Cycle Ambiguity Estimation for Aircraft Precision Landing Using the Global Positioning System

Measurements of the Global Positioning System carrier phase can provide the basis for the highest level of satellite-based navigation performance. In particular, the potential exists to exceed even the stringent navigation requirements for aircraft precision approach and landing. The principal difficulty in this use of carrier phase, however, lies in the real-time, high-integrity resolution of the unknown integer cycle ambiguities. A new methodology is introduced, using carrier phase measurements from ground-based pseudolites, for explicit estimation of the cycle ambiguities. The mathematical basis of the new approach is detailed, and high-speed nonlinear information smoothing algorithms suitable for real-time airborne execution are derived. Extensive flight-test data, including the results of automatic landings of a Boeing 737 aircraft, are presented as experimental validation of algorithm performance.