Rozprawy doktorskie na temat „GNSS Techniques”

This thesis collects the outcomes of a Ph.D. course in Telecommunications Engineering and it is focused on the study and design of possible techniques able to counteract interference signal in Global Navigation Satellite System (GNSS) systems. The subject is the jamming threat in navigation systems, that has become a very increasingly important topic in recent years, due to the wide diffusion of GNSS-based civil applications. Detection and mitigation techniques are developed in order to fight out jamming signals, tested in different scenarios and including sophisticated signals. The thesis is organized in two main parts, which deal with management of GNSS intentional counterfeit signals. The first part deals with the interference management, focusing on the intentional interfering signal. In particular, a technique for the detection and localization of the interfering signal level in the GNSS bands in frequency domain has been proposed. In addition, an effective mitigation technique which exploits the periodic characteristics of the common jamming signals reducing interfering effects at the receiver side has been introduced. Moreover, this technique has been also tested in a different and more complicated scenario resulting still effective in mitigation and cancellation of the interfering signal, without high complexity. The second part still deals with the problem of interference management, but regarding with more sophisticated signal. The attention is focused on the detection of spoofing signal, which is the most complex among the jamming signal types. Due to this highly difficulty in detect and mitigate this kind of signal, spoofing threat is considered the most dangerous. In this work, a possible techniques able to detect this sophisticated signal has been proposed, observing and exploiting jointly the outputs of several operational block measurements of the GNSS receiver operating chain.

This thesis collects the outcomes of a Ph.D. course in Telecommunications Engineering and it is focused on the study and design of possible techniques able to counteract interference signal in Global Navigation Satellite System (GNSS) systems. The subject is the jamming threat in navigation systems, that has become a very increasingly important topic in recent years, due to the wide diffusion of GNSS-based civil applications. Detection and mitigation techniques are developed in order to fight out jamming signals, tested in different scenarios and including sophisticated signals. The thesis is organized in two main parts, which deal with management of GNSS intentional counterfeit signals. The first part deals with the interference management, focusing on the intentional interfering signal. In particular, a technique for the detection and localization of the interfering signal level in the GNSS bands in frequency domain has been proposed. In addition, an effective mitigation technique which exploits the periodic characteristics of the common jamming signals reducing interfering effects at the receiver side has been introduced. Moreover, this technique has been also tested in a different and more complicated scenario resulting still effective in mitigation and cancellation of the interfering signal, without high complexity. The second part still deals with the problem of interference management, but regarding with more sophisticated signal. The attention is focused on the detection of spoofing signal, which is the most complex among the jamming signal types. Due to this highly difficulty in detect and mitigate this kind of signal, spoofing threat is considered the most dangerous. In this work, a possible techniques able to detect this sophisticated signal has been proposed, observing and exploiting jointly the outputs of several operational block measurements of the GNSS receiver operating chain.

El gran éxito y la facilidad de uso de los sistemas de navegación global por satélite (GNSSs) ha conducido a la definición de una gran cantidad de aplicaciones basadas en GNSS sin precedentes. De hecho, la tendencia muestra una nueva era de aplicaciones basadas en GNSS, las denominadas aplicaciones críticas, en las que la integridad física de los usuarios puede estar en riesgo en caso de un fallo del sistema. Un requisito importante en estas aplicaciones es la integridad, definida como una medida de la fiabilidad y confianza que se tiene en la información proporcionada por el sistema. Los primeros algoritmos de integridad fueron diseñados para trabajar en entornos aéreos, en concreto para aviación civil. Desafortunadamente, las aplicaciones críticas basadas en GNSS suelen estar asociadas con entornos terrestres y por lo tanto los algoritmos de integridad tradicionales suelen fallar. El principal motivo son los efectos locales como interferencias, multi-camino o el denominado spoofing que nos podemos encontrar en entornos terrestres. Estos efectos se asumen que están controlados en aviación civil, pero ese no es el caso en entornos terrestres. De este modo, se necesitan nuevas técnicas de integridad para aplicaciones críticas basadas en GNSS, la denominada integridad a nivel de señal (signal-level integrity). Esta tesis investiga nuevos algoritmos de detección con el objetivo de proporcionar una nueva generación de técnicas de integridad en GNSS. Para ello, se considera el campo de detección de cambios estadísticos (SCD). Este campo es de interés porque considera la dimensión temporal, requisito indispensable para aplicaciones críticas ya que una detección rápida es necesaria. Por lo tanto, la primera parte de esta tesis se ocupa del estudio del campo de SCD, incluyendo tanto la detección rápida de cambios (QCD) como la detección de cambios transitorios (TCD). Se aportan nuevas contribuciones en el campo de TCD, incluyendo la denominada solución FMA y su caracterización estadística. Además, resultados numéricos muestran la superioridad de nuestras contribuciones con respecto otras contribuciones en la literatura de TCD. Finalmente, para concluir nuestro estudio de SCD, lo comparamos con esquemas clásicos de detección bajo el mismo marco matemático. Esta comparación muestra la conveniencia de SCD cuando se trata de detecciones rápida. La principal contribución de esta tesis es la aplicación del campo de SCD a la detección de amenazas e integridad en GNSS. Para ello, primero investigamos varias propiedades de la señal GNSS que pueden ser de utilidad para la detección de amenazas locales. En segundo lugar, damos un paso adelante en el campo de detección de amenazas en GNSS proponiendo un nuevo marco basado en QCD. Sin embargo, para fines de integridad es deseable un retardo limitado y es aquí donde la teoría de TCD es interesante. Por esta razón, se considera un nuevo marco basado en TCD para la detección de multi-camino y algoritmos de integridad en GNSS, lo que conduce a la provisión de la integridad de nivel de señal. Se muestra una mejora notable por la soluciones propuestas de TCD con respecto a las soluciones actuales. En la última parte de la tesis, se validan los detectores de amenazas y el algoritmo de integridad a nivel de señal propuestos. Esto se hace utilizando seles GNSS reales capturadas en el contexto de un proyecto de investigación financiado por la Comisión Europea. Los resultados obtenidos en un escenario realista muestran la mejora de la precisión y la integridad mediante el uso de la solución propuesta con respecto a los algoritmos de integridad actuales. Además, se muestra que la solución propuesta trabaja en tiempo real, siendo por lo tanto muy atractiva para mejorar los algoritmos de integridad actuales y fácilmente implementables.
The provision of accurate positioning is becoming essential to our modern society. One of the main reasons is the great success and ease of use of Global Navigation Satellite Systems (GNSSs), which has led to an unprecedented amount of GNSS-based applications. In particular, the current trend shows that a new era of GNSS-based applications and services is emerging. These applications are the so-called critical applications, in which the physical safety of users may be in danger due to a miss-performance of the system. These applications have stringent requirements in terms of integrity, which is a measure of reliability and trust that can be placed on the information provided by the system. Unfortunately, GNSS-based critical applications are usually associated with terrestrial environments and original integrity algorithms usually fail. The main impairments are due to local effects such as interference, multipath or spoofing, which are assumed to be controlled in civil aviation but they are not in terrestrial environments. Thus, a new methodology for integrity is necessary in order to detect local effects and provide the additional level of integrity needed for GNSS-based critical applications; the so-called signal-level integrity. This thesis investigates novel detection algorithms with the aim of providing a new generation of integrity techniques in GNSS. For this purpose, the framework of Statistical Change Detection (SCD) is considered. This framework is of particular interest because its optimal criterion target the temporal dimension. This is an indispensable requirement for critical applications, in which a prompt detection is necessary. Therefore, the first part of this dissertation deals with the study of the field of SCD, including both Quickest Change Detection (QCD) and Transient Change Detection (TCD). Novel contributions are provided in the field of TCD, including the finite moving average solution and its statistical characterization. Numerical results show the superiority of our contributions. Finally, to conclude our study of SCD we compare it with classical detection schemes under the same mathematical framework. This comparison shows the appropriateness of SCD when dealing with timely detections. The main contribution of this thesis is the application of the SCD framework to threat detection and integrity in GNSS. To this end, we first investigate several properties of the received GNSS signal that may be useful for local threat detection. This leads us to move a step forward in the field of threat detection by proposing a novel QCD-based framework. Nonetheless, for integrity purposes a bounded delay is desirable, and it is here where TCD is of interest. For this reason, a novel TCD-based framework is considered for both multipath detection and integrity algorithms in GNSS, thus leading to the provision of signal-level integrity. A notable improvement is shown by the proposed TCD-based solutions considered in this thesis with respect to current solutions. In the last part of the thesis, the goal is to validate the proposed threat detectors and signal-level integrity algorithm using real GNSS signals. Real signal gathered in the context of an EC-funded research project is processed to show and validate the results of the implemented detectors. The results obtained in a realistic scenario show the improvement of the accuracy and integrity by using the proposed solution for signal-level integrity, with respect to current integrity algorithms. Furthermore, the proposed solution is shown to have real-time processing capabilities, thus being very attractive to improve current integrity algorithms and easily implementable in mass-market receivers.

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

The Global Navigation Satellite Systems (GNSS) usage is growing at a very high rate, and more applications are relying on GNSS for correct functioning. With the introduction of new GNSSs, like the European Galileo and the Chinese Beidou, in addition to the existing ones, the United States Global Positioning System (GPS) and the Russian GLONASS, the applications, accuracy of the position and usage of the signals are increasing by the day. Given that GNSS signals are received with very low power, they are prone to interference events that may reduce the usage or decrease the accuracy. From these interference, the spoofing attack is the one that has drawn major concerns in the GNSS community. A spoofing attack consist on the transmission of GNSS-like signals, with the goal of taking control of the receiver and make it compute an erroneous position and time solution. In the thesis, we focus on the design and validation of different signal processing techniques, that aim at detection and mitigation of the spoofing attack effects. These are standalone techniques, working at the receiver’s level and providing discrimination of spoofing events without the need of external hardware or communication links. Four different techniques are explored, each of them with its unique sets of advantages and disadvantages, and a unique approach to spoofing detection. For these techniques, a spoofing detection algorithm is designed and implemented, and its capabilities are validated by means of a set of datasets containing spoofing signals. The thesis focuses on two different aspects of the techniques, divided as per detection and mitigation capabilities. Both detection techniques are complementary, their joint use is explored and experimental results are shown that demonstrate the advantages. In addition, each mitigation technique is analyzed separately as they require specialized receiver architecture in order to achieve spoofing detection and mitigation. These techniques are able to decrease the effects of the spoofing attacks, to the point of removing the spoofing signal from the receiver and compute navigation solutions that are not controlled by the spoofer and lead in more accurate end results. The main contributions of this thesis are: the description of a multidimensional ratio metric test for distinction between spoofing and multipath effects; the introduction of a cross-check between automatic gain control measurements and the carrier to noise density ratio, for distinction between spoofing attacks and other interference events; the description of a novel signal processing method for detection and mitigation of spoofing effects, based on the use of linear regression algorithms; and the description of a spoofing detection algorithm based on a feedback tracking architecture.

Los sistemas de radionavegación por satélite (GNSSs) se han convertido en una herramienta indispensable de la vida diaria, ya que nos ofrecen la posibilidad de conocer de manera precisa nuestra ubicación en tiempo real y en entornos al aire libre. Desde la aparición de estos sistemas, han surgido una gran cantidad de exitosas aplicaciones de GNSS. Algunos ejemplos de estas aplicaciones son los siguientes: navegación para automóviles, rastreo de vuelos, seguimiento de actividad deportiva y juegos de realidad aumentada. Debido al éxito alcanzado por los sistemas de GNSS, un gran interés está surgiendo para extender sus servicios a entornos más complicados tales como cañones urbanos e interiores. No obstante, en estos entornos los receptores de GNSS tienen grandes dificultades para poder detectar las señales recibidas desde los satélites, las cuales son muy débiles ya que sufren una severa atenuación a causa de la presencia de obstáculos en el camino de propagación entre los satélites y el receptor. Esta tesis aborda varios problemas del procesamiento de señales de GNSS débiles como la detección en la etapa de adquisición, la determinación de la calidad de la señal y las estimaciones de la frecuencia Doppler y el tiempo de retraso. Para ello, se emplean las herramientas de detección y estimación de la señal, que se basan en teoría de probabilidad y estadística. Para poder emplear estas herramientas es necesario tener un conocimiento sobre la arquitectura y las señales que transmiten los sistemas de GNSS. Por este motivo, la primera parte de la tesis se centra en describir las principales características de dos de los sistemas de GNSS más conocidos el americano GPS y el europeo Galileo. Además, tratamos los fundamentos de los receptores y analizamos las señales que están implementadas actualmente en estos sistemas. Después, se explican los fundamentos de teoría de detección requeridos, que son el Neyman-pearson criterion, el Generalized likelihood Ratio Test y el Bayesian approach. Más adelante, se realiza una revisión del estado del arte sobre la detección de señales de GNSS. Las principales contribuciones de esta tesis ocupan lugar en la segunda parte, las cuales tratan de derivar los detectores óptimos para adquirir las señales de GNSS débiles. Hemos encontrado que el detector óptimo depende de las características de la señal trasmitida por el satélite, que puede variar dependiendo de la constelación seleccionada. Los resultados teóricos y simulados demuestran que los detectores propuestos en esta tesis superan claramente el rendimiento de los detectores utilizados en la práctica actualmente. Además, se concluye en qué condiciones es mejor utilizar un detector u otro. También, en esta tesis se aborda el problema de estimar la relación portadora a ruido de las señales de GNSS débiles. Esta relación aporta información esencial ya que se utiliza en todas las etapas de los receptores de GNSS. En esta tesis proponemos nuevos estimadores de la relación portadora a ruido, que son muy sencillos de implementar en receptores de alta sensibilidad de GNSS y ofrecen una mejora de precisión con respecto a los estimadores propuestos en la literatura. Finalmente, la última parte de la tesis se centra en las binary offset carrier (BOC) de alto orden, un tipo de señal que está implementada en el sistema Galileo. Más precisamente, esta parte está dedicada a proponer estimadores precisos de tiempo de retardo y frecuencia Doppler. Estos estimadores mejoran la precisión del método generalmente aplicado en la práctica para estimar estos parámetros.
Global Navigation Satellite Systems (GNSSs) have become an indispensable tool of daily life, since they offer us the possibility of accurately knowing our location in real time and in open-sky environments. Since the advent of these systems, a large number of successful GNSS applications have emerged. Some examples of these applications are: car navigation, flight tracking, sport activity tracking and augmented reality games. Due to the success achieved by GNSS, a great interest is emerging to extend its services to harsher environments such as urban canyons and indoor scenarios. However, in these environments GNSS receivers face great difficulties to detect the signals received from the satellites, which are very weak since they suffer from severe attenuation due to the presence of obstacles in the propagation path between satellites and the receiver. This thesis addresses several problems of processing weak GNSS signals, such as the detection at the acquisition stage, the determination of their signal quality and the time delay and Doppler frequency estimations. To do so, detection and estimation tools are used, which are based on the probability theory and statistics. In order to use these tools, it is necessary to understand the architecture and the signals that GNSSs transmit. For this reason, the first part of the thesis focuses on describing the main features of two of the best-known GNSSs, the American GPS and the European Galileo. In addition, we describe the fundamentals of the receivers and analyze the signals that are implemented in these systems. After that, we explain the required fundamentals of detection theory, namely the Neyman-pearson criterion, the Generalized Likelihood Ratio Test and the Bayesian approach. Then, a review of the state of the art in the detection of GNSS signals is carried out. The main contribution of this thesis is provided in the second part, which tackles the problem of deriving optimal detectors to acquire weak GNSS signals. We have found that the optimal detector depends on the characteristics of the signal transmitted by the satellite, which is different depending on the selected constellation. The theoretical and simulated results show that the detectors proposed in this thesis clearly outperform the detectors currently used in practice. In addition, we conclude when it is better to apply each detector. Moreover, this thesis addresses the problem of estimating the carrier-to-noise ratio of weak GNSS signals. This parameter provides essential information since it is used in all stages of GNSS receivers. In this thesis, we propose new estimators of the carrier-to-noise ratio, which are very simple to implement in high-sensitivity GNSS receivers and offer an enhanced accuracy with respect to the estimators proposed in the literature. Finally, the last part of the thesis focuses on the so-called high-order binary offset carrier (BOC) signals, a kind of signal that is implemented in the Galileo system. More precisely, this part is devoted to proposing accurate estimators of time delay and Doppler frequency. These estimators improve the accuracy of the method usually applied in practice to estimate these parameters.

Any commercially viable wireless solution onboard Smartphones should resolve the technical issues as well as preserving the limited resources available such as processing and battery. Therefore, integrating/combining the process of more than one function will free up much needed resources that can be then reused to enhance these functions further. This thesis details my innovative solutions that integrate multi-GNSS signals of specific civilian transmission from GPS, Galileo and GLONASS systems, and process them in a single RF front-end channel (detection and acquisition), ideal for GNSS software receiver onboard Smartphones. During the course of my PhD study, the focus of my work was on improving the reception and processing of localisation techniques based on signals from multi-satellite systems. I have published seven papers on new acquisition solutions for single and multi-GNSS signals based on the bandpass sampling and the compressive sensing techniques. These solutions, when applied onboard Smartphones, shall not only enhance the performance of the GNSS localisation solution but also reduce the implementation complexity (size and processing requirements) and thus save valuable processing time and battery energy. Firstly, my research has exploited the bandpass sampling technique, if being a good candidate for processing multi-signals at the same time. This portion of the work has produced three methods. The first method is designed to detect the GPS, Galileo and GLONASS-CDMA signals’ presence at an early stage before the acquisition process. This is to avoid wasting processing resources that are normally spent on chasing signals not present/non-existent. The second focuses on overcoming the ambiguity when acquiring Galileo-OS signal at a code phase resolution equal to 0.5 Chip or higher and this achieved by multiplying the received signal with the generated sub-carrier frequency. This new conversion saves doing a complete correlation chain processing when compared to conventionally used methods. The third method simplifies the joining implementation of the Galileo-OS data-pilot signal acquisition by constructing an orthogonal signal so as to acquire them in a single correlation chain, yet offering the same performance as using two correlation chains. Secondly, the compressive sensing technique is used to acquire multi-GNSS signals to achieve computation complexity reduction over correlator based methods, like Matched Filter, while still maintaining acquisition integrity. As a result of this research work, four implementation methods were produced to handle single or multi-GNSS signals. The first of these methods is designed to change dynamically the number and the size of the required channels/correlators according to the received GPS signal-power during the acquisition process. This adaptive solution offers better fix capability when the GPS receiver is located in a harsh signal environment, or it will save valuable processing/decoding time when the receiver is outdoors. The second method enhances the sensing process of the compressive sensing framework by using a deterministic orthogonal waveform such as the Hadamard matrix, which enabled us to sample the signal at the information band and reconstruct it without information loss. This experience in compressive sensing led the research to manage more reduction in terms of computational complexity and memory requirements in the third method that decomposes the dictionary matrix (representing a bank of correlators), saving more than 80% in signal acquisition process without loss of the integration between the code and frequency, irrespective of the signal strength. The decomposition is realised by removing the generated Doppler shifts from the dictionary matrix, while keeping the carrier frequency fixed for all these generated shifted satellites codes. This novelty of the decomposed dictionary implementation enabled other GNSS signals to be combined with the GPS signal without large overhead if the two, or more, signals are folded or down-converted to the same intermediate frequency. The fourth method is, therefore, implemented for the first time, a novel compressive sensing software receiver that acquires both GPS and Galileo signals simultaneously. The performance of this method is as good as that of a Matched Filter implementation performance. However, this implementation achieves a saving of 50% in processing time and produces a fine frequency for the Doppler shift at resolution within 10Hz. Our experimental results, based on actual RF captured signals and other simulation environments, have proven that all above seven implementation methods produced by this thesis retain much valuable battery energy and processing resources onboard Smartphones.

With the rapid development of digital techniques, the concept of software-defined radio (SDR) emerged which accelerates the first appearance of of the real-time GNSS software receiver at the beginning of this century, in the frame of a software receiver, this thesis mainly explores the possible improvement in parameters estimate such as frequency estimate, code delay estimate and phase estimate. In the first stage, acquisition process is focused, the theoretical mathematical expression of the cross-ambiguity function (CAF) is exploited to analyze the grid and improve the accuracy of the frequency estimate. Based on the simple equation derived from this mathematical expression of the CAF, a family of novel algorithms are proposed to refine the Doppler frequency estimate. In an ideal scenario where there is no noise and other nuisances, the frequency estimation error can be theoretically reduced to zero. On the other hand, in the presence of noise, the new algorithm almost reaches the Cramer-Rao Lower Bound (CRLB) which is derived as benchmark. For comparison, a least-square (LS) method is proposed. It is shown that the proposed solution achieves the same performance of LS, but requires a dramatically reduced computational burden. An averaging method is proposed to mitigate the influence of noise, especially when signal-to-noise ratio (SNR) is low. Finally, the influence of the grid resolution in the search space is analyzed in both time and frequency domains. In the next step, a new FLL discriminator based on energy is proposed to adapt to the changes brought by the new introduced signal modulation. This new discriminator can determine the frequency error only using the minimum period of data, it can also extend the pull-in range to nearly six times larger as the traditional arctangent discriminator. The whole derivation of the method is presented. From the comparison with traditional ATAN and another similar discriminator that is also based on energy, it is shown that the new proposed discriminator can inherit the merits of these two references, avoiding their drawbacks at the same time. Owing to the property of the new discriminator, in case of composite GNSS signals such as Galileo E1 Open Service (OS) signal, coherent combination of data and pilot channels can be adopted to improve the frequency estimate by exploiting the full transmitted power. In order to incorporate all the available information, the structure of a tracking loop with Extended Kalman Filter (EKF) is analyzed and implemented. The structure of an EKF-based software receiver is proposed including the special modules dedicated to the initialization and maintenance of the tracking loop. The EKF-based tracking architecture has been compared with a traditional one based on an FLL/PLL+DLL architecture, and the benefit of the EKF within the tracking stage has been evaluated in terms of final positioning accuracy. Further tests have been carried out to compare the Position-Velocity-Time (PVT) solution of this receiver with the one provided by two commercial receivers: a mass-market GPS module (Ublox LEA-5T) and a professional one (Septentrio PolaRx2e@). The results show that the accuracy in PVT of the software receiver can be remarkably improved if the tracking is designed with a proper EKF architecture and the performance we can achieve is even better than the one obtained by the mass market receiver, even when a simple one-shot least-squares approach is adopted for the computation of the navigation solution. Furthermore in depth, KF-based tracking loop is analyzed, a control model is derived to link the KF system and the traditional one which can provide an insight into the advantages of KF system. Finally, conclusions and main recommendations are presented.

A new, open-access Global Positioning System (GPS) signal, known as L1C, is the most recent of several modernized Global Positioning System (GPS) signals. The first launch of a GPS satellite with this signal is expected to occur within a few years. One of the interesting features of modern Global Navigation Satellite System (GNSS) signals, including GPS L1C, is the presence of data and pilot components. The pilot component is a carrier with a deterministic overlay code but no data symbols; whereas, the data component carries the navigation data symbols used in the receiver processing. A unique aspect of GPS L1C is the asymmetrical power split between the two components, 75% of the power is used for the pilot and the remaining power, or 25%, for the data. In addition, the pilot and the data components are transmitted in phase with orthogonal spreading codes. Unassisted acquisition of GNSS spread spectrum signals requires a two-dimensional search for the spreading code delay and Doppler frequency. For modern two-component GNSS signals, conventional GNSS acquisition schemes may be used on either component, correlating the received signal with either the pilot or the data spreading code. One obvious disadvantage of this approach is the wasting of power; hence, new techniques for combining, or joint acquisition of the pilot and the data components, have been proposed. In this dissertation, acquisition of GPS L1C is analyzed and receiver techniques are proposed for improving acquisition sensitivity. Optimal detectors for GPS L1C acquisition in additive white Gaussian noise are derived, based on various scenarios for a GPS receiver. Monte Carlo simulations are used to determine the performance of these optimal detectors, based on detection and false alarm probabilities. After investigating the optimal detectors for GPS L1C acquisition, various sub-optimal detectors that are more efficient to implement are thoroughly investigated and compared. Finally, schemes for joint acquisition of L1C and the legacy GPS C/A code signal are proposed and analyzed.

Las tecnologías de posicionamiento por satélite (GNSS, del inglés global navigation satellite systems) se han convertido en una herramienta indispensable en diferentes ámbitos de nuestra sociedad moderna. Algunos ejemplos de aplicaciones son el posicionamiento y la navegación en entornos terrestre, marítimo y aéreo, así como usos destinados a la agricultura, topografía o aplicaciones de sincronización precisa en sistemas de telecomunicaciones o finanzas. El módulo de tracking es una de las etapas centrales para mantener los receptores alineados con los satélites, y hasta ahora se han empleado técnicas de tracking convencionales de fácil implementación que son suficientes para operar en escenarios con unas condiciones de trabajo favorables. Sin embargo, en los últimos años, el éxito de GNSS en entornos a cielo abierto ha propiciado su expansión hacia aplicaciones en escenarios más exigentes, tales como cañones urbanos o interiores. La tendencia es dotar a los terminales móviles (smartphones) de capacidades de posicionamiento en entornos en donde se enfrentan a nuevos retos tecnológicos dados por los problemas de propagación que abundan. En este sentido, el centelleo ionosférico (ionospheric scintillation en inglés) es uno de los problemas que degradan las prestaciones de los receptores, particularmente en zonas ecuatoriales y a altas latitudes. Es un efecto que introduce rápidas variaciones aleatorias en la fase y la potencia de la señal útil, y tiene un efecto perjudicial precisamente en la etapa de tracking del receptor. El objetivo de esta tesis es diseñar y desarrollar nuevas técnicas para el tracking robusto de señales GNSS afectadas por el efecto de centelleo ionosférico. La propuesta que se presenta está basada en el uso de técnicas de filtrado de Kalman, y las contribuciones principales de esta tesis son tres. En primer lugar se estudia el efecto de centelleo ionosférico y el tracking de la dinámica del receptor a pesar de su presencia. Diseñamos un filtro de Kalman con una formulación híbrida que permite monitorizar ambas contribuciones por separado de manera robusta. Esto surge de realizar un análisis detallado del centelleo ionosférico en el que se concluye que las variaciones de fase se pueden caracterizar a través de procesos autoregresivos, los cuales se pueden tratar mediante el filtro de Kalman de manera natural. En segundo lugar se diseñan técnicas de filtrado de Kalman adaptativas que permiten ajustar su ancho de banda en función de las condiciones de centelleo, las cuales suelen ser variantes en el tiempo en la práctica. Esta parte incluye un detector de presencia de centelleo, un estimador en tiempo real de los parámetros del modelo autoregresivo, y una implementación para lidiar con las atenuaciones no lineales introducidas por el mismo centelleo. El funcionamiento de las técnicas propuestas se valida posteriormente mediante una campaña extensiva de simulaciones utilizando tanto datos sintéticos como datos reales de centelleo ionosférico, y se cuantifica la región de ganancia respecto a las técnicas convencionales. Por último se propone un innovador método para derivar expresiones para la denominada cota Bayesiana de Cramér-Rao (BCRB, del inglés Bayesian Cramér-Rao bound) que permiten caracterizar el comportamiento de los filtros de Kalman de manera cerrada. Esto supone una contribución a la literatura de gran interés práctico para diseñar filtros de Kalman para cualquier tipo de aplicación.
Global Navigation Satellite Systems (GNSS) have become an indispensable tool in different areas in our modern society for positioning purposes using radio-frequency ranging signals. Some application examples are the positioning and navigation in ground, maritime and aviation environments, as well as their use in agriculture, surveying and precise timing and synchronization in communication systems and finances. The tracking stage is one of the core tasks within a GNSS receiver to keep aligned with the satellites and, to date, most receivers equip conventional tracking techniques with ease of implementation that suffice to operate in environments with favorable working conditions. However, in the recent years, the success of GNSS in open-sky environments has led to the emergence of applications that expand toward scenarios with harsher conditions, such as urban canyons and soft-indoor environments. The trend is to provide user mobile terminals such as smartphones with positioning capabilities in scenarios where receivers face new technological challenges owing to the abounding propagation impairments. In this sense, the so-called ionospheric scintillation is one of the issues degrading the performance of GNSS receivers, particularly in equatorial regions and at high latitudes. It introduces rapid carrier phase and signal power variations, and has a detrimental effect particularly onto the tracking stage. The objective of this thesis is to design and develop new techniques for the robust tracking of GNSS signals affected by ionospheric scintillation disturbances. The presented approach is based on the use of Kalman filtering techniques, and the main contributions of the thesis are three. First, the analysis of ionospheric scintillation and the tracking of carrier dynamics despite the presence of the former. We design a Kalman filter with a hybrid formulation that allows the robust monitoring of both contributions separately. This arises from carrying out a detailed analysis of ionospheric scintillation which concludes that scintillation phase variations can be characterized through autoregressive processes, and thus be dealt with within the Kalman filter in a natural manner. Second, the design of adaptive Kalman filter-based techniques that allow self-adjusting their loop bandwidth to the actual scintillation conditions, which are rather time-varying in practice. This part includes a scintillation detector, a real-time estimator of the autoregressive model parameters, and an implementation to address the problem of non-linear signal amplitude attenuation introduced by scintillation itself. The goodness of the proposed techniques is later validated by carrying out an extensive simulation campaign using both synthetic data and real scintillation time series, and the outperformance region with respect to conventional tracking techniques is quantified. Third, a novel method for the derivation of expressions for the termed Bayesian Cramér-Rao bound (BCRB), which allow characterizing the behavior of Kalman filters in a closed-form manner, thus becoming a contribution to the literature of practical usefulness to design Kalman filters for any kind of application.

Navigation is defined as the science of getting a craft or person from one place to another. The development of radio in the past century brought fort new navigation aids that enabled users, or rather their receivers, to compute their position with the help of signals from one or more radio-navigation system . The U.S. Global Positioning System (GPS) was envisioned as a satellite system for three-dimensional position and velocity determination fulfilling the following key attributes: global coverage, continuous/all weather operation, ability to serve high-dynamic platforms, and high accuracy. It represents the fruition of several technologies, which matured and came together in the second half of the 20th century. In particular, stable space-born platforms, ultra-stable atomic frequency standards, spread spectrum signaling, and microelectronics are the key developments in the realization and success of GPS. While GPS was under development, the Soviet Union undertook to develop a similar system called GLObalnaya NAvigatsionnaya Sputnikovaya Sistema (GLONASS). Both GLONASS and GPS were designed primarily for the military, but have transitioned in the past decades towards providing civilian and Safety-of-Life services as well. Other Global Navigation Satellite Systems (GNSS) are now being developed and deployed by governments, international consortia, and commercial interests. Among these are the European system Galileo and the Chinese system Beidou. Other regional systems are the Japanese Quasi-Zenith Satellite System and the Indian Gagan. GNSS have become a crucial component in countless modern systems, e.g. in telecommunication, navigation, remote sensing, precise agriculture, aviation and timing. One of the main threats to the reliable and safe operation of GNSS are the variable propagation conditions encountered by GNSS signals as they pass through the upper atmosphere of the Earth. In particular, irregular concentration of electrons in the ionosphere induce fast fluctuations in the amplitude and phase of GNSS signals called scintillations. The latter can greatly degrade the performance of GNSS receivers, with consequent economical impacts on service providers and users of high performance applications. New GNSS navigation signals and codes are expected to help mitigate such effects, although to what degree is still unknown. Furthermore, these new technologies will only come on line incrementally over the next decade as new GNSS satellites become operational. In the meantime, GPS users who need high performance navigation solution, e.g., offshore drilling companies, might be forced to postpone operations for which precision position knowledge is required until the ionospheric disturbances are over. For this reason continuous monitoring of scintillations has become a priority in order to try to predict its occurrence. Indeed, it is a growing scientific and industrial activity. However, Radio Frequency (RF) Interference from other telecommunication systems might threaten the monitoring of scintillation activity. Currently, the majority of the GNSS based application are highly exposed to unintentional or intentional interference issues. The extremely weak power of the GNSS signals, which is actually completely buried in the noise floor at the user receiver antenna level, puts interference among the external error contributions that most degrade GNSS performance. It is then of interest to study the effects these external systems may have on the estimation of ionosphere activity with GNSS. In this dissertation, we investigate the effect of propagation issues in GNSS, focusing on scintillations, interference and the joint effect of the two phenomena.

The Global Navigation Satellite Systems (GNSS) applications are growing and more pervasive in the modern society. The presence of multi-constellation GNSS receivers able to use signals coming from different systems like the american Global Positioning System (GPS), the european Galileo, the Chinese Beidou and the russian GLONASS, permits to have more accuracy in position solution. All the receivers provide always more reliable solution but it is important to monitor the possible presence of problems in the position computation. These problems could be caused by the presence of impairments given by unintentional sources like multipath generated by the environment or intentional sources like spoofing attacks. In this thesis we focus on design algorithms at signal processing level used to assist Integrity operations in terms of Fault Detection and Exclusion (FDE). These are standalone algorithms all implemented in a software receiver without using external information. The first step was the creation of a detector for correlation distortion due to the multipath with his limitations. Once the detection is performed a quality index for the signal is computed and a decision about the exclusion of a specific Satellite Vehicle (SV) is taken. The exclusion could be not feasible so an alternative approach could be the inflation of the variance of the error models used in the position computation. The quality signal can be even used for spoofinng applications and a novel mitigation technique is developed and presented. In addition, the mitigation of the multipath can be reached at pseudoranges level by using new method to compute the position solution. The main contributions of this thesis are: the development of a multipath, or more in general, impairments detector at signal processing level; the creation of an index to measure the quality of a signal based on the detector’s output; the description of a novel signal processing method for detection and mitigation of spoofing effects, based on the use of linear regression algorithms; An alternative method to compute the Position Velocity and Time (PVT) solution by using different well known algorithms in order to mitigate the effects of the multipath on the position domain.

Aquesta tesi gira al voltant del disseny de receptors per a sistemes globals de navegació per satèl·lit (Global Navigation Satellite Systems, GNSS). El terme GNSS fa referència a tots aquells sistemes de navegació basats en una constel·lació de satèl·lits que emeten senyals de navegació útils per a posicionament. El més popular és l'americà GPS, emprat globalment. Els esforços d'Europa per a tenir un sistema similar veuran el seu fruit en un futur proper, el sistema s'anomena Galileo. Altres sistemes globals i regionals existeixen dissenyats per al mateix objectiu: calcular la posició dels receptors. Inicialment la tesi presenta l'estat de l'art en GNSS, a nivell de l'estructura dels actuals senyals de navegació i pel que fa a l'arquitectura dels receptors.

El disseny d'un receptor per a GNSS consta d'un seguit de blocs funcionals. Començant per l'antena receptora fins al càlcul final de la posició del receptor, el disseny proporciona una gran motivació per a la recerca en diversos àmbits. Tot i que la cadena de Radiofreqüència del receptor també és comentada a la tesis, l'objectiu principal de la recerca realitzada recau en els algorismes de processament de senyal emprats un cop realitzada la digitalització del senyal rebut. En un receptor per a GNSS, aquests algorismes es poden dividir en dues classes: els de sincronisme i els de posicionament. Aquesta classificació correspon als dos grans processos que típicament realitza el receptor. Primer, s'estima la distancia relativa entre el receptor i el conjunt de satèl·lits visibles. Aquestes distancies es calculen estimant el retard patit pel senyal des de que és emès pel corresponent satèl·lit fins que és rebut pel receptor. De l'estimació i seguiment del retard se n'encarrega l'algorisme de sincronisme. Un cop calculades la distancies relatives als satèl·lits, multiplicant per la velocitat de la llum el retards estimats, l'algorisme de posicionament pot operar. El posicionament es realitza típicament pel procés de trilateralització: intersecció del conjunt d'esferes centrades als satèl·lits visibles i de radi les distancies estimades relatives al receptor GNSS. Així doncs, sincronització i posicionament es realitzen de forma seqüencial i ininterrompudament. La tesi fa contribucions a ambdues parts, com explicita el subtítol del document.

Per una banda, la tesi investiga l'ús del filtrat Bayesià en el seguiment dels paràmetres de sincronisme (retards, desviaments Doppler i phases de portadora) del senyal rebut. Una de les fonts de degradació de la precisió en receptors GNSS és la presència de repliques del senyal directe, degudes a rebots en obstacles propers. És per això que els algorismes proposats en aquesta part de la tesi tenen com a objectiu la mitigació de l'efecte multicamí. La dissertació realitza una introducció dels fonaments teòrics del filtrat Bayesià, incloent un recull dels algorismes més populars. En particular, el Filtrat de Partícules (Particle Filter, PF) s'estudia com una de les alternatives més interessants actualment per a enfrontar-se a sistemes no-lineals i/o no-Gaussians. Els PF són mètodes basats en el mètode de Monte Carlo que realitzen una caracterització discreta de la funció de probabilitat a posteriori del sistema. Al contrari d'altres mètodes basats en simulacions, els PF tenen resultats de convergència que els fan especialment atractius en casos on la solució òptima no es pot trobar. En aquest sentit es proposa un PF que incorpora un seguit de característiques que el fan assolir millors prestacions i robustesa que altres algorismes, amb un nombre de partícules reduït. Per una banda, es fa un seguiment dels estats lineals del sistema mitjançant un Filtre de Kalman (KF), procediment conegut com a Rao-Blackwellization. Aquest fet provoca que la variància de les partícules decreixi i que un menor nombre d'elles siguin necessàries per a assolir una certa precisió en l'estimació de la distribució a posteriori. D'altra banda, un dels punts crítics en el disseny de PF és el disseny d'una funció d'importància (emprada per a generar les partícules) similar a l'òptima, que resulta ésser el posterior. Aquesta funció òptima no està disponible en general. En aquesta tesi, es proposa una aproximació de la funció d'importància òptima basada en el mètode de Laplace. Paral·lelament es proposen algorismes com l'Extended Kalman Filter (EKF) i l'Unscented Kalman Filter (UKF), comparant-los amb el PF proposat mitjançant simulacions numèriques.

Per altra banda, la presentació d'un nou enfocament al problema del posicionament és una de les aportacions originals de la tesi. Si habitualment els receptors operen en dos passos (sincronització i posicionament), la proposta de la tesi rau en l'Estimació Directa de la Posició (Direct Position Estimation, DPE) a partir del senyal digital. Tenint en compte la novetat del mètode, es proporcionen motivacions qualitatives i quantitatives per a l'ús de DPE enfront al mètode convencional de posicionament. Se n'ha estudiat l'estimador de màxima versemblança (Maximum Likelihood, ML) i un algorisme per a la seva implementació pràctica basat en l'algorisme Accelerated Random Search (ARS). Els resultats de les simulacions numèriques mostren la robustesa de DPE a escenaris on el mètode convencional es veu degradat, com per exemple el cas d'escenaris rics en multicamí. Una de les reflexions fruit dels resultats és que l'ús conjunt dels senyals provinents dels satèl·lits visibles proporciona millores en l'estimació de la posició, doncs cada senyal està afectada per un canal de propagació independent. La tesi també presenta l'extensió de DPE dins el marc Bayesià: Bayesian DPE (BDPE). BDPE manté la filosofia de DPE, tot incloent-hi possibles fonts d'informació a priori referents al moviment del receptor. Es comenten algunes de les opcions com l'ús de sistemes de navegació inercials o la inclusió d'informació atmosfèrica. Tot i així, cal tenir en compte que la llista només està limitada per la imaginació i l'aplicació concreta on el marc BDPE s'implementi.

Finalment, la tesi els límits teòrics en la precisió dels receptors GNSS. Alguns d'aquests límits teòrics eren ja coneguts, d'altres veuen ara la llum. El límit de Cramér-Rao (Cramér-Rao Bound, CRB) ens prediu la mínima variància que es pot obtenir en estimar un paràmetre mitjançant un estimador no esbiaixat. La tesi recorda el CRB dels paràmetres de sincronisme, resultat ja conegut. Una de les aportacions és la derivació del CRB de l'estimador de la posició pel cas convencional i seguint la metodologia DPE. Aquests resultats proporcionen una comparativa asimptòtica dels dos procediments pel posicionament de receptors GNSS. D'aquesta manera, el CRB de sincronisme pel cas Bayesià (Posterior Cramér-Rao Bound, PCRB) es presenta, com a límit teòric dels filtres Bayesians proposats en la tesi.
This dissertation deals with the design of satellite-based navigation receivers. The term Global Navigation Satellite Systems (GNSS) refers to those navigation systems based on a constellation of satellites, which emit ranging signals useful for positioning. Although the american GPS is probably the most popular, the european contribution (Galileo) will be operative soon. Other global and regional systems exist, all with the same objective: aid user's positioning. Initially, the thesis provides the state-of-the-art in GNSS: navigation signals structure and receiver architecture. The design of a GNSS receiver consists of a number of functional blocks. From the antenna to the final position calculation, the design poses challenges in many research areas. Although the Radio Frequency chain of the receiver is commented in the thesis, the main objective of the dissertation is on the signal processing algorithms applied after signal digitation. These algorithms can be divided into two: synchronization and positioning. This classification corresponds to the two main processes typically performed by a GNSS receiver. First, the relative distance between the receiver and the set of visible satellites is estimated. These distances are calculated after estimating the delay suffered by the signal traveling from its emission at the corresponding satellite to its reception at the receiver's antenna. Estimation and tracking of these parameters is performed by the synchronization algorithm. After the relative distances to the satellites are estimated, the positioning algorithm starts its operation. Positioning is typically performed by a process referred to as trilateration: intersection of a set of spheres centered at the visible satellites and with radii the corresponding relative distances. Therefore, synchronization and positioning are processes performed sequentially and in parallel. The thesis contributes to both topics, as expressed by the subtitle of the dissertation.

On the one hand, the thesis delves into the use of Bayesian filtering for the tracking of synchronization parameters (time-delays, Doppler-shifts and carrier-phases) of the received signal. One of the main sources of error in high precision GNSS receivers is the presence of multipath replicas apart from the line-of-sight signal (LOSS). Wherefore the algorithms proposed in this part of the thesis aim at mitigating the multipath effect on synchronization estimates. The dissertation provides an introduction to the basics of Bayesian filtering, including a compendium of the most popular algorithms. Particularly, Particle Filters (PF) are studied as one of the promising alternatives to deal with nonlinear/nonGaussian systems. PF are a set of simulation-based algorithms, based on Monte-Carlo methods. PF provide a discrete characterization of the posterior distribution of the system. Conversely to other simulation-based methods, PF are supported by convergence results which make them attractive in cases where the optimal solution cannot be analytically found. In that vein, a PF that incorporates a set of features to enhance its performance and robustness with a reduced number of particles is proposed. First, the linear part of the system is optimally handled by a Kalman Filter (KF), procedure referred to as Rao-Blackwellization. The latter causes a reduction on the variance of the particles and, thus, a reduction on the number of required particles to attain a given accuracy when characterizing the posterior distribution. A second feature is the design of an importance density function (from which particles are generated) close to the optimal, not available in general. The selection of this function is typically a key issue in PF designs. The dissertation proposes an approximation of the optimal importance function using Laplace's method. In parallel, Extended Kalman Filter (EKF) and Unscented Kalman Filter (UKF) algorithms are considered, comparing these algorithms with the proposed PF by computer simulations.

On the other hand, a novel point of view in the positioning problem constitutes one of the original contributions of the thesis. Whereas conventional receivers operate in a two-steps procedure (synchronization and positioning), the proposal of the thesis is a Direct Position Estimation (DPE) from the digitized signal. Considering the novelty of the approach, the dissertation provides both qualitative and quantitative motivations for the use of DPE instead of the conventional two-steps approach. DPE is studied following the Maximum Likelihood (ML) principle and an algorithm based on the Accelerated Random Search (ARS) is considered for a practical implementation of the derived estimator. Computer simulation results carried show the robustness of DPE in scenarios where the conventional approach fails, for instance in multipath-rich scenarios. One of the conclusions of the thesis is that joint processing of satellite's signals provides enhance positioning performances, due to the independent propagation channels between satellite links. The dissertation also presents the extension of DPE to the Bayesian framework: Bayesian DPE (BDPE). BDPE maintains DPE's philosophy, including the possibility of accounting for sources of side/prior information. Some examples are given, such as the use of Inertial Measurement Systems and atmospheric models. Nevertheless, we have to keep in mind that the list is only limited by imagination and the particular applications were BDPE is implemented. Finally, the dissertation studied the theoretical lower bounds of accuracy of GNSS receivers. Some of those limits were already known, others see the light as a result of the research reported in the dissertation. The Cramér-Rao Bound (CRB) is the theoretical lower bound of accuracy of any unbiased estimator of a parameter. The dissertation recalls the CRB of synchronization parameters, result already known. A novel contribution of
the thesis is the derivation of the CRB of the position estimator for either conventional and DPE approaches. These results provide an asymptotical comparison of both GNSS positioning approaches. Similarly, the CRB of synchronization parameters for the Bayesian case (Posterior Cramér-Rao Bound, PCRB) is given, used as a fundamental limit of the Bayesian filters proposed in the thesis.

El inminente lanzamiento de la misión Soil Moisture and Ocean Salinity (SMOS, humedad del terreno y salinidad del mar) de la Agencia Espacial Europea (ESA) permitirá la recuperación sistemática y a escala global de la salinidad superficial del mar, con el consecuente beneficio tanto para oceanografía como para la climatología. No obstante, primero es necesario modelar y compensar adecuadamente el impacto de la rugosidad del mar en las medidas radiométricas, a fin de reducir el error inducido en la SSS recuperada y obtener valores significativos. En los últimos años el uso de señales reflejadas de sistemas de navegación global por satélite (GNSS-R) ha mostrado su potencial para obtener parámetros geofísicos, inicialmente altimetría y más recientemente estado del mar. La metodología más comúnmente empleada era comparar la forma de onda medida (correlación para diferentes retardos) con la modelada. Uno de los objetivos que motivó la presentación del proyecto Passive Advance Unit (PAU, Unidad Pasiva Avanzada) a la fundación EURYI fue el estudiar la relación directa entre la temperatura de brillo radiométrica y algunos observables GNSS-R por definir. Para ello se obtendrían medidas colocadas con una radiómetro en banda L y un reflectómetro GPS, y se procedería a la recuperación completa de la salinidad con ayuda de un radiómetro de infrarrojos adicional. El proyecto PAU se ha desarrollado dentro del Grupo de Teledetección Pasiva del Remote Sensing Lab, en el departamento de Teoría de la Señal y Comunicaciones del la Universitat Politècnica de Catalunya.

La presente tesis doctoral describe el trabajo desarrollado entre 2004 y 2008 en aspectos tanto teóricos como de implementación hardware dentro del campo de la reflectometría GNSS. Más concretamente, el capítulo 1 introduce brevemente la recuperación de SSS mediante teledetección y describe el proyecto PAU. Por su parte, el capítulo 2 esta dedicado a los fundamentos de la reflectometría GNSS, mientras que el capítulo 3 hace hincapié en el observable GNSS-R elegido, el delay-Doppler Map (DDM) completo. Así, se presenta una nueva y eficiente aproximación a la simulación de DDMs junto a las clásicas expresiones de Zavorotny-Voronovich para la señal GNSS dispersada. Posteriormente se estudia la parametrización de DDMs en el capítulo 4, donde algunos de los parámetros derivados son subsecuentemente relacionados con el estado del mar. Por otro lado, en el capítulo 5 se ofrece una descripción pormenorizada del diseño, implementación y validación del un reflectómetro capaz de generar DDMs en tiempo real basado en un dispositivo FGPA, mientras que en el capítulo 6 se presenta la campaña de medidas ALBATROSS 08, donde se utilizó el instrumento PAU-GNSS/R desarrollado para verificar la idoneidad de los parámetros GNSS-R propuestos para describir el estado del mar. Finalmente, las conclusiones y el trabajo futuro se consignan en el capítulo 7.
With the upcoming launch of the ESA's Soil Moisture and Ocean Salinity (SMOS) mission, the retrieval of Sea Surface Salinity (SSS) from space will benefit both the oceanography and climatology communities. However, the impact of the sea roughness on the radiometric measurement has to be accurately modeled and accounted for first, so that to reduce the induced error on the retrieved SSS and yield meaningful values. In recent years the use of reflected Global Navigation Satellite System Signals (GNSS-R) has shown its potential to retrieve geophysical parameters, mainly altimetry and more recently sea state. The approach consisted of comparing the measured waveform (correlation at different delays) with a modeled one. One of the rationales that motivated the submission of the Passive Advanced Unit (PAU) project to the EURYI foundation was to study the direct relationship between the radiometric brightness temperature and some to-be-defined GNSS-R observables by obtaining co-located measurements with an L-band radiometer and a GPS reflectometer, and perform the actual SSS retrieval with the aid of an infrared radiometer. The PAU project has been developed by the Passive Remote Sensing Group of the Remote Sensing Lab, at the Department of Signal Theory and Communications of the Universitat Politènica de Catalunya.

The present PhD dissertation describes the work undertaken between 2004 and 2008 in both theoretical and hardware issues within the field of GNSS-R reflectometry. More specifically, in chapter 1 a brief introduction to SSS retrieval is given along with the description of the PAU project. Chapter 2 is devoted to the basics of GNSS reflectometry, whereas chapter 3 is focused into the simulation of the chosen GNSS-R observable, the whole Delay-Doppler Map (DDM). A new approach to DDM simulation is introduced along with the review of the classical implementation of the Zavorotny-Voronovich expressions for the reflected GNSS signal. After that, the parameterization of the DDMs is studied in chapter 4, where some of the derived parameters are to be linked to the actual sea state. Chapter 5 offers a detailed description of the design, implementation and validation of a real- time FPGA-based DDM reflectometer, whereas chapter 6 describes the ALBATROSS 08 measurement campaign, where the developed PAU-GNSS/R was tested. The conclusions and the future work are listed in chapter 7.

In Intelligent Transport Systems (ITS), specifically in autonomous driving operations, accurate vehicle localization is essential for safe operations. The localization accuracy depends on both position and positioning error estimates. Technologies aiming to improve positioning error estimation are required and are currently being researched. This project has investigated machine learning algorithms applied to positioning error estimation by assessing relevant information obtained from a GNSS receiver and adding environmental information  coming from a camera mounted on a radio controlled vehicle testing platform. The research was done in two stages. The first stage consists of the machine learning algorithms training and testing on existing GNSS data coming from Waysure´s data base from tests ran in 2016, which did not consider the environment surrounding the GNSS receiver used during the tests. The second stage consists of the machine learning algorithms training and testing on GNSS data coming from new test runs carried on May 2019, which include the environment surrounding the GNSS receiver used. The results of both stages are compared. The relevant features are obtained as a result of the machine learning decision trees algorithm and are presented. This report concludes that there is no statistical evidence indicating that the tested environmental input from the camera could improve positioning error estimation accuracy with the built machine learning models.
Inom Intelligenta transportsystem (ITS), specifikt för självkörande fordon, så är en exakt fordonspositionering en nödvändighet för ökad trafiksäkerhet. Positionsnoggrannheten beror på estimering av både positionen samt positionsfelet. Olika tekniker och tillämpningar som siktar på att förbättra positionsfeluppskattningen behövs, vilket det nu forskas kring. Denna uppsats undersöker olika maskininlärningsalgoritmer inriktade på estimering av positionsfel. Algoritmerna utvärderar relevant information från en GNSS-mottagare, samt information från en kamera om den kringliggande miljön. En GNSS-mottagare och kamera monterades på en radiostyrd mobil testplattform för insamling av data.  Examensarbetet består av två delar. Första delen innehåller träning och testning av valda maskininlärningsalgoritmer med GNSS-data tillhandahållen av Waysure från tester gjorda under 2016. Denna data inkluderar ingen information från den omkringliggande miljön runt GNSS-mottagaren. Andra delen består av träning och testning av valda maskininlärningsalgoritmer på GNSS-data som kommer från nya tester gjorda under maj 2019, vilka inkluderar miljöinformation runt GNSS-mottagaren. Resultaten från båda delar analyseras. De viktigaste egenskaper som erhålls från en trädbaserad modell, algoritmens beslutsträd, presenteras. Slutsatsen från denna rapport är att det inte går att statistiskt säkerställa att inkludering av information från den omkringliggande miljön från en kamera förbättrar noggrannheten vid estimering av positionsfelet med de valda maskininlärningsmodellerna.

Les organismes de standardisation de l'aviation civile (OACI, RTCA, EUROCAE) mènent actuellement des études sur l'utilisation des systèmes de navigation par satellite fournissant une couverture globale, tels GPS ou Galileo, en tant que moyen de navigation embarque unique. L'OACI regroupe l’ensemble de ces systèmes de navigation satellitaires et de leurs systèmes d’augmentation sous la dénomination GNSS. Pour des raisons de sécurité évidentes, les performances des récepteurs GNSS embarques doivent garantir des minima propres à chaque phase de vol et chaque procédure d’approche. Ces exigences de performances sont spécifiées dans les spécifications des performances opérationnelles minimales, documents publiés (ou en cours de publication) par les autorités sus-citées. Le GNSS est en passe d'être amélioré par la diffusion de nouveaux signaux. Parmi eux, les signaux Galileo E5 et GPS L5 devraient permettre l'amélioration du service de navigation par satellite. Cependant, ces signaux seront émis dans une bande déjà utilisée par des systèmes radiofréquences. Il est donc primordial de s'assurer de la possibilité de la coexistence de ces systèmes. Plus particulièrement, il est nécessaire de s'assurer que les récepteurs GNSS embarqués utilisant les signaux sus-cités respectent les exigences de performance. La menace principale au bon fonctionnement des récepteurs GNSS utilisant les signaux E5/L5 a été identifiée comme étant les émissions pulsées des systèmes DME, TACAN, JTIDS et MIDS. Sans moyen de lutte contre ces interférences, les performances des récepteurs GNSS embarqués peuvent être dégradées de manières significatives, empêchant les récepteurs de se conformer aux exigences de sécurité sur l’ensemble du monde, et plus particulièrement sur des ≪ points chauds ≫ ayant été identifies comme les lieux ou l'impact de ces interférences sur lesdits récepteurs est la plus importante. Deux techniques de réduction d’interférences ont été proposées pour lutter contre cette menace, le Blanker temporel et le Frequency Domain Interference Suppressor (FDIS). Le Blanker temporel est une technique de traitement du signal consistant en un test de puissance, relativement simple a mettre en oeuvre et dont la capacité de rejection des interférences a été démontrée suffisante pour assurer les exigences de l’aviation civile dans toutes les phases de vols sur l’ensemble du monde pour les récepteurs GPS et Galileo utilisant respectivement les signaux L5 et E5, dans [Bastide, 2004]. Toutefois, cette technique permet de respecter les exigences avec une marge faible, dans les environnements les plus riches en interférences, autrement dit les « points chauds ». En revanche, le FDIS est une technique de lutte contre les interférences pulsées beaucoup plus exigeante en termes de ressources, puisque basée sur l’excision des interférences dans le domaine fréquentiel. Cependant, elle permet une amélioration sensible des performances du récepteur, et donc une augmentation des marges vis-à-vis des exigences fixées par l'Aviation Civile. Le FDIS a été propose comme une alternative au blanker temporel, mais ses problèmes d'implantation et ses performances n’ont été que peu étudies. La dissertation a pour but de participer a cette étude de performance afin de valider son intérêt. Le plan de la thèse est le suivant : tout d'abord, les signaux de navigation, Galileo E5a/E5b et GPS L5, les interférences pulsées, ainsi que leur impact sur les performances des récepteurs GNSS sont présentes. Ensuite, une description des techniques de suppression d’interférences (blanker temporel, FDIS), leurs caractéristiques théoriques et les dégradations de performances subies par un récepteur GNSS utilisant ces techniques en présence d'interférences pulsées sont présentées. Les conditions dans lesquelles ont été obtenues ces performances, c’est à dire le choix des scenarios joues ainsi que des paramètres observés, ou encore les outils de simulation sont décrits. La conclusion résume l’analyse des performances, les compare aux exigences de l’Aviation Civile, et propose des recommandations pour la conception de récepteurs GNSS embarqués
Civil Aviation standardisation bodies (ICAO, RTCA, EUROCAE) are currently investigating the use of the Global Navigation Satellite System (GNSS) as a stand-alone navigation solution for civil aircraft. For obvious safety reasons, on-board GNSS receivers must guarantee minimum performance requirements in given phases of flights. These requirements, dependent upon the system and signals used, are stated in the Minimum Operational Performance Specification (MOPS), published (or being published) by the corresponding authorities. With that respect, the future use of Galileo E5 and GPS L5 bands has raised, among others, interference issues. Indeed, pre-existent RF systems emit in this band, thus interfering with the E5/L5 signals. The main threat was identified as being DME/TACAN ground beacons pulsed emissions. Without any mitigation capability, these systems can disturb the proper operation of on-board GNSS receivers, preventing them from complying with safety requirements. Two Interference Mitigation Techniques (IMT) have been proposed to fight this threat, the Temporal Blanker and the Frequency Domain Interference Suppressor (FDIS). The Temporal Blanker technique offers a fairly simple implementation and was shown to provide enough benefits to ensure that the specified requirements were met in all phases of flight for a GPS L5 or Galileo E5 receiver. However, it was also demonstrated that the resulting performances were meeting the requirements by only a small margin on the worst DME/TACAN interference environment that can be found in Europe and USA, so called the European and USA “hot spots”. In contrast, the FDIS is a more demanding mitigation technique against pulsed interference in terms of required resources but improves the performances of the receiver, thus allowing larger margins with respect to the civil aviation requirements. The core of the study is the analysis of the performances of GNSS receivers using FDIS as IMT. The dissertation architecture is the following: first, the navigation signals, Galileo E5a/E5b and GPS L5, as long as the interferences that constitute a threat for GNSS navigation and their impact on GNSS receivers operations are presented. Then, a description of the studied IMTs (Temporal Blanker, FDIS), their theoretical characteristics and the theoretical derivations of the post-correlation C/N0 degradation suffered by a receiver using these techniques in presence of pulsed interference are depicted. Afterwards, all the results obtained concerning the IMTs performance assessments are presented. Firstly, the Figures Of Merit chosen to analyze the performance of both techniques are presented and their choice is motivated. Then, the chosen interference and signal scenarios, along with the simulation tools and means are finely detailed. Finally, a confrontation of Temporal Blanker and FDIS performances is given using the previously described FOMs. The conclusion summarizes the performances analysis, compares them to - 6 - civil aviation performances requirements, and proposes recommendations for on-board GNSS receivers design

Les systèmes de navigation par satellites sont de plus en plus présents dans notre vie quotidienne. De nouveaux besoins émergent, majoritairement en environnement urbain. Dans ce type d'environnement très obstrué, le signal reçu par l'utilisateur a subit des atténuations ainsi que des réfractions/diffractions, ce qui rend difficile la démodulation des données et le calcul de position de l'utilisateur. Les signaux de navigation par satellites étant initialement conçus dans un contexte d'environnement dégagé, leurs performances de démodulation sont donc généralement étudiées dans le modèle de canal de propagation AWGN associé. Or aujourd'hui ils sont utilisés aussi en environnements dégradés. Il est donc indispensable de fournir et d'étudier leurs performances de démodulation dans des modèles de canal de propagation urbain. C'est dans ce contexte que s'inscrit cette thèse, le but final étant d'améliorer les performances de démodulation des signaux GNSS en milieux urbains, en proposant un nouveau signal. Afin de pouvoir fournir et analyser les performances de démodulation des signaux de navigation par satellite en milieux urbains, un outil de simulation a été développé dans le cadre de cette thèse : SiGMeP pour « Simulator for GNSS Message Performance ». Il permet de simuler la chaine entière d'émission/réception d'un signal de navigation par satellites et de calculer ses performances de démodulation en milieu urbain. Les performances de démodulation des signaux existants et modernisés ont donc été calculées avec SiGMeP en environnement urbain. Afin de représenter au mieux ces performances pour qu'elles soient le plus réalistes possibles, une nouvelle méthode adaptée au cas urbain est proposée dans ce manuscrit. Ensuite, pour améliorer ces performances de démodulation, l'axe de recherche s'est essentiellement porté sur le « codage canal ». Pour décoder l'information utile transmise, le récepteur calcule une fonction de détection à l'entrée du décodeur. Or la fonction de détection utilisée dans les récepteurs classiques correspond à un modèle de canal AWGN. Ce manuscrit propose donc une fonction de détection avancée, qui s'adapte au canal de propagation dans lequel l'utilisateur évolue, ce qui améliore considérablement les performances de démodulation, en ne modifiant que la partie récepteur du système. Enfin, dans le but de concevoir un nouveau signal avec de meilleures performances de démodulation en environnement urbain que celles des signaux existants ou futurs, un nouveau codage canal de type LDPC a été optimisé pour une modulation CSK. En effet, la modulation CSK est une modulation prometteuse dans le monde des signaux de type spectre étalé, qui permet de se débarrasser des limitations en termes de débit de données qu'impliquent les modulations actuelles des signaux de navigation par satellites
Global Navigation Satellite Systems (GNSS) are increasingly present in our everyday life. Further operational needs are emerging, mainly in urban environments. In these obstructed environments, the signal emitted by the satellite is severely degraded due to the many obstacles. Consequently, the data demodulation and the user position calculation are difficult. GNSS signals being initially designed in an open environment context, their demodulation performance is thus generally studied in the associated AWGN propagation channel model. But nowadays, GNSS signals are also used in degraded environments. It is thus essential to provide and study their demodulation performance in urban propagation channel models. It is in this context that this PhD thesis is related, the final goal being to improve GNSS signals demodulation performance in urban areas, proposing a new signal. In order to be able to provide and study GNSS signals demodulation performance in urban environments, a simulation tool has been developed in this PhD thesis context: SiGMeP for ‘Simulator for GNSS Message Performance'. It allows simulating the entire emission/reception GNSS signal chain in urban environment. Existing and modernized signals demodulation performance has thus been computed with SiGMeP in urban environments. In order to represent this demodulation performance faithfully to reality, a new methodology adapted to urban channels is proposed in this dissertation. Then, to improve GNSS signals demodulation performance in urban environments, the research axis of this thesis has focused on the ‘Channel Coding' aspect. In order to decode the transmitted useful information, the receiver computes a detection function at the decoder input. But the detection function used in classic receivers corresponds to an AWGN propagation channel. This dissertation thus proposes an advanced detection function which is adapting to the propagation channel where the user is moving. This advanced detection function computation considerably improves demodulation performance, just in modifying the receiver part of the system. Finally, in order to design a new signal with better demodulation performance in urban environments than one of existing and future signals, a new LDPC channel code has been optimized for a CSK modulation. Indeed, the CSK modulation is a promising modulation in the spread spectrum signals world, which permits to free from limitation sin terms of data rate implied by current GNSS signals modulations

La Terre est une planète en constante évolution et sa surface ne cesse de se transformer. Ses déformations soulèvent des questionnements. Depuis plusieurs années, le L2G de l'ESGT s'intéresse à l'étude des déformations par inter comparaison de techniques. Il dispose en cela de différents procédés de mesure. Puis au fil du temps, le laboratoire s'interroge sur l'intérêt de réaliser une combinaison entre différentes techniques de mesure afin d'observer des déformations fines et précises (quelques millimètres).L'objectif de cette thèse est de démontrer l'intérêt de combiner des mesures GNSS et des mesures topométriques, celles-ci semblant être les plus utilisées, et de les concrétiser. Les résultats présentés sont basés sur des simulations et sur des campagnes de mesures combinées des techniques de GNSS et de topométrie effectuée sur un réseau test d'une étendue locale. Les calculs évoluent en fonction de la distance de la ligne de base et en modifiant les durées de sessions de mesures. Nous montrons qu'une combinaison par cumul des équations normales améliore la précision du positionnement non seulement par rapport à l'utilisation de chaque technique séparée, mais également par rapport aux méthodes classiques basées sur la combinaison des coordonnées issues des techniques de GNSS et de topométrie.

L'approche actuelle pour la réalisation du Repère Terrestre International de Reference (International Terrestrial Reference Frame - ITRF) consiste à réduire les observations de chaque technique de géodésie spatiale dans des solutions indépendantes. Le seul moyen de rattacher les repères spécifiques à chaque technique pour obtenir un repère combiné homogène est alors d'utiliser des rattachements topométriques entre les stations des différentes techniques co-localisées sur le même site d'observations. Cependant, les incohérences entre ces rattachements locaux et les estimations des positions des stations par géodésie spatiale sont aujourd'hui un facteur limitant majeur de la qualité de l'ITRF. Un autre moyen de rattacher les différentes techniques de géodésie spatiale consiste en l'utilisation de satellites multi-techniques, équipés d'instruments de plus d'une technique de géodésie spatiale. Le principal défi d'utiliser un tel satellite comme un rattachement inter-technique se trouve dans la connaissance (ou estimation) précise des vecteurs entre le centre de masse du satellite (ou autre point de référence sur le satellite) et les points de référence des différents instruments (i. E. Les liens spatiaux). Dans cette thèse, nous présentons les résultats d'analyses multi-techniques (GPS + SLR + DORIS) impliquant le satellite Jason-2, et nous les comparons aux résultats des analyses traditionnelles mono-technique. Nous évaluons en particulier l'effet de traiter simultanément les observations des trois techniques avec le satellite Jason-2 comme lien inter-technique sur la résolution des ambiguïtés de phase GPS, sur l'estimation simultanée des orbites des satellites de la constellation GPS et de Jason-2 et sur l'estimation des positions des stations au sol. En outre, les résultats de l'estimation des liens spatiaux de Jason-2 sont présentés, afin d'évaluer la qualité des valeurs actuellement disponibles
In the present approach used to produce the International Terrestrial Reference Frame (ITRF), observations of the different space geodetic techniques are reduced in independent analyses. The only mean to tie the resulting technique-specific frames into a homogeneous combined frame is then to use local topometric ties between stations of different techniques co-located at the same observatory. However, inconsistencies between these local ties and space geodesy estimates of the station positions are today a major limiting factor of the ITRF quality. An alternative way of tying the different space geodetic techniques together is through the use of multitechnique satellites equipped with instruments of more than one technique. The main challenge of using such a satellite as an inter-technique link resides in the accurate knowledge (or estimation) of the vectors between the satellite's center of mass and the reference points of its different instruments (i. E. Space ties). In this thesis we present the results from multi-technique (GPS+SLR+DORIS) analyses involving the Jason-2 satellite, and we compare them to the results from traditional single-technique analyses. We assess in particular the effect of simultaneously processing the observations of the three techniques with Jason-2 as inter-technique link on the resolution of the GPS phase ambiguities, on the estimation of the GPS and Jason-2 satellite orbits and on the estimation of the ground station positions. Moreover, results of the estimation of the Jason-2 space ties are presented, in order to assess the quality of the presently available values

Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Elétrica, 2017.
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Clientes de Sistemas Globais de Navegação por Satélites, do inglês Global Navigation Satellite System (GNSS), dependem da estimação do atraso para estimar a posição do usuário. [1] Isto é feito fazendo a correlação do sinal recebido com sequências-réplicas para separar o sinal de cada satélite e estimar o atraso. Como componentes de multipercurso são cópias atrasadas do sinal original, estes alteram a função de correlação cruzada, assim gerando erros na estimação de atraso. Nesta dissertação estudamos um algoritmo estado-da-arte em mitigação de multipercursos para estimação de atraso baseado no autofiltro da decomposição em valores singular de alta ordem, do inglês Higher-Order Singular Value Decomposition (HOSVD), de posto unitário, [2] e propomos dois esquemas tensoriais para mitigação de multipercurso e estimação de atraso, para qual o esquema baseado em HOSVD é usado para comparação. O primeiro esquema tensorial é um método em três etapas que aplica estimação da direção de chegada, do inglês Direction of Arrival (DoA), e fatorização Khatri-Rao, do inglês Khatri-Rao factorization (KRF), para separar o código de cada componente incidente de forma fechada. O segundo esquema calcula uma matrix de covariância multimodo como aproximação do desdobramento Hermitian duplamente simétrico [3] com qual, alternando entre a solução do problema ortogonal de Procrustes, do inglês Orthogonal Procrustes Problem (OPP), [4] e fatorização Khatri-Rao de mínimos quadrados, do inglês Least Squares Khatri-Rao Factorization (LSKRF), [5] se estima iterativamente as matrizes-fator do canal, que são então usadas para separar o código de cada componente incidente. Ambos esquemas geram resultados melhores que o estado-da-arte baseado no autofiltro de alta ordem.
Global Navigation Satellite System (GNSS) clients rely on time-delay estimation to estimate a user’s position. [1] This is done by correlating the incoming signal with replica sequences to separate each satellite and perform time-delay estimation. Since multipath components are delayed copies of the original signal, this affects the cross-correlation function, thus impacting time-delay estimation. 1 In this thesis, we study a state-of-the-art approach for multipath mitigation time-delay estimation algorithm based on the rank-one Higher-Order Singular Value Decomposition (HOSVD) eigenfilter, [2] and propose two tensorbased schemes for multipath mitigation and time-delay estimation, for which the HOSVD-based scheme is a basis of comparison. The first scheme is a three step tensor-based approach applying direction of arrival (DoA) estimation and Khatri-Rao factorization (KRF) to separate the code for each impinging component in a closed fashion. The second approach calculates a multimode covariance matrix as an approximation of the dualsymmetric Hermitian unfolding [3] with which, by alternating between a solution to the orthogonal Procrustes problem (OPP) [4] and least squares Khatri-Rao factorization, [5] iteratively estimates the channel factor matrices which are then used to separate the code of each impinging component. Both our schemes outperforms the HOSVD-based eigenfilter state-of-the-art solution.

Radio signals from Global Navigation Satellite Systems (GNSS) satellites suffer delay as they propagate through the atmosphere (neutral and non-neutral) and this delay is partially driven by the water vapour content in the atmosphere. The delay component due to the non-neutral atmosphere (ionosphere) is removed through the use of dual frequency GNSS receivers. The main tropospheric parameter is the zenith tropospheric (or total) delay (ZTD), which is a widely accepted parameter with which to express the total delay in the signal from all satellites due to the neutral atmosphere. The ZTD is a measure of the integrated tropospheric condition over a GNSS receiver station. Accordingly, the integrated water vapour or precipitable water vapour (PWV) can be obtained from a portion of the ZTD, if the atmospheric pressure and temperature at the station are known through a concept often referred to as GNSS meteorology. A number of GNSS receivers have been deployed for mapping and geodetic services in Nigeria under the African reference frame initiative, but unfortunately most of these receivers do not have co-located meteorological sensors for pressure and temperature measurements. The prospect of incorporating GNSS meteorology into weather monitoring and climate analysis in Nigeria was investigated and is reported in this thesis. During the first task of this research, the technical basis for ground-based GNSS meteorology was reviewed and the potentials and challenges of the approach to meteorological activities in Africa (including Nigeria) were identified. Thereafter an in-depth analysis of the spatial and temporal variability of ZTD over Nigeria for the period of 2010-2014 was conducted; results revealed weak spatial dependence among the stations. Tidal oscillations (of the diurnal and semidiurnal components) were observed at the GNSS stations of which the diurnal ZTD cycles exhibited significant seasonal dependence, affirming the prospective relevance of ground-based GNSS data to atmospheric studies. Also in this research, the accuracy and suitability of using reanalysis datasets (ERA-Interim and NCEP/NCAR) and a GPT2 neutral model in retrieving PWV from GNSS observations over Nigeria were investigated; results showed that PWV can be retrieved to within a precision of about 1 mm, provided GNSS-derived ZTD is of high precision. A fundamental issue for GNSS meteorology in the West African region was yet again addressed in this research; this is the development of a weighted tropospheric mean temperature model for use in current and future GNSS meteorology activities in the region. A multitechnique comparison of PWV estimates showed good agreement between GNSS estimates and other techniques (i.e. the atmospheric infrared sounder, and ERAInterim reanalysis). This result is suggestive of the potential of assimilating GNSS atmospheric products into reanalysis and climate models. Diurnal and seasonal variability of GNSS PWV estimates exhibits strong correlation with weather events that influence the region (i.e. solar activity and rainfall events); this further demonstrated the immense contribution of the approach to efficient weather forecasting and climate monitoring for Nigeria.
Thesis (PhD)--University of Pretoria, 2017.
Geography, Geoinformatics and Meteorology
PhD
Unrestricted

This thesis investigates the use of innovative interference detection and mitigation techniques for GNSS based applications. The main purpose of this thesis is the development of advanced signal processing techniques outperforming current interference mitigation algorithms already implemented in off-the-shelf GNSS receivers. State-of-the-art interference countermeasures already investigated in literature, which process the signal at the ADC output, provide interference components suppression in the time domain or in the frequency domain, thus leading to a significant signal degradation in harmful interference scenarios where the GNSS signals spectra at the receiver antenna is completely jammed by external intentional or unintentional RFI sources. The proposed advanced interference countermeasures overcome such a limit, since they are based on particular signal processing techniques which manipulate the received samples at the ADC output, providing a representation in new domains where interference component can be better detected and separated from the rest of the signal, minimizing the useful signal distortion even in presence of multiple interference sources. At the cost of an increased computational complexity, such techniques can be optimized for increasing the sensitivity and the robustness of GNSS receiver merged in harmful environments. The work of this thesis addresses the design of such techniques by means of theoretical analyses, their performance assessment by means of simulation and their validation by means of synthetic and real GNSS data. Furthermore performance comparison with more traditional interference countermeasures is also presented considering a variety of harmful interference scenarios. In addition to the investigation of such new interference countermeasures, part of the thesis deals with the limit of current interference suppression technique, such as the pulse blanking, and its impact on the data demodulation performance. A very general investigation of the pulse blanking impact on the data demodulation performance for un-coded BPSK DSSS is provided. Then, the analysis focuses on the assessment of the navigation data demodulation performance for the current SBAS, then providing a proposal for system improvements, in terms of robustness and data rate increase, in future SBAS generation. Among the different interference scenarios considered, the thesis focuses on the potential interference environment expected in aviation context, since the Galileo E5 and GPS L5 bands, where the future GNSS based aviation services will be broadcast, are shared with other ARNS broadcasting strong pulsed interfering signals, which may seriously threat the on-board GNSS receiver operations . For such scenarios, simulation and analytic models are discussed and used as benchmark cases for assessing the mitigation techniques, in terms of SNR gain and data demodulation capability. The presence of interference (mitigated or not) causes a loss in the carrier to noise density ratio CN0 value for the received signal. For this reason, in order to reliably deal with such signals, the GNSS receiver must be able to feature high-sensitivity algorithms at the acquisition and tracking stages. For this reason the last part of the thesis investigates HS acquisition schemes for very weak GNSS signal detection. In particular, the purpose of this part of the work is to present a theoretical methodology for the design of an acquisition scheme capable of detecting signal down to 5 dB-Hz. The analysis carried out assuming the presence of assistance information which allows the receiver employing long coherent integration time (order of seconds). The particular scenario of the GNSS space environment is taken into consideration and the analysis is also focused on the definition of the requirements on the accuracy for potential Doppler aiding sources at the receiver level. The theoretical analysis is also supported by fully software simulation.

Cette activité de recherche concerne le domaine de la navigation par satellite qui utilise lessystèmes GNSS (Global Navigation Satellite Systems). Elle vise à améliorer les performances globalesd’un système de navigation, c’est à dire la robustesse, la disponibilité et l’intégrité d’un récepteurutilisant les signaux GNSS pour élaborer sa position et sa vitesse. L’enjeu est important et on noteque les représentations des nouveaux signaux proposés pour GPS et GALILEO visent à diminuer lacorrélation entre les signaux, faciliter la poursuite de ces signaux en abaissant le niveau des seuils depoursuite, réduire l’effet des interférences. La navigation basée sur les signaux GNSS reste toutefoisdépendante du canal de propagation et est particulièrement affectée en cas réflexion, réfraction,diffraction, diffusion, et de blocage du signal émis par le satellite. Il en résulte une dégradationimportante des performances en environnement urbain. L’objectif de cette recherche est ainsi deproposer, d’analyser et de caractériser des architectures de récepteur robuste, permettantd’adresser efficacement le problème de la navigation dans des environnements difficiles où le signalGNSS est affecté par de fortes perturbations. De nombreux travaux de recherche visant à améliorer les performances des algorithmes de poursuite du signal au sein d’un récepteur ont été conduites, en particulier pour adresser leproblème de cette poursuite dans des environnements difficiles, en présence de multi-trajets. Lesapproches les plus connues traitent le signal de post-corrélation. Ainsi l’utilisation de corrélateursétroits permet de réduire l’impact des multi-trajets générant un retard important. De même destechniques utilisant un banc de corrélateurs pour estimer les paramètres des multi-trajets ont étéétudiées. La présence de multi-trajets demeure toutefois une importante source d’erreur pour desrécepteurs opérant en environnement urbain. L’amélioration des performances des récepteurs dansce contexte reste un enjeu important et de nombreuses études sont conduites en vue d’améliorer ladisponibilité, la robustesse, la fiabilité et l’intégrité de ces récepteurs. Le principal objectif de cette thèse est de proposer une architecture de poursuite adaptive exploitant des techniques de poursuite vectorielle (Vector Tracking Loop – VTL). Les récepteurs conventionnels utilisent une architecture directe où une poursuite scalaire du signal (Scalar TrackingLoop – STL) est réalisée en amont du navigateur. Cette architecture n’utilise pas les informationsélaborées par le navigateur pour améliorer les performances de la poursuite. Au contrairel’architecture vectorielle permet à la poursuite de bénéficier de la connaissance de la position et dela vitesse estimées par le récepteur. Il peut en résulter une dégradation de la poursuite lorsque le navigateur ne sait pas isoler une mesure contaminée. Cet architecture rend donc les performances d’un canal très dépendantes des mesures utilisées par le navigateur, et donc en particulier des autres canaux. L’approche qui est explorée ici vise à combiner les approches de poursuite STL et VTL pour améliorer les performances des récepteurs en environnement urbain, dans un contexte multiconstellation
Present research activities in the field of Global Navigation Satellite Systems (GNSS) aim atenhancing the overall navigation performance by providing better and more robust navigationsignals compared the ones available today. These GNSS signals are designed to provide betterimproved cross-correlation protection, lower tracking thresholds and reduced susceptibility tonarrow band interferences. However navigation based on GNSS signals remains sensitive topropagation impairments such as reflection, refraction, diffraction and scattering, and sometimesblockage of the line of sight signals. These effects are especially important in urban environment.Therefore, a better and more robust receiver design and implementation is crucial to meet anappropriate navigation performance using GNSS signals. Improving signal tracking algorithms inside the receiver is an attractive approach. This is particularly true in the case of urban environments where interference and multipath severely degrade the performance of the GPS positioning. Despite the many efforts of performance enhancement, multipath still remains as the dominant source of error and the limiting factor for many applications. Consequently improving the performance of a receiver in multipath environment is a great challenge and many studies are carried out to satisfy the above requirements in term of availability, reliability and integrity. The main goal of this PhD thesis is to propose a new adaptive tracking algorithm based on vector tracking loop (VTL) approach. Currently, the conventional technique (i.e., Scalar Tracking Loop (STL)) is implemented in a forward-only strategy which doesn’t exploit the position, velocity and time (PVT) solution provided by the Navigation System (NS). Standard VTL on the other hand, suffers from measurements contamination from the exploitation of PVT provided by the NS. This adaptiveapproach will take advantage of both tracking methods for providing reliable measurements in amulti-constellation context

It is crucial to find a good balance between positioning accuracy and cost when developing navigation systems for ground vehicles. In open sky or even in a semi-urban environment, a single global navigation satellite system (GNSS) constellation performs sufficiently well. However, the positioning accuracy decreases drastically in urban environments. Because of the limitation in tracking performance for standalone GNSS, particularly in cities, many solutions are now moving toward integrated systems that combine complementary sensors. In this master thesis the improvement of tracking performance for a low-cost ground vehicle navigation system is evaluated when complementary sensors are added and different filtering techniques are used. How the GNSS aided inertial navigation system (INS) is used to track ground vehicles is explained in this thesis. This has shown to be a very effective way of tracking a vehicle through GNSS outages. Measurements from an accelerometer and a gyroscope are used as inputs to inertial navigation equations. GNSS measurements are then used to correct the tracking solution and to estimate the biases in the inertial sensors. When velocity constraints on the vehicle’s motion in the y- and z-axis are included, the GNSS aided INS has shown very good performance, even during long GNSS outages. Two versions of the Rauch-Tung-Striebel (RTS) smoother and a particle filter (PF) version of the GNSS aided INS have also been implemented and evaluated. The PF has shown to be computationally demanding in comparison with the other approaches and a real-time implementation on the considered embedded system is not doable. The RTS smoother has shown to give a smoother trajectory but a lot of extra information needs to be stored and the position accuracy is not significantly improved. Moreover, map matching has been combined with GNSS measurements and estimates from the GNSS aided INS. The Viterbi algorithm is used to output the the road segment identification numbers of the most likely path and then the estimates are matched to the closest position of these roads. A suggested solution to acquire reliable tracking with high accuracy in all environments is to run the GNSS aided INS in real-time in the vehicle and simultaneously send the horizontal position coordinates to a back office where map information is kept and map matching is performed.

La mesure du niveau de la mer par satellite a atteint un niveau sans précédent en termes de précision et de couverture spatio-temporelle. Ces observations nous ont permis d'améliorer notre compréhension de la dynamique à grande échelle des océans, mais leur exploitation reste un défi à l’approche de la côte, où les incertitudes liées à la marée océanique et aux fines échelles du géoïde sont plus importantes. L’objectif de cette thèse est de développer de nouvelles méthodologies s’appuyant sur les mesures mobiles du niveau de la mer par GNSS et la modélisation hydrodynamique afin de mieux exploiter les mesures altimétriques côtière et de préparer l’arrivée des futures missions. Lors d’une campagne menée avec le drone marin PAMELi en Juillet 2020 dans les Pertuis Charentais, une cartographie du niveau marin est réalisée le long d’un itinéraire préprogrammé. Cette cartographie est exploitée afin d’évaluer un modèle de marée sous une trace altimétrique, et démontrer le potentiel d’un drone pour étendre spatialement nos capacités de validation. Par la suite, on estime les pentes de géoïde dans la zone à partir du même jeu de données, en combinant mesures in-situ et modèle hydrodynamique. On montre que la modélisation des gradients de topographie dynamique permet d’améliorer la précision de la cartographie des pentes de géoïde. Ces deux études exploitent une méthodologie basée sur les différences aux points de croisement, et offrent des perspectives sur l'utilisation des drones marins dans le contexte de la future mission SWOT. Enfin, on présente une méthode de prédiction du trait de côte basée sur l’utilisation d’un MNT et du modèle hydrodynamique, appliquée aux passage Sentinel-3A afin d’évaluer l’impact des bancs découvrant sur la mesure altimétrique. Dans leur ensemble, ces travaux constituent un socle méthodologique qui permettra de mieux comprendre et utiliser les mesures altimétriques dans les environnements côtiers, et préparer l’arrivée de la future mission SWOT
Satellite altimetry has recently reached an unprecedented level of accuracy and coverage. Although altimeters were originally designed to observe the oceans and have improved our understanding of their large-scale dynamics, the exploitation in coastal areas remains a challenge. One of the challenges of coastal altimetry remains the lack of precision in geophysical corrections, which are essential to compute accurate sea level anomalies near the coast. The main objective of this thesis is to develop new methodologies based on mobile sea level GNSS measurements and hydrodynamic modelling in order to better exploit altimetry measurements in coastal environments and to prepare the arrival of future missions. During a campaign carried out with the PAMELi marine drone in July 2020 in the Pertuis Charentais, a sea-level cartography was carried out along a pre-programmed route. In a first study, this cartography is used to assess a tidal model under an altimetric pass, and thus demonstrate the potential of a drone to extend spatially our validation capabilities. Then, the same dataset is used to estimate the geoid slopes in the region, by combining in-situ measurements and the hydrodynamic model. We show that the use of our model to correct the dynamic topography gradients improves drastically the coherence and the accuracy of geoid slopes. These two studies exploit a methodology based on crossover height differences, and offer perspectives on the use of autonomous platforms in the context of the future SWOT mission. In a last chapter, a coastline prediction method based on the use of a DEM and the hydrodynamic model is presented, and applied to Sentinel-3A passages in order to evaluate the impact of intertidal areas on altimeter measurements. This overall thesis work provides methodological insights for a better understanding and exploitation of altimetry measurements in coastal environments, and will help to prepare the scientific exploitation of the future SWOT mission

En segmentation d’images, les informations de couleur et de texture sont très utilisées. Le premier apport de cette thèse se situe au niveau de l’utilisation conjointe de ces deux sources d’informations. Nous proposons alors une méthode de combinaison couleur/texture, adaptative et non paramétrique, qui consiste à combiner un (ou plus) gradient couleur et un (ou plus) gradient texture pour ensuite générer un gradient structurel utilisé comme image de potentiel dans l’algorithme de croissance de régions par LPE. L’originalité de notre méthode réside dans l’étude de la dispersion d’un nuage de point 3D dans l’espace, en utilisant une étude comparative des valeurs propres obtenues par une analyse des composantes principales de la matrice de covariance de ce nuage de points. L’approche de combinaison couleur/texture proposée est d’abord testée sur deux bases d’images, à savoir la base générique d’images couleur de BERKELEY et la base d’images de texture VISTEX. Cette thèse s’inscrivant dans le cadre des projets ViLoc (RFC) et CAPLOC (PREDIT), le deuxième apport de celle-ci se situe au niveau de la caractérisation de l’environnement de réception des signaux GNSS pour améliorer le calcul de la position d’un mobile en milieu urbain. Dans ce cadre, nous proposons d’exclure certains satellites (NLOS dont les signaux sont reçus par réflexion voir totalement bloqués par les obstacles environnants) dans le calcul de la position d’un mobile. Deux approches de caractérisation, basées sur le traitement d’images, sont alors proposées. La première approche consiste à appliquer la méthode de combinaison couleur/texture proposée sur deux bases d’images réelles acquises en mobilité, à l’aide d’une caméra fisheye installée sur le toit du véhicule de laboratoire, suivie d’une classification binaire permettant d’obtenir les deux classes d’intérêt « ciel » (signaux LOS) et « non ciel » (signaux NLOS). Afin de satisfaire la contrainte temps réel exigée par le projet CAPLOC, nous avons proposé une deuxième approche basée sur une simplification de l’image couplée à une classification pixellaire adaptée. Le principe d’exclusion des satellites NLOS permet d’améliorer la précision de la position estimée, mais uniquement lorsque les satellites LOS (dont les signaux sont reçus de manière direct) sont géométriquement bien distribués dans l’espace. Dans le but de prendre en compte cette connaissance relative à la distribution des satellites, et par conséquent, améliorer la précision de localisation, nous avons proposé une nouvelle stratégie pour l’estimation de position, basée sur l’exclusion des satellites NLOS (identifiés par le traitement d’images), conditionnée par l’information DOP, contenue dans les trames GPS
Color and texture are two main information used in image segmentation. The first contribution of this thesis focuses on the joint use of color and texture information by developing a robust and non parametric method combining color and texture gradients. The proposed color/texture combination allows defining a structural gradient that is used as potential image in watershed algorithm. The originality of the proposed method consists in studying a 3D points cloud generated by color and texture descriptors, followed by an eigenvalue analysis. The color/texture combination method is firstly tested and compared with well known methods in the literature, using two databases (generic BERKELEY database of color images and the VISTEX database of texture images). The applied part of the thesis is within ViLoc project (funded by RFC regional council) and CAPLOC project (funded by PREDIT). In this framework, the second contribution of the thesis concerns the characterization of the environment of GNSS signals reception. In this part, we aim to improve estimated position of a mobile in urban environment by excluding NLOS satellites (for which the signal is masked or received after reflections on obstacles surrounding the antenna environment). For that, we propose two approaches to characterize the environment of GNSS signals reception using image processing. The first one consists in applying the proposed color/texture combination on images acquired in mobility with a fisheye camera located on the roof of a vehicle and oriented toward the sky. The segmentation step is followed by a binary classification to extract two classes « sky » (LOS signals) and « not sky » (NLOS signals). The second approach is proposed in order to satisfy the real-time constraint required by the application. This approach is based on image simplification and adaptive pixel classification. The NLOS satellites exclusion principle is interesting, in terms of improving precision of position, when the LOS satellites (for which the signals are received directly) are well geometrically distributed in space. To take into account the knowledge of satellite distribution and then increase the precision of position, we propose a new strategy of position estimation, based on the exclusion of NLOS satellites (identified by the image processing step), conditioned by DOP information, which is provided by GPS data

This thesis implements a state-of-the-art solution separation advanced RAIM (ARAIM) algorithm as it is written as reported in the literature. Specifically, a GNSS fault detection and exclusion algorithm for a multi-constellation GNSS was implemented in software and tested against simulated data. RAIM algorithms have been created in many forms over the last couple of decades and are still in development today. The position solution results produced by this ARAIM algorithm were compared to that of a snapshot weighted least squares (WLS) solution in which failed satellites are removed before processing and an WLS solution with no corrections applied. In addition, the difference in position solution between ARAIM and the simulation truth was compared to the ARAIM reported horizontal and vertical protection limits, as well as, the position performance criteria. This thesis also investigates the performance of the exclusion method and how it affects the performance of the overall ARAIM algorithm. The algorithm implemented and tested in this thesis will be used as a basis of comparison for on-going research into robust GNSS processing techniques.

Tandis que les humains explorent la nature sans relâche, ils font également attention à être plus conscients d'eux-mêmes, à mieux connaître ce qui les entourent, et, par exemple, à être informés de leurs positions, vitesses, ou trajectoires où qu'ils se trouvent. Les systèmes de positionnement par satellites (GNSS) ont fourni une manière de le faire à l'extérieur, devenant un assistant indispensable pour nous. Après le succès de GPS et GLONASS, Galileo et BeiDou sont actuellement en cours de déploiement, offrant plus de choix pour le positionnement autonome ou assisté. Toutefois, les signaux GNSS sont vulnérables aux obstacles: il n'y a presque pas de service GNSS à l'intérieur des bâtiments, dans les tunnels, ou dans les parkings souterrains; la continuité des services de positionnement par satellites n'est toujours pas assurée dans les "canyons urbains". Afin de faire face à ce problème, cette thèse est consacrée au positionnement en environnements contraints (où le GNSS n'est pas disponible), en y incluant la conception, les algorithmes et les technologies correspondantes. Un état de l'art est élaboré sur les systèmes de positionnement à radio ou à l'inertie. Parmi les technologies possibles, la discussion ne se limite pas à l'approche basée sur GNSS, mais elle est centrée sur cette dernière à cause de ses avantages et aussi de l’implication profonde de notre groupe de recherche dans ce domaine. Nous avons, d'une part, étudié la possibilité ainsi que les limites du positionnement avec une précision centimétrique en déployant notre système Repealite (i.e. un système de positionnement à l'intérieur d'une base des émetteurs GNSS spéciaux); et proposé, d'autre part, une méthode de localisation en groupe d'objets dynamiques communicants. Cette méthode procède d'une problématique délicate que l'on rencontre dans les approches GNSS, qu'est la détermination de la position initiale du récepteur. On montre en quoi elle permet également d'aller au-delà de la portée des approches classiques GNSS
While the human beings explore the nature tirelessly, they also put significant concerns to be aware of themselves, to know better of the circumstances, and to be informed with their precise positions, velocities, trajectories, and so on, in local environments. The Global Navigation Satellite Systems (GNSS) have provided an efficient method to do so outdoors, and have already become an indispensable assistant of many people. After the success of GPS and GLONASS, Galileo and BeiDou are currently under deployment, offering more choices of the independent or collaborative positioning. However, the GNSS signal is vulnerable to obstructions: almost no GNSS services are available inside buildings, tunnels, or underground parkings; the services are not always coherent in urban canyons. In order to address this problem, this thesis is dedicated to the design frameworks for the positioning in GNSS-challenged environments, as well as the corresponding algorithms and technologies. A brief survey of the latest radio-based and inertial positioning/tracking systems is provided. Among the feasible technologies, the discussion is centered on but not limited to the GNSS-based approach, which is due to the inherited advantages of this approach and also the deep engagement of our research group in this domain. We have, on one hand, explored the possibility and limitations on the centimeter-accuracy positioning with our Repealite system (i.e. a GNSS-base indoor positioning system with specific features); on the other hand, a method of batch localization for the nodes in a network of dynamic communicating objects is proposed, which is originated from an issue of the GNSS-based approach - the resolution of the receiver initial point, but then it goes beyond the scope of the “classical” GNSS-based approach

Space geodesy is one of the disciplines that contributes uniquely to the global society; its applications have grown to such an extent that system Earth is better understood today. The current accuracy of the Global Navigation Satellite Systems (GNSS) technique is below centimetre level and this allows very accurate determination of velocity field parameters. This study focused on utilizing GNSS to determine the inter-continental plate velocity field for Africa in support of the African Geodetic Reference Frame (AFREF). Data spanning 12.4 years were processed in the International Terrestrial Reference Frame (ITRF2008) using GAMIT/GLOBK 10.4 (developed at the Massachusetts Institute of Technology). Primarily, processing of data focused on International GNSS Service (IGS) stations with a few non-IGS stations (which are of geodetic quality) included, such as Hamburg (HAMB) and Matjiesfontein (MATJ). The same data set was analysed using the Combination and Analyses of Terrestrial Reference Frame (CATREF) software developed at Institut National de l’Information Géographique et Forestière (IGN). Validation of the results was achieved through comparison of the velocity solution from this study with a solution obtained from a core of IGS GNSS stations processed by the Jet Propulsion Laboratory (JPL). No significant differences were evident between the GAMIT/GLOBK 10.4, CATREF and JPL solutions. The results from the Matjiesfontein station indicated that the proposed Matjiesfontein Observatory site shows no significant vertical or horizontal local motion; this information is valuable in that there is no obvious local site instability. The velocity field as derived by GNSS displays no unexpected deviations and supports current understanding of the motion of the Nubian, Somalian and Arabian plates. Furthermore, the comparison of the velocity vectors derived from the IGS station HRAO, Satellite Laser Ranging (SLR) MOBLAS-6 station and 26 m Very Long Baseline Interferometry (VLBI) telescope, which are collocated at the Hartebeesthoek Radio Astronomy Observatory (HartRAO) indicated good agreement and both techniques exhibit no significant vertical motion. This study also contributed to the first computation of the AFREF solution. It is envisaged that as more stations are added to the sparsely distributed current network, more accurate results and better tectonic models can be derived. The availability of station velocities will facilitate adjustments within the AFREF.
Dissertation (MSc)--University of Pretoria, 2013.
gm2014
Geography, Geoinformatics and Meteorology
unrestricted

A utilização dos sistemas de navegação global por satélite, conhecidos pela sigla GNSS (Global Navigation Satellite System), cresceu vertiginosamente durante a última década. Atualmente, os receptores GNSS são ferramentas seguras, eficientes e altamente produtivas para a realização de observações aos satélites, possibilitando determinar coordenadas geodésicas sobre a superfície terrestre. As ferramentas e tecnologias disponíveis no mercado são de essencial importância no desenvolvimento eficiente dos projetos de engenharia. No entanto, o domínio das técnicas de trabalho e o conhecimento profundo de todos os métodos de execução são os principais obstáculos para a introdução de uma nova metodologia em projetos de engenharia. Este trabalho tem por objetivo esclarecer e testar a associação dessa tecnologia com o uso da telefonia celular, em especial com a utilização da conexão GSM (Global System for Mobile Communication) / GPRS (General Packet Radio Service), disponíveis no Brasil. O posicionamento preciso em tempo real tradicionalmente envia as observações de fase da onda portadora entre o receptor GNSS base e móvel através de frequências de rádio. Isso possibilita a determinação de coordenadas geodésicas e topográficas instantaneamente. Entretanto, obstáculos como áreas de relevo acidentado, edificações ou a baixa potência do rádio que envia os sinais fazem com que a comunicação entre os equipamentos seja interrompida com a perda frequente da solução instantânea. Apesar disso, este método de trabalho está consagrado como o mais produtivo, mantendo precisões topográficas, sendo que superar as restrições citadas seria uma inovação na área de Geodésia e Topografia. Com o avanço de tecnologias correlatas, criou-se uma nova maneira de enviar as observações de fase utilizando a conexão GSM através do pacote de dados GPRS. A conexão GSM é aplicada na tecnologia móvel padrão, que se tornou a mais popular para telefones celulares, de fácil acesso a qualquer usuário. Adequando o tradicional protocolo RTCM (Radio Technical Commission for Maritime Services) em um formato capaz de ser transmitido por GPRS, desenvolveu-se assim o serviço NTRIP (Network Transport of RTCM via Internet Protocol). Com esta nova concepção da conexão GSM/GPRS é possível realizar levantamentos com a técnica RTK (Real Time Kinematic) com vetores de até 100 km, mantendo as precisões atingidas com a metodologia atual de pós-processamento. Os tipos de equipamentos, os limites de distâncias e a qualidade dos dados obtidos estão sendo discutidos nesta pesquisa e analisados de forma a verificar os resultados atingidos em termos de precisão e acurácia.
The use of Global Navigation Satellite System has dramatically grown over the last decade. Currently, GNSS receivers are secure, efficient and highly productive for carrying out observations for the geodetic coordinates determination on the Earth\'s surface. The tools and technologies available on the market are essential in the establishment of engineering projects. However, the total knowledge of the techniques and the total domain of the execution methods are the first obstacles to the full incorporation of the technology in the engineering projects. This work is to clarify and to teste the technology described in this dissertation related to the facilities of cell phone coverage, particularly the GSM/GPRS connection able to be used in Brazil. The precise positioning in real-time traditionally involves the transmission of phase measurements between base and rover GNSS receivers; this is traditionally carried out through radio frequencies. This allows determining geodetic and topographic coordinates instantaneously. However, obstacles like accident topography terrain, buildings or low power of radio basis transmission, provoke constant interruptions in the communication among the radios and the consequent losing of the instant solution. Nevertheless, this methodology is the most productive for a centimetric accuracy; so the major challenge in geodetic positioning is to overcome the mentioned difficulties. With the high development of technologies related to mobile phone, a new way to transmit the observations using the GSM/GPRS connection was created. The GSM connection is a standard mobile technology, the most popular for cell phones, which became of easy access to any person. The traditional RTCM protocol in a convenient format can be transmitted by GSM/GPRS connection which is known as NTRIP service, becoming a full digital communication system. As of this new concept, it is possible to note vectors up to 100 km in RTK technique employment with the same high quality measurement. The equipment characteristics, distance limits and quality of the data recorded have been discussed and analyzed here in order to verify whether the results can achieve the necessary precision and accuracy.

The improvement of maritime traffic safety and security is a subject of growing interest, since the traffic is constantly increasing. In fact, a large number of human activities take place in maritime domain, varying from cruise and trading ships up to vessels involved in nefarious activities such as piracy, human smuggling or terrorist actions. The systems based on Automatic Identification System (AIS) transponder cannot cope with non-cooperative or non-equipped vessels that instead can be detected, tracked and identified by means of radar system. In particular, passive bistatic radar (PBR) systems can perform these tasks without a dedicated transmitter, since they exploit illuminators of opportunity as transmitters. The lack of a dedicated transmitter makes such systems low cost and suitable to be employed in areas where active sensors cannot be placed such as, for example, marine protected areas. Innovative solutions based on terrestrial transmitters have been considered in order to increase maritime safety and security, but these kinds of sources cannot guarantee a global coverage, such as in open sea. To overcome this problem, the exploitation of global navigation satellites system (GNSS) as transmitters of opportunity is a prospective solution. The global, reliable and persistent nature of these sources makes them potentially able to guarantee the permanent monitoring of both coastal and open sea areas. To this aim, this thesis addresses the exploitation of Global Navigation Satellite Systems (GNSS) as transmitters of opportunity in passive bistatic radar (PBR) systems for maritime surveillance. The main limitation of this technology is the restricted power budget provided by navigation satellites, which makes it necessary to define innovative moving target detection techniques specifically tailored for the system under consideration. For this reason, this thesis puts forward long integration time techniques able to collect the signal energy over long time intervals (tens of seconds), allowing the retrieval of suitable levels of signal-to-disturbance ratios for detection purposes. The feasibility of this novel application is firstly investigated in a bistatic system configuration. A long integration time moving target detection technique working in bistatic range&Doppler plane is proposed and its effectiveness is proved against synthetic and experimental datasets. Subsequently the exploitation of multiple transmitters for the joint detection and localization of vessels at sea is also investigated. A single-stage approach to jointly detect and localize the ship targets by making use of long integration times (tens of seconds) and properly exploiting the spatial diversity offered by such a configuration is proposed. Furthermore, the potential of the system to extract information concerning the detected target characteristics for further target classification is assessed.

碩士
國立臺灣海洋大學
通訊與導航工程學系
104
The global navigation satellite system (GNSS) has been widely used by militaries as well as civilians. The use of GPS in mission-critical applications demands not only precise navigation solutions but solutions which can be used with absolute confidence. Spoofing is a deliberate interference that aims to coerce global navigation satellite system receivers into generating false position/navigation solutions. The GPS system is generally lack of immunity against spoofing attack. As such, spoofing and anti-spoofing algorithms have become an important research topic within the GPS discipline. Currently, Spoofing mitigation technique of anti-spoofing is mainly on positioning solution. This thesis to solve the problems of spoofing signal of robust estimation, using MEKF and MUKF, which are EKF (Extended Kalman Filter) and UKF (Unscented Kalman Filter) combined with M-estimation. And joining the detection mechanism, so that using optimal estimate when did not suffer spoofing signal; on the other hand, if suffer spoofing signal starting M-estimator and using robust estimate to solve position/navigation solutions. MEKF and MUKF can not only solve the nonlinear problems but also against spoofing signal, which have greatly improved the robust of estimation, and positional accuracy.

This dissertation investigates a novel Multipurpose Earth Orbit Navigation System (MEONS) architecture aiming at providing a generalized GNSS based spacecraft orbit estimation kernel matching the modern navigation instance of enhanced flexibility with respect to multiple Space Service Volume (SSV) applications (Precise Orbit Determination for Earth Observation satellite, Low Thrust Low to High Autonomous Orbit Rising, formation flying relative navigation, Small Satellite Autonomous Orbit Acquisition). The possibility to address theoretical and operational solutions within a unified framework is a foundamental step for the implementation of a reusable and configurable high performance navigation capability on next generation platforms.

The demand for outdoor precise location is increasing with the development of new applications such as autonomous vehicles, exploration robots and wireless sensor networks. Global Navigation Satellite System (GNSS) is the go-to system for outdoor localization. This thesis focuses on developing new methods for GNSS single-point positioning (SPP) model, where no access to a reference station or precise GNSS parameters is needed. We investigated the limitations of the standard method, least- squares adjustment (LSA), and we derived the Cramer-Rao bounds for the SPP estimation problem. We also investigated different techniques to formulate the positioning problem with the goal to increase the accuracy. A new method is developed by reformulating the problem as difference-of-convex program (DC program) and utilizing convex-concave procedure (CCCP) to solve the positioning problem without linearizing the observation equations. In addition, we examined the potential of multiple-receiver systems in increasing the accuracy. We formulated the multiple- receiver SPP estimation problem, and we proposed to configure the multiple receivers in a fixed equilateral triangle to exploit the symmetry and the geometrical constraints of the configuration. We extended the use of LSA in multiple-receiver system. We also developed a modification of LSA algorithm, named least-squares adjustment extension (LSAE), that utilizes attitude information and the constraints of the multiple-receiver system. In addition, we developed a new algorithm to optimizes the SPP estimates over the equilateral triangles Riemannian manifold, which enforces the geometrical constraints of the multiple-receiver system. Furthermore, we derived the constrained and the unconstrained Cramer-Rao bounds (CRB and CCRB) for the multiple-receiver SPP problem. Moreover, we investigated the influence of both attitude information and the equilateral triangle baseline length on the algorithms’ performances and the derived CCRB. Finally, we carried out a numerical analysis by implementing the algorithms and the bounds in MATLAB, where we tested the algorithms on simulated GNSS scenarios. The proposed multiple-receiver methods provide more precise estimates for the SPP problem in comparison to the single receiver methods.

In this thesis, we analyze the performance of the Post Detection Integration (PDI) techniques used for detection of weak DS/CDMA signals in the presence of uncertainty in the frequency, noise variance and data bits. Such weak signal detection problems arise, for example, in the first step of code acquisition for applications such as the Global Navigation Satellite Systems (GNSS) based position localization. Typically, in such applications, a combination of coherent and post-coherent integration stages are used to improve the reliability of signal detection. We show that the feasibility of using fully coherent processing is limited due to the presence of unknown data-bits and/or frequency uncertainty. We analyze the performance of the two conventional PDI techniques, namely, the Non-coherent PDI (NC-PDI) and the Differential-PDI (D-PDI), in the presence of noise and data bit uncertainty, to establish their robustness for weak signal detection. We show that the NC-PDI technique is robust to uncertainty in the data bits, but a fundamental detection limit exists due to uncertainty in the noise variance. The D-PDI technique, on the other hand, is robust to uncertainty in the noise variance, but its performance degrades in the presence of unknown data bits. We also analyze the following different variants of the NC-PDI and D-PDI techniques: Quadratic NC-PDI technique, Non-quadratic NC-PDI, D-PDI with real component (D-PDI (Real)) and D-PDI with absolute component (D-PDI (Abs)). We show that the likelihood ratio based test statistic derived in the presence of data bits is non-robust in the presence of noise uncertainty. We propose two novel PDI techniques as a solution to the above mentioned shortcomings in the conventional PDI methods. The first is a cyclostationarity based sub-optimal PDI technique, that exploits the periodicity introduced due to the data bits. We establish the exact mathematical relationship between the D-PDI and cyclostationarity-based signal detection methods. The second method we propose is a modified PDI technique, which is robust against both noise and data bit uncertainties. We derive two variants of the modified technique, which are tailored for data and pilot channels, respectively. We characterize the performance of the conventional and proposed PDI techniques in terms of their false alarm and detection probabilities and compare them through the receiver operating characteristic (ROC) curves. We derive the sample complexity of the test-statistic in order to achieve a given performance in terms of detection and false alarm probabilities in the presence of model uncertainties. We validate the theoretical results and illustrate the improved performance that can be obtained using our proposed PDI protocols through Monte-Carlo simulations.

碩士
國立成功大學
電機工程學系碩博士班
93
The thesis is concerned with the use of multicorrelator technique in reducing multipath effect in GNSS application. Although GNSS has been widely used in navigation and survey, its performance is subject to several errors such as ionosphere delay, troposphere delay and multipath. Among which, the multipath effect constitutes one of the most unpredictable error sources. The multicorrelator techniques is analyzed in the thesis to assess its effectiveness in multipath mitigation. Both BPSK and BOC modulations are considered.

碩士
國立成功大學
測量及空間資訊學系碩博士班
101
Recently the useage of mobile mapping platform have been raised gradually in Taiwan. Currently mobile mapping technologies always apply INS/GNSS integrated system to get exterior orientation of image by Direct Georeferencing (DG). But the accuracy of DG is affected significantly by the accuracy of INS/GNSS integrated system because the error propagation from INS/GNSS integrated system to DG is linear. So the primary objective to increase the accuracy of mobile mapping system is to enhance the accuracy of INS/GNSS integrated system. This research investigates the impact different kinematic satellite positioning method on the positioning and orientation accuracy of an INS/GNSS integrated system. It uses raw measurements of INS/GNSS integrated system to perform three satellite positioning processes, including Differential GNSS (DGNSS), Precise Point Positioning (PPP) and post-processed Virtual Reference Station (VRS). The result shows the accuracy of using VRS in INS/GNSS integrated system satellite positioning is superior compared to other methods. Now the development of Network RTK (Network Real Time Kinematic, NRTK) in Taiwan is gradually becomimg mature. National Land Surveying and Mapping Center established e-GPS based on VRS and the provate company also set up a similar system known as Civil NET. Using post-processed VRS to do satellite positioning can save the cost of manpower which is needed in traditional DGNSS and still remain the accuracy which is needed in mobile mapping system.

Low-cost unmanned aerial vehicles (UAVs) utilizing push-broom hyperspectral scanners are poised to become a popular alternative to conventional remote sensing platforms such as manned aircraft and satellites. In order to employ this emerging technology in fields such as high-throughput phenotyping and precision agriculture, direct georeferencing of hyperspectral data using onboard integrated global navigation satellite systems (GNSS) and inertial navigation systems (INS) is required. Directly deriving the scanner position and orientation requires the spatial and rotational relationship between the coordinate systems of the GNSS/INS unit and hyperspectral scanner to be evaluated. The spatial offset (lever arm) between the scanner and GNSS/INS unit can be measured manually. However, the angular relationship (boresight angles) between the scanner and GNSS/INS coordinate systems, which is more critical for accurate generation of georeferenced products, is difficult to establish. This research presents three alternative calibration approaches to estimate the boresight angles relating hyperspectral push-broom scanner and GNSS/INS coordinate systems. For reliable/practical estimation of the boresight angles, the thesis starts with establishing the optimal/minimal flight and control/tie point configuration through a bias impact analysis starting from the point positioning equation. Then, an approximate calibration procedure utilizing tie points in overlapping scenes is presented after making some assumptions about the flight trajectory and topography of covered terrain. Next, two rigorous approaches are introduced – one using Ground Control Points (GCPs) and one using tie points. The approximate/rigorous approaches are based on enforcing the collinearity and coplanarity of the light rays connecting the perspective centers of the imaging scanner, object point, and the respective image points. To evaluate the accuracy of the proposed approaches, estimated boresight angles are used for ortho-rectification of six hyperspectral UAV datasets acquired over an agricultural field. Qualitative and quantitative evaluations of the results have shown significant improvement in the derived orthophotos to a level equivalent to the Ground Sampling Distance (GSD) of the used scanner (namely, 3-5 cm when flying at 60 m).