Transmitting raw GNSS measurements as part of ADS-B: Why, how, and flight test results

Future Aircraft Surveillance Applications System (ASAS) such as conflict detection, final approach and runway occupancy, and airport surface situational awareness methods will benefit from the introduction of Automatic Dependent Surveillance-Broadcast (ADS-B). An alternative ADS-B implementation, which transmits raw measurements from the Global Navigation Satellite System (GNSS) instead of aircraft state vectors in the current implementation, was proposed in a previous paper to improve surveillance performance. Advantages of this implementation include 1) increased observability, 2) independence of datum reference, 3) the availability of an intrinsic duality indicator through the estimator's covariance matrix, 4) a guaranteed incorporation of existing correlations in the estimator, 5) optimal weighting of the measurements, and 6) the ability to perform data screening and other integrity methods. This paper summarizes the proposed methodology, discusses the initial flight test results of this alternative ADS-B implementation, and analyzes the performance of this method as a function of various system parameters such as bandwidth and update rate.