Session B4: GNSS Integrity and Augmentation

Dual Frequency Multi-Constellation (DFMC) Ground Based Augmentation Systems (GBAS) Position and Integrity Propagation
Tim Murphy, Boeing; Gary McGraw, PNT Consultant (Genova Technologies); John Studenny, CMC Electronics
Location: Beacon B

ICAO (International Civil Aviation Organization) has been developing an update to Standards and Recommended Practices (SARPs) to enable an extension of ground-based augmentation systems (GBAS) to exploit the availability of new constellations and dual frequency GNSS signals. The relevant expert body has converged on an architecture for dual-frequency, multi-constellation (DFMC) GBAS which is based on uplinking unsmoothed code phase observations and carrier measurements from the ground reference receivers to allow pseudoranges to be smoothed in the airborne equipment in an optimal manner. Because of datalink capacity limitations this results in ground measurements being uplinked at a relatively low rate (e.g. 1/3 Hz) when compared with single frequency GBAS (2 Hz). This paper explains the constraints that lead to this low update rate and gives details on how ground measurements are expected to be processed by the air segment to support high accuracy positioning with integrity at a high rate (e.g. 5 – 20 Hz) required by the airborne applications. The paper includes a discussion of how full-resolution ground observations are reconstructed in the airborne equipment. Then a discussion of how airborne solution can be propagated between ground system updates using carrier-only based relative positioning. Finally, the paper describes the overall concept for maintaining integrity including monitoring requirements for the ground and the air including how integrity is assured during propagation of the position between ground updates.