A Component-Level Model of Automatic Dependent Surveillance - Broadcast (ADS-B)

Abstract

Automatic Dependent Surveillance – Broadcast (ADS-B) is being employed in numerous peer-to-peer initiatives attempting to expand the capacity of the National Airspace System (NAS) or enable mixed operations of manned and unmanned vehicles. Safety assessments of these initiatives rely, in part, on modeling the accuracy of ADS-B in reporting the position and direction of an ownship and surrounding traffic. Frequently, these initiatives utilize a position uncertainty model that applies a reported ADS-B estimation position uncertainty (EPU) value to a Rayleigh distribution and uses a Gauss-Markov random walk to add error to the ADS-B output of a vehicle. This model of ADS-B state error is easy to implement and apply to numerous problems. However, it has a couple of drawbacks. First, the ADS-B state errors are equally probable in all directions. This is a good assumption in situations where aircraft maneuvering is not constrained. However, in situations where the aircraft maneuvering is constrained such as landing, the error distribution is likely to exhibit directionality and the non-directional model may skew results especially when assessing very low probabilities (e.g., 10-9) of catastrophic encounters. Second, the model does not account for processing latency in the receiving aircraft. NASA Langley Research Center (LaRC) recently examined the feasibility of decreasing the spacing of aircraft on parallel approaches to runways separated by as little as 700 feet [Perry2013]. For Monte-Carlo analysis using a high-fidelity simulation of a large transport, LaRC started with a Gauss-Markov model of ADS-B error but then developed a component level model of ADS-B error to increase the fidelity of results. This LaRC assessment of parallel approaches had a forward looking time frame of five to ten years. Therefore, the component level model assumes that the ADS-B system is fed directly from and synchronized with an autonomous Global Positioning System (GPS) receiver. This model covers the end-to-end reporting and consumption of ADS-B state from the GPS receiver on the transmitting aircraft to processing of the ADS-B report on the receiving aircraft. The model essentially divides the ADS-B path into four systems: the GPS receiver, the ADS-B OUT system, the ADS-B IN system, and the target application. A common error source in each system is latency and each system may vary in the duration of its processing latency and how much of that latency the system attempts to https://ntrs.nasa.gov/search.jsp?R=20190000876 2020-05-07T22:03:10+00:00Z