We are using it in XRWorkout to automatically sync up ingame recordings with external recordings, we are using the audible version instead of the ultrasound version so a human can sync it up too if they are using a regular video editor instead of doing it automatically in our own tools
Here is an example how that sounds https://xrworkout.nyc3.digitaloceanspaces.com/data/video/036...
https://en.wikipedia.org/wiki/Trellis_coded_modulation
The acoustic channel is bound to suffer from multipath too, so some equalization may be needed too.
https://en.wikipedia.org/wiki/Equalization_(communications) https://www.ti.com/lit/an/spra140/spra140.pdf
In order to receive the signal far from the transmitter, some form of spread spectrum encoding could be used, like CDMA. The spreading factor could be negotiated.
https://en.wikipedia.org/wiki/Direct-sequence_spread_spectru...
https://softspectrum48.weebly.com/notes/tape-loading-routine...
I always assumed that PWM was the go-to method for this kind of low bandwidth / high noise medium, I wonder why the author didn't go that route and used FM instead
Is that not FM, more specifically FSK, just with some extra harmonics?
It went something like this: You install some app on your phone, which then listens for incoming audio in the ultrasonic range. The audio is coded instructions, which then would do things like blink a light on your phone or whatever. The idea was that this could be used at events (sport, music, whatever) to create light shows on the mobiles, without relying on good wifi coverage or similar in the avenue. As you could use the PA for the data transmission.
See https://anil.recoil.org/papers/audio-networking.pdf sec 2.1 for the 2003 paper and some ancient videos at https://anil.recoil.org/projects/ubiqinteraction if you want some Nokia nostalgia :-)
Sadly never got picked up, although we proved the concept could work - but it certainly had it's challenges.
For comparison, medical imaging ultrasound is 2-20 MHz (that's MEGA hertz) I think,
adzm•2h ago
Though after a certain point it stops recognizing it, I was still surprised how well it did with noise. I'm sure noise in higher frequencies (or the right harmonics) would be much harder to handle, but solvable in interesting ways too