Dynamic Uploading for GPS Accuracy

Kenneth Brown, William Mathon, Arthur Dorsey, Margaret Larezos

Abstract:	As part of the GPS Accuracy Improvement Initiative (AII), studies at Lockheed Martin Federal Systems have addressed tuning, accuracy, and uploading issues for the OCS in the future AII environment of single-partition Kalman filtering and added Monitor Stations (MSs). Modified OCS software was used to process recorded data from 24 SVs via the 5 existing GPS MSs plus 6 additional NIMA MSs, using optimal (unpartitioned) filtering. The best tuning parameters found to date are similar to those of the 2SOPS (Second Space Operation Squadron) EEE study for the current operational environment, but AII accuracies are much improved, benefiting both from the added NIMA stations and from single-partition filtering. Because the accuracy available to PPS users depends heavily on age of data, these studies also addressed procedures and criteria for scheduling uploads of navigation data to the SVs. These included increased scheduled uploads, increased "contingency" uploads (invoked dynamically when an SV exceeds a given error level), and also mixed dynamic methods in which both scheduled and contingency uploads exist and even scheduled uploads are enabled dynamically, based in part on accuracy. A system tradeoff plot of URE vs. uploads/day is used to show the choices available through different thresholds and different approaches. Results show how improved uploading allows very substantial reductions in Signal In Space (SIS) URE - larger than the reductions due to retuning, added MSs, and single-partition filtering combined. Moreover, various "dynamic" or accuracy-based uploading approaches can dramatically reduce the number of uploads needed to achieve a given SIS URE. Such methods can meet not only current AII objectives but offer a clear path to more aggressive performance goals for the future.
Published in:	Proceedings of the 10th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1997) September 16 - 19, 1997 Kansas City, MO
Pages:	351 - 363
Cite this article:	Updated citation: Published in NAVIGATION: Journal of the Institute of Navigation
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In