An Approach to GPS Satellite Failure Detection

A. Jakab

Abstract:	Anomalous GPS satellite signals can have a very unfavorable impact on GPS receiver integrity. In a Wide Area Augmentation System (WAAS) or Local Area Augmentation System (LAAS) the corrections must accurately reflect the current satellite signal integrity. For airborne users who rely solely on this information for navigation purposes it is especially critical they not be led into a potentially hazardous and life threatening situation. They must be quickly warned of any problems that would lead them astray and then take appropriate action. Since these satellite anomalies are assumed to be based in circuit reality, we can expect only a few possible types of waveforms. However, when combined together, these anomalous signals can have a very deleterious (some may say “evil”) effect on safety critical navigation systems. Current techniques to detect and guard against these “Evil Waveforms” are discussed which include the use of broadcast satellite information, multiple correlators, Receiver Autonomous Integrity Monitoring (RAIM), and adjustable correlator widths. Most methods have limitations that relate to current receiver technologies and stringent time to alarm (TTA) constraints. An important aspect to realize is that a single receiver with a single observation cannot distinguish between a multipath condition and an anomalous satellite signal. Multipath observed at a stationary receiver is repeatable day to day, but anomalous satellite signals are not, therefore these two errors are separable if some time history is analyzed. NovAtel has researched methods for mitigating the effects of anomalous GPS signals for WAAS and LASS receiver applications. In addition, an approach to the detection of GPS signal anomalies is presented using a NovAtel MiLLeniumä receiver configured to track one satellite signal with a very large number of correlators. Experimental results will be presented from data collected in a variety of signal conditions. Conclusions will also be drawn from these results.
Published in:	Proceedings of the 12th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1999) September 14 - 17, 1999 Nashville, TN
Pages:	751 - 760
Cite this article:	Jakab, A., "An Approach to GPS Satellite Failure Detection," Proceedings of the 12th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1999), Nashville, TN, September 1999, pp. 751-760.
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