Government officials warn that new plans for a national high-speed wireless broadband network would cause harmful interference with GPS signals. 

Defense and transportation officials say testing shows no practical solution to the threat posed by the network, planned by the Virginia company LightSquared. 

The officials wrote a letter released Friday by the Federal Aviation Administration. One concern is about potential interference with GPS-based navigation by airplanes. 

The letter was signed by Deputy Defense Secretary Ashton Carter and Deputy Transportation Secretary John Porcari. 

LightSquared has rights to use a section of the electromagnetic spectrum that abuts the part used by GPS.