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Investigation of Potentially Critical
Interference Environments for GPS/Galileo Mass
Market ReceiversGNSS Signals 2007Christian
Weber, Andriy Konovaltsev, Michael Meurer DLR
Presentation Christian Weber (christian.weber_at_dl
r.de)
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Common View on GPS/Galileo

• GPS is located in a protected frequency band and
  does not have to compete with other services in
  L1
• Allowed Services are (in Germany)
• GNSS
• Fixed Service
• Military Use
• Galileo will allocate new frequency bands and
  therefore will have to compete

gt Future mass market receivers will track
Galileo AND GPS with larger bandwidths than
traditional GPS receivers. Therefore, the
situation for GPS changes as well, as former
unused frequencies are suddenly used.
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Measurements on a train by DLR

• Part of GJU-funded GIRASOLE project
• Measurements during train ride
• Route leading from Munich to Hamburg
• Measurements in L1/E1 E6 E5a/b
• Snapshots of approx. 25 ms every 1.5 minutes
• Produced gt 160 GBytes of measurements

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Measurement Campaign Equipment

• Measurement van (property of ESA)
• Spectrum Analyser
• ESA-Equipment
• Agilent E4443A
• GPS-Systems
• Ashtech G12
• Leica GSP1200
• Antennas
• Hemispherical Antenna
• GPS-Antennas
• Directional Antennas

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Encounter Wideband Interference

• 7 MHz wide
• -87.4 dBm average Power
• Equals to 42.6 dB Interference-to-Signal-Ratio
  (ISR)

GPS carrier
Galileo BOC(1,1) carriers
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Encounter Wideband Interference

• 7 MHz wide
• -87.4 dBm average Power
• Equals to 42.6 dB Interference-to-Signal-Ratio
  (ISR)

• TDMA system
• Slot size 552 µs
• Used over whole L1 band

GPS carrier
Galileo BOC(1,1) carriers
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Encounter Wideband Interference

• 7 MHz wide
• -87.4 dBm average Power
• Equals to 42.6 dB Interference-to-Signal-Ratio
  (ISR)

• TDMA system
• Slot size 552 µs
• Used over whole L1 band
• Several sub carriers with 2 MHz bandwidth each

GPS carrier
Galileo BOC(1,1) carriers
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Multiple Encounters 1st Encounter at Bremen
Train Station
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Multiple Encounters Located between Bremen and
Hamburg
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Multiple Encounters Hamburg
Train Station
Hamburg Harbour
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Modeling of Interference

• Red generated Signal
• 3x BPSK (2 MHz symbol rate)
• Rectangular symbols
• 3 MHz between carriers
• 7 MHz total
• Time Slots of 552 µs

• Blue measured band limited Signal

The blue and red signals have different power
levels for visibility only!
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Impact Equipment and Assumptions

• DLR Software Receiver
• GPS/Galileo/GIOVE-A Acquisition and Tracking
• 4 MHz Bandwidth (3 dB), 4 Bit ADC
• Code Tracking 20 ms Integration 1 Hz Loop
  Bandwidth
• Carrier Tracking 10 ms Integration 5 Hz Loop
  Bandwidth
• Hardware
• Generators
• Extended Spirent 7790 GNSS Signal Generator (DLR
  MASTER)
• Agilent E8267D Signal Generator
• Receivers
• NordNAV R30 (4 MHz, 4 Bit ADC)
• Novatel Aviation Receiver
• In both cases Simulation with worst case
  (Interference on L1 centre frequency)

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Impact Software Results - GPS

• Loss of Lock at 35 dB ISR
• Unable to Acquire at 25 dB ISR

AcquisitionThreshold
TrackingThreshold
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Impact Software Results - Galileo E1

• Loss of Lock at 35 dB ISR
• Unable to Acquire at 30 dB ISR

AcquisitionThreshold
TrackingThreshold
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Impact Hardware Results for GPS

• NordNAV
• Loss of Lock at 40 dB ISR
• Unable to Acquire at 33 dB ISR
• Novatel
• Loss of Lock at 40 dB ISR
• Unable to Acquire at 26 dB ISR

AcquisitionThreshold
Remember The measured average power was 42.6 dB
ISR
AcquisitionThreshold
TrackingThreshold
TrackingThreshold
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Conclusions and Future Work

• Conclusions
• An interference source was identified that is a
  potentially big threat to Galileo AND future GPS
  receivers
• The interference was categorised and modelled to
  be of wideband TDMA structure
• The impact on future Galileo AND GPS receivers
  was verified by software and hardware tools and
  is considered as potentially severe
• Future Work
• Further analysis of the existing measurements to
  identify more potential interference
• Identification of this TDMA interference source
• Usage of this information for detection and
  mitigation purposes

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Thank You!