Proposed commercial broadband wireless service LightSquared claims that, despite recent congressional scrutiny, its technology is not flawed. Rather, says the company, LightSquared interferes with GPS technology only because GPS manufacturers are not compliant with Defense Department and Federal Communications Commission standards. 

"GPS manufacturers have, in fact, ignored government standards in the development of receivers," wrote LightSquared Executive Vice President of Regulatory Affairs and Public Policy Jeffrey Carlisle in an Oct. 3 letter (.pdf) to Chairman Julius Genachowski.

"Although no law mandates how GPS receivers are built, there are established standards governing whether and under what circumstances interference protection may be sought for GPS receivers," wrote Carlisle.

Specifically, LightSquared says GPS manufacturers make GPS devices without "sharp cut-off filters." The DoD's Standard Positioning Service Performance Standards specify that GPS devices should employ a sharp-cutoff filter, which GPS receivers use to block reception of transmissions from adjacent spectrum bands, noted Carlisle.

"One also would think DoD would need this [minimum usage assumption] in light of the deep concerns that have been expressed about the vulnerability of GPS receivers to jamming," wrote Carlisle.

The letter also highlights what LightSquared views as a faulty regulation. According to Code of Federal Regulation 47, Section 15 "incumbent users...must use receivers that reasonably discriminate against reception of signals outside their allocated spectrum." This means if a GPS receiver, acting as an unintentional radiator, is overloaded it must accept interference, wrote Carlisle.

During a Sept. 15 House subcommittee hearing a DoD official disclosed that in tests LightSquared signals interfered with every type of receiver. Many military, aircraft and agricultural technologies depend upon GPS. Since the test, LightSquared has offered an alternative plan that would only use lower power broadcasts and only the lower 10 megahertz of their frequencies, but at the time of the hearing, DoD had not received a sufficiently clear description of LightSquared's alternative plan and was unable to analyze the new aggregate interference environment.

In a press briefing Oct. 3, Carlisle told reporters LightSquared would take legal action if it is denied permission to build its planned LTE network. 

For more:
- see the LightSquared letter (.pdf)

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