A recovery system for SUAV operations in GPS-denied environments using timing advance measurements

This paper describes a recovery system for Small Unmanned Aerial Vehicles (SUAVs) operated in and around urban areas. The purpose of the system is to provide guidance to a SUAV allowing safe navigation to an area where it can be recovered in the event of a GPS outage using current technology and implement the solution within a one year timeframe. The prototype SUAV system presented in this paper made use of a federated filtering approach to calculate position, velocity, and attitude in GPS-denied environments. An Attitude Heading Reference System computed attitude followed by an air-data based dead reckoning navigator to determine the velocity and position of the SUAV. This system was aided by position fixes derived from the onboard cell phone receiver. Coarsely discretized time-of-arrival (TOA) information from the receiver bounded the position error of the dead reckoning navigator. The short-term performance of the system was evaluated through flight testing incorporating 2-5 minute GPS outages. Hardware-in-the-loop (HIL) simulations were conducted to demonstrate the system performance during extended (30 minute) GPS outages. The average position error magnitude of an un-aided dead reckoning navigator at the end of 25 Monte Carlo HIL simulations was 5275 m. In spite of the coarse TOA data, the cell phone-aided system out-performed the un-aided solution and bounded the average error to 166 m.