Recent tests “did show that LightSquared signals caused harmful interference to the majority of other tested general-purpose GPS receivers,” according to a statement issued yesterday by Anthony Russo, director of the National Coordination Office, on behalf of the National Executive Committee for Space-Based Positioning, Navigation and Timing.
Command and control
Draft data covering recent DOD and FAA tests of cellphones and other consumer GPS devices revealed that 75 percent “experienced harmful interference” when within 100 meters of a LightSquared base station, according to a report in Bloomberg News on December 9.
LightSquared is coming under pressure from several separate directions, as opponents to its plans provide more specific support to their positions on legal, financial and technical issues. And in the background, a telecom industry heavyweight with whom LightSquared hopes to form an alliance wants clarity by year-end.
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.
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.