Carrier Phase Integer Ambiguity Resolution Using Dual Frequency Pseudolites

Jonathan M. Stone, J. David Powell

Abstract:	Pseudolites have been shown to provide additional availability and improved accuracy in settings that have obstructions causing high elevation mask angles. For example, using pseudolites in an open-pit mine could provide continuous GPS operation where stand-alone GPS would only be available 20% of the time due to the steep walls. Carrier phase tracking has been shown to provide centimeter level positioning when the integer ambiguities have been resolved. Resolving the carrier phase integer ambiguities without using significant motion of the user vehicle or satellites can be accomplished using dual frequency pseudolites. This work describes the ongoing research to provide a complete precise positioning system for open pit mining or other applications in which obstructions cause high elevation mask angles. Due to the large obstruction angles, standard integer ambiguity resolution methods may not be usable. Many require satellite motion or large prescribed user motion. Dual frequency pseudolites were developed to continuously broadcast carrier frequencies modulated by GPS C/A codes. The GEC Plessey Semiconductor (recently acquired by Mitel Semiconductor) GPS Builder 2 receiver was modified to receive dual frequency pseudolite signals and to provide carrier phase as an output. Due to the frequency down-conversion scheme within the Mitel chipset, several fundamental frequencies may be received and correlated with minor filter adjustments. The second RF front end may be used for the secondary frequency but then requires a separate channel in the 12 channel receiver. Differential code phase positioning may be used to provide an estimate of the differential carrier phase integers, and a “wide-lane” method can further refine the estimate using the two frequencies from the pseudolites. A roof-top patio area surrounded by walls was used as an open pit test site in which 40% of the time less than 4 satellites were visible. A pseudolite was placed on the rim of the area to augment the satellites and a differential carrier phase positioning system was demonstrated with centimeter level accuracy. Dual frequency pseudolite and receiver hardware has been developed and tested that will be used for implementing and verifying the integer resolution algorithm in the near future.
Published in:	Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998) September 15 - 18, 1998 Nashville, TN
Pages:	961 - 968
Cite this article:	Stone, Jonathan M., Powell, J. David, "Carrier Phase Integer Ambiguity Resolution Using Dual Frequency Pseudolites," Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998), Nashville, TN, September 1998, pp. 961-968.
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