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Chicken Little report: Sat-nav dependency spells DISASTER!

Quango pushes 1940s tech as backup for GPS

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Analysis A heavyweight UK tech body has just issued a report claiming that growing dependence on satellite navigation systems poses serious economic and safety risks to society. There's some truth in the report, but unfortunately it verges on scaremongering at times and appears to have been unduly influenced by organisations which can't be regarded as impartial.

So what does the report from the Royal Academy of Engineering (PDF/984KB) have to say?

Much of it covers well-trodden ground that many Reg readers will be familiar with. Satnav receivers (almost always using the US military Global Positioning System satellite constellation, GPS, at the moment) are now ubiquitous. Quite apart from car dashboard units, GPS receivers are now found in phones, tracking bugs, aircraft, ships, drones, automated combine harvesters etc etc.

Somewhat fewer of us are aware that GPS also offers a very precise timing service – it naturally has to, as the ability to measure very small intervals of time is required in order to work out one's position using GPS signals. These days a lot of hardware makes use of the GPS timing signals for purposes unrelated to navigation: for instance to synchronise the precise clocks often needed in digital communication systems, or to put exact time stamps on financial transactions. Using GPS is often cheaper than installing a highly accurate timepiece.

All this, according to the RAE report, introduces vulnerabilities. GPS signals received on the ground are weak, which means they can easily be interfered with – by natural phenomena such as solar storms, accidentally by faulty equipment, or on purpose. This could mean serious economic disruption or in some cases injuries and deaths.

So what should we be doing about that – in the opinion of the report's distinguished authors?

Again, it's mostly common sense. Users shouldn't develop an over-reliance on GPS – or satnav generally, once complementary services such as Europe's Galileo or Russia's GLONASS expand their coverage. Designers should build systems so that a loss of signal won't be catastrophic: quite a lot of communications hardware apparently has no option for timing other than GPS, for instance, and this should be rectified.

So far, so uncontroversial. But then we get onto the question of backup systems. The report says:

The provision of a widely available [navigation and timing] service as an alternative to [satellite services such as GPS] is an essential part of the national infrastructure. It should be cost effective to incorporate and free to use. Ideally it should provide additional benefits, such as availability inside buildings ... We are encouraged by progress with eLORAN [enhanced LORAN] in this context.

LORAN is a nav system dating from the 1940s, using long-range lower frequency radio signals from ground stations. It is wildly inaccurate compared to GPS or other satnav methods, but it was widely used at sea in the pre-GPS era as it was often the only electronic navigation aid available. The UK had a different system called Decca.

Here in the UK (and Ireland), Decca was formerly run by an organisation known as the General Lighthouse Authorities (GLAs), an alliance of the organisations set up to run lighthouses in the mainland UK (Trinity House and the Northern Lighthouse Board) and Ireland (the Commissioners of Irish Lights).

Trinity House tends to set the lead for the GLAs. It is an interesting organisation: partly an arm of government funded by a special tax (the "light dues" paid by ships visiting English ports), partly a private-sector offshore contractor and pilot bureau, and partly a seafarers' charity. The GLAs as a whole are in the nature of a sector-straddling quango, at least partly dependent on government funding to exist – but not really under any serious government supervision and operating in many ways like a private firm.

Decca was always highly unreliable and inaccurate (your correspondent, as a Royal Navy navigating officer at sea in the early 1990s, was furnished with GPS only occasionally and thus had to make occasional reluctant use of Decca). As soon as GPS got into widespread use, even back in the old days when the civilian GPS signal's accuracy was purposely degraded by the Americans, Decca was dead. It was finally switched off in 2000.

At first the GLAs thought they might find a replacement for their lost Decca portfolio in operating a new network of ground stations delivering a service known as "differential GPS". This was a workaround which eliminated the deliberate inaccuracy built into the civil GPS signal: a ground station, knowing its own position, would calculate the error in near-real-time and transmit corrections on a radio channel. Thus a dGPS receiver in range of a GLAs station would obtain something close to the full accuracy the system could deliver, an error of a few metres at most, instead of the 100-150m accuracy the US defense department wanted to offer to people not in possession of a military P-code receiver and accompanying crypto keys.

The GLAs' free-to-air dGPS network got running in 2002, enabling a fairly seamless transition from Decca for the organisation. Unfortunately dGPS had already been rendered obsolete for all but specialist applications, as President Clinton had ordered that the civil GPS signal no longer be degraded two years earlier.

A dGPS receiver is still somewhat more accurate than an unassisted GPS – perhaps a single metre of error – but hardly anybody needs such accuracy right now. By the time they do, say a decade or two from today, Galileo and the new GPS Block III satellites will offer 1m accuracy without any ground-station assistance. The case for maintaining the GLAs' free-to-air dGPS ground stations at public expense is already shaky, and soon enough it will be untenable.

Funnily enough, the GLAs have now switched from trying to augment satellites to saying that they are unreliable and that some kind of publicly funded backup nav-and-timing service – provided by ground signal stations – is essential. They already have a government deal to run a central LORAN transmitter at the famous (in radio circles) Anthorn station in Cumbria – also the location of the UK's very-low-frequency transmitter, used for communications with submerged nuclear submarines.

There's a major problem with LORAN, though – it is very inaccurate. Ordinary LORAN-C only tells you where you are to within several hundred metres or worse: it is basically useless for anything but long-range maritime or air navigation (often no good even for that as it offers no coverage far out in the ocean). It can't as it stands act as a backup for GPS in bringing ships into harbour or planes down to runways; it would be entirely pointless on a car dashboard, in a tracking device etc.

The GLAs really don't like to mention the accuracy of the "enhanced LORAN" – eLORAN – system they are pushing now. No figures are given in the RAE report.

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