precise positioning in multi-gnss mode

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)

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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