Gov't Tests Confirm LightSquared Interference with GPS

Government tests appear to confirm earlier tests done by the GPS industry: LightSquared's proposed mobile broadband network disrupts GPS devices in the area. The data is given more weight by the impartiality of the testing, but wasn't a surprise: LightSquared's spectrum block is right next to that used by GPS receivers.

All GPS devices tested were affected, but some more than others. The government's tests were overseen by the National PNT Engineering Forum, a federal advisory group of engineers. Some devices simply saw signal strength degrade. Others were completely disabled. For example, the tests found that GM's OnStar system saw a "significant degradation of service" on most receivers tested.

A separate FAA-commissioned study found that "GPS operations below 2000 feet [of elevation] would be unavailable over a large radius of metro (areas)" for aircraft. Meanwhile, James Kirkland, vice president and general counsel of GPS maker Trimble Navigation said, "It will cause interference. It will cause devastating interference. There is not a solution here. In our view it's time to stop squandering resources on this and find alternative spectrum for them."

An alternative spectrum block would move LightSquared's operations away from that of GPS receives, eliminating the interference. The FCC gave LightSquared preliminary approval for the network in January pending interference tests.

The tests also suggested that professional, more precise GPS devices used by corporate and government users would be more likely to affected by LightSquared interference than cheaper consumer units.

Possible solutions include the aforementioned move of LightSquared's service to a different spectrum block. Or, the spectrum block could be reduced in size. Another possibility, though a daunting one, would be to install filters on GPS receivers to limit LightSquared interference.

A joint industry report from LightSquared and the GPS industry is due on June 15th; there will then be a public comment period before the FCC makes its final decision.