roman_zeyde

há 8 anosdiscuss

Unfortunately, VoIP doesn't allow reliable OFDM communication... It's preferable to transmit and receive the audio as-is (without any compression).

roman_zeyde

há 8 anosdiscuss

Thanks, great to hear :)

roman_zeyde

há 8 anosdiscuss

QAM is using both carrier's amplitude and phase to encode information, so I/Q can be thought as [1]:

  I = amplitude*cos(phase)
  Q = amplitude*sin(phase)

[1] http://whiteboard.ping.se/SDR/IQ

roman_zeyde

há 8 anosdiscuss

The original goal was transmitting ~10kB in a few seconds over an audio cable, so I didn't try to improve the transmission speed much further. I guess that adding error correction coding will allow increasing the highest possible bit-rate (currently I'm using only CRC-32 for error detection).

roman_zeyde

há 8 anosdiscuss

Thanks a lot, I definitely agree :)

I didn't try Google Nearby, since I was developing the modem to run on a desktop machine (but later I've created a simple Android app [1], supporting the lowest bit-rate).

Unfortunately, I don't have a working web-based version of my modem...

[1] https://play.google.com/store/apps/details?id=bit.zeyde.audi...

roman_zeyde

há 8 anosdiscuss

Nice idea :)

However, I'm not aware of any such protocol...

roman_zeyde

há 8 anosdiscuss

No, I've used it only on my Linux machine.

I guess it should also work on MacOS, since it depends on `numpy` [1] and `portaudio19-dev` [2] Debian packages (which should be installable via Pip/Homebrew).

[1] http://www.numpy.org/

[2] https://people.csail.mit.edu/hubert/pyaudio/

roman_zeyde

há 8 anosdiscuss

Thanks :)

roman_zeyde

há 8 anosdiscuss

Both :)

The initial use-case was performing air-gapped communication for signing Bitcoin transactions [1] on an offline machine.

[1] https://github.com/spesmilo/electrum/pull/964

roman_zeyde

há 8 anosdiscuss

Thanks!

Using an audio cable (for better SNR), I have managed to achieve and sustain 60kbps for long periods time - so 3MB file should take ~7 minutes to transmit.

roman_zeyde

há 8 anosdiscuss

Currently, it does not - mainly because I've tried to use all available bandwidth (to increase the bit-rate).

Please take a look at https://github.com/quiet/quiet-js for an ultrasonic data transmission.

roman_zeyde

há 8 anosdiscuss

~3 meters is indeed quite a challenging scenario. I've tested it with the lowest bit-rate supported (1 kbps), but it doesn't work reliably.

You can try my Android app [1] to reproduce the experiments for short transmissions.

[1] https://play.google.com/store/apps/details?id=bit.zeyde.audi...

roman_zeyde

há 8 anosdiscuss

Author here, thanks for posting this :)

Would be happy to answer any question.

roman_zeyde

há 9 anosdiscuss

I can suggest using TREZOR and Ledger Nano S hardware devices for common GnuPG operations, e.g. signatures and decryption.

Please take a look at https://github.com/romanz/trezor-agent/blob/master/README-GP... for more details.

Disclosure: I am the main developer of this project.

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