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Pianos, torpedos and mobile phones
Profile of Hedy Lamarr, The Economist, June 21 2003
piano, military technology, Hollywood, radio
Saturday, June 28, 2003 01:34 GMT

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.



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.