GPS User Position Accuracy with Block IIR Autonomous Navigation

Harold Bernstein, Andro F. Bowden, and James H. Gartside

Abstract:	The GPS Block IIR satellites are Block IIA replacement satellites that will be launched in the mid-1990s. These satellites have the option of operating in the autonomous navigation (AUTONAV) mode, where daily clock and ephemeris uploads from the operational control segment (OCS) to each satellite are not necessary to maintain accuracy. The operational situation is examined for the following three conditions: 1. The Block IIR satellites are not in the AUTONAV mode and the OCS uploads clock and ephemeris data daily to each satellite. This mode is the same as the Block IIA mode where the L-Band data delivered to the GPS user is a re-broadcast of the OCS upload. The Block IIR satellites are in the AUTONAV mode and the OCS uploads clock and ephemeris data monthly to each satellite. The L-Band data delivered to the GPS user is the OCS-uploaded data corrected by data processing on board the satellites. The Block IIR satellites are in the AUTONAV mode and the OCS is non-functional. The satellites operate for six months without ground contact. User range error (URE) for the second and third conditions is presented based upon simulated data. The simulation used the WGS-84 earth gravity error model and updates information presented in earlier papers which used the WGS-72 error model. The specification accuracy of all three conditions is almost the same; however, the data now indicates that the accuracy that can be achieved in AUTONAV is a factor of four better than specifications. Furthermore, there are AUTONAV algorithm modifications that have the potential of even further URE improvements. The AUTONAV algorithm can be reprogrammed on-orbit. User position accuracy probability distribution functions for various position error attributes are presented. These are universal curves which allow picking off spherical error probability, circular error probability, vertical error probability, etc., as a function of URE and time in the AUTONAV mode without OCS contact. This information shows how GPS user position accuracy in the AUTONAV mode is affected by earth motion errors (because there is no satellite-to-ground contact). Users with high accuracy receivers as well as users whose measurements are corrupted by selective availability can determine the various attributes of their position accuracy, in or out of the AUTONAV mode.
Published in:	Proceedings of the 6th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1993) September 22 - 24, 1993 Salt Palace Convention Center Salt Lake City, UT
Pages:	1389 - 1399
Cite this article:	Bernstein, Harold, Bowden, Andro F., Gartside, James H., "GPS User Position Accuracy with Block IIR Autonomous Navigation," Proceedings of the 6th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1993), Salt Lake City, UT, September 1993, pp. 1389-1399.
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