Possible GPS Signal Interference Caused by L-Band Bent-Pipe Transponders on Geostationary Satellites

Vaclav G. Ujcik, Karl L. Kovach

Abstract:	There are a number of proposals currently on the table aimed at providing augmentation services to civil users of the Navstar GPS. Proposed augmentation services include several different types of GPS integrity channels (GICs), local- and/or wide-area differential GPS (DGPS) broadcasts, and pseudo- satellite (pseudolite) signals which can serve as an additional source of ranging measurements. Each of these GPS augmentation services requires a communication path to send the requisite information to the participating user’s GPS receiver. A popular concept for the augmentation service communication path has evolved based on placing L- band bent-pipe transponders on board satellites in geostationary orbit over the earth. This concept has earned its popularity through a clever combination of both elegant simplicity and robust features. The simplicity results from the uncomplicated bent-pipe design of the transponder and keeping all signal generation and synchronization complexity on the ground at the earth station. The robust features include using a “GPS-like” signal at L-band that can be received with only minor modifications to existing GPS receivers, and being able to cover a third of the Earth’s surface with a single transponder. There is, however, a significant possibility that GPS- like signals from these transponders will interfere with the normal navigation signals from GPS satellites. Based on a novel analysis from the perspective of a non-augmentation service provider, this paper explains how and why L-band bent-pipe transponders are inherently prone to causing such interference. It identifies techniques which may be used by the satellite owner/service provider to minimize the impacts of this interference on GPS users and describes transponder design changes which will eliminate the risk of that interference.
Published in:	Proceedings of the 5th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1992) September 16 - 18, 1992 Albuquerque, NM
Pages:	177 - 185
Cite this article:	Ujcik, Vaclav G., Kovach, Karl L., "Possible GPS Signal Interference Caused by L-Band Bent-Pipe Transponders on Geostationary Satellites," Proceedings of the 5th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1992), Albuquerque, NM, September 1992, pp. 177-185.
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