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GPS makers trade barbs with LightSquared
- — 01 July, 2011 05:38
A GPS industry group dismissed mobile startup LightSquared's alternative proposal for an LTE network that would operate on frequencies close to the GPS band, saying the company hasn't presented any clear plan to reduce interference.
LightSquared formally submitted its new proposal to the U.S. Federal Communications Commission on Thursday, along with test results that showed severe interference with GPS (Global Positioning System) receivers when an LTE (Long-Term Evolution) network was using some adjacent frequencies. LightSquared blamed GPS device makers for the problem, saying they did not build in strong enough filters.
The Coalition to Save Our GPS struck back immediately in a Thursday morning conference call, saying LightSquared's plans violate the laws of physics and can't be made to work in harmony with GPS.
"We do not see a solution other than putting these operations in a band where they won't interfere with GPS," said Jim Kirkland, vice president and general counsel of GPS equipment vendor Trimble, on the conference call.
LightSquared wants to supplement a satellite-based mobile service covering the whole U.S. with a faster LTE network that would reach 100 million people by the end of 2012. In January, the FCC granted the company a conditional waiver to operate that LTE network in spectrum bands that so far have been used for satellite services, which transmit at lower power.
The months of test results that were disclosed on Thursday, as expected, showed that GPS receivers were hobbled by LTE signals in the upper part of LightSquared's spectrum, which is directly below the GPS band. The carrier's alternative plan would leave that upper band alone while service is launched on lower frequencies, which LightSquared said won't affect 99.5 percent of all GPS receivers. The company said it also would transmit at lower power.
The FCC has put both documents out for public comment for 30 days, followed by 15 days for responses. At some point after that, the FCC's International Bureau, which regulates the satellite band, will issue an order on how LightSquared can proceed. That order could be appealed to the full commission.
"We will not permit LightSquared to begin commercial service without first resolving our concerns about potential harmful interference to GPS devices. Nevertheless, our nation cannot afford to let spectrum go underutilized," FCC spokesman Neil Grace said in a written statement.
The GPS group said LightSquared's proposal came too late for adequate testing to support the claim that most receivers wouldn't be affected, and said the plan for lower power needed more detail.
But the conflict goes deeper than that. LightSquared and the companies represented by the coalition, which include Garmin International, John Deere, FedEx, and the Aircraft Owners and Pilots Association, disagree about the fundamental cause of the interference. The Coalition said GPS receivers have to be sensitive enough across a wide band to pick up faint satellite signals, so they are overpowered by very strong signals even if they are in other frequency bands.
"There's no way you could design a receiver in order to block out a billions-of-times-stronger signal in that next band. It's just not possible," Trimble's Kirkland said.
LightSquared's deployment of an LTE network anywhere in the MSS (Mobile Satellite Service) band, if approved by the FCC, effectively would change the rules for that band after decades of GPS gear coexisting easily with satellite systems that have used it, he said.
"The GPS industry has invested billions and billions of dollars making very good equipment that is very precise, and now you've got a new use that's incompatible, and they're blaming the victim," Kirkland said.
LightSquared caught the industry off-guard by submitting its new plan after the testing program was finished, the Coalition said.
"LightSquared was supposed to put forward ideas for mitigation that could be tested, and for the first time now, after the results are in, they're making proposals for how to mitigate," Kirkland said.
The company disputed that charge. LightSquared changed its test plan to reflect the lower band and lower transmission power halfway through the testing program, and all 130 receivers involved were tested with those parameters, LightSquared Executive Vice President Martin Harriman said. In addition, LightSquared introduced vendors of GPS filters to the technical group, but GPS receiver makers showed little interest, he said.