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The Commerce Department's National Telecommunications and Information Administration has called for further testing of possible interference between LightSquared Inc.’s proposed high-speed wireless network and critical global positioning systems operations.
In a letter to Defense Deputy Secretary William Lynn and Transportation Deputy Secretary John Porcari, NTIA Administrator Lawrence Strickling urged both agencies to work with LightSquared to test whether the proposed network would still interfere with GPS devices on 10 megahertz of spectrum that is lower in the L-band and further from GPS operations than the block of spectrum the company originally planned to use for deployment.
Strickling advised the federal agencies to focus testing, at least for now, on cellular and personal navigation receivers.
“That data, combined with information the Federal Communications Commission is collecting on receiver design and specifications, will allow us to understand more completely the interference interaction and causation and provide necessary information to determine whether we need to propose any additional operating condition on LightSquared to mitigate overload from LightSquared base stations to these types of devices,” Strickling wrote in a letter dated Sept. 9.
The company's plan, revised in June to address interference concerns, proposes to initially deploy a nationwide 4G (fourth-generation), wholesale LTE (long-term evolution) network using 10 MHz of downlink spectrum that is furthest in the L-band from GPS operations. It also recommends limiting the permitted power level of an estimated 40,000 base stations that are needed for nationwide rollout to avoid overwhelming the faint signals of GPS devices.
Recent test results have confirmed that use of the company's upper 10 MHz block of frequencies—not the lower block, the block that LightSquared now proposes to use for initial rollout—interfered with GPS receivers used by the Coast Guard, NASA, and the Federal Aviation Administration, and caused GPS receivers used by state police, fire, and ambulance crews to lose reception.
LightSquared claims moving operations to the lower 10 MHz will alleviate interference problems with most GPS devices, at a cost to company of $100 million.
Although the company has said no new tests are necessary, the company greeted the letter with optimism.
“The NTIA's letter has established a path forward that will finally allow LightSquared to put concerns about the impact of its network on GPS to rest,” LightSquared Chief Executive Officer Sanjiv Ahuja said in a statement Sept. 12. “LightSquared has already undergone one of the most extensive batteries of interference testing ever conducted and remains confident that this new round of testing will confirm those earlier results.”
“We have always said that we believe this to be a resolvable engineering issue, and we are completely confident in our ability—working in cooperation with the GPS industry—to find a solution to the interference problem,” he added.
LightSquared has also agreed to further reduce power levels and underwrite the development of new filtering technologies to avoid interference with GPS. The company detailed those commitments in a new proposal just filed with the Federal Communications Commission.
Specifically, under the proposal, LightSquared agreed to the following power limits on the ground: -30dBm (decibels below 1 milliwatt) now, -27 dBm after Jan. 1, 2015, and -24 dBm after Jan. 1, 2017. The company also said it will provide a long-term satellite signal for a GPS augmentation link at a frequency near the top of its downlink band in the 1555-1559 MHz band, which would further reduce the chance of interference to precision receivers.
LightSquared said testing done by the working group mandated by the FCC shows that its proposed ground-level power limits would address nearly all cases of interference to GPS receivers. On the issue of high-precision devices, LightSquared said that 10 of the 38 receivers tested “appear compatible” with the -30 dBm power level on the ground using the lower 10 MHz. As part of the proposal, LightSquared offers solutions to retrofit or upgrade precision receivers with a universal filter.
In response, the Coalition to Save Our GPS said the proposal “appears to be a positive step,” but noted that more testing is needed to address interference to high-precision GPS receivers.
“Even if additional testing confirms that LightSquared's third proposal will reduce interference to some devices, it still leaves a huge gap because it does not claim to solve interference to high-precision GPS receivers, many of which were designed to use satellite services provided by LightSquared in the MSS [Mobile Satellite Services] band,” the coalition said in a statement.
The coalition, which includes FedEx Corp., United Parcel Service Inc., GPS-unit makers Trimble and Garmin Ltd. and the Air Transport Association with members Delta Air Lines Inc. and American Airlines, further pointed that the primary focus of testing thus far was a “spectrum configuration” that LightSquared has now abandoned. The testing of the configuration that LightSquared now proposes to use—the lower 10 MHz of its spectrum—was only conducted on a “limited basis” shortly before the conclusion of testing, it said.
By Paul Barbagallo
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