Inter-Satellite Link Enhanced Orbit Determination for BeiDou-3

Abstract

The third generation of the BeiDou navigation satellite system (BDS-3) is a global navigation system, and is expected to be in full operation by 2020. High-precision orbits are a precondition for BDS-3 to provide a highly accurate service, which needs a global tracking and monitoring capability for the operational satellites. However, it is difficult for BDS to construct global ground monitoring stations. Fortunately, Ka-band Inter-Satellite Link (ISL) antennae fitted to the BDS-3 satellites can be used to extend the visible arc of the Medium Earth Orbit (MEO) satellites and to enhance the ground stations for orbit determination. This paper analyses the ISL-enhanced orbit determination for eight BDS-3 satellites, using the data from ten Chinese domestic stations and 13 international Global Navigation Satellite System (GNSS) Monitoring and Assessment System (iGMAS) overseas stations. The results show that the Three-Dimensional (3D) position Root Mean Square (RMS) error of the Overlapping Orbit Differences (OODs) is approximately 1 m when only ten regional stations are used. When the ISL measurements are added, the 3D position RMS error is decreased to 0·5 m, and the accuracy of the 24-hour orbit prediction can also be improved from 2 m to 0·7 m, which is even better than that of the orbits determined using globally distributed stations. It can be expected that with the subsequent launch of BDS-3 satellites and the increasing number of ISLs, the advantage of the ISL enhanced orbit determination will become more significant.

Basic performance and future developments of BeiDou global navigation satellite system

“…The BeiDou global navigation satellite system, (BDS-3), is the third step of China's satellite navigation system construction [1,2]. In addition to the positioning, navigation and timing (PNT) service provided by all GNSSs, BDS-3 also provides regional message communication (1000 Chinese characters per time) and global short message communication (40 Chinese characters per time), global search and rescue service (SAR), regional precise point positioning (PPP) service, embedded satellite-based augmentation service (BDS-BAS), and space environment monitoring function [3][4][5].…”

“…The BDS-3 baseline system with 18 MEO satellites has begun providing initial services to global users on December 27, 2018, and at least five satellites are visible for global users. Many scholars have described the BDS-3 status and the main service function indexes [2][3][4][5][6], including the constellation design, service type, navigation signal system, space-time datum and orbit determination method of BDS-3 system, etc. The spacetime datum, signal-in-space quality, accuracy of satellite broadcast ephemeris, the accuracy of the post-processing precise orbit, time synchronization accuracy, satellite clock offset accuracy and the basic PNT service performance of the BDS-3 baseline system have be calculated and analyzed [3][4][5][7][8][9][10].…”

“…Many scholars have described the BDS-3 status and the main service function indexes [2][3][4][5][6], including the constellation design, service type, navigation signal system, space-time datum and orbit determination method of BDS-3 system, etc. The spacetime datum, signal-in-space quality, accuracy of satellite broadcast ephemeris, the accuracy of the post-processing precise orbit, time synchronization accuracy, satellite clock offset accuracy and the basic PNT service performance of the BDS-3 baseline system have be calculated and analyzed [3][4][5][7][8][9][10]. Because BDS-3 satellites are equipped with inter-satellite links (ISL), more research achievements have been made in the fields of ISL supported determination of satellite orbit and clock offset [3][4][5][11][12][13].…”

“…The spacetime datum, signal-in-space quality, accuracy of satellite broadcast ephemeris, the accuracy of the post-processing precise orbit, time synchronization accuracy, satellite clock offset accuracy and the basic PNT service performance of the BDS-3 baseline system have be calculated and analyzed [3][4][5][7][8][9][10]. Because BDS-3 satellites are equipped with inter-satellite links (ISL), more research achievements have been made in the fields of ISL supported determination of satellite orbit and clock offset [3][4][5][11][12][13]. According to the preliminary calculation results, the ranging accuracy of the ISLs of BDS-3 is about 4 cm; if the satellite orbits are determined using only regional station observations, the three-dimensional orbit accuracy of the overlapping arc is about 60 cm; with ISL measurements, the orbit accuracy is about 30 cm, the 24-h orbit prediction accuracy is also raised from 140 to 51 cm [3][4][5], and the radial accuracy can reach 10 cm, as evaluated through laser observations.…”

“…The timing accuracy is better than 19.1 ns (95%), which satisfies the system service performance specifications. Compared with BDS-2, BDS-3 exhibits significant improvement in system coverage, spatial signal accuracy, availability and continuity [2][3][4][5]. At the user's end, service improvements such as the BDS-3 signal design and optimal receiving mode [14], precision orbit determination [3-5, 9, 15], and precise point positioning technology [16] have been reported in relevant literature and will not be repeated herein.…”