GUS Code-Carrier Control Algorithm

R. Kumar and P. Munjal

Abstract:	FAA is currently implementing wide area augmentation system which involves the ground segment comprising reference stations, master stations, and Geo uplink stations and terrestrial communication network. One critical component of WAAS ground data processing is the various algorithms designed to meet the necessary time synchronization, orbit determination of the geostationary satellites, code and carrier coherence, and the ionospheric measurements at the WAAS reference stations. This paper presents an algorithm for maintaining coherence between the L t carrier phase and the C/A code phase in the signal transponded by the Geo satellite in a civil aviation wide area augmented GPS network, so that the signal mimics standard GPS signals when received by any GPS receiver. A close-loop control for this purpose is required to estimate and compensate for various sources of divergence including the uplink ionospheric delay divergence between the code and carrier phase, and the local oscillator phase noise introduced at the Geo transponder. The other objective of the presented algorithm is to maintain synchronization between the C/A code timing at the Geo transmit antenna phase center and the time standard at the Geo Earth station in the presence of time-varying C-band uplink range and uplink ionospheric delay. The algorithm is based on optimal estimation approach and makes use of both the C-band and Ll-band code and carrier phase measurements available at the Geo Earth station, taking into account various delays or offsets arising at the Geo satellite transponder, ionosphere, and the Earth station.
Published in:	Proceedings of the 1997 National Technical Meeting of The Institute of Navigation January 14 - 16, 1997 Loews Santa Monica Hotel Santa Monica, CA
Pages:	683 - 693
Cite this article:	Kumar, R., Munjal, P., "GUS Code-Carrier Control Algorithm," Proceedings of the 1997 National Technical Meeting of The Institute of Navigation, Santa Monica, CA, January 1997, pp. 683-693.
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