A position domain relative RAIM method

The GNSS Evolutionary Architecture Study (GEAS) Panel was formed by the FAA in October 2006 with the objective of evaluating future GNSS-based architectures to provide robust worldwide instrument approach guidance known as LPV-200 in the 2025 to 2030 time frame. One of the architectures being considered by GEAS is based on a new concept called Relative Receiver Autonomous Integrity Monitoring (RRAIM). In this architecture, RRAIM is used with a WAAS-like system or an integrity-assured GPS III system that meets all LPV-200 requirements except for the integrity time-to-alert requirement. Such a system provides integrity but with a delay of several seconds up to a few minutes. During the period of this delay, RRAIM fills the gap as follows. User equipment estimates the change in user position by measuring accumulated carrier phase single differences of range measurements of satellites used in the position solution. Then Receiver Autonomous Integrity Monitoring (RAIM) is used to assure integrity in the change in position. Since the nominal errors associated with the carrier phase measurements are significantly smaller than those of pseudorange measurements, much tighter thresholds and thus smaller Vertical Protection Level (VPL) can be obtained in times of relatively poor geometry, resulting in improved service availability.