, leaving the rest of the receiver operations (mainly, tracking, navigation message decoding, code and phase observables, and basic Position, Velocity and Time (PVT) solution) to a Software De ned Radio (SDR) receiver running in a personal computer, processing in real-time the spatially- ltered signal sample stream coming from the platform using a Gigabit Ethernet bus data link. In the last part of this Dissertation, we close the loop by designing and implementing such software receiver. The proposed software receiver targets multi-constellation/multi-frequency architectures, pursuing the goals of e ciency, modularity, interoperability, and exibility demanded by user domains that require non-standard features, such as intermediate signals or data extraction and algorithms interchangeability. In this context, we introduce an open-source, real-time GNSS software de ned receiver (so-named GNSS-SDR) that contributes with several novel features such as the use of software design patterns and shared memory techniques to manage e ciently the data ow between receiver blocks, the use of hardware-accelerated instructions for time-consuming vector operations like carrier wipe-o and code correlation, and the availability to compile and run on multiple software platforms and hardware architectures. At this time of writing (April 2012), the receiver enjoys of a 2-dimensional Distance Root Mean Square (DRMS) error lower than 2 meters for a GPS L1 C/A scenario with 8 satellites in lock and a Horizontal Dilution Of Precision (HDOP) of 1.2.
Esta tesis aborda el problema de la adquisición de la señal usando arrays de antenas en el marco general de los receptores de Sistemas Globales de Navegación por Satélite (GNSS). El término GNSS engloba aquellos sistemas de navegación basados en una constelación de satélites que emiten señales útiles para el posicionamiento. Aunque el GPS americano ya está disponible, coexistiendo con el renovado sistema ruso GLONASS, actualmente se está realizando un gran esfuerzo para que la contribución europea (Galileo), junto con el nuevo sistema chino Compass, estén operativos en breve. Por lo tanto, una gran variedad de constelaciones de satélites y señales estarán disponibles en los próximos años. Estos sistemas proporcionan las infraestructuras necesarias para una multitud de aplicaciones y servicios que demandan un servicio de posicionamiento confiable y preciso. La disponibilidad de posicionamiento se debe garantizar en todo momento, especialmente en los servicios críticos para la seguridad de las personas y los bienes. Cuando examinamos las amenazas de la disponibilidad del servicio que ofrecen los GNSSs, es importante tener en cuenta que todos los sistemas presentes y los sistemas futuros ya planificados hacen uso de técnicas de multiplexación por división de código (CDMA). Las señales transmitidas por los satélites son recibidas con una relación señal-ruido (SNR) muy baja, medida antes de la correlación (del orden de -22 dB para un receptor ubicado en la superficie de la tierra). A pesar de que la ganancia de procesado CDMA ofrece una protección inherente contra las interferencias de radiofrecuencia (RFI), esta protección es limitada. Una interferencia con una relación de potencia de interferencia a potencia de la señal que excede la ganancia de procesado puede degradar el rendimiento de los receptores o incluso negar por completo el servicio GNSS. Este riesgo es especialmente importante en receptores convencionales equipados con un nivel mínimo o básico de protección frente las RFIs. Como consecuencia, las RFIs (ya sean intencionadas o no intencionadas), se identifican como la causa más importante de la degradación del rendimiento en GNSS. El problema esta causando una preocupación creciente en los últimos tiempos, ya que cada vez hay más servicios que dependen de los GNSSs Si centramos la atención en el receptor GNSS, es conocido que la adquisición de la señal tiene la menor sensibilidad de todas las operaciones del receptor, y, en consecuencia, se convierte en el factor limitador en la presencia de señales interferentes. Un receptor de una sola antena puede hacer uso de la diversidad en tiempo y frecuencia para mitigar las interferencias, aunque el rendimiento de estas técnicas se ve comprometido en escenarios con baja SNR o en presencia de interferencias de banda ancha. Por otro lado, los receptores basados en múltiples antenas se pueden beneficiar del procesado espacial, y por lo tanto mitigar los efectos de las señales interferentes. La diversidad espacial se ha aplicado tradicionalmente a la operación de tracking de la señal en receptores GNSS. Sin embargo, las condiciones iniciales del tracking dependen del resultado de la adquisición de la señal, y como hemos visto antes, hay un número de situaciones en las que el proceso de adquisición puede fallar. En base a nuestro grado de conocimiento, la aplicación de los arrays de antenas a la adquisición de la señal GNSS no ha recibido mucha atención, sorprendentemente. El objetivo de esta tesis doctoral es doble: por un lado, proponer nuevos algoritmos para la adquisición basados en arrays de antenas, usando como marco la teoría de la detección de señal estadística, y por otro lado, demostrar la viabilidad de su implementación y ejecución en tiempo real, así como su medir su rendimiento en escenarios realistas. La tesis comienza con una breve introducción a los fundamentos de los receptores GNSS, proporcionando algunos detalles sobre la estructura de las señales de navegación y la arquitectura del receptor aplicada a los sistemas GPS y Galileo. Continua con el análisis de la adquisición GNSS como un problema de detección, aplicando la teoría del detector Neyman-Pearson (NP) y el modelo de señal de una única antena. El marco teórico del detector NP se utiliza aquí para derivar tanto el detector óptimo (conocido como detector clarividente) como la denominada Prueba Generalizada de la Razón de Verosimilitud (en inglés, Generalized Likelihood Ratio Test (GLRT)), que forma la base de prácticamente todos los algoritmos de adquisición del estado del arte actual. Yendo más lejos, proponemos un nuevo detector diseñado para adquirir simultáneamente un conjunto de satélites, por lo tanto, obtiene una reducción del tiempo de adquisición y de los recursos computacionales necesarios en el proceso, respecto a las técnicas convencionales. El efecto del ancho de banda del receptor también se ha tenido en cuenta en los análisis. A continuación, el detector GLRT se extiende al modelo de señal de array de antenas para obtener un detector nuevo que es capaz de mitigar interferencias no correladas temporalmente, incluso utilizando arrays no estructurados y moderadamente descalibrados, convirtiéndose así en una de las principales aportaciones de esta tesis. La clave del detector es asumir una matriz de covarianza de ruido arbitraria y desconocida en el modelo de señal, que trata de captar el comportamiento estadístico de las interferencias y otras señales no deseadas, mientras que utiliza la dimensión espacial proporcionada por los arrays de antenas. Se han derivado las expresiones que modelan las probabilidades teóricas de detección y falsa alarma. El rendimiento del detector y su capacidad de rechazo a interferencias se han modelado y comparado con su límite teórico. El algoritmo propuesto también ha sido comparado con técnicas de adquisición convencionales, ejecutadas utilizando la salida de conformadores de haz que utilizan algoritmos de filtrado de interferencias, como el algoritmo de minimización de la potencia. Además, el detector se ha analizado bajo condiciones realistas, representadas con la presencia de errores en la estimación de covarianzas, errores residuales en la estimación del Doppler y el retardo de señal, y los efectos de la cuantificación. Los resultados teóricos se apoyan en simulaciones de Monte Carlo. Como otra contribución principal de esta tesis, la segunda parte del trabajo trata sobre el diseño y la implementación de una nueva plataforma para receptores GNSS en tiempo real basados en array de antenas que utiliza la tecnología de matriz programable de puertas lógicas (en ingles Field Programmable Gate Array (FPGA)). La plataforma está destinada a ser utilizada como una herramienta de investigación estrechamente acoplada con receptores GNSS definidos por software. Se ha diseñado, implementado y verificado la cadena completa de recepción, incluyendo el array de antenas y el front-end multi-canal para las señales GPS L1 y Galileo E1. El documento explica en detalle el procesado de señal que se realiza, como por ejemplo, la implementación del módulo de extracción de estadísticas de la señal. Los compromisos de diseño y las complejidades derivadas han sido cuidadosamente analizadas y tenidas en cuenta. La plataforma ha sido utilizada como prueba de concepto para solucionar el problema presentado de la vulnerabilidad del GNSS a las interferencias. Los algoritmos de adquisición introducidos en esta tesis se han implementado y probado en condiciones realistas. El rendimiento de los algoritmos se comparó con las técnicas de adquisición basadas en una sola antena. Se han realizado pruebas en escenarios que contienen interferencias dentro de la banda GNSS, incluyendo interferencias de banda estrecha y banda ancha y señales de comunicación. La plataforma fue diseñada para demostrar la viabilidad de la implementación de nuevos algoritmos de adquisición basados en array de antenas, dejando el resto de las operaciones del receptor (principalmente, los módulos de tracking, decodificación del mensaje de navegación, los observables de código y fase, y la solución básica de Posición, Velocidad y Tiempo (PVT)) a un receptor basado en el concepto de Radio Definida por Software (SDR), el cual se ejecuta en un ordenador personal. El receptor procesa en tiempo real las muestras de la señal filltradas espacialmente, transmitidas usando el bus de datos Gigabit Ethernet. En la última parte de esta Tesis, cerramos ciclo diseñando e implementando completamente este receptor basado en software. El receptor propuesto está dirigido a las arquitecturas de multi-constalación GNSS y multi-frecuencia, persiguiendo los objetivos de eficiencia, modularidad, interoperabilidad y flexibilidad demandada por los usuarios que requieren características no estándar, tales como la extracción de señales intermedias o de datos y intercambio de algoritmos. En este contexto, se presenta un receptor de código abierto que puede trabajar en tiempo real, llamado GNSS-SDR, que contribuye con varias características nuevas. Entre ellas destacan el uso de patrones de diseño de software y técnicas de memoria compartida para administrar de manera eficiente el uso de datos entre los bloques del receptor, el uso de la aceleración por hardware para las operaciones vectoriales más costosas, como la eliminación de la frecuencia Doppler y la correlación de código, y la disponibilidad para compilar y ejecutar el receptor en múltiples plataformas de software y arquitecturas de hardware. A fecha de la escritura de esta Tesis (abril de 2012), el receptor obtiene un rendimiento basado en la medida de la raíz cuadrada del error cuadrático medio en la distancia bidimensional (en inglés, 2-dimensional Distance Root Mean Square (DRMS) error) menor de 2 metros para un escenario GPS L1 C/A con 8 satélites visibles y una dilución de la precisión horizontal (en inglés, Horizontal Dilution Of Precision (HDOP)) de 1.2.

Global Navigation Satellite Systems (GNSS) signals are broadly used for positioning, navigation and timing (PNT) in many different applications and use cases, Athough different PNT technologies are available, GNSS is expected to be a key player in the derivation of positioning and timing for many future applications, including those in the context of the Internet of Things (IOT) or autonomous vehicles, since it has the imponant advantage of being open access and worldwide available. Indeed, GNSS is performing very well in mild propagation conditions, achieving position and time synchronization accuracies down to the cm and ns levels, respectively. Nevertheless, the exploitation of GNSS in harsh propagation conditions typical of urban and indoor scenarios is very challenging, resulting in position errors of up to tens or even hundreds of meters, and timing accuracies of hundreds of ns. This thesis deals with the processing of GNSS signals for positioning and timing in harsh propagation conditions. In particular, the focus is on signal processing techniques exploiting the spatial diversities present both at transmission and reception levels when multiple GNSS satellites are in view by multiple receiver antennas, which form a multiple-input multiple-output (MIMO) system. In this context, three problems or research areas open in the GNSS literature are targeted. The first research area is the unambiguous estimation of and positioning with high-order binary offset carrier (BOC) signals. The second research area is the time synchronization in indoor conditions. And the third research area is the positioning with co-located and distributed receiver antennas. In the first research area, this thesis shows that the robust unambiguous positioning with high-order BOC signals in harsh propagation conditions is possible when jointly exploiting these signals in the position domain and taking advantage of the spatial diversity introduced by arrays of antennas. The proposed estimators introduce an important benefit with respect to singlesatellite-based unambiguous techniques (operating at pseudorange level) thanks to the processing gain introduced by the MIMO-GNSS system formed. Indeed, when multiple antennas are featured by the receiver, the proposed approach allows the exploitation of high-order BOC signals even in indoor conditions, achieving positioning accuracies of few meters in propagation conditions for which BPSK(I) signals can only achieve accuracies of tens of meters. In the second research area, this thesis proposes a joint time and channel estimation approach for static indoor GNSS receivers featuring an array of antennas in order to improve the timing accuracy in indoor propagation conditions. This approach exploits both the structure of the diffuse multipath components of the indoor channel and the MIMO system formed by all the GNSS signals received via an array of antennas, Simulation results with a wideband satellite-to-indoor channel model show that the proposed timing estimators allow an important mitigation of the dominant indoor multipath conditions. Finally, in the third research area, this thesis proposes the exploitation of co-located and distributed receiver antennas for positioning in harsh propagation conditions. In order to improve the performance achieved with co-located antennas, a distributed array processing approach for collaborative GNSS-based snapshot positioning is proposed in the MIMO-GNSS framework. In this solution, one of the receivers is used as anchor and a distributed array is formed, allowing to transform the positioning problem into an angle estimation problem in order to reduce the computational burden.
La señales transmitidas por los sistemas globales de navegación por satélite (Global Navigation Satellite Systems, GNSS) son comúnmente utilizadas para posicionamiento y sincronización en muchas y diversas aplicaciones. De hecho, se espera que los sistemas GNSS sean clave en futuras aplicaciones como el Internet de las cosas o los vehículos autónomos, ya que su uso es abierto, gratuito y global. No obstante, aunque las prestaciones que se pueden obtener con las señales GNSS son excelentes en condiciones de propagación favorables, la explotación de estas señales en condiciones más adversas típicas de entornos urbanos o de interior sigue siendo un problema complejo en la actualidad, Esta tesis aborda el procesado de señales GNSS para posicionamiento y sincronización en condiciones de propagación adversas, centrándose en la explotación de la diversidad espacial disponible cuando un array de antenas es utilizado para recibir las señales de varios satélites GNSS en vista. En concreto, esta tesis tiene como objetivo tres problemas o áreas de investigación abiertas en la literatura. La primera área de investigación trata la estimación no ambigua de la posición con señales BOC (Binary Offset Carrier) de alto orden. La segunda área de investigación se centra en el problema de sincronización basado en GNSS en entornos de interior. Y la tercera área de investigación aborda el problema de posicionamiento con arrays de antenas y arrays de receptores distribuidos.