What do we mean by GNSS resilience?

GNSS signals come from 20,000km away and hence are inherently weak and vulnerable to RF interference and intentional jamming.

This disruption impairs the ability of the GNSS receiver to calculate position to a good level of accuracy and may even lead to complete denial of service, whilst spoofing will trick the receiver into believing it's somewhere that it's not.

GNSS resiliency is therefore all about finding ways to make the GNSS system (antenna + receiver) more resilient to external interference.

Jamming vs Spoofing

Is GNSS resilience the same as Assured PNT?

GNSS resilience is a component part, but Assured PNT looks beyond GNSS to include supplementary mechanisms for obtaining PNT data; for instance, using an inertial navigation system (INS), LEO-based PNT service (such as Iridium PNT) or a regional terrestrial solution (e.g., R-Mode in the Baltic region) where applicable.

Where can resiliency be improved within a GNSS system?

GNSS receiver

GNSS receiver

At a basic level, some resiliency measures can be built into the GNSS receiver itself. For instance, notch filtering to detect and remove interfering signals within the GNSS bands.

Good as some of these mechanisms can be, they're no match for sophisticated jammers that are specifically targeted at overcoming the GNSS receiver's resources or saturating its RF front end.

CRPx

GNSS antenna

In many ways, the GNSS antenna is the best first line of defence against interference and jamming.

A passive horizon nulling antenna such as Helix's HNA is one approach: providing reduced sensitivity to signals at low elevations, thereby blocking out ground-based interference and jammers.

Handling more sophisticated attacks involving numerous mobile jammers and more complex waveforms requires an antenna that can dynamically optimise its reception pattern to neutralise the jammers whilst maximising GNSS signal reception - Controlled Reception Pattern Antennas (CRPAs) do just that; Helix's CRPx is a good example.

CRPA + receiver system

GNSS CRPA + receiver

Optimum resiliency can be achieved by combining the two; the CRPA removing interference and jamming to deliver a clean GNSS signal to the receiver. The receiver then employing detailed signal processing to search for and reject any anomalies that might have been introduced via spoofing.

For this to work, it's essential that the CRPA outputs a clean GNSS signal otherwise any artefacts are likely to trigger false-positives. Unfortunately, this is not the case for many CRPAs, their focus on jamming suppression creating anomalies that wreak havoc downstream in GNSS receivers.

Not so with Helix's CRPx which has been specifically engineered to work well with all GNSS receivers and their anti-jamming/spoofing capabilities.

Can multi-frequency, multi-constellation improve GNSS resiliency?

To some extent, yes; utilising multiple GNSS bands (e.g., L1 + either L2 or L5) and/or more than one GNSS constellation (e.g., GPS & Galileo) makes it a lot harder for a jammer to successfully disrupt all of the available GNSS satellite signals.

Or at least, that used to be the case. With multi-band/multi-constellation jamming equipment now easily accessible from the Internet, this mitigation tactic is no longer sufficient - the jammers must be combated directly using technology such as a CRPA.

Are there any fallback options for GNSS?

For heavily-contested GNSS environments, such as in conflict zones, where GNSS service may be completely denied, potential options might include:

  • LEO-based PNT services - benefit from much stronger satellite signals (due to the low Earth orbit), although are not completely immune to jamming, and positional accuracy & latency also tends to fall behind that of GNSS.

  • INS systems - derive their positioning through a range of motion sensors hence can continue providing positioning through dead reckoning. But only for a short while - without GNSS to correct it, the INS will start to drift, and can quickly become unreliable for navigation.

So, a better approach is to improve GNSS resiliency?

Yes

Improving resiliency will reinstate some level of GNSS availability, even in heavily-contested regions, and thereby reduce large zones of GNSS-denial into much smaller pockets of GNSS outage.

The INS component of the system can then 'plug the gap' during these outages, with GNSS position fixes becoming periodically available for resetting the errors accumulating in the INS.

Helix_GNSS-assisted INS with & without protection

What is the best solution for resilient PNT?

  1. First and foremost, improve resiliency of the GNSS component through combining CRPA anti-jamming with a receiver's anti-spoofing capabilities.  Helix's CRPx is an ideal candidate and proven to work very well with all GNSS receivers.

  2. Where needed, incorporate this resilient GNSS component into a GNSS-assisted INS navigation system for traversing heavily-contested areas (such as conflict zones).

  3. If available, integrate the GNSS/INS system with a regional terrestrial service (e.g., R-Mode in the Baltic region) and/or a LEO-based PNT as a further backup.

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Engineered for a wide range of applications

Maritime

GNSS is critical for navigation in modern maritime operations but increasingly under threat.

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Drones (UAVs)

Resilient GNSS in a compact form factor is fundamental to the operation of drones & UAVs.

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Military UxVs

Unmanned aerial and surface vehicles (UxVs) are revolutionising modern warfare but crucially dependent on resilient GNSS.

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Civil Aviation

Mitigating inadvertent GNSS interference from conflict zones is paramount to ensuring the safety of aircraft and crew.

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