Comparison of GPS/GLONASS Clock Solutions · 362.6 ns −17.7 ns −12.8 ns 149.3 ns 11.2...

Comparison of GPS/GLONASS Clock Solutions

R. Dach1, S. Schaer2, and M. Meindl1

1Astronomical Institute, University of BernSidlerstrasse 5, CH-3012 Bern

2Federal Office of Topography swisstopo

IGS–Workshop on GNSS–Biases

Bern, Switzerland, 18.-19. January 2012

source: https://doi.org/10.7892/boris.17810 | downloaded: 25.1.2021

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Outline

Dach, Schaer and Meindl: Comparison of GPS/GLONASS Clock Solution – 2 / 34

Comparison of GPS/GLONASS Clock Solutions

1. Direct comparison of the satellite clocks

2. Comparison of the submitted ISB/IFB

3. Precise Point Positioning solutions

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Overview on the Contributions


Clock SolutionAnalysis Center Systems satell. stations

COD Center for OrbitDetermination in Europe,AIUB, Switzerland

GPS+GLONASS 30 sec 300 sec

EMR Natural Resources Canada,Canada

GPS+GLONASS 30 sec —

ESA European Space OperationsCenter, ESA, Germany


GFZ GeoForschungsZentrum,Germany


GRG GRGS-CNES/CLS,Toulouse, France


IAC Information-AnalyticalCentre, Russia


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Satellite Clock Series (Reference clock: G15)


Deviation from the median

−1

0

1

G02

in n

s

COD EMR ESA GFZ GRG IAC

−1

0

1

G12

in n

s


−1

0

1

G22

in n

s

0 4 8 12 16 20 24

DOY 2011−348 (hours)


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−300

0

300

R02

in n

s


−300

0

300

R12

in n

s


−300

0

300

R22

in n

s

0 4 8 12 16 20 24



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Biases in GPS/GLONASS (Clock) Processing


� DCB: differential code biasdifferent hardware delays forP– and C–Code

� ISB: inter–system biasdifferent hardware delays formeasurements of differentGNSS

� IFB: inter–frequency biasfrequency–dependent hard-ware delays for the differentGLONASS–signals

We can only extract the sumof delays from a GPS/GLONASSdata processing.

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Biases in GPS/GLONASS (Clock) Processing


The different biases are realized in different ways in the six contributingsolutions. We can extract the following biases from the (satellite) clock timeseries:

� ISB: inter–system biasone common offset between all GPS and GLONASS clocks from each ofthe solutions

� IFB: inter–frequency biasone offset for each GLONASS clock with respect to all GPS clocks of thesolution

Note, all offsets are realized as median to be robust against outliers.

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Deviation from the median, ISB subtracted

−30

0

30

R02

in n

s


−30

0

30

R12

in n

s


−30

0

30

R22

in n

s

0 4 8 12 16 20 24



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Deviation from the median, ISB+IFB subtracted

−1

0

1

R02

in n

s


−1

0

1

R12

in n

s


−1

0

1

R22

in n

s

0 4 8 12 16 20 24



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ISB/IFB as Extracted from Satellite Clocks


−100

−50

0

50

IFB

in n

s

Analysis center

362.6 ns −17.7 ns −12.8 ns 149.3 ns 11.2 ns−491171344.7 ns


Conclusion

� The ISB/IFB can be estimated from the satellite clock solutions ofdifferent ACs.

� Appling these corrections allows for a GLONASS satellite clockcombination following the same technology as for GPS.

� The estimated ISB/IFB can be rather inhomogeneous if a satellite is notincluded in all solutions (which has no influence on a PPP–solution).

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−100−50

050

100

R02

in n

s

COD ESA GFZ GRG

−100−50

050

100

R12

in n

s

COD ESA GFZ GRG

−100−50

050

100

R22

in n

s

0 4 8 12 16 20 24


COD ESA GFZ GRG

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Deviation from the median, ISB subtracted

−30

0

30

R02

in n

s

COD ESA GFZ GRG

−30

0

30

R12

in n

s

COD ESA GFZ GRG

−30

0

30

R22

in n

s

0 4 8 12 16 20 24


COD ESA GFZ GRG

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Deviation from the median, ISB+IFB subtracted

−1

0

1

R02

in n

s

COD ESA GFZ GRG

−1

0

1

R12

in n

s

COD ESA GFZ GRG

−1

0

1

R22

in n

s

0 4 8 12 16 20 24


COD ESA GFZ GRG

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−100

−50

0

50

IFB

in n

s

Analysis center

362.6 ns −17.7 ns −12.8 ns 149.3 ns 11.2 ns−491171344.7 ns


−100

−50

0

50

IFB

in n

s

Analysis center

−13.5 ns 2.9 ns −2.8 ns 29.4 ns

COD ESA GFZ GRG

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−100

−50

0

50

IFB

in n

s

Analysis center

362.6 ns −17.7 ns −12.8 ns 149.3 ns 11.2 ns−491171344.7 ns


Conclusion – 2� To apply the mean ISB/IFB per satellite from the satellite clock solutions helps to

reduce the differences between the solutions.

� Nevertheless, additional ISB/IFB need to be estimated from the satellite clocksolutions of different ACs to achieve the consistency level necessary for thecombination.

� The problem of ISB/IFB estimation from satellites not included in all solutions isreduced but not solved.

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IFB/ISB Computed by the Analysis Centers


Repeatability of the IFB/ISB (as they are)

−10

0

10

R02

in n

s 49.2 ns −321.1 ns −158.4 ns −327.2 ns

COD ESA GFZ GRG

−10

0

10

R12

in n

s 49.2 ns −331.0 ns −159.6 ns −321.3 ns

COD ESA GFZ GRG

−10

0

10

R22

in n

s

Analysis center

48.9 ns −323.6 ns −158.3 ns −343.2 ns

COD ESA GFZ GRG

Station: MATE – Matera, IT

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Repeatability of the IFB/ISB (as they are)

−10

0

10

R02

in n

s 35.7 ns −335.6 ns −173.1 ns −331.9 ns

COD ESA GFZ GRG

−10

0

10

R12

in n

s 41.6 ns −340.1 ns −168.0 ns −329.3 ns

COD ESA GFZ GRG

−10

0

10

R22

in n

s

Analysis center

36.8 ns −335.1 ns −171.0 ns −353.4 ns

COD ESA GFZ GRG

Station: CONZ – Concepcion, CL

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Repeatability of the IFB/ISB (unified reference)

−10

0

10

R02

in n

s 49.6 ns −320.9 ns −158.8 ns −320.1 ns

COD ESA GFZ GRG

−10

0

10

R12

in n

s 49.4 ns −334.5 ns −159.7 ns −321.7 ns

COD ESA GFZ GRG

−10

0

10

R22

in n

s

Analysis center

48.7 ns −321.6 ns −158.4 ns −341.3 ns

COD ESA GFZ GRG


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Repeatability of the IFB/ISB (unified reference)

−10

0

10

R02

in n

s 35.8 ns −335.1 ns −173.0 ns −332.6 ns

COD ESA GFZ GRG

−10

0

10

R12

in n

s 41.6 ns −342.7 ns −168.1 ns −327.9 ns

COD ESA GFZ GRG

−10

0

10

R22

in n

s

Analysis center

36.8 ns −333.5 ns −171.0 ns −352.0 ns

COD ESA GFZ GRG

Station: CONZ – Concepcion, CL

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Conclusion� The IFB/ISB series from daily independent solutions need to be unitfied regarding

their reference.

� The stability of the IFB with unified reference depend on the stability of thedifferences between the IFB between two satellites from the day to day in theoriginal series.

� In the best cases we achieve a peak-to-peak stability of 2 to 3 ns.

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ISB characteristic of the receivers

−100

0

100

200

300

400

500

ISB

in n

s

Stations

ASHTECH Z18 JAVAD TRE_G3T DELTA JAVAD TRE_G3TH DELTA JPS EGGDTJPS E_GGD JPS LEGACY LEICA GRX1200+GNSS LEICA GRX1200GGPRONOV OEMV3 TPS E_GGD TPS GB−1000 TPS LEGACYTPS NET−G3A TPS NETG3 TPS ODYSSEY_E TRIMBLE NETR5TRIMBLE NETR8 TRIMBLE NETR9

Analyse centrum: COD

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−400

−300

−200

−100

0

100

200

300

ISB

in n

s

Stations


Analyse centrum: GFZ

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−600

−500

−400

−300

−200

−100

0

100

ISB

in n

s

Stations


Analyse centrum: ESA

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−400

−300

−200

−100

0

100

200

300

ISB

in n

s

Stations


Analyse centrum: GRG

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Differences between ISB characteristic of the receivers

−230

−220

−210

−200

−190

−180

ISB

in n

s

Stations


Analyse centrum: COD−GFZ

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−390

−380

−370

−360

−350

ISB

in n

s

Stations


Analyse centrum: COD−ESA

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−180

−170

−160

−150

−140

ISB

in n

s

Stations


Analyse centrum: GFZ−ESA

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−440

−420

−400

−380

−360

−340

−320

−300

−280

−260

−240

ISB

in n

s

Stations


Analyse centrum: COD−GRG

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−220

−200

−180

−160

−140

−120

−100

−80

−60

−40

−20

ISB

in n

s

Stations


Analyse centrum: GFZ−GRG

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−60

−40

−20

0

20

40

60

80

100

120

140

ISB

in n

s

Stations


Analyse centrum: ESA−GRG

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Num. of Mean Median RMSDifference Stations in ns in ns in ns

COD − GFZ 52 −210.6 −209.4 4.9COD − ESA 39 −377.5 −377.6 5.1GFZ − ESA 36 −167.7 −168.2 6.1COD − GRG 50 −371.9 −372.2 18.7GFZ − GRG 46 −162.1 −163.0 19.2ESA − GRG 34 6.1 5.8 20.6

� High consistency (low RMS) with a proper IFB–handling(enough weight for the code measurements?)

� Test whether the ACs select the same type of code observations(CODE differs from ESA and GFZ)

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Number of Satellites in the Solutions


Number of satellites per system

0

8

16

24

32

Num

ber

of s

at. GPS


0

8

16

24

32

Num

ber

of s

at.

Analysis center

GLONASS


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RMS of Orbit–fit using Bernese Software


Mean over all satellites of each system

0

5

10

Mea

n in

mm GPS


0

5

10

Mea

n in

mm

Analysis center

GLONASS


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RMS of Orbit–fit using Bernese Software


Median from all satellites of each system

0

5

10

Med

ian

in m

m GPS


0

5

10

Med

ian

in m

m

Analysis center

GLONASS


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Comparison in the PPP–Performance


How the following Solutions Have Been Generated?1. Data import and screening

(a) if high–rate satellite clock corrections are available:Phase–data are screened based on PPP with a sophisticated algorithmbefore the first PPP–solution using post–fit residual screening.

(b) without high–rate satellite clock corrections:Only the consistency between code– and phase–data is checked before thefirst PPP–solution using post–fit residual screening.

2. static PPP using GPS/GLONASS dataassuming satellite–specific inter–system/inter–frequency code biases without

ambiguity resolution for the phase data

3. pseudo–kinematic PPP using GPS/GLONASS data(same as above)

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Statistics of the PPP Solution (after screening)


Number of code measurements (300 sec. sampling)

0

1000

2000

3000

Cod

e ob

serv

. GPS


0

1000

2000

3000

Cod

e ob

serv

.

Analysis center

GLONASS


Station: ONSA – Onsala, SE

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Number of phase measurements (300 sec. sampling)

0

1000

2000

3000

Pha

se o

bser

v. GPS


0

1000

2000

3000

Pha

se o

bser

v.

Analysis center

GLONASS



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Number of ambiguity parameters

0

100

200

Am

bigu

ities

GPS


0

100

200

Am

bigu

ities

Analysis center

GLONASS



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A posteriori unit of weight

0

1

2

RM

S in

mm

GPS/GLONASS with common receiver clock


0

1

2

RM

S in

mm

Analysis center

GPS/GLONASS with independent receiver clock



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Coordinate Comparison from PPP Solutions


Coordinate difference to IGS08.SNX

−15−10

−505

1015

Nor

th in

mm

GPS


−15−10

−505

1015

Nor

th in

mm

Analysis center

GLONASS



IGS08.SNX

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−15−10

−505

1015

Nor

th in

mm



−15−10

−505

1015

Nor

th in

mm

Analysis center




IGS08.SNX

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−15−10

−505

1015

Eas

t in

mm

GPS


−15−10

−505

1015

Eas

t in

mm

Analysis center

GLONASS



IGS08.SNX

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−15−10

−505

1015

Eas

t in

mm



−15−10

−505

1015

Eas

t in

mm

Analysis center




IGS08.SNX

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−30−20−10

0102030

Up

in m

m

GPS


−30−20−10

0102030

Up

in m

m

Analysis center

GLONASS



IGS08.SNX

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−30−20−10

0102030

Up

in m

m



−30−20−10

0102030

Up

in m

m

Analysis center




IGS08.SNX

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Pseudo–Kinematic PPP Solutions


RMS of the differences w.r.t. the static solutions

0

10

20

Nor

th in

mm

GPS


0

10

20

Nor

th in

mm

Analysis center

GLONASS



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0

10

20

Nor

th in

mm



0

10

20

Nor

th in

mm

Analysis center




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0

10

20

Eas

t in

mm

GPS


0

10

20

Eas

t in

mm

Analysis center

GLONASS



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0

10

20

Eas

t in

mm



0

10

20

Eas

t in

mm

Analysis center




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0

20

40

Up

in m

m

GPS


0

20

40

Up

in m

m

Analysis center

GLONASS



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0

20

40

Up

in m

m



0

20

40

Up

in m

m

Analysis center




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GLONASS: Interfrequency–Biases


IFB as they are estimated in the static PPP–solution

−10

−5

0

5

10

15

IFB

in n

s

GLONASS−only


−10

−5

0

5

10

15

IFB

in n

s

Analysis center




Comparison of GPS/GLONASS Clock Solutions · 362.6 ns −17.7 ns −12.8 ns 149.3 ns 11.2...

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