LAAS Ground Facility Design Improvements to Meet Proposed Requirements for Category II/III Operations

Abstract

Stanford University has developed a Local Area Augmentation System (LAAS) ground facility prototype known as the Integrity Monitor Testbed (IMT) to demonstrate the feasibility of LAAS precision approaches under Category I conditions. While the Category I IMT is essentially complete, research on IMT algorithms continues to improve its performance so that it can eventually meet Category II/III approach requirements. To the extent possible, it is desirable to satisfy Category II/III requirements with modifications to the existing single-frequency (L1) LAAS architecture in order to provide Category II/III initial operational capability (IOC) before the second civil frequency (L5) is present on a sufficient number of GPS satellites. This will also provide a backup operational mode in a future dual- frequency LAAS if either L1 or L5 is interfered with. This paper addresses IMT improvements to detection of satellite signal deformation, code-carrier divergence monitoring of both potential satellite failures and ionosphere spatial anomalies, and position-error monitoring at a “remote” monitor receiver that is some distance away from the existing reference receiver antennas. With these relatively-limited modifications to the existing Category I LGF architecture, significant performance improvements are demonstrated. While the degree to which these improvements are sufficient depends on changes now being considered to the Category II/III requirements, we believe that, with further refinement, they will be sufficient to provide acceptable IOC and dual-frequency backup availability.