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Han et al. Satell Navig (2021) 2:18 Satellite Navigation
https://doi.org/10.1186/s43020-021-00044-0
https://satellite-navigation.springeropen.com/

ORIGINAL ARTICLE Open Access

The space–time references of BeiDou

Navigation Satellite System

2*
1,2
2
2
Chunhao Han , Li Liu , Zhiwu Cai and Yuting Lin
Abstract
The BeiDou Navigation Satellite System (BDS) is essentially a precise time measurement and time synchronization
system for a large-scale space near the Earth. General relativity is the basic theoretical framework for the information
processing in the master control station of BDS. Having introduced the basic conceptions of relativistic space–time
reference systems, the space–time references of BDS are analyzed and the function and acquisition method of the
Earth Orientation Parameters (EOP) are briefy discussed. The basic space reference of BDS is BeiDou Coordinate
System (BDCS), and the time standard is the BDS Time (BDT). BDCS and BDT are the realizations of the Geocentric
Terrestrial Reference System (GTRS) and the Terrestrial Time (TT) for BDS, respectively. The station coordinates in the
BDCS are consistent with those in International Terrestrial Reference Frame (ITRF)2014 at the cm–level and the dif-
ference in scale is about 1.1 × 10 . The time deviation of BDT relative to International Atomic Time (TAI) is less than
−8
50 ns and the frequency deviation is less than 2 × 10 −14 . The Geocentric Celestial Reference System (GCRS) and the
solar Barycentric Celestial Reference System (BCRS) are also involved in the operation of BDS. The observation models
for time synchronization and precise orbit determination are established within the GCRS framework. The coordinate
transformation between BDCS and GCRS is consistent with the International Earth Rotation and Reference Systems
Service (IERS). In the autonomous operation mode without the support of the ground master control station, Earth
Orientation Parameters (EOP) is obtained by means of long-term prediction and on-board observation. The observa-
tion models for the on-board astrometry should be established within the BCRS framework.
Keywords: BDS, BDT, Space–time references, BeiDou coordinate system, Earth orientation parameters

Introduction Precise orbit determination and time synchronization are
Since July 31, 2020, BeiDou-3 Navigation Satellite Sys- conducted with diferent methods, but the basic observation
tem (BDS-3) has been ofcially operational. As a major data are the same, i.e., pseudo-ranges at the ground moni-
national infrastructure, BDS-3 provides global position- tor stations. Te joint calculation method of satellite orbit
ing, navigation, and timing, as well as Global Short Mes- and satellite clock ofset is adopted by Global Positioning
sage Communication (GSMC) and Search and Rescue System (GPS) and Galileo Navigation Satellite System (Gali-
(SAR) services. It also provides Satellite-Based Augmen- leo), which will result in a strong correlation between the
tation Service (SBAS), Precise Point Positioning (PPP), derived satellite orbit and satellite clock ofset (Demetrios
Regional Short Message Communication (RSMC) and et al., 2008). Tere is no doubt that the longer the satellite’s
other services in and around China (Yang et al., 2018; tracking arc and the higher the frequency stability of the on-
Guo et al., 2019). board clock, the more accurate the results of the orbit and
the clock ofset will be. Considering the limited deployment
range of monitor stations and the non-ideal stability of the
satellite clocks during the initial construction of BeiDou
*Correspondence: lliu@shao.ac.cn Navigation Satellite (Regional) System (BDS-2) (the daily
2 Beijing Satellite Navigation Center, Beijing 100094, China stability was at 1 × 10 −13 level), to prevent the mutual error
Full list of author information is available at the end of the article

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