Some big names in the GPS industry – such as Garmin and Trimble got together with U.S. GPS Industry Council got together and published a study to warn FCC that the proposed 4G network by LightSquared would jam everyday GPS devices such as Garmin 265W and even FAA certified GNS 430W (general aviation receiver) from literally miles and miles away.
The heart of the problem is that LightSquared intends to use L Band 1 (1525 MHz—1559 MHz), which is right next to where the GPS frequencies of 1559—1610 MHz. If the proposal by LightSquared goes through they’d be covering the nation with with 40,000 transmitters which would turn vast areas of U.S. into a big dead zone for GPS receivers.
Read more here:4G Broadband interferes with GPS? Garmin says yes.