A Baseline GPS RAIM Scheme and a Note on the Equivalence of Three RAIM Methods

The RTCA GPS Minimum Operational Performance Standards (MOPS) have now been released, and airborne equipment manufacturers will be expected to meet the specifications therein. A considerable portion of the MOPS is devoted to GPS integrity requirements and the associated receiver testing procedures. The GPS Integrity Channel (GIC) is still a few years away, so some form of Receiver Autonomous Integrity Monitoring (RAIM) must be relied upon in the interim period (and perhaps beyond). Many different RAIM schemes have been proposed over the past few years, each with its respective advantages and disadvantages. This paper proposes a baseline RAIM scheme that can serve as a standard for performance comparisons. The proposed scheme is based on a unified theory which says that under the condition of equal alarm rates, the range-comparison, least-squares-residuals, and parity RAIM methods all yield identical results. This scheme is a straightforward, workable RAIM method that is easily understood by all. It is a good scheme, but there is no claim that it is optimal.