global navigation satellite system (gnss) … vulnerabilities.pdfpage 1 global navigation satellite...

Global Navigation Satellite System (GNSS) Vulnerabilities

CNS/SG/5

WP/10A

Prosper Zo’o Minto’o, Regional Officer ICAO Communication, Navigation

and Surveillance (CNS)

Eastern and Southern African Office

1. Introduction

2. GNSS signal vulnerabilities

3. Assessing likelihood of GNSS outages

4. Reducing the likelihood of GNSS outages

5. Mitigating the effects of GNSS outages

6. Outcome of AN-Conf/12 on GNSS

7. Conclusion

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Presentation

1 - Introduction

• GNSS is being introduced throughout the world:

– Potential to meet performance requirements for all phases

of flight

– Improvement of safety and efficiency of air navigation

• It is essential that the service providers

– identify the vulnerabilies of this system; and

– develop the necessary mitigations

2 – GNSS signal vulnerabilities - Interference

• Source of interference: low signal power received from GNSS core satellite

constellations and satellite-based augmentation system (SBAS)

• GBAS service depends on the core satellite signals while the very high

frequency (VHF) data broadcast of a ground-based augmentation system

(GBAS) is more difficult to interfere (its signal power is similar to that of

terrestrial navigation aids)

• Interfering signals are limited to line-of-sight propagation

– (e.g. the interference region at 600 m (2 000 ft) above ground level is inherently limited

to approximately 110 km (60 NM) for a ground-based interferer).

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2 - GNSS signal vulnerabilities

- Interference

• Unintentional interference

– Majority of reported GNSS interference events have been traced to on-board systems

– Sources of unintentional interference (e.g. spurious emissions or harmonics of VHF communications equipment and the out-of-band and spurious emissions from satellite communications equipment).

– Portable electronic devices can also cause interference to GNSS and other navigation systems.

• Sources of unintentional interference

– Low power transmitters can cause interference to GNSS

– To be taken into consideration though civil aircraft interference have not been recorded so far

ACARS

Service

Processor

ARINC / SITA

Private

WANs

VHF

Remote Ground

Station

Routing tables

• Spoofing is the intentional corruption of the navigation signals to cause

aircraft to deviate and follow a false flight path

• Spoofing of satellite-based GNSS signals is technologically much more

complex than spoofing of conventional ground-based navigation aids

• (Spoofing of the GBAS data broadcast is as difficult as spoofing

conventional landing aids).

• Detection through normal procedures (e.g. by monitoring of flight path

and distance to waypoints and by radar surveillance).

• GPWS and ACAS provide additional protection against collision with the

ground and with other aircraft.

2 - GNSS signal vulnerabilities

- Spoofing

• Precipitations

– Heavy precipitation attenuates GNSS satellite signals by only a small fraction of 1 dB and does not impact operations.

• Tropospheric effects

– Tropospheric effects are addressed by system design and do not represent a vulnerability issue.

• Ionospheric effects

– Rapid and large ionospheric changes, and scintillation. Ionospheric changes result in range errors that must be accounted for in system design.

– Scintillation may result in temporary loss of GNSS signals from one or more satellites.

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2 - GNSS signal vulnerabilities – Ionospheric

and other atmospheric effects

• Ground segment – Constellation control segment failure or human error can potentially

cause the failure of multiple satellites

• Space segment – There is a risk of an insufficient number of satellites in a given

constellation due to lack of resources to maintain a constellation, launch failure(s) or satellite failure.

• Service interruption or degradation – National emergency situation

– Denial of service in a limited area

– Degradation or denial of core satellite or satellite augmentation signals throughout the coverage area.

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2 - GNSS signal vulnerabilities–

Other vulnerabilities

• Operational risks associated with GNSS vulnerabilities

– Likelihood of GNSS outage

• Unintentional interference

• Operational experience is the best way to assess this risk. The likelihood of unintentional interference is often a function of geography.

• Large cities with significant radio frequency (RF) interference sources, industrial sites, etc., are more prone to the unintentional interference than remote regions

• Intentional interference

• Because of the low power of GNSS signals, it is possible for low power transmitters to jam the GNSS signal. While there have been no recorded instances of intentional jamming directed at civil aircraft, the possibility of intentional interference must be considered and evaluated as a threat.

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3 – Assessing GNSS outages risks

– Ionospheric effects

•Rapid and large changes in the ionosphere are frequently observed near the geomagnetic equator, but their effect is not large enough to impact en-route through non-precision approach operations.

For approach with vertical guidance (APV) and precision approach (PA) operations, the effects of these changes can be assessed and mitigated when designing augmentation systems.

•Ionospheric scintillation

•Ionospheric scintillation is insignificant at mid-latitudes. In equatorial regions, and to a lesser extent at high latitudes, scintillation may result in the temporary loss of one or more satellite signals.

• Scintillation can interrupt reception of broadcasts from a SBAS geostationary orbit (GEO) satellite.

3 – Assessing GNSS outages risks

• The impact of a GNSS outage on navigation services depends on the

following factors:

– type of airspace,

– air traffic density,

– level of service,

– availability and equipage of other navigation systems, radar

surveillance, extent of outage,

– outage assessment, and

– weather conditions

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3 - Assessing impact of GNSS outage

• The impact of a GNSS outage on other services should also be

considered. GNSS is

– frequently used as a source of precision timing information within

communication and radar systems, and may be used for automatic

dependent surveillance (ADS) services. Timing vulnerabilities can be

addressed through system design.

3 - Assessing impact of GNSS outage

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• Installation and operation

– On-aircraft interference can be prevented by proper installation of

GNSS equipment, its integration with other aircraft systems (e.g.

shielding, antenna separation, out-of-band filtering) and restrictions

on the use of portable electronic devices on board aircraft

– Spectrum management

• creation of regulations/laws that control the use of spectrum;

enforcement of those regulations/laws; and vigilance in evaluating

new RF sources (new systems) to ensure that they do not interfere

with GNSS.

• New signals and constellations

• Stronger signals, diverse frequencies, additional

satellites/constellations, future GEO satellites using satellites

which lines of sight are separated by at least 45°.

4 – Reducing the likelihood of

GNSS outages

• Inertial navigation systems and receiver technologies :

– Use of INS RNAV capability after the loss of GNSS or other position updating

– Use of technologies that add robustness to GNSS receivers to mitigate interference : Anti-jam technologies include advanced antennas (e.g. spatial nulling) and receiver signal processing techniques

• Procedural methods

– aircraft can revert visual navigation, ATC, air-to-air communications within non - ATC or non - radar airspace

• Terrestrial radio navigation aids

– RNAV DME supporting infrastructure (en route, TMA and approach within area coverage), or ILS/MLS infrastructure for precision approach.

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5 – Mitigating the effects of GNSS

outages

• Recommendation 6/7–Assistance to States in mitigating global navigation satellite system vulnerabilities

• Recommendation 6/8–Planning for mitigation of global navigation satellite system vulnerabilities

• Recommendation 6/9–Ionosphere and space weather information for future global navigation satellite system implementation

6 - AN-Conf/12 & GNSS

• That ICAO:

• a) continue technical evaluation of known threats to the global navigation satellite system, including space weather issues, and make the information available to States;

• b) compile and publish more detailed guidance for States to use in the assessment of global navigation satellite system vulnerabilities;

• c) develop a formal mechanism with the International Telecommunication Union and other appropriate UN bodies to address specific cases of harmful interference to the global navigation satellite system reported by States to ICAO; and

• d) assess the need for, and feasibility of, an alternative position, navigation and timing system.

6 - Recommendation 6/7–

Assistance to States in mitigating global navigation satellite system vulnerabilities

• That States: – a) assess the likelihood and effects of global navigation satellite system vulnerabilities in their

airspace and apply, as necessary, recognized and available mitigation methods;

– b) provide effective spectrum management and protection of global navigation satellite system (GNSS) frequencies to reduce the likelihood of unintentional interference or degradation of GNSS performance;

– c) report to ICAO cases of harmful interference to global navigation satellite system that may have an impact on international civil aviation operations;

– d) develop and enforce a strong regulatory framework governing the use of global navigation satellite system repeaters, pseudolites, spoofers and jammers;

– e) allow for realization of the full advantages of on-board mitigation techniques, particularly inertial navigation systems; and

– f) where it is determined that terrestrial aids are needed as part of a mitigation strategy, give priority to retention of distance measuring equipment (DME) in support of inertial navigation system (INS)/DME or DME/DME area navigation, and of instrument landing system at selected runways.

6 - AN-Conf/12

Recommendation 6/8–Planning for mitigation of global navigation satellite system vulnerabilities

That ICAO:

• a) coordinate regional and global activities on ionosphere characterization for global navigation satellite system implementation;

• b) continue its effort to address the global navigation satellite system (GNSS) vulnerability to space weather to assist States in GNSS implementation taking into account of long-term GNSS evolution as well as projected space weather phenomena; and

• c) study the optimum use of space weather information that is globally applicable from low to high magnetic latitude regions for enhanced global navigation satellite system performance at a global context.

That States:

• d) consider a collaborative approach to resolve ionospheric issues including ionospheric characterization for cost-effective, harmonized and regionally suitable global navigation satellite system implementation.

6 - AN-Conf/12

Recommendation 6/9–Ionosphere and space weather information for future global navigation satellite system implementation

7 - Conclusion

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• States should :

– Assess GNSS vulnerability in their airspace :

• Unintentional interference (environment), intentional interference (security)

• Ionospheric scintillation in equatorial and auroral regions

• Other vulnerability

– Implement appropriate mitigations depending on

– the airspace in question; and

– the operations that must be supported.

• Mitigations should ensure safe operations in transition to

GNSS and enable States to :

– Avoid the provision of new terrestrial navigation aids

– Reduce existing terrestrial navigation aids, and

– Discontinue them in certain areas.

7- Conclusion

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