House, Senate Letters Call For Closer Look at GPS Interference

June 10, 2011

Mounting evidence of interference with Global Positioning System (GPS) satellites from a proposed broadband communications network has attracted scrutiny from the United States Congress. On June 7, members of the House of Representatives sent a letter to the Federal Communications Commission, asking the agency to take a more proactive role in heading off potential problems with the technology now in development by cellular provider LightSquared.

“We write to express concern about a conditional waiver that the International Bureau granted in January 2011 after an abbreviated process,” states the letter, signed by 66 Democrat and Republican lawmakers. “This action has serious implications for all GPS technologies, and could negatively impact millions of Americans.”

Review the full letter (196 KB, PDF)

As NBAA reported June 6, tests conducted by LightSquared throughout the southwestern U.S. revealed the potential for severe interference with signals from GPS satellites. Those findings support data from industry tests of the technology, including a study by electronics manufacturer Garmin International.

Once tests are completed and the Federal Communications Commission (FCC) grants its approval, LightSquared plans to build 40,000 transmission towers across the U.S. to dramatically increase access to mobile satellite spectrum (MSS) communications. MSS is used by “cloud”-based computing services, and provides 4G wireless Internet access for laptop computers and smartphones.

The House letter asserts that signals from those towers would be “one billion times more powerful than GPS… Since the intended spectrum usage is immediately adjacent to GPS spectrum, it could lead to severe interference that effectively renders the technology useless.” In addition to the impact against GPS-based aircraft navigation systems, lawmakers add that interference would potentially have “devastating effects” on the military, emergency providers, and ground-based industries including forestry and construction.

The House letter follows a similar request, sent May 19 and signed by over 30 U.S. Senators, to FCC Chairman Julius Genachowski. “We request the full commission require LightSquared to demonstrate non-interference of GPS as a condition prior to any operation of its proposed service,” the Senate letter states, “and we request the Commission rescind LightSquared’s waiver until this demonstration can be made.”

Review the full Senate letter to the FCC (6.5MB, PDF)

There is some hope it may be possible for LightSquared to modify its systems to safely coexist with GPS, by slightly reducing the strength of the 4G signal and limiting use of the upper- most frequency band adjacent to the GPS spectrum. To the latter point, a May 26 RTCA study determined, “[f]rom an aviation perspective, LightSquared upper channel operation should not be allowed,” though the group cautioned “the analysis is based upon the assumption that all equipment is minimally compliant with the interference rejection requirements in harmonized domestic and international standards.”

LightSquared and its testing partners are expected to submit their final report to the FCC, detailing the findings from its tests of the system over the southwestern U.S., by June 15, 2011. The company states the report will include recommendations on how to minimize the impact to GPS signals.

NBAA has been actively involved in efforts calling for LightSquared to demonstrate technology fully compatible with GPS. Earlier this year, the Association joined the Coalition to Save Our GPS, which now has more than 200 members. That group is committed to resolving the threat to GPS and preserving its benefits for industries, government and citizens. Later this month, a House Committee is expected to having a hearing on this issue. NBAA President and CEO Ed Bolen plans to submit written testimony at the scheduled June 23 hearing.

For additional information on this issue, contact NBAA’s Operations Service Group at