In-flight Cell Calls Possible, but Solution is Complex

"Passengers don't know what kind of technology they've got in the phones, and the likelihood is that an airplane would have all the flavors of technology on board."


Qualcomm research has shown it's possible to use cell phones aboard airplanes without undue ground network interference, but the company is not surprised by this week's FCC proposal to drop the idea entirely.

Federal Communications Commission chairman Kevin J. Martin on Thursday said that he has recommended that the commission reject a proposal to allow the use of cell phones aboard airplanes because of the potential for interference on the nation's cellular networks.

Paul Guckian, vice president of engineering for San Diego-based Qualcomm, said yesterday that the wireless company has devised ways to prevent interference on the cellular networks. But the solution is complicated and costly, one that wireless carriers are not eager to pursue.

"We did a proof of concept to show that, conceptually, it is doable," Guckian said. "But the technical solution was complex."

Signals from airplanes can potentially confuse cellular networks.

On the ground, a cell phone regularly connects to the nearest cellular antenna to let the system know where it is and that it is available to receive calls. As the cell phone moves, say, in a vehicle, the signal is handed off from one antenna to the next. A cell phone thousands of feet overhead could contact numerous antennas, potentially dropping calls of users on the ground.

Qualcomm is considered one of the world's leading researchers on the potential of interference from cell phones on airplanes. It has spent the past several years studying the effects of cell phone transmissions aboard airplanes for both the airline and wireless industries in the United States.

The company even partnered with American Airlines in 2004 for a "proof of concept" test using cell phones aboard an MD-80 aircraft flying over Dallas. The two-hour test, done with the permission of the FCC and the Federal Aviation Administration, successfully showed that it was possible to make cell phone calls in flight without interfering with the ground network or with the aircraft's communication and navigation system.

To eliminate the problem of a phone contacting many cell towers on the ground, Qualcomm installed a small cell phone antenna, called a pico cell, on the plane that linked the calls to a satellite system and then to the Sprint network on the ground.

The idea was that cell phones aboard the plane would communicate with the pico cell instead of searching for a network on the ground. It worked well for cell phones that use Qualcomm's code division multiple access, or CDMA, technology. Verizon Wireless and Sprint are among the U.S. carriers whose networks are CDMA-based.

But Qualcomm found in additional tests that other wireless technologies, including GSM, TDMA and analog cell phone technologies, were more likely to cause interference on the wireless networks, despite the use of pico cells aboard the planes.

Guckian said CDMA cell phones work at lower power levels, thus having less potential to interfere with ground networks.

If the United States were to allow cell phones to be used on airplanes, then it is only practical to allow all cell phones to be used, not just some of them, Guckian said.

"Passengers don't know what kind of technology they've got in the phones, and the likelihood is that an airplane would have all the flavors of technology on board," he said. "Some people have cell phones that are 10 years old that they keep in a drawer until they go on holiday. Designing a system that is capable of managing all of these technologies is quite a challenge."

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