GPS Orbit and Clock Error Distributions, 2005 to 2012

C. Cohenour, F. van Graas

Abstract:	Receiver Autonomous Integrity Monitoring /Exclusion (RAIM/E) is one mechanism to support high-integrity operations such as aircraft navigation and landing. GPS Signal in Space (SIS) fault probabilities and error distributions are necessary to design fault detection and exclusion algorithms and to compute horizontal and vertical protection levels (HPL, VPL). In a previous paper by the authors, integrity faults and distributions were presented for the three-year period from June 2005 through May 2008. Since then, more than 4 years have elapsed and several questions can be posed, including: did the error distributions change since 2008, do the new Block IIF satellites have better accuracy and integrity performance, do the older Block IIA satellites still have larger errors than the other satellites in the constellation? To address these questions in a rigorous manner, additional data sets were processed using truth ephemerides, broadcast ephemerides and worldwide monitor station measurements for the last four years through June 2012. A number of metrics are considered to accommodate both stand-alone and differential users. Stand-alone users (e.g. enroute navigation, non-precision approach and precise point positioning) will be interested in the combined radial less clock error, and Signal in Space Range Error (SISRE). Differential users will be more concerned with along track and cross track errors. Distributions and Gaussian overbounds are provided for each metric for all four satellite block types; IIA, IIR, IIRM, and IIF. Anomalous events are tabulated, along with event durations to enable computation of historical fault performance. In addition, corrected ephemerides are computed using a three-state model, estimating errors in the reference time of ephemeris (TOE), satellite clock offset (AF0), and satellite frequency offset (AF1). The corrected orbit statistics are provided along with distributions and frequency content of the ephemeris corrections.
Published in:	Proceedings of the ION 2013 Pacific PNT Meeting April 23 - 25, 2013 Marriott Waikiki Beach Resort & Spa Honolulu, Hawaii
Pages:	946 - 958
Cite this article:	Cohenour, C., van Graas, F., "GPS Orbit and Clock Error Distributions, 2005 to 2012," Proceedings of the ION 2013 Pacific PNT Meeting, Honolulu, Hawaii, April 2013, pp. 946-958.
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