Underwater acoustic communications breakthrough!

[JimRemington]

For a couple of decades, several research groups and startups have gotten nowhere with the idea of cheap underwater acoustic communications. However, there has recently been a real breakthrough. Jeff Neasham and colleagues at Newcastle University in the U.K. have developed spread spectrum acoustic modems (called "nanomodems"): very cheap ($70 instead of $7000), very low power, small and yet long range (km). Data rates are low, but fine for sensor networks.

https://www.economist.com/news/science-and-technology/21741965-tiny-acoustic-modems-will-do-job-better-way-transmit-messages-underwater

https://www.york.ac.uk/electronic-engineering/research/communication-technologies/projects/smart-dust-underwater-wireless-sensing/

I would hope that commercial versions of these might appear in the next couple of years.

[Conrad Hoffman]

Hedy Lamarr strikes again!

[thermistor-guy]

According to the Economist:

.... They are able, as an existing modem is, to broadcast over a distance of up to 2km...

... The transmission rate is a mere 40 bits per second...

Are the researchers taking advantage of the Deep Sound Channel? From https://en.wikipedia.org/wiki/SOFAR_channel

...Near Bermuda, the sound channel axis occurs at a depth of around 1000 metres. In temperate waters, the axis is shallower, and at high latitudes (above about 60°N or below 60°S) it reaches the surface....

It's possible to get close to the Shannon limit with good coding e.g.
https://en.wikipedia.org/wiki/Turbo_code
https://en.wikipedia.org/wiki/Low-density_parity-check_code

But more processing means more power consumption. It would be interesting to know how close to the limit these modems get.

[JimRemington]

Technical details on how the spread spectrum modem actually works are here: https://udrc.eng.ed.ac.uk/sites/udrc.eng.ed.ac.uk/files/attachments/Towards%20large%20scale%20underwater%20communication%20networks.pdf

(PDF slide show by Jeff Neasham).

[CopperCone]

I wonder if its more or less annoying to fish and whales

[SiliconWizard]

I wonder if its more or less annoying to fish and whales

Science and ethics... still a long way to go.

[tggzzz]

I wonder if its more or less annoying to fish and whales

Much less annoying, I presume. There is an awful lot of white noise in the ocean for all sorts of natural sources, and they cope with that.

Indeed the text says it is (as I would expect) almost inaudible; and at any given frequency there is probably a negative signal-to-noise ratio. See, in particular, p15 of that pdf slideshow - the "constellation before despreading".

Correlation has to be seen to be believed.