Performance Improvement Using NMCT and the Analysis of J/S for Fast Acquisition in PGM Applications

Sultan Mahmood, Joseph Solomon and Rick James

Abstract:	The use of GPS for precision guided munitions (PGMs) in adverse weather and jamming scenarios requires special error reduction and signal acquisition/tracking techniques. Sverdrup Technology Inc. (TEAS Group) is supporting a number of weapon acquisition and R&D programs at Eglin AFB, FL., and has developed concepts and simulations for studying these issues. Unclassified results from these studies, performed for the Joint Direct Attack Munition (JDAM) Program Office .in support of the Product Improvement Program (PIP), are presented in this paper. The recent implementation of the Navigation Message Correction Tables (NMCT) by the MCS, and potential receiver improvements are exploited to study a technique for high accuracy GPS navigation. The use of NMCT along with other receiver enhancements is shown to make the tropo error observable. This is modeled as a correlated bias and estimated by incorporating a fifth satellite measurement. Results of a Monte-Carlo simulation of an integrated GPS/Inertial navigation for a PGM, using this approach are presented demonstrating a less than 2 meter CEP. A key requirement for achieving high accuracy state- vector update is the fast acquisition of GPS signals themselves after launch. The short time of flight of PGMs and/or the presence of higher than normal jamming places stringent requirements on the direct Y-code and C/A -to-Y code signal acquisition time. This paper extends the results of a previous parametric study of the acquisition time to the PGM application, for various antenna placements, jammer layouts, dynamics and parallel correlator receiver architecture. The use of parallel processing allows signal acquisition in jamming levels significantly higher than normal; but after a threshold the advantage decreases rapidly and alternate schemes are required to combat jamming. Analysis guidelines are provided to determine the jamming margin of an existing design, or specify the anti-jam level required for a receiver to perform in a given scenario.
Published in:	Proceedings of the 9th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1996) September 17 - 20, 1996 Kansas City, MO
Pages:	1905 - 1916
Cite this article:	Mahmood, Sultan, Solomon, Joseph, James, Rick, "Performance Improvement Using NMCT and the Analysis of J/S for Fast Acquisition in PGM Applications," Proceedings of the 9th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1996), Kansas City, MO, September 1996, pp. 1905-1916.
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