Instrumentation & Measurement Magazine 24-4 - 20

The time difference between station A and station B can be
obtained by (3) minus (4) [9]:
Re 1
t t 
 t
AB
AB
fT IGST fT IGST
 Re 2 
Analysis of Test Results
This experiment is based on the Galileo observation data
within 30 s sampling intervals at NTSC and ORB, and the precision
products of orbit and clock offset published by IGS
analysis centers include GFZ, CODE, and SHAO, in which the
short baseline and high precision long distance time comparison
based on Galileo PPP are analyzed, respectively.
Analysis of the Pseudo-range Multipath Error
Pseudo-range multipath error directly affects the accuracy of
receiving satellite signals in PNT. In the multipath calculation,
the error effect by multipath noise can be estimated by pseudorange
P and carrier phase φ observations, and the model can be
described in (6) as follows [10]:
22
MP  
i 22 22 j j
ij ij
ff f2
 
f f ff

ij

i i

Where MP is the code multipath, the subscript i and j represent
the carrier frequency, and B is phase ambiguity including
hardware delay.
In this paper, the pseudo-range and carrier phase observation
of frequency E1 and E5a within 300 s sampling intervals
at NTSC during May 3, 2020 and the Galileo signal code
multipath noise are analyzed by using (6). Fig. 2 shows the
multipath noise at E1 and E5a of all Galileo satellites in one
day, and the value of MP are within ±1 m of E1 and E5a.
Short Baseline PPP Time Comparison
In the experiment of short baseline Galileo PPP time comparison,
two receivers are used with the independent antenna
and connected to the same frequency reference. The influence
of external frequency source can be eliminated, and only included
is the hardware delay, so the characteristic is stable
relatively in short term. In this paper, the Galileo observation
data from NTSC two receivers are used within 300 s sampling
intervals from May 2-9, 2020. The distance between the two
2 j
  P Bij
i
(6)
Long Distance PPP Time Comparison
Based on the time frequency reference systems of UTC(NTSC)
and UTC(ORB), the pseudo-range and carrier phase observation
data of Galileo from different time keeping laboratories
from May 2-9, 2020 are used, and the precision orbit and clock
offset are used from GFZ, CODE and SHAO and compared
with the results of BIPM at last.
The time keeping laboratories span Asia and Eurasia, and
the distance from NTSC to ORB is about 7537 km. In this experiment,
Table 2 shows the relevant information for the receivers
which are used in two laboratories: the types of time transfer
receivers and antenna that are used and that the receivers in
both laboratories are high-performance receivers.
Fig. 4 shows the time differences between UTC(NTSC) and
UTC(ORB) calculated by using the Galileo PPP and published
by BIPM, respectively. In the figure, the fluctuation of time difference
between UTC(NTSC) and UTC(ORB) is kept within
3 ns, and the time difference between two laboratories calculated
by using Galileo PPP has the same trend with GPS PPP,
and the residual values of Galileo PPP time link relative to the
GPS PPP is within ±0.5 ns.
The following figures show the frequency stability of the
time difference between two time keeping laboratories by using
Galileo PPP. It can be seen from Fig. 5 and Table 3 that the
stability of Galileo PPP has the same magnitude with that of
GPS PPP, and the stability is E-15/day.
Table 2 - Receivers used in the labs
Lab
Fig. 2. Relationship between the MP and elevation for E1 and E5a.
20
Receiver
code
Receiver type
Antenna type
NTSC NTP5 SEPT POLARX5TR SEPCHOKE_MC
ORB
IEEE Instrumentation & Measurement Magazine
BRUX SEPT POLARX5TR JAVRINGANT_DM
June 2021
(5)
Fig. 3. The time difference of CCD.
antennas is less than 5 m, the precision products of three analysis
centers are used, and the short baselines common clock
difference (CCD) [11], [12] is shown in Fig. 3. In the figure, the
short baseline CCD based on Galileo PPP by using different
precision products analysis centers are within ±0.5 ns, and the
three results have good consistency, where the standard deviation
of CCD are 0.1680 ns (GFZ), 0.1678 ns (CODE) and 0.1762
ns (SHAO), respectively.

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