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

摘要

Stanford University has developed a Local AreaAugmentation System (LAAS) ground facility prototypeknown as the Integrity Monitor Testbed (IMT) todemonstrate the feasibility of LAAS precision approachesunder Category I conditions. While the Category I IMT isessentially complete, research on IMT algorithmscontinues to improve its performance so that it caneventually meet Category II/III approach requirements.To the extent possible, it is desirable to satisfy CategoryII/III requirements with modifications to the existingsingle-frequency (L1) LAAS architecture in order toprovide Category II/III initial operational capability (IOC)before the second civil frequency (L5) is present on asufficient number of GPS satellites. This will alsoprovide 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 ofsatellite signal deformation, code-carrier divergencemonitoring of both potential satellite failures andionosphere spatial anomalies, and position-errormonitoring at a .remote. monitor receiver that is somedistance away from the existing reference receiverantennas. With these relatively-limited modifications tothe existing Category I LGF architecture, significantperformance improvements are demonstrated. While thedegree to which these improvements are sufficientdepends on changes now being considered to theCategory II/III requirements, we believe that, with furtherrefinement, they will be sufficient to provide acceptableIOC and dual-frequency backup availability.