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Precise positioningin multi-GNSS modeCécile Deprez
POSITIONING
ALTERATIONSWhat are the factors impacting satellite positioning?
Limited view angle
POSITIONING
ALTERATIONSWhat are the factors impacting satellite positioning?
POSITIONING
ALTERATIONS
Low number of visible satellites
What are the factors impacting satellite positioning?
Poor geometry: visible satellites gathered in a limited space
What are the factors impacting satellite positioning?POSITIONING
ALTERATIONS
Poor geometry: visible satellites gathered in a limited space
High PDOP
Good geometry: visible satellites spread around the receiver
Low PDOP
The impact of the geometry on positioning is characterized by the PDOP: Position
Dilution
Of
Precision
PDOP = Position Dilution Of Precision
= Impact of satellite geometry
The geometry of the satellites affects the positioning precision :
High PDOP values degrade the positioning precision
2
𝜎𝑃𝑂𝑆 = PDOP . 𝜎𝑂𝐵𝑆
POSITIONING
ALTERATIONS
Forest, city -
Signal obstructions = multipath
What are the factors impacting satellite positioning?POSITIONING
ALTERATIONS
Receiver quality
What are the factors impacting satellite positioning?POSITIONING
ALTERATIONS
Cécile Deprez & René Warnant - Université de Liège
How could multi-GNSSimprove
this situation?
ESA images (https://www.esa.int)
±
ESA images (https://www.esa.int)
±
ESA images (https://www.esa.int)
±
•
•
ESA images (https://www.esa.int)
ESA images (https://www.esa.int)
POSITIONING
ALTERATIONS
Low number of visible satellites
What are the factors impacting satellite positioning?
Low number of visible satellites
MULTI-GNSS IMPROVEMENTS
Poor geometry: visible satellites gathered in a limited space
What are the factors impacting satellite positioning?POSITIONING
ALTERATIONS
Cécile Deprez & René Warnant - Université de Liège
MULTI-GNSS IMPROVEMENTS
0
1
2
3
4
5
6
GPS Galileo BDS
PD
OP
0
1
2
3
4
5
6
E1/L1 E5a/L5 E5b/B2
Poor geometry: visible satellites gathered in a limited space
PDOP evolution
GPS + Galileo GPS + Galileo BeiDou + Galileo
Forest, city -
Signal obstructions = multipath
What are the factors impacting satellite positioning?POSITIONING
ALTERATIONS
Forest, city -
Signal obstructions = multipath
MULTI-GNSS IMPROVEMENTS
Signal precisions
Receiver quality
What are the factors impacting satellite positioning?POSITIONING
ALTERATIONS
u-blox image
RECEIVER’SFEATURES
Low-Cost receiversGeodetic receivers
$$$ (Thousands USDs ) $$ (Hundreds USDs)
Multi-GNSS Multi-Frequency
Multi-GNSS Single-Frequency
Septentrio image
Trimble image
E5a E6
L2B2 B3
Lower L-Band
L5
E1
L1
B1
Upper L-Band
Frequency (Mhz)
GPS BeiDouGalileo
E5b
GNSS constellations
are compatible
COMPATIBILITIES
Positioning with Galileo
Galileo E1:
Galileo E1Position 2D: 0.71 mPosition 3D: 1.10 m
Galileo E1:
GPS L1Position 2D: 0.81 mPosition 3D: 1.32 m
Galileo E1Position 2D: 0.72 mPosition 3D: 1.13 m
Positioning with GPS
GPS L1:
Positioning with Galileo + GPS
Galileo E1+
GPS L1 :
Galileo E1 +
GPS L1
Position 2D: 0.43 mPosition 3D: 0.85 m
Overlapping frequencies= single-frequency
Positioning with Galileo + GPS
Galileo E5a+
GPS L5 :
Galileo E5a +
GPS L5
Position 2D: 0.45 mPosition 3D: 0.73 m
Overlapping frequencies= single-frequency
Cécile Deprez & René Warnant - Université de Liège
Drawbacks of multi-GNSS positioning
Differences
lead to additional biases!
Time systems
Coordinate systems
Hardware delays
between GNSS
Cécile Deprez & René Warnant - Université de Liège
DRAWBACKS
= Inter-System Biases= ISBs
Mixed-receiver pairs
2
1
Met
ers
32
ISBs are receiver-dependent
Identical-receiver pairs
Mean: 1.52 m
Mean:0.00 m
+
+
0.2
0
0.2
Met
ers
04:00 08:00 12:00 16:00 20:00 24:00Hours
(a)
(b)
Trimble NetR9 Septentrio X4
Septentrio X4Septentrio X4
ISBS
2
1
Met
res
4
2
1
4
2
1
4
04:00 08:00 12:00 16:00 20:00
Hours04:00 08:00 12:00 16:00 20:00
Hours
04:00 08:00 12:00 16:00
Hours
33
2014 2015 2016
ISBs are stable over time
Mean: 2.84 m
Mean: 2.82 m
Mean: 2.86 m
(a) (b) (c)
ISBS
34
Firmware updatesfor phases
ISBs might be affected by
After
Before
04:00 08:00 12:00 16:00 20:00
Hours
Receiver multipath filter for codes
After
Before
04:00 08:00 12:00 16:00 20:00
Hours
-2
-3
-4
-1
0
1C
enti
met
ers
3
4
5
6
7
Met
ers
ISBS
POSITIONING
WITH/OUT ISBS
IMPACT OF
ISBS
0.6380.85
2.47
0.2740.47
1.15
0
1
2
Obs. Pos 2D Pos 3D
ISBs ignored ISBs removed
Met
res
ISBs removal on a DD SB 5.6 m on DOY 32 of 2018 (E1) between u-blox and Trimble R9 :- Geodetic antennas- 30s. data- Min elevation: 10°- Multipath filters OFF- Max PDOP: 6
Multi-GNSS improves positioning solutions Higher number of visible satellites Lower PDOP values Signals of new GNSSs (BeiDou, Galileo)
designed to be more robust to multipath Position precision improved regardless of
the receiver brand
Cécile Deprez & René Warnant - Université de Liège
CONCLUSIONS
Multi-GNSS solution affected by additional biases ISBs are receiver-dependent Most of these biases reveal constant in time => they can be
estimated and removed from positioning equation Intrinsic changes on receiver modify ISBs
Cécile DeprezDoctorante en GNSS et géodésieUnité de Géomatique - Université de Liège
Phone : +32 4 366 58 80Email: cecile.deprez@uliege.beLinkedIn
CONTACT
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