Marine Drones, Jamming and Full Frontal Nudity

Hah got your attention there. The connection is Austrian-American actress Hedy Lamarr pionere of Cinematic nudity, Marine drone technology and the anti jamming anti interference technology on which WiFi is based.

Notable for the first Hollywood (update: Kaleberg notes that the scene was in “Ecstasy” and that Ecstasy was a Czech production) full frontal nudity scene and the concept of an un jammable, uninterceptable, radio controlled torpedo. Lamarr was born in Austria and married a guy who owned a company which made torpedoes. Post WWI when Austria became land locked, the guy felt a bit Von Trapped. He welcomed the anschluss, she did not, leaving him and Austria. Later she married another guy who made player pianos (update 2:Kaleberg also notes that the player piano guy wasn’t one of Lamarr’s many husbands — I blame The Economist for this mistake (but can’t share the agony of the ecstasy mistake)).

Trying to deal with trouble with her native now annexed country, she thought of combining torpedo and player piano technology with the idea of an un-jammable radio controlled torpedo with player piano mechanisms in the torpedo and the craft that launched it synchronized to change the freequency of transmission/reception in an apparently random pattern. This is the technology my WiFi modem is using to avoid interfering with my neighbor’s WiFi modem.

There is another approach to avoiding accidental jamming (which works just as well to prevent deliberate jamming). It is the way cell phones avoid jamming each other. Unlike the Hedy Lamarr technology it is inherently digital. First consider digital to be 1 and -1 not 1 and zero. Then choose an apparently random series of 1 and -1 (the code) and multiply it by the signal. The product will be apparently random numbers to anyone who doesn’t know the code.

This can be used to make an unjammable signal at the expense of bauds (or whatever bits per second are called these days). make a slowed signal with always 100 1s or -1s in a row. Mutliply it by the apparently random 1s and -1s. send it (allong with dozens of other similar signals from the other guys phone). If you multiply by the code, then you get the 100 1s or -1s in a row plus background noise with variance 0.01 – or with dozens of competing signals variance — well low enough that rounding to 1 or -1 eliminates it.

The two approaches can be combined if the signal is not 100 1s in a row, but 1 sent over 100 different frequencies and the apparently random 1 and -1 is 1 for 50 frequencies and -1 for 50 frequencies. If one doesn’t know the apparently random pattern of 1 and -1, one can’t jam the signal. Figuring it out is like breaking a modern code — it is an NP problem which can be solved once one gets quantum computers to work.

Importantly the apparently random series is made with a pseudo random number generator based on a seed. A new seed can be transmitted (the coding prevents intereception as well as preventing jamming) so the code can be changed say once a second.

All of this requires digital technology which costs cents and weighs a fraction of a gram. It can be put in cardboard drones.

Now there is a strong rule — don’t put all your eggs in one basket — that one should not count on technology which one hopes will never fail but which has a common failure mode. In spite of that, I think counting on unjammable signal technology keeping ahead of jamming technology is the best available bet and propose going full drone and giving up on manned aircraft and crewed ships.

Update: Angrybear 9/21/2023 New York Times 9/22/2023 “The drones have begun to make a difference in one corner of a stagnant war, soldiers, commanders and pilots said in interviews, because their different materials and variable frequencies can evade enemy jamming systems” , “starting in the summer, a flurry of tweaks to drone designs and radio frequencies began to allow Ukrainian pilots, who had initially lost dozens of drones in the opening weeks of a counteroffensive in the south, to send their drones far beyond the front line”, “Operators also switch between frequencies mid-flight or fly close to the ground to evade Russian units trying to track them”, and “The solution his teams have created — using drones with few metal parts and frequently shifting radio frequencies”.

Hedy Lamarr thought of that before she ever took her clothes off in front of a camera.