magicGNSS’ RTCM-based Service, a Leap Forward Towards Multi-GNSS High Accuracy Real-Time Processing

G. Tobías, J.D. Calle, A.J. García, D. Luque, I. Rodríguez

Peer Reviewed

Abstract:	Over the recent years, the GNSS community has witnessed how the upcoming GNSS constellations; Galileo, BeiDou and QZSS are becoming a tangible reality together with the already consolidated GPS and GLONASS constellations. The early stages of the aforementioned constellations are falling behind, and new algorithmic improvements, capabilities and services are being developed thanks to the new signals, modulations and frequencies available. These advantages do not come “for free”. New challenges need to be faced too; such as the implementation of new attitude models and new Solar Radiation Pressure models in order to be able to provide the GNSS community with precise satellite orbits and clocks to enable their usage for High Accuracy (HA) applications, such as PPP (Precise Point Positioning). Regarding the precise multi-GNSS product generation, the International GNSS Service (IGS) has been consistently providing precise GPS products for the last 25 years to the GNSS community, which are considered to define the “state-of-the-art” on GPS processing; however, the leap for generating precise multi-GNSS products has not been officially taken yet. For the time being, IGS’s Multi-GNSS Experiment project (MGEX) provides precise multi-GNSS orbits and clocks from different Analysis Centers (ACs). This initiative is definitely contributing to boost the development of multiGNSS services and applications, but these products are not to be considered as official IGS products yet. In this regard, GMV’s magicGNSS suite, already allows a registered user to perform multi-GNSS precise satellite orbit and clock determination processing based on observation RINEX files. With respect to multi-GNSS PPP processing, several online PPP services are currently available for the GNSS user; CSRS-PPP (by the Natural Resources Canada), GAPS (by the University of New Brunswick), APPS (by the Jet Propulsion Laboratory) and magicPPP (GMV). Many performance comparisons between these services have been performed and published, showing remarkable consistencies among them. The main difference lies on the fact that whereas the first three services are GPSbased, magicGNSS’ PPP service provides a user with the capability of computing a multi-GNSS PPP solution using GMVs rapid products, which are generated on a daily basis using the IGS’ MGEX station network as reference. Beyond the post-processing capabilities, GMV has been developing over the last years an infrastructure for the generation of precise multi-GNSS orbits and clocks in real time. This infrastructure acquires via Networked Transport of RTCM via Internet Protocol (NTRIP) data streams from IGS’ MGEX station network, which provide multi-GNSS observations in RTCM format via MultiSignal Messages (MSM). Based on these observations, it produces orbit updates every fifteen minutes and clock updates every second from a combined multi-GNSS 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 multi-GNSS PPP client has been also developed and integrated in an Android-based device supporting in-the-field real-time PPP processing. This terminal connects to a standard geodetic-class receiver through a serial interface in order to retrieve GNSS observations in RTCM format, and allows mobile communications with the PPP corrections server. There are already several real time high accuracy multiGNSS solutions; omniSTAR, RTX, StarFire, VERIPOS Appex, etc. However, these are closed solutions, which rely on their own station networks for the generation of precise multi-GNSS products, and use proprietary messages for feeding their own PPP solutions. In this regard, GMV has embraced RTCM as the standard to be used within their multi-GNSS infrastructure in order to allow interoperability with third party solutions which are aligned with the RTCM standard. This RTCM-based real time multi-GNSS infrastructure has been evaluated under several field scenarios representing many situations that potential users could address in real operations. These include; static, kinematic and combined use cases. In the tests, different visibility conditions have been assessed (open sky or different types of obstacles such as trees or walls), as well as the robustness of the solution against communication losses of different durations. The real-time PPP solutions have been validated against Real-Time Kinematic (RTK) and/or post-processed PPP. Throughout this paper, magicGNSS` multi-GNSS realtime orbits and clocks generation server and the real-time PPP client developments undertaken are described, together with both the server (i.e. orbit and clock) performances achieved when compared to IGS and the resulting positioning performances, emphasizing how any RTCM-based software can be easily tested and integrated within the presented infrastructure, providing a powerful tool for the GNSS community. The emphasis will be put on describing how the complete service architecture deals with the processing of an increasing number of GNSS signals, the support of multiple combinations of different constellations and implementation of an adaptable and flexible RTCM-based service.
Published in:	Proceedings of the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2015) September 14 - 18, 2015 Tampa Convention Center Tampa, Florida
Pages:	2632 - 2642
Cite this article:	Tobías, G., Calle, J.D., García, A.J., Luque, D., Rodríguez, I., "magicGNSS’ RTCM-based Service, a Leap Forward Towards Multi-GNSS High Accuracy Real-Time Processing," Proceedings of the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2015), Tampa, Florida, September 2015, pp. 2632-2642.
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