Initial Positioning Results with Decoded Iridium NEXT Signals Using a TDOA Approach

Global navigation satellite systems (GNSS) are essential for modern navigation, but face limitations in environments where signals are obstructed, jammed or spoofed. With the aim of overcoming these challenges, this paper presents an innovative navigation framework using low Earth orbit (LEO) Iridium NEXT satellites as signals of opportunity. The proposed system exploits Iridium ring alert messages, which are transmitted every 90 ms at 1626.270 MHz, and uses the time difference of arrival technique with least mean squares to determine the receiver position. An extended Kalman filter is integrated to improve the accuracy by predicting the receiver state and refining estimates using satellite data. Experimental results from a 15-minute static test using signals from six Iridium satellites indicated two-dimensional positioning accuracy with a root mean square error of 31.66 m. These results highlight the potential of the framework as a robust alternative or backup for a GNSS in environments such as urban canyons, indoor environments, and remote areas. Future developments will aim to integrate Iridium signals of opportunity with other LEO constellations, such as Orbcomm, Starlink and OneWeb, to further improve accuracy, resilience and coverage, which will represent a significant step forward in reliable navigation solutions.significant step forward in reliable navigation solutions.