4G wireless broadband provider claims fix for GPS interference

Nov 21, 2011 12:00 AM

The company behind a controversial new 4G wireless broadband service that critics say could interfere with GPS signals claims it has fixed the problem.

Sanjiv Ahuja, the chief executive of Virginia-based LightSquared, said his company will move its radio spectrum farther away from the core GPS frequencies, preventing interference to the vast majority of devices.

In a statement released in late September 2011, he faulted the GPS industry for not developing devices capable of withstanding his company's electromagnetic signals and said only "high precision" GPS devices would still be affected. LightSquared plans to resolve the remaining interference by retrofitting affected GPS units with a proprietary filter.

Such high-precision devices are already in use in certain industries, like agriculture, surveying, construction and defense. The company said it would cover the cost of the upgrades for government receivers.

Opponents were quick to dispute his claims. The Coalition to Save Our GPS, an umbrella organization comprising GPS industry stakeholders, called the proposed fix a "non-starter," and said it would "defy the law of physics."

"LightSquared has, as usual, oversimplified and greatly overstated the significance of the claims of a single vendor to have "solved" the interference issue," a Coalition spokesperson said in a statement, adding that LightSquared's plans would "severely cripple GPS."

The Federal Communications Commission (FCC) has ordered more tests of LightSquared's system.

The 2009 U.S. National Broadband Plan directed the FCC to ensure every American has "access to broadband capability," especially in rural and under-served areas. In January 2011, the FCC gave conditional approval to LightSquared's proposal to meet that goal using $14 billion of private capital to expand its nationwide 4G-LTE wireless broadband network.

But the network would operate in a radio spectrum (between 1525 MHz and 1660.5 MHz) close to the signals used by Global Navigation Satellite Systems (GNSS). Experts fear the weaker GPS signals would be drowned out by signal spillover from transmissions from more than 40,000 LightSquared base stations.

Those transmissions could be as much as one billion times more powerful than GPS signals, causing interference for hundreds of millions of GPS users, including the commercial maritime industry and private boaters. According to some estimates, the disruption to GPS signals could create tens of thousands of dead spots — each miles in diameter — throughout the country.

In 2009, President Obama directed the U.S. Coast Guard to discontinue Loran-C, contingent upon two criteria: certification that termination would not adversely impact maritime navigation, and that Loran-C was not needed as a backup to the GPS system. In 2010, the Coast Guard terminated Loran-C, ending hopes for eLoran — an enhanced Loran system widely used in other parts of the world as a backup to the GPS network — along with it.

"As a pilot, GPS is an integral part of our working on ships in this day and age, and an interruption would be significant to us," said Capt. Robert Johnson of the Columbia River Bar Pilots Association. "That being said, as a pilot, your intimate knowledge of your grounds means that GPS is a backup position-finding mechanism, not a primary one.

"The electronic tools are becoming more of an element, and we're using them more as we get experience with them and their reliability increases," he said.

The National Telecommunications and Information Administration asked the FCC to investigate the issue. Other agencies, including the Department of Defense and the U.S. Air Force Space Command, expressed similar concerns, as did marine users including BoatUS and the National Ocean Industries Association.

Mary Glackin, deputy undersecretary for operations at the National Oceanic and Atmospheric Administration (NOAA), recently told Congress that even at the newly proposed frequencies, LightSquared's signals would interfere with high-precision GPS receivers like those used by NOAA.

"We must protect existing GPS users from disruption of the services they depend on today and ensure that innovative new GPS applications can be developed in the future," she said.

At FCC insistence, LightSquared led an industry group comprising GPS and telecommunications stakeholders to examine the issue and consider both short- and long-term technical solutions. That led to its newly announced remedy, which would add a filter made by U.S.-based Javad GNSS to drown out interferences. The company said the Javad GNSS filter could be adapted to work with high-precision GPS devices. Calls to LightSquared were not immediately returned.

Chris Bernard

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