The GPS industry’s failure to comply with the Department of Defense’s (DoD) filtering standards is the root cause of potential interference issues involving LightSquared’s proposed broadband wireless network, LightSquared Executive Vice President for Regulatory Affairs & Public Policy Jeffrey Carlisle wrote in a letter filed today with the Federal Communications Commission.

“Had the GPS industry complied with DoD’s recommended filtering standards for GPS receivers, there would be no issue with LightSquared’s operations in the lower portion of its downlink band,” Carlisle stated in the FCC filing.

The DoD’s Global Positioning System Standard Positioning Service Performance Standard, issued in September 2008, calls for GPS receivers to filter out transmissions from adjacent bands in order to achieve the performance intended to be provided by the GPS system.

In addition to ignoring the DoD standard, the GPS industry also has spurned international recommendations for GPS receiver design. Since 2000, the International Telecommunication Union (ITU), the United Nations agency that sets international standards for radio and satellite spectrum, has cautioned that “a more stringent pre-correlator filter may be needed to protect [GPS] receiver operations from adjacent band RF emissions.”

The DoD standard, in effect, grants GPS a 4 MHz “guard band.” Now, however, the GPS manufacturers are rejecting LightSquared’s offer of a 23 MHz guard band that would be created by LightSquared’s decision to begin its terrestrial operations in the lower half of the downlink band.
Instead, the GPS industry unreasonably insists on a 34 MHz guard band – 8.5 times as wide as the DoD recommendation.