Signal Deformation Monitoring for Dual-Frequency WAAS

R. Eric Phelts, Gabriel Wong, Todd Walter, and Per Enge

Abstract:	Previous signal deformation analyses and monitor designs have primarily focused only on threats to the L1 C/A code. They have traditionally relied on a combination of empirical measurements and analytical models of the threats and the user receivers. In the future however, to mitigate ionospheric errors, WAAS will leverage the L5 signal in addition to L1. This means both signals will need to be monitored. While many familiar C/A code signal deformation monitor analyses can be extended and applied to the L5 codes, the monitor needs to be far more sensitive since the dual-frequency combination designed to remove ionospheric errors will amplify any range biases on the signal. At the same time, this correction will drive the range error limits to be smaller. In addition, the new signal deformation monitor needs to detect potential faults on the L5 signal—a something the current design is not easily adapted to do. In this paper, background is provided on the current WAAS signal deformation monitor along with key measures of its accompanying performance analysis. In addition, the existing L1 fault threat analyses and user constraints are applied to L5 codes and future receivers. Measured data from a dual-frequency prototype signal deformation monitor receiver are then used to infer a reasonable noise model to compare current and proposed monitor designs. From this data, a new signal deformation fault detection algorithm is analyzed and applied to the case of dual-frequency users to determine its performance, relative to the current system. Finally, the results are used to make recommendations on constraints on dual-frequency user receiver configurations. It is believed that the monitor design approach used here may be readily extended for signal deformation monitoring of other GNSS signals of various code modulations.
Published in:	Proceedings of the 2013 International Technical Meeting of The Institute of Navigation January 29 - 27, 2013 Catamaran Resort Hotel San Diego, California
Pages:	93 - 106
Cite this article:	Phelts, R. Eric, Wong, Gabriel, Walter, Todd, Enge, Per, "Signal Deformation Monitoring for Dual-Frequency WAAS," Proceedings of the 2013 International Technical Meeting of The Institute of Navigation, San Diego, California, January 2013, pp. 93-106.
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