Direct Digital Sampling and Processing of L-Band GPS Signals: A Fully Digital Receiver Architecture

Barry Wolt and Alison Brown

Abstract:	This paper describes the architecture of a digital GPS receiver for use in precision space-based geodesy. The unique design of this receiver allows phase coherent measurements to be made across a broad range of frequencies, enabling measure- ments to be optimally combined from signals on different frequencies, for example GPS Ll, L2, and L3, GLONASS, or pseudolites. In addition, the receiver methodology provides precise absolute positioning measurements by maintaining phase coherency between l-1 and L2 by direct L-band digital sampling. The receiver uses digital down- conversion by bandpass sampling for a baseband aliased result. The digitized L-band signals are processed through a digital filter to provide 4-bit in-phase and quadrature-phase samples of the selected frequency for correlation processing. Design of the receiver digital front-end (DFE) provides coherency between the code and carrier phase of the measurements across a 400 MHz bandwidth. A highly flexible “software receiver” architecture has been developed to allow the receiver to be dynamically reconfigured for different applications. This allows the receiver channels to be used for GPS navigation, ionospheric calibration, attitude determination, or even GLONASS navigation simply through software commands. In the paper, the AGR hardware topology is discussed with respect to its inherent flexibility that enables tracking any frequencies over a range with only software changes. Test data is also presented to demonstrate the performance of the DFE.
Published in:	Proceedings of the 6th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1993) September 22 - 24, 1993 Salt Palace Convention Center Salt Lake City, UT
Pages:	985 - 992
Cite this article:	Wolt, Barry, Brown, Alison, "Direct Digital Sampling and Processing of L-Band GPS Signals: A Fully Digital Receiver Architecture," Proceedings of the 6th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1993), Salt Lake City, UT, September 1993, pp. 985-992.
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