In the days of the run-up to the Iraq war, I wrote an Editorial decrying the vulnerability of the US GPS (Global Positioning Satellite) system. I argued that GPS jammers, homemade and commercial, might be a threat to military systems that depend on the satellite system for precision timing signals and geographic location data. To underscore my point, I outlined some circuit details for home-constructed jammer transmitters.
At the time, others were more sanguine. In an article in the October 2001 issue of
Global Positioning and Navigation News, the author stated US aerospace and defense spokesmen were confident the US arsenal of anti-jamming technology, coupled with the ability to knock out brute-force relatively high-power GPS jammers, would ultimately prevail in a conflict.
Nonetheless, the
Global Positioning article's author argued that the cost/benefit calculation needed to fix the problem could turn Pentagon military budget planning "on its ear," with huge investments in anti-jamming systems needed to combat portable jammers. "America's sharpest engineering minds, with millions of dollars at their disposal, could be locked in long-distance intellectual combat against technicians sitting in mud huts, holding propane soldering irons and surrounded by off-the-shelf parts."
In 2002, Mario Casabona, president of Electro-Radiation Inc., posted a paid advertorial that appeared in the December issue of
GPS World magazine. "With the schematics you can get on the Internet," said Casabona, "you can build a jammer. The US military is concerned about that."
Weak-Signal ReceptionThe problem then, and now, is that GPS receivers rely on signals from multiple satellites in a constellation of orbits at distances of more than 13,000 miles. "The distance and power of the constellation signal is the chief weakness of GPS," noted Murray Rosen, Technical Director of Electro-Radiation. "It's easy to jam or spoof the low-power signal."
In a paper entitled
Protection Solution to GPS Vulnerability, Rosen described the weak signal problem in engineering terms. "A commercial GPS receiver is vulnerable to a simple 1 W jammer at up to 135 km. A typical tracking military receiver using inertial aiding, with about 62 dB of jamming immunity, can lose code track within 54 km of a 1 kW CW jammer," he said.
Rosen noted that a receiver could lose track within 17 km of a 100 W noise jammer. And, adding 35 dB of additional CW anti-jam and 25 dB of noise anti-jam would reduce GPS vulnerability to 1 km."
So, here we are in 2008, and the military is reporting any number of GPS outages. Most result from so-called blue-on-blue interfering transmissions from friendly forces. But, there are other factors at play.
As was the case in 2002, Internet sales of GPS jammers continue. Go ahead and do a Google search on the phrase "GPS blocker" and you'll see what I mean.
As you might expect, the Federal Communications Commission frowns on such sales. In May of this year, the FCC issued an
Official Citation to David Steele Enterprises, a US company specializing in spy-vs-spy equipment. Steele was cited for marketing unauthorized RF devices in violation of Section 302(b) of the US Communications Act, as well as Sections 2.803 and 15.205(a) of FCC Rules. Steele's little box was actually an import from Taiwan, of all places.
Based on the original Russian designs, it’s likely that jammers have also been shipped from North Korea, especially to countries in the Middle East. The latest twist comes from our good friends in China. According to an alarming on-line
article on Newsmax, the Chinese are deploying mobile vans equipped to jam GPS. In an ironic twist, US intelligence agencies claim to have satellite photos of these vans.
Apparently the threat is serious enough that the National Geospatial Intelligence Agency has
activated a Jammer Location Master Station at its control center. The JLOC system uses sensors to collect information about GPS jamming and interference. It then analyzes navigation denial impacts and acts as a central clearing house for jamming and interference information.
JLOC works because most of today's military GPS receivers can detect interference and provide reports indicating higher than normal signals or lower than normal signal-to-noise ratios. Networked JLOC GPS receivers then send this data to the JLOC Master Station. JLOC claims thousands of sensor reports are now being processed every day.
Has anything significantly changed in the ensuing years since the articles in 2001 and 2002 appeared, along with my
Editorial?
With even more widespread deployment, is the GPS system less vulnerable than it was eight or nine years ago?
