Variational Bayes Phase Tracking for Correlated Dual-Frequency Measurements with Slow Dynamics

We consider the problem of estimating the absolute phase of a noisy signal when this latter consists of correlated dual-frequency measurements. This scenario may arise in many application areas such as global navigation satellite system (GNSS). In this paper, we assume a slow varying phase and propose accordingly a Bayesian filtering technique that makes use of the frequency diversity. More specifically, the method results from a variational Bayes approximation and belongs to the class of nonlinear filters. Numerical simulations are performed to assess the performance of the tracking technique especially in terms of mean square error and cycle-slip rate. Comparison with a more conventional approach, namely a Gaussian sum estimator, shows substantial improvements when the signal-to-noise ratio and/or the correlation of the measurements are low

On the Mitigation of Ionospheric Scintillation in Advanced GNSS Receivers

Ionospheric scintillation is one of the major threats and most challenging propagation scenarios affecting Global Navigation Satellite Systems (GNSS) and related applications. The fact that this phenomenon causes severe degradations only in equatorial and high latitude regions has led to very few contributions dealing with the fundamental scintillation mitigation problem, being of paramount importance in safety critical applications and advanced integrity receivers. The goal of this paper is twofold, first to bring together the most relevant contributions on GNSS receiver design under scintillation conditions, and then, to propose a new GNSS carrier tracking framework and scintillation mitigation methodology. Scintillation complex gain components are modeled as AR processes and embedded into the state-space formulation, providing the filter the capability to distinguish between dynamics and phase scintillation contributions. In addition, the actual need of robust solutions is solved by using an adaptive filtering approach and directly operating with the baseband received signal. Simulation results, using both synthetic and real scintillation data, are provided to support the theoretical discussion and to show the performance improvements of such new approach

Advanced Tracking Loop Architectures for Multi-frequency GNSS Receiver

The multi-frequency Global Navigation Satellite System (GNSS) signals are designed to overcome the inherent performance limitations of single-frequency receivers. However, the processing of multiple frequency signals in a time-varying GNSS signal environment which are potentially affected by multipath, ionosphere scintillation, blockage, and interference is quite challenging, as each signal is influenced differently by channel effects according to its Radio Frequency (RF). In order to get benefit of synchronously/coherently generated multiple frequency signals, advanced receiver signal processing techniques need to be developed.The aim of this research thesis is to extract the best performance benefits out of multifrequency GNSS signals in a time-varying GNSS signal environment. To accomplish this objective, it is necessary to analyze the multi-frequency signal characteristics and to investigate suitable signal processing algorithms in order to enable the best performance of each signal. The GNSS receiver position accuracy and reliability are majorly determined by the signal tracking-loop performance, hence, the primary focus of this thesis is on improving the tracking-loop performance of coherently generated multi-frequency signals.In the first phase of this research, the performance of multi-frequency GNSS signals is analyzed using conventional signal processing algorithms. Furthermore, the performance of a combination of multi-frequency signals is evaluated in order to find the optimum two-frequency signal combination for standalone and differential positioning applications. The limitations of the conventional multi-frequency signal processing algorithms are identified and an optimum dual-frequency signal processing architecture is proposed for robust and precise positioning applications.By making use of the inherent linear relation between the Line-of-Sight (LOS) Doppler shifts of multi-frequency GNSS signals, a computationally efficient Centralized Dynamics Tracking Loop (CTL) architecture is also proposed. In the CTL architecture, the common geometric Doppler shift in the received multi-frequency signals is estimated using a higher-order wide-band filter by making use of multiple frequency channel measurements in a coordinated manner. Additionally, the residual-phase variations specific to each frequency channel are tracked using Phase Lock Loop (PLL) with a narrow bandwidth filter. The CTL filter provides the geometric Doppler shift aid to individual frequency channels. The common Doppler-aided narrow-band signal tracking enhances the signal tracking sensitivity and robustness to the in-band interference in each frequency channel. This further reduces the noise in the linear combination of pseudorange observations.In real GNSS signal environment, multiple frequency signals are often subjected to intentional or unintentional RF interference either at the same time or at different time instants. Moreover, each of these signals is influenced differently by RF interference. To track signals in such time-varying signal conditions, the CTL using an Adaptive Kalman Filter (AKF) is proposed to enable an adaptive tracking loop bandwidth in response to received signal power level and signal dynamics. The central task of the AKF is to effectively blend multiple frequency carrier-phase observations to estimate the common geometric Doppler frequency of received multiple frequency signals. A suitable collaboration in multi-frequency channel tracking using centralized dynamics tracking loop enables a robust carrier tracking even if some of the frequency channels are affected by ionospheric scintillation, multipath, or interference.The performance of the proposed multi-frequency GNSS signal processing algorithms is demonstrated using analytical methods and experimental results based on live satellite data collected over GPS L1, L2C, and L5 signal frequencies. The dual-frequency signal processing architecture proposed in this research thesis has reduced the position error by 50%. The centralized dynamics multi-frequency carrier tracking loop has enhanced the individual channel tracking loop threshold by 7 dB in challenging signal conditions

The Telecommunications and Data Acquisition Report

Reports on developments in programs managed by JPL's Office of Telecommunications and Data Acquisition (TDA) are provided. In space communications, radio navigation, radio science, and ground-based radio and radar astronomy, it reports on activities of the Deep Space Network (DSN) in planning, supporting research and technology, implementation, and operations. Also included are standards activity at JPL for space data and information systems and reimbursable DSN work performed for other agencies through NASA

Diversité et traitements non-linéaires pour les récepteurs modernes

Depuis le doctorat, les travaux de recherche auxquels j'ai contribué ont porté essentiellement sur des problèmes d'estimation d'un signal d'intérêt noyé dans du bruit. Les domaines d'application visés sont majoritairement le radar, mais aussi le GNSS et l'imagerie ultrasonore. Bien que différents, ces domaines sont soumis à des tendances similaires qui caractérisent ou caractériseront certainement les récepteurs modernes. En effet, les enjeux applicatifs requièrent de repousser sans cesse les limites de performance des traitements : le radariste cherche à détecter des petites cibles dans des environnements de plus en plus difficiles ; en GNSS, des solutions de positionnement haute précision sont recherchées dans des milieux très contraints tels les canyons urbains ; en imagerie médicale, une qualité accrue des images est recherchée pour améliorer les diagnostics, pour ne citer que quelques exemples. Parmi les tendances qui permettront de repousser les performances des récepteurs modernes, deux sont particulièrement présentes dans les travaux conduits jusqu'ici : la diversité des signaux et les traitements non linéaires. Le document illustre ceci en se focalisant sur deux des thématiques de recherche conduites jusqu’ici, à savoir « Le traitement du signal pour des radars de détection à large bande instantanée » et « La poursuite robuste de la phase d'un signal GNSS multifréquence ». Pour conclure, les perspectives de recherche d’un point de vue méthodologique et applicatif sont discutées

Solid Earth science in the 1990s. Volume 3: Measurement techniques and technology

Reports are contained from the NASA Workshop on Solid Earth Science in the 1990s. The techniques and technologies needed to address the program objectives are discussed. The Measurement Technique and Technology Panel identified (1) candidate measurement systems for each of the measurements required for the Solid Earth Science Program that would fall under the NASA purview; (2) the capabilities and limitations of each technique; and (3) the developments necessary for each technique to meet the science panel requirements. In nearly all cases, current technology or a development path with existing technology was identified as capable of meeting the requirements of the science panels. These technologies and development paths are discussed

The 1995 Goddard Conference on Space Applications of Artificial Intelligence and Emerging Information Technologies

This publication comprises the papers presented at the 1995 Goddard Conference on Space Applications of Artificial Intelligence and Emerging Information Technologies held at the NASA/Goddard Space Flight Center, Greenbelt, Maryland, on May 9-11, 1995. The purpose of this annual conference is to provide a forum in which current research and development directed at space applications of artificial intelligence can be presented and discussed

Commonwealth of Independent States aerospace science and technology, 1992: A bibliography with indexes

This bibliography contains 1237 annotated references to reports and journal articles of Commonwealth of Independent States (CIS) intellectual origin entered into the NASA Scientific and Technical Information System during 1992. Representative subject areas include the following: aeronautics, astronautics, chemistry and materials, engineering, geosciences, life sciences, mathematical and computer sciences, physics, social sciences, and space sciences

Research and Technology Objectives and Plans Summary (RTOPS)

A compilation of summary portions of each of the Research and Technology Objectives and Plans (RTOPS) used for management review and control of research currently in progress throughout NASA is presented. Subject, technical monitors, responsible NASA organization, and RTOP number indexes are included

Bibliography of global change, 1992

This bibliography lists 585 reports, articles, and other documents introduced in the NASA Scientific and Technical Information Database in 1992. The areas covered include global change, decision making, earth observation (from space), forecasting, global warming, policies, and trends