As 4G takes off, can you hear the flight attendant now?

As wireless service providers race to sell 4G services, a proposed LTE phone network has been proven to interfere with GPS

By Keir Thomas, PC World |  Mobile & Wireless, 4G, broadband

For years, flight attendants have asked passengers to turn off personal electronic equipment before flights take off. This is because such devices aren't electromagnetically shielded to aviation standards, and could therefore interfere with airplane electronics. It's a slight risk, but one worth taking seriously.

However, the risk could become significantly higher if you fly in the future with a 4G phone with proposed new services underpinned by technology from LightSquared, a startup that hopes to create its own LTE mobile phone network to rival the likes of Sprint and Verizon.

At least that's according to GPS technology maker Garmin, which has shown that LightSquared's proposed technology can interfere seriously with global positioning system signals.

Clearly the rollout of next-generation phone services isn't going to be smooth. Meanwhile, on the subject of signal interference, European LTE cell phone users might want to keep their phones away from their TVs if they don't want to scramble the picture.

In both cases, the problems relate to radio frequencies. LightSquared intends to offer an LTE service in the United States that operates in the range of 1525 to 1559MHz. That's worryingly close to the 1559 to 1610MHz band used for GPS--too close for comfort, in fact.

Cell phone towers pump out significantly higher power signals compared with what GPS uses, and Garmin has proved that it might not even take an errant cell phone tower to cause issues. Creating a transmitter broadcasting at LightSquared's proposed frequencies, Garmin managed to knock out the GPS fix of one of its most popular consumer devices when it was just over a half a mile away.

More worryingly, an aviation device Garmin sells lost its GPS fix at a distance of just under 14 miles away, and was totally jammed five and a half miles away (Click here for Garmin's report (PDF)).

And that's caused by a single transmitter. Cell phone towers work by being part of a grid of many transmitters that hand calls to and from each other. With multiple transmitters in a town, GPS would in all likelihood be killed dead, and within range in the skies above too.

However, LightSquared is confident that it can overcome the frequency contamination issues, saying that its "rollout of full commercial service will satisfy the concerns about the possibility of inadvertent harmful interference to certain GPS devices."


Originally published on PC World |  Click here to read the original story.
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