The Multi-GNSS Experiment (MGEX) of the International GNSS Service (IGS) - Achievements, prospects and challenges

In this contribution, we present a GPS+GLONASS+BeiDou+Galileo four-system model to fully exploit the observations of all these four navigation satellite systems for real-time precise orbit determination, clock estimation and positioning. A rigorous multi-GNSS analysis is performed to achieve the best possible consistency by processing the observations from different GNSS together in one common parameter estimation procedure. Meanwhile, an efficient multi-GNSS real-time precise positioning service system is designed and demonstrated by using the multi-GNSS Experiment, BeiDou Experimental Tracking Network, and International GNSS Service networks including stations all over the world. The statistical analysis of the 6-h predicted orbits show that the radial and cross root mean square (RMS) values are smaller than 10 cm for BeiDou and Galileo, and smaller than 5 cm for both GLONASS and GPS satellites, respectively. The RMS values of the clock differences between real-time and batch-processed solutions for GPS satellites are about 0.10 ns, while the RMS values for BeiDou, Galileo and GLONASS are 0.13, 0.13 and 0.14 ns, respectively. The addition of the BeiDou, Galileo and GLONASS systems to the standard GPS-only processing, reduces the convergence time almost by 70 %, while the positioning accuracy is improved by about 25 %. Some outliers in the GPS-only solutions vanish when multi-GNSS observations are processed simultaneous. The availability and reliability of GPS precise positioning decrease dramatically as the elevation cutoff increases. However, the accuracy of multi-GNSS precise point positioning (PPP) is hardly decreased and few centimeter are still achievable in the horizontal components even with 40
 $$^{\circ }$$
 elevation cutoff. At 30
 $$^{\circ }$$
 and 40
 $$^{\circ }$$
 elevation cutoffs, the availability rates of GPS-only solution drop significantly to only around 70 and 40 %, respectively. However, multi-GNSS PPP can provide precise position estimates continuously (availability rate is more than 99.5 %) even up to 40
 $$^{\circ }$$
 elevation cutoff (e.g., in urban canyons).

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Accuracy and reliability of multi-GNSS real-time precise positioning: GPS, GLONASS, BeiDou, and Galileo

Bernese GNSS Software Version 5.2

: This document is intended to define the standard reference systems realized by the International Earth Rotation and Reference Systems Service (IERS) and the models and procedures used for this purpose. It is a continuation of the series of documents begun with the Project MERIT (Monitor Earth Rotation and Intercompare the Techniques) Standards (Melbourne et al., 1983) and continued with the IERS Standards (McCarthy, 1989; McCarthy, 1992) and IERS Conventions (McCarthy, 1996; McCarthy and Petit, 2004). The current issue of the IERS Conventions is called the IERS Conventions (2010). The reference systems and procedures of the IERS are based on the resolutions of international scientific unions. The celestial system is based on IAU (International Astronomical Union) Resolution A4 (1991). It was officially initiated and named International Celestial Reference System (ICRS) by IAU Resolution B2 (1997) and its definition was further refined by IAU Resolution B1 (2000) and by IAU Resolution B3 (2009). The terrestrial system is based on IUGG (International Union of Geodesy and Geophysics) Resolution 2 (1991). It was officially endorsed as the International Terrestrial Reference System (ITRS) by IUGG Resolution 2 (2007). The transformation between celestial and terrestrial systems is based on IAU Resolution B1 (2000) and was complemented by IAU Resolutions B1 and B2 (2006). The definition of time coordinates and time transformations, the models for light propagation and the motion of massive bodies are based on IAU Resolution A4 (1991), further refined by IAU Resolution B1 (2000) and IAU Resolution B3 (2006). In some cases, the procedures used by the IERS, and the resulting conventional frames produced by the IERS, do not completely follow these resolutions. These cases are identified in this document and procedures to obtain results consistent with the resolutions are indicated.

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IERS Conventions (2010)

The International global navigation satellite system (GNSS ) Service (IGS ) is an organization devoted to the generation of high-precision GNSS data and products; a service that benefits science and society. It is a voluntary federation of over 200 self-funding agencies, universities, and research institutions in more than 100 countries. Established in 1992 and formally launched on 1st January 1994, the IGS has delivered an uninterrupted time series of products that are utilized by a broad spectrum of users. IGS products have evolved over time, including the provision of GNSS data for constellations other than GPS , and the addition of real-time GNSS data and products.

The International GNSS Service

With a total of four new and emerging constellations
(BeiDou, Galileo, QZSS, IRN
SS) as well as the ongoing
modernization of GPS and GLONASS the world of
satellite navigation presently experiences dramatic
changes. Facing these challenges, the International
GNSS Service (IGS) has initiated the Multi-GNSS
Experiment (MGEX) to enable an early familiarization
with the new systems and to
prepare their incorporation
into high-precision GNSS modeling and analysis. The
paper reports on the status of the new constellations and
the MGEX project as of September 2013. The offline
and real-time segment of the multi-GNSS network built
up so far are described and initial data products are
presented. Recent results for individual systems are
highlighted and necessary steps towards a
comprehensive multi-GNSS service are identified.

/pdf/igs-mgex-preparing-the-ground-for-multi-constellation-gnss-5h46b2xgsz.pdf

IGS-MGEX: Preparing the Ground for Multi-Constellation GNSS Science

Within the framework of EUREF, the Federal Agency for Cartography and Geodesy (BKG) has developed a new technique using the open Internet for the real-time collection and exchange of GNSS data, as well as for broadcasting derived products. A major purpose of these activities is the dissemination of Differential GPS corrections (DGPS) for precise positioning and navigation. This paper describes the http-based technique for streaming GNSS data to mobile users connected to the Internet via Mobile IP-Networks like GSM, GPRS, EDGE, or UMTS. The technique establishes a format called Networked Transport of RTCM via Internet Protocol (Ntrip).

Networked Transport of RTCM via Internet Protocol (NTRIP)

The International GNSS Real-Time Service

The International GNSS Service (IGS), formerly the In-ternational GPS Service, is a voluntary federation of more than 200 worldwide agencies that pool resources and permanent GPS & GLONASS station data to generate precise GPS & GLONASS products. The IGS is commit-ted to providing the highest quality data and products as the standard for Global Navigation Satellite Systems (GNSS) in support of Earth science research, multidisci-plinary applications, and education. Currently the IGS includes two GNSSs: GPS and the Russian GLONASS. In view of the ongoing GPS modernisation and the build-up of new navigation systems such as BeiDou, Galileo and QZSS, the IGS has recently established the Multi-GNSS Experiment (MGEX). MGEX serves as a platform for early experimentation and familiarisation with the emerging new signals and constellations. Aside from col-lecting multi-GNSS tracking data from a global network implemented in parallel to the core IGS network, MGEX promotes the generation of dedicated multi-GNSS orbit and clock products and the development of advanced pro-cessing algorithms. The paper describes the current status of the MGEX project, discusses early achievements and presents the long-term vision for transitioning the IGS into a fully generic multi-GNSS service

Georg Weber

Papers

The Multi-GNSS Experiment (MGEX) of the International GNSS Service (IGS) - Achievements, prospects and challenges

IGS-MGEX: Preparing the Ground for Multi-Constellation GNSS Science

Networked Transport of RTCM via Internet Protocol (NTRIP)

The International GNSS Real-Time Service

The IGS MGEX Experiment as a Milestone for a Comprehensive Multi-GNSS Service