Timing System Design for PNT Satellite Constellation: Time Scale Generation and Distributed Clock Synchronization

Abstract

Accurate positioning and time keeping are the most important services provided by the PNT satellite systems. In recent years, the need for higher accuracy positioning and time keeping, more extensive coverage, and better safety for the PNT satellites has increased. Designing new PNT satellite constellations to enhance or replace existing architectures has attracted significant interest. This research examines two key aspects of timing systems for PNT constellations: generating a stable time scale and clock synchronization between the satellites. To generate a stable time scale, this research introduces a mixed clock ensemble algorithm and a linear quadratic Gaussian clock steering algorithm for its realization. This Kalman filter-based algorithm allows for the combination and enhancement of individual clocks' stability. Results indicate that the time scale generated by the algorithm yields better performance than any single clock in the group, and the capability of the control algorithm to achieve this time scale. For clock synchronization, this work investigates two approaches. The first approach is to utilize the existing PNT constellation, such as GPS. An extended Kalman filter method is introduced to identify the clock bias between satellite time and GPS time. Simulation results demonstrate that the algorithm tracks the biases accurately. The second approach is using the consensus algorithm for synchronization. This method is based on the communication between the satellites in the constellation, which provides robustness and less dependence on external sources. Numerical simulation shows that synchronization can be achieved quickly with the consensus algorithm.