The proposed national broadband network, planned by LightSquared, was rejected by a U.S. federal committee in January due to “harmful interference” to some GPS-based systems.

The 4G-LTE network would cause interference to many GPS receivers and create incompatibility with GPS-dependent aircraft safety systems, according to the National Space-Based Position, Navigation and Timing (PNT) executive committee. PNT is a group established for matters concerning GPS and related systems.

The committee stated that tests showed the network didn’t interfere with cellular phones, which are equipped to block the specific GPS signals, but did cause significant interference to other general purpose GPS receivers and aircraft safety systems that warn pilots of approaching terrain.

The committee unanimously concluded that the proposed network did not mitigate the harmful interference caused to the GPS bandwidth, according to several news reports.

The committee worked with LightSquared to test possible solutions to the interference, but none of the proposed methods were accepted by the group. The committee reported that there would be no further testing.

The proposed network was to be the basis of the U.S. National Broadband Plan, which was mandated by Congress in 2009 and directed by the Federal Communications Commission (FCC) to ensure every American has access to broadband capability, especially in rural and under-served areas.

The government gave Virginia-based LightSquared conditional approval a year ago and the private company, using $14 billion of private capital, proposed the plan to expand its nationwide 4G-LTE wireless broadband network integrated with satellite coverage.

Concerns that the proximity and strengths of LightSquared’s signals would overpower the relatively weak GPS satellite signals were presented last summer by several groups representing GPS consumers, including those in maritime, aviation, military and smart phone applications. Those fears were upheld by the committee this month.

At issue was the concern that although LightSquared had its own radio band, that band was considered so close to the GPS signals that most GPS devices would pick up the stronger LightSquared signal and become overloaded or jammed.

Aeronautical tests from last year showed that receivers on transport-category aircraft would be unable to track GPS satellites in certain regions near land-based towers. LightSquared’s plan included 400,000 towers. 

Several megayacht industry sources noted that less than 1 percent of GPS devices would have been impacted, predominantly older units without filters that protect from interference and high precision level GPS use.

"Precision frequencies are different than the ones most maritime operations use," said Peter Prowant, SE regional manager of Furuno USA, which sells marine navigational equipment.

Navigation along the coastal United States and its inland waterways would probably have been more affected by signal interference than high seas operations, Prowant said.

The committee’s rejection of the proposed plan is being contested by LightSquared, which claims the committee is biased. The company filed the complaint with the NASA Investigator General’s office regarding “potential conflicts of interest in the advisory board.”

Postings on LightSquared's Web site this month stated that the government's testing included obsolete and off-market GPS receivers that were more likely to fail. The company also said that the mass market device that reportedly failed the government’s tests in fact “performed flawlessly during Technical Working Group” testing.

And its press release asserts that the failure was ensured with tests that were performed at a power level 32 times greater than the level at which LightSquared's network would operate.

At press time, LightSquared had posted a video on its Web site demonstrating a solution for the high precision GPS interference.

About the Author

Dorie Cox

Associate Editor