Дисертації з теми "GNSS Interference"

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

This 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.

Les récepteurs GNSS sont utilisés pour estimer la position et la vitesse d’un véhicule à partir de signauxtransmis par des satellites. L’estimation est habituellement réalisée en plusieurs étapes. Lesparamètres des signaux qui concernent le délai de propagation, la phase et la fréquence Dopplerde la porteuse, sont estimés et exploités pour estimer des mesures de pseudo-distances et de delta-distances.Ces mesures sont ensuite utilisées comme observation de la position et de la vitesse parl’algorithme de navigation qui délivre l’état du véhicule. En environnement GNSS dégradé les signauxémis par les satellites GPS peuvent subir des réflexions, des réfractions, et suivre ainsi deschemins multiples, communément connus sous le nom de multi-trajets. Ces signaux induisent desdéformations du signal à différents niveaux dans les récepteurs. En particulier il en résulte une distorsiondes fonctions de corrélation et des fonctions de discrimination, ce qui conduit à des erreursdans les estimées de pseudo-distances et de delta-distances et, en conséquence, à une erreur depositionnement. Bénéficiant d’un état de l’art des approches développées pour l’atténuation deseffets des interférences, de nouvelles techniques sont proposées dans cette thèse afin de réduirel’impact des MT sur les performances des récepteurs, et d’améliorer ainsi la précision de positionnementGPS
Global Navigation Satellite Systems (GNSS) receivers calculate the user position, velocity and timeby using the signals received from a set of navigation satellites. In constricted environments, suchas urban canyons or other intensive obstruction scenarios, the signal transmitted by the satelliteis subject to reflection or diffraction and can follow different paths, commonly known as multipath(MP) interferences, before arriving at the antenna of the GNSS receiver. The MP interferencesaffect the signal processing results at different stages in the receiver. For instance, MP signals modifythe correlation and discriminator functions and can introduce errors in pseudo-range (PR) andcarrier phase measurements, resulting finally in GNSS-based positioning errors. Therefore the MPinterference can be considered as a dominant error source in these complex situations. This thesisinvestigates MP mitigation techniques based on signal processing methods at different stages ofthe GNSS receiver. By analyzing and comparing the state-of-the-art MP mitigation approaches, innovativeMP mitigation techniques are proposed in order to reduce the impact of MP interferenceson the GNSS receiver, and to improve the positioning accuracy based on GNSS

Due to the low cost of GNSS receivers and their consequent diffusion, a wide range of location-aware applications are arising. Some of these applications are critical and have strict requirements in terms of availability, integrity and reliability. Examples of critical applications are precision landing and en-route navigation in air transportations; automated highways and mileage-based toll in road transportations; search and rescue in safety of life applications. A failure in fulfilling one or more requirements of a critical application may have dramatic consequences and cause serious damage. One of the most challenging threats for critical GNSS application, is represented by interference. In particular, jamming devices, operating inside GNSS bands, are easily and cheaply purchasable on the Internet. These devices transmit disturbing signals with the aim of preventing the correct operations of GNSS receivers. In order to satisfy the requirements of critical applications, it is necessary to promptly detect, localize and remove such interfering sources. Moreover, it is important to characterize the interfering signals in order to develop interference avoidance and mitigation techniques that ensure robustness of GNSS receivers to interference. This thesis studies the problem of interference in GNSS, from a cooperative perspective.

Esta tesis aborda la sincronización de una o varias réplicas de una señal conocida recibidas en un entorno con propagación multicamino e interferencias direccionales. Uno de los hilos conductores de este trabajo es la aplicación sistemática del principio de máxima verosimilitud (ML) junto con un modelo de señal en el cual las armas espaciales no tienen estructura, y en cual el ruido es Gaussiano y presenta una matriz de correlación desconocida. Esta última suposición es fundamental a la hora de obtener estimadores capaces de atenuar las señales interferentes que presentan algún tipo de estructura, y esto se consigue sin necesidad de recurrir a la estimación de ciertos parámetros de dichas señales. Por otra parte, la suposición de que las armas espaciales carecen de estructura tiene ventajas desde un punto de vista práctico, al mismo tiempo que simplifica la estimación del resto de parámetros ya que las estimaciones de estas firmas se pueden calcular de forma cerrada. Esto constituye un primer paso hacia la eliminación de las búsquedas en múltiples dimensiones, que es otro de los objetivos perseguidos en este trabajo.

En la primera parte de la tesis se deduce la solución de máxima verosimilitud para el problema general de estimación de retardos cuando el ruido tiene correlación espacial desconocida. Se demuestra que el criterio resultante para los retardos es consistente y asintóticamente eficiente, pero también es altamente no-lineal debido a la presencia del determinante de una matriz y no permite, por tanto, el uso de procedimientos sencillos de optimización. Asimismo, se demuestra y se argumenta intuitivamente que el criterio _ optimo ML se puede aproximar por una función de coste más sencilla que es asintóticamente equivalente. A diferencia de otros problemas de estimación, en el caso tratado aquí, el primer término del desarrollo de Taylor del estimador ML no conserva la eficiencia asintótica. La característica esencial de la nueva función de coste es que depende linealmente de la matriz de proyección sobre el subespacio de las señales y, por lo tanto, admite ser minimizada mediante el algoritmo IQML, que es eficiente desde el punto de vista computacional. Además, la existencia de métodos de inicialización sencillos y robustos a las interferencias, los cuales se basan en el uso de una matriz de pesos igual a la identidad y posiblemente también en el algoritmo ESPRIT, hace que el esquema de estimación propuesto pueda ser viable para un diseño práctico. La nueva función de coste se puede aplicar de la misma manera a la estimación del retardo en un canal FIR. En este caso, el algoritmo IQML se puede modificar de forma que, en cada iteración, la estimación del retardo se obtiene a partir de las raíces de un polinomio cuyo orden es igual a la longitud del canal.

El objetivo perseguido por los estimadores presentados en la segunda parte de la tesis es aprovechar una particularidad de los sistemas GNSS (Global Navigation Satellite Systems), que consiste en que la dirección de llegada de la señal directa puede ser conocida a priori. Basándose en esta información adicional y suponiendo que el array está calibrado, se propone un modelo simplificado, aunque al mismo tiempo aproximado, para la señal recibida. En este modelo todas las señales excepto la señal directa se engloban en un término con correlación espacial desconocida. Se analizan los estimadores ML del retardo y de la fase de portadora de la señal directa. El sesgo producido por las componentes multicamino al utilizar estos estimadores se reduce de forma muy importante con respecto al sesgo que sufren otros métodos. De hecho, el error cuadrático medio de los estimadores propuestos es en muchas ocasiones muy próximo o incluso inferior al mínimo error que se puede alcanzar con modelos más detallados del canal multicamino. Asimismo, se presentan dos algoritmos de estimación del retardo basados en el cálculo de las raíces de un polinomio. Se demuestra también que las estimaciones ML se pueden obtener a partir de la señal de salida de un conformador de haz híbrido. Debido a que el propio conformador depende de las estimaciones del retardo y de la amplitud de la señal directa, el uso de un algoritmo iterativo surge de forma natural. La formulación mediante el conformador híbrido proporciona una interpretación alternativa interesante de la estimación ML, y podrá ser apropiada para una realización práctica. Finalmente, se demuestra analíticamente y numéricamente que el estimador propuesto para el retardo es robusto frente a errores en el valor nominal del vector de enfoque de la señal directa, y se presenta una manera de extender el margen tolerable de errores de apuntamiento.

En la última parte de la tesis se trata la sincronización de un usuario deseado que transmite una secuencia de entrenamiento conocida en un sistema de comunicaciones DS-CDMA.
El modelo de señal utilizado agrupa el ruido, y la interferencia externa y de acceso múltiple en un término de ruido equivalente que presenta una matriz de correlación espacio-temporal desconocida. Partiendo de este modelo, se deduce un estimador del retardo que es una aproximación para un numero grande de muestras del estimador ML exacto y que es apropiado para canales con desvanecimientos lentos y noselectivos en frecuencia. El estimador propuesto es una técnica de un solo usuario y es resistente al efecto near-far. Su importancia radica en el hecho de que aprovecha la estructura de las señales en el dominio temporal y espacial, lo que contrasta con otros métodos existentes que, a pesar de utilizar un array de antenas, sólo utilizan la estructura de las señales en uno de los dos dominios. En un sistema de comunicaciones móviles, el usuario deseado está interferido por un número generalmente elevado de señales de otros usuarios y por posibles interferencias externas. En concordancia con este hecho, los resultados numéricos han mostrado que el uso conjunto de todos los grados de libertad espacio-temporales es indispensable para la correcta adquisición y seguimiento del retardo en sistemas con una carga elevada de usuarios y/o en presencia de interferencias externas.
The thesis deals with the synchronization of one or several replicas of a known signal received in a scenario with multipath propagation and directional interference. A connecting theme along this work is the systematic application of the maximum likelihood (ML) principle together with a signal model in which the spatial signatures are unstructured and the noise term is Gaussian with an unknown correlation matrix. This last assumption is key in obtaining estimators that are capable of mitigating the disturbing signals that exhibit certain structure. On the other hand, the assumption of unstructured spatial signatures is interesting from a practical standpoint and facilitates the estimation. The elimination of the multidimensional searches required by many estimators is one of the main objectives of the thesis.

In the first part of the thesis, the maximum likelihood solution to the general time delay estimation problem for the case of noise with unknown spatial correlation is derived. The resulting criterion for the delays is shown to be consistent and asymptotically efficient; but it is highly non-linear, and does not lead to simple optimization procedures. It is shown that the optimal ML criterion can be approximated by an asymptotically equivalent cost function. The cost function depends linearly on the projection matrix onto the subspace spanned by the signals, and hence it can be minimized using the IQML algorithm. The existence of simple initialization schemes based on identity weightings or ESPRIT makes the approach viable for practical implementation. The proposed cost function can be applied to the estimation of the delay in a FIR channel. In this case, each iteration of IQML comes down to rooting a polynomial.

The goal of the estimators presented in the second part of the thesis is to take advantage of one particularity of the GNSS (Global Navigation Satellite Systems) systems, such as GPS and GLONASS, consisting in that the direction-of-arrival of the line-of-sight signal may be known a priori. A simplified and approximate model for the received signal is proposed. The ML estimators of the time delay and carrier phase of the direct signal largely reduce the bias produced by multipath components. Their RMSE is in many situations very close to or even better than the best possible performance attainable with more detailed models of the multipath channel. It is also shown that the ML estimates can be obtained from the output signal of a hybrid beamformer.

In the last part of the thesis, the synchronization of a desired user transmitting a known training sequence in a DS-CDMA communication system is addressed. Multiple-access interference, external interference and noise are assumed to have unknown space-time correlation. A large-sample ML code-timing estimator that operates in frequency-nonselective, slowly fading channels is derived. It is a single-user and near-far resistant method. It is shown that the use of all spatial and temporal degrees of freedom is indispensable for the correct acquisition and tracking of the synchronization parameters in heavily loaded systems and/or in the presence of external interference.

Målsättningen med examensarbetet är att utvärdera en metod för att upprätta en kommunikationslänk från en mobil satellitterminal till en geostationär kommunikationssatellit utan kännedom om satellitterminalens position på jordytan. Målsättningen är intressant då GNSS-operatörer (främst i det allmänna USA-drivna GPS-systemet men möjligen även i de tillkommande franska, kinesiska, ryska och europeiska systemen) begränsar den allmänna tillgängligheten av taktiska/strategiska skäl vid konflikter och kriser. Därtill att allmänna globala navigationssatellittjänster, GNSS-system, ofta bygger på mottagningsantenner med låg riktverkan vilka kan störas ut av lokala störningskällor. En mobil satellitterminal blir därmed beroende av manuell inmatning av riktningsvinklar för att upprätta nya satellitkommunikationslänkar. Systemet blir då mycket sårbart. I denna rapport återges resultat från mätserier inhämtade vid satellitterminalinstallationer utförda i Frankrike, Indonesien, Kanada, Polen, Sverige och USA.
The objective of the thesis is to evaluate a method for establishing a communication link from a mobile earth station to a geostationary communication satellite without prior knowledge of the position of the earth station. The objective is interesting as the GNSS-operators (mainly in the United States-run GPS-system, but possibly also in the French, Chinese, Russian and European systems) limits the general availability of tactical/strategic reasons during conflicts and crises. Furthermore, general GNSS-systems are based on receiving antennas with low directivity which can be disrupted by a local opponent or by other local sources of interference. A mobile earth station, lacking proper positioning information, depends on manual entry of directional angles to establish new satellite communication links. The system then becomes very vulnerable. This report evaluates measurement data gathered from deployed satellite terminal installations in Canada, France, Indonesia, Poland, Sweden and the U.S.

Actuellement, on constate dans le domaine de la navigation, un besoin croissant de localisation par satellites. Apres une course a l'amelioration de la precision (maintenant proche de quelques centimetres grace a des techniques de lever d'ambiguite sur des mesures de phase), la releve du nouveau defi de l'amelioration de l'integrite du GNSS (GPS, Galileo) est a present engagee. L'integrite represente le degre de confiance que l'on peut placer dans l'exactitude des informations fournies par le systeme, ainsi que la capacite a avertir l'utilisateur d'un dysfonctionnement du GNSS dans un delai raisonnable. Le concept d'integrite du GNSS multi-constellation necessite une coordination au niveau de l'architecture des futurs recepteurs combines (GPS-Galileo). Le fonctionnement d'un tel recepteur dans le cas de passage du systeme multi-constellation en mode degrade est un probleme tres important pour l'integrite de navigation. Cette these se focalise sur les problemes lies a la navigation aeronautique multiconstellation et multi-systeme GNSS. En particulier, les conditions de fourniture de solution de navigation integre sont evaluees durant la phase d'approche APV I (avec guidage vertical). En disposant du GPS existant, du systeme Galileo et d'un systeme complementaire geostationnaire (SBAS), dont les satellites emettent sur des frequences aeronautiques en bande ARNS, la question fondamentale est comment tirer tous les benefices d'un tel systeme multi-constellation pour un recepteur embarque a bord d'un avion civil. En particulier, la question du maintien du niveau de performance durant cette phase de vol APV, en termes de precision, continuite, integrite et disponibilite, lorsque l'une des composantes du systeme est degradee ou perdu, doit etre resolue. L'objectif de ce travail de these est donc d'etudier la capacite d'un recepteur combine avionique d'effectuer la tache de reconfiguration de l'algorithme de traitement apres l'apparition de pannes ou d'interferences dans une partie du systeme GNSS multiconstellation et d'emettre un signal d'alarme dans le cas ou les performances de la partie du systeme non contaminee ne sont pas suffisantes pour continuer l'operation en cours en respectant les exigences de l'aviation civile. Egalement, l'objectif de ce travail est d'etudier les methodes associees a l'execution de cette reconfiguration pour garantir l'utilisation de la partie du systeme GNSS multi-constellation non contaminee dans les meilleures conditions. Cette etude a donc un interet pour les constructeurs des futurs recepteurs avioniques multiconstellation
The International Civil Aviation Organization (ICAO) has defined the concept of Global Navigation Satellite System (GNSS), which corresponds to the set of systems allowing to perform satellite-based navigation while fulfilling ICAO requirements. The US Global Positioning Sysem (GPS) is a satellite-based navigation system which constitutes one of the components of the GNSS. Currently, this system broadcasts a civil signal, called L1 C/A, within an Aeronautical Radio Navigation Services (ARNS) band. The GPS is being modernized and will broadcast two new civil signals: L2C (not in an ARNS band) and L5 in another ARNS band. Galileo is the European counterpart of GPS. It will broadcast three signals in an ARNS band: Galileo E1 OS (Open Service) will be transmitted in the GPS L1 frequency band and Galileo E5a and E5b will be broadcasted in the same 960-1215 MHz ARNS band than that of GPS L5. GPS L5 and Galileo E1, E5a, E5b components are expected to provide operational benefits for civil aviation use. However, civil aviation requirements are very stringent and up to now, the bare systems alone cannot be used as a means of navigation. For instance, the GPS standalone does not implement sufficient integrity monitoring. Therefore, in order to ensure the levels of performance required by civil aviation in terms of accuracy, integrity, continuity of service and availability, ICAO standards define different systems/algorithms to augment the basic constellations. GPS, Galileo and the augmentation systems could be combined to comply with the ICAO requirements and complete the lack of GPS or Galileo standalone performance. In order to take benefits of new GNSS signals, and to provide the service level required by the ICAO, the architecture of future combined GNSS receivers must be standardized. The European Organization for Civil Aviation Equipment (EUROCAE) Working Group 62, which is in charge of Galileo standardization for civil aviation in Europe, proposes new combined receivers architectures, in coordination with the Radio Technical Commission for Aeronautics (RTCA). The main objective of this thesis is to contribute to the efforts made by the WG 62 by providing inputs necessary to build future receivers architecture to take benefits of GPS, Galileo and augmentation systems. In this report, we propose some key elements of the combined receivers' architecture to comply with approach phases of flight requirements. In case of perturbation preventing one of the needed GNSS components to meet a phase of flight required performance, it is necessary to be able to switch to another available component in order to try to maintain if possible the level of performance in terms of continuity, integrity, availability and accuracy. That is why future combined receivers must be capable of detecting the impact of perturbations that may lead to the loss of one GNSS component, in order to be able to initiate a switch. These perturbations are mainly atmospheric disturbances, interferences and multipath. In this thesis we focus on the particular cases of interferences and ionosphere perturbations. The interferences are among the most feared events in civil aviation use of GNSS. Detection, estimation and removal of the effect of interference on GNSS signals remain open issues and may affect pseudorange measurements accuracy, as well as integrity, continuity and availability of these measurements. In literature, many different interference detection algorithms have been proposed, at the receiver antenna level, at the front-end level. Detection within tracking loops is not widely studied to our knowledge. That is why, in this thesis, we address the problem of interference detection at the correlators outputs. The particular case of CW interferences detection on the GPS L1 C/A and Galileo E1 OS signals processing is proposed. Nominal dual frequency measurements provide a good estimation of ionospheric delay. In addition, the combination of GPS or GALILEO navigation signals processing at the receiver level is expected to provide important improvements for civil aviation. It could, potentially with augmentations, provide better accuracy and availability of ionospheric correction measurements. Indeed, GPS users will be able to combine GPS L1 and L5 frequencies, and future GALILEO E1 and E5 signals will bring their contribution. However, if affected by a Radio Frequency Interference, a receiver can lose one or more frequencies leading to the use of only one frequency to estimate the ionospheric code delay. Therefore, it is felt by the authors as an important task to investigate techniques aimed at sustaining multi-frequency performance when a multi constellation receiver installed in an aircraft is suddenly affected by radiofrequency interference, during critical phases of flight. This problem is identified for instance in [NATS, 2003]. Consequently, in this thesis, we investigate techniques to maintain dual frequency performances when a frequency is lost (L1 C/A or E1 OS for instance) after an interference occurrence

Dans le but de fournir un service GNSS (Global Navigation Satellite System) de localisation continu et disponible partout, les systèmes utilisant des pseudolites et des répéteurs semblent être des solutions pertinentes pour la localisation en indoor. Le système à répélites, inspiré de ces deux méthodes (répéteurs et pseudolites), est aussi proposé pour résoudre cette problématique. Les répélites sont des transmetteurs locaux qui, installés en intérieur, formeront une constellation locale. Ils émettent tous un signal GNSS unique mais déphasé par un délai spécifique à chacun d'eux. Ces délais sont nécessaires pour distinguer les différents signaux reçus au niveau du récepteur. Les travaux de cette thèses sont réalisés dans le cadre du système à répélites et dans l'objectif d'améliorer son architecture et de réduire ses interférences inter-système. En effet, l'architecture du système (un peu encombrante) et les interférences éventuelles avec les signaux satellitaires reçus par un récepteur placé à l'extérieur font partie des inconvénients de ce système. On cherche donc à traiter ces deux difficultés de façon à minimiser leurs effets. Dans une première partie, on étudie les différents codes GNSS existants dans la littérature ainsi que les techniques de modulation employées. Ceci nous mène à proposer des codes ayant un niveau d'interférence équivalent à la référence GPS (obtenue entre deux codes GPS) pour les bandes L1 de GPS et G1 de Glonass. Dans une seconde étape, on développe la modulation IMBOC (Indoor Modified Binary Offset Carrier) pour générer de nouveaux codes caractérisés par des niveaux d'interférence réduits (comparés à la référence GPS). Parmi ces codes il y a deux catégories : ceux qui sont adaptés aux systèmes à répélites (émettant un code unique) et ceux qui sont adaptés aux systèmes pseudolites. Une étude théorique et des simulations des niveaux d'interférences pour les codes émis dans la bande GPS et Glonass sont réalisées pour déterminer les gains en termes de niveaux de bruit. Ce gain (par rapport à la référence GPS) en puissance d'interférence s'élève à 16 dB pour Glonass et 20 dB pour GPS. Pour valider les performances de ces codes, on génère les signaux IMBOC et on observe les interférences réelles qu'ils induisent sur un récepteur GPS recevant un signal satellitaire. Dans la deuxième partie, on utilise la fibre optique pour transmettre le signal du générateur jusqu'aux répélites et pour créer les délais initiaux par propagation du signal dans des bobines de fibre. Ainsi on remplace les câbles coaxiaux et les montages électroniques (de déphasage) par des bobines de fibres plus légères, facile à installer et à faible perte de puissance. Il reste cependant à évaluer avec une précision centimétrique les délais réels induits sur chaque signal dans le but de garantir une précision de localisation inférieure au mètre. Cette précision semble en effet représenter un bon compromis entre complexité globale du système de localisation et réponse à un ensemble suffisant de besoins des utilisateurs potentiels. On développe alors une technique d'estimation des délais basée sur la mesure de déphasage (entre deux signaux sinusoïdaux) et une analyse statistique des séries de mesures. Pour finir, on présente quelques résultats de localisation obtenus avec notre système à répélites déployé dans un environnement indoor typique

This thesis studies the relevance of DS SDR architectures applied to Galileo receivers in the specific context of Civil Aviation, characterized in particular by strict requirements of robustness to interference, in particular, interference caused by DME or CW signals. The Software Defined Radio concept renders the major tendency, inside the receiver, to move the demodulation part from an analog technology to digital signal processing, that is software. The choice of this kind of design is nearly generalized in new receiver architectures so it was considered the case in this work. The Direct Sampling method consists in digitizing the signal as close as possible to the antenna, typically after the LNA and the associated RF bandpass filter. So this technique does not use any conversion to an intermediate frequency, using as much as possible the bandpass sampling principle in order to minimize the sampling frequency and consequently the downstream computational costs. What is more, this thesis aiming at the greatest simplification of the analog part of the receiver, the decision was made to suppress the analog AGC which equips the receivers of classical architecture. Only fixed gained amplifiers should precede the ADC. This document exposes the work done to determine if these choices can apply to a multifrequency (E5a and E1 signals) Galileo receiver intended for a Civil Aviation use. The structure of the document reflects the approach used during this thesis. It progresses step by step from the antenna down to the digital signal, to be processed then by the SDR part. After an introduction detailing the problem to study and its context, the second chapter investigates the Civil Aviation requirements of robustness to interference a satellite navigation receiver must comply with. It is the basis which completely conditions the design process. The third chapter is devoted to the determination of the sampling frequency. Two sampling architectures are proposed: the first implements coherent sampling of the two E5a and E1 bands while the second uses separate sampling. In both cases the necessity to use extra RF filters is shown. The minimum attenuation to be provided by these filters is also specified. These requirements are strong enough to justify a feasibility investigation. It is the subject of chapter four where an experimental study, based on a SAW filter chip available on the shelf, is related. The issue of the sampling clock jitter, of concern with the Direct Sampling technique because of the high frequency of the signal to digitize, is investigated in chapter five. Some simulation results are presented and a dimensioning of the quality of the sampling clock is proposed. In chapter six, quantization, a byproduct of digitization, is detailed. Precisely it is the calculation of the number of bits the ADC must have to digitally represent the whole dynamic of, not only the useful signal, but also of the potential interference. Considering the high binary throughput highlighted in chapters three and six, chapter seven evaluates the possibility to reduce the coding dynamic of the digital signal at the output of the ADC by means of compression functions. The last chapter is focused on the digital separation of the two E5a and E1 bands in the coherent sampling architecture presented in chapter two. Here also specifications of minimum attenuation are given. Lastly the conclusions synthesize the contributions of this thesis and proposes ideas for future work to enrich them and more generally the subject of DS-SDR Galileo receivers for Civil Aviation.

La présente étude s'inscrit dans le domaine des interférences GNSS, en particulier les interférences de leurrage. Le leurrage consiste à induire une fausse position à un récepteur, c'est-à-dire une position différente de celle où il localisé. Cette étude consiste à proposer une approche de détection d'interférences de leurrage pour drone autonome utilisant les données directement issues des récepteurs. En réalisant un état de l'art des méthodes de détection de leurrage, le contrôle du biais d'horloge est apparu comme une approche potentielle. Une modélisation numérique d'une attaque de leurrage sur un récepteur a mis en évidence que le biais d'horloge présente des sauts lorsqu'il passe de la constellation GNSS à la constellation du leurre. En reproduisant cette attaque sur des récepteurs commerciaux utilisant de vrais signaux, le biais d'horloge présente des sauts plus importants que prévus par le modèle, et dans certains cas sur la dérive du biais également. Ces sauts ont été observés sur différents scénarios d'attaque plus ou moins subtiles, cependant l'amplitude de ces sauts semble aléatoire.Pour aller plus loin que la simple détection de leurrage, une approche utilisant une formation de drones communicants a été proposée dans le but de faire une estimation de la localisation du leurre. Cette méthode est basée sur un protocole de déplacement permettant à la formation de délimiter une zone de l'espace où le leurre est supposé être localisé. Le protocole actuel n'est pas encore complètement abouti mais il offre déjà une base prometteuse.L'étude du comportement du biais d'horloge a permis de mettre en évidence son intérêt dans une stratégie de détection de leurrage GNSS. A partir de ce constat, de futurs travaux pourront être menés sur le développement et l'implémentation sur un drone volant d'un algorithme de détection basé sur le contrôle du biais d'horloge. L'étude de l'utilisation d'une formation de drone pour la localisation d'un leurre a permis de poser les bases d'une solution prometteuse. De futurs travaux peuvent être menés afin de compléter le protocole de déplacement et de valider son efficacité face à différents types de leurres
This study is part of the field of GNSS interference detection, in particular spoofing interferences. Spoofing consist in inducing a false position to a receiver, i.e a position different from the receiver's true position. The study's aim is to propose an approach for detecting spoofing interferences on an autonomous UAV using data directly available on the receivers. With the study of the state of the art of spoofing detection methods, the monitoring of the clock bias seemed like a potential method. A numerical modeling of a spoofing attack on a receiver showed that the clock bias undergoes jumps when it switch from the GNSS constellation to the spoofing constellation. By replicating this attack on a commercial receivers using real signals, the clock bias shows higher jumps than expected by the model and in some cases the clock drift also show some jumps. These jumps have been observed on different more or less subtle attack scenarios, however the amplitude of the jumps seems random.To go further than the simple spoofing detection, an approach using a communicating drone formation has been proposed. This method is based on a movement protocol allowing to delimit a space area where the spoofer is supposed to be located. The current protocol is not yet fully completed but it offers a promising basis.The study of the behavior of the clock bias highlighted its interest in a GNSS spoofing detection strategy. Based on this observation, further work could be carried out on the development and implementation on a UAV of a detection algorithm based on the monitoring of the clock bias. The study of the use of a drone formation for the localization of a spoofer led to the basis of a promising solution. Further work could be carried out in order to complete the movement protocol and to validate its efficiency against different types of spoofers

碩士
輔仁大學
電機工程學系碩士在職專班
104
PNDs (Portable Navigation Devices) are widely used in commercial and military applications. GNSS (global navigation satellite system) signals typically have low strengths when reaching a PND and are therefore susceptible to various interference signals. In this paper, we will study the effects of interference resulted from various sources, including electromagnetic interference, continuous-wave interference and multi-path reception interference. Furthermore, countermeasures are proposed to reduce the bad effects. Test system was built and examined to show the improvement on the quality of GNSS signals.

M.Ing.
The increase of interest in the development of radio communications, both terrestrial and satellite is reaching far and beyond the most optimistic expectations. There has been an accelerated emergence of newer technologies, all claiming highly coveted radio frequency spectrum resources. With the push for the development of location based services, utilizing satellite com- communications for military purposes and later for civilian use; there has been a parallel development in terrestrial communications technology making it possible to implement cost efficient reliable user systems for voice and data services ...