Instrumentation & Measurement Magazine 25-5 - 35

Table 3 - RMS of average of MP
B1I
B2I
Mean
B1C
B2a
0.4499 m 0.3167 m 0.1784 m 0.1474 m
BDS-3 satellites are equipped with better satellite clocks
than BDS-2 satellites. Meanwhile, the BPSK (10) modulation is
used by B2a signal, and the QMBOC (6, 1, 4/33) modulation is
used by B1C signal. The B2a signal contained within the 20.46
MHz bandwidth with a center frequency of 1176.45 MHz, and
the B1C signal contained within the 32.736 MHz bandwidth
with a center frequency of 1575.42 MHz. Therefore, the noise of
B2a multipath is smaller than other frequency points.
Short-baseline Time Comparison Based on
BDS-3 PPP
For the short-baseline, the distance between two receivers
is less than 5 m, and the two receivers connect the same frequency
reference with an independent antenna. The principle
of the system connection is shown in Fig. 8. To evaluate the
results of the comparison experiment with BDS-3 PPP, a shortbaseline
common clock difference (CCD) [19], [20] comparison
was carried out using two receivers. The two receivers were
connected to the same reference frequency. This method can
reduce the impact of the common frequency source noise and
includes only the relative hardware delay. This method is also
widely used by BIPM to carry out the relative calibration time
link between the different time keeping laboratories involved
in the UTC calculation.
Fig. 9 shows the short-baseline comparison of the two
receivers, based on BDS-2 and BDS-3 PPP, and the BDS observation
data with a sampling interval of 300 s from July 3-6,
2020, were used from NTSC two POLARX5TR_PRO receivers.
The results show that the short-baseline CCD was kept within
± 0.1 ns, the standard deviation of the result using BDS-2 is
Fig. 9. The CCD of BDS PPP time comparisons at NTSC.
0.0341 ns, and BDS-3 is 0.0296 ns. The standard deviation of
BDS-3 is smaller than that of BDS-2. In the time comparison,
the smaller the standard deviation of short-baseline time comparison,
the better the performance of time comparison. That
is to say, the short-baseline time comparison performance of
BDS-3 PPP is better than that of BDS-2, and the standard deviation
of BDS-3 PPP has increased by 13.19% compared with
BDS-2. It is shown that the noise of CCD by using BDS-3 is
smaller than BDS-2.
Long-baseline time comparison based on
BDS-3 PPP
To evaluate the long-baseline PPP time comparison performance
based on BDS-3 new signals, the pseudo-range and
carrier phase observations of B1C and B2a data with 300 s sampling
interval at NTSC and TP from July 3-6, 2020 were used.
As shown in Fig. 10, the two laboratories are located in Asia
and Europe, respectively, and the distance between NTSC and
TP is about 7058 km. Table 4 shows the relevant information
for the two stations.
Fig. 10. The geographical distribution of station.
Table 4 - Receivers used in the labs
Lab
Fig. 8. The Principle of CCD.
August 2022
Receiver
code
Receiver type
JAVAD TRE_3
Antenna type
NTSC NTP5 POLARX5TR_PRO SEPCHOKE_MC
TP TP01
NOV850
IEEE Instrumentation & Measurement Magazine
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