LightSquared GPS interference issue flares again in senators' letter

Fri, 04/15/2011 - 8:15am
Maisie Ramsay, Wireless Week

Senators Pat Roberts (R-Kan.) and Ben Nelson (D-Neb.) want the FCC to stop LightSquared from deploying its LTE network until it proves its service doesn't interfere with GPS services.

In an open letter released yesterday, the lawmakers asked their fellow senators to call on the FCC to ensure that GPS service is not compromised in any way by LightSquared's planned hybrid-satellite LTE network.

LightSquared plans to deploy its services on spectrum directly adjacent to GPS bands. The company has developed filters to stop its signal from bleeding into GPS service, but major GPS stakeholders, including the Defense Department, fear that widespread GPS "dead zones" are inevitable if LightSquared's network goes live.

"The full Commission must be involved and require LightSquared to objectively demonstrate non-interference as a condition prior to any operation of its proposed service," the Senators wrote in their letter. "Anything less is an unacceptable risk to public safety."

GPS systems are used by the military, public safety, aviation and consumers. The technology is also used in critical applications across a wide swath of U.S. industries, including agriculture and civil engineering.

LightSquared received a waiver from the FCC earlier this year to use spectrum formerly reserved for satellite services for land-based LTE services. The L-Band spectrum is located next to bandwidth used by highly sensitive GPS receivers, which also use parts of the L-Band spectrum to fine-tune their coordinates.

Many in the GPS industry say the signal sent out by LightSquared's network of 40,000 base stations will create major interference problems that will overwhelm GPS receivers.

"LightSquared is trying to define the potential for interference in a very narrow way – if they filter it so none of the signals go out of their band, that's all they have to do," says Jim Kirkland, general counsel at Trimble. "They say we're eavesdropping on their band, but I would say we can't help but hearing what they're doing in their band."

The FCC has said it will not allow LightSquared to launch commercial services until the GPS interference issue is addressed, but that has done little to assuage fears of the GPS industry.

SkyTerra, which later became part of LightSquared, first proposed incorporating a land-based component into its L-Band satellite services in 2003. The company also worked with the U.S. GPS Industry Council (USGIC) at the time to manage interference posed by out-of-band emissions.

Manufacturers of GPS equipment continued building receivers that listened in to portions of the L-Band after 2003, a practice Kirkland says is for legitimate technical and business reasons.

Jeff Carlisle, head of government and regulatory affairs at LightSquared, says GPS receivers should have been designed differently after 2003. The FCC does not regulate receivers, only transmitters, adding to the complexity of the issue.

"Even though our transmitter is doing exactly what it's supposed to do and not sending any signal into GPS, the receiver is looking into our spectrum either by accident or design," Carlisle said in an interview conducted earlier this month. "There's no problem with that until the receiver crosses the boundary into our area. After 2003, the receivers should have been designed so they were protecting themselves from that interference."

LightSquared says it spent $9 million to develop filters to minimize interference issues and has formed an FCC-mandated technical working group with the U.S. GPS Industry Council (USGIC) to study the issue. LightSquared is set to file a new report from the technical working group today.

Carlisle said that LightSquared is confident the interference issues can be addressed and reiterated the company's intention to launch commercial operations only after the FCC is satisfied with the review process.

"To ensure that the LightSquared network and the GPS systems can coexist, we will continue to work collaboratively with federal agencies and the GPS community, just as we have over the past ten years since the proposed scope of LightSquared's terrestrial network was first publicly announced," Carlisle said.

LightSquared has already signed up Best Buy and Cricket Communications for its wholesale LTE service and plans to begin commercial operations in the first quarter of next year. It is not clear whether the issues with potential GPS interference could affect the company's launch plans.


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