LEO-PNT: applications and algorithms for future positioning and navigation services

Positioning in all environments has become a very important topic in recent years. Applications demand higher and higher localization performance in all kinds of environments. In outdoor environments, Global Navigation Satellite Systems (GNSS) can be used to provide an accurate position fix. However, these systems are not perfect, and multiple shortcomings are inherent to their design. Due to their Medium Earth Orbits (MEOs), the satellite signals arrive with a low Power on Ground (PoG), leading to both low availability in indoor and urban situations and increased vulnerability to jamming attacks. Furthermore, the relatively slow movement of GNSS satellites across the sky results in long Precise Point Positioning convergence times. Finally, due to Code Division Multiple Access (CDMA), the computational complexity in acquiring and tracking the signal can be relatively high, leading to increased power consumption. By using satellites in Low Earth Orbit for Positioning Navigation and Timing (LEO-PNT), these shortcomings can be mitigated or resolved. In this study, we present a novel interpretation of the least squares algorithm, which has been extensively used and proven for satellite navigation positioning, in a standalone LEO-PNT scenario. Moreover, we investigate the possibility of combining code-based and Doppler-based positioning readings with a factor graph approach. By analyzing the computational complexity, positioning accuracy, and convergence time of this alternative fixing algorithm, we intend to pave the road for multi-layered positioning services from LEO space-based architectures.