gnss signal observations - stanford and...

Institute for Communications and Navigation –

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


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


GNSS Signals, 1978-2003


Signals around 2015


Benefits of the New Signals

BW [MHz] RX Power [dBW] CRB [cm]

Galileo E1bc 4 -155 20.0



Galileo E5 51 -152 0.9

Galileo E5 90 -152 0.8

Galileo E5a 24 -155 5.0


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


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


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


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


Data sampling with large antennas

Stanford DLR

Courtesy: SRI


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


Spectrum Galileo L1

BOC(1,1) BOC(15,2.5)

January 24th, 20061575.42 MHz


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


Eye DiagrammOS code

chip boundary

PRS codechip boundary

OS subcarriertransition

PRS subcarriertransition

[=µs]


Satellite TX Model

Details unknownprimary candidate for imperfections: power amplifier


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


Non-linear Power Amplifier

TWTA Model (25MHz)

Saleh Model (25MHz), α=0.11


Dispersive Behavior

Find an equivalent Wiener Filter

amplitude phase and group delay

15-15 15-15


Simulation Result – IQ Diagram

Measured (24.01.2006)Simulated using the filter

and non-linear


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


Signal B2 and B3 of Beidou M Satellite


Signal B1 of Beidou M Satellite

14. May 2007 24. May 2007


Stanford GNSS Monitor Station

Utilizes a 1.8 m parabolic antenna with automated tracking/controlOn roof of GPS Laboratory allowing for on demand access


Stanford GNSS Monitor Station


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


“Portable” Ground Station set up


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


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)


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


SNS (Salinas)DME @ 1173.0 MHz


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


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


Not Just a GPS Problem!

E5a (1176.45 MHz) PSD E5b (1207.14 MHz) PSD


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


Measurement Equipment

Spectrum Vector analyzerR&S FSH6R&S FSP3Agilent E4443A

GPS-ReceiversAshtech G12Leica GSP1200

AntennasHemisphericalGPS-patchdirectional


Examples of interference patterns

E6-BandL1-Band kT=-174 [dBm-Hz]

L1: 1575.42MHz

E6: 1278.75 MHz


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


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


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


EVNet Sensor Station Network

Galileo Sensor stations Operational EVnet-Stations

Toulouse

Neustrelitz

Kiruna

OP

Bandung

StanfordUniversity

Brazil

Africa

JapanCanariesIsland

Quebec

intended Stations


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

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