Performance Limits for Navigation based on Signals of Opportunity from Low Earth Orbit Satellites

This thesis investigates the performance limits of navigation using signals of op- portunity (SoOp) coming from low earth orbit (LEO) satellites, since the critical aspects of global navigation satellite system (GNSS) justify the need of finding al- ternative navigation methods. LEO SoOp oer several advantages, such as shorter distance between satellite and receiver, potentially reduced path loss and better signal availability, in particular for challenging environments. A critical assessment is conducted using the modified Cramér-Rao lower bound (MCRLB) to evaluate the estimation accuracy of signal parameters, focusing on four LEO constellations: Starlink, OneWeb, Iridium, and Orbcomm. The analysis reveals that higher frequency signals, such as those from Starlink and OneWeb, coupled with their wide bandwidth, oer the best potential accuracy in position estimation. Simulations performed to test the acquisition of Starlink signals demonstrate that the accuracy of time of arrival (TOA) and Doppler shift estimations is rela- tively close with their respective MCRLBs when the carrier to noise density ra- tio (CNDR) is higher than 65 dB-Hz. Below this threshold, accuracy degrades significantly. The study also identifies some critical issues associated to navigation with LEO SoOp, including the high dynamicity of the space vehicles (SVs), the prediction of the error caused by the atmosphere and the lack of essential information such as transmission time and satellite identity.