Precise GNSS Positioning
Transcript of Precise GNSS Positioning
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PrecisePrecise GNSSGNSS positioningpositioningThreatsThreats andand opportunitiesopportunities
Department of Mathematical Geodesy and PositioningDepartment of Mathematical Geodesy and Positioning
Delft University of TechnologyDelft University of Technology
The NetherlandsThe Netherlands
KeesKees de Jongde Jong
Simpósio Brasileiro de Geomática
UNESP, Presidente Prudente, July 2002
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ContentsContents
Modernized GPS and Galileo
GNSS vulnerabilities
Integrated GPS/Galileo ambiguity resolution
Major error sources
Trends in RTK positioning
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No Selective Availability (SA)
Second civil signal on L2
Third civil signal on new L5frequency (1176.45 MHz)
Switched off on 2 May 2000
GPS modernizationGPS modernization
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Availability of new GPS signalsAvailability of new GPS signals
New civil signal on L2
Stronger signals on L1 and L2
First launch in 2003
Block IIR
L5 frequency (1176.45 MHz)
New civil signals on L2 en L5Stronger signals on L1, L2 and L5
First launch 2005
Block IIF
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Availability of new GPS signalsAvailability of new GPS signals
0
2
4
6
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10
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1618
20
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26
28
30
F e b - 0 3
A u g - 0 3
F e b - 0 4
A u g - 0 4
F e b - 0 5
A u g - 0 5
F e b - 0 6
A u g - 0 6
F e b - 0 7
A u g - 0 7
F e b - 0 8
A u g - 0 8
F e b - 0 9
A u g - 0 9
F e b - 1 0
A u g - 1 0
F e b - 1 1
A u g - 1 1
N u m b e r o f s a t e l l i t e s
Block IIR (L1, L2)
Block IIF (L1, L2, L5)
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Galileo orbits and frequency bandsGalileo orbits and frequency bands
Orbital planes 3
Satellites/plane 10
Semi-major axis 29900 km
Inclination 56°
Orbits
E1 1587-1591 MHz
E2 1559-1563 MHz
E4 1254-1258 MHz
E5 1164-1214 MHz
E6 1260-1300 MHz
Frequency bands
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Satellite constellationSatellite constellation
GPS
Galileo
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GNSSGNSS frequency allocationfrequency allocation
Galileo E5/A
GPS L2
Galileo E5/B
Glonass
G2
Galileo E6
GPS L1
Glonass
G2
ARNS
RNSS* RNSS*RNSS RNSS
ARNS ARNS
Galileo C1
RNSS
G a l i l e o E 3
GPS L5
G a l i l e o
E 1
G a l i l e o
E 2
G a l i l e o
E 4
Upper L-BandLower L-Band C-Band
E 5 : 1 1 6 4 - 1
2 1 4 M H z
E 4 : 1 2 5
4 - 1 2 5
8 M H z
E 6 : 1 2 6
0 - 1 3
0 0 M H z
E 2 : 1 5 5
9 - 1 5
6 3 M H z
E 1 : 1 5 8
7 - 1 5
9 1 M H z
C 1 : 5
0 1 0 - 5
0 3 0 M H z
Lower L-band Upper L-band C-band
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1210 1220 1230 1240 1250 1260 1270 1280 1290 1300 f [MHz]
L2
1227.60
E6
1278.75
1560 1570 1580 1590 f [MHz]
1575.42
L1 E1E2
1176.45
L5 (E5a) E5b
1176.45 1202.25
1160 1170 1180 1190 1200 1210 1220 f [MHz]
GPS civil signal
Galileo civil signal
Galileo commercial signal
GPS precision signal
Galileo precision signal
Non--civil signal
GPS and Galileo signalsGPS and Galileo signals
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Galileo scheduleGalileo schedule
Official go-ahead on 26 March 2002
First experimental satellite in 2004
(Galileo System Test Bed)First four operational satellites in 2005-2006
Full operational constellation in 2008
See also http://www.europa.eu.int/comm/energy_transport/en/gal_en.html
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Visible satellitesVisible satellites
0
3
6
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0 : 0 0 : 0 0 . 0
1 : 0 0 : 0 0 . 0
2 : 0 0 : 0 0 . 0
3 : 0 0 : 0 0 . 0
4 : 0 0 : 0 0 . 0
5 : 0 0 : 0 0 . 0
6 : 0 0 : 0 0 . 0
7 : 0 0 : 0 0 . 0
8 : 0 0 : 0 0 . 0
9 : 0 0 : 0 0 . 0
1 0 : 0 0 : 0 0 . 0
1 1 : 0 0 : 0 0 . 0
1 2 : 0 0 : 0 0 . 0
1 3 : 0 0 : 0 0 . 0
1 4 : 0 0 : 0 0 . 0
1 5 : 0 0 : 0 0 . 0
1 6 : 0 0 : 0 0 . 0
1 7 : 0 0 : 0 0 . 0
1 8 : 0 0 : 0 0 . 0
1 9 : 0 0 : 0 0 . 0
2 0 : 0 0 : 0 0 . 0
2 1 : 0 0 : 0 0 . 0
2 2 : 0 0 : 0 0 . 0
2 3 : 0 0 : 0 0 . 0
N u m b e r o f s a t e l l i t e s
GPS
Galileo
Total
Location: Presidente Prudente Date: 11 July 2002 Minimum elevation: 10°
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GPS system vulnerabilitiesGPS system vulnerabilities
Radio-frequency interference (RFI)
GPS testing
Ionosphere (solar maximum)
Spectrum congestion
Unintentional interference
See Volpe vulnerability report (august 2001)http://www.navcen.uscg.gov
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GPS system vulnerabilitiesGPS system vulnerabilities
Jamming: denial of use of GPS
Spoofing: broadcast wrong GPS-like signals
Meaconing: rebroadcast GPS signals
System damage: satellites or ground control segment
Intentional interference
Errors, over-reliance, lack of knowledge/training
Human factors
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JammingJamming
Simple, 1 watt: 10/85 km (loss/no acquisition)
GPS-like, 1 watt: 1000 km (no acquisition)
Characteristics
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JammersJammers
Russian, 4 Watt, L1 and L2, GPS
and GLONASS, US$ 4,000
USA, 1 Watt
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Miniature L1Miniature L1 jammer jammer
TNO-FEL: Physics research lab of the Netherlands
organization for applied research
1 mW output
Range > 125 m
Power consumption 9 V, 30 mA
Size of one cubic inch feasible
TNO-FEL prototype jammer
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Sources of interferenceSources of interference
Technical enthusiastsStudents or people that cannot withstand the challenge
Criminals
Car or cargo theft, free access to toll-roads
TerroristsBlock airports, rescue and police
Military
Jam potential enemy to deny use of GPS, Galileo and Glonass signals
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GPSGPS
GalileoGalileo
Precise GNSS positioningPrecise GNSS positioning
Carrier ambiguity resolution is the key to precise positioningwith a Global Navigation Satellite System (GNSS) such as
I n t e g r a t e dI n t e g r a t e d
GPS/GalileoGPS/Galileo
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GNSS processing stepsGNSS processing steps
LAMBDA method‘Float’ solution ‘Fixed’ solution
Least squares Integer least squares Least squares
Estimate
position andcarrier ambiguities
Estimate
position(ambiguitiesfixed)
Estimate
integer ambiguities
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Success-rateSuccess-rate
Probability (number in interval [0-100%]) of fixing thecarrier ambiguities to their correct integer values
Requires satellite almanac and approximateuser position, but no actual data
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Ionosphere modelsIonosphere models
Ionosphere float (long baseline)
New ionosphere parameter for each satellite at each observationepoch (equivalent to eliminating ionosphere)
Ionosphere weighted (medium baseline)
New ionosphere parameter for each satellite at each observationepoch constrained by a priori standard deviation
Ionosphere fixed (short baseline)
Ionosphere assumed absent
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Design parameters - frequenciesDesign parameters - frequencies
L1 1575.420 MHz
L2 1227.600 MHz
L5 1176.450 MHz
GPS
E2-L1-E1 1575.420 MHz
E5b 1202.025 MHz
E6 1278.750 MHz
Galileo
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Design parametersDesign parameters
Location: Presidente Prudente (22° S, 51° W)
Date: 11 July 2002
Minimum elevation: 10°
Standard deviation carrier: 0.003 m
Ionosphere weight: 0.05 m (medium baseline only)
Computation of instantaneous success-rates(single-epoch ambiguity resolution)
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Design parameters - code observationsDesign parameters - code observations
Standard deviation code
L1 0.30 E2-L1-E1 0.15L2 0.30 E5b 0.10
L5 0.10 E6 0.10
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Interpretation of resultsInterpretation of results
0%
3%
44%
57%
100% 100%
0%
20%
40%
60%
80%
100%
Dual-frequency Triple-frequency
S u c c e s s r a t e [ % ]
Long baseline Medium baseline Short baseline
Succes-rate is 57% or higher in 95% percent of all cases
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GPS onlyGPS only
0%
3%
44%
57%
100% 100%
0%
20%
40%
60%
80%
100%
Dual-frequency Triple-frequency
S u c c e s s r a t e [ % ]
Long baseline Medium baseline Short baseline
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Integrated GPS and GalileoIntegrated GPS and Galileo
3%
45%
87%92%
100% 100%
0%
20%
40%
60%
80%
100%
Dual-frequency Triple-frequency
S u c c e s s r a t e [ % ]
Long baseline Medium baseline Short baseline
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Code observations - alternativesCode observations - alternatives
Standard precision
L1 0.30 E2-L1-E1 0.15
L5 0.10 E5b 0.10
High precision
L1 0.30 E2-L1-E1 0.10
L5 0.05 E5b 0.05
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Integrated GPS and Galileo (2Integrated GPS and Galileo (2 freqfreq.).)
27%
59%
91% 94%100% 100%
0%
20%
40%
60%
80%
100%
Standard precision High precision
S u c c e s s r a t e [ % ]
Long baseline Medium baseline Short baseline
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Integrated GPS and Galileo (2Integrated GPS and Galileo (2 freqfreq.).)
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10
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0 : 0 0 : 0 0 . 0
1 : 0 0 : 0 0 . 0
2 : 0 0 : 0 0 . 0
3 : 0 0 : 0 0 . 0
4 : 0 0 : 0 0 . 0
5 : 0 0 : 0 0 . 0
6 : 0 0 : 0 0 . 0
7 : 0 0 : 0 0 . 0
8 : 0 0 : 0 0 . 0
9 : 0 0 : 0 0 . 0
1 0 : 0 0 : 0 0 . 0
1 1 : 0 0 : 0 0 . 0
1 2 : 0 0 : 0 0 . 0
1 3 : 0 0 : 0 0 . 0
1 4 : 0 0 : 0 0 . 0
1 5 : 0 0 : 0 0 . 0
1 6 : 0 0 : 0 0 . 0
1 7 : 0 0 : 0 0 . 0
1 8 : 0 0 : 0 0 . 0
1 9 : 0 0 : 0 0 . 0
2 0 : 0 0 : 0 0 . 0
2 1 : 0 0 : 0 0 . 0
2 2 : 0 0 : 0 0 . 0
2 3 : 0 0 : 0 0 . 0
N u m b e r o f e p o c h s
0
5
10
15
20
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N u m b e r o f s
a t e l l i t e s
High precision Standard precision Satellites
Success-rate 99%, medium baseline
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Integrated GPS and GalileoIntegrated GPS and Galileo
Integrated use of GPS and Galileo significantlyincreases ambiguity succes-rate
Single-epoch ambiguity resolution becomes feasible if ionospheric effects can be constrained
Very long-baseline ambiguity resolution requires morethan one observation epoch and benefits most fromtriple-frequency integrated system
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Major GNSS error sourcesMajor GNSS error sources
Ionosphere
Multipath
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IonosphereIonosphere
Ionosphere is dispersive: effect is frequency dependent
Effect depends on free electron density in atmosphere
Electron density is related to solar activity
Solar activity has period of 11 years and is characterisedby sunspot numbers
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SunspotsSunspots
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Solar cycle and sunspot numbersSolar cycle and sunspot numbers
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50
100
150
200
250
300
1 7 4 9
1 7 6 1
1 7 7 3
1 7 8 5
1 7 9 7
1 8 0 9
1 8 2 1
1 8 3 3
1 8 4 5
1 8 5 7
1 8 6 9
1 8 8 1
1 8 9 3
1 9 0 5
1 9 1 7
1 9 2 9
1 9 4 1
1 9 5 3
1 9 6 5
1 9 7 7
1 9 8 9
2 0 0 1
S u n s p o t n u
m b e r
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Sunspot number predictionSunspot number prediction
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Effects of ionosphereEffects of ionosphere
Poor GPS satellite tracking
Disturbance of GPS data links
Positioning biases
Incorrect ambiguity resolution(also results in positioning biases)
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Ionosphere and positioningIonosphere and positioning
Two permanent GPS receivers, 4 km apart(short baseline) in The Netherlands (52° N)
Known baseline, continuously monitored
Measurement set-up
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Ionosphere and positioningIonosphere and positioning
Compute daily percentage of height errorsgreater than 5 cm for period of two months
Correlate this percentage to daily variationsin Total Electron Content (TEC)
Analysis procedure
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Height biases and TECHeight biases and TEC
H e i g h t b i a s > 5 c m [
% ]
D a i l y v a r i a t i o n T E
C [ t e c u ]
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Effects dueEffects due multipathmultipath
Observations
Estimated positions (if same satellites are used)
Biases repeat every 23h56m
Periodic biases in
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MultipathMultipath in observationsin observations
GPS SV06, L2-code
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Aim
MultipathMultipath detection in positionsdetection in positions
Set-up
Background
GPS constellation has 23h56m repeatability satellite-reflector-antenna geometry re-occurs every day
Collect data over 2×24 hours and determine presence of repeatable effects with period 23h56m
Show multipath explicitly in stationary baselines
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Height errorsHeight errors
2nd day shifted 4 minutes
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Real-timeReal-time kinematickinematic (RTK) positioning(RTK) positioning
Centimeter accuracy in real-time, providedcarrier ambiguities can be resolved to their correct integer values
Ideal world
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RTK positioning in the real worldRTK positioning in the real world
Correct height estimates
Incorrect height estimates due to wronginitialization of carrier ambiguities
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Precise RTK GNSS positioningPrecise RTK GNSS positioning
Choose reference stations carefully toavoid multipath as much as possible
Integrate RTK GPS with other sensors
Validate estimated carrier ambiguities
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Trends in RTK positioningTrends in RTK positioning
From single-reference stationto network-based RTK
Higher reliability
Longer baselines
Less reference stations
Advantages
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Fugro StarfixFugro Starfix HPHP
Regional sub-networks of global Starfix network
Decimeter accuracy for distances up to 500 km
Starfix HP (High Performance)
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Jet Propulsion Laboratory’s IGDGJet Propulsion Laboratory’s IGDG
Global network of reference stations
Reference station data collection via the Internet
Data dissemination to users via the Internet
Decimeter positioning accuracy
Internet-based Global Differential GPS (IGSG)
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IGDG - demonstration resultsIGDG - demonstration results
See also http://gipsy.jpl.nasa.gov/igdg
Last 30 minutes
Last six hours
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ConclusionsConclusions
Modernized GPS and future Galileo offer unprecedented accuracy and availability
Both systems are vulnerable to intentional and
unintentional interference
Error sources (ionosphere, multipath) remainmajor concern
Network-based RTK will result in longer baseline
lengths and less reference stations