His Coordinates


“The threats of interference, jamming and spoofing are real and serious”

Jul 2018 | No Comment

Professor David Last

Consultant Engineer and Expert Witness in an interview with Coordinates while sharing his views on a range of issues pertaining to GNSS technology

This is a world of multi-GNSS systems. What advantages do you see about this scenario?

The advantages to countries or regions of providing their own GNSS are political, not technical. Indeed, so many satellites are now transmitting in the same narrow radio bands that the additional ones are raising the noise level with which they all have to cope!

But many countries are unwilling to have their critical national infrastructure or military capabilities dependent on a satellite system controlled by a foreign state, that will always put its own interests first.

Many countries plan GNSS systems primarily because of defence and security needs. Do you think that this may trigger a race with more countries joining in? What would be the implications?

That is correct. It already has triggered such a race: GPS was followed by the global systems: GLONASS, BEIDOU and Galileo and the regional systems: QZSS and IRNSS. Also, by a host of augmentation systems: WAAS, EGNOS, SDCM, MSAS, GAGAN. Now the UK is exploring the possibility of launching its own GNSS and Australia has recently announced a national augmentation system. The limitation is likely to be financial: satellite navigation systems are immensely expensive and beyond the wallets of many countries.

Recently, the Government of UK has released a report on “Satellite-derived Time and Position: A study of critical dependencies”. What are the key recommendations and what is your take?

This revue was initiated by the UK government and directed by its Chief Scientific Adviser. It explored the breadth, scale and implications of the reliance of the UK’s critical national infrastructure (CNI) on the “invisible utility” that is satellite position, navigation and timing (PNT). Government departments and agencies, academia and industry were all consulted. I was a member of the Expert Panel.

The resulting report recommended that Cabinet Office (the top level of government) should require all CNI operators to assess and record their dependence on GNSS. This vulnerability should feature in the National Risk Register and be taken into account in allocating radio spectrum. The government should consider legal sanctions for selling, owning and using jammers and whether to monitor interference at key sites, including ports. Those specifying equipment for CNI should stipulate performance standards. National expertise in PNT should be mapped and coordinated.

The report called for GNSS-independent back-up systems, recommending a range of mitigations, different for each user sector: for example, better holdover clocks for precise time distribution. But for every sector “a terrestrial radio system” has a part to play.

The report showed widespread acceptance by those consulted of the vulnerabilities of GNSS and their agreement on the need to tackle them. But in my view, the key outcome of the report was that the UK government at its highest level, the Cabinet Office, recognised the seriousness of PNT vulnerability and took ownership of the problem. Already, they have started to implement its recommendations. I believe that this is the only way that governments will succeed in overcoming the vulnerabilities of GNSS; we have seen in many countries that leaving it to individual departments simply does not work.

How serious are the threats like interference, jamming and spoofing? How prepared is the GNSS community to deal with it?

Many recent incidents, and many surveys, have shown that the threats of interference, jamming and spoofing are real and serious. The professional GNSS community has come to accept that; indeed, many technical meetings are now dominated by papers on these problems and proposed solutions. But in contrast, recognition of this vulnerability among policy-makers and governments remains rare. Indeed, in many countries and regions, notably in Europe, the need to defend one’s own highcost GNSS program has resulted in denial of the issue of vulnerability. Until there is acceptance of the problem by governments, the critical national infrastructure of their nations will remain at risk.

The recent government-commissioned report by London Economics estimated the cost to the UK economy of a one-off loss of GNSS lasting 5 days at £5.2B (USD7.1B). In my book, that’s a serious threat!

Given this, what’s your opinion on GNSS back-ups?

It would be hard now to find a satellite navigation professional who has studied the question of vulnerability and still believes that a single GNSS alone can provide resilient PNT. Equally, most now agree that one GNSS cannot back-up another GNSS, given that they use the same radio frequency bands and are, in effect, slightly different versions of the same technology. The need for our various GNSS to be mutually compatible and interoperable means that when one is lost to interference and jamming, they all may be. And there are now low-cost multi-GNSS spoofers!

So, any back-up must employ a different technology from the GNSS it is to complement. For precise timing that might be a very stable clock. In the air it will be one of the many non-GNSS systems – DME, ILS, VOR, NDB, inertial – that have been retained for both commercial and general aviation. The best backup will depend on the application.

What’s is your take on eLoran?

I am strongly in favour of eLoran, having watched closely the UK and Ireland prototype system that demonstrated its technical viability and excellent performance over more than 2 years. This system employed the transmissions of the legacy Loran-C stations across North-West Europe, until they reached their closedown dates, adding a data channel broadcast from a new UK station. It operated in both stand-alone and differential modes.

ELoran, originally proposed by the US Federal Aviation Administration, has the great benefit of sharing almost no vulnerabilities with GNSS: it operates at low-frequencies (not the microwaves of GNSS), with high power transmissions (not the very low powers of GNSS) and terrestrial transmitters (not space-based). Yet, in many applications, eLoran can take over automatically and seamlessly when GNSS is interrupted, so allowing operation to continue, meeting the same standards. That has been demonstrated at sea, on land and in the distribution of precise time, including to receivers indoors and under-ground. But eLoran comes up against a profound prejudice: given that GNSS replaced an earlier generation of terrestrial radio navigation systems, recommending a terrestrial system to overcome the vulnerability of GNSS is to swim against a powerful tide!

The London Economics report identified eLoran as one of two technologies that offered “the most applicable mitigation strategies for the largest number of applications”. The UK government then signalled its support for the system.

US had to deal with LightSquared a few years before and now again grappling with Ligado. Would you like to suggest some approach in handling such issues?

This has been, and remains, a very hot topic in the US! In my view it is essential to recognise: that nations must take PNT resilience into account in allocating radio spectrum; that GNSS is of profound economic value to contemporary societies; that our use of GNSS will depend heavily on legacy equipment continuing to operate uninterrupted; and that any decisions should be based on firm evidence.

You have been working on legal issues pertaining to GNSS. Your presentation at INC 2017 was titled “Beyond reasonable doubt – Satellite navigation comes to court”. Would you like to share some of key issues that you often come across?

Yes, since I retired from my university position, crime has become an important part of my life! As GNSS has become deeply embedded in all aspects of our society, so it has increasingly featured in evidence in criminal and civil legal cases. For example, a car may now run many million lines of code, across 70 processors. It will record on board vast amounts of data including PNT information: its location, speed, direction of travel, rates of acceleration, braking and cornering, may all have been captured at frequent intervals. When presented with such data as evidence of criminal activity by the occupants of the vehicle, a court will rightly question the accuracy and integrity of the data; and that is familiar territory to us PNT specialists.

Then, some criminals themselves make use of our technologies to monitor their competitors: in addition to bugging them, they will deploy GPS trackers that gather large volumes of data. They will use jammers both to defend themselves and to disable the tracking systems intended to protect highvalue targets they seek to hi-jack. In addition, the rapid growth in telematics systems (including those deployed by vehicle insurance companies) provides detailed evidence of events leading up to and during collisions that may support a charge of dangerous driving. It may also form evidence in civil cases concerning liability for death and injury.

How GPS Forensics works?

An expert witness in GPS Forensics advises the court on the accuracy of the evidence and the degree to which it can be relied upon. Interestingly, all the recent and current activity in our PNT community plays into the forensics world. For example, a switched-on defence lawyer will know that: GNSS is vulnerable to jamming and spoofing and that GNSS satellites have failed or data uploads have gone wrong, causing erroneous positions. This knowledge will lead to attacks on telematics data presented in evidence. So an expert must be able to analyse the data to establish whether the GNSS system involved, from satellites to receiver, was working correctly and demonstrate this to the court.

Then, there is the question of accuracy. It is remarkable how many folk who know a little bit about GPS are still living in the era of Selective Availability! Many companies in the telematics industry quote open-site performance figures, whereas in reality the accuracy of GPS positions recorded in urban areas is dominated by multipath propagation. I find myself examining crime scenes with a knowledge of microwave radio propagation and estimating the expected spread of the scatter of fixes there. Unfortunately, many of the commercial systems that document the tracks of vehicles fail to record the measures of quality provided by their GNSS receiver chips. As a result, implausible position fixes due – for example – to the vehicle’s being in an underground car park cannot be identified and explained, so undermining the whole set of evidence.

Much of the data that finds its way into court, even in cases of serious crime, is generated by companies whose professional standards fall well short of those of readers of Coordinates!

What influences do you envisage in satellite navigation in the near future given the advancements in the field of AI, Autonomous Vehicles, UAV, etc.?

AI will play an increasing role in the downstream applications of satellite navigation. There is a lively debate concerning the mix of sensors needed to navigate autonomous vehicles, including UAVs. The integrity required in these guidance systems, and the complexity of the environments in which they operate, can be extreme; a navigation system that can guide a ship on the open sea or even in a harbour falls well short of what is required to navigate a car through a crowded and chaotic city. Indeed, it is not clear to many of those struggling to find solutions that satellite navigation has much, or even any, part to play there!

How do you perceive the direction of satellite navigation?

Satellite navigation was one of the outstanding innovative technologies of the late twentieth century, arguably the most successful, being widely adopted with remarkably few downsides, either social or environmental. Through the first decade of the twenty-first century the technology was refined: devices became much smaller, much cheaper, more powerful, and gained superior accuracy, integrity, availability and continuity. But by now we are 45 years on from the meeting at which the principal parameters of GPS were settled.

Satellite navigation has become a very mature technology in which major change is unlikely. Thus its direction will be more about an increase in the numbers of systems, satellites and receivers, all based on essentially the same old technology. But I do expect to see the cost of satellite systems and launchers continuing to fall.

What impacts do you think Brexit may have on Galileo?

Brexit has already led to a conflict between the UK and the rest of the EU concerning future UK access to the Public Regulated Service (PRS), the military-grade part of Galileo. According to the EU, only member states have the right to access the PRS. The UK, requiring either PRS or an equivalent for military purposes has countered by stating that it will consider developing its own independent GNSS. Studies of this option are currently under way.

The row is complicated by the substantial role that UK companies, or the UK parts of multi-national companies, have played and are continuing to play in the development of Galileo. Brexit could end that cooperation, leaving unanswered questions concerning the intellectual property involved. It could also throw into uncertainty the position of the European Space Agency (ESA) which is not part of the EU but acts for it in certain ways.

It remains to be seen whether this conflict is genuine or part of the manoeuvring between the UK and the EU over the terms of Brexit and the future relationship between the two. Divorces can be messy affairs!

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