FCC Approval of 4G Transmitters Threatens GPS

4G or not 4G? That is the question. Wide ranging broadband Internet access via portable devices would sure be great, but it could come at a high cost of GPS functionality. A plan to construct 40,000 broadband transmitters for the 4G broadband network could have a "disastrous" effect on GPS reception, according to a report in GPS World.

A company named LightSquared has already received approval from the FCC to launch the 4G network, but a study by GPS stakeholders, including Garmin, could cause wiser heads to prevail in the long run. Each of the 40,000 transmitters has the capability to totally disable a Garmin 430 receiver at a range of as much as five miles. The study conducted by the stakeholders called the multibillion-dollar LightSquared network, "… a disastrous interference problem for GPS receiver operation to the point where GPS receivers will cease to operate when in the vicinity of these transmitters." Given the breadth of the coverage so many transmitters will generate, the plan could, "… deny GPS service over vast areas of the United States," according to the stakeholders' report. LightSquared claims that "properly filtered" GPS devices won't be affected, and the company is working with the GPS industry (under an FCC mandate) to identify devices that could be compromised.

The problem centers on the L Band 1 where the transmitters will operate — 1525 MHz to 1559 MHz. That's perilously close to the GPS frequencies — 1559 MHz to 1610 MHz. The study shows that a Garmin 430, for example, starts to show the effects of interference at as far away as 13 miles from the transmitter. The iconic GA navigator completely loses a fix at 5.3 miles. Current tests are scheduled to determine what filtering will be necessary to protect the GPS receivers, how that filtering might be achieved and how much it might ultimately cost.