Transmissions from the nationwide cellular network planned by startup LightSquared knocked out GPS receivers operating at distances of 600 feet to 185 miles from the company's base station, according to the latest test report on interference caused by the company's system.
Deane Bunce, the Federal Aviation Administration co-chairman of the National Position, Navigation and Timing Engineering Forum, a multiagency group chartered to assess GPS technical issues, told a meeting of the National Space-Based PNT Advisory Board on Thursday that tests in April showed "all GPS receiver applications [are] impacted by [the] proposed LightSquared network."
The Federal Communications Commission on Jan. 26 approved LightSquared's hybrid satellite-terrestrial network, which will include 40,000 base stations.The agency directed the company to work with the GPS industry to determine the potential effect its terrestrial transmitters, which operate in the 1525-1559 MHz and 1626.5-1660.5 MHz bands, would have on GPS systems that operate in the nearby 1559-1610 MHz band.
Bunce said simulation of the planned LightSquared network showed it would "degrade or result in loss of GPS function . . . at standoff distances ranging from a few kilometers and extending to space operations."
In his presentation to the advisory board, chaired by former secretary of Defense James Schlesinger, Bunce said Defense Department tests of the LightSquared system and its effects on GPS at White Sands Missile Range, N.M., April 4 to 7 showed that all FAA aviation receivers, Deere and Co. precision farming receivers, and survey receivers tested "lost their GPS solution," meaning they could not function in the presence of the LightSquared base station.
Bunce added that the tests, conducted in a special chamber at White Sands that isolates test signals from outside radio interference, also showed that the LightSquared system knocked out a personal navigation GPS receiver from Garmin International and would have an undefined impact on a precision GPS network operated by the Coast Guard.
He also said more details on a previously issued report on the interference LightSquared caused to GPS receivers that first responders used with a LightSquared transmitter mounted on a 100-foot tower at Holloman Air Force Base, N.M. In this instance, a GPS receiver in a police cruiser lost its signal 600 feet from the tower and the GPS receiver in an ambulance showed the vehicle was moving at a speed of 9 mile per hour, when in fact it was stopped.
General Motors OnStar system, installed in close to 6 million vehicles, and used for emergency road services and GPS-based turn-by-turn navigation, experienced "significant degradation of service" during the Holloman tests, which ran from April 14 to 17, Bunce said.
NASA's Jet Propulsion Lab determined that the LightSquared system showed "significant interference" to GPS receivers at a distance of 185 miles, he added.
Jeff Carlisle, executive vice president for regulatory affairs at LightSquared, pointed out that Bunce did report that when operated in the lower frequency band of its allocated spectrum, it caused minimal effects on the limited number of receivers that were tested, a conclusion an FAA advisory group reached last month.
Carlisle said LightSquared will work with the government and the GPS industry to develop interference mitigation strategies, including lower transmitter power and use of filters on transmitters and GPS receivers to reduce interference.
Bunce suggested receiver filters as a possible mitigation strategy, but said it would result in "considerable expense and [a] lengthy transition period" to replace existing GPS receivers with new ones that can filter out the LightSquared signal. He also suggested LightSquared use only its lower band, which Carlisle said LightSquared could go along with on an initial deployment. But, Carlisle said, eventually the company intends to use all the spectrum allocated to it by FCC.
This is a high-stakes battle. LightSquared has spent $1 billion to build and launch a powerful broadband satellite and industry officials estimate it will cost the company between $6 billion and $9 billion to build a national terrestrial broadband cellular network. In addition, LightSquared has spent $100 million on chip-set technology for dual satellite-terrestrial handsets and data cards, Carlisle said.
According to the GPS Industry Council, a trade group, GPS represents a $22 billion investment by the federal government and billions of dollars more by end users to develop applications that serve defense, public safety and homeland security needs, as well as a range of industries.
LightSquared, the GPS industry and federal agencies will file a final report on the interference tests with FCC next Wednesday and after that FCC is expected to allow the public to comment.