Just recently, we have seen the Federal Communications Commission [FCC] suspend indefinitely its provisional approval of a new wireless broadband Internet service, proposed by LightSquared, because of concerns about potential interference with the Global Positioning System [GPS]. As I’ve noted before, the GPS is used for much more than those little direction-finding gizmos in your car. Besides the potential problems associated with large new deployments, like the proposed LightSquared system, there is an ongoing problem with deliberate jamming of GPS signals.
Jamming GPS signals is not technically difficult. The signals are coming from satellites ~20,000 km away, and the radiated power is ~ 100 watts, not much more than a typical terrestrial cell phone tower. (By way of comparison, LightSquared’s proposed ground stations would each have radiated ~15,000 watts .) So GPS devices must be able to receive very weak signals, which means that generating enough “static” to mask the desired signal does not take a very large or powerful transmitter.
Some new research, summarized in an article at New Scientist, surveyed the incidence of GPS jamming in the UK since September of last year. The research, carried out by a group organized by the Government’s Technology Strategy Board [TSB]. and led by Chronos Technology, found that jamming is a very real problem.
A secret network of 20 roadside listening stations across the UK has confirmed that criminals are attempting to jam GPS signals on a regular basis, a conference at the National Physical Laboratory, in London, will hear later today. Set up by the government’s Technology Strategy Board (TSB) and run by Chronos Technology of the Forest of Dean, UK, the Sentinel network has sensed an average of ten jamming incidents per month since September 2011.
The results, which are being presented this week at a conference sponsored by the TSB, indicate that GPS jamming takes place ~10 times per month at the monitored locations. (BBC News also has an article on this research.) In many countries (including, I believe, the UK) the sale or use of GPS jamming equipment is illegal. Nonetheless. it seems to be easily available via the Internet.
One prime suspect in the investigation so far is the trucking industry. GPS devices are used widely: in some cases, to track vehicle movements in order to assess tolls; in other cases, to keep tabs on the vehicle drivers. These situations obviously have significant potential motives for jamming. The New Scientist suggests another possible reason, based on the ability of a good GPS system to give directions “off the beaten track”"
Vigilantes could be one source: a major problem with GPS is the way some small villages and towns suffer visits from dangerously outsized trucks – which often get stuck in tiny streets – attempting to follow satnav-advised shortcuts. So it is possible locals are placing jammers to prevent drivers’ antisocial behaviour.
I hope these results will stimulate more work on jamming prevention, from both the technical and legal viewpoints. As I’ve said in the LightSquared case, GPS technology is just too useful, in too many ways, to be compromised because of carelessness.