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photo from Idaho National Laboratory from flicker​

House Subcommittee Explores Whether Wireless Broadband Expansion Could Affect Aviation Safety

An up and coming broadband company is building a network that would make wireless Internet available to everyone in America. LightSquared’s network would combine satellite and land service that would deliver 4G anywhere in North American and up to 200 miles off the coasts. But initial tests showed that even at levels below what LightSquared planned to operate, their powerful transmitters interfered with GPS signals.

Now their plans to connect the entire country are facing criticism from aviation and GPS companies who say expansion of wireless broadband services shouldn’t trump the importance of safety in aviation and maritime operations. Representatives from the Air Transport Association of America (ATA), Inc., the Aircraft Owners and Pilots Association (AOPA), Garmin International, Inc., and the Radio Technical Commission for Aeronautics (RTCA) voiced their concerns on the impact of LightSquared’s plans before the House Committee on Transportation and Infrastructure and the Subcommittee on Aviation.

Jeffrey Carlisle, executive vice president of Regulatory Affairs and Public Policy at LightSquared testified that when the FCC first authorized their ground stations, they were granted use of the radio spectrum directly adjacent to the spectrum used to transmit GPS signals.

Carlisle argued that the concerns from interference don’t come from the LightSquared frequency spilling over into the GPS band – the company had even made an agreement with the U.S. GPS Council to limit emissions close to the GPS spectrum - but fromnewer GPS devices that were built to pick up signals in their band [1]as well. “As a result of their design, these receivers can be desensitized, or overloaded by our signals in our licensed spectrum,” Carlisle said.

It’s because GPS signals are fragile, Tom Hendricks ATA senior vice president for safety and security operations said. GPS signals come from satellites in space and operate on about the same amount of power as a light bulb; the distance and low power make them very sensitive, he said. Hendricks said LightSquared’s signals that would be interfering are about “one billion times more powerful than GPS signals.” It would in effect, drown them out completely.

Craig Fuller, president of AOPA, wants the whole idea scrapped. “We want to be very clear,” Fuller said, “Putting the nation’s GPS system as risk is unacceptable…no further development of this system can be allowed [2].”

Approximately 70 percent of AOPA members use GPS as their primary navigation tool. The other 30 use it as their secondary, Fuller testified.

“While AOPA members fully support the expansion of broadband services, especially to underserved and rural communities, such expansion cannot take place at the expense of the safety of the hundreds of millions of Americans who rely on our national air transportation system,” he said.

It’s the development of GPS that has made all-weather landings possible. It helps with air traffic data and aircraft identification, and shortens flights by allowing planes tofly point-to-point instead of having to fly paths in range of ground radio transmission [3] towers. Ships rely on GPS to guide them at night and most public safety operations use one form of GPS for everyday operations. Compromising this system would be unsafe and hinder advancement of the aviation field, Fuller said. A U.S. Coast Guard official testified that without mitigation,Department of Homeland Security Operations would be severly affected [4].

A study on LightSquared’s systems by RTCA reported that “the impact of a LightSquared upper channel spectrum deployment is expected to be complete loss of GPS receiver function,” but using a channel5MHz lower would allow their system to co-exist with aviation’s use of GPS [5]. RCTA explored the impact of modifications to GPS receivers but concluded that it would take too long and be too expensive to modify every existing aircraft that operates in North America to only pick up GPS bands. ATA says the technology to do it doesn’t even exist yet. “Further study is recommended,” RTCA’s report concluded. 

Carlisle testified that it would be no problem for LightSquared to broadcast without causing disruptions to GPS using a lower band within their spectrum. He also testified that initial tests showed that there were no negative impacts on public safety devices.

“The potential for interference from our operation on the lower channel is almost exclusively limited to receivers in the categories referred to as ‘high-precision,’ ‘network,’ and ‘timing.’ We do not minimize the importance of these devices, but we estimate that they represent no more than roughly one million devices. Filtered antennas are available for timing devices that will permit them to continue to be used without interruption,” Carlisle said.

To keep interference to as little as possible, he said that LightSquared is willing tooperate base stations at a lower level [6], suspend use of its space on the spectrum adjacent to GPS, only use sections of the spectrum that won’t interfere with GPS devices, and share the cost of finding a solution for devices at risk.

​“It needs more study, which is what we’ve being saying all along,” LightSquared spokesperson Christ Stern told Security Management. “The message from the Department of Transportation, the Coast Guard, and RCTA was that there needs to be more study at the lower ten. Depending on where you are in the government, it’s a goal to get broadband all over the country so there’s people who really want to see a new network, but nobody wants to see public safety put at risk at the same time. It’s just a matter of working it out over time.”