Time dissemination and synchronization methods to support Galileo timing interfaces

Precise timing is an important factor in the modern information-oriented society and culture. Timing is one of the key technologies for such basic and everyday things, like cellular communications, Internet, satellite navigation and many others. Satellite navigation systems offer cost-efficient and high-performance timing services, and GPS is presently the unchallenged market leader. However, GPS is under military control and does not offer availability and performance guarantees. From a user perspective, this situation will change with the advent of the European satellite navigation system Galileo which shall be operated on a commercial basis by civil entities and shall accept certain liabilities for its services providing also guaranteed service performances. This work is motivated by the new opportunities and challenges related to Galileo timekeeping and applications, and in particular by the necessity to (a) produce and maintain a stable, accurate and robust system timescale which can serve for both accurate prediction of satellite clocks and for the metrological purposes, (b) establish accurate and reliable timing interface to GPS to facilitate Galileo interoperability, (c) maximize user benefits from the new system features like service guarantees and support application development by enabling their certification. The thesis starts with overview of atomic clocks, timekeeping and timing applications. Further Galileo project and system architecture are described and details on Galileo timekeeping concept are given. In addition, the state-of-the-art timekeeping and time dissemination methods and algorithms are presented. Main findings of the thesis focus on (a) Galileo timekeeping. Various options for generation of Galileo system time are proposed and compared with respect to the key performance parameters (stability and reliability). Galileo System Time (GST) stability requirements driven by its navigation and metrological functions are derived. In addition, achievable level of GST stability (considering hardware components) is analyzed. Further, optimization of the present baseline with respect to the design of Galileo Precise Timing Facility (PTF), and its redundancy and switching concepts is undertaken. Finally, performance analysis of different options for generation of the ensemble time is performed and considerations with respect to the role of the ensemble time in Galileo are provided, (b) GPS Galileo timing interface. The magnitude and statistical properties of the time offset are investigated and the impact of the time offset onto the user positioning and timing accuracy is studied with the help of simulated GPS and Galileo observations. Here a novel simulation concept which is based on utilization of GPS data and their scaling for Galileo is proposed. Both GPS and Galileo baseline foresees that the GPS/Galileo time offset shall be determined and broadcast to users in the navigation messages. For this purposes, the offset shall be predicted using available measurement data. Simulations of GPS Galileo time offset determination and prediction are presented. The prediction is made relying on both traditional method and on the advanced techniques like Box-Jenkins prediction (based on the autoregressive moving average approach) and Kalman filter. The end-to-end budgets for different options of GPS Galileo time offset determination are also presented. (c) Galileo interface to timing users (Galileo timing service). The relevance of GST restitution from the metrological point of view is discussed and recognition of GST as a legal time reference is proposed. Assessment of the accuracy of the Galileo timing service is presented. Finally, recommendations for Galileo are provided based on the findings of the thesis

USNO GPS program

Initial test results indicated that the Global Positioning System/Time Transfer Unit (GPS/TTU) performed well within the + or - 100 nanosecond range required by the original system specification. Subsequent testing involved the verification of GPS time at the master control site via portable clocks and the acquisition and tracking of as many passes of the space vehicles currently in operation as possible. A description and discussion of the testing, system modifications, test results obtained, and an evaluation of both GPS and the GPS/TTU are presented

The 26th Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting

This document is a compilation of technical papers presented at the 26th Annual PTTI Applications and Planning Meeting. Papers are in the following categories: (1) Recent developments in rubidium, cesium, and hydrogen-based frequency standards, and in cryogenic and trapped-ion technology; (2) International and transnational applications of Precise Time and Time Interval technology with emphasis on satellite laser tracking, GLONASS timing, intercomparison of national time scales and international telecommunications; (3) Applications of Precise Time and Time Interval technology to the telecommunications, power distribution, platform positioning, and geophysical survey industries; (4) Applications of PTTI technology to evolving military communications and navigation systems; and (5) Dissemination of precise time and frequency by means of GPS, GLONASS, MILSTAR, LORAN, and synchronous communications satellites

Performance of new GNSS satellite clocks

In Global Navigation Satellite Systems (GNSS), the on-board clocks are a key component from which timing and navigation signals are generated. This thesis reviews the performance of the first Passive Hydrogen Maser (PHM) launched by the Galileo system in 2008; and demonstrates how the new PHM can be consider as the best clock in space, pushing the physical clock error contribution below the noise floor of geodetic time transfer capabilities. Furthermore, overall GNSS clock peformance is reviewe

Undifferenced and Uncombined GNSS Time Transfer and its Space Applications

This thesis presents a framework for developing a state-of-the-art undifferenced and uncombined (UDUC) time transfer technique for space applications. It addresses challenges in GNSS time transfer, such as multi-frequency signal modelling, satellite clock estimation, and hardware delay variations. The thesis introduces the UDUC POD method for GNSS time transfer in space and explores the feasibility of constructing a LEO-based space-time reference. This PhD dissertation is among the first to investigate the UDUC GNSS time transfer

INSTITUTE OF PHYSICS PUBLISHING

doi:10.1088/0026-1394/42/4/005 Geodetic techniques for time and frequency comparisons using GPS phase and code measurement

Timing Experiments with Global Navigation Satellite System Clocks

The science of timekeeping is crucial in many dierent applications around the world. One of the most signicative applications in which time and frequency metrology has an essential role are Global Navigation Satellite Systems (GNSS). Any satellite navigation system indeed, is based on the transmission of signals from a constellation of satellites: processing these signals it is possible to estimate the position of a user, provided that the time of transmission is indicated with extremely high accuracy. In fact, being the distance measured from a time, any error in the measure of time will be directly mapped into an error in the user position, which has to be kept below its specied limits. The positioning accuracy is widely determined by the clocks quality. It is why all the satellites need to y very accurate atomic clocks: fundamental for their excellent stability. An agreement between the European Community and the European Space Agency (ESA) gave rise to a new European satellite system: Galileo. The Istituto Nazionale di Ricerca Metrologica (INRiM) is deeply involved in the Galileo project, mainly concerning the activities related to the experimental phases, such as the generation of an experimental reference time scale for the system and the metrological characterization of atomic clocks employed onboard satellites. This thesis will describe the timing experiments carried out in these years of doctorate with GNSS clocks, both with space and ground clocks, within the experimental phases of the Galileo project

Advanced tracking systems design and analysis

The results of an assessment of several types of high-accuracy tracking systems proposed to track the spacecraft in the National Aeronautics and Space Administration (NASA) Advanced Tracking and Data Relay Satellite System (ATDRSS) are summarized. Tracking systems based on the use of interferometry and ranging are investigated. For each system, the top-level system design and operations concept are provided. A comparative system assessment is presented in terms of orbit determination performance, ATDRSS impacts, life-cycle cost, and technological risk

White Paper #1: Fundamental Physics

The Standard Model (SM) of particle physics and General Relativity (GR) are the two pillars of our current understanding of Nature. Both theories have been probed individually with ever increasing precision and are consistent with nearly all experimental observations. However, they fail to explain dark matter, dark energy, or the imbalance between matter and anti-matter in the universe. Yet, dark matter and dark energy represent 95% of the energy content of our universe while known matter (atoms, molecules) amounts to only 5%. Today, dark matter and dark energy have an unknown origin and there is a great deal of experimental and theoretical activity to solve this puzzle. In summary, the clustering of large-scale structure and the accelerated behaviour of cosmic fluid could be addressed whether finding out new (unknown) forms of matter or assuming that gravity behaves in different ways at infrared scales. Furthermore, the lack of a self-consistent theory of Quantum Gravity prevents the unification of SM and GR at ultraviolet scales. This is one of the biggest challenges that theoretical physics is facing today. String theory or loop quantum gravity are good candidates to solve this puzzle and interestingly both of them foresee violations of the Einstein's Equivalence Principle. With that respect the Einstein's Equivalence Principle assumes a central role in the search for a quantum theory of gravity. The open problems in fundamental physics investigated in this white paper are: (i) Validity of the Einstein's Equivalence Principle; (ii) Origin and nature of dark matter and dark energy; (iii) Decoherence and collapse models in quantum mechanics; (iv) Quantum many-body physics. They will be addressed from different research corners and with different experimental methods: (i) Ultracold atoms; (ii) High stability and accuracy atomic clocks; (iii) Matter-wave interferometry; (iv) Classical and quantum links. The cosmos is a particularly attractive laboratory as it provides particles (cosmic rays) or objects (black holes, neutron stars) which are not produced in manmade laboratories. Space is also an excellent environment for high precision physics as the absence of atmosphere or drag-free satellites provide unique observation opportunities. For instance the MICROSCOPE mission has taken advantage of extremely long free-fall conditions in Earth orbit to set the record in testing the Equivalence Principle beyond what has been possible on Earth. Large velocity, velocity variations and large variation of the gravitational potential are accessible on board a spacecraft, thus providing wide signals for testing GR. Finally, the huge free propagation distances available in space provide very long baselines to test the spacetime metric with high performance links both classical and quantum