Need for Resilient PNT Has Never Been Greater

Article By : Guy Buesnel

Users of GNSS positioning, navigation and timing data must now deal with a growing spectrum of threats to their systems.

Real-world instances of Global Navigation Satellite System (GNSS) jamming and spoofing have been steadily increasing in recent years. High-profile incidents include spoofing attacks on hundreds of commercial ships in the Black Sea and repeated GNSS jamming affecting commercial aviation in Norway.

During 2019 alone, pilots reported more than 3,500 instances of GPS jamming, air traffic management organization  Eurocontrol recently disclosed.


In the U.S., the Federal Communications Commission has conditionally approved an application by satellite communications provider Ligado Networks to deploy a low-power terrestrial nationwide network in the L-band to support 5G and IoT services. The decision means that GNSS systems and devices must be capable of resisting adjacent-band radio-frequency interference at extremely high power levels while still providing extremely accurate and precise data to users.

Meanwhile, most, if not all, of the major GNSS providers are experiencing space, control, and user-segment issues. The transmitted data from satellites can contain errors or be corrupted to such an extent that it becomes practically unusable.

There is little doubt that users of GNSS positioning and timing data will be dealing with a growing spectrum of threats to their services. While the weak power of GNSS signals remains a fundamental issue for users on the ground, overdependence is another concern.

GNSS has become an “invisible utility,” its use deeply embedded in our society. We often rely on GNSS to obtain precise timing or positioning data for the operation of key elements of our critical national infrastructures. In many cases, the dependencies and reliance on GNSS-derived data are not fully understood; in some cases, they are not even identified. All of this leaves vital services extremely vulnerable to any disruption or denial of GNSS signals.

Identifying dependencies

European and U.S. policymakers have recognized the dependence of critical national infrastructure on GNSS signals, along with the vulnerability of such systems to GNSS disruption or denial.

In the U.S., “father of GPS” Bradford Parkinson has proposed a “Protect, Toughen, Augment” framework for GNSS. This triad encourages a systems-level, multi-strand approach to improving the situation when using position, navigation, and timing (PNT) data.

Elsewhere, the U.K. government commissioned a review of GNSS dependencies on satellite-derived time and position. The review recommended several measures to improve the resilience of U.K. systems.

A key aim of the U.K. report was to ensure PNT resilience at the point of use, not to prescribe technology solutions. Again, the study strongly advocates a system-of-systems approach to boosting PNT resilience.

Both approaches make clear there is no silver-bullet solution to our GNSS dilemma. Rather, there needs to be a well-coordinated approach to the problem that provides users with the education, policies, standards, and guidance needed to increase PNT resilience.

System and device testing to gauge their ability to withstand interference has become important, shedding light on whether, and how well, they can perform as expected when there is disruption or denial of GNSS services. Testing also uncovers the consequences when performance is compromised. It is an essential part of any risk assessment.

Mitigation technologies

Cost-effective mitigation should adopt the system-of-systems approach encouraged by both U.K. and U.S. policymakers. This means looking beyond GNSS device resilience to ensure operational procedures are in place to cover situations when GNSS is disrupted or denied. Where necessary, mitigation also involves augmenting or complementing the precise positioning and timing data from GNSS with information from other sensors.

Hardening existing GNSS systems could include improving antenna technology and investing in multi-constellation, multi-frequency GNSS receivers. Alternative or complementary PNT sources must also be considered, including the use of improved holdover technologies for timing and the use of additional terrestrial or space-based positioning and timing services as they become available.

Examples include time over fiber, enhanced long-range navigation (eLORAN), and broader use of low Earth orbit (LEO) satellite net-works, along with the use of inertial or dead-reckoning technology for dynamic platforms. All of these solutions offer improved resilience or robustness when implemented properly.

Improving the resilience of our GNSS-dependent infrastructure is no longer optional; the rising incidence of real-world threats makes it essential. Improving GNSS resilience and solving dependencies based on quantifiable evidence will help ensure a safer world driven by precise and reliable use of PNT services.

This is not an unsolvable problem. We just need to act.

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