Precise positioning in multi-GNSS mode

(1)

Precise positioning

in multi-GNSS mode

(2)

(3)

POSITIONING

(4)

Limited view angle

POSITIONING

(5)

POSITIONING ALTERATIONS

Low number of visible satellites

(6)

Poor geometry: visible satellites gathered in a limited space

What are the factors impacting satellite positioning?

POSITIONING

(7)

High PDOP

Good geometry: visible satellites spread around the receiver

Low PDOP

The impact of the

geometry on positioning is characterized by the PDOP: _P_osition Dilution Of Precision

(8)

PDOP

=

P

osition

D

ilution

O

f

P

recision = Impact of satellite geometry

The

geometry

of the satellites affects the positioning precision :

High PDOP values degrade the positioning precision

2

𝜎_𝑃𝑂𝑆 = PDOP . 𝜎_𝑂𝐵𝑆

POSITIONING

(9)

Forest, city

-Signal obstructions = multipath

POSITIONING

(10)

Receiver quality

POSITIONING

(11)

Cécile Deprez & René Warnant - Université de Liège

How could

multi-GNSS

improve

(12)

(13)

±

(14)

±

(15)

±

• •

(16)

(17)

POSITIONING ALTERATIONS

Low number of visible satellites

(18)

Low number of visible satellites MULTI-GNSS

(19)

POSITIONING

(20)

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

(21)

Forest, city

-Signal obstructions = multipath

POSITIONING

(22)

Forest, city

-Signal obstructions = multipath MULTI-GNSS

IMPROVEMENTS

(23)

Receiver quality

POSITIONING

(24)

u-blox image

RECEIVER’S

FEATURES

Low-Cost receivers

Geodetic receivers

$$$ (Thousands USDs ) $$ (Hundreds USDs)

 Multi-GNSS  Multi-Frequency  Multi-GNSS  Single-Frequency Septentrio image Trimble image

(25)

E5a _E6 L2 B2 B3 Lower L-Band L5 E1 L1 B1 Upper L-Band Frequency (Mhz) GPS Galileo BeiDou E5b

G

NSS constellations are

compatible

COMPATIBILITIES

(26)

Positioning with

Galileo

Galileo E1:

Galileo E1

Position 2D: 0.71 m Position 3D: 1.10 m

(27)

Galileo E1:

GPS L1

Galileo E1

Positioning with

GPS

GPS L1:

(28)

Positioning with Galileo +

GPS

Galileo E1

+

GPS L1 :

Galileo E1

+

GPS L1

Position 2D: 0.43 m Position 3D: 0.85 m Overlapping frequencies = single-frequency

(29)

Positioning with Galileo +

GPS

Galileo E5a

+

GPS L5 :

Galileo E5a

+

GPS L5

Position 2D: 0.45 m Position 3D: 0.73 m Overlapping frequencies = single-frequency

(30)

Drawbacks

of multi-GNSS

(31)

Differences

lead to

additional biases!

Time systems

Coordinate systems

Hardware delays

between GNSS

DRAWBACKS

= Inter-System Biases

= ISBs

(32)

Mixed-receiver pairs 2 1 Me ter s 32

ISBs

are

receiver-dependent

Identical-receiver pairs Mean: 1.52 m Mean: 0.00 m

+

0.2 0 0.2 Me ter s 04:00 08:00 12:00 16:00 20:00 24:00 Hours (a) (b)

Trimble NetR9 Septentrio X4

Septentrio X4 Septentrio X4

(33)

2 1 Me tr es 4 2 1 4 2 1 4 04:00 08:00 12:00 16:00 20:00 Hours 04:00 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)

34

Firmware updates for 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 1 Cen tim et er s 3 4 5 6 7 Me ter s ISBS

(35)

P

OSITIONING

WITH

/

OUT

ISB

S

IMPACT OF ISBS 0.638 0.85 2.47 0.274 0.47 1.15 0 1 2

Obs. Pos 2D Pos 3D

ISBs ignored ISBs removed

Me

tr

es

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

(36)

 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

C

ONCLUSIONS

 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

(37)

Cécile Deprez

Doctorante en GNSS et géodésie

Unité de Géomatique - Université de Liège Phone : +32 4 366 58 80

Email: cecile.deprez@uliege.be LinkedIn