Maritime navigation systems need to function effectively in GNSS‑denied and degraded environments. Controlled reception pattern antennas (CRPAs) can improve GNSS resilience, but it's far from simple.
Since the earliest days of maritime navigation, mariners have needed a means to north-find, and so the simple compass became a core component of navigation. With the advent of steel hulls the use of magnetic compasses quickly became challenging. Innovative solutions emerged to offset the magnetic signatures of early steel ships, but as ships got bigger (today’s bulk container ships can exceed 200,000 tonnes fully laden) the challenge of measuring the earth’s magnetic field became near impossible to achieve with a magnetic compass.
Today’s modern marine compass is a highly sophisticated digital device based on GNSS (GPS, Galileo) which precisely measures the difference in position and time-of-arrival between two antennas (a fixed distance apart) and is combined with an inertial navigation system (INS) comprising a 3-axis accelerometer and gyroscope for pitch, roll, and yaw, to create a moving-baseline of the ship’s attitude, heading, and course information.
With most commercial vessels these days operating with a limited crew there is an increasing dependence on autopilots to maintain course and navigate. Such autopilots are entirely reliant on GNSS-based compasses to provide continuous and reliable navigation data to the vessel's autonomous control system.
GNSS is also key for providing data for use within safety systems such as the Automatic Identification System (AIS), a core component of the International Maritime Organization’s SOLAS (Safety of Life at Sea) that provides safety-critical infrastructure for global shipping.
AIS is mandatorily fitted aboard more than 1.6m merchant vessels and passenger ships for broadcasting the vessel's position, speed, heading, and identity to other vessels in the vicinity to enhance safety, transparency, and traceability across global maritime traffic.
For both autonomous navigation and AIS, GNSS is critical. But GNSS signals are inherently weak, and without protection are easily overpowered by strong RF signals emitted by attackers intent on causing disruption. Such jamming attacks have the effect of degrading positional accuracy, potentially to the point of service denial, whilst more sophisticated spoofing attacks fool the GNSS receiver into believing it's somewhere that it's not.
Meaconing is the most insidious form of spoofing, modifying the position by only small amounts thereby hijacking the navigation system and steering the ship on a new pirated course without tripping alarms that alert the crew.
Any disruption to GNSS through jamming or spoofing compromises positional accuracy and attitude awareness, increasing the risk of collisions and groundings that may endanger crew safety, result in oil spills, or even lead to vessels unintentionally violating territorial waters.
Incidents of GNSS interference have surged since 2022 to more than a 1,000 ships per day, and is now affecting all main commercial shipping corridors around the Eastern Mediterranean, Red Sea, Persian Gulf, and the Black Sea.
Maritime hotspots such as in the Black Sea and around the Strait of Hormuz are particularly plagued with GNSS interference from a range of sources including shore-based high-power jammers, shipborne/mobile jammers and Electronic Warfare spillover that create corridors of degraded GNSS availability that can extend hundreds of km and last for many hours for vessels traversing them.
Entering such regions typically leads to a loss of GNSS service resulting in immediate ECDIS (Electronic Chart Display and Information System) warnings followed by frozen or incorrect positions and AIS going dark - a huge risk to maritime safety.
In the face of this disruption, insurance premiums are doubling or tripling with some underwriters limiting the maximum value they're willing to insure, and some routes potentially becoming uninsurable causing ships to reroute with substantial increases in voyage time and cost.
The issue of GNSS disruption within the maritime industry has become critical, the IMO now flagging it as a systemic risk that endangers the safety of crew and cargo, and with the very real possibility of it causing a cascade of vessel collisions totalling billions in damages.
And it’s not just shipping that’s affected. GNSS is fundamental to many other maritime operations including its extensive use in offshore drilling and construction vessels for maintaining station with cm to sub-meter accuracy; any loss of signal creating numerous environmental and safety hazards.
Ensuring maritime positioning and navigation systems can function effectively in GNSS‑degraded and denied environments is of utmost importance.
The answer is to take a layered approach, developing a navigation system built around a tightly-coupled GNSS-assisted INS to provide robust navigation data as the vessel moves through GNSS-contested waters.
In such an approach, the INS provides a moving-baseline of the vessel’s attitude and course information as well as position and velocity with corrections from the GNSS component, and with a dual-GNSS configuration contributing heading. As the vessel starts to experience interference and jamming, the system relies increasingly on the INS component for position and velocity (dead reckoning).
But it will only be able to do so for a short while. Without GNSS to correct it, the INS measurements start to drift, and in periods of heavily-disrupted or denied GNSS the INS data will quickly degrade and become unreliable for navigation, and insufficient for AIS - nowhere near enough time for the vessel to transition through many of the areas now experiencing GNSS disruption, and likely to result in the vessel becoming paralysed and unable to safely proceed.
Hardening the GNSS component to make it more resilient against interference and jamming is therefore vital.
Driven by the military use of autonomous drones, the primary solution to jamming is to use controlled reception pattern antennas (CRPAs) that adapt their antenna pattern to null out sources of interference thereby enabling the GNSS receiver to maintain lock for longer, and speed reacquisition time if lock is momentarily lost. In doing so, CRPAs can be effective in shrinking the footprint of GNSS-denied zones and boost performance in GNSS-contested areas.
In the case of a GNSS compass though, simply substituting the fixed radiation pattern GNSS antennas for commercial off-the-shelf CRPAs doesn’t work.
Such CRPAs tend to provide insufficient antenna performance for the precise phase measurements needed for north-finding. Many of these CRPAs also significantly impair and compromise the anti-spoofing and anti-meaconing algorithms deployed in modern GNSS receivers (such as Septentrio’s ASP+), in some cases rendering them unusable and undermining the overall resilience of the navigation system.
Having already disrupted the resilient GNSS market with a CRPA providing the highest performance and lowest SWAP-C in category, this was a challenge that Helix Geospace set out to solve.
Combining its industry-leading CRPx GNSS Anti-Jamming System with an advanced INS, Helix has developed the CRPA-based Resilient GNSS-assisted INS that successfully meets market needs across a wide range of maritime applications.
Using its proprietary and patented DielectriX Antenna and Array technology ensures phase coherence is maintained for accurately computing vessel heading, minimises multipath sensitivity due to clutter and sea reflections, and through multi-band/multi-constellation support maximises the number of satellites in view for optimal navigation. Crucially, GNSS signal integrity is also maintained, ensuring that downstream anti-spoofing and anti-meaconing algorithms are uncompromised.
With >50dB of jamming suppression (J/S >100dB), and an ability to mitigate in-band, adjacent band, high-power & multi-jamming scenarios (non-blocking), the Resilient GNSS-assisted INS ensures that vessels can continue operations in even the most aggressive of GNSS-contested waters.
All this, and in a compact integrated form factor with minimal cabling and standard interfaces for convenient retrofitting to existing vessels.