Coded orthogonal frequency-division multiplexing television

COFDMTV is based on COFDM (coded orthogonal frequency-division multiplexing) technology:

• 160 ms long OFDM symbols

• 6.25 Hz per sub-carrier

• ¹⁄₈ guard interval

• Differentially encoded PSK (phase-shift keying) modulation

• Systematic polar codes for forward error correction

• Open-source modem specification and implementation

Following modes are supported:

Using SPC(64800, 43072):

• Mode 6: 8PSK, 2700 Hz BW and about 10 seconds long

• Mode 7: 8PSK, 2500 Hz BW and about 11 seconds long

• Mode 8: QPSK, 2500 Hz BW and about 16 seconds long

• Mode 9: QPSK, 2250 Hz BW and about 18 seconds long

Using SPC(64512, 43072):

• Mode 10: 8PSK, 3200 Hz BW and about 9 seconds long

• Mode 11: 8PSK, 2400 Hz BW and about 11 seconds long

• Mode 12: QPSK, 2400 Hz BW and about 16 seconds long

• Mode 13: QPSK, 1600 Hz BW and about 24 seconds long

Payload must be smaller or equal to 5380 bytes.

JPEG, PNG and WebP image formats are supported.

Width and height are limited to between 16 and 1024 pixels.

Shredpix

You can install Shredpix from the Google Play Store:

https://play.google.com/store/apps/details?id=com.aicodix.shredpix

See the manual for Shredpix here: manual

Shredpix converts images to COFDMTV encoded audio signals and is based on open-source software:

• OFDM modem encoder and specification:
  https://github.com/aicodix/modem
  BSD Zero Clause License

• Polar and BCH codes:
  https://github.com/aicodix/code
  BSD Zero Clause License

• Fast Fourier Transform:
  https://github.com/aicodix/dsp
  BSD Zero Clause License

• Launcher icon:
  http://tango.freedesktop.org/Tango_Desktop_Project
  Public Domain

Assempix

You can install Assempix from the Google Play Store:

https://play.google.com/store/apps/details?id=com.aicodix.assempix

See the manual for Assempix here: manual

Assempix decodes COFDMTV encoded audio signals to images and is based on open-source software:

• OFDM modem decoder and specification:
  https://github.com/aicodix/modem
  BSD Zero Clause License

• Polar list and ordered statistics decoding:
  https://github.com/aicodix/code
  BSD Zero Clause License

• Digital signal processing:
  https://github.com/aicodix/dsp
  BSD Zero Clause License

• Launcher icon:
  https://github.com/google/material-design-icons
  Apache License 2.0

Privacy Policy

To decode COFDMTV encoded audio signals, the apps need access to the microphone.
Having access to the microphone is considered to be a sensitive permission and you
have the right to know what the apps do with that access:
The data recorded from the microphone is only used to feed the COFDMTV decoder,
VU meter and the spectrum analyzer for visualization of its frequency content.
The apps use a very small temporary buffer in volatile memory and constantly
overwrite this buffer with new data from the microphone.
The resulting image and text from the COFDMTV decoder is the only data that gets stored
in persistent storage on your Android device.