The official report was prepared for the National Coordination Office for Space-based Positioning, Navigation and Timing, an advisory committee made up of government and industry professionals, and confirms earlier findings that the proposed 4G network could cause harmful interference. Following these earlier tests, LightSquared, which is wholly owned by Harbinger Capital Partners, a hedge fund run by millionaire Philip Falcone, agreed to reduce the power of its transmitters and use only frequencies furthest from the GPS frequencies to avoid interference.

...plans to ‘work with the Federal Aviation Administration (FAA) on addressing the one remaining issue regarding terrain avoidance systems.’ However, he said the company disagrees with the conclusion that the network would interfere with general navigation devices...

GPS signals are weak and can be easily outpunched [overridden] by poorly controlled signals from television towers, devices such as laptops and MP3 players, or even mobile satellite services," Andrew Dempster, a professor from the University of New South Wales School of Surveying and Spatial Information Systems, told a March conference on GPS vulnerability in Australia.

"This is not only a significant hazard for military, industrial, and civilian transport and communication systems, but criminals have worked out how they can jam GPS," he says.

The US military has sought for years to fortify or find alternatives to the GPS system of satellites, which are used for both military and civilian purposes. In 2003, a “Vulnerability Assessment Team” at Los Alamos National Laboratory published research explaining how weak GPS signals were easily overwhelmed with a stronger local signal.

“A more pernicious attack involves feeding the GPS receiver fake GPS signals so that it believes it is located somewhere in space and time that it is not,” reads the Los Alamos report. “In a sophisticated spoofing attack, the adversary would send a false signal reporting the moving target’s true position and then gradually walk the target to a false position.”