Tac Talks: GNSS ‘in Troubled Waters’

Introduction

Technical Lecture - GNSS ‘in Troubled Waters’ - Presentation to the AIN by Professor Chris Rizos

On 11 September 2019, at the regular monthly meeting in Sydney, Professor Chris Rizos provided a most interesting and relevant presentation to the AIN, Nautical Institute and CMM on the challenges facing Global Navigation Satellite Systems (GNSS) into the future.

The Challenge - High Accuracy with High Assurance!

While the last 20 years has seen the costs of accessing GNSS dramatically drop and the services have become readily accessible and widespread, an emerging challenge is that it is also cheap and easy to jam or spoof the GNSS signals - either deliberately or inadvertently.

To date it has been acceptable to have lower accuracy with more assured services for some industries (such as aviation and maritime), and vice versa for other commercial uses. However, there are increasingly more applications that require greater accuracy and more assured services. Professor Rizos indicated that this was the likely growth area for future GNSS services.

Multi-Constellation GNSS

Prof Rizos noted that the various GNSS satellite constellations in combination now had a very large number of satellites visible at any one time on any location on Earth, and that multi-constellation capable receivers was at least part of the answer for improved accuracy and assuredness.

Multi-GNSS is in fact a ‘smorgasbord’ of systems, signals and services, and brings considerable advantages. The large number of satellites provide readily available signals, the multiple constellations improve robustness, and the multiple frequencies used across the constellations improve accuracy.

However, while the GNSS’ are in effect ‘global utilities’ used by billions of people around the world, they are controlled and operated by powerful nation-states. The US has built the GPS constellation to its full strength (32 satellites), the other constellations (GLONASS - Russia; Galileo - European; and BeiDou - China) are currently at a total of 64 satellites, and expect this number to continue to increase to over 90 satellites at maturity. There are also other smaller constellations being fielded (including QZSS, NAVIC and KPS).

Space-Based Augmentation System

Prof Rizos noted the rise of Space Based Augmentation Systems (SBAS) around the globe as a partial answer to providing GNSS assurance. SBAS offers improved positioning accuracy (sub-metre) and also improved integrity - contributing to meeting the emerging requirements of many commercial users. A trial system is currently being tested over the Australia region (the trial commenced in 2018, but has been extended into 2020). Australia is a late-comer to the capability, and has been the last major geographic area to establish an SBAS capability.

In the past, determining the integrity of the GNSS signal has traditionally been the responsibility of the industry sector seeking to use the GNSS, e.g. aviation, marine, etc. For example, SBAS was one such response by the aviation community to the GNSS integrity challenge for aviation.

Alternates to GNSS

Increasingly, GNSS users seeking higher levels of assurance are recognising that GNSS should not be the only positioning, navigation and timing (PNT) technology for mission-critical, safety-critical or liability-critical applications. It will be the primary capability for the foreseeable future, but needs to have another system (or systems) as backup.

There are no shortage of alternatives to GNSS, including several Australian-designed options. One such system is WASP, being developed by CSIRO that uses wireless tracking for indoor applications (such as athletes and mining/mine safety). However, it has limited coverage.

No. 3 Control and Reporting Unit deployment site at Crowdy Head in NSW - supporting Exercise TASMAN SHIELD 2021.

Some of the alternatives are appropriate for the mass market, while others only offer a localised and niche capability. Few can provide high accuracy PNT capability indoors or where signals are obstructed. One is the Locata technology developed by a Canberra-based company that is currently being deployed at several automated container ports.

One of the key drivers (no pun intended!) of this move to GNSS backed-up by multiple alternative PNT systems with differing characteristics is the need for ‘trustworthy positioning’ for highly automated driving (known as ‘HAD’) and for machine automation in general (agriculture, port operations, logistics, construction, mines, etc.) as well as autonomous air, land and sea platforms.

For these HAD and autonomous vehicle applications the ‘design space’ is relatively high accuracy and high integrity. However, there is still work to be done to define exactly what the accuracy and integrity requirements are according to each industry or user case.

For example, positioning in vehicles is going from ‘passive’ to ‘active’ levels of autonomy, with passive providing a backup to a human primarily in control, and ‘active’ for (near) full autonomy of operation. This passive to active range includes supporting simple navigation to information about traffic to warnings about hazards to actively avoiding hazards to enabling autonomous operations.

Prof Rizos noted that there are many inherent errors and inaccuracies that need to be considered when using GNSS. GNSS errors will be the result of errors introduced through routine operations of the satellite system, equipment malfunctions, environmental effects, and other factors. Some examples are:

A simplified taxonomy of man-made RF threats to GNSS.

• Unannounced or unplanned manoeuvres of the satellites
• Faulty clock, signal generator, or antenna positioning
• Faulty broadcast messages
• Atmospheric effects
• Space weather (e.g. solar storms)
• Ionospheric disturbances
• Correction messages from SBAS
• Loss of uplink communications
• Software, and other, errors

Prof Rizos noted that increasingly there are challenges to the integrity of the GNSS arising from interference, including:

Examples of readily available modest cost (US$200-300!) GNSS jamming systems.

• Jamming
• Non-intentional (e.g. multipath, M-GNSS, out-of-bound emissions, etc.)
• Deception
• Spoofing
• Meaconing

Protect, Toughen and Augment (PTA)

Prof Rizos noted that one of the founders of GPS, Dr Bradford Patterson, has recommended a coordinated program of Protect, Toughen and Augment (PTA) as the best way ahead.

Protect...the clear and truthful signals

• Legal responses, e.g. ban jammers, penalties, prosecute offenders
• Geolocate jammers, apprehend offender and neutralise jammer threat
• Ban use of transmitters in neighbouring bands
• Designate GNSS as “Critical Infrastructure”

Toughen...user receivers to use GNSS

• Increase receiver jam resistance, e.g. signal processing, antennas, etc.
• Authentication of signals or services, “smart” receivers, etc.
• Diversify, e.g. use other GNSS signals and/or frequencies

Augment...or substitute PNT sources

• Densify and diversify signal sources, e.g. interoperability and compatibility
• Worldwide integrity monitoring, e.g. IGMA, A-RAIM, SBAS
• Complementary/alternative PNT technologies, e.g. eLoran, Locata, etc.

Several improvements could be made to GNSS signals to further enhance PTA including improved receiver signal processing, using beam-forming antennas, use of more non-GNSS technologies, ultra-tight integration with inertial measurement units, multi-sensor systems, and using integrity monitoring service(s).

Real-World Examples of GNSS Interference

There is increasing evidence of wide-ranging GNSS jamming and spoofing, from state-led activities through to ‘lone wolf privacy patriots’.

Recently a year-long German-led research project was conducted aboard a cargo ship that travelled ocean routes across the globe. It detected interference in the GNSS frequencies. While most interference was found near the port areas, there was still some interference in the open ocean. The results of this study are still being analysed and further papers are expected to be published in the future.

Left: GNSS interference was detected along much of the route of this ship over a one year period. Right: HMAS Ballarat's boarding team transfers seized small arms ammunition and bags of chemical fertiliser to HMAS Ballarat for disposal. Photographer: LSIS Bradley Darvill.

Ships sailing in the Strait of Hormuz and the Persian Gulf have been experiencing GPS jamming that the US has attributed to deliberate jamming by Iran. An advisory was issued in August 2019 warning vessels of this GNSS jamming. In addition to GPS jamming, commercial vessels have reported bridge-to-bridge communications spoofing and other interference. It appears that Iran seeks to have non-Iranian vessels get off track and enter Iranian waters where they can be seized.

Also GNSS interference, including with the maritime safety system (AIS) has been reported in Shanghai Harbour. In one case, a US flagged vessel noted erroneous readings of position and speed for other ships nearby, and also lost signal for both GPS receivers on the vessel for an extended period.

Impact of GNSS Interference

GNSS is a critical infrastructure and even relatively brief interruptions of the GNSS signal will be costly to industry dependent on accurate PNT. It is also a vital military capability. Potential consequences of GNSS performance degradation include:

• Reduced operational capability and effectiveness
• Reduction in safety and potential loss of life
• Environmental damage
• Economic losses
• Loss of ‘timing and synchronisation’ can severely disrupt communications, data networks, electricity grid, etc.

Unfortunately, many authorities responsible for critical systems seem ill-prepared for GNSS failure. This is partly due to the high cost of maintaining alternatives to GNSS when GNSS is so cost-effective.

Head of Air Force Capability Air Vice-Marshal Cath Roberts AM, CSC, right, speaks with Professor Russell Boyce about the M2 CubeSat at the University of NSW, Canberra. Photographer: SGT Oliver Carter.

Summary

Prof Rizos concluded by noting that GNSS is a critical civilian infrastructure and a vital military capability. GNSS has been a remarkably reliable PNT technology, but satellite signals are very weak and can be disturbed. GNSS can suffer loss of availability or integrity functions due to natural causes or human actions. A new trend is an increasing prevalence of GNSS jamming and spoofing. There is an increasing need for trustworthy positioning... within required navigation performance limits (e.g. accuracy, integrity). Addressing all GNSS vulnerability is a challenge...it is expensive and complicated.