Analyses of raw GNSS observations collectedby the Android device Xiaomi Mi8

Vaclavovic P.1, Kala M.1,2, Dousa J.1

1Geodetic Observatory Pecny, RIGTC2Czech Technical University in Prague

Czech Republic

GNSS Raw Measurements Taskforce Workshop26th June, 2019, Prague, Czech Republic

Vaclavovic P., Kala M., Dousa J. GNSS Raw Measurements Taskforce Workshop 26th June 2019 1 / 15

Outline

1 Motivation

2 Equipment description

3 GNSS observations collection

4 GNSS observations analyses

5 Precise Point Positioning

6 Conclusion

Vaclavovic P., Kala M., Dousa J. GNSS Raw Measurements Taskforce Workshop 26th June 2019 2 / 15

Motivation

1 Getting first experience with raw GNSS observations from asmartphone

I Quality, availability, accuracy and stability of estimated coordinatesand tropospheric parameters

2 Initiate an integration of our desktop GNSS software into Android

Vaclavovic P., Kala M., Dousa J. GNSS Raw Measurements Taskforce Workshop 26th June 2019 3 / 15

Equipment description

1 Xiaomi Mi-8

2 The smartphone is equippedby the dual frequency chipBroadcom BCM47755

3 Supported frequenciesI GPS (L1/L5)I Galileo (E1/E5a)I GLONASS (G1)I BeiDou (B1)

Vaclavovic P., Kala M., Dousa J. GNSS Raw Measurements Taskforce Workshop 26th June 2019 4 / 15

GNSS observations collection

1 First, we have used the Geo++ RINEX Logger (Geo++ GmbH)I Storing observations in RINEX format

2 Second, we have implemented our new Android apk for storingraw GNSS observations

I Internal ASCII formatF Receiver positions provided by the chipset itselfF GNSS observations (GNSS Clock, GNSS Measurements classes)

I Temporal working name of the apk is G-Nut Client

Vaclavovic P., Kala M., Dousa J. GNSS Raw Measurements Taskforce Workshop 26th June 2019 5 / 15

GNSS observations collection

1 First, we have used the Geo++ RINEX Logger (Geo++ GmbH)I Storing observations in RINEX format

2 Second, we have implemented our new Android apk for storingraw GNSS observations

I Internal ASCII formatF Receiver positions provided by the chipset itselfF GNSS observations (GNSS Clock, GNSS Measurements classes)

I Temporal working name of the apk is G-Nut Client

Vaclavovic P., Kala M., Dousa J. GNSS Raw Measurements Taskforce Workshop 26th June 2019 5 / 15

GNSS observations collectionG-Nut Client

Vaclavovic P., Kala M., Dousa J. GNSS Raw Measurements Taskforce Workshop 26th June 2019 6 / 15

GNSS observations analyses

1 GNSS data have been analyzed using the G-Nut/Anubis software

2 Characteristics

I Number of tracked satellites

I Signal strength

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GNSS observations analysesSkyplot and signal strength

GPS L1 GPS L5 GAL E1 GAL E5 GLO BDS

GOPE 44.4 47.0 44.1 46.2 45.4 42.4G-Nut Client 34.6 30.7 30.0 30.2 32.6 33.5 [dB-Hz]Geo++ 34.0 30.2 33.5 31.8 32.6 33.9

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GNSS observations analysesNumber of tracked satellites

0 4 8 12 16 20 240

2

4

6

8

10

12

14

16

Time [h]

#Satellites

GPS - chipset

0 4 8 12 16 20 240

2

4

6

8

10

12

14

16

Time [h]

#Satellites

GPS - G-Nut Client

0 4 8 12 16 20 240

2

4

6

8

10

12

14

16

Time [h]

#Satellites

GPS - Geo++

0 4 8 12 16 20 240

2

4

6

8

10

12

14

16

Time [h]

#Satellites

GPS - GOPE

0 4 8 12 16 20 240

2

4

6

8

10

12

14

16

Time [h]

#Satellites

GAL - chipset

0 4 8 12 16 20 240

2

4

6

8

10

12

14

16

Time [h]

#Satellites

GAL - G-Nut Client

0 4 8 12 16 20 240

2

4

6

8

10

12

14

16

Time [h]

#Satellites

GAL - Geo++

0 4 8 12 16 20 240

2

4

6

8

10

12

14

16

Time [h]

#Satellites

GAL - GOPE

0 4 8 12 16 20 240

2

4

6

8

10

12

14

16

Time [h]

#Satellites

GLO - chipset

0 4 8 12 16 20 240

2

4

6

8

10

12

14

16

Time [h]

#Satellites

GLO - G-Nut Client

0 4 8 12 16 20 240

2

4

6

8

10

12

14

16

Time [h]

#Satellites

GLO - Geo++

0 4 8 12 16 20 240

2

4

6

8

10

12

14

16

Time [h]

#Satellites

GLO - GOPE

0 4 8 12 16 20 240

2

4

6

8

10

12

14

16

Time [h]

#Satellites

BDS - chipset

0 4 8 12 16 20 240

2

4

6

8

10

12

14

16

Time [h]

#Satellites

BDS - G-Nut Client

0 4 8 12 16 20 240

2

4

6

8

10

12

14

16

Time [h]

#Satellites

BDS - Geo++

0 4 8 12 16 20 240

2

4

6

8

10

12

14

16

Time [h]

#Satellites

BDS - GOPE

Vaclavovic P., Kala M., Dousa J. GNSS Raw Measurements Taskforce Workshop 26th June 2019 9 / 15

Precise Point Positioning

1 We mounted the smartphone on the roof of our observatory

2 Co-located with the IGS permanent station GOPE (geodeticantenna)

3 Not enough dual-frequency observation => combination withsingle frequency observations

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Precise Point PositioningProcessing strategy

GNSS - GPS+GLO+GAL+BDSCode biases not used due to ambiguous obs. signal assignmentIonosphere model: IONEXTroposphere: ZWD estimated, ZHD corrected by theSaastamoinenOrbits/clocks: MGEX

I Precise clocks cannot be used for L5 directly => Inter frequencyclock bias

Observations: code + carrier phase (combination single and dualfreq.)Observation data length is 12 hours with 10s sampling

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Precise Point PositioningAchieved accuracy of ZTD

Co-located IGS station GOPE used for comparison of ZTDs

2.24

2.26

2.28

2.30

2.32

12 13 14 15 16 17 18 19 20 21 22 23 00

ZT

D [m

]

07-JUN-2019

Zenith Total Delay

Xiaomi Mi8GOPE

StdDev = 27 mm

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Precise Point PositioningAchieved coordinates precision

Static positioning

-2.00

-1.00

0.00

1.00

2.00

12 13 14 15 16 17 18 19 20 21 22 23 00

N, E

, U

[m

]

07-JUN-2019

NorthEast

Up

Repeatability:N = 0.17 mE = 0.32 mU = 0.37 m

Kinematic positioning

-2.00

-1.00

0.00

1.00

2.00

12 13 14 15 16 17 18 19 20 21 22 23 00

N, E

, U

[m

]

07-JUN-2019

NorthEast

Up

Repeatability:N = 1.2 mE = 2.0 mU = 1.7 m

Precision of coordinates given by the chipset itselfI North = 9.4 mI East = 7.1 mI Up = 21.2 m

Vaclavovic P., Kala M., Dousa J. GNSS Raw Measurements Taskforce Workshop 26th June 2019 13 / 15

Precise Point PositioningAchieved coordinates precision

Static positioning

-2.00

-1.00

0.00

1.00

2.00

12 13 14 15 16 17 18 19 20 21 22 23 00

N, E

, U

[m

]

07-JUN-2019

NorthEast

Up

Repeatability:N = 0.17 mE = 0.32 mU = 0.37 m

Kinematic positioning

-2.00

-1.00

0.00

1.00

2.00

12 13 14 15 16 17 18 19 20 21 22 23 00

N, E

, U

[m

]

07-JUN-2019

NorthEast

Up

Repeatability:N = 1.2 mE = 2.0 mU = 1.7 m

Precision of coordinates given by the chipset itselfI North = 9.4 mI East = 7.1 mI Up = 21.2 m

Vaclavovic P., Kala M., Dousa J. GNSS Raw Measurements Taskforce Workshop 26th June 2019 13 / 15

Conclusion

1 The G-Nut Client will hopefully be released via Google Play soon

2 There are issues in long term satellites trackingI The chipset seems to have a problem with long-term satellite

tracking

3 Providing GNSS raw observations significantly improvepositioning accuracy

4 Careful cycle slips detection and estimation will be necessary

5 Ambiguity resolution will be very challenging

Vaclavovic P., Kala M., Dousa J. GNSS Raw Measurements Taskforce Workshop 26th June 2019 14 / 15

Future plans

1 RINEX encoder implementation

2 Releasing the Android application

3 Integration of our G-Nut software

Vaclavovic P., Kala M., Dousa J. GNSS Raw Measurements Taskforce Workshop 26th June 2019 15 / 15