Detecting Multiple failures in GPS/INS integrated system: A Novel architecture for Integrity Monitoring

Abstract

GPS is a widely used satellite navigation system. By design, there is no provision for real time integrity information within the Standard Positioning Service (SPS) which is available to the civilian community. However, in safety critical sectors like aviation, stringent integrity performance requirements must be met. This can be achieved using the GIC (GPS Integrity Channel) or RAIM (Receiver Autonomous Integrity Monitoring) or both. RAIM, the most cost effective method relies on data consistency, and therefore requires redundant measurements for its operation. An external aid to provide this redundancy can be in the form of an Inertial Navigation system (INS). This should enable continued performance even during RAIM holes. RAIM algorithms have traditionally been designed for the situation when only one failure occurs at a time. However, due to tighter alert limits and usage of GPS in urban environments there is now a focus on extending the RAIM concept to include multiple failures. Furthermore, in aviation, detection of simultaneous multiple slowly growing errors (SGE) is very challenging particularly in the case of integrated GPS/INS systems. This paper provides a detailed survey of RAIM approaches used to detect multiple failures proposed by navigation and geodesy communities. Furthermore the paper extends a previous algorithm proposed by the authors for the detection of a single SGE to the simultaneous multiple failure case for stand-alone GPS and integrated GPS/INS systems. Simulated and real data results attest to the effectiveness of the approach proposed. The developed algorithm is successful in the detection of multiple failures in GPS as well as in the INS. Furthermore isolation of the faulty sensor (GPS or INS) is possible with the same parallel filter structure. Hence, this approach will enhance the integrity of a GPS/INS integrated system installed on an aircraft.