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4 Operation
NOTE:
RTCM Type 1's and Type 9's can be broadcast by themselves and used for GPS-Only operation
similar to section 4.7
4.8 INTEGRITY ALGORITHM
NovAtel Inc. has implemented an integrity algorithm to improve the reliability of the MiLLennium-GLONASS
receiver. The increased redundancy offered by tracking more satellites improves the chance of statistically catching
a measurement blunder. The integrity algorithm is designed to detect, and attempt to isolate, single-satellite
failures. A satellite failure, in this instance, is defined as a ranging error on a pseudorange measurement. The
detection algorithm is based on a least-squares-residuals approach (see Brown et al., A Baseline GPS RAIM Scheme
and a Note on the Equivalence of Three RAIM Methods, Journal of the Institute of Navigation, Vol. 39, No. 3, Fall
1992).
When an integrity failure is detected, the solution status flag is set to BAD INTEGRITY. If a satellite was
successfully isolated then the reject code for that satellite will be set to BAD INTEGRITY and the satellite will be
removed from subsequent processing for 30 minutes. If operating in RTK mode, the RTK filter will be reset and
the isolated satellite will be rejected in the ensuing processing for the same period of time. If an integrity failure is
detected but a satellite cannot be isolated, then all Glonass satellites will be flagged as BAD INTEGRITY and a
GPS-only solution will be attempted on the next measurement epoch.
This integrity algorithm differs from a RAIM algorithm in that it is not designed to protect against specified
minimum performance levels. In RAIM, the position solution is considered suspect if the satellite geometry is
insufficient to detect a measurement error that could cause a position error greater than a given threshold. This
approach is very conservative and was developed for stringent in-flight position tolerances. The integrity algorithm
in the NovAtel MiLLennium-GLONASS card does not use this minimum detectable blunder concept but will
check for any satellite failure based on the strength of the current satellite geometry.
GPS/GLONASS Receiver User Manual Rev 1
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