A proposed nationwide, open-access 4G wireless broadband network has hit another snag. Testing carried out by a federal agency at the behest of the Department of Defense, Federal Aviation Administration, and a handful of GPS makers showed that the proposed broadband service messed with the performance of 75 percent of the GPS receivers tested. According to a draft of the report obtained by Bloomberg News, LightSquared's signals "caused harmful interference to majority [sic] of GPS receivers tested. No additional testing is required to confirm harmful interference exists."

LightSquared has planned to build a $14 billion nationwide network that it would then resell to wholesale providers (the company says it has no interest in retail). It owns a chunk of spectrum that it plans to devote to the network, but that spectrum—in the area between 1525MHz and 1660.5MHz—is uncomfortably close to that used by many GPS devices.

LightSquared announced plans for its network in July 2010, saying that it would offer the "first truly open and net neutral wireless network." Given the state of broadband penetration and competition in the US, many greeted the company's plans with enthusiasm. Not so the DoD and Department of Transportation. Last April, the two government departments wrote a letter to the Federal Communications Commission asking the agency to look into the possibility of GPS interference.

The GPS industry was also alarmed at the possibility of a nationwide network with over 40,000 towers wreaking havoc with its devices. The industry warned of "tens of thousands of 'dead spots'" miles in diameter where drivers wouldn't be able to get their GPS position or directions. For its part, LightSquared accused the GPS industry of designing products that "depend on using spectrum assigned to other FCC licensees," but did not directly address the question of interference.

The leaked data appears to strengthen the hand of the GPS makers and others who are critical of the proposed 4G network. Testing, which was carried out between October 31 and November 4, showed that 69 of 92 GPS receivers "experienced harmful interference" when within 100 meters of a LightSquared base station.

In a statement e-mailed to Bloomberg, LightSquared executive VP Martin Harriman said that it was "outraged" by the release of the data. "This breach attempts to draw an inaccurate conclusion to negatively influence the future of LightSquared and narrowly serve the business interests of the GPS industry," he told Bloomberg. At the same time, Harriman said that if his company's network is indeed interfering with GPS devices, "we'd like to be sure that doesn't happen."

The full report will be presented on December 14 in Washington, DC.