Multi-GNSS Real-time Precise Point Positioning: GPS, GLONASS, BeiDou, and
Galileo Xingxing Li, Maorong Ge, Mathias Fritsche, Yang Liu, Zhiguo
Deng, Jens Wickert, and Harald Schuh
The German Research Centre for Geosciences (GFZ) Telegrafenberg, Potsdam, Germany. [email protected]
1 Multi-GNSS status 2 Multi-GNSS data processing 3 Multi-GNSS orbit and clock 4 Multi-GNSS real-time PPP 5 Discussions
Content
1 Current multi-GNSS status
3
Figure 1. Ground tracks of four satellite navigation systems: BeiDou (14), Galileo (8+), GLONASS (24) and GPS (32).
1 Current multi-GNSS status
4
Figure 2. Satellite visibility of Galileo, BeiDou, GLONASS and GPS at the four-system station GMSD (Japan) on September 3, 2013 .
Li et al (2015), Precise positioning with current multi-constellation Globa l Naviga t ion Sa te l l i t e Systems: GPS, GLONASS, Galileo and BeiDou. Sci Rep., 5, 8328.
1 Current multi-GNSS status
5
Figure 3. Distribution of MGEX stations and their supported constellations (as of 2014, almost 90 stations); some IGS stations (the red circles, GPS-only) are also included.
1 2 30
2
4
6
8
180oW 120oW 60oW 0o 60oE 120oE 180oW
60oS
30oS
0o
30oN
60oN
180oW 120oW 60oW 0o 60oE 120oE 180oW
60oS
30oS
0o
30oN
60oN
BeiDou GPS GLONASS Galileo
1 Current multi-GNSS status
6
Figure 4. BETN (WHU) and a local CORS network equipped with GPS+BeiDou capable dual-system receivers. The small map indicates the local CORS network and the
large one is for BETN.
7
2 Multi-GNSS data processing Initial Satellite Orbit
Multi-GNSS POD(Batch-processing, Every 3h)
Orbit Prediction Using Orbit Integrator
(6h Predicted Orbits)
Multi-GNSS Real-Time PCE(Sequential Processing,Every 5s)
Multi-GNSS PPP(Sequential Processing)
UPD Estimation(Sequential processing from PPP
float amb)
NTRIP Caster
Optional
Optional
Multi-GNSS OBS(MGEX+BETN+IGS)
Antenna & Receiver Info.
Site Coordinatese.g.SINEX
Inter-system BiasInter-frequency Bias
UncalibratedPhase Delays
UD Integer Ambiguity
Real-Time Orbit CorrectionsReal-Time Clock Corrections
Optional
Optional
Optional
R1 R2
R3
RnR4
Multi-GNSS Receiver
PPP Solution 1:Coord,clk,ZTD,iono, ISB&IFB,amb
PPP Solution 2:Coord,clk,ZTD,iono, ISB&IFB,amb
……PPP Solution n:Coord,clk,ZTD,iono, ISB&IFB,amb
Figure 5. The structure of the prototype multi-GNSS real-time PPP
service system at GFZ.
2 Multi-GNSS data processing
8
Table 1. Multi-GNSS data processing strategy, observation models and estimated parameters for POD, PCE, and PPP
Item Models Satellites BeiDou+Galileo+GLONASS+GPS; about 74 satellites
Procedure Integrated processing, all the observations from different GNSS in one common parameter adjustment procedure
Estimator LSQ in batch mode for POD; LSQ in sequential mode for PCE & PPP
Observations Undifferenced phase and code observations
Combination mode Ionosphere-free combination for POD/PCE network solution; raw observations on individual frequencies for PPP
Signal selection GPS: L1/L2; GLONASS: L1/L2; BeiDou: B1/B2; Galileo: E1/E5a
Tracking data IGS+MGEX+BETN (about 120 stations) for POD and PCE; Local CORS and some MGEX stations are selected for PPP
Sampling rate 30s Elevation cutoff 7°
Observation weight Elevation dependent weight
Phase-windup effect Corrected
Earth rotation parameter Estimated with tight constraint (He et al., 2013b)
Tropospheric delay Initial model + random-walk process
Ionospheric delay Eliminated by IF combination in POD and PCE; estimated as parameters in PPP
Receiver clock Estimated, white noise
ISB and IFB Estimated as constant with zero mean conditions in post; introduced as known values in RT
Station displacement Solid Earth tide, pole tide, ocean tide loading, IERS Convention 2003 (McCarthy and Petit, 2003)
Satellite antenna phase center Corrected using MGEX and IGS values
Receiver antenna phase center Corrected using GPS values
Terrestrial frame ITRF2008 (Altamimi et al., 2011)
Satellite orbit Estimated in POD; Fixed in PCE&PPP using the products from POD
Satellite clock Estimated in POD and PCE, white noise; Fixed in PPP using the products from PCE
Station coordinate Fixed (or tightly constrained) in POD and PCE; Estimated in epoch-wise kinematic for PPP
Phase ambiguities Constant for each arc; DD AR for network solution, undifferenced AR if UPD
Li et al (2015), Accuracy and reliability of multi-GNSS real-time precise positioning: GPS, GLONASS, BeiDou, and Galileo. J. Geod., 2015, 89(6): 607-635.
2 Multi-GNSS data processing
9
Table 2. Dynamical models involved for multi-GNSS POD.
Item Models Orbit arc 3-day solution Geopotential EGM96 model (12×12)
Tide Solid Earth tide, pole tide, ocean tide IERS Conventions 2003
M-body gravity Sun, Moon and all planets (JPL DE405)
Solar Radiation Pressure Bern five parameters with no initial value
Relativistic Effect Applied Velocity breaks Every other 12 hours
Attitude model
Nominal attitude for GPS/GLONASS/Galileo; Nominal attitude with yaw maneuver for MEO and IGSO satellites of BeiDou; Yaw-fixed attitude mode used for GEO satellites of BeiDou
3 Multi-GNSS orbit and clock
10
Figure 6. Averaged RMS values of 48 h orbit and clock overlap differences in radial, cross, and along directions .
3 Real-time orbit and clock
Figure 7. Averaged RMS values of orbit and clock differences between the real-time and post-processed solutions
3 Real-time orbit and clock
Table 3. The averaged RMS values of predicted orbit differences in along- (A), cross-track (C) and radial (R) components.
Satellite R(cm) C(cm) A(cm) 3D(cm)
BeiDou IGSO 8.3 7.5 13.0 17.1
BeiDou MEO 6.3 6.2 12.0 14.9
BeiDou GEO 10.1 6.8 92.7 93.4
Galileo 2.9 6.8 9.8 12.2
GLONASS 2.2 3.1 5.9 7.0
GPS 1.8 3.0 3.2 4.7
4 Multi-GNSS real-time PPP
Figure 8.Comparisons of GPS, BeiDou and GPS/BeiDou kinematic PPP solutions at station CENT.
-0.5-0.3-0.10.10.30.5
(a) G
PS[m
]
Up East North
-0.5-0.3-0.10.10.30.5
(b) B
eiDo
u[m
]
-0.5-0.3-0.10.10.30.5
(c) G
/C[m
]
Hours
0 2 4 6 8 10 12 14 16 18 20 22 2405
1015202530
(d) N
um o
f Sat
Hours
G C G/C
4 Multi-GNSS real-time PPP
Figure 9.Kinematic PPP solutions of single-system, dual-system and four-system modes at station GMSD.
-0.5-0.3-0.10.10.30.5
(a) G
PS
[m]
Up East North
-0.5-0.3-0.10.10.30.5
(e) G
/R/E
/C[m
]
Up East North
-0.5-0.3-0.10.10.30.5
(b) G
LON
AS
S[m
]
-0.5-0.3-0.10.10.30.5
(f) G
/R[m
]
-0.5-0.3-0.10.10.30.5
(c) B
eiD
ou[m
]
-0.5-0.3-0.10.10.30.5
(g) G
/C[m
]
0 2 4 6 8 10 12 14 16 18 20 22 24-0.5-0.3-0.10.10.30.5
(d) G
alile
o[m
]
Hours0 2 4 6 8 10 12 14 16 18 20 22 24
-0.5-0.3-0.10.10.30.5
(h) G
/E[m
]
Hours
4 Multi-GNSS real-time PPP
Figure 10.Kinematic PPP solutions of single-system, dual-system and four-system modes at station CUT0.
4 Multi-GNSS real-time PPP
Figure 11. Comparisons of PPP results from different
single-system and combined solutions in the east, north
and up components, respectively at station CUT0.
-0.5-0.3-0.10.10.30.5
(a) E
[m]
C E R G G/C G/E G/R G/R/E/C
-0.5-0.3-0.10.10.30.5
(b) N
[m]
-0.5-0.3-0.10.10.30.5
(c) U
[m]
05
10152025303540
(d) N
um o
f Sat
G G/R/E/C
0 2 4 6 8 10 12 14 16 18 20 22 240
12345
(e) P
DO
P
Hours
G G/R/E/C
4 Multi-GNSS real-time PPP
Figure 12. Sky plots (azimuth vs elevation) of the four GNSS (BeiDou in pink, Galileo in red, GPS in blue and GLONASS in
green) for CUT0.
4 Multi-GNSS real-time PPP
Figure 13.The averaged RMS values of all the stations for kinematic PPP solutions in north, east and up components.
4 Multi-GNSS real-time PPP
Figure 14.Comparisons of PPP results in single- and multi-system modes under different elevation cutoffs (from 10° to 40°) at
station CUT0.
-0.4-0.2
00.20.4
East
[m]
G G/R/E/C
-0.4-0.2
00.20.4
North
[m]
-0.4-0.2
00.20.4
Up[m
]
0 4 8 12 16 20 2405
1015202530
Num
of S
at
0 4 8 12 16 20 24 0 4 8 12 16 20 24 0 4 8 12 16 20 24
0 4 8 12 16 20 240369
1215
PDO
P
CutOff 10°0 4 8 12 16 20 24
CutOff 20°0 4 8 12 16 20 24
CutOff 30°0 4 8 12 16 20 24
CutOff 40°
4 Multi-GNSS real-time PPP
Table 4. The empirical availability rates (in %) for the single- and
multi-GNSS under different elevation cutoffs (from 10° to 40°) .
Station GPS(%) G/R/E/C(%)
10° 20° 30° 40° 10° 20° 30° 40°
CENT 100.0 99.6 89.2 41.5 100.0 100.0 100.0 100.0
CHDU 99.7 98.3 84.7 46.0 100.0 100.0 100.0 100.0
SIGP 94.8 93.7 72.1 39.2 100.0 100.0 99.9 99.5
CUT0 96.8 95.0 89.3 57.6 100.0 100.0 100.0 100.0
GMSD 98.1 97.6 79.5 30.2 100.0 100.0 100.0 99.8
NNOR 99.2 93.8 78.6 37.8 100.0 100.0 100.0 100.0
ONS1 96.1 93.3 62.5 30.6 100.0 100.0 99.9 99.6
preciseavailability
total
Nf
N =
Discussions
u The performance of the multi-GNSS processing will be further improved in the next years along with the launch of more satellites and the setup of more multi-GNSS stations.
u The Multi-GNSS will bring many benefits for Geosciences applications: Li et al. (2015), Retrieving of atmospheric parameters from multi-GNSS in real-time: Validation with
water vapor radiometer and numerical weather model. JGR.
Li et al. (2015), Retrieving high-resolution tropospheric gradients from multi-constellation GNSS observations. GRL, DOI:10.1002/2015GL063856
Lu et al. (2015), Real-time retrieval of precipitable water vapor from GPS and BeiDou observations. Journal of Geodesy, DOI:10.1007/s00190-015-0818-0
Li et al. (2015), Multi-GNSS meteorology: Real-time retrieving of atmospheric water vapor from BeiDou, Galileo, GLONASS and GPS observations. IEEE Transactions on Geoscience and Remote Sensing, DOI:10.1109/TGRS.2015.2438395
……
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