Abstract
An autonomous remote clock control system is proposed to provide time synchronization and frequency syntonization for satellite to satellite or ground to satellite time transfer, with the system comprising on-board voltage controlled oven controlled crystal oscillators (VC-OCXOs) that are disciplined to a remote master atomic clock or oscillator. The synchronization loop aims to provide autonomous operation over extended periods, be widely applicable to a variety of scenarios and robust. A new architecture comprising the use of frequency division duplex (FDD), synchronous time division (STDD) duplex and code division multiple access (CDMA) with a centralized topology is employed. This new design utilizes dual one-way ranging methods to precisely measure the clock error, adopts least square (LS) methods to predict the clock error and employs a third-order phase lock loop (PLL) to generate the voltage control signal. A general functional model for this system is proposed and the error sources and delays that affect the time synchronization are discussed. Related algorithms for estimating and correcting these errors are also proposed. The performance of the proposed system is simulated and guidance for selecting the clock is provided.
Highlights
Some existing satellite time synchronization systems, such as the gravity recovery and climate experiment (GRACE) achieve synchronization by means of compensating the clock errors at the ground station rather than producing the synchronized and syntonized timing signals [1,2]
The orbit data from the GRACE mission and Beidou G2 & Beidou A2 were employed via Satellite Tool Kit (STK) because they have significantly different inter-satellite baselines and relative velocities
In order to evaluate the stability of the synchronization loop, statistics relating to the synchronization error data ε n from the first hour to the 24th h have been determined for an arbitrary number of initial conditions
Summary
Some existing satellite time synchronization systems, such as the gravity recovery and climate experiment (GRACE) achieve synchronization by means of compensating the clock errors at the ground station rather than producing the synchronized and syntonized timing signals [1,2]. Atomic clocks have better long-term stability and worse short-term stability, greater volume, weight, power, price and shorter lifetime compared with a high quality crystal oscillator ( chip-scale atomic clocks have been developed, their stability is not as good as full-scale atomic clocks and they are not space qualified) For this reason, global navigation satellite systems (GNSS), such as the global positioning system (GPS), adopts a time-keeping system (TKS) that couples the atomic clock with a voltage-controlled crystal oscillator (VCXO) on-board the satellite to produce the reference timing signal [3,4]. Unlike the LS based relative motion compensation methods that makes use of pseudo-range, carrier phase and even Doppler observations [15,16], the proposed method only requires pseudo-range observations and ephemeris information, and the error originates from relative motion could be calculated by means of one communication link It proposes a cost-effective and energy-effective way to achieve the desired synchronization and syntonization performance of satellite systems.
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