Institute for Communications and Navigation – Page 1
GNSS Signal Observations - Stanford and DLRChristoph Günther, Sherman LoContributors: Dennis Akos, Alan Chen, Johann Furthner, Grace Gao,Sebastian Graf, David de Lorenzo, Oliver Montenbruck, AlexanderSteingass, Christian Weber
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Four GNSS Programs under Development andEvolution
GPS ModernizationII-RM with L2C signals, II-F with L5WAAS broadcast of L5 wideband civil signalBlock III with L1C
GalileoOS and SoL on L1, E5a, E5bAdditional signals on L1 and E6
COMPASSthe great unknown… B1, B1-2, B2, B3
GLONASSthinking heavily of including a CDMA signal compatible to othersystems
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GNSS Signals, 1978-2003
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Signals around 2015
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Benefits of the New Signals
BW [MHz] RX Power [dBW] CRB [cm]
Galileo E1bc 4 -155 20.0
Galileo E1bc 8 -155 14.7
Galileo E1bc 24 -155 8.7
Galileo E5 51 -152 0.9
Galileo E5 90 -152 0.8
Galileo E5a 24 -155 5.0
Galileo E6bc 24 -155 7.0
GPS L1C/A 2 -160 89.6
GPS L1C/A 4 -160 65.0
GPS L1C/A 24 -160 27.2
GPS L2C 24 -157 19.3
GPS L5P 20 -154 4.5
• Noise performance – Cramer Rao bound
• Dual and triple frequency linear combinations of codes and carriersundifferenced
• Integrity
• Interoperability
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Unrealized Potential
Without careful thought, study, and design of the signals, we canpotentially be leaving a lot on the tablePerformance, Signal design, Interoperability all need to be well studied
Cap
abili
tyC
apab
ility
Near & Mid TermNear & Mid TermCompatibilityCompatibility
DecisionsDecisions
GNSSGNSSEvolvedEvolved
cooperativelycooperatively
GNSSGNSSEvolvedEvolved
individuallyindividually
GNSS as itGNSS as itstands todaystands today
NowNow 5 Years5 Years 10 Years10 Years
GNSSGNSSEvolved inEvolved in
ConflictConflict
With apologies to the US National PNT Architecture Study Group
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Signal Observations
Needed to understand real world performancefor the verification and validation of systems, e.g. Galileo
signals, clocks,…for understanding the situation with Beidou/Compass
signal compatibility/interoperabilityfor analyzing potential threats
interference, signal deformationsfor studying monitoring and augmentation algorithms
LAAS/GBAS, RRAIM,…Rapid response and diagnosis of system faults
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Analysis Capabilities
Data sampling on reflector antennas from 1.8 m to 45 msignal quality and performance
Data sampling on hemispherical antennasinterference analysis
Experimental networks for monitoring and augmentationtest of augmentation systemssatellite clock analysis
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Data sampling with large antennas
Stanford DLR
Courtesy: SRI
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Measurement Setup - Cassegrain
LNA1 LNA2
parabolic reflector 30 m
hyperbolic sub-reflector 4 m
Rhode & Schwarz FSIQ26Agilent E4440 PSA
PC forAnalysis
feed
sub-reflector
~60 [dB]
antenna gain 52 dB:
approx. 108 samples/s
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Spectrum Galileo L1
BOC(1,1) BOC(15,2.5)
January 24th, 20061575.42 MHz
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Measured IQ-Diagram
Measured (24.01.2006) Simulated
1. the PRS transition with I=0 has an eye2. the two exterior groups of PRS transitions are tilted wrto the central one3. the orbits of the “OS(+PRS)” transitions are different
PRS only transition
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Eye DiagrammOS code
chip boundary
PRS codechip boundary
OS subcarriertransition
PRS subcarriertransition
[=µs]
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Satellite TX Model
Details unknownprimary candidate for imperfections: power amplifier
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Potential Explanations
yesnever(rotation only)yesyesdispersion
yes
tiltin the IQ-diagram
noonly forextremevalues
nevernon-linearity
orbitsin the IQ-diagram
eye openingin the IQ-diagram
asymmetryin the
spectrum
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Non-linear Power Amplifier
TWTA Model (25MHz)
Saleh Model (25MHz), α=0.11
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Dispersive Behavior
Find an equivalent Wiener Filter
amplitude phase and group delay
15-15 15-15
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Simulation Result – IQ Diagram
Measured (24.01.2006)Simulated using the filter
and non-linear
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Galileo E5 Signal
AltBOC(15,10), or two BPSK(10) with center frequencies separated by 2x15x1.023 MHz
GIOVE-A, 12.6.2006, Weilheim
E5a: 1176.45 MHzE5b: 1207.14 MHz
E5: 1191.795 MHz
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Signal B2 and B3 of Beidou M Satellite
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Signal B1 of Beidou M Satellite
14. May 2007 24. May 2007
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Stanford GNSS Monitor Station
Utilizes a 1.8 m parabolic antenna with automated tracking/controlOn roof of GPS Laboratory allowing for on demand access
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Stanford GNSS Monitor Station
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Data CollectionBOC(1,1)
BOC(15,2.5)
GIOVE-A E1-L1-E2
• Dish allowed us to see GIOVE-A signal when transmission was initialized• Same set up used in SRI dish• Vector Signal Analyzer used to capture data from transmission
OR
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“Portable” Ground Station set up
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Observations of New GNSSs
Galileo – GIOVE-ADecoded E1 BOC(1,1) Signal on Jan 11, 2006Later discovered the code bits to be 98% correct (using high gaindish data)E5a + E5b codes were determined solely using data from
Compass – Beidou 2BUsed data collected from SGMS to determine codes on multiplefrequenciesSole source of data used for code determination
WAAS L5, Modernized GLONASS, GPS L2C also observed usingSGMS
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Captured a 200 msecond record of 36 MHz bandwidth about the 1227.6 MHz L1carrier frequencyThe first lobe of the L2C code and primary lobes of the L2 P(Y) code spectrum areclearly visibleA significant RFI component is clearly visible in either frequency but not in the timedomain representation – likely a result of local radar activity
1205 1210 1215 1220 1225 1230 1235 1240 1245 1250-150
-145
-140
-135
-130
-125
-120
frequency (MHz)
mag
nitu
de
Frequency Domain
0 0.05 0.1 0.15 0.2 0.25 0.3
-4
-3
-2
-1
0
1
2
3
4
5x 10-3
time (msec)am
plitu
de
Time Domain of the Baseband Signal
L2 Data From IIR-M GPS SV (SVN53/PRN17)
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L5 WAAS Test Data from the
Galaxy 15 Geostationary Satellite
Captured a 200 msecond record of 36 MHz bandwidth about the 1176.45 MHz L5carrier frequencyThe primary lobe of the 10.23 MHz L5 PRN code spectrum is apparentMultiple significant RFI components are visible in both the frequency and time domainrepresentations
Pulsed interferences from the inband DMEs in the surrounding areaExpand time domain plots to confirm/verify this
1155 1160 1165 1170 1175 1180 1185 1190 1195 1200-150
-140
-130
-120
-110
-100
-90
frequency (MHz)
mag
nitu
de
Frequency Domain
0 0.05 0.1 0.15 0.2 0.25 0.3
-0.06
-0.04
-0.02
0
0.02
0.04
0.06
time (msec)am
plitu
de
Time Domain of the Baseband Signal
SNS (Salinas)DME @ 1173.0 MHz
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Expanded Time Domain View of L5 Band WAAS Data
The GNSS L5 signals will experience pulsedinterference as a result of the inband DMEtransmissions
Data collections at Stanford show the presenceof a number of different DME, identifiable bytheir underlying frequencies, with varying signalstrength within the collected data
0 0.05 0.1 0.15 0.2 0.25 0.3
-0.06
-0.04
-0.02
0
0.02
0.04
0.06
time (msec)
ampl
itude
Time Domain of the Baseband SignalZoomed
View
0.155 0.16 0.165 0.17 0.175 0.18 0.185 0.19 0.195 0.2 0.205
-0.06
-0.04
-0.02
0
0.02
0.04
0.06
time (msec)am
plitu
de
Time Domain of the Baseband Signal
L5 (E5A/B) GNSS receivers will utilize pulseblanking to minimize the impact of theinband DME broadcasts
Stanford GNSS monitor station utilizesextended dynamic range to receive/processboth DME and GNSS L5 signals
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Not Just a GPS Problem!
E5a (1176.45 MHz) PSD E5b (1207.14 MHz) PSD
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Mobile Interference Measurement Setup
Spectral analysisE5 : 1146-1238 MHz (including L2)E6 : 1260-1300 MHzE1-L1-E2 : 1555-1596 MHz
Potential interfererNarrowband (single carriers etc.)Broadband (DVB-T, UMTS etc.)Very broadband (UWB, etc.)+ pulsed interference
Planned campaign next year near Frankfurt with up to 48 DME
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Measurement Equipment
Spectrum Vector analyzerR&S FSH6R&S FSP3Agilent E4443A
GPS-ReceiversAshtech G12Leica GSP1200
AntennasHemisphericalGPS-patchdirectional
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Examples of interference patterns
E6-BandL1-Band kT=-174 [dBm-Hz]
L1: 1575.42MHz
E6: 1278.75 MHz
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Wideband Interference in L1
7 MHz wide-87.4 dBm average PowerInterference-to-Signal-Ratio (ISR) 42.6 dB
GPS carrier Galileo BOC(1,1) main lobes
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Jammer Mitigation with Adaptive Beamforming
Estimated C/N0 valueAntenna array processing
Single antenna (common case)
Time of interference occurrence
SW receiver loses tracking
SW Receiver tracks GPS L1signal with acceptable C/N0
Estimated C/N0 value
C/N0 tracking threshold
Beamforminggain
Combination of ESPRIT+ constrained minimum variance (LCMV)
beamforming
Interferers have been mitigated byproducing spatial nulls
Satellite signal hasbeen detected and
enhanced
2X2 Antenna array
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GNSS SensorStation
1
GNSS SensorStation
2
GNSS SensorStation
N...
Central Processingand Control Facility
ProcessingCentre
DataArchive
UserConfiguration Broadcaster
C&
C
User Component
1
User Component
2
UserComponent
L...
ExternalProcessingFacility 1
ExternalProcessingFacility M
...
RT* Data
Archive Data
EVnetAdministrator
EVnetOperator C&C*
RT
Dat
a
C&
C
RT
Dat
a
C&C
EVNet – Architecture
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EVNet Sensor Station Network
Galileo Sensor stations Operational EVnet-Stations
Toulouse
Neustrelitz
Kiruna
OP
Bandung
StanfordUniversity
Brazil
Africa
JapanCanariesIsland
Quebec
intended Stations
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Conclusion
New signals in new bands: GPS, Galileo, GLONASS, CompassNew opportunities for improved navigation performanceAnalysis of the performance of the satellites: signals characteristics,clock stability, biases,…Understanding and mitigating the interference situation in the new bandsand even L1Stanford and DLR have developed and are developing tools andmethods for these tasks, with a particular focus on aeronauticsWe have started a very promising cooperation in this and other fieldsrelevant to aeronautical navigation