Resilient Navigation: Augmenting Inertial Navigation Systems with Satellite Signals of Opportunity

In a GNSS-denied environment, it is important to have alternative navigation systems that can provide accurate and reliable positioning, navigation, and timing (PNT) information. This is particularly critical in scenarios where PNT is essential for safety or mission-critical applications, such as in aviation, maritime navigation, and military operations.

This research aims to develop a 4D (position/navigation/time) system by passively receiving downlink signals from large constellations of low Earth orbit satellites, such as OneWeb, Starlink, and GlobalStar. These constellations will not support pseudorange-based navigation because they will not carry atomic clocks and will not broadcast downlink signals that support pseudorange measurements. Instead, the system will use carrier Doppler shift as the only navigation observable, using eight or more measurements to determine 3D position, receiver clock offset, velocity, and receiver clock offset rate.

The research focused on a Doppler shift measurement model. Convergence techniques for non-linear optimization were explored and the expected accuracy was evaluated through the development of Geometric Dilution of Precision (GDOP) formulations. A simulator was developed to assess navigation performance in static environments and predict GDOP at any given time and receiver location. Additionally, the research included a hardware implementation on a smartphone device as well as investigation into the effect of atmospheric and orbital errors on the navigation system.