GPS Group Seeks Partial Ban on LightSquared

A group of GPS vendors and users has asked the U.S. Federal Communications Commission to permanently block LightSquared from using the upper band of its licensed radio spectrum for a cellular data network.

LightSquared wants to build an LTE (Long-Term Evolution) network using frequencies near the band used by GPS (Global Positioning System). The FCC has said it can only do so if interference between the two systems is resolved. After tests showed strong interference in the upper 10MHz band of LightSquared's frequencies, the carrier said it would start by operating on a lower band, which is also 10MHz wide. However, it holds out hope of using the upper band in the future.

In a filing (PDF) to the FCC on Tuesday, the Coalition to Save Our GPS asked the agency to immediately rule out use of the upper band of spectrum. The group, a longtime critic of LightSquared, said uncertainty about how interference in that block will be addressed is hurting efforts to deal with the lower block.

"The FCC owes it to all concerned to immediately act to ensure that this cloud is removed and that LightSquared is put on clear notice that it will not be allowed to pursue future terrestrial use of the upper MSS spectrum," the filing said. "A prompt ruling responsive to the Coalition's request will also create a much more constructive and solutions-oriented process for completion of consideration of LightSquared's proposed lower band operations."

Though there is no dispute that engineers from both sides have cooperated on interference tests and continue to do so, there has been a vicious war of words over LightSquared's plans to use either of the frequency bands. LightSquared maintains that an LTE network operating in the lower band would only affect high-precision GPS receivers and that there are already filters available to solve that problem. The GPS group still questions whether those filters will work and has balked at LightSquared's proposal that GPS vendors and users should pay for much of the proposed retrofitting for privately owned receivers.

In its filing, the Coalition said the GPS industry is worried about an even more expensive and time-consuming retrofitting effort for the upper band later, should LightSquared again go after that band for additional capacity. Tests in the upper band, conducted earlier this year, showed strong interference affecting a wide range of common GPS receivers.

Also in the filing, the Coalition said that the earlier tests showed a harmonic effect caused specifically by using both bands at the same time. If LightSquared eventually had its LTE network use both the upper and the lower band, this "intermodulation" would create signals inside the GPS band itself, separate from LightSquared's own licensed spectrum. This argument is different from most of the debate so far, which has focused on interference that takes place without any signals being transmitted outside an assigned band. Instead, the conflict has focused on GPS receivers scanning for weak satellite signals across a wide range of frequencies and being overpowered by strong LTE signals that are within LightSquared's band.

LightSquared attacked the Coalition's filing on Monday and repeated its call for GPS vendors to stop their receivers from using any of LightSquared's frequencies. "Now the industry is demanding that the government formally expropriate part of LightSquared's spectrum -- worth billions of dollars -- and turn it over to the GPS industry in perpetuity," LightSquared said in a written statement. "Today's filing is little more than a land grab designed to reward spectrum squatters who have failed to innovate their technology."

Stephen Lawson covers mobile, storage and networking technologies for The IDG News Service. Follow Stephen on Twitter at @sdlawsonmedia. Stephen's e-mail address is stephen_lawson@idg.com

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