GPS and broadband battle signal interference

During the State of the Union address in January, President Obama stated that making broadband available for 98% of Americans is essential to “winning the future.” According to the Federal Communications Commission’s (FCC, www.fcc.gov) National Broadband Plan, broadband can serve as the foundation for long-term economic growth, investment and job creation.

The following day, the FCC approved a waiver allowing LightSquared LLC—a satellite firm based in Reston, VA—to build its 40,000 planned ground support stations (terrestrial transmitters) for wireless communication in frequencies on either side of the GPS L1 band. LightSquared’s goal is to build an open wireless broadband network able to support current and future wireless devices without restriction. The technology, called Long Term Evolution (LTE) is a widely adopted 4G mobile standard globally. This LTE network will be combined with commercial satellites to create not only nationwide 4G coverage, but a LTE-satellite network—a first in the world.

The FCC and LightSquared see the launch of a nationwide broadband service as an opportunity to introduce a new competitive force into the market for high-speed wireless internet services, a service that would affect all 260 million Americans.

Initial opposition

After several companies, GPS system providers and government agencies opposed the waiver due to worries of interference with their satellite-based product and vehicle offerings, LightSquared’s waiver was granted on the condition that solutions were found and the interference problems resolved.

Objections from the GPS industry included worry that the transmitters from LightSquared would cause interference that could affect safety due to inoperable or unreliable signals.

On February 25, the proposed work plan (as required by FCC per the waiver agreement), developed in cooperation with the U.S. GPS Industry Council (USGIC), was submitted to analyze the potential interference to GPS devices. The group would identify and agree upon interference analysis, evaluate test methodologies, determine the devices and scenarios to be tested (both lab and field test environments) and analyze test results to determine measures to correct any interference problems.

In a letter to the FCC from Fugro EarthData Inc. president Edward Saade stated, "Resolution of interference has to be the obligation of LightSquared, not the extensive GPS user community. LightSquared must bear the costs of preventing interference emanating from their devices."

The FCC argued the "responsibility for protecting services rests not only on new entrants to a spectrum, but also on incumbent users themselves who must use receivers that reasonably discriminate against the reception of signals outside their allocated spectrum. In the case of GPS, we note that extensive terrestrial operations have been anticipated in the L-band for at least 8 years."

LightSquared assures that it is not its waves bleeding into the GPS spectrum, but rather GPS bleeding into the LightSquared spectrum because the devices have been designed over the years without the proper filtration.

"Nonetheless, it was such a big problem that LightSquared is going to rearrange the way it’s going to launch and has proposed to move to a different slice of spectrum as far away from GPS as it can go," says Chris Stern, spokesman for LightSquared. "The proposal is currently [as of July 15] in front of the FCC and takes care of 99.5% of all GPS devices, essentially 300 million cell phones.

"The 0.5% of precision GPS is still a problem," he admits, though he also adds that LightSquared looks forward to working together with the GPS industry and engineers to find a solution.

Precise positioning opposition

In the past couple of month, the GPS industry, industry organizations in construction, agriculture and transportation, as well as the Association of Equipment Manufacturers (AEM) have been relentlessly campaigning to protect GPS signals and the industries that use them.