Aircraft Automatic Landing Over Parabolic Trajectory Using Smoothed Pseudorange Measurements

A standard single frequency Global Positioning System (GPS) receiver provides a positioning accuracy of approximately 4-20 m. This precision can be further enhanced with dual frequency receivers which are able to provide accuracy around 1-12 m. However, these errors are quite large when it comes to safety of life applications such as aircraft landings. Differential GPS (DGPS) allows for precise positioning using information from reference stations on the ground. Carrier phase tracking is one such D-GPS approach which allows range determination with centimeter level accuracy. However, carrier phase measurements require estimation of unknown fixed integer ambiguities before the receiver can start determining its position. Using single difference smoothed pseudorange measurements the integer ambiguities can be estimated with reasonable accuracy. This methodology brings the position error down to centimeter level which can meet the Federal Aviation Authority (FAA) regulations for Category-III (CAT-III) precision approaches. This paper examines an aircraft automatic landing using single differenced smoothed pseudorange measurements as the primary navigation source for an aircraft following a parabolic descent trajectory. Simulations demonstrate positioning with centimeter level accuracy using smoothed pseudorange measurements which enable a fully automatic CAT-III landing. General Terms Algorithm, Measurement, Performance, Reliability