GPS Group Delay Differential Variation Impact on Civil Users

Theodore Dass

Abstract:	On November 1, 2013, GPS SVN 61 (PRN 2) suffered from an L-band hardware anomaly that caused some significant range errors (on the order of 6 meters) to be flagged in the GPS Master Control Station (MCS). The performance information presented by the MCS indicated that the satellite clock appeared to have taken a ~6 meter phase step. Yet at the same time, the Jet Propulsion Laboratory Global Differential GPS System (JPL GDGPS) indicated little range error for SVN 61. The standard action for the 2 SOPS to remedy this problem is to absorb the 6 meter error into the SV clock bias state and re-upload fresh data to reduce the SV broadcast clock error. When this upload remedied the observed range errors for the authorized, dual-frequency users, at the same time the JPL GDGPS indicated a ~7 meter error. In hindsight, the anomaly was not due to a problem with the on-board SV time-keeping system, but was instead caused by an L-band anomaly that caused a variation in group delay. This paper will show how that group delay variation manifested into the observed errors that were different between civil users (single frequency) and military users (dual frequency) due to differences in ionospheric delay processing.
Published in:	Proceedings of the ION 2015 Pacific PNT Meeting April 20 - 23, 2015 Marriott Waikiki Beach Resort & Spa Honolulu, Hawaii
Pages:	95 - 99
Cite this article:	Dass, Theodore, "GPS Group Delay Differential Variation Impact on Civil Users," Proceedings of the ION 2015 Pacific PNT Meeting, Honolulu, Hawaii, April 2015, pp. 95-99.
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