Integration Of Galileo Research Articles

Assessing the benefits of Galileo to high-precision GNSS positioning – RTK, PPP and post-processing

Abstract On February 11, 2019, the latest batch of four Galileo satellites has been commissioned for operational use, accelerating the evolution of the Galileo system toward Full Operational Capability (FOC). To exploit the advantages of the European GNSS constellation, all the Galileo signals in the E1 and E5 frequency band have been successfully integrated in Leica GNSS positioning technologies, with the expectation of improved availability, accuracy and reliability. From the user’s perspective, this paper assesses the benefits of Galileo to high-precision GNSS in the real-time kinematic (RTK), real-time precise point positioning (PPP) and post-processing scenarios. Representative measuring conditions, such as open sky, multipath environments and tree canopy, are considered. The RTK results show that in challenging environments, the integration of Galileo significantly improves the RTK fix availability and effectively reduces decimeter-to-meter-level position errors caused by incorrect ambiguity fixes. To characterize the RTK performance of individual GNSS systems, Galileo-only positions are compared with GPS-only and GLONASS-only solutions. The PPP results demonstrate how Galileo benefits the convergence time and positioning accuracy. The post-processing studies show that the inclusion of Galileo provides more accurate solutions for short data durations and long baselines, particularly for data collected under strong multipath conditions.

Galileo-based precise point positioning with different MGEX products

Considering the remarkable progress of the Galileo constellation in recent years, the main objective of this study is to evaluate the performance of dual- and single-frequency Galileo-based precise point positioning (PPP), and its contribution to GPS and Galileo integration with different precise products generated by four analysis centers (ACs) within the context of the Multi-GNSS Experiment (MGEX) of the International GNSS Service (IGS). For this purpose, the daily observation dataset collected at ten IGS stations over one month was processed in both static and kinematic modes for Galileo-only, GPS-only, and GPS/Galileo PPP scenarios. For dual-frequency PPP, the results demonstrate that while the Galileo-only solutions are highly comparable with GPS-only PPP for the static mode, the mean 3D positioning errors for Galileo-only processes are approximately 1-cm higher than those obtained from GPS-only solutions for all agencies. The analysis to evaluate the influence of Galileo satellites with highly eccentric orbits, namely E14 and E18, on dual-frequency Galileo-only PPP performance indicates that including or excluding these satellites has no significant effect on the results. For single-frequency PPP, which is dependent on the GRAPHIC combination, Galileo-only PPP performs significantly better, approximately 40%, than GPS-only solutions in the static mode, whereas kinematic Galileo-only and GPS-only PPP solutions are quite similar for all agencies except for WHU. In addition, the RMS of observation residuals for Galileo in single-frequency PPP was noticeably lower than that for GPS, demonstrating that the observation quality of Galileo code measurements is better than those of GPS. Among the ACs, Galileo-based PPP solutions applying CODE products produced slightly better results than those obtained for GFZ and CNES/CLS in general, whereas processes using WHU products resulted in a worse performance, both in terms of positioning accuracy and of convergence time. The integration of Galileo with GPS was shown to enhance PPP performance significantly in both static and kinematic modes.

Test of the gravitational redshift with stable clocks in eccentric orbits: application to Galileo satellites 5 and 6

The Einstein Equivalence Principle (EEP) is one of the foundations of the theory of General Relativity and several alternative theories of gravitation predict violations of the EEP. Experimental constraints on this fundamental principle of nature are therefore of paramount importance. The EEP can be split into three sub-principles: the universality of free fall (UFF), the local Lorentz invariance (LLI) and the local position invariance (LPI). In this paper we propose to use stable clocks in eccentric orbits to perform a test of the gravitational redshift, a consequence of the LPI. The best test to date was performed with the Gravity Probe A (GP-A) experiment in 1976 with an uncertainty of Our proposal considers the opportunity of using Galileo satellites 5 and 6 to improve on the GP-A test uncertainty. We show that considering realistic noise and systematic effects, and thanks to a highly eccentric orbit, it is possible to improve on the GP-A limit to an uncertainty around after one year of integration of Galileo 5 and 6 data.

Galileo Signal and Positioning Performance Analysis Based on Four IOV Satellites

With the availability of Galileo signals from four in-orbit validation (IOV) satellites, positioning with Galileo-only observations has become possible, which allows us to assess its positioning performance. The performance of the Galileo system is evaluated in respect of carrier-to-noise density ratio (C/N0), pseudorange multipath (including noise), Galileo broadcast satellite orbit and satellite clock errors, and single point positioning (SPP) accuracy in Galileo-only mode as well as in GPS/Galileo combined mode. The precision of the broadcast ephemeris data is assessed using the precise satellite orbit and clock products from the Institute of Astronomical and Physical Geodesy of the Technische Universität München (IAPG/TUM) as references. The GPS-Galileo time offset (GGTO) is estimated using datasets from different types of GNSS receivers and the results indicate that a systematic bias exists between different receiver types. Positioning solutions indicate that Galileo-only SPP can achieve a three-dimensional position accuracy of about six metres. The integration of Galileo and GPS data can improve the positioning accuracies by about 10% in the vertical components compared with GPS-only solutions.

Precise orbit determination and point positioning using GPS, Glonass, Galileo and BeiDou

AbstractState of the art Precise Point Positioning (PPP) is currently based on dual-frequency processing of GPS and Glonass navigation systems. The International GNSS Service (IGS) is routinely providing the most accurate orbit and clock products for these constellations, allowing point positioning at centimeter-level accuracy. At the same time, the GNSS landscape is evolving rapidly, with the deployment of new constellations, such as Galileo and BeiDou. The BeiDou constellation currently consists of 14 operational satellites, and the 4 Galileo In-Orbit Validation (IOV) satellites are transmitting initial Galileo signals. This paper focuses on the integration of Galileo and BeiDou in PPP, together with GPS and Glonass. Satellite orbits and clocks for all constellations are generated using a network adjustment with observation data collected by the IGS Multi-GNSS Experiment (MGEX), as well as from Fugro proprietary reference station network. The orbit processing strategy is described, and orbit accuracy for Galileo and BeiDou is assessed via orbit overlaps, for different arc lengths. Kinematic post-processed multi-GNSS positioning results are presented. The benefits of multiconstellation PPP are discussed in terms of enhanced availability and positioning accuracy.

Study of GNSS SIS Error Worst User Location Algorithm

Signal-In-Space Error (SISE) is important for the system integrity of GNSS. Real-time monitoring SISE has been one of the effective solutions used for improving GNSS system-level integrity. As one of the typical solutions, the Galileo integrity concept uses Signal-In-Space Accuracy (SISA) and Signal-In-Space Monitoring Accuracy (SISMA) respectively to transmit the quality of SIS and the integrity alarming information to users. As an important component of the Galileo Integrity Concept, Worst User Location (WUL) is of great importance for the computation of SISA and SISMA. An improved WUL algorithm based on a geometrical model is given in this paper, which needs no iterative search and is simple when compared with the existing models. The WUL accuracy requirement is discussed based on an analysis of the magnitude of the orbit errors and SIS ranging resolution and error. The conclusion is that, considering the metre-level orbital error observed in the orbit determination process, as long as the orientation error of the WUL is less than three degrees, the projection error of SISE can be kept to centimetre levels. This will satisfy the requirements of most users. The algorithm is further optimised to omit the non-linear iterative parts based on the above assumption. The optimisation reduces computation load and enhances the real-time capability. GPS raw measurements are used to validate the correctness and reliability of the algorithms.

Single epoch estimation of the Galileo integrity chain sensor station clock offsets

The Galileo integrity chain depends on a number of key factors, one of which is contamination of the signal-in-space errors with residual errors other than imperfect modelling of satellite orbits and clocks. A potential consequence of this is that the user protection limit is driven not by the errors associated with the imperfect orbit and clock modelling, but by the distortions induced by noise and bias in the integrity chain. These distortions increase the minimum bias the integrity chain can guarantee to detect, which is reflected in the user protection limit. A contributor to this distortion is the inaccuracy associated with the estimation of the offset between the Galileo sensor station (GSS) receiver clocks and the Galileo system time (GST). This offset is termed the receiver clock synchronization error (CSE). This paper describes the research carried out to determine both the CSE and its associated error using GPS data as captured with the Galileo System Test Bed Version 1 (GSTB-V1). In the study we simulate open access to a time datum using IGS data. Two methods are compared for determining CSE and the corresponding uncertainty (noise) across a global network of tracking stations. The single-epoch single-station method is an ‘averaging’ technique that uses a single epoch of data, and is carried out at individual sensor stations, without recourse to the data from other stations. The global network solution method is also single epoch based, but uses the inversion of a linearised model of the global system to solve for the CSE simultaneously at all GSS along with a number of other parameters that would otherwise be absorbed into the CSE estimate in the averaging technique. To test the effectiveness of various configurations in the two methods the estimated synchronisation errors across the GSS network (comprising 25 stations) are compared to the same values as estimated by the International GPS Service (IGS) using a global tracking network of around 150 stations, as well as precise orbit and satellite clock models determined by a combination of global analysis centres. The results show that the averaging technique is vulnerable to unmodelled errors in the satellite clock offsets from system time, leading to receiver CSE errors in the region of 12 ns (3.7 m), this value being largely driven by the satellite CSE errors. The global network approach is capable of delivering CSE errors at the level of 1.5 ns (46 cm) depending on the number of parameters in the linearised model. The International GNSS Service (IGS) receiver clock estimates were used as a truth model for comparative assessment.

An Efficient Worst User Location Algorithm for the Generation of the Galileo Integrity Flag

This paper proposes a computation method for the determination of the worst user location (WUL) instead of the current grid search-based methods. The WUL is a key parameter in the estimation of the Galileo integrity data. Since a satellite clock error is the same for all users whereas the orbital error is different depending on the location of users, the WUL depends on the satellite orbit errors which can be estimated using the measurements from the Galileo sensor stations. The proposed algorithm uses the resolved orbital errors to calculate an approximate WUL on a spherical model of the Earth. The next step is to determine the WUL on a specified ellipsoid model using an iterative transformation process. Results show that the proposed method is more accurate and computationally efficient than the current search-based methods. The computation time required is minimal making it valuable in meeting the real time requirements for the generation of the Galileo integrity flag.

Galileo, Sunspots, and the Motions of the Earth: Redux

In the Third Day of the Dialogue Concerning the Two Chief World Systems (1632), Galileo presents an argument for the motion of the earth based on the annual motion of sunspots. Presented in a rather obscure and seemingly unorganized manner, this demonstration has been the source of much confusion and debate. Two key writings are Arthur Koestler's attack on Galileo's integrity, based on his reading of the proof as a piece of sophistry, and A. Mark Smith's defense of Galileo, based on a comparison of the Ptolemaic and Copernican explanations of the phenomenon. This essay reexamines the arguments of Galileo and others, uncovering especially a key flaw: that they disregarded, omitted, or trivialized the crucial role played by the precession of the equinoxes.