Adaptive filtering applications to satellite navigation

PhDDifferential Global Navigation Satellite Systems employ the extended Kalman filter to estimate the reference position error. High accuracy integrated navigation systems have the ability to mix traditional inertial sensor outputs with navigation satellite based position information and can be used to develop high accuracy landing systems for aircraft. This thesis considers a host of estimation problems associated with aircraft navigation systems that currently rely on the extended Kalman filter and proposes to use a nonlinear estimation algorithm, the unscented Kalman filter (UKF) that does not rely on Jacobian linearisation. The objective is to develop high accuracy positioning algorithms to facilitate the use of GNSS or DGNSS for aircraft landing. Firstly, the position error in a typical satellite navigation problem depends on the accuracy of the orbital ephemeris. The thesis presents results for the prediction of the orbital ephemeris from a customised navigation satellite receiver's data message. The SDP4/SDP8 algorithms and suitable noise models are used to establish the measured data. Secondly, the differential station common mode position error not including the contribution due to errors in the ephemeris is usually estimated by employing an EKF. The thesis then considers the application of the UKF to the mixing problem, so as to facilitate the mixing of measurements made by either a GNSS or a DGNSS and a variety of low cost or high-precision INS sensors. Precise, adaptive UKFs and a suitable nonlinear propagation method are used to estimate the orbit ephemeris and the differential position and the navigation filter mixing errors. The results indicate the method is particularly suitable for estimating the orbit ephemeris of navigation satellites and the differential position and navigation filter mixing errors, thus facilitating interoperable DGNSS operation for aircraft landing

Real-time relative positioning of spacecraft over long baselines

This paper deals with the problem of real-time onboard relative positioning of low Earth orbit spacecraft over long baselines using the Global Positioning System. Large inter-satellite separations, up to hundreds of kilometers, are of interest to multistatic and bistatic Synthetic Aperture Radar applications, in which highly accurate relative positioning may be required in spite of the long baseline. To compute the baseline with high accuracy the integer nature of dual-frequency, double-difference carrier-phase ambiguities can be exploited. However, the large inter-satellite separation complicates the integer ambiguities determination task due to the presence of significant differential ionospheric delays and broadcast ephemeris errors. To overcome this problem, an original approach is proposed, combining an extended Kalman filter with an integer least square estimator in a closed-loop scheme, capable of fast on-the-fly integer ambiguities resolution. These integer solutions are then used to compute the relative positions with a single-epoch kinematic least square algorithm that processes ionospheric-free combinations of de-biased carrier-phase measurements. Approach performance and robustness are assessed by using the flight data of the Gravity Recovery and Climate Experiment mission. Results show that the baseline can be computed in real-time with decimeter-level accuracy in different operating conditions

Designing a Universal GNSS Simulator for Pseudorange Calculation

The development of GNSS (Global Navigation Satellite System) receivers, especially mass market receivers, has to face cost constraints. To reduce the time to market, and thus the costs, the usage of a GNSS signal simulation facility is one possibility. GNSS signal simulators provide an effective tool for simulating the behavior of satellite-based navigation systems. The challenge is that they have to be model the real world as close as possible, taking satellite orbits, atmospheric effects, satellite clock errors, multipath effects, etc. into account. Thus these simulators achieve lower hardware complexity and precise position determination even when proper signal from satellites is absent. The aim is to design a simulator which can simulate the satellite signals while keeping the all the errors as low as possible while keeping the G.D.O.P. in the range of 4 to 5. DOI: 10.17762/ijritcc2321-8169.15017

Robust GNSS Carrier Phase-based Position and Attitude Estimation Theory and Applications

Mención Internacional en el título de doctorNavigation information is an essential element for the functioning of robotic platforms and intelligent transportation systems. Among the existing technologies, Global Navigation Satellite Systems (GNSS) have established as the cornerstone for outdoor navigation, allowing for all-weather, all-time positioning and timing at a worldwide scale. GNSS is the generic term for referring to a constellation of satellites which transmit radio signals used primarily for ranging information. Therefore, the successful operation and deployment of prospective autonomous systems is subject to our capabilities to support GNSS in the provision of robust and precise navigational estimates. GNSS signals enable two types of ranging observations: –code pseudorange, which is a measure of the time difference between the signal’s emission and reception at the satellite and receiver, respectively, scaled by the speed of light; –carrier phase pseudorange, which measures the beat of the carrier signal and the number of accumulated full carrier cycles. While code pseudoranges provides an unambiguous measure of the distance between satellites and receiver, with a dm-level precision when disregarding atmospheric delays and clock offsets, carrier phase measurements present a much higher precision, at the cost of being ambiguous by an unknown number of integer cycles, commonly denoted as ambiguities. Thus, the maximum potential of GNSS, in terms of navigational precision, can be reach by the use of carrier phase observations which, in turn, lead to complicated estimation problems. This thesis deals with the estimation theory behind the provision of carrier phase-based precise navigation for vehicles traversing scenarios with harsh signal propagation conditions. Contributions to such a broad topic are made in three directions. First, the ultimate positioning performance is addressed, by proposing lower bounds on the signal processing realized at the receiver level and for the mixed real- and integer-valued problem related to carrier phase-based positioning. Second, multi-antenna configurations are considered for the computation of a vehicle’s orientation, introducing a new model for the joint position and attitude estimation problems and proposing new deterministic and recursive estimators based on Lie Theory. Finally, the framework of robust statistics is explored to propose new solutions to code- and carrier phase-based navigation, able to deal with outlying impulsive noises.La información de navegación es un elemental fundamental para el funcionamiento de sistemas de transporte inteligentes y plataformas robóticas. Entre las tecnologías existentes, los Sistemas Globales de Navegación por Satélite (GNSS) se han consolidado como la piedra angular para la navegación en exteriores, dando acceso a localización y sincronización temporal a una escala global, irrespectivamente de la condición meteorológica. GNSS es el término genérico que define una constelación de satélites que transmiten señales de radio, usadas primordinalmente para proporcionar información de distancia. Por lo tanto, la operatibilidad y funcionamiento de los futuros sistemas autónomos pende de nuestra capacidad para explotar GNSS y estimar soluciones de navegación robustas y precisas. Las señales GNSS permiten dos tipos de observaciones de alcance: –pseudorangos de código, que miden el tiempo transcurrido entre la emisión de las señales en los satélites y su acquisición en la tierra por parte de un receptor; –pseudorangos de fase de portadora, que miden la fase de la onda sinusoide que portan dichas señales y el número acumulado de ciclos completos. Los pseudorangos de código proporcionan una medida inequívoca de la distancia entre los satélites y el receptor, con una precisión de decímetros cuando no se tienen en cuenta los retrasos atmosféricos y los desfases del reloj. En contraposición, las observaciones de la portadora son super precisas, alcanzando el milímetro de exactidud, a expensas de ser ambiguas por un número entero y desconocido de ciclos. Por ende, el alcanzar la máxima precisión con GNSS queda condicionado al uso de las medidas de fase de la portadora, lo cual implica unos problemas de estimación de elevada complejidad. Esta tesis versa sobre la teoría de estimación relacionada con la provisión de navegación precisa basada en la fase de la portadora, especialmente para vehículos que transitan escenarios donde las señales no se propagan fácilmente, como es el caso de las ciudades. Para ello, primero se aborda la máxima efectividad del problema de localización, proponiendo cotas inferiores para el procesamiento de la señal en el receptor y para el problema de estimación mixto (es decir, cuando las incógnitas pertenecen al espacio de números reales y enteros). En segundo lugar, se consideran las configuraciones multiantena para el cálculo de la orientación de un vehículo, presentando un nuevo modelo para la estimación conjunta de posición y rumbo, y proponiendo estimadores deterministas y recursivos basados en la teoría de Lie. Por último, se explora el marco de la estadística robusta para proporcionar nuevas soluciones de navegación precisa, capaces de hacer frente a los ruidos atípicos.Programa de Doctorado en Ciencia y Tecnología Informática por la Universidad Carlos III de MadridPresidente: José Manuel Molina López.- Secretario: Giorgi Gabriele.- Vocal: Fabio Dovi

Effects of Parent and Peer Behaviors on Adolescent Sexual Behavior: Are Positive and Negative Peer Behaviors Moderators?

Adolescents and young adults account for a significantly high proportion of unintended pregnancy and sexually transmitted infection cases in the United States. According to Jessor\u27s Problem Behavior Theory, combined protective factors, such as exposure to positive parenting and peer behaviors, create an environment that is supportive of conventional behaviors and discouraging of problem behaviors. There is an extensive amount of literature on parent and peer influences on adolescent sexual behavior but few studies address the interactive influence of both parent and peer behaviors on adolescent sexual risk-taking. The purpose of this study was to examine the relationship between maternal supportiveness and strictness on adolescent sexual risk-taking, as well as the moderating influence of peer involvement in positive or negative activities. A sample of 14-16 year old adolescents was drawn from the National Longitudinal Survey of Youth-1997 (NLSY-97; N = 4,008, 50.5% male, 59.4% White, 26.5% Black, and 13.3% other). Higher levels of maternal supportiveness, maternal strictness, and positive peer behaviors were each associated with lower levels of sexual risk-taking two years later. High levels of negative peer behaviors were related to high sexual-risk taking two years later. No interaction terms were significant. Important implications for positive peer relationships were also found. Future research should focus on the comparison of parental warmth and control variables as moderators for the relationship between peer influence and adolescent sexual risk-taking

GNSS precise point positioning :the enhancement with GLONASS

PhD ThesisPrecise Point Positioning (PPP) provides GNSS navigation using a stand-alone receiver with no base station. As a technique PPP suffers from long convergence times and quality degradation during periods of poo satellite visibility or geometry. Many applications require reliable realtime centimetre level positioning with worldwide coverage, and a short initialisation time. To achieve these goals, this thesis considers the use of GLONASS in conjunction with GPS in kinematic PPP. This increases the number of satellites visible to the receiver, improving the geometry of the visible satellite constellation. To assess the impact of using GLONASS with PPP, it was necessary to build a real time mode PPP program. pppncl was constructed using a combination of Fortran and Python to be capable of processing GNSS observations with precise satellite ephemeris data in the standardised RINEX and SP3 formats respectively. pppncl was validated in GPS mode using both staticsites and kinematic datasets.In GPS only mode,one sigma accuracy of 6.4mm and 13mm in the horizontal and vertical respectively for 24h static positioning was seen. Kinematic horizontal and vertical accuracies of 21mm and 33mm were demonstrated. pppncl was extended to assess the impact of using GLONASS observations in addi- tion to GPS instatic and kinematic PPP. Using ESA and Veripos Apex G2 satel- lite orbit and clock products,the average time until 10cm 1D static accuracy was achieved, over arange of globally distributed sites, was seen to reduce by up to 47%. Kinematic positioning was tested for different modes of transport using real world datasets. GPS/GLONAS SPPP reduced the convergence time to decimetre accuracy by up to a factor of three. Positioning was seen to be more robust in comparison to GPS only PPP, primarily due to cycle slips not being present on both satellite systems on the occasions when they occurred,and the reduced impact of undetected outliersEngineering and Physical Sciences Research Council, Verip os/Subsea

DGNSS-Vision Integration for Robust and Accurate Relative Spacecraft Navigation

Relative spacecraft navigation based on Global Navigation Satellite System (GNSS) has been already successfully performed in low earth orbit (LEO). Very high accuracy, of the order of the millimeter, has been achieved in postprocessing using carrier phase differential GNSS (CDGNSS) and recovering the integer number of wavelength (Ambiguity) between the GNSS transmitters and the receiver. However the performance achievable on-board, in real time, above LEO and the GNSS constellation would be significantly lower due to limited computational resources, weaker signals, and worse geometric dilution of precision (GDOP). At the same time, monocular vision provides lower accuracy than CDGNSS when there is significant spacecraft separation, and it becomes even lower for larger baselines and wider field of views (FOVs). In order to increase the robustness, continuity, and accuracy of a real-time on-board GNSS-based relative navigation solution in a GNSS degraded environment such as Geosynchronous and High Earth Orbits, we propose a novel navigation architecture based on a tight fusion of carrier phase GNSS observations and monocular vision-based measurements, which enables fast autonomous relative pose estimation of cooperative spacecraft also in case of high GDOP and low GNSS visibility, where the GNSS signals are degraded, weak, or cannot be tracked continuously. In this paper we describe the architecture and implementation of a multi-sensor navigation solution and validate the proposed method in simulation. We use a dataset of images synthetically generated according to a chaser/target relative motion in Geostationary Earth Orbit (GEO) and realistic carrier phase and code-based GNSS observations simulated at the receiver position in the same orbits. We demonstrate that our fusion solution provides higher accuracy, higher robustness, and faster ambiguity resolution in case of degraded GNSS signal conditions, even when using high FOV cameras

Vector Tracking Loop Design for Degraded Signal Environment

The performance of GPS degrades significantly in urban canyons and in indoor environments. There has been significant research in order to enhance the performance of a GPS receiver in such challenging environment but still the traditional GPS receivers fall short of optimal performance in degraded signal environment where the carrier to noise density ratio(?C/N?_0) drops significantly and when GPS signal is obstructed by the surrounding environment. Improving GPS receiver performance in GPS challenged environment has become one of the very important driving factors of ongoing research in the field of GPS technologies. This thesis presents a modern GPS receiver architecture which is based on vector tracking loops. Traditional GPS receivers employ scalar tracking loops for tracking the satellite signals. Scalar tracking loops treat each channel independently. Therefore aiding of weaker satellite signals is not possible by the stronger signals. In a standard GPS receiver a Delay Lock Loop is used to track the Pseudo-Random Noise (PRN) sequence and a Costas loop is used to track the carrier part of the signal. On the other hand, vector tracking loops process the signals in an aggregate way and can provide better tracking in degraded signal environment. The task of tracking and navigation is done in one algorithm by using an extended Kalman filter. Due to the coupling of tracking and navigation in one processor aiding of weaker signals by the stronger signals is present. With vector tracking approach GPS receiver can take advantage of the redundancy of the GPS measurements that is not possible in the traditional GPS receiver architecture. A vector delay lock loop based on non-linear discriminator function has been implemented in this thesis and its ability to reacquire signals after momentarily blockage has been studied. The simulation results show the better performance of VDLL than conventional tracking methods. /Kir1

LQG 기반 벡터 신호 추적 루프를 적용한 GNSS 수신기의 위치 및 측정치 정확도 분석

학위논문 (석사)-- 서울대학교 대학원 : 기계항공공학부, 2017. 2. 기창돈.With the expansion of the navigation by GNSS, various studies have been conducted to improve the performance of navigation. From GNSS receivers point of view, it can be possible to improve the performance of navigation by estimating more accurate position and measurements and developing more robust signal tracking loop in case of temporal signal block or decrement. To improve the accuracy of position and measurements, various studies based on estimation theory and control theory have been tried instead of using conventional loop filter. In this situation, through LQG theory, which combines optimal estimation theory, and optimal control theory, NCO inputs guarantee optimality under particular performance index. In addition, to improve the robustness of the signal tracking loop, vector tracking loop has been proposed. Eventually, by integrating LQG controller and vector tracking loop, LQG based vector tracking loop has been proposed as signal tracking loop. In this paper, simulation tool is developed to verify LQG based vector tracking loop in various conditions. First LQG based scalar tracking loop is designed to verify the performance of LQG controller. Measurements estimation errors in LQG based scalar tracking loop is smaller than those in LF based scalar tracking loop under various users dynamic. Second LQG based vector tracking loop is designed. From the simple case, only pseudorange measurement and position state, simulation expands the complex case like pseudorange, carrier phase, and Doppler measurements and position, velocity, and clock bias state. As the number of satellites increase, the position and measurements estimation errors decrease. Also measurements estimation errors decrease compared to LQG based scalar tracking loop. Finally, in case of temporal signal power reduction, LQG based vector tracking loop is more robust than conventional signal tracking loop. From this study, the performance of LQG based vector tracking loop is verified. Before applying LQG based vector tracking loop to GNSS receiver, performance analysis can be achieved rapidly using this simulation tool.I. Introduction 1 1. Motivation and Objective 1 2. Trends of Research 4 3. Research Contents and Method 8 4. Contribution 9 II. Signal Tracking Loop of GNSS Receiver 12 1. Structure of GPS Signal 12 2. Structure and Principle of GPS Receiver 15 3. Conventional Signal Tracking Loop 19 4. Structure of Signal Tracking Loop 27 III. LQG based Signal Tracking Loop 31 1. LQG controller 31 2. LQG based Scalar Tracking Loop 34 3. LQG based Vector Tracking Loop 39 IV. Simulation Environment and Results 44 1. Simulation Tool 44 2. Simulation Order 52 3. Measurement Estimation Error of LQG-STL 53 4. Position/Measurement Estimation Error of LQG-VTL 60 V. Conclusion 74 Reference 76 초 록 80Maste