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, according to a letter filed to the U.S. Federal Communications Commision (FCC) Thursday by Jeffery Carlisle, executive vice president for regulatory affairs and public policy at LightSquared (Reston, Va., U.S.A.).
“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.
According to LightSquared, the DoD’s GPS 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.
The company also claims the GPS industry spurned international recommendations for GPS receiver design, citing that 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 grants GPS a 4 MHz “guard band.” According to LightSquared, the GPS manufacturers are rejecting its 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 insists on a 34 MHz guard band – 8.5 times as wide as the DoD recommendation, according to LightSquared.
“If all spectrum users demanded the irrational guard band solutions that GPS manufacturers are demanding, we would not have broadband in this country and efficient spectrum use would take a backseat to the squeakiest wheel,” Carlisle said. “This type of precedent would set back the United States' competitiveness by decades. The GPS industry turned a blind eye to the Department of Defense’s recommendations regarding the manufacturing of commercial GPS receivers and a blind eye to the ITU’s long-standing recommendations regarding GPS receiver performance.”
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