The Effect of Geometry on Integrity Monitoring Performance

A variety of integrity monitoring and failure detection algorithms have been described in previous lite:ature for G~S and inertial. navigation systems. .These ~gorlthms have In common their use of redundant 1DfOrmatl~n to detect and identify system component faults. Receiver Autonomous Integrity Monitoring (RAIM) algorithms designedfor GPS receiversmake use or redundant measurementsto GPS satellites to detect and isolate faults in any individual satellite signal. Fault-tolerant in~rtial navigationsystemsused~tafr?m redundant instruments in a similar Cashionto detect and Identify faults in any instrument. Onekey areaof interestis the minimum GPSsatellitegeometry conditions that are required for RAIM algorithms to be effective. The Radio Technical Commission for Aeronautics (RTCA) Special Committee 159 has prepared a -Uinimum bperational Performance Standard (MOPS) which specifies the alarm threshold, detection probability and allowable false alarm rate for different pqasesof flight. This paper derives a geometry parameterthat canbe usedto definewhenRAIM is effectivefor ea.chphaseof flight. . . The integrity geometry parameters can also be app~ed. in evaluating the performance of redundant inertial naVIgation systems in the presenceof single or multiple instrument faults. To continue navigating.in tae presenceof a failure, it is necessarynot only to detect that a failure occurred but also identify the faulty component. The integrity geometry parameter allows the optimum geometry to be determined for maximizing the probability of failure detectionand isolationin the presenceof multiple instrument faults.