Mon. Oct 2nd, 2023
Using GBAS Corrections for UAV Navigation

The Ground Based Augmentation System (GBAS) is a precision approach and landing system that corrects Global Positioning System (GPS) navigation signals for airborne users. It provides integrity parameters to bound residual position errors and reference coordinates for approach guidance. GBAS data is broadcast from a ground station and is freely accessible to users.

GBAS is mainly used for precision approaches of large aircraft, but this study explores its potential for Unmanned Aerial Vehicles (UAVs). UAVs require accurate navigation systems, and GBAS corrections and integrity parameters could enhance their navigation capabilities.

GBAS stations are typically located within airport security perimeters and provide high-quality equipment to minimize errors. They guarantee performance levels and continuously monitor data integrity.

However, GBAS is not widely used due to the limited availability of ground stations at airports and the lack of equipped aircraft. The installation and maintenance costs of a GBAS ground station are expensive, and aircraft operators are reluctant to equip their fleet without operational benefits.

Previous research has investigated the use of GBAS-like Local Area Differential GNSS (LADGNSS) for UAV navigation. LADGNSS removes expensive hardware and maintains high levels of integrity. Multipath errors are considered critical for integrity, and residual errors in UAVs are assumed to be bounded by error models developed for large transport aircraft.

Another study analyzed the theoretical performance of a Differentially Corrected Positioning Service (DCPS) for GBAS, which enables use-cases beyond precision approach guidance. The study evaluated the GBAS messages transmitted by the ground station at Zurich Airport and compared the theoretical protection levels with SBAS (Satellite-Based Augmentation System).

The results showed that GBAS could provide operational benefits within a radius of about 57 km from the airport. Beyond this distance, GBAS protection levels become larger than SBAS protection levels, making GBAS less advantageous.

In this study, the focus is on using GBAS corrections for UAV navigation within 50 km from the ground station. One challenge is the limited ability to receive VHF-based transmission at low flight altitudes. The study explores receiving and decoding GBAS messages near the airport and applying the corrections and integrity parameters to correct and bound positioning errors in UAVs.

To evaluate navigation performance, a flight test was conducted using a UAV. GBAS corrections and integrity parameters were recorded from the GBAS at Zurich Airport and augmented with UAV GNSS data for post-processing analysis.

Overall, this study aims to assess the performance and operational aspects of using GBAS corrections for UAV navigation.