Transcript Future GNSS
2013 Surveying Expo
The Institution of Surveyors, Victoria
Improved High Precision GNSS Positioning
with New Satellites and Signals
Nick Talbot
Research Fellow,
Trimble Navigation Australia
Overview
Introduction
GNSS Constellation Status
BeiDou System
CMRx Format
RTK Test Campaign
Test Results
Summary
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
GNSS Constellation Status
System
Origin Current
GPS
USA
Future
31 satellites;
3-Freq. fully available ~ 2018
20 IIA + IIR satellites with L1C/A, L2 PY GPS III ~ 2022
7 IIR-M satellites with L1C/A, L2C
4 IIF satellites with L1C/A, L2C, L5
GLONASS Russia 24 satellites;
FDMA L1, L2
CDMA signals added in new Kseries 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 GEO
with B1, B2, B3
Full constellation (35 sats – 5
GEO; 30 MEO) ~ 2020
GNSS Spectrum
E5
L5
L5
L5
L5
E1
E6
G3
B2
L2
G2
L1
B3
L2
LEX
RTX /
OmniSTAR
B1
L1
L1
G1
Frequency [MHz]
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
GPS (US)
Galileo (Europe)
GLONASS (Russia)
InmarSAT
QZSS (Japan)
IRNSS (India)
BeiDou (China)
SBAS (US)
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
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
BeiDou Broadcast Orbit Daily Performance –
Based on RTX tracking network
RMS [m]
BeiDou dual-frequency code residuals, 7 May, 2013
RTX Station
CMRx Data Format
Additional satellite observations
naturally increases the size of
the GNSS correction stream
GNSS corrections need to be
transmitted to rover from a
reference station or VRS
network
Many radio solutions
have limited bandwidth
CMRx format provides a high level
of data compression, with strong
resistance to transmission errors
CMRx Data Format vs RTCM 3.x
RTCM 3.1
GPS (L1, L2) + GLONASS (L1, L2)
700
600
500
400
300
200
100
0
12
8
4
6
8
GPS
10
12
lo
na
ss
4
G
bytes/sec
9600 baud with 1 repeater (426 bytes/s)
CMRx Data Format vs RTCM 3.x
CMRx
GPS (L1, L2, L5) + GLONASS (L1, L2) + BeiDou (B1, B2)
700
600
500
400
300
200
100
0
12
12/ 12
88 / 8
4
6
8
GPS
10
12
lo
na
ss
4
4/ 4
G
bytes/sec
9600 baud with 1 repeater (426 bytes/s)
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
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
Collective Results –
Vertical 95%
Christchurch,
New Zealand
Collective Results –
Horizontal 95%
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
Moderate Environment (Xi’an) –
Base Station (not a recommended setup)
R10 GNSS
Base Receiver
Moderate Environment (Xi’an) –
Rover
R10 GNSS
Rover
Receiver
Moderate Environment (Xi’an) –
Satellite Tracking
Moderate Environment (Xi’an) –
PDOP
Moderate Environment (Xi’an) –
Height Error
Moderate Environment (Xi’an) –
Horizontal Position Error
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
Number of satellites in RTK
Height Error
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
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
Questions?
Acknowledgements:
Stuart Riley and Sunnyvale Team
Eric Leroy (QA)
App Firmware Team
HCC/Survey/Infra/InTech H/W Team
Timo Allison, Markus Glocker (Terrasat)
TNZ & Westminster field testing
Xi’an China team
Dave Vanden Berg & InTech Beijing