Cooperative Relative Navigation of Multiple Aircraft in Global Positioning System-Denied/Degraded Environments

Abstract

This paper introduces a method for enabling multiple small unmanned aircraft to improve navigational accuracy in Global Positioning System (GPS)-denied environments by cooperatively sharing information. The method uses a multilevel framework called relative navigation and visual-inertial odometry: both of which have been used for single-vehicle GPS-denied navigation. This work modifies the relative navigation architecture by adding the necessary elements to enable decentralized, cooperative operations. The proposed framework also includes the ability to incorporate intervehicle measurements and uses a new concept called the coordinated reset, which is necessary for optimizing the cooperative odometry and improving localization. A simple communication protocol is presented, as well as flight-test results that show its effectiveness. The method is first demonstrated in simulation, including Monte Carlo testing, to show the expected improvement gained from cooperation. Finally, results from hardware testing are presented that show the ability of the system to reject initialization errors, to operate with temporary communications dropouts, and to greatly reduce the total amount of shared data compared to a naive approach. The proposed method is able to improve both global navigation accuracy and the accuracy of the relative aircraft positions for missions that require formation flying.