On-the-fly carrier phase ambiguity resolution for precise aircraft landing

Successful GPS on-the-fly (OTF) carrier phase ambiguity resolution for precise positioning at the centimetre level has already been demonstrated. This has usually been in good observation conditions, e.g. over short distances, lots of satellites, P-code pseudoranges available, and small unmodelled errors. In order for GPS to fulfil the rigorous ICAO Cat. III precise landing navigation requirements centimetre-level accuracy must also be obtained in more realistic conditions, e.g. A-S on, high-unmodelled errors and less than six satellites. Integrating GPS with other sensors, e.g. INS, is likely to aid ambiguity resolution in such conditions, but there are limitations. After discussing critically the OTF methods, approaches are examined which will provide the precise accuracy, reliability and integrity required. Combining GPS with one, or more, pseudolites to provide an extra geometrical constraint to aid ambiguity resolution is described. Flight tests using different configurations of pseudolites are carried out and analysed.