From Newsgroup: comp.misc

I’ve been reading some old issues of “Galaxy” Science Fiction magazine from the 1950s, courtesy of archive.org.

In the September 1957 issue (available online at <https://archive.org/details/galaxymagazine-1957-09>), there is a
story “The Pod In The Barrier”, by Theodore Sturgeon. On pages 28-29,
I came across this passage:

“Whuh? Oh,” said the missile expert. “I guess I was off base
about the jamming. Suddenly it seems to me that’s so obvious, it
must have been tried and it doesn’t work.”
“Right, it doesn’t. That’s because the frequency and amplitude
of the control pulses make like purest noise — they’re genuinely
random. So trying to jam them is like trying to jam FM with an AM
signal. You hit it so seldom, you might as well not try.”
“What do you mean, random? You can’t control anything with
random noise.”
The captain thumbed over his shoulder at the Luanae Galaxy.
“They can. There’s a synchronous generator in the missiles that
reproduces the *same random noise*, peak by pulse. Once you do
that, modulation’s no problem. I don’t know *how* they do it. They
just do. The Luanae can’t explain it; the planetoid developed it.”
England put his head down almost to the table. “The same
random,” he whispered from the very edge of sanity.

This is very much a description of spread-spectrum modulation. Only,
instead of being something so unimaginably far ahead of 20th-century
Earth technology as to seem like impossible magic (as per Clarke’s
Third Law), it was in fact already at least a theoretical possibility.
The famous patent by Hedy Lamarr and George Antheil for
frequency-hopping spread spectrum (FHSS) was granted in 1942, though I
don’t think any practical implementation came about until the
suitable development of transistor technology in the 1960s.

I think also direct-sequence spread spectrum (DSSS), as used in wi-fi
networks today, was invented around that time, though it remained a
military secret for a few years after that.

It could be that Sturgeon never knew about the Lamarr/Antheil patent,
that the technique he describes comes from a leap of his own
imagination -- if only because it seems like cheating to try to pass
off an idea that already seemed to be within the grasp of contemporary technology as something somehow exclusive to a far more advanced
civilization. And also because that patent wouldn’t have made sense to
any reader unless you accepted the idea that “random” numbers don’t actually have to be random.

You see, the one small difference between sci-fi magic and practical
technology is that the pulse sequence doesn’t have to be really
random, it only has to be pseudorandom. Both transmitter and receiver
run the same algorithm with the same seed starting point, and they
will both reproduce the exact same sequence; if the sequence generator algorithm is sufficiently good, then even if an eavesdropper knows
that algorithm, so long as they don’t know the starting seed, they
won’t be able to (easily) figure it out from the signal pulses so far
and predict the rest of the sequence.

Science-fiction fans are fond of pointing out how, every now and then, something that was originally just a far-fetched idea in some SF story eventually comes about in reality. Sometimes that happens rather
sooner than other times.
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