CSAC Drift Modeling Considering GPS Signal Quality in the Case of GPS Signal Unavailability

TL;DR

This paper proposes a weighted CSAC model that maintains low clock error during GPS signal disruptions by considering satellite visibility and geometry, achieving less than 4 microseconds error over 12 hours without GPS signals.

Contribution

It introduces a novel weighted model for CSAC that accounts for satellite factors to improve onboard clock accuracy during GPS outages.

Findings

CSAC can keep error below 4 microseconds for 12 hours without GPS.

The model effectively mitigates clock errors during GPS signal disruptions.

Satellite visibility and geometry significantly impact clock accuracy.

Abstract

The Global Positioning System (GPS), one of the Global Navigation Satellite Systems (GNSS), provides accurate position, navigation and time (PNT) information to various applications. One of the application that is highly receiving attention is satellite vehicles, especially Low Earth Orbit (LEO) satellites. Due to their limited ways to get PNT information and low performance of their onboard clocks, GPS system time (GPST) provided by GPS is a good reference clock to synchronize. However, GPS is well-known for its vulnerability to intentional or unintentional interference. This study aims to maintain the onboard clock with less error relative to the GPST even when the GPS signal is disrupted. In this study, we analyzed two major factors that affects the quality of the GPS measurements: the number of the visible satellites and the geometry of the satellites. Then, we proposed a weighted model for a Chip-Scale Atomic Clock (CSAC) that mitigates the clock error relative to the GPST while considering the two factors. Based on this model, a stand-alone CSAC could maintain its error less than 4 microseconds, even in a situation where no GPS signals are received for 12 hours.