Applications of two-way satellite time and frequency
transfer in the BeiDou navigation satellite system<xref rid="fn2" ref-type="Recommend" xml:lang="en"><sup>?</sup></xref>

ShanShi Zhou; XiaoGong Hu; Li Liu; Rui Guo; LingFeng Zhu; ZhiQiao Chang; ChengPan Tang; XiuQiang Gong; Ran Li; Yang Yu

doi:10.1007/s11433-016-0185-6

SCIENCE CHINA Physics, Mechanics & Astronomy

SCIENCE CHINA Physics, Mechanics & Astronomy, Volume 59, Issue 10: 109511(2016) https://doi.org/10.1007/s11433-016-0185-6

Applications of two-way satellite time and frequency transfer in the BeiDou navigation satellite system^?

ShanShi Zhou^1,*, XiaoGong Hu¹, Li Liu², Rui Guo², LingFeng Zhu², ZhiQiao Chang², ChengPan Tang¹, XiuQiang Gong¹, Ran Li¹, Yang Yu¹

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ReceivedMay 10, 2016
AcceptedJun 15, 2016
PublishedAug 22, 2016

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Abstract

A two-way satellite time and frequency transfer (TWSTFT) device equipped in the BeiDou navigation satellite system (BDS) can calculate clock error between satellite and ground master clock. TWSTFT is a real-time method with high accuracy because most system errors such as orbital error, station position error, and tropospheric and ionospheric delay error can be eliminated by calculating the two-way pseudorange difference. Another method, the multi-satellite precision orbit determination (MPOD) method, can be applied to estimate satellite clock errors. By comparison with MPOD clock estimations, this paper discusses the applications of the BDS TWSTFT clock observations in satellite clock measurement, satellite clock prediction, navigation system time monitor, and satellite clock performance assessment in orbit. The results show that with TWSTFT clock observations, the accuracy of satellite clock prediction is higher than MPOD. Five continuous weeks of comparisons with three international GNSS Service (IGS) analysis centers (ACs) show that the reference time difference between BeiDou time (BDT) and golbal positoning system (GPS) time (GPST) realized IGS ACs is in the tens of nanoseconds. Applying the TWSTFT clock error observations may obtain more accurate satellite clock performance evaluation in the 10⁴ s interval because the accuracy of the MPOD clock estimation is not sufficiently high. By comparing the BDS and GPS satellite clock performance, we found that the BDS clock stability at the 10³ s interval is approximately 10^?12, which is similar to the GPS IIR.

Funded by

The National Natural Sciences Foundation of China(41574029)

Acknowledgment

This work was supported by the National Natural Sciences Foundation of China (Grant No. 41574029) and Youth Innovation Promotion Association CAS (Grant No. 2016242). We would like to thank the Beijing Global Information Application and Development Center for providing the TWSTFT observations of the BDS. We also thank IGS for providing the BDS satellite clock products. The authors gratefully acknowledge the support of all individuals and institutions that have supported this work.

References

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Figure 1
(Color online) Diagram of TWSTFT measure.
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Figure 2
(Color online) TWSTFT and MPOD clock comparison time series. (a) Shows the GEO satellite clock comparisons; (b) shows the IGSO; (c) shows MEO. Different colors represent different satellites listed in the right legends.
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Figure 3
(Color online) TWSTFT and MPOD clock linear fitting RMS and a1 time series. The left subplots show the TWSTFT residual and the MPOD clock fitting residual in blue and red, respectively. The right subplots show the linear fitting parameter (a1) time series. The blue points represent TWSTFT fitting results, and red points represent MPOD results.
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Figure 4
(Color online) Satellite clock prediction error time series for TWSTFT and MPOD. The blue represents TWSTFT clock prediction error, the red MPOD clock predictions error. (a)-(c) Represent C01 (GEO), C08 (IGSO), C11 (MEO) satellite clock prediction error respectively.
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Figure 5
(Color online) Comparisons of TWSTFT and three AC MPOD clocks. The three rows represent three ACs, (a) the comparison between TWSTFT and CODE MPOD clock; (b) the comparison between TWSTFT and GFZ; (c) the comparison between TWSTFT and WHU. Different colors represent different satellites listed in the right legends.
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Figure 6
(Color online) Satellite performance evaluations in orbit. The blue and red curves represent Allan variances calculated by TWSTFT and by GFZ MPOD clock data, respectively. (a)-(c) Represent C01 (GEO), C08 (IGSO), C11 (MEO).
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Figure 7
(Color online) Comparison of GPS and BDS satellite performance evaluations in orbit. The black points represent BDS Allan variance, and the other colors represent GPS. The same color represents the same GPS block type.

Table 1 Error sources for TWSTFT and MPOD clock errors

Error source	TWSTFT	MPOD
System error	residual ionospheric delay device bias	orbital correlated error
White noise	0.707′pseudorange noise	BDS ionospheric free combination B1/B2: 2.90′phase noise B1/B3: 3.53′phase noise
Satellite reference position	B3 send phase center	LC combination phase center
Ground reference time	BDT: ground atomic time	the GPST realized at each AC (see ref. [5])

Table 2 TWSTFT and MPOD clock comparison: MEAN and STD

SATID	Mean (ns)	STD (ns)	SATID	Mean (ns)	STD (ns)
01	13.181	1.591	08	16.585	0.472
02	–13.801	1.328	09	6.220	0.360
03	0.928	1.252	10	–1.083	0.528
04	–0.421	0.864	11	0.441	0.385
05	–9.354	1.589	12	–10.542	0.270
06	17.422	0.314	14	–23.356	0.360
07	17.844	0.533	–	–	–

Table 3 Satellite clock error fitting residual comparison

SATID	GFZ (ns)	TWSTFT (ns)	SATID	GFZ (ns)	TWSTFT (ns)
C01	0.108	0.126	C08	0.304	0.321
C02	0.116	0.128	C09	0.079	0.128
C03	0.068	0.111	C10	0.134	0.176
C04	0.176	0.176	C11	0.154	0.218
C05	0.086	0.138	C12	0.075	0.152
C06	0.153	0.175	C14	0.053	0.156
C07	0.093	0.129	–	–	–
			Mean (all satellites): GFZ: 0.126 TWSTFT: 0.166

Table 4 Satellite clock prediction error for TWSTFT and MPOD

SATID	TWSTFT (ns)	MPOD (ns)	SATID	TWSTFT (ns)	MPOD (ns)
01	0.556	1.072	08	1.505	1.636
02	0.462	1.239	09	0.435	0.708
03	0.369	0.764	10	0.682	0.888
04	0.726	1.553	11	0.620	0.816
05	0.787	1.475	12	0.450	0.762
06	1.268	1.280	14	0.613	0.734
07	0.582	0.874	mean	0.697	1.062

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06.30.Ft	Time and frequency
91.10.Fc	Space and satellite geodesy; applications of global positioning systems
93.85.Bc	Computational methods and data processing, data acquisition and storage
91.10.Fc	Space and satellite geodesy; applications of global positioning systems
93.85.Bc	Computational methods and data processing, data acquisition and storag