improved high precision gnss positioning with new satellites and signals nick talbot research...
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Improved High Precision GNSS Positioning with New Satellites and Signals
Nick TalbotResearch Fellow, Trimble Navigation Australia
2013 Surveying ExpoThe Institution of Surveyors, Victoria
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Overview
Introduction
GNSS Constellation Status
BeiDou System
CMRx Format
RTK Test Campaign
Test Results
Summary
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Introduction Currently 75 GNSS satellites in space
Expect to have 90 GNSS satellites in space by 2015; 120 satellites by 2020
45+ GNSS satellites in view over Asia / Pacific simultaneously by 2020
All GNSS satellites are capable of supporting metre-level and high-precision positioning at centimetre-level
Following presentation describes some of the challenges presented by new satellites and signals
Test results provided to illustrate the benefit of new satellites and signals with latest RTK hardware / firmware
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GNSS Constellation StatusSystem Origin Current Future
GPS USA 31 satellites;20 IIA + IIR satellites with L1C/A, L2 PY7 IIR-M satellites with L1C/A, L2C4 IIF satellites with L1C/A, L2C, L5
3-Freq. fully available ~ 2018GPS III ~ 2022
GLONASS Russia 24 satellites;FDMA L1, L2
CDMA signals added in new K-series sats (L1, L2, L5);Planned compatibility with GPS, Galileo
QZSS Japan 1 satellite;Modernized GPS L1, L2, L5+ LEX signal
Planned launch of 3 additional satellites by 2017 (1 GEO)
Galileo EU 4 operational satellites with E1, E5A, E5B, E6(E1 compatible with GPS L1C)
Full constellation (30 sats) ~ 2020
BeiDou China 14 satellites;5 GEO; 6 MEO; 3 Inclined GEOwith B1, B2, B3
Full constellation (35 sats – 5 GEO; 30 MEO) ~ 2020
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L5L5L5
L2 LEXL1L1
L5L2 L1G2
G3
G1
E1E5 E6
B1B3
B2RTX /
OmniSTAR
1164
1189
1214
1217
1237
1257
1260
1300
1525
1551
1559
1565
1571
1579
1585
1590
1599
1614
Frequency [MHz]
GPS (US)
Galileo (Europe)
GLONASS (Russia)
InmarSAT
QZSS (Japan)
IRNSS (India)
BeiDou (China)
SBAS (US)
GNSS Spectrum
GNSS antennas and receiver RF components expanded to capture usable signals from E5 to G1 spectrum
Good compatibility between GPS, QZSS and SBAS signal structure
Long term compatibility on L1C and E1 signals with frequency and coding
Galileo-E6; BeiDou-B3; and QZSS-LEX bands are to be regulated (limited access), even though B3 can be tracked and used today for RTK
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BeiDou System Three satellite systems
– BeiDou-1 (active ranging system) no Trimble support
– BeiDou-2 (current system) used to be called Compass – subject of this talk
– BeiDou-3 (proposal to move B1 to L1) first MEO satellites may launch in 2014
Current constellation– 5 GEOs / 5 Inclined GEOs / 4 MEOs / More MEOs
in 2014– GEOs are harder to acquire & track due to high
data rate (2ms versus 20ms pre detection interval)
– Multipath errors are constant for static users of GEOs
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BeiDou System Signals
– B1, B2 – supported by Maxwell VI ASIC
What’s public– B1 Open Service is “fully” public– B2 is an Open Service – not in the current ICD– B2 is the same signal as B1 so it is supported– B3 is officially a restricted signal – even though current
codes appear to follow a defined polynomial
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BeiDou Broadcast Orbit Daily Performance –Based on RTX tracking network
BeiDou dual-frequency code residuals, 7 May, 2013
RTX Station
RM
S [
m]
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CMRx Data Format
GNSS corrections need to be transmitted to rover from a reference station or VRS network
Additional satellite observations naturally increases the size of the GNSS correction stream
Many radio solutions have limited bandwidth
CMRx format provides a high level of data compression, with strong resistance to transmission errors
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CMRx Data Format vs RTCM 3.x
0100200300400500600700
by
tes
/se
c
4 6 8 10 12
48
12
GPS Glo
nass
RTCM 3.1GPS (L1, L2) + GLONASS (L1, L2)
9600 baud with 1 repeater (426 bytes/s)
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CMRx Data Format vs RTCM 3.x
CMRxGPS (L1, L2, L5) + GLONASS (L1, L2) + BeiDou (B1, B2)
9600 baud with 1 repeater (426 bytes/s)
0100200300400500600700
by
tes
/se
c
4 6 8 10 12
48
12
GPS Glo
nass
GLONASS +
BeiD
ou
4 / 4
8 / 8
12 / 12
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RTK Test Campaign A test campaign was run in several regions around the world
where GPS, GLONASS, BeiDou, QZSS and Galileo satellites are currently visible, including China, Australia and New Zealand
Data collected on baselines from 2km – 22km in a variety of environments:
Most in high multipath, trees, significantly masked environments
Some in relatively benign environments
15 different baselines
Most data collected in China
22km line from Perth Australia
6km line from Christchurch New Zealand
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RTK Test Campaign Tests conducted with Trimble R10; NetR9 receiver + Zephyr
Geodetic 2 antenna, hardware
Real-time system testing performed in the field
PC version of RTK processor used to process logged GNSS data and analyze performance with various satellite systems enabled / disabled
Truth computed using post-processed RTX
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Collective Results – Vertical 95%
Christchurch, New Zealand
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Collective Results – Horizontal 95%
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RTK Example – Moderate Environment (Xi’an)
Data collected using R10 GNSS receiver in China– Supports GPS/GLONASS/Galileo/QZSS/BeiDou
Processed using a PC build of the real-time RTK engine– Operates in the same mode as real-time, no backward processing– Radio latency modeled– Operating mode set to kinematic– Data reprocessed with/without BeiDou
Environment was moderately difficult
Baseline length approximately 5km– Data collected in Xi’an
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R10 GNSSBase Receiver
Moderate Environment (Xi’an) – Base Station (not a recommended setup)
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R10 GNSSRover Receiver
Moderate Environment (Xi’an) – Rover
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Moderate Environment (Xi’an) – Satellite Tracking
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Moderate Environment (Xi’an) – PDOP
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Moderate Environment (Xi’an) – Height Error
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Moderate Environment (Xi’an) – Horizontal Position Error
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Galileo RTK• Galileo satellites are currently unhealthy• Trimble firmware is Galileo capable/ready.• Modify firmware to force the satellites to report they
are healthy and hence are used in the RTK solution• Evaluate the RTK performance
– 2-hour period with 3 Galileo satellites.– 2 identical rovers on an 8.9km line – real time test
• Common antenna• Located in Melbourne Australia• RX1 = GPS+GLN+QZSS+BDS+Galileo• RX2 = GPS+GLN+QZSS+BDS
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Number of satellites in RTK
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Height Error
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Summary Current BeiDou constellation nearly doubles the
number of visible satellites over Asia Additional satellites improve accuracy of position
estimates Tests show addition of BeiDou improved 95%
position errors by:– 5-75% horizontal– 8-68% vertical
Additional satellites help to reduce the overall impact of measurement noise and multipath errors
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Summary Similar incremental improvements in position
accuracy noted with Galileo satellites in RTK solution
Additional satellites lead to increases in RTK correction bandwidth
CMRx format designed for increased satellite counts
CMRx roughly 55% smaller than RTCM v3.x
Expect to see significant improvements in position availability and accuracy when BeiDou, QZSS, Galileo constellations fully populated
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Questions?
Acknowledgements:
Stuart Riley and Sunnyvale TeamEric Leroy (QA)App Firmware TeamHCC/Survey/Infra/InTech H/W TeamTimo Allison, Markus Glocker (Terrasat)TNZ & Westminster field testingXi’an China teamDave Vanden Berg & InTech Beijing