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<nettime> Pianos, torpedos and mobile phones
Rana Dasgupta on Sat, 28 Jun 2003 18:30:05 +0200 (CEST)


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<nettime> Pianos, torpedos and mobile phones



Came across this in the Economist recently.  It's a fascinating story of
how music (specifically, player pianos) provided a technology that was
used to solve a military problem and that went on to be a part of modern
telecommunications.  All thought up by a Hollywood femme fatale.

R


PLAYER-PIANO PIONEER

Profile of Hedy Lamarr, The Economist, June 21 2003

She is chiefly remembered as a femme fatale and a pioneer of the nude
scene. But Hedy Lamarr, a Hollywood actress who died in 2000 also played
an unlikely off-screen role as a technological pioneer, co-inventing in
the 1940s an early incarnation of spread-spectrum wireless technology.

Lamarr accompanied her husband, Fritz Mandl, an Austrian arms dealer, to
numerous meetings and dinners, and became familiar with the problem of
sending control signals to a torpedo after it was launched from a ship.
Using wire several miles long was impractical, so the obvious alternative
was to use radio instead.  But that would alert the enemy that a torpedo
was on its way, allowing its signal to be jammed.

After divorcing her husband, Lamarr ran away to America in 1937.  She
found success in Hollywood, where she met George Antheil, an experimental
composer, at a dinner party in 1940.  He was knows for composing music for
"player pianos", mechanical instruments that play back music encoded as
holes punched in a role of paper.  Lamarr realised that Antheil, who
shared her opposition to the Nazis, could help her develop an idea to make
radio transmissions extremely difficult to jam or intercept.

The pair were jointly awarded a patent in 1942 for a "secret communication
system".  The idea at its heart was that of "frequency-hopping".  By
changing the frequency of a radio transmission many times a second,
causing it to leap around in an apparently random fashion, a radio signal
could be made almost impossible to intercept.  Only a receiver programmed
with the same random sequence would be able to follow the signal as it
hopped from one frequency to another.

Both sending and receiving stations would, however, need some mechanism to
encode and control the frequency-hopping pattern.  Lamarr and Antheil
proposed using a punched paper roll - like that of a player piano.  Their
system would hop between 88 different frequencies, the number of keys on a
modern piano.  The player-piano rolls in the transmitter (aboard the ship)
and receiver (in the torpedo) would be started at exactly the same moment
and would stay synchronised after lunch, providing a secure radio link
from the ship to the torpedo.

This idea is known today as "frequency-hopping spread spectrum" (FHSS)
since the signal, as it hops, is thus spread across a range of the radio
spectrum, rather than remaining on a single frequency.  Lamarr and Antheil
offered their idea to America's armed forces, but it was not taken
seriously.

It was nearly 20 years before a radio based on FHSS was eventually
constructed, using electronic components rather than mechanical components
and paper rolls.  It was used to secure communications during the Cuban
missile crisis in 1962.  Code-division multiple access (CMDA) is based on
another approach, called "direct-sequence spread spectrum" (DSSS), so it
is not directly descended from Lamarr's work.  But FHSS lives on in
today's mobile phones: it is the basis of Bluetooth, a short-range
wireless protocol that is used to connect handsets to other nearby
devices.


::::::::::::::::::::: 
Rana Dasgupta www.ranadasgupta.com
:::::::::::::::::::::




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