Precise Precise GNSS GNSS positioningpositioningThreatsThreats and and opportunitiesopportunities

Department of Mathematical Geodesy and PositioningDepartment of Mathematical Geodesy and Positioning

Delft University of TechnologyDelft University of Technology

The NetherlandsThe Netherlands

KeesKees de Jong de Jong

Simpósio Brasileiro de Geomática

UNESP, Presidente Prudente, July 2002

ContentsContents

Modernized GPS and Galileo

GNSS vulnerabilities

Integrated GPS/Galileo ambiguity resolution

Major error sources

Trends in RTK positioning

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

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 L5

Stronger signals on L1, L2 and L5

First launch 2005

Block IIF

Availability of new GPS signalsAvailability of new GPS signals

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Block IIR (L1, L2)

Block IIF (L1, L2, L5)

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

Satellite constellationSatellite constellation

GPS

Galileo

GNSS GNSS frequency allocationfrequency allocation

Galileo E5/A

GPS L2

Galileo E5/B

GlonassG2

Galileo E6

GPS L1

GlonassG2

ARNS

RNSS* RNSS*RNSS RNSS

ARNS ARNS

Galileo C1

RNSS

Gal

ileo

E3

GPS L5

Gal

ileo

E1

Gal

ileo

E2

Gal

ileo

E4

Upper L-BandLower L-Band C-Band

E5: 11

64-1

214 M

Hz

E4: 12

54-1

258 M

Hz

E6: 12

60-1

300 M

Hz

E2: 15

59-1

563 M

Hz

E1: 15

87-1

591 M

Hz

C1: 5

010-

5030

MHz

Lower L-band Upper L-band C-band

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

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

Visible satellitesVisible satellites

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GPSGalileoTotal

Location: Presidente Prudente Date: 11 July 2002 Minimum elevation: 10°

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

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

JammingJamming

Simple, 1 watt: 10/85 km (loss/no acquisition)

GPS-like, 1 watt: 1000 km (no acquisition)

Characteristics

JammersJammers

Russian, 4 Watt, L1 and L2, GPSand GLONASS, US$ 4,000

USA, 1 Watt

Miniature L1 Miniature L1 jammerjammer

TNO-FEL: Physics research lab of the Netherlandsorganization 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

Sources of interferenceSources of interference

Technical enthusiastsStudents or people that cannot withstand the challenge

CriminalsCar or cargo theft, free access to toll-roads

TerroristsBlock airports, rescue and police

MilitaryJam potential enemy to deny use of GPS, Galileo and Glonass signals

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

GNSS processing stepsGNSS processing steps

LAMBDA method‘Float’ solution ‘Fixed’ solution

Least squares Integer least squares Least squares

Estimateposition andcarrierambiguities

Estimateposition(ambiguitiesfixed)

Estimateintegerambiguities

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

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

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

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)

Design parameters - code observationsDesign parameters - code observations

Standard deviation code

L1 0.30 E2-L1-E1 0.15

L2 0.30 E5b 0.10

L5 0.10 E6 0.10

Interpretation of resultsInterpretation of results

0%3%

44%

57%

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100%

Dual-frequency Triple-frequency

Su

cces

s ra

te [

%]

Long baseline Medium baseline Short baseline

Succes-rate is 57% orhigher in 95% percent ofall cases

GPS onlyGPS only

0%3%

44%

57%

100% 100%

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100%

Dual-frequency Triple-frequency

Su

cces

s ra

te [

%]

Long baseline Medium baseline Short baseline

Integrated GPS and GalileoIntegrated GPS and Galileo

3%

45%

87%92%

100% 100%

0%

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100%

Dual-frequency Triple-frequency

Su

cces

s ra

te [

%]

Long baseline Medium baseline Short baseline

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

Integrated GPS and Galileo (2 Integrated GPS and Galileo (2 freqfreq.).)

27%

59%

91% 94%100% 100%

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100%

Standard precision High precision

Su

cces

s ra

te [

%]

Long baseline Medium baseline Short baseline

Integrated GPS and Galileo (2 Integrated GPS and Galileo (2 freqfreq.).)

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High precision Standard precision Satellites

Success-rate 99%, medium baseline

Integrated GPS and GalileoIntegrated GPS and Galileo

Integrated use of GPS and Galileo significantlyincreases ambiguity succes-rate

Single-epoch ambiguity resolution becomes feasible ifionospheric effects can be constrained

Very long-baseline ambiguity resolution requires morethan one observation epoch and benefits most fromtriple-frequency integrated system

Major GNSS error sourcesMajor GNSS error sources

Ionosphere

Multipath

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

SunspotsSunspots

Solar cycle and sunspot numbersSolar cycle and sunspot numbers

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30017

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1761

1773

1785

1797

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1833

1845

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1929

1941

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Sunspot number predictionSunspot number prediction

Effects of ionosphereEffects of ionosphere

Poor GPS satellite tracking

Disturbance of GPS data links

Positioning biases

Incorrect ambiguity resolution(also results in positioning biases)

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

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

Height biases and TECHeight biases and TEC

Hei

ght b

ias

> 5

cm

[%]

Dai

ly v

aria

tion

TE

C [t

ecu]

Effects due Effects due multipathmultipath

Observations

Estimated positions (if same satellites are used)

Biases repeat every 23h56m

Periodic biases in

Multipath Multipath in observationsin observations

GPS SV06, L2-code

Aim

MultipathMultipath detection in positions detection 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 ofrepeatable effects with period 23h56m

Show multipath explicitly in stationary baselines

Height errorsHeight errors

2nd day shifted 4 minutes

Real-time Real-time kinematic kinematic (RTK) positioning(RTK) positioning

Centimeter accuracy in real-time, providedcarrier ambiguities can be resolved to theircorrect integer values

Ideal world

RTK positioning in the real worldRTK positioning in the real world

Correct height estimates

Incorrect height estimates due to wronginitialization of carrier ambiguities

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

Trends in RTK positioningTrends in RTK positioning

From single-reference stationto network-based RTK

Higher reliability

Longer baselines

Less reference stations

Advantages

Fugro StarfixFugro Starfix globalglobal DGPS DGPS networknetwork

Fugro StarfixFugro Starfix HP HP

Regional sub-networks of global Starfix network

Decimeter accuracy for distances up to 500 km

Starfix HP (High Performance)

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)

IGDG - demonstration resultsIGDG - demonstration results

See also http://gipsy.jpl.nasa.gov/igdg

Last 30 minutes

Last six hours

ConclusionsConclusions

Modernized GPS and future Galileo offerunprecedented accuracy and availability

Both systems are vulnerable to intentional andunintentional interference

Error sources (ionosphere, multipath) remainmajor concern

Network-based RTK will result in longer baselinelengths and less reference stations