
Olivia MFSK - peter_d_sherman
https://en.wikipedia.org/wiki/Olivia_MFSK
======
vardump
Now that Fountain Code patents have started to expire, hopefully they'll start
to be incorporated in applications like these. Most recently this one [0]
expired today, on June 11th!

With fountain codes [1], you could decode the correct encoded message after
receiving a certain number of _any_ randomly generated sub-messages. The
number of required sub-messages depends on the original encoding parameters.
This encoding is great for very lossy one-way channels.

[0]:
[https://patents.google.com/patent/US6307487B1/en](https://patents.google.com/patent/US6307487B1/en)

[1]:
[https://en.wikipedia.org/wiki/Fountain_code](https://en.wikipedia.org/wiki/Fountain_code)

~~~
seaish
This expired in February. Google Patents puts the current status as today's
date, so it looks like this happened today but it did not.

~~~
vardump
Oh, good catch!

That's pretty misleading. Especially because I was expecting it to be expired
this year, but didn't remember when exactly.

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santix
I would love to read an ELI5 explanation on how it is possible to decode
something that is under the noise floor.

~~~
tonyarkles
The sibling post did a good job at outlining some techniques. I’m going to
give you a simple example that might help with “ahhh you can get stuff under
the noise”

Let’s say you have a noise source made up of random numbers from -1 to 1 (mean
0). And a signal that represents a binary 1 as 0.1 and a binary 0 as -0.1. Our
binary signal gets added to the noise.

With one bit and one noise sample, we don’t really get much out of it. 0.567 -
0.1 = 0.467 and 0.567 + 0.1 = 0.667. Looking at 0.467 and 0.667, we can’t
really make any judgement of whether either of those samples is a 1 or a 0.

If you extend your bits out though so that, say, one bit gets transmitted 100
times, then you can take 100 samples on the receive end and take the mean of
those. Because the noise source has mean zero, the noise component of the
(noise+sample) mean should come out around zero. So you get a mean of maybe
-0.075, or a mean of 0.083. At that point, it’s reasonable to say “it was
likely a -0.1 or 0.1” that was transmitted.

All of the fancy techniques enhance this process, but at its core that’s
fundamentally what’s happening. Some of the techniques spread things out over
different frequencies, some spread out over time, but it’s all roughly the
same idea.

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lifeisstillgood
Hang on ... intercontinental radio contact with one watt RF power

I know that's not a lot of power but can anyone provide comparisons to
"normal" communications intercontinental?

~~~
baybal2
Compare to how much power a single long range fibre line eats + all copper
network in between it and end users.

Olivia was designed to trade a lot of band _width_ for great noise immunity.
In comparison, FSK31 is like 70% as good and is just 31hz wide.

~~~
ryacko
Spectral density is a major factor.

It is a shame that SMS and other low MTU packets aren't transmitted over a low
bandwidth channel, or at least as a failover option. SMS coverage would be
doubled in range, at least.

~~~
jcims
Like pagers? Probably just a function of effectively duplicating all of the
management/authentication/security on top of another physical layer.

~~~
ryacko
No, like LTE Cat NB1 or LTE Cat 0, but at higher transmit power.

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walrus01
Those interested in this may also find the linked Wikipedia page for PSK31 and
PSK63 of interest.

Also, JT65 and FT8.

~~~
tinix
Also
[https://en.wikipedia.org/wiki/WSPR_(amateur_radio_software)](https://en.wikipedia.org/wiki/WSPR_\(amateur_radio_software\))

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amelius
You can also use this modulation scheme to embed hidden messages in image
files.

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upaquin
Any HF capable SDR can be used to receive HF Olivia under $20 with a simple
mod called direct sampling.

[https://phasenoise.livejournal.com/1723.html](https://phasenoise.livejournal.com/1723.html)

~~~
jcims
For folks that want to sniff around a little first, you can hit websdr.org and
listen to receivers all around the world. Most digital mode demodulation
software just listens to the audio pipeline on the PC, so you can actually
decode Olivia, FT8, JT65, CW, etc from these sites as well.

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libria
[Meta] This is probably the one clickbait practice at HN I like: a no-context,
you'll-find-out link to Wikipedia. Don't change it! A description would be a
spoiler.

