roman_zeyde

4 ms·

1. 1.▲
   by roman_zeyde 8y ago

   Unfortunately, VoIP doesn't allow reliable OFDM communication... It's preferable to transmit and receive the audio as-is (without any compression).
2. 2.▲
   by roman_zeyde 8y ago

   Thanks, great to hear :)
3. 3.▲
   by roman_zeyde 8y ago

   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
4. 4.▲
   by roman_zeyde 8y ago

   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-r
5. 5.▲
   by roman_zeyde 8y ago

   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&#
6. 6.▲
   by roman_zeyde 8y ago

   Nice idea :) However, I'm not aware of any such protocol...
7. 7.▲
   by roman_zeyde 8y ago

   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.n
8. 8.▲
   by roman_zeyde 8y ago

   Thanks :)
9. 9.▲
   by roman_zeyde 8y ago

   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
10. 10.▲
    by roman_zeyde 8y ago

    Indeed, I am using OFDM [1], which uses several carriers, each modulated via QAM [2]. [1] https://en.wikipedia.org/wiki/Orthogonal_frequency-division_... [2] https://en.wikipedia.org/wiki/Quadratur
11. 11.▲
    by roman_zeyde 8y ago

    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.
12. 12.▲
    by roman_zeyde 8y ago

    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.
13. 13.▲
    by roman_zeyde 8y ago

    ~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]
14. 14.▲
    by roman_zeyde 8y ago

    Author here, thanks for posting this :) Would be happy to answer any question.
15. 15.▲
    by roman_zeyde 9y ago

    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-G