High-order pseudorange rate measurement model for multi-constellation LEO/INS integration: Case of Iridium-NEXT, Orbcomm, and Globalstar

Abstract

An inertial navigation method augmented by Signals of Opportunity (SOPs) of three low earth orbit (LEO) constellations is presented. The downlink signal characteristics of the Iridium-NEXT, Orbcomm, and Globalstar LEO constellations are discussed. Furthermore, a tightly coupled integration model of the inertial navigation system and high-order LEO-SOP Doppler measurement model is designed. We presented a second-order measurement model of the LEO-SOP/INS integration using a second-order extended Kalman filter in which all the unknown states of the receiver and LEO satellites are estimated. The state parameters of the second-order EKF model are the position and velocity of both the receiver and the satellites, as well as the receiver’s orientation, the clock bias, and clock drift of the LEO satellites, and the constant bias of the Inertial Measurement Unit. An experiment is performed using a ground aerial vehicle equipped with a Multi-Constellation Software-Defined Receiver (MC-SDR). The Doppler measurements are provided by observing the downlinks from multiple satellites of the Iridium-NEXT and Orbcomm constellations. As well, the predicted measurement of a Globalstar satellite is used in the designed model. The results show the positioning accuracy of less than 10 m being achieved during a dynamic ground experiment, representing an 82% precision gain as compared against the regular single constellation EKF method.