The Coalition to Save Our GPS sent a letter today to the FCC asking the agency to “promptly rule” that LightSquared be barred from using the upper mobile satellite spectrum (MSS) band for high-powered terrestrial operations.
Command and control
To the puzzlement of the GPS community and independent radio propagation experts, the FCC ruled on September 13 that LightSquared should conduct further tests of its signal transmissions on its alternate, lower L-band frequency farther removed from the GPS frequency. Tests on a LightSquared frequency closer to GPS earlier this year produced extreme interference.
A confidential briefing on the LightSquared/GPS situation presented by Gen. William Shelton, chief of the Air Force Space Command, to senior staff at the Department of Defense and the White House Office of Management and Budget (OMB) was promptly leaked to LightSquared.
On Tuesday, the FCC approved LightSquared’s fallback plan to move from a frequency close to that of GPS in the upper L-band–where tests had shown severe interference–to a lower 10-MHz portion of the same spectrum where reduced interference was expected.
Low-powered incoming GPS signals are allocated 1559-1610 MHz in the L-Band radio spectrum. The neighboring spectrum–from 1525-1559 Mhz–is allocated to other, equally low-powered, incoming satellite signals, such as Sky Terra’s. GPS receivers are open to signals above the blue line shown, but filter out signals below it, and require modification to accept Glonass.
Possibly recognizing that the July 1 final report on GPS testing showed that interference was worse than predicted, LightSquared lawyers are now bypassing the FCC and submitting technical papers directly to the UN’s International Telecommunications Union (ITU) in Geneva, according to published reports.
The ongoing controversy about whether LightSquared’s proposed network of 40,000 powerful ground-based stations transmitting high-speed Internet across the nation would interfere with adjacent GPS frequencies became more intense last month.
“The test data discussed today makes clear that there is substantial interference to GPS if LightSquared turns on high-powered terrestrial facilities in the spectrum next door to GPS,” Trimble vice president and general counsel Jim Kirkland said today at an event sponsored by the National Space-Based PNT Advisory Board. Kirkland is also a founding member of the Coalition to Save Our GPS.
LightSquared documents submitted to the FCC last week reveal that its transmitters were transmitting at only half power during the tests recently conducted in the Las Vegas area to check for interference with GPS receivers. This means that any interference detected by the GPS units could be as much as half that expected when the LightSquared transmitters operate at their eventual planned power levels.
The confrontation between LightSquared and the U.S. government and industry GPS interests is heating up. LightSquared was able to obtain an FCC waiver of its satellite broadcast license to build a supplemental terrestrial transmitter network for broadband wireless. The GPS community claims that LightSquared’s plan, using a radio frequency close to that of GPS, will create interference. On Friday, Rep.