Cycle Ambiguity Reacquisition in UAV Applications Using a Novel GPS/INS Integration Algorithm

摘要

A novel GPS/INS integration algorithm that is adaptable to high satellite blockage environments is developed. Aviation applications such as autonomous shipboard landing require high degrees of accuracy and integrity which warrants the use of a carrier phase differential GPS navigation architecture. In order to achieve the high positioning accuracy achievable with the carrier phase, it is necessary to resolve the integer cycle ambiguity. To include satellites that are acquired (or lost and reacquired) after the initial fix, a ‘dual-track' fixing method is introduced. In this algorithm an independent fixing track is implemented in which constrained-integrity fixes are continuously attempted with the newly acquired satellites. rnThe performance of the dual track fixing algorithm is further enhanced by the integration of an inertial navigation system (INS) with the GPS carrier phase. In qualitative terms, during brief satellite outages the accurate position propagation provided from the output of the INS will translate into knowledge of the cycle ambiguities for the reacquired satellite. In this work, the integration concept is implemented in a novel GPS/INS mechanization that combines GPS and INS states (including cycle ambiguity states) in one centralized Kalman filter. A covariance analysis of the integrated architecture is carried out for the autonomous shipboard landing application, and the findings are expressed in terms of availability. The result of this work is a navigation architecture capable of providing instrument landing support for a Case-I approach; a feat as yet unrealized.