Independent URA Monitor for GPS IIIC

Ronald Braff, Brian Bian, and Curtis Shively

Peer Reviewed

Abstract: Each GPS IIIC space vehicle (SV) will broadcast a user range accuracy (URA) that bounds the errors in that SV’s signal-in-space (SIS). An independent URA monitor (IUM) is examined as part of the next generation GPS Control Segment (OCX) to ensure URA bounding of errors in the SV ephemeris and clock corrections. Since the IUM operates on single snapshot data to maintain timely integrity, the minimum monitorable URAs (MMUs) are larger than if based on continuous tracking data and an orbital model. Operational feasibility of the IUM is assessed for the Localizer Performance with Vertical guidance (LPV) aircraft approach down to a 200 ft decision altitude (LPV200). Although the MMUs are larger than the URAs previously envisioned for GPS IIIC, availability for LPV200 would be sufficiently high at U.S. locations, including Alaska and Hawaii, but would be less than 0.99 at some non-U.S. locations analyzed, particularly in the Southern Hemisphere.
Published in: NAVIGATION: Journal of the Institute of Navigation, Volume 59, Number 1
Pages: 37 - 49
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