In what may be the death knell for nascent L-band broadband provider LightSquared, nine federal agencies that have analysed the potential interference to GPS receivers from network over the past year agree that the system can not coexist with GPS operations.
"Based on testing and analysis, there appear to be no practical solutions or mitigations that would permit the LightSquared broadband service, as proposed, to operate in the next few months or years without significantly interfering with GPS," said the Deputy Secretary of Defence, Ashton Carter, and Deputy Secretary of Transportation, John Porcari, in a 13 January letter to the National Telecommunications and Information Administration (NTIA), part of the Commerce Department.
Carter and Porcari were speaking for the nine federal departments or agencies that make up the National space-based positioning, navigation and timing (PNT) executive committees (EXCOM).
The work was done at the request of the NTIA and the US Federal Communication Commission (FCC), which gave LightSquared a conditional approval to launch the new network one year ago, pending proof that it could co-exist with GPS.
"Substantial federal resources have been expended and diverted from other programmes in testing analysing LightSquared's proposal," the letter noted.
LightSquared's initial roll out plans, featuring two operational bands, one closer to the GPS operational frequency and one farther away, was shown to have a drastic impact on GPS operations for aviation and other safety-critical functions earlier this year. An amended plan by LightSquared, offering to operate in the lower frequency band only, had been tested by the US Air Force and analysed by the US Federal Aviation Administration (FAA) over past three months.
"It is the unanimous conclusion of the test findings by the National Space-Based PNT EXCOM agencies that both LightSquared's original and modified plans for its proposed mobile network would cause harmful interference to GPS receivers," said Carter and Porcari. "Additionally, an analysis by the FAA has concluded that the LightSquared proposals are not compatible with several GPS-dependent aircraft safety-of-flight systems."
The group said that while it supports the Obama administration's 28 June 2010 request to make available a total of 500MHz of spectrum available over the next 10 years for broadband, that GPS must be protected.
"We propose to draft new GPS spectrum interference standards that will help inform future proposals for non-space, commercial uses in the bands adjacent to the GPS signals and ensure that any such proposals are implemented without affecting existing and evolving uses of space-based PNT services vital to economic, public safety, scientific and national security needs," said the EXCOM.