Joint Doppler and Azimuth DOA Tracking for Positioning with Iridium LEO Satellites

Abstract

A receiver capable of estimating the Doppler and azimuth direction-of-arrival (DOA) of Iridium NEXT low Earth orbit (LEO) signals of opportunity (SOPs) is presented. The proposed receiver operates in three stages: (i) Fast Fourier Transform (FFT)based Doppler acquisition, (ii) Kalman filter (KF)-based Doppler tracking, and (iii) Doppler-compensated MUltiple SIgnal Classification (MUSIC)-based algorithm for DOA tracking. Experimental results are presented demonstrating successful tracking of the Doppler frequency and azimuth DOA of an Iridium NEXT LEO satellite, achieving a Doppler root mean square error (RMSE) of 8.1 Hz over 120 seconds and an azimuth DOA RMSE of 1.04 degrees over 60 seconds. The Doppler and azimuth DOA measurements are fused via an extended Kalman filter (EKF) to localize a stationary receiver. Starting with an initial estimate 7 km away from the true receiver's position, the Doppler-only measurements yielded a final positioning error of 656.m, while the Doppler and azimuth DOA measurements reduced the error to 289.5 m.