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Proceedings ArticleDOI

Comparing the ‘Big 4’ - A User's View on GNSS Performance

TL;DR: The determination and prediction of GNSS satellite orbits and clocks from measurements of global receiver networks, which forms the basis for precise point positioning applications, are discussed and the significance of satellite metadata knowledge is highlighted.
Abstract: With BeiDou-3 and Galileo complementing the legacy systems GPS and GLONASS, a total of four global navigation satellite systems (GNSS) has now become available that offer free and ubiquitous access to accurate positioning, navigation, and timing (PNT). Following an overview of the system status and capabilities, we compare the Big 4 GNSSs in terms of signal and clock characteristics. The signal-in-space range error (SISRE) are assessed and related to the achievable single-point positioning accuracy. Furthermore, service stability and availability aspects are adressed. With respect to geodetic users, we discuss the determination and prediction of GNSS satellite orbits and clocks from measurements of global receiver networks, which forms the basis for precise point positioning applications. Within the International GNSS Service (IGS) various analysis centers independently provide such products based on data of the IGS multi-GNSS network. The challenges in generating precise orbit and clock solutions for the individual constellations are discussed, and the significance of satellite metadata knowledge is highlighted.
Citations
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Journal ArticleDOI
TL;DR: The results show that the inter-satellite link (ISL) contributes a lot to the accuracy improvement of orbit determination and time synchronization for the whole constellation.
Abstract: BeiDou Global Navigation Satellite System (BDS-3) not only performs the normal positioning, navigation and timing (PNT) functions, but also provides featured services, which are divided into geostationary orbit (GEO) and medium earth orbit (MEO) satellite-based featured services in this paper. The former refers to regional services consisting of the regional short message communication service (RSMCS), the radio determination satellite service (RDSS), the BDS satellite-based augmented service (BDSBAS) and the satellite-based precise point positioning service via B2b signal (B2b-PPP). The latter refers to global services consisting of the global short message communication service (GSMCS) and the MEO satellite-based search and rescue (MEOSAR) service. The focus of this paper is to describe these featured services and evaluate their performances. The results show that the inter-satellite link (ISL) contributes a lot to the accuracy improvement of orbit determination and time synchronization for the whole constellation. Compared with some other final products, the root mean squares (RMS) of the BDS-3 precise orbits and broadcast clock are 25.1 cm and 2.01 ns, respectively. The positioning accuracy of single frequency is better than 6 m, and that of the generalized RDSS is usually better than 12 m. For featured services, the success rates of RSMCS and GSMCS are better than 99.9% and 95.6%, respectively; the positioning accuracies of single and dual frequency BDSBAS are better than 3 and 2 m, respectively; the positioning accuracy of B2b-PPP is better than 0.6 m, and the convergence time is usually smaller than 30 min; the single station test shows that the success rate of MEOSAR is better than 99%. Due to the ISL realization in the BDS-3 constellation, the performance and capacities of the global featured services are improved significantly.

53 citations

Journal ArticleDOI
TL;DR: In this article, the authors discuss how far and in what directions, atomic clock technology should be pushed to provide maximum benefits to GNSS performance, reliability and cost, and provide a baseline by reviewing current GNSS satellite atomic clock technologies.
Abstract: Global Navigation Satellite Systems (GNSS) are enabled by atomic clocks, which provide the timing precision and accuracy required for the ranging measurements. Significant investments have been made and will continue to be made, to improve GNSS atomic clock technology and reduce the signal-in-space user range error. After providing a baseline by reviewing current GNSS satellite atomic clock technology, we discuss how far, and in what directions, atomic clock technology should be pushed to provide maximum benefits to GNSS performance, reliability and cost.

26 citations

Journal ArticleDOI
01 Jan 2022-Sensors
TL;DR: In this paper , a combination method of iGMAS orbit and clock products is described, and the performance of the combined solutions is evaluated by various means, which indicates that consistent weights should be assigned for individual constellations and analysis centers included in the combination.
Abstract: Global navigation services from the quad-constellation of GPS, GLONASS, BDS, and Galileo are now available. The international GNSS monitoring and assessment system (iGMAS) aims to evaluate the navigation performance of the current quad systems under a unified framework. In order to assess impact of orbit and clock errors on the positioning accuracy, the user range error (URE) is always taken as a metric by comparison with the precise products. Compared with the solutions from a single analysis center, the combined solutions derived from multiple analysis centers are characterized with robustness and reliability and preferred to be used as references to assess the performance of broadcast ephemerides. In this paper, the combination method of iGMAS orbit and clock products is described, and the performance of the combined solutions is evaluated by various means. There are different internal precisions of the combined orbit and clock for different constellations, which indicates that consistent weights should be assigned for individual constellations and analysis centers included in the combination. For BDS-3, Galileo, and GLONASS combined orbits of iGMAS, the root-mean-square error (RMSE) of 5 cm is achieved by satellite laser ranging (SLR) observations. Meanwhile, the SLR residuals are characterized with a linear pattern with respect to the position of the sun, which indicates that the solar radiation pressure (SRP) model adopted in precise orbit determination needs further improvement. The consistency between combined orbit and clock of quad-constellation is validated by precise point positioning (PPP), and the accuracies of simulated kinematic tests are 1.4, 1.2, and 2.9 cm for east, north, and up components, respectively.

17 citations

28 Jan 2015
TL;DR: In this article, a signal-in-space range error (SISRE) of about 1.1 m is obtained for the CNAV message whereas it is 0.6 m for the legacy navigation message (LNAV).
Abstract: Following an initial test campaign in June 2013, the GPS Directorate has initiated a pre-operational routine generation and transmission of the Civil Navigation Message CNAV starting on 28 April 2014. The new message is broadcast by Block IIR-M satellites on the L2C signal as well as the L2C and L5 signals of the Block IIF satellites. The improved resolution and larger number of parameters in the new CNAV ephemeris message offers a notably reduced ephemeris fitting error and largely avoids the discontinuities of consecutive ephemeris messages from the same upload. CNAV data of the Block IIR-M and IIF satellites have been collected since the start of transmission using a small set of globally distributed receivers offering an almost continuous coverage. Based on comparison with precise ephemerides of the International GNSS Service (IGS), a Signal-in-Space Range Error (SISRE) of about 1.1 m is obtained for the CNAV message whereas it is 0.6 m for the legacy navigation message (LNAV). This degraded performance is related to less frequent CNAV updates resulting in prediction times of up to four days. For a three week period with a daily CNAV update rate almost the same SISRE is obtained as for LNAV. Complementary to the SISRE analysis, the new Inter-Signal Corrections (ISCs) have been monitored, which enable users to correctly account for differential code biases (DCBs) when using other signals than the L1/L2 P(Y)-code observations in real-time positioning applications. The broadcast ISC values agree with DCBs derived in the frame of the IGS Multi-GNSS Experiment and DCBs from the Center for Orbit Determination in Europe on the 0.1 – 2 ns level depending on the ISC type. While users of the the civil L1C/A and L2C signals have, so far, experienced a notably degraded positioning, the ISCs now enable a single point positioning accuracy that is fully competitive with that of semi-codeless P(Y)-code receivers.

14 citations

References
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Journal ArticleDOI
TL;DR: This work determines precise GPS satellite positions and clock corrections from a globally distributed network of GPS receivers, and analysis of data from hundreds to thousands of sites every day with 40-Mflop computers yields results comparable in quality to the simultaneous analysis of all data.
Abstract: Networks of dozens to hundreds of permanently operating precision Global Positioning System (GPS) receivers are emerging at spatial scales that range from 10(exp 0) to 10(exp 3) km. To keep the computational burden associated with the analysis of such data economically feasible, one approach is to first determine precise GPS satellite positions and clock corrections from a globally distributed network of GPS receivers. Their, data from the local network are analyzed by estimating receiver- specific parameters with receiver-specific data satellite parameters are held fixed at their values determined in the global solution. This "precise point positioning" allows analysis of data from hundreds to thousands of sites every (lay with 40-Mflop computers, with results comparable in quality to the simultaneous analysis of all data. The reference frames for the global and network solutions can be free of distortion imposed by erroneous fiducial constraints on any sites.

3,013 citations

Journal ArticleDOI
TL;DR: The IGS Strategic Plan and future directions of the globally-coordinated ~400 station IGS network, tracking data and information products, and outlines the scope of a few of its numerous working groups and pilot projects as the world anticipates a truly multi-system GNSS in the coming decade are discussed.
Abstract: The International GNSS Service (IGS) is an international activity involving more than 200 participating organisations in over 80 countries with a track record of one and a half decades of successful operations. The IGS is a service of the International Association of Geodesy (IAG). It primarily supports scientific research based on highly precise and accurate Earth observations using the technologies of Global Navigation Satellite Systems (GNSS), primarily the US Global Positioning System (GPS). The mission of the IGS is “to provide the highest-quality GNSS data and products in support of the terrestrial reference frame, Earth rotation, Earth observation and research, positioning, navigation and timing and other applications that benefit society”. The IGS will continue to support the IAG’s initiative to coordinate cross-technique global geodesy for the next decade, via the development of the Global Geodetic Observing System (GGOS), which focuses on the needs of global geodesy at the mm-level. IGS activities are fundamental to scientific disciplines related to climate, weather, sea level change, and space weather. The IGS also supports many other applications, including precise navigation, machine automation, and surveying and mapping. This article discusses the IGS Strategic Plan and future directions of the globally-coordinated ~400 station IGS network, tracking data and information products, and outlines the scope of a few of its numerous working groups and pilot projects as the world anticipates a truly multi-system GNSS in the coming decade.

1,442 citations


"Comparing the ‘Big 4’ - A User's Vi..." refers background in this paper

  • ...Since its foundation, the International GNSS Service has aimed at the provision of highest-quality products for GNSS users on a free basis to support a diverse range of scientific and engineering applications [50], [51]....

    [...]

  • ...2 for two stations contributing to the multi-GNSS network [49] of the International GNSS Service (IGS; [50], [51])....

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Journal ArticleDOI
TL;DR: The status and tracking capabilities of the IGS monitoring station network are presented and the multi-GNSS products derived from this resource are discussed and the achieved performance is assessed and related to the current level of space segment and user equipment characterization.

645 citations


"Comparing the ‘Big 4’ - A User's Vi..." refers background in this paper

  • ...have gradually been added to the IGS service portfolio [49]....

    [...]

  • ...2 for two stations contributing to the multi-GNSS network [49] of the International GNSS Service (IGS; [50], [51])....

    [...]

Journal ArticleDOI
TL;DR: The development and numerical values of the new absolute phase-center correction model for GPS receiver and satellite antennas, as adopted by the International GNSS (global navigation satellite systems) Service, are presented and the benefits from switching from relative to absolute antenna phase- center corrections are demonstrated.
Abstract: The development and numerical values of the new absolute phase-center correction model for GPS receiver and satellite antennas, as adopted by the International GNSS (global navigation satellite systems) Service, are presented. Fixing absolute receiver antenna phase-center corrections to robot-based calibrations, the GeoForschungsZentrum Potsdam (GFZ) and the Technische Universitat Munchen reprocessed more than 10 years of GPS data in order to generate a consistent set of nadir-dependent phase-center variations (PCVs) and offsets in the z-direction pointing toward the Earth for all GPS satellites in orbit during that period. The agreement between the two solutions estimated by independent software packages is better than 1 mm for the PCVs and about 4 cm for the z-offsets. In addition, the long time-series facilitates the study of correlations of the satellite antenna corrections with several other parameters such as the global terrestrial scale or the orientation of the orbital planes with respect to the Sun. Finally, completely reprocessed GPS solutions using different phase-center correction models demonstrate the benefits from switching from relative to absolute antenna phase-center corrections. For example, tropospheric zenith delay biases between GPS and very long baseline interferometry (VLBI), as well as the drift of the terrestrial scale, are reduced and the GPS orbit consistency is improved.

458 citations


"Comparing the ‘Big 4’ - A User's Vi..." refers background in this paper

  • ...of the terrestrial reference frame through GPS observations [88] clearly demonstrate the benefit that independent metadata would also bring for this constellation....

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ReportDOI
01 Jan 2008
TL;DR: The National Institute of Standards and Technology (NIST) as discussed by the authors was established by Congress to assist industry in the development of technology needed to improve product quality, to modernize manufacturing processes, to ensure product reliability, and to facilitate rapid commercialization of products based on new scientific discoveries.
Abstract: he National Institute of Standards and Technology was established in 1988 by Congress to " assist industry in the development of technology ... needed to improve product quality, to modernize manufacturing processes, to ensure product reliability ... and to facilitate rapid commercialization ... of products based on new scientific discoveries. " NIST, originally founded as the National Institute of Standards in 1901, works to strengthen U.S. industry's competitiveness; advance science and engineering; and improve public health, safety, and the environment. One of the agency's basic functions is to develop, maintain, and retain custody of the national standards of measurement, and provide the means and methods for comparing standards used in science, engineering, manufacturing, commerce, industry, and education with the standards adopted or recognized by the Federal Government. As an agency of the U.S. Commerce Department's Technology Administration, NIST conducts basic and applied research in the physical sciences and engineering, and develops measurement techniques, test methods, standards, and related services. The Institute does generic and precompetitive work on new and advanced technologies. NIST's research facilities are located at Gaithersburg, MD 20899, and at Boulder, CO 80305. Major technical operating units and their principal activities are listed below. For more information visit the NIST Website at http://www.nist.gov, or contact the Publications and Program Inquiries Desk, 301-975-3058.

424 citations