Carrier phase recovery for array navigation receiver : a fast phase retrieval approach

A fast carrier phase recovery scheme is developed for satellite navigation receiver using an antenna array based on the phase retrieval theory, in which the antenna array provides sufficient measurement information for the phase recovery algorithm. First, the complex satellite signal model after coherent integration is established using the antenna array. Then, considering symbol uncertainty of the navigation data during the coherent integration time, the carrier phase estimation is formulated as a typical phase retrieval problem. At last, using the squared iterative method (SQUAREM), which is capable of superlinear convergence, a fast variant of the Wirtinger Flow (WF) algorithm is derived to solve the phase recovery problem efficiently without compromising the balance between simplicity and stability. As demonstrated by numerical results, the proposed algorithm outperforms the state-of-the-art in terms of the mean squared error (MSE) convergence. Moreover, the adjustment processes of the carrier phase in the proposed method is validated

Analysis and Detection of Outliers in GNSS Measurements by Means of Machine Learning Algorithms

L'abstract è presente nell'allegato / the abstract is in the attachmen

Software Simulator and Signal Analysis for Galileo E5 band Signals

Galileo is the European Global Navigation Satellite System (GNSS) that aims at providing high availability, increased accuracy, and various location services under the civilian control. Four in-orbit validation satellites have already been launched till date and the system is estimated to be fully deployed by the year 2020. The Galileo navigation signals are transmitted at four frequency bands, which are named E5a, E5b, E6, and E1 bands. The signal of interest in this thesis is Galileo E5a band and Galileo E5b band signals. Signal acquisition and signal tracking are the main functions in a GNSS receiver. Acquisition identifies all the visible satellites and estimates the coarse values of carrier frequency and code phase estimates of the satellite signal. Tracking refines the coarse carrier frequency and code phase estimates, and keeps track of the satellite. The objective of this thesis has been to design and implement Galileo E5a and E5b signals receiver which can acquire all the visible E5a and E5b signals and which gives coarse estimate of carrier frequency and code phase. Such a receiver has been successfully designed in Matlab starting from the Matlab initial files provided by the Finnish Geodetic Institute (FGI) provided tool. In this thesis, two different software implementations are analyzed: 1) The acquisition and tracking of simulated Galileo E5a signals generated in the Matlab Simulink E1-E5 model; and 2) The acquisition of real-time Galileo E5b signals received from the satellite provided by Finnish Geodetic Institute (FGI), Masala, Finland. In the Simulink implementation, the whole E5 signal is generated and propagated through different channel profiles. The received signals are tested with acquisition and tracking and the results are compared for different channel profile and Carrier-to-Noise density ratio. Similarly, the real-time Galileo signals from four satellites now available on sky from the Galileo constellation were received and performed acquisition. In both implementations, a sharp triangular peak was observed at the rough frequency and code phase estimates, proving that the Galileo E5a/b signals can be indeed acquired correctly with the implemented simulator

Performance of precise marine positioning using future modernised global satellite positioning systems and a novel partial ambiguity resolution technique

The International Maritime Organisation (IMO) established a set of positioning requirements for future Global Navigation Satellite System (GNSS) constellations in IMO resolution A.915. It is important to be able to determine if these requirements can be met, and what shore infrastructure would be required. This thesis describes the collection of data in a marine environment and the analysis of these data with regards to the requirements. The data collection exercise was held at the beginning of May 2008 and saw THV Alert navigate into Harwich Harbour whilst Global Positioning System (GPS) observation data were recorded from onboard the vessel and from shore-based reference stations. Additional data were obtained from nearby Ordnance Survey reference stations, and two total stations were used to track the vessel’s passage to provide a truth model. Several modernised GPS satellites were tracked. The data were processed under different scenarios, using software developed at UCL, and the positioning performance was analysed in the context of the IMO requirements. Potential performance improvements from modernised GPS and Galileo were then discussed. Providing integrity through single-epoch real-time kinematic positioning, required to meet the strictest IMO requirements, is particularly difficult. The identification of phase observation outliers is not possible before the integer ambiguities are resolved, but an undetected outlier could prevent successful ambiguity resolution. It will not always be necessary to fix all the ambiguities to achieve the required positioning precision, particularly with a multi-GNSS constellation. This thesis introduces a new algorithm for partial ambiguity resolution in the presence of measurement bias. Although computationally intensive, this algorithm significantly improves the ambiguity resolution success rate, increasing the maximum baseline length over which the highest requirements are met with dual-frequency GPS from 1 km to 66 km

Modes dégradés résultant de l'utilisation multi constellation du GNSS

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. ABSTRACT : 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

Analysis and improvement of GNSS navigation message demodulation performance in urban environments

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

Ionospheric scintillation sensitive GNSS tracking error models and mitigation approaches

Ionospheric scintillation refers to the rapid and random fluctuations in intensity and phase of radio frequency signals when they propagate through plasma density irregularities in the ionosphere. It is more frequently observed in the auroral to polar regions and the equatorial to low latitude regions. When scintillation occurs on Global Navigation Satellite System (GNSS), the GNSS signal quality and receiver performance can be significantly degraded, thus increasing the errors in positioning and navigation. Under strong scintillation, the GNSS receiver can even lose the lock on the signals, posing serious threats to safety-critical GNSS applications and precise positioning. For a better understanding of scintillation effects on GNSS signals and receivers, as well as to mitigate the scintillation effects on GNSS positioning, research is carried out in this thesis focusing on the following three aspects: (1) characterizing the GNSS signal intensity fadings under scintillation, (2) modelling scintillation effects on GNSS receiver tracking loops and (3) developing scintillation mitigation approaches to support high accuracy GNSS positioning under scintillation. Signal intensity fadings is one of the reasons that degrade the GNSS receiver tracking performance. By exploiting three months of raw scintillation data recorded by an ionospheric scintillation monitoring receiver (ISMR) deployed at low latitudes, signal intensity fadings due to scintillation are detected and characterized. Their effects on receiver tracking performance are analysed, which contributes to better understanding the low latitude scintillation effects on GNSS receivers. In order to quantitatively model the scintillation effects on GNSS receiver Phase Locked Loops (PLLs) and Delayed Locked Loop (DLLs), the phase and code jitter are estimated, respectively, at the output of PLL and DLL, taking scintillation effects into consideration. The existing models to estimate the phase and code jitters are studied. To address the concerns of the existing models, an alternative approach is developed to estimate the phase and code jitter under scintillation using the output of tracking loop discriminators, which better reflects the actual PLL and DLL tracking performance under scintillation. Additionally, the distribution of the tracking errors are analysed in the presence of scintillation. A customer-defined probability density function is proposed for the first time, which successfully describes the distribution of the PLL tracking errors under different levels of scintillation. The approach to mitigate scintillation effects on GNSS positioning is studied. This thesis employs a phase and code jitter weighting approach to reduce the positioning errors caused by scintillation. In this approach, the positioning stochastic models are improved using the estimated phase and code jitter values considering scintillation effects. In order to improve the performance of this approach, 1-second scintillation indices are proposed in this thesis, which shows more effectiveness in describing the signal fluctuations under scintillation compared with the widely used 1-minute scintillation indices. Additionally, the 1-second scintillation indices outperform the 1-minute ones when used in mitigating positioning errors under scintillation. To implement the scintillation mitigation approach on generic receivers, which are not able to estimate the scintillation indices and consequently the phase and code jitter, the concept of phase and code jitter maps is exploited in this thesis. In this way, generic receivers can extract and calculate the jitter values directly from these maps for each measurement. Regional phase and code jitter maps are constructed in northern Canada using the scintillation data recorded during the geomagnetic storm in September 2017. Results show that with the help of the jitter maps constructed in this thesis, the positioning accuracy at both the ISMR and generic receiver stations can be greatly improved under scintillation

Ionospheric scintillation sensitive GNSS tracking error models and mitigation approaches

Ionospheric scintillation refers to the rapid and random fluctuations in intensity and phase of radio frequency signals when they propagate through plasma density irregularities in the ionosphere. It is more frequently observed in the auroral to polar regions and the equatorial to low latitude regions. When scintillation occurs on Global Navigation Satellite System (GNSS), the GNSS signal quality and receiver performance can be significantly degraded, thus increasing the errors in positioning and navigation. Under strong scintillation, the GNSS receiver can even lose the lock on the signals, posing serious threats to safety-critical GNSS applications and precise positioning. For a better understanding of scintillation effects on GNSS signals and receivers, as well as to mitigate the scintillation effects on GNSS positioning, research is carried out in this thesis focusing on the following three aspects: (1) characterizing the GNSS signal intensity fadings under scintillation, (2) modelling scintillation effects on GNSS receiver tracking loops and (3) developing scintillation mitigation approaches to support high accuracy GNSS positioning under scintillation. Signal intensity fadings is one of the reasons that degrade the GNSS receiver tracking performance. By exploiting three months of raw scintillation data recorded by an ionospheric scintillation monitoring receiver (ISMR) deployed at low latitudes, signal intensity fadings due to scintillation are detected and characterized. Their effects on receiver tracking performance are analysed, which contributes to better understanding the low latitude scintillation effects on GNSS receivers. In order to quantitatively model the scintillation effects on GNSS receiver Phase Locked Loops (PLLs) and Delayed Locked Loop (DLLs), the phase and code jitter are estimated, respectively, at the output of PLL and DLL, taking scintillation effects into consideration. The existing models to estimate the phase and code jitters are studied. To address the concerns of the existing models, an alternative approach is developed to estimate the phase and code jitter under scintillation using the output of tracking loop discriminators, which better reflects the actual PLL and DLL tracking performance under scintillation. Additionally, the distribution of the tracking errors are analysed in the presence of scintillation. A customer-defined probability density function is proposed for the first time, which successfully describes the distribution of the PLL tracking errors under different levels of scintillation. The approach to mitigate scintillation effects on GNSS positioning is studied. This thesis employs a phase and code jitter weighting approach to reduce the positioning errors caused by scintillation. In this approach, the positioning stochastic models are improved using the estimated phase and code jitter values considering scintillation effects. In order to improve the performance of this approach, 1-second scintillation indices are proposed in this thesis, which shows more effectiveness in describing the signal fluctuations under scintillation compared with the widely used 1-minute scintillation indices. Additionally, the 1-second scintillation indices outperform the 1-minute ones when used in mitigating positioning errors under scintillation. To implement the scintillation mitigation approach on generic receivers, which are not able to estimate the scintillation indices and consequently the phase and code jitter, the concept of phase and code jitter maps is exploited in this thesis. In this way, generic receivers can extract and calculate the jitter values directly from these maps for each measurement. Regional phase and code jitter maps are constructed in northern Canada using the scintillation data recorded during the geomagnetic storm in September 2017. Results show that with the help of the jitter maps constructed in this thesis, the positioning accuracy at both the ISMR and generic receiver stations can be greatly improved under scintillation

Galileo AltBOC receivers - Analysis of receiver architectures, acquisition strategies and multipath mitigation techniques for the E5 AltBOC signal

Master of Science Thesi