The Stability Analysis of

GNSS Satellite DCB

Shuli Song , Junchen Xue , Zhengbiao Zou

ShangHai Astronomical Observatory 2016-02-12 Sydeny

l Introduction

l GPS DCB analysis

l GLONASS DCB analysis

l BDS DCB analysis

l GALILEO DCB analysis

Outline

1. Introduction

The instrumental differential code bias(DCB) is one of the important parameters for GNSS navigation, positioning and time service, and also the main source error of TEC estimation. How stable these DCBs are? How often we need to re-estimate their values? How about the Galileo/BDS DCBs? Can we use monthly mean values for BDS/Galileo post-processing as GPS/GLONASS?...... Here,the DCB series of GNSS main frequency from CODE and SHAO iGMAS Analysis Center are analyzed.

Original daily GPS satellite DCB from 1998 to 2013 from CODE

2.GPS P1P2 DCB Analysis

1998 2000 2002 2004 2006 2008 2010 2012 2014-6

-4

-2

0

2

4CODE DCB

year

DC

B/n

s

PRN6 PRN15 PRN30

2010 2011 2012 2013 2014-1

0

1

2

3

4 BLOCK IIR-M: PRN DCB

year

DC

B/n

s

PRN5PRN7PRN12PRN15PRN17PRN29PRN31

The DCB series are not so smooth with many jumps. What’s that?

Why the variations are large before 2002?

1998 2000 2002 2004 2006 2008 2010 2012 201424

26

28

30

32

number of GPS satellites

year0 4 8 12 16 20 24 28 32

-0.3

-0.2

-0.1

0

0.1DCB difference between doy 155 and 156 of 2010

PRNdi

ffer

ence

/ns

before remove bias after remove bias

The GPS satellite numbers in ION/DCB calculation change at all times.

There’re artificial biases in DCB series due to the variation of satellite

number.So,the biases have to be removed before the stability analysis.

2002 2004 2006 2008 2010 2012 2014-6

-4

-2

0

2

4 BLOCK IIA: PRN DCB

year

DCB/

ns

PRN3PRN4PRN6PRN8PRN9PRN10PRN13PRN26

2002 2004 2006 2008 2010 2012 2014-3

-2

-1

0

1

2

3

4 BLOCK IIA: PRN DCB(after remove bias)

year

DCB/

ns

PRN3PRN4PRN6PRN8PRN9PRN10PRN13PRN26

Long-term Stability of GPS P1P2 DCB

Linear trends of all GPS satellites during 2002-2013. Most GPS DCB long-

term trend are less than 100ps.Block IIF and Block IIA DCBs are more

stable .

2 14 15 16 17 18 19 210

0.05

0.1

0.15Block II satellites

3 4 6 8 9 10 13 260

0.05

0.1

0.15Block IIA satellites during 1998-2002

3 4 6 8 9 10 13 260

0.05

0.1

0.15Block IIA satellites during 2003-2013

11 14 16 18 20 21 280

0.05

0.1

0.15Block IIR-A satellites

5 7 12 15 17 29 310

0.05

0.1

0.15Block IIR-M satellites

PRN1 2 19 22 23 25

0

0.05

0.1

0.15Block IIF and IIR-B satellites

month

ly sta

bility

/ns

PRN

Mean monthly stability of GPS satellite DCBs

Block II and Block IIA(before 2002) with mean monthly stability about

100ps,Block IIA(after 2002) and other Blocks with less than 50ps.

00.10.2

PRN3

00.10.2

PRN4

00.10.2

PRN6

00.10.2

PRN8

00.10.2

PRN9

00.10.2

PRN10

2004 2006 2008 2010 2012 20140

0.10.2

PRN13

year

mon

thly

sta

bilit

y/ns

2004 2006 2008 2010 2012 20140

0.10.2

PRN26

year

Monthly variations of Block IIA satellite DCBs

Most are less than 100 ps.

0.02

0.03

0.04

0.05

0.06 Monthly stability of satellites DCB and solar activity

year

mon

thly

stab

ility/

ns

2004 2006 2008 2010 20120

20

40

60

80

SUNS

POT

PRN3PRN4PRN6PRN8PRN9PRN10PRN13PRN26sunspot

Variation of annual average of monthly stability of Block IIA

satellite DCBs with yearly sunspot, though the amplitude is not

two large.

Short-term stability of GPS P1P2 DCB

Daily variation

1 week

2 weeks …..

8 weeks variation

Dif between 4weeks and week : no difference for Block II, but large than

other Blocks.Others: changed in 8~21ps with the statistic interval expand

3.GLONASS DCB Analysis

2004 2006 2008 2010 2012 20145

10

15

20

25GLONASS 卫星数变化情况

year

satellite numbers variation

2004 2004.5 2005 2005.5 2006 2006.5 2007 2007.5

-10

-5

0

5

GLONASS 卫星 DCB

year

DC

B/n

s

R02R03R04R18R21R22

2004 2004.5 2005 2005.5 2006 2006.5 2007 2007.5

-10

-5

0

5

GLONASS 卫星 DCB

year

DC

B/n

s

R02R03R04R18R21R22

2009 2010 2011 2012 2013 2014

-10

-5

0

5

GLONASS-M 卫星 DCB

year

DCB/

ns

R11R13R15R18R19R20

2009 2010 2011 2012 2013 2014

-10

-5

0

5

GLONASS-M 卫星 DCB

year

DCB/

ns

R11R13R15R18R19R20

Before bias remove After bias remove

Long-term Stability of GLONASS P1P2 DCB

Some Glonass satellites have a little large long-term trend. Most Glonass-

M are better than Glonass satellites.

0

0.5

1R02

0

0.5

1R03

0

0.5

1R04

0

0.5

1 R18

2004 2005 2006 20070

0.5

1R21

year2004 2005 2006 20070

0.5

1R22

year

unit:

ns

GLONASS 卫星 DCB 月稳定性

0

0.5

1R11

0

0.5

1R13

0

0.5

1R15

0

0.5

1R18

2010 2012 20140

0.5

1R19

year2010 2012 2014

0

0.5

1R20

year

unit:

ns

GLONASS-M 卫星 DCB 月稳定性

Monthly variations of GLONASS satellite DCBs

DCB DCB

Most are less than 200 ps.

Dif between 4weeks and week: GLONASS 90-160ps,GLONASS-M 40~60ps

Short-term stability of GLONASS P1P2 DCB

Daily variation

1 week

2 week …..

8 week variation

GAL E1-E5a DCBs for GPS/Galileo/BDS combined estimation mode determined as compared to DLR

4. Galileo DCB Analysis

The number of receivers involved in the estimation of GAL DCBs

DCB E11 E12 E19

E1-E5 0.14 0.11 0.14

E1-E5a 0.17 0.13 0.16

E1-E5b 0.16 0.12 0.15

Standard deviations for GALILEO satellite differential code biases for the entire time series (units: ns)

Long-term Stability of Galileo DCB

PRN DCB 7d 14d 21d 28d 35d 42d

E11

E1-E5 0.13 0.13 0.13 0.13 0.15 0.13

E1-E5a 0.16 0.16 0.16 0.16 0.18 0.16

E1-E5b 0.15 0.15 0.15 0.15 0.17 0.15

E12

E1-E5 0.11 0.11 0.11 0.11 0.12 0.11

E1-E5a 0.12 0.12 0.12 0.12 0.13 0.12

E1-E5b 0.11 0.11 0.11 0.11 0.12 0.11

E19

E1-E5 0.13 0.13 0.13 0.14 0.15 0.13

E1-E5a 0.14 0.15 0.15 0.15 0.16 0.15

E1-E5b 0.14 0.14 0.14 0.14 0.16 0.14

Time ranged stability statistics (E1-E5, E1-E5a, and E1-E5b) differential code biases (unit: ns)

Short-term stability of Galileo DCB

Comparison of the STDs for the 4weeks and week interval shows that the

maximal difference does not exceed 10ps for all satellite DCBs. This indicates it

is practical to provide post users with monthly-averaged GAL satellite DCBs.

Beidou satellite (DCBs) calculated together with ION GIM from GPS/BDS

observations in SHAO iGMAS Analysis Center with about 40 BDS tracking stations.

5. BDS DCB Analysis

(a) B1B2 DCBs (2014) (b) B1B3 DCBs ( 2014)

TYP GEO IGSO MEO

PRN C01 C02 C03 C04 C05 C06 C07 C08 C09 C10 C11 C12 C13 C14

B1-B2 0.22 0.23 0.24 0.31 0.25 0.13 0.15 0.12 0.11 0.12 0.17 0.22 0.20 0.16

B1-B3 0.23 0.21 0.33 0.36 0.24 0.15 0.18 0.15 0.14 0.17 0.22 0.28 - 0.20

IGSO with the best stability, most less than 150ps ,GEO is the worst.B1B3 is

a little big than B1B2.

Long-term Stability of BDS B1B2 DCB

Standard deviations for Beidou DCbs (units: ns)

Short-term stability of BDS B1B2 DCB

　   PRN 7d 14d 21d 28d 35d 42d

GEO

C01 0.20 0.21 0.22 0.22 0.24 0.23 C02 0.21 0.22 0.23 0.24 0.24 0.24 C03 0.20 0.21 0.22 0.22 0.22 0.23 C04 0.27 0.30 0.31 0.32 0.35 0.33 C05 0.23 0.24 0.25 0.27 0.26 0.26

IGSO

C06 0.13 0.14 0.14 0.15 0.16 0.15 C07 0.15 0.16 0.16 0.18 0.20 0.19 C08 0.13 0.13 0.14 0.14 0.14 0.15 C09 0.10 0.11 0.11 0.11 0.12 0.11 C10 0.11 0.12 0.12 0.13 0.13 0.13

MEO

C11 0.17 0.17 0.17 0.17 0.18 0.18 C12 0.24 0.25 0.25 0.26 0.27 0.27 C13 0.18 0.18 0.18 0.19 0.19 0.19 C14 0.16 0.17 0.16 0.17 0.17 0.17

A comparison for the 4weeks and week interval showed that the STD

differences did not exceed 60ps for all B1–B2 satellite DCBs .

Short-term stability of BDS B1B3 DCB

　   PRN 7d 14d 21d 28d 35d 42d

GEO

C01 0.16 0.17 0.17 0.17 0.19 0.18 C02 0.20 0.22 0.22 0.22 0.23 0.23 C03 0.21 0.23 0.24 0.23 0.26 0.26 C04 0.23 0.25 0.25 0.25 0.25 0.27 C05 0.22 0.23 0.23 0.25 0.25 0.24

IGSO

C06 0.13 0.13 0.14 0.15 0.15 0.14 C07 0.17 0.19 0.19 0.21 0.20 0.20 C08 0.12 0.13 0.13 0.13 0.15 0.14 C09 0.10 0.11 0.11 0.11 0.12 0.12 C10 0.13 0.14 0.15 0.14 0.15 0.16

MEO

C11 0.20 0.20 0.20 0.20 0.21 0.20 C12 0.27 0.26 0.26 0.26 0.26 0.26 C14 0.20 0.20 0.20 0.20 0.21 0.21

Comparison for the 4weeks and week interval showed that the STD differences did not exceed 40ps for all B1–B3 DCBs. This clearly illustrates the viability of using monthly-averaged BDS satellite DCB in BDS post-processing.

BDS GEO DCB stability with the tracking stations expandation

BDS tracking stations

BDS IGSO/MEO DCB stability with the tracking stations expandation

BDS tracking stations

Summary

•  With present calculate method, there’re biases in GNSS DCB series due to the satellite number changes.

•  Before the stability analysis of DCB series estimated together with ionosphere, the biases have to be removed firstly.

•  The stability of GNSS satellite DCB is correlated with the ground tracking network. BDS and Galileo DCB will be better if there’re more stations.

•  For BDS/Galileo,the monthly mean value can be used in post-processing.