Navigation Message Correction Tables: A Proposal

Jim Butts and Chris Shank

Abstract:	An operational concept for reducing the GPS clock and ephemeris errors is described which would significantly reduce the PPS navigation error in the near term. The idea is to include in each satellite upload a table of clmk and ephemeris corrections for all other satellites. The corrections would be based on the most recent clock and ephemeris state estimates at the Master Control Station (MCS), Falcon AFB. These tables would fit on one of the currently unused pages of Subframe 4 and would be repeated every 12.5 minutes in the navigation message. A user would identify the most recently uploaded satellite within his field of view and use the corrections in that satellite to correct the ephemeris and clock data of the satellites used in his navigation solution. This will provide to the user clock and ephemeris data all having effectively the same age and the expected value of the age of these data will be significantly less than 12 hours (the average age of data with the current upload procedure). If the clock and ephemeris tables were uploaded to satellites over the theater of conflict during wartime, the users in the theater could be guaranteed data less than one hour old. Implementation of this concept involves relatively straightforward software changes in the user’s equipment set and minor modifications in the data upload to the satellite by the control segment. The payoff is that user range error due to clock and ephemeris will be reduced from the 3 - 4 meter range being achieved today to less than 2 meters.
Published in:	Proceedings of the 1995 National Technical Meeting of The Institute of Navigation January 18 - 20, 1995 Disneyland Hotel Anaheim, CA
Pages:	97 - 104
Cite this article:	Butts, Jim, Shank, Chris, "Navigation Message Correction Tables: A Proposal," Proceedings of the 1995 National Technical Meeting of The Institute of Navigation, Anaheim, CA, January 1995, pp. 97-104.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In