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Will 4G Interfere with GPS? Wireless Firm LightSquared Denies the Charge

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The U.S. has been widely criticized in recent years for falling behind other developed countries in its deployment of high-speed wireless networks. The current dustup involving LightSquared, Bloomberg News and several government agencies provides some clues as to the complexity of the problem.

LightSquared is proposing to build a high-speed nationwide 4G LTE (long-term evolution) network and lease capacity on that network to different wireless carriers, including Sprint Nextel Corp. LightSquared and Sprint subsequently signed a 15-year deal in July through which LightSquared will invest billions of dollars to build and operate Sprint's wireless network. The 4G LTE network will operate on the L-Band spectrum that LightSquared has licensed from the Federal Communications Commission (FCC).

Therein lies a big part of the problem. Because the L-Band is adjacent to the portion of the electromagnetic spectrum used by global positioning system (GPS) services, some purveyors and users of this service fear that LightSquared's 4G network will interfere with GPS used by consumers, businesses and even the military. The 4G networks being rolled out by carriers such as Verizon and AT&T do not operate near the GPS spectrum and so are not at issue here.

In addition to the FCC's monitoring the situation, the National Telecommunications & Information Administration (NTIA), a Department of Commerce agency that oversees airwaves use, requested a test to determine whether LightSquared's 4G wireless service interfered with GPS receivers.

Bloomberg News reported on Friday that thus far 75 percent of the GPS devices tested had experienced interference from LightSquared's 4G network.

The report incensed LightSquared Chairman and CEO Sanjiv Ahuja. On Monday he wrote a letter (pdf) to Ashton Carter and John Porcari , the deputy secretaries of the departments of Defense and Transportation, respectively, demanding an investigation into skewed information he claims was leaked to Bloomberg News. Carter and Porcari are also chairs of the National Executive Committee for Space-Based Positioning, Navigation, and Timing (PNT), the executive-branch advisory group in charge of running the tests.

Ahuja claims that portions of internal analyses of ongoing tests were selectively disseminated in order to "damage LightSquared's reputation, spread false information in the marketplace, and prejudice public opinion against LightSquared before a full and complete analysis of the testing results had been presented."

Ahuja disputes the incomplete results that were presented by Bloomberg, which reported that the PNT found that 69 of 92 of receivers tested "experienced harmful interference" at the equivalent of 100 meters from a LightSquared base station. Ahuja countered by saying, "To achieve that level of threshold of failure, the leaked internal analysis assumes that the power levels of LightSquared networks are 32 times greater than the power levels at which LightSquared will actually operate." Ahuja claims that realistic information was not used in the analysis of the test results. "Based on our review of Bloomberg News' reporting, the leak was based on an incomplete, selective, and slanted analysis of the data of the testing of general location/navigation devices," according to Ahuja.

"LightSquared's own analysis shows that the vast majority of general location/navigation will experience no interference from LightSquared's network," Ahuja adds.

The NTIA acknowledges that the testing of LighSquared's network is not yet complete. The current phase of testing focused on GPS receivers found in mobile phones and personal/general-navigation GPS and was completed by November 30. The NTIA has received the data from this stage of testing but has not yet analyzed the results, says Moira Vahey, an agency spokeswoman. The second phase of NTIA testing will focus on GPS receivers used for high-precision and timing applications.

Whereas Bloomberg reported that results of the NTIA tests would be revealed at an agency meeting on Wednesday, Vahey says they will not be issuing a policy recommendation until all testing is complete. The agency has not yet stated a timeline but is working to address the issues promptly and conclusively, she adds.

Image a taxi ride in Kyoto (aided by a GPS) courtesy of Paul Vlaar, via Wikimedia Commons

The views expressed are those of the author and are not necessarily those of Scientific American.

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