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GPS: jam today; jamming tomorrow

26 February 2013

Like the Internet, other hugely important resources at our everyday disposal can be abused. GPS, rather disconcertingly, is not immune to such abuse, according to recent research.

An event held at the UK's National Physical Laboratory last month, highlighted recent research into the biggest threat to navigation and timing signals in the UK and the best ways to counter it. 'GNSS Vulnerabilities 2013: Countering the Threat', organised by the ICT Knowledge Transfer Network, presented the latest research into GPS jamming and also demonstrated the new technologies, including intelligent receivers and radio-based back-ups that will protect against the impact of these jammers.

It is thought that moonlighting van drivers may be to blame for the growing problem of GPS jamming on Britain's roads. Recent research reveals how a network of sensors recently detected up to 100 potentially dangerous jamming incidents a day near a major UK airport. When trying to work out what might be causing such a high level of interference, the researchers noticed that most of it occurred during the week, dropping off at weekends, which ruled out solar weather events that occur randomly.

Jamming also increased during peak traffic periods, which pointed to commercial vehicles being the culprits rather than, as previously suspected, vehicle thieves trying to foil security tracking systems. So the pattern suggests it might be civilian-sourced jamming devices - most likely deployed to evade tracking within commercial vehicles when they are used for other non-work purposes. Researchers think that van drivers may want to hide unauthorised use of delivery vans, using jammers to confuse the central tracking software now used by all major delivery networks.

Bob Cockshott, Director of Position, Navigation and Timing at the ICT Knowledge Transfer Network and organiser of the conference said our more complete understanding of the risks posed to GNSS (Global Navigation Satellite Systems) is bringing forward new mitigation technologies and approaches. "There is no one solution that fits all," he warns. "Instead, we need to combine the right protection and back-up technologies with legal reforms which punish the ownership and use of these jammers, and finally advise government and industry on new commercial and civil policies that will reduce the incentive to jam in the first place."

The latest figures on GPS jammer use on British roads comes from the Technology Strategy Board funded SENTINEL Project and its new suite of detectors which includes one deployed close to a busy airport that has been logging as many as ten interference events per day. Concerns have been raised in the past about the potential impact of jamming on air traffic control systems and aviation landing technology.

This data also provides a profile of the likely sources of this jamming. The interference profile, with marked peaks during the week and a dearth of hits at the weekend, strongly indicate it is human activity that is the primary cause, rather than natural sources of interference such as the effects of space weather. More specifically, marked peaks during the times of rush hour traffic suggest the main users of jammers are commercial drivers of company vehicles rather than organised criminal gangs who have been caught with jammers in lorry hijackings.

Charles Curry, founder of Chronos Technology and a leader of the project, says that over the past four months the sensors near this airport have detected nearly 100 events on Mondays, but this falls to less than 30 on a Sunday. The pattern of behaviour suggests it is likely to be civilian sourced jamming and most likely the evasion of tracking within commercial vehicles for moonlighting activities or for other non-work purposes.

"More broadly, we are also seeing an overall increase in interference incidence which is worrying at a time when GPS is being thrust upon people more and more with GPS tracked car insurances, company vehicle tracking, criminal tagging or asset tracking," says Mr Curry. The SENTINEL project is able to deploy small test networks to organisations with critical infrastructure dependent on GPS signals so they can quantify the problem for themselves and take the appropriate action to counter the threat.

The danger of these jammers was confirmed by new results from the STAVOG project, which were presented at the conference. STAVOG has developed state-of-the-art interference simulations in conjunction with Spirent, a UK based simulator manufacturer. These mimic the various threats to GNSS signal covering both extreme solar weather and the latest illegal jamming devices available online. In partnership with the General Lighthouse Authorities, STAVOG then tested these interference simulations on a variety of marine grade receivers used in most big commercial shipping vessels.

It found that, despite simulating intense solar activity, the perceived threat from solar weather only resulted in minor signal interference and no complete outages for any of the tested marine receivers. In contrast, even the cheapest jammers resulted in complete outages across all receivers currently on the market. Some were jammed without the users even knowing and continued to give out inaccurate results, potentially leaving shipping at risk of grounding or collision.

Chaz Dixon, Project Manager of STAVOG said results from the simulated solar storms were "unexpectedly dull."

"Concerns over the impact of space weather on the most precise use of GPS such as offshore oil operations are legitimate, but our testing proved that modern receivers cope remarkably well with even high levels of disturbance," he adds. "Instead, the real danger seems to come from illegal jammers which other studies have shown are increasingly common.

"Even the cheapest ones available online can cause complete outages of the receiver signal. It is in anticipation of this threat that we will be making this service available for any GPS users to understand and protect themselves against the vulnerabilities in their positioning and timing systems."

Mitigation technologies
The General Lighthouse Authorities announced details of the first demonstration of a new type of jamming-proof receiving system for the shipping industry to take advantage of the recently unveiled back-up eLoran radio-navigation signal for the world's busiest shipping lanes in the Dover Strait.

The receiving system is the first in the world to switch automatically and seamlessly to eLoran should the GPS signal be lost. It was demonstrated on board the GLA vessel Galatea on several excursions from Harwich, starting on 25 February, during which its GPS navigation system was jammed.

Raytheon outlined how the modernisation and miniaturisation of controlled reception patterns antennas (CRPA) technology, within the military domain, can be transferred to the non-military arena. CRPA systems have been used in military applications for many years but are only now available at the reduced cost, size and power consumption which makes them applicable to civil operations, particularly those of high critically such as in aircraft positioning and landing.

In aviation there is some concern over the increasing use of GNSS as a critical component of systems such as ADS-B for en-route and airfield operations, coupled with the increasing recognition that GNSS vulnerability needs to be tackled in the non-military domain.

Meanwhile, Mike Jones, a senior consultant engineer at Roke Manor Research, discussed the barriers to wider adoption of military anti-jam technology, and previewed a new miniaturised anti-jamming product aimed at critical infrastructure, security and civilian markets.

Mr Jones also touched upon the geo-location of jamming sources, suggesting the types of technology that could be used to enable monitoring, enforcement and prosecution of GNSS spectrum offences.

Les Hunt

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