GPS and Interference: Ghosts, Fear or Reality

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GPS and InterferenceGhosts, Fear or Reality?

• Prof.dr.ir. Durk van Willigen
• reelektronika b.v. / GAUSS Research Foundation
• HSB/NIN/NVG Workshop GPS soms zit het tegen
• Delft, 19 April 2002

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GNSS and Jamming

• Why do we discuss this anyway?
• Jamming, Spoofing and Meaconing
• Is it difficult to disable GNSS?
• Society and Single-Point-Failure Infrastructures
• Who might do that?
• Military Demands and Fears
• Safety-of-Life Operations
• Civil-Users Unawareness
• Law-enforcement
• Governmental Fairy-Tales and Responsibility

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Heavens Fears

• Volpe Vulnerability Report
• 29 August 2001
• http//www.navcen.uscg.gov
• Jamming
• Simple 1 Watt (GSM-like) 10/85 km (loss/no acq)
• GPS-like 1 Watt (GSM-like) 1000 km (no acq)
• Spoofing
• Mislead user by broadcasting GPS look-alike, but
  wrong signals
• Meaconing
• Rebroadcast real GPS signals

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From Moscow with Jammers
4 Watt L1 L2 GPS GLONASS 4,000
Source Aviation Week Space Technology
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American Reply - 1
Source Aviation Week Space Technology12
October 1998
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American Reply - 2
Langhorne Bond ATCA, Dublin,20-Jul-2001 US DoD
never commits its personnel, ordnance or vehicles
to GPS sole-means navigation
Source Aviation Week Space Technology23
November 1998
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GNSS and Jammer Power Levels

• GPS
• Approximately 50 Watt transmitter power to
  illuminate about 200 million km²
• ? 38 of earth surface gt -126 dBW/m2
• gt -155 dBW at antenna output (semi spherical)
• GPS Specifications gt -160 dbW at antenna output
• Jammer
• 1 mW yields catastrophic 40 dB stronger than
  GPS-signal level at distance of 175 meters
• 1 W (GSM power level) gives range of gt 5 km

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Simple L1 Jammer

• TNO-FEL lab prototype
• 1 mW output
• Range gt125 meters (C/A)
• 5 switching carriers
• Power consumption9 V - 30 mA
• Piece of cake for any smart telecom student
• 1 Cubic inch feasible

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Hackers and Worse

• Mini transmitter in mobile phone (GSM)
• Portable and not visible
• Hide in stone, football, cow manure, childrens
  toys
• Random, or remote/noise controlled on/off
  switching
• Weather balloon is robust carrier
• Smart spoofing makes operation fail while not
  being detected by RAIM
• GPS for toll roads is exiting and predictable
  challenge
• Smart telecom students may learn GPS jamming
  skills at ITS faculty of TU Delft
• Compare challenge of jamming with that of hacking
  important computer networks

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Who Causes Interference?

• Technical enthusiasts (unpredictable)
• Students or people that just cannot withstand the
  challenge of executing large influence
• Criminals (very predictable)
• Car or cargo theft, free toll-road rides
• Terrorists (likely)
• Block airports, rescue and police
• Military (of course)
• Jamming potential enemy on GPS as well as on
  Galileo/GLONASS

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Terrestrial Players

• Political and economical terrorism
• Avoid single-point-failure character (SPF)
• Langhorne Bond (Former FAA-administrator)
• Refreshing, clear, logical, consequent
• Authorities
• US is active, PCCIP (15 July 1996)PCCIP
  Presidents Commission on Critical Infrastructure
  Protection
• Europe ??
• Is there a problem? If so, please dont tell,
  dont ask!
• Users
• Uninterested and ignorant, especially in Europe

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The Smart American ?

• GPS is there, its accurate, and it is for free
• C/A code on L1 and L2 to solve ionosphere delay
• SA is off
• Dan Goldin (NASA-boss) ? GNSS 2000 in Edinburgh
  (UK)
• Langhorne Bond SA is OFF because jamming works
  !!
• Some Europeans Galileo threat works !!
• GPS can do everything that Galileo can?
• USA publicly declared current Galileo frequency
  plan unacceptable
• Office of the Spokesman, Washington, DC, USA,
  7-Mar-02

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The Smart European ?

• Galileo
• More satellites and better high latitude coverage
• Good for Europe
• Maintain level of navigation science
• Serve European industry and users
• Better political and strategic balance between US
  and Europe
• Questions
• Better than GPS?
• For free?
• In many aspects not dissimilar from GPS SPF !!
• Will Europe phase out all terrestrial systems
  without any proof that satellite systems can
  serve all users needs?

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US Goals

• Keep world leadership in navigation for
  strategic, economic and military reasons
• Keep Galileo grounded or stay ahead of it
• Continuous upgrading of GPS
• Continuation of implementation of WAAS and LAAS
• Terrestrial systems will not be phased out as
  long as satellite systems have not proven
  required level of reliability for safety- and
  environmental-critical transport operations
• See FRP 2001, published by DoD and DoT on
  19-Mar-02

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Interference

• Interference stems from
• Intentional/unintentional man-made signals
• Other GPS satellites (cross-correlation ? 0)
• Multipath
• Effectiveness of interference is characterized
  by
• Frequency
• Modulation
• Signal-to-Interference Ratio (SIR) at the input
  of the GPS receiver
• D.J. Moelker, Interference in Satellite
  Navigation and Mobile Communication, Delft
  University Press, 1998, ISBN 90-407-1762-1/CIP

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Counter Measures

• Improve signal-to-interference ratio in the
• Spatial domain by
• Null-steering antenna
• Low-multipath antenna (Ohio University)
• Beam-steering antennas
• Signal amplitude/time domain by
• Estimate and remove interference
• Signal frequency/phase domain by
• Notch filters

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Null-Steering Antenna

• Omni-directional pattern with deep null towards
  jammer
• Mobile users need automatic steering to
  anticipate movements of antenna
• Simple antennas do reject one jammer only
• Larger antennas may reject multiple jammers

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2-Element Null-Steering Antenna
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Low-Multipath Antenna

• Used for stationary application, like DGPS
  reference stations at airports (LAAS)
• Antenna is DME-like tall vertical tube
• Rejects ground-based multipath and interference
• Early types required dual receivers with careful
  phase-offset calibration
• Newer types operate with single receiver

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Beam-Steering Antenna

• Array of multiple antennas to form beams towards
  selected satellites
• Gain and directivity of antenna depends on size
  of array
• Jamming rejection is ratio of antenna gains
  toward satellite and jammer
• Complex steering for multiple-satellite tracking
  makes costs high
• Mobile application feasible (aviation)

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2-Element Beam-Steering Antenna
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Signal Processing

• Improve SIR by maximizing discrimination between
  GPS and interference signals
• Estimate (characterize) interference in the three
  signal domains
• Frequency and phase
• Amplitude
• Modulation
• If successful, remove it !
• Deselect entire or part of GPS signal that can be
  characterized as non-repairable
• Multipath

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Military Aspects

• USA wants capability to use GPS while denying GPS
  AND Galileo to the enemy during military actions
• M-code and C/A jamming
• Frequency planning conflict USA/Europe
• USA wants capability to mislead GPS-using enemy
  through spoofing
• Enemy wants to deny GPS and Galileo to the USA to
  make them less vulnerable

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L1/C Frequency Spectrum
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L2/L5 Frequency Spectrum
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L1 Spectrum (US at Ease)
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L1 Spectrum (US in Action)
Spot Beam Mode-138 dBW (20 dB)
All non M-code signals on L1, L2, and L5 can be
jammed
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Targets to be Jammed?

• Vehicles to be stolen
• Vehicles tracked for road-tolling
• Police forces
• Military
• Smart bombs
• Small Navy boats
• GLS
• GPS-dependent competitors

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Conclusions

• Investigate and quantify safety and economic
  risks of your GNSS-controlled operations
• The US (PCCIP) recognizes Single-Point-Failure
  risks more than Europe
• Avoid single-point-failure infrastructures by
  applying highly dissimilar systems
• If continuity of service is essential have always
  a dissimilar full backup system standby
• Some European governments ignore discussions
  about responsibility and continuity of service

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Final Remark

• GPS is a devils dilemma
• GPS is a too good offer you cant refuse, but
• GPS is too vulnerable to unconditionally rely on
• So, its just up to you to judge your benefits
  and your risks!