Parity space methods for autonomous fault detection and exclusion using GPS carrier phase

Abstract

Kinematic carrier phase positioning provides navigation integrity. The sub-centimeter precision of carrier phase measurements can be used to leverage receiver autonomous integrity monitoring (RAIM) in the sense that extremely tight fault detection thresholds can be set on the least-squares residual (ensuring navigation integrity) without incurring high false alarm rates. In addition, the high precision of carrier phase, when compared with code phase, lowers the integrity risk associated with the fault identification process. This is true because carrier phase provides a much cleaner observation of the effect of a given failure on the residual. Thus, for the same improvement in navigation continuity (obtained from fault isolation), misidentification will be less likely. This paper is focused on the use of parity space methods to investigate the limits of high-integrity and high-continuity GPS performance. In this regard, prototype algorithms for receiver autonomous fault detection and exclusion were developed with the goal of maximizing navigation continuity subject to the constraint of maintaining high integrity (by repressing mis-identifications). Fault detection and exclusion performance was demonstrated through analysis and extensive simulation. In addition, the prototype algorithms were implemented in a real-time airborne kinematic positioning architecture and tested by deliberately inducing failures in the post-processing of raw flight data.