A New Real-Time Global GPS and GLONASS Precise Positioning Correction Service: Apex

Christian Rocken, Leos Mervart, James Johnson, Zdenek Lukes, Tim Springer, Ted Iwabuchi, Shaun Cummins

Abstract:	GPS Solutions and VERIPOS have jointly implemented an operational system for the real-time estimation and distribution ofglobal orbit and clock corrections for both the GPS and the GLONASS constellations. The corrections for this global augmentation service, called Apex, allow for precise point positioning (PPP) at the several cm-level. The system is based on a 75-stationglobal tracking network (75dual frequency GPS and 45dual frequency GLONASS tracking sites). All dual frequency reference sites are dually redundant (two receivers and two antennas at each site) and stream their phase and pseudorange observations to threeredundant processing centers. Two processing centers are located separately near Aberdeen, Scotland and a third one is located in Singapore. The top three priorities for the processing system are reliability, accuracy, and speed. Reliability is required for VERIPOS customers, many of them performing high cost and challengingoperations in a marine environment. The system is capable of global high-accuracy positioning at the sub-decimeter level in both the horizontal the vertical component. The required processing speed of the system is also related to accuracy because the lower the latency of the transmitted corrections the higher the real-timepositioning accuracy. The corrections are transmitted to users via 7 geostationary satellites, providing full global coverage and specifically targeting users in a marine environment. The process that packages the orbit and clock corrections for transmission is responsible for switching between the duty and backup systems at each of theprocessing centers, if needed. This redundant processing system together with the dual-redundant reference sites guarantees a very high level of reliability for the Apex GPS & GLONASS augmentation service. In this paper we describe the system that we developed, present example positioningresults for testclients, focus on the advantages of using GLONASS in PPP, and discussthe performance of this new system.
Published in:	Proceedings of the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2011) September 20 - 23, 2011 Oregon Convention Center, Portland, Oregon Portland, OR
Pages:	1825 - 1838
Cite this article:	Rocken, Christian, Mervart, Leos, Johnson, James, Lukes, Zdenek, Springer, Tim, Iwabuchi, Ted, Cummins, Shaun, "A New Real-Time Global GPS and GLONASS Precise Positioning Correction Service: Apex," Proceedings of the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2011), Portland, OR, September 2011, pp. 1825-1838.
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