Will 4G break your GPS?

All four major US cell carriers are beginning to roll out '4G' service via LTE or Wimax, and engineers are worried that GPS coverage will be disrupted over large portions of the country. Apparently, 4G and GPS satellites use similar areas of the spectrum, and when the two types of units get close, 4G signals win.

Guess we can always get a ...shudder... map

Physorg.com recently cited two Garmin engineers who tested for interference between 4G transmitters and GPS receivers. They found that:

"The [handheld] GPS began to experience interference when 5.8 km or closer to the simulated transmitter and lost the fix altogether when 1.1 km away. Interference started at 22.1 km for the aviation receiver, and total loss of fix occurred at 9.0 km from the transmitter." 

The U.S. Air Force has also expressed concern over likely GPS disruption, but is optimistic about working with 4G infrastructure provider LightSquared to remedy the issue.

GPS deadzones might prove a bigger problem for planes, which
rely on GPS to determine speed. And to navigate through
clouds and across oceans! Not to mention ships...

Lightsquared Spokesperson Jeff Carlisle said that the 4G base stations are not at fault. Instead, he explained that some GPS units can 'see into' adjacent frequencies, including the one which Lightsquared uses.