Real-Time PPP with Galileo, Paving the Way to European High Accuracy Positioning

Guillermo Tobías, J. David Calle, Pedro Navarro, Irma Rodríguez and Daniel Rodríguez

Abstract:	Precise Point Positioning (PPP) is a positioning technique providing centimeter-level error. PPP processes dual-frequency pseudorange and carrier-phase measurements from a single user receiver, using detailed physical models and corrections, and precise GNSS orbit and clock products calculated beforehand. PPP is different from other precise-positioning approaches like RTK in that no reference stations are needed in the vicinity of the user receiver. The only observation data that must be processed are measurements from the user receiver. Another advantage of PPP is that since the GNSS orbit and clock products are by nature global, the PPP solutions are also global, i.e., the PPP approach works for a receiver located anywhere on or above the Earth surface, and the resulting position is referred to a well-known terrestrial reference frame (normally ITRF). PPP can be applied at post-processing level and also in real-time applications, provided that real-time input orbits and clocks are available. One disadvantage of standard PPP however is its relatively slow convergence time, which is of the order of half an hour for decimetric accuracy, as compared to nearly instantaneous convergence with centimetric accuracy in short-baseline RTK. After the last launch of Galileo IOV satellites in October 2012 and the foreseen launches in late 2014 and early 2015, the European GNSS constellation will soon reach a worthy of consideration size. Even before it reaches its Full Operational Capability, Galileo is already providing an increase in satellite availability with respect to the GPS+GLONASS scenario, providing the additional advantage with regard to the GPS+GLONASS scenario of not having to estimate the so-called inter-frequency biases (as for the case of GLONASS), but a single inter-system bias with respect to GPS. GMV’s magicGNSS suite (www.magicgnss.gmv.com), already allows a registered user to perform multi-GNSS Precise Orbit Determination (POD) processing based on observation RINEX files. The products for the different satellite constellations are generated in an Orbit Determination and Time Synchronisation (ODTS) process. This process receives as input dual-frequency code and phase measurements from a network of reference stations and produces as output satellite orbits and clocks, together with additional estimated parameters such as station clock biases, tropospheric delays and phase ambiguities. The disposition of the 4 Galileo IOV satellites provides up to 3 hours of common view over Europe, making it feasible to perform a Galileo only PPP solution. By means of the aforementioned magicGNSS suite, GMV has already tested the achievable performances of a Galileo only PPP in batch mode, obtaining centimetric positioning error. GMV has been developing over the last years an infrastructure for the generation of precise GPS and GLONASS orbits and clocks in real time. This infrastructure acquires via NTRIP data streams from a worldwide IGS station network, and produces orbit updates every fifteen minutes and clock updates every second from a combined GPS and GLONASS solution that can be then used consistently for real-time PPP applications. In parallel to the real time HA products generation platform, a real-time GPS+GLONASS PPP client has been also developed and integrated in a portable hardware device supporting in-the-field real-time PPP. This device connects to a standard geodetic-class receiver through a serial interface to retrieve the observations, and features mobile communications with the PPP corrections server using GSM or Iridium. The communications have been optimized in order to provide a good balance between the data provider costs (mainly when using Iridium) and the positioning performances. This approach allows the use of a real-time PPP service with many existing geodetic-class receiver (although in the future it is foreseen the availability of dual-frequency receivers at reasonable prices) without the need for upgrading or replacing them, thus extending their operational capabilities. Both the aforementioned real-time products generation server and the real-time PPP client have been recently redesigned and evolved in order to turn them into a fully multi-GNSS infrastructure. This has enabled GMV to test in the end user improvements obtained when adding Galileo to the already processed GPS and GLONASS constellations. In this paper we describe the real-time server and PPP client developments undertaken, and we present both the server (i.e. orbit and clock) performances achieved and the resulting positioning performances, together with the performance improvement when adding Galileo to a challenging kinematic PPP scenario.
Published in:	Proceedings of the 27th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2014) September 8 - 12, 2014 Tampa Convention Center Tampa, Florida
Pages:	2354 - 2362
Cite this article:	Tobías, Guillermo, Calle, J. David, Navarro, Pedro, Rodríguez, Irma, Rodríguez, Daniel, "Real-Time PPP with Galileo, Paving the Way to European High Accuracy Positioning," Proceedings of the 27th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2014), Tampa, Florida, September 2014, pp. 2354-2362.
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