Potential Vulnerability of GPS to Interference

　　Space-based global positioning system (GPS) signals to guide smart bombs and cruise missiles to attack targets, supporting the U.S. strategy. America's technological superiority on the battlefield. However, it is also an American Achilles because it jams relatively easily. American military forces. Although the integrity of the GPS signal was maintained in the war with Iraq, the enemy's attempts to corrupt it underscored the need to protect GPS-dependent weapons and navigation systems. Faced with a more capable enemy, GPS could find itself one of the first victims of any new conflict.

　　Jack Spencer, a defense analyst in Washington,"It is generally believed that GPS signals are vulnerable to attack."The Washington-based Heritage Foundation is lobbying for GPS to be declared a critical infrastructure under the homeland security umbrella.GPS is a system of 24 satellites that constantly sends navigation signals to the earth. Each satellite transmits two signals, one for civilian use and the other for an encrypted version for military purposes. But a broadband transmitter generating electronic “noise“ at the right frequencies can overwhelm these signals, which are weaker than the average radio signal people listen to every day.

　　In fact, it was the potential vulnerability of GPS to interference that prompted Iraq to purchase some GPS jammers from Aviaconversiya Ltd. This Russian company has been peddling GPS jammers at military hardware exhibitions since 1999. The high-cost and high-power GPS jammer from Avia Versiya are said to be able to jam GPS signals for miles around. The Iraqi military used at least six of these high-powered GPS jammers during the war, each selling for $40,000 or more. All six were quickly eliminated by the U.S.Nan in the course of two nights. Officials were reluctant to provide details, but given the speed with which they solved the problem, the Iraqi GPS jammers might have been effective initially.

　　The failure of the Iraqi military to continually throw GPS-equipped Joint Direct Attack Munition (JDAM) bombs and Tomahawk cruise missiles severely off course can be attributed to several factors. Among the most important was the installation of backup inertial navigation systems (INS) that could keep the bombs and missiles on target if the GPS signal was compromised. INS systems are slightly less accurate than GPS, however, so there is a greater risk that INS-guided weapons might be a tad off course, raising the risk of collateral damage and casualties in densely populated areas. Still, the danger may be short-lived: high-power GPS jammers can easily be traced back to their origins, effectively portraying themselves as Bull's-eyes. In fact, we used the GPS weapon to destroy the GPS jammer. U.S. major general Victor Renuart described the attack on the GPS jammer to reporters at a news conference in Qatar.

　　Iraqi efforts at jamming could also be frustrated by a new type of signal-enhancement technology that has been secretly deployed in Iraq to overwhelm GPS jammers. The airborne pseudo satellite installed on the Global Hawk or Predator drone, nicknamed "pseudo satellite", can create a miniature GPS constellation over Iraq. These pseudolites would have captured the weak GPS signals from space and then relayed them, at substantially higher power and at closer range, to airborne bombs and missiles or to forces on the ground. Like satellites in space, four pseudo satellites are needed to map the navigation solution. Tests performed in April 2000 by the Defense Advanced Research Projects Agency (DARPA), the Pentagon‘s research arm, convinced the military that the pseudowires were powerful enough to overcome jamming. The special beam-forming antenna and signal processor are developed to allow the pseudo-satellite to acquire satellite-borne GPS signals even when attacked. The new receivers, called precision lightweight GPS receivers (PLGRS), or“Plugs,” have been used for pseudo satellites.