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From: dave@westmark.westmark.com (Dave Levenson)
Newsgroups: comp.dcom.telecom
Subject: Re: Cellular Phone Use on Airport Runway
Message-ID: <12337@accuvax.nwu.edu>
Date: 19 Sep 90 01:30:10 GMT
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In article <12175@accuvax.nwu.edu>, monty@sunne.east.sun.com (Monty
Solomon) writes:

> How does cellular phone use in the air interfere with users on the
> ground?

The cellular telephone system depends upon spatial diversity.  The
channel you're using is also in use at numerous other cell sites, far
enough from your location that others may use them without
interference.  A cellular phone in a plane, being approximately
equi-distant from numerous cell sites, occupies a channel
simultaneously throughout the cellular system.  This may impose a
heavy switching load on the cellular switch, which may continually try
to hand the call off among the numerous cell sites, each of which
thinks it's got a close location to the mobile unit.  It may also
cause interference with other calls on the same frequency.

It is also possible that the cellular phone's transmitter, aboard the
aircraft, would cause interference with the navigation or
communication radio equipment aboard the same plane.  When the plane's
autopilot, having been misguided by the interfering signal on a
coupled approach, attempts to land the plane somewhere _near_ the
airport rather than on it, people on the ground may get hurt (not to
mention the danger to people on the plane).  This is why the operation
of most portable electronic devices is prohibited in flight.

> It would seem reasonable to permit cellular phone use from the plane
> once it lands.  Why did the FCC prohibit this as well?

As the original article described, it would be difficult to ensure
that the use ends as the plane takes off.


Dave Levenson			Voice: 908 647 0900  Fax: 908 647 6857
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