Late this January the FCC issued an order for LightSquared to submit a plan to analyze GPS interference issues with its new 4G network. LightSquared, a telecommunications firm from Reston, Virginia, has been operating a voice and low-speed data service via satellite since 1996. In November 2010, LightSquared applied for an “update” of its plans for offering service to include a terrestrial 4G network.
The existing satellite network has been operating in the “L band”, the same band that GPS satellites operate in. The frequency range is 1525-1559 MHz, nearby the GPS L1 frequency of 1575.42 MHz. So far the two services have not had interference issues. With the addition of the terrestrial-based 4G network, there would be 40,000 new 4G base stations added to the system, broadcasting in the same 1525-1559 MHz range.
In a January 16 report to the FCC, they state that the change from very low power space-to-earth signals to fixed, high-power terrestrial broadband service on L Band 1 will seriously damage GPS reception. The report was written by two engineers from Garmin International, a GPS firm based in Olathe, Kansas. The conditions were tested in a controlled laboratory environment by Garmin using two common GPS devices, one consumer-level, and one FAA-certified.
While the bands do not currently interfere, Garmin states this is due only to the signals currently being transmitted at very low power from space. Once the high-power ground-based transmitters are active, Garmin says GPS receivers will experience a complete loss of fix when nearby.