Instrumentation & Measurement Magazine 24-4 - 18

Research on Time Comparison
Based on Galileo PPP
Jihai Zhang, Shaowu Dong, Haibo Yuan, Wei Guang, and Wei Li
T
ime comparison based on global navigation satellite
system (GNSS) is one of the main techniques in Coordinated
Universal Time (UTC) calculation. At present,
there is a goal to promote the Galileo system to join the UTC calculation
to provide high-precision services for users all over
the world. In this paper, the Precision Point Positioning (PPP)
time comparison based on Galileo is studied. The data used in
this paper include the original data of pseudo-range and carrier
phase from National Time Service Center of Chinese Academy
of Sciences (NTSC) and Royal Observatory of Belgium (ROB),
and the data of precision orbit and clock offset released by International
GNSS Service (IGS) which includes the German
Research Center for Geoscience (GFZ), Centre for Orbit Determination
in Europe (CODE) and Shanghai Astronomical
Observatory (SHAO). The results show that the pseudo-range
multipath noise of E1 and E5a are all less than ±1 m. When the
Galileo PPP is applied to the short baseline common clock time
comparison, the time difference by using the precision products
of three analysis centers are less than ±0.5 ns, and the standard
deviation of the time difference are less than 0.2 ns. For long
baseline of Asia Europe time comparison, based on the precision
products of three IGS analysis centers, the time comparison
between UTC(NTSC) and UTC(TP) by using Galileo PPP have
the same trend as the GPS PPP, which is released by International
Bureau of Weights and Measures (BIPM), the stability of
Galileo PPP is the same with GPS PPP, and it can reach to E-15/
day. As a result, with the performance improvement of Galileo
system, the high-precision time comparison based on Galileo
will provide better services for users, and the experiment results
indicate that the Galileo can also be used as one of the formal
methods by BIPM for precision time comparison in the future.
Research Background and Significance
Time comparison based on the GNSS is widely used by different
time keeping laboratories and BIPM for UTC calculation
all over the world [1]. Now, because the Global Position System
(GPS) was built earlier than the other systems, it has more
than one hundred monitoring stations around world. The
IGS provides related precision products for GPS high precision
data processing; therefore, the GPS PPP time comparison
has become the main method for users to choose. Meanwhile,
the data processing software used by BIPM for UTC calculation
every month is NRcan-PPP, which is only based on GPS
PPP. At present, there are more than 80 time keeping laboratories
registered in BIPM, and more than 50 time keeping
laboratories steer their UTC(k) (k is the different time keeping
laboratory) to UTC by GPS PPP time link [2]. With the vigorous
development of new navigation systems such as Galileo
and Beidou, in order to improve the accuracy, stability and reliability
of UTC, and to confirm stability of the international
time link, the Consultative Committee for Time and Frequency
(CCTF) recommend and encourage the multi-time comparison
technologies be used in the UTC calculation in 2009. The time
difference between GLONASS time and UTC was first published
by BIPM in December 2009, and the data are available
for users to carry out relevant research work. In 2012, the IGS
began to establish the Multi-GNSS Experiment (MGEX) project,
in which various navigation systems satellites are modeled
and analyzed, and the precision products of satellites are released.
After several years of development, the IGS and related
research institutes have provided the products of the navigation
systems; the products include ultra-fast, fast and final for
global users with a variety of options. With the construction of
the Galileo satellite navigation system by European organizations
in recent years, the initial service was announced on 15
December 2016 by Galileo, and the Positioning, Navigation
and Timing (PNT) service are provided for users. At present,
the launched satellites will continue to be used to complete the
constellation layout, and the system performance and global
availability are improved gradually. The Galileo system will
This research is supported by National Time Service Center (NTSC) programs of " Young creative talents "
(Grant No. NTSC-201804), Western Light Young Scholars Project (Grant No. XAB2019B13) and
National Natural Science Foundation of China (Grant No.11773030).
18
IEEE Instrumentation & Measurement Magazine
1094-6969/21/$25.00©2021IEEE
June 2021

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