1. 2013 Western Australia Surveying Conference
BeiDou? First Australian results of BeiDou + GPS positioning
Dennis Odijk, Robert Odolinski, Nandakumaran Nadarajah, Boris Padovan, Peter Teunissen
GNSS Research Centre, Curtin University
First results of combined Beidou + GPS outside China
2013 Western Australia Surveying Conference

2. Presentation Outline BeiDou
Presentation Outline
BeiDou
What is it?
Constellation + Signals
Time and Coordinate Systems
First ever results of Beidou+GPS, computed by GNSS Research Centre:
Single Point Positioning (SPP)
Real-Time Kinematic Positioning (RTK)
Attitude determination (Pitch, Roll and Yaw)
Conclusions
BeiDou? First Australian results of a combined …

3. BeiDou – What is it? 北斗 Big Dipper or Plough, Northern Dipper
BeiDou – What is it? 北斗
Big Dipper or Plough, Northern Dipper
Chinese satellite navigation system
Demonstration system (BeiDou-1) completed in 2003
Second generation under construction (BeiDou-2; previously known as COMPASS)
SIS ICD released in December 2012
BeiDou signals will be free of charge
Full global constellation expected in 2020
Beidou attained initial regional operational status in December SIS ICD contains signal structure, navigation message description etc
BeiDou? First Australian results of a combined …

4. BeiDou – Constellation
BeiDou – Constellation
Operational constellation:
35 satellites (GPS currently 31 - MEO)
5 Geosynchronous Earth Obiter (GEO)
3 Inclined GeoSynchronous Orbiter (IGSO)
27 Medium Earth Orbiter (MEO)
Global coverage
Current (2013) Constellation:
14 satellites
5 GEO, 5 IGSO and 4 MEO satellites
Fully operational in the Asia Pacific region
Sky plots for Perth
GEO orbit: 36,000 km; IGSO: 2 orbits at 36,000 km with 55 deg inclination; MEOs at 21,500 km. GEO satellites are more or less motionless from an observer at earth, but IGSO orbits the ground track is 8-shaped; a so-called analemma
In Australia we are lucky to track the current Beidou constellation.
BeiDou? First Australian results of a combined …

5. BeiDou – Signal Frequencies
BeiDou – Signal Frequencies
BeiDou: (Modernized) GPS:
B1: MHz cm
B2: MHz cm
B3: MHz cm
L1: MHz cm
L2: MHz cm
L5: MHz cm
At present: 3 GPS satellites transmit on L5 B2 B3 B1
BEIDOU
BeiDou, GPS (and Galileo) signals are based on Code Division Multiple Access (CDMA)
BeiDou? First Australian results of a combined …

6. BeiDou – Time and Coordinate Systems
BeiDou Time System:
Beidou time (BDT) is synchronized with UTC within 100 ns
Offset BDT and GPS time (GPST)/Galileo time (GST) is broadcast by satellites
BeiDou Coordinate System:
BeiDou uses China Geodetic System 2000 (CGS2000)
Coincides with ITRF at few centimetre level; for most (surveying) applications difference between CGS2000 and ITRF can be ignored
BeiDou? First Australian results of a combined …

7. Combined BeiDou + GPS: Increased model strength and availability
Combined BeiDou + GPS: Increased model strength and availability
Suitable for e.g.:
Strength of combination of Beidou with GPS: more satellites, roughly doubled, thus better availability and geometry for challenging positioning applications, such as in urban canyons but also open pit mines. Furthermore for precision farming.
Developing and operating mines
Agriculture (wheat belt in dark yellow)
BeiDou? First Australian results of a combined …

8. GNSS Satellite Availability in Challenging Environments
“urban canyons”
open pit mines
BeiDou? First Australian results of a combined …

9. BeiDou + GPS: Single Point Positioning (SPP)
BeiDou + GPS: Single Point Positioning (SPP)
B1 BEIDOU.
24 h of data (07/07/12) tracked at Curtin’s permanent GNSS station (Trimble NetR9)
Single-frequency Beidou (B1 code) + GPS (L1 C/A code) data used; cut off = 10 deg
Satellite orbits/clocks from nav. message
Estimate parameters: 3D position + 1 receiver clock error per constellation
Position errors computed by subtracting estimated position from known coordinates
We will now give examples of positioning with Beidou+GPS. First SPP, based on pseudorange data of at least 4 sat. for one constellation, and 5 for combined (since 2 clock errors). Precision of combined slightly better than GPS-only, since basically similar atmospheric and other errors are dominating the solution.
One day of data, # Beidou in view 7-10, # GPS: 7-12, # combined: PDOP for Beidou only worse than for GPS only due to satellite distribution with stationary GEO satellites above equator and few sats in South. This is also visible from position error scatterplots with North component worse determined than East.
Beidou-only: North component is worse due to satellite geometry (GEO stationary all day only few sat in South)
BeiDou? First Australian results of a combined …

10. BeiDou + GPS: Real-Time Kinematic (RTK) Positioning
BeiDou + GPS: Real-Time Kinematic (RTK) Positioning
Relative (2 receivers) positioning based on code (pseudorange) and carrier phase
Integer carrier-phase ambiguity resolution (IAR) = key to high-precision (mm-cm level) positioning
Short baseline: elimination of clocks + atmospheric errors
Most challenging: single-frequency BeiDou (B1 code) + GPS (L1 C/A code) single-epoch RTK
Double-differenced observations with unknown parameters: 3D relative position + double-differenced phase ambiguities per constellation
CUTA (Left; reference) and CUTT (Right; rover) GNSS antennas, baseline distance ~1 km
Highest positioning accuracy can be obtained if precise carrier phase data are used, however they are ambiguous, and integer ambiguities need to be determined before high precision is attainable. This is done in RTK positioning. Most challenging is single-epoch single-frequency combined case, since usually dual-freq. single system ASR close to 100%. With single frequency, number of satellites for SF IAR is really crucial: it should be at least 8 for single constellation (9 in combined).
BeiDou? First Australian results of a combined …

11.
Single-frequency RTK ambiguity resolution + positioning results – cut-off elevation: 35 deg
BeiDou-only B1
Beidou only with 35 deg cut-off still quite good, because still at least 4 sat available and positioning can be done.
System/
Ambiguity resolution
Frequency
success rate %
for cut-off [deg] 10 15 20 25 30 35
BEIDOU B1
96.4
96.1
86.9
83.4
66.8
51.5
GPS L1
79.4
68.9
52.6
33.4
19.3
9.0
COMBINED
B1+L1
98.1
100
99.4
97.0
24 h of data (21/04/13)
BeiDou? First Australian results of a combined …

12.
Single-frequency RTK ambiguity resolution + positioning results – cut-off elevation: 35 deg
GPS-only L1
GPS only with 35 deg cutoff very poor due to periods with less than 4 sat (no positioning possible) or very poor geometry.
System/
Ambiguity resolution
Frequency
success rate %
for cut-off [deg] 10 15 20 25 30 35
BEIDOU B1
96.4
96.1
86.9
83.4
66.8
51.5
GPS L1
79.4
68.9
52.6
33.4
19.3
9.0
COMBINED
B1+L1
98.1
100
99.4
97.0
24 h of data (21/04/13)
BeiDou? First Australian results of a combined …

13.
Single-frequency RTK ambiguity resolution + positioning results – cut-off elevation: 35 deg
BeiDou B1 + GPS L1
In combined case always at least 8 satellites even with 35 deg cutoff, thus high ASR about 97%.
System/
Ambiguity resolution
Frequency
success rate %
for cut-off [deg] 10 15 20 25 30 35
BEIDOU B1
96.4
96.1
86.9
83.4
66.8
51.5
GPS L1
79.4
68.9
52.6
33.4
19.3
9.0
COMBINED
B1+L1
98.1
100
99.4
97.0
24 h of data (21/04/13)
BeiDou? First Australian results of a combined …

14. Beidou + GPS Attitude Determination
Beidou + GPS Attitude Determination
Determination of the relative orientation
between reference systems
Determining relative orientation of a body frame fixed to moving object and ECEF coordinate frame.
BeiDou? First Australian results of a combined …

15. Beidou + GPS Attitude Determination
Beidou + GPS Attitude Determination
24 h of data (17/03/13)
8-m baseline
Instantaneous ambiguity resolution success-rates
For precise AD also IAR is crucial. We investigated ASR using standard RTK AR and AR taken geometry constraints into account (baseline lengths and angles between).
GPS only SF ASR low for standard IAR but already much higher using constrained IAR, but not 100% for higher cut-off elevation. Combined GPS+Beidou still 92% ASR with cutoff of 40 deg!
LAMBDA: “standard” (RTK) ambiguity resolution; C-LAMBDA: baseline-constrained ambiguity resolution
BeiDou? First Australian results of a combined …

16.
Conclusions
BeiDou is now operational in Asia-Pacific region and signals can be tracked by multi-GNSS receivers
Combined BeiDou+GPS: increased availability of satellites and frequencies
Data quality BeiDou ≈ GPS
First ever Australian combined BeiDou+GPS results were presented, computed using in-house software of Curtin’s GNSS Research Centre
Combined Beidou+GPS seems to be much more robust for single-frequency RTK positioning and attitude determination in challenging environments, compared to one constellation
RTK ambiguity resolution success rate for 10 deg cut-off elevation: ~99%
RTK ambiguity resolution success rate for 35 deg cut-off elevation: ~97%
AD ambiguity resolution success rate for 10 deg cut-off elevation: ~100%
AD ambiguity resolution success rate for 40 deg cut-off elevation: ~92%
BeiDou? First Australian results of a combined …

17. Acknowledgments
This work has been executed in the framework of the CRC-SI Positioning Program Project 1.01 ”New carrier-phase processing strategies for achieving precise and reliable multi-satellite multi-frequency GNSS/RSS positioning in Australia”
Curtin PhD student Mr Robert Odolinski for processing the SPP and RTK examples
Curtin researcher Dr Nanthi Nadarajah for processing the attitude examples
BeiDou? First Australian results of a combined …

18. More information? Contact: GNSS Research Centre,
Department of Spatial Sciences, Curtin University
BeiDou? First Australian results of a combined …

19. Thanks for your attention!
Questions?
BeiDou? First Australian results of a combined …

20. BeiDou + GPS: “DGNSS” Positioning
BeiDou + GPS: “DGNSS” Positioning
CUTA (Left; reference) and CUTT (Right; rover) GNSS antennas, baseline distance ~1 km
Relative (2 receivers) code (pseudorange) based positioning
Short baselines: reduction/elimination of orbit, clock + atmospheric errors
Single-frequency BeiDou (B1 code) + GPS (L1 C/A code) data used
Double-differenced observations with unknown parameters: 3D relative position
Position errors of CUTT :
computed by subtracting estimated position from known coordinates
Systematic errors such as orbit, clocks and atmosphere are reduced or even eliminated in differential setup where at least two receivers are used of which 1 is reference at known location and 2nd is rover to be determined. This example distance between receivers is 1 km and position errors in North East Up are as follows.
Stdev of Beidou-only: < 1m, and reduced to < 0.5 m for combined
B1 BEIDOU
L1 GPS
B1 BEIDOU + L1 GPS
BeiDou? First Australian results of a combined …

21. Single-frequency RTK ambiguity resolution + positioning results – cut-off elevation: 10 deg
BeiDou-only B1
System/
Ambiguity resolution
Frequency
success rate %
for cut-off [deg] 10 15 20 25 30 35
BEIDOU B1
96.4
96.1
86.9
83.4
66.8
51.5
GPS L1
79.4
68.9
52.6
33.4
19.3
9.0
COMBINED
B1+L1
98.1
100
99.4
97.0
BeiDou? First Australian results of a combined …

22. Single-frequency RTK ambiguity resolution + positioning results – cut-off elevation: 10 deg
GPS-only L1
System/
Ambiguity resolution
Frequency
success rate %
for cut-off [deg] 10 15 20 25 30 35
BEIDOU B1
96.4
96.1
86.9
83.4
66.8
51.5
GPS L1
79.4
68.9
52.6
33.4
19.3
9.0
COMBINED
B1+L1
98.1
100
99.4
97.0
BeiDou? First Australian results of a combined …

23. Single-frequency RTK ambiguity resolution + positioning results – cut-off elevation: 10 deg
BeiDou B1 + GPS L1
System/
Ambiguity resolution
Frequency
success rate %
for cut-off [deg] 10 15 20 25 30 35
BEIDOU B1
96.4
96.1
86.9
83.4
66.8
51.5
GPS L1
79.4
68.9
52.6
33.4
19.3
9.0
COMBINED
B1+L1
98.1
100
99.4
97.0
BeiDou? First Australian results of a combined …