Space-time forward error correction for dimmable undersampled frequency shift ON-OFF keying camera communications (CamCom)

Camera communications is the use of an image sensor to receive LED modulated data. This paper shows how frequency shift ON-OFF keying - at frequencies that avoid flicker - can be used to encode bits while at the same time being successfully decoded by a low frame rate camera using subsampling. This is done by selecting mark and space frequencies that are harmonics of the camera frame rate and then processing the subsampled aliased frequencies to decode bit data. PWM dimming is supported via data modulation of the PWM frequency, but requires that FEC be added - in the form of space-time multi-phase sampling - due to asynchronous clocking.