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Inside Science and Technology 

Simple, Inexpensive Jammers Threaten GPS 

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By Dan Parsons 

When hunting for a particular restaurant or driving to a business meeting in an unfamiliar city, the global positioning system can be a lifesaver.

The satellite constellation also provides the backbone for nearly every navigational system used by the U.S. military. It is one of the tools that Air Force officials repeatedly describe as a “must have” in operations from routine training to combat missions on the ground, at sea and in the air.

Gen. William Shelton, commander of U.S. Space Command, said in June that the 31-satellite GPS system in orbit is “performing extremely well.”

“This constellation just keeps on ticking,” he said.

Such a valuable asset to the U.S. military and commercial sector, GPS presents a juicy target to potential adversaries and criminals alike, the Department of Homeland Security has recognized. Industry, acting on those concerns, is preemptively developing technologies to protect the GPS signal and identify anyone trying to disrupt its transmission.

The Air Force awarded contracts for the first eight satellites of the next-generation GPS constellation that will improve its capability and security. But back on Earth, technology has progressed to where portable, inexpensive, readily-available jammers threaten the GPS signal for commercial, civilian and military users.

GPS receivers have shrunk to fit inside a smartphone or in the dashboard of a car. But the same developments have made the signal that guides a person to the grocery store, or a warship into a harbor, vulnerable to interference.

An inexpensive Chinese-made jammer the size of a pack of playing cards can scramble a GPS signal enough to make trucks invisible to GPS tracking. Multiple jammers in one area have the potential to throw ships off course or interfere with airline navigation, Kevin Farrell, general manager for ITT Exelis’ position, navigation and timing division, told National Defense.

Exelis recognized the vulnerability and preemptively developed a device that can turn the GPS infrastructure around on those trying to disrupt it. Signal Sentry can detect and geolocate the jamming signal so authorities can stop the interference.

“Jamming is a technology that is very simple and is available at the entry level — you can buy a $20 GPS jammer from the Chinese to keep your boss from knowing where you are delivering goods,” Farrell said. “We have proactively developed the ability to geolocate multiple jammers and give law enforcement, port authorities or local governments that critical infrastructure.”

GPS jamming is the act of interfering with the ability of receivers to lock onto the GPS signal, eliminating the ability of the user to determine 3D positioning or calculate other information such as time, speed, bearing, track, trip distance and distance to destination.

The availability and usage of low-cost GPS jamming devices have resulted in the increased threat of intentional and unintentional disruption to commercial and industrial systems that rely on precise GPS data.

There are several nefarious uses for GPS jammers, which are not illegal to own. Convicts serving house arrest can use them to confuse court-ordered ankle monitors. Commercial truckers can carry one to jam roll-through tollbooths or to evade efforts by their employers to track their routes.

Exelis originally developed Signal Sentry based on a DHS concern that GPS jamming might pose a risk to the United States, said Joe Rolli, program manager for the technology. Jammers could hypothetically be used to interfere with shipping on land and at sea, or to snarl navigation through maritime channels or at airports, he said.

“As commercial industry becomes more reliant on GPS, it creates a vulnerability to the nation’s infrastructure,” Rolli said. “There are a lot of people, for one reason or another, that don’t want to be tracked. It might not be for an illegal reason, but they don’t realize the unintentional impact they have on the larger infrastructure. There are more powerful devices that can be used intentionally to any number of ends.”

The shipping lanes in and out of ports in New York and New Jersey are, for example, very narrow. Large container ships rely on GPS — especially in foul weather — to guide them into those ports. Several trucks with jamming devices all pulled into a port at once could severely disrupt commerce and have a ripple effect on the U.S. economy, Rolli said. GPS is even used to track VIPs and dignitaries at events like the Super Bowl, where jammers could be used to disguise their whereabouts for a number of purposes, including a potential kidnapping. National Football League officials have expressed interest in deploying anti-jamming technologies at the game, Rolli said.

The system is deployed in two parts. A network of sensors is placed throughout an area that could be targeted or unintentionally affected by GPS jamming. The array automatically detects jamming signals, gathers information about the device and geolocates the offender by displaying it on an Internet-based visual map of the area. The system can simultaneously identify and locate multiple jamming signals within a specified area.

“It works even without an operational GPS signal,” said Joe Iaquinto, chief engineer for the Signal Sentry.

The company will soon host a demonstration somewhere in the Washington, D.C., area involving an array of 10 sensors networked to a server accessible to multiple local law enforcement agencies, Farrell said. Participants will survey an area of interest, deploy the sensors and then respond to a simulated GPS jamming incident.

The 1000 series Signal Sentry is aimed specifically at the civilian law enforcement and commercial sectors. Exelis officials have identified military uses and plan to launch a system designed for the Defense Department sometime in 2014, Farrell said.

The military uses its own, hardened GPS signal separate from the one that directs civilian users to the nearest drug store. M-code, as the signal is called, has a higher tolerance for jamming, but is not invulnerable.

Security for military GPS will be heightened when the Air Force finishes replacing the existing constellation with GPS Block 3. The service plans to buy as many as 32 satellites from Lockheed Martin that will add bandwidth and expand coverage worldwide. The first satellite is scheduled for launch in 2014.

Exelis has partnered with Raytheon and Lockheed to develop the next-generation GPS satellites. Both companies have had a hand in the system’s development since it became operational in 1994. Exelis will provide the navigation technology on the spacecraft and for the control centers on earth. Exelis’ first payload for the system is scheduled for delivery to the Air Force this calendar year, Farrell said.
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