Cell Phone Threat Prompts GPS Jamming Study

Urgent efforts are under way to head off a threat of widespread and severe jamming of GPS following US government approval of plans by wireless broadband communications provider LightSquared to install thousands of powerful transmitters that could block the signals from navigation satellites.

Despite objections from the Federal Aviation Administration and the Defense Department because of the threat of interference with GPS, the Federal Communications Commission (FCC) in January gave conditional approval to LightSquared’s plan to install up to 40,000 terrestrial cell phone base stations across the U.S. to augment its mobile satellite communications service. To be deployed beginning this year, LightSquared’s terrestrial transmitters will operate at L-band frequencies adjacent to the main L1 frequency used by civil and military GPS systems. Because signals from navigation satellites have very low power, there are concerns the high-power transmissions will overload sensitive GPS receivers. “We are concerned about the possibility of interference with GPS services and looking forward to further testing,” says the FAA. Conditional approval of LightSquared’s plan came as a surprise to the GPS community. “We are at a loss to know why [it was approved],” says an official close to the issue. Transmitting high-power terrestrial signals is a fundamental change in the use of L-band frequencies set aside for low-power, space-to-earth services, says the U.S. GPS Industry Council (USGIC). Overcoming interference may not be easy. ”We are up against some pretty fundamental physics,” says Executive Director Mike Swiek.