Independent Position Validation with Space-Based ADS-B

Aircraft operators, Air Navigation Service Providers (ANSP), air traffic control organizations, and others rely heavily on data and associated systems to safely and efficiently operate and navigate aircraft throughout the airspace. From takeoff to touchdown and beyond, positional data is critical. But what happens when the systems fail? What if GPS goes down or data is somehow compromised?

For 10 years, Aireon LLC Aireon has pioneered the use of global automatic dependent surveillance-broadcast (ADS-B) data from space, marrying the high-fidelity nature of an air traffic surveillance pedigree with the innovation that unlocks the inherent power of ADS-B data sets and metadata. While other aviation data companies are just beginning to explore the use of satellites for ADS-B, Aireon has set the standard for the industry, and is delivering new space-based ADS-B data products for the next generation of aviation stakeholders.

And we’re taking that data even further to bring new insights and operational support to airspace operators. Aireon has developed a proof-of-concept multilateration solution that allows for independent position determination of ADS-B-equipped aircraft. This solution will allow Aireon to continue tracking aircraft even when they are unable to broadcast their GPS position using only their transmitted 24-bit aircraft address and the time of reception at the Aireon Hosted Payloads onboard the Iridium satellites. This is done through a Satellite Wide Area Multilateration (SWAM) application that uses Time Difference of Arrival (TDOA) measurements from simultaneous detection of ADS-B transmissions on multiple payloads. This solution leverages traditional multilateration techniques used by terrestrial systems but applied via satellite.

This application will give Aireon another method of delivering aircraft positions that is not dependent on GPS, effectively mitigating a potential mode of failure in ADS-B transponders. By combining both the reported and derived positions of the aircraft, Aireon can provide a robust solution that allows for improved monitoring of aircraft around the globe.

Aireon has already begun leveraging these capabilities to create an ADS-B position validation solution that can estimate if a reported aircraft position is accurate, but not determine the truth position itself. This validation solution uses similar techniques as a full-blown multilateration solution, such as TDOA measurements, but is only being used to flag suspect position reports.?

ADS-B is dependent on GPS to deliver an aircraft’s position, any issues with the onboard GPS equipment or external GPS interference can cause an ADS-B equipped aircraft to be unable to transmit their position. Even in the absence of GPS, ADS-B transponders continue to transmit allowing these of messages to be used for multilateration. GPS interference is an emerging safety risk with hotspots identified in the Middle East where a significant number of ADS-B equipped aircraft lose their GPS position.

Aireon’s prototype multilateration solution has been evaluated using Aireon’s own operational ADS-B data to check its performance in the real-world. Using data captured from around Iqaluit, Canada, the performance shows a position accuracy of 557 meters, 95th percentile. Further work is envisioned to improve this accuracy through improvements to the algorithm and smoothing techniques. The data also shows that the proof-of-concept also meets the necessary 8-second update interval for Enroute air traffic separation.

Michael Garcia Giuseppe Sirigu, PhD John Dolan

To learn more, contact [email protected].