2013 Western Australia Surveying Conference 30.07.2010 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 16.05.2013

Presentation Outline BeiDou 30.07.2010 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 … 16.05.2013

BeiDou – What is it? 北斗 Big Dipper or Plough, Northern Dipper 30.07.2010 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 2011. SIS ICD contains signal structure, navigation message description etc BeiDou? First Australian results of a combined … 16.05.2013

BeiDou – Constellation 30.07.2010 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 … 16.05.2013

BeiDou – Signal Frequencies 30.07.2010 BeiDou – Signal Frequencies BeiDou: (Modernized) GPS: B1: 1561.098 MHz 19.20 cm B2: 1207.140 MHz 24.83 cm B3: 1268.520 MHz 23.63 cm L1: 1575.420 MHz 19.03 cm L2: 1227.600 MHz 24.42 cm L5: 1176.450 MHz 25.48 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 … 16.05.2013

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 … 16.05.2013

Combined BeiDou + GPS: Increased model strength and availability 30.07.2010 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 … 16.05.2013

GNSS Satellite Availability in Challenging Environments “urban canyons” open pit mines BeiDou? First Australian results of a combined … 16.05.2013

BeiDou + GPS: Single Point Positioning (SPP) 30.07.2010 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: 14-20. 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 and @equator; only few sat in South) BeiDou? First Australian results of a combined … 16.05.2013

BeiDou + GPS: Real-Time Kinematic (RTK) Positioning 30.07.2010 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 … 16.05.2013

30.07.2010 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 … 16.05.2013

30.07.2010 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 … 16.05.2013

30.07.2010 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 … 16.05.2013

Beidou + GPS Attitude Determination 30.07.2010 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 … 16.05.2013

Beidou + GPS Attitude Determination 30.07.2010 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 … 16.05.2013

30.07.2010 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 … 16.05.2013

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 (Robert.Odolinski@curtin.edu.au) for processing the SPP and RTK examples Curtin researcher Dr Nanthi Nadarajah (N.Nadarajah@curtin.edu.au) for processing the attitude examples BeiDou? First Australian results of a combined … 16.05.2013

More information? Contact: GNSS Research Centre, Department of Spatial Sciences, Curtin University Email: p.teunissen@curtin.edu.au BeiDou? First Australian results of a combined … 16.05.2013

Thanks for your attention! Questions? BeiDou? First Australian results of a combined … 16.05.2013

BeiDou + GPS: “DGNSS” Positioning 30.07.2010 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 … 16.05.2013

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 … 16.05.2013

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 … 16.05.2013

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 … 16.05.2013