Simulation, Optimization, and Comparisons Among LEO-PNT Constellations

Abstract

Unlike 25 years ago, today's satellite navigation provides critical services across vari­ous domains such as transportation, finance, telecommunications, surveillance, and, most relevant for this dissertation, Positioning, Navigation and Timing (PNT) sys­tems. Recent advancements in small-scale Low-Earth Orbit (LEO) satellites have lowered costs, sparking numerous mega-constellation projects (e.g., Starlink, One Web, Kuiper). Closer proximity to Earth enables fast orbital movement and strong signals, indicating that Low-Earth Orbit-based Positioning, Navigation, and Timing (LEO­PNT) systems could provide superior PNT signals compared to traditional Medium Earth Orbit (MEO) and Geosynchronous Equatorial Orbit (GEO) satellite net­works. Consequently, there is a growing interest in LEO-PNT systems, which are considered either complementary to or as potential standalone alternatives to exist­ing Global Navigation Satellite Systems (GNSS). However, there are still numerous challenges in designing effective LEO-PNT systems, and many of these have not yet been fully explored in current research.

This dissertation is focused on the development of novel LEO-PNT constella­tions and provides a comprehensive analysis of their PNT performance compared to existing systems, contributing to the 6eEd of LEO-PNT research. The primary goal is on dedicated standalone LEO-PNT satellite constellation optimization for PNT purposes and focuses on identifying th.e key parameters for designing LEO-PNT constellations. The secondary goal is to explore combination and comparison of the performance of these potential LEO-PNT constellations with existing LEO systems and GNSS. Thus, this dissertation provides a contribution to the satellite navigation domain by providing novel LEO-PNT constellation designs with the potential to improve upon existing technologies.

The dissertation contains two major contributions. The first contribution is an optimization study, aiming to find Pareto-optimal multi-shell constellation config­urations for LEO-PNT applications. This part addresses state-of-the-art constellation design approaches, introduces relevant performance and feasibility metrics, and identifies key concepts and trade-offs crucial for LEO-PNT system design. In addition, using selected results, a detailed performance analysis is presented for sev­eral relevant scenarios with varying receiver location properties considering factors such as indoor/ outdoor environments, rural/ urban settings, and line-of-sight/ non­line-of-sight cases, presenting LEO-PNT constellation designs capable of rivaling or surpassing existing LEO and GNSS constellations from a performance perspective. The second contribution explores dedicated standalone LEO-PNT constellations and shows their potential to enhance existing PNT systems, both as independent systems and when combined with existing PNT networks. In addition, the potential perfor­mance of two experimental LEO-PNT constellations is compared against existing GNSS and LEO constellations, in various configurations and scenarios including both indoor and outdoor situations, presenting an insight on the performance of the Pareto-optimal constellation configurations. Furthermore, possible combinations of three GNSS and two LEO-PNT systems, were also investigated in these scenarios from a positioning perspective. Notably, combining two small-scale LEO-PNT sys­tems or one mega-constellation (such as Starlink) with one or more existing GNSS constellations can significantly enhance the indoor coverage, as well as improve the signal quality and geometric configuration, when the carrier frequencies are similar to those used in GNSS.