The All-Purpose DIGPS Signal Model

Michael S. Braasch

Abstract:	As the Global Positioning System (GPS) nears operational status, the user community is growing exponentially. Although many of these users are content with the accuracy provided by the GPS Standard Positioning Service (SPS), an increasing number of applications require the precision provided either by code-differential or carrier-differential techniques. The research, development, test and evaluation of candidate differential systems typically requires bench testing and software simulation to minimize costly and time-consuming field trials. The evaluation of candidate precision positioning architectures will involve the testing of differential processing schemes and ambiguity resolution techniques along with the interfacing of the GPS- derived data with other subsystems. It is thus apparent that a model is required which can emulate both the GPS signal-in-space and the receiver processing. The signal model described in this paper performs both of these functions. The signal model must accurately generate the typical kinds of raw data which are output from modern receivers in a variety of environments. The pseudorange, instantaneous and integrated Doppler measurements vary from the true values because of propagation-media and receiver-dependent effects as well as Selective Availability. Previous signal modeling efforts by the author and others have focused mainly on the stand-alone (non-differential) use of GPS. However, the signal model described in this paper can support differential-code and differential carrier-phase operations as well. Furthermore, the model is able to emulate a variety of receiver architectures. Since the model is software-centered, it can run in fast-time. A description of the model will be given along with test results.
Published in:	Proceedings of the 1994 National Technical Meeting of The Institute of Navigation January 24 - 26, 1994 Catamaran Resort Hotel San Diego, CA
Pages:	63 - 67
Cite this article:	Braasch, Michael S., "The All-Purpose DIGPS Signal Model," Proceedings of the 1994 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 1994, pp. 63-67.
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