Expert Advice: GNSS Interference, Detection, and Mitigation

May 1, 2011  - By

Sally Basker

Interference, detection, and mitigation — these have become topics of paramount importance to the GNSS community recently, surpassing at times even those old familiar standards accuracy, availability, and integrity.

In March, a large expert audience attended a GNSS Interference, Detection, and Mitigation (IDM) conference at the United Kingdom’s National Physical Laboratory near London. My conclusions first, followed by reportage of the details. In brief, GNSS has revolutionized positioning, navigation, and timing (PNT), but clearly, GNSS vulnerability is real, the risk is ever increasing, and we need urgently to improve interference, detection, and mitigation.

Many GNSS-related benefits that we enjoy today come from integrated systems, automation, and new, high-performance concepts of operation with fewer and less-skilled people. Reversion to older concepts of operation is not an option in many cases, and so we must build resilience into our systems.

Resilience costs money. It can be accomplished piecemeal, where each sector does its own thing, but ubiquitous solutions — standards and backup systems, among others — that draw on economies of scale will be more cost-effective.

I suspect that productive response will be hindered by a combination of ignorance, disbelief, over-confidence, technical complexity, and economic sensitivity. To wit:

  • ignorance of the role of GNSS in embedded systems;
  • disbelief that policy makers could have put all the eggs in one basket and burnt the other basket;
  • overconfidence because in-car navigators work so well;
  • the difficulty of explaining complex, technology causal loops and their impact at a business level;
  • the lack of desire to spend money at this point of the economic cycle.

I hope I am proved wrong.

Just prior to the conference, the UK’s Royal Academy of Engineering released its report warning of over-reliance on global navigation satellite systems. The balanced report makes key recommendations on raising awareness and analying impact, policy responses, and increasing resilience.

Further presentations during the day addressed high-level policy issues in the UK and U.S., interference detection using terrestrial and space techniques, and mitigation based on improving receiver and antenna design, integration and eLoran. All this was underpinned by a number of themes based on the ever-increasing risks (reliance and threat) and the emerging detection and mitigation response.

James Caverley (U.S. Department of Homeland Security, DHS) and Martyn Thomas (UK Royal Academy of Engineering) both addressed reliance. Caverley stressed the level of ignorance outside the GNSS community, particularly with embedded systems. He discussed a DHS timing study that found GPS timing was essential for 11 of 18 critical infrastructure and key resource sectors — although their leaders originally said GPS wasn’t needed!

Thomas stated the UK and other developed countries are dangerously dependent on GPS as a source of PNT, and that nobody has a full picture of the dependencies or vulnerabilities. But the real cause for concern is that up to 7 percent of Europe’s gross domestic product is dependent on GNSS, and many of the backups are inadequate and not exercised.

The increasing interference threat is based on capability and intent. Caverley noted the commercialization of GPS jammers, and that Canada has intercepted large numbers of jammers intended for the criminal market. The intent is varied: career criminals covering their tracks, lovesick swains wanting privacy, and the general public objecting to poor policy implementation (for example, road user charging) using GPS. Mentioning Lightsquared, Caverley stated that the DHS had been surprised by the FCC decision and that it was working hard to ensure that interference is not a problem.

IDM is at the early stage of its product life-cycle, and so a number of different detection techniques are being considered. The main challenge is that it is very hard to detect mobile interferers. The UK Technology Strategy Board has funded several projects: Charles Curry (Chronos Technology) discussed the GAARDIAN and SENTINEL projects developing IDM probe networks. Stuart Eves (Surrey Satellite Technology) discussed space-based techniques. Washington Ochieng (Imperial College) gave a fascinating presentation on the use of integrity monitoring for detecting interference. Nigel Davies (Qinetiq) described a jamming and interference mitigation system funded by the EC.

Mitigation is an even wider topic. Stephen Harding (Ofcom) outlined the UK’s regulatory options and discussions with the police of enhancing current laws. He revealed that Europe has been in discussions with LightSquared for two years. Peter Soar (Qinetiq) outlined how technical design and integration with inertial systems can mitigate jamming to some extent, but noted that best-practice is not discussed because companies want to protect their intellectual property.

Thomas expressed strong support for eLoran as a backup, and George Shaw (General Lighthouse Authorities) described a business case where eLoran had the largest, positive economic return over the cost-benefit period; all other approaches were negative. Caverley stated that a nationally accessible backup for timing is important, but he is not sure whether the U.S. needs a ubiquitous system.

Sally Basker, former director of research and radionavigation at the General Lighthouse Authorities of the UK and IReland, has opened Sally Basker Consulting: strategy, business, and technology advice with expertise in navigation services. See

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