Saturday, February 9, 2013

Hedwig and the Mobile Web

I had no idea of this until I ran across it in a Sporcle quiz:  Actress Hedy Lamarr, best known for her Hollywood roles in the 40s and 50s, and inspiration for Anne Hathaway's interpretation of Catwoman in The Dark Knight Rises, was also co-holder of a patent for "spectrum hopping" technology that eventually came to be used in WiFi, Bluetooth and CDMA.  The actual names on the patent are Hedy Kiesler Markey (Lamarr's legal name at the time) and avant-garde composer George Anthiel, a neighbor of hers who developed a means of controlling multiple player pianos.

This doesn't seem to be the first patent for such technology.  Earlier work by Otto Blackwell et. al. uses essentially the same idea.  Both use multiple frequencies, and both use a shared key to determine how to shift between frequencies.  The main difference appears to be that Blackwell uses telegraph tape as a keying mechanism while Lamarr and Antheil use player piano rolls.  However, there is little doubt that Lamarr's contributions to the invention were real and that the invention is significant.

It's interesting that both patents are presented as secret communication systems, as someone listening on only one frequency would only get part of the message.  However, it doesn't seem like it would take long for an enemy to hit on the idea of listening on more than one frequency and combining the signals.  So maybe I'm missing something [if power consumption isn't an issue, you could fill all the bands with padding -- anything that statistically looked like the real signal -- which would make the combined signal much less useful].  Today we use spread spectrum technology to increase bandwidth or decrease "power flux density" -- which I assume means about what it says.

It's also worth noting that Lamarr and Antheil didn't benefit significantly from their invention, which was not used in practice until after the patent had expired.  Lamarr did receive stock in a wireless technology company two years before her death, but it's not clear whether that came to anything.  Having made and spent millions over the course of her career, Lamarr spent much of her later years broke, and was twice arrested for shoplifting.

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