  The current increasing need for privacy-preserving voice communications is
leading to new ideas for securing voice transmission. This paper refers to a
relatively new concept of sending encrypted data or speech as pseudo-speech in
the audio domain over existing voice communication infrastructures, like 3G
cellular network and Voice over IP (VoIP). The distinctive characteristic of
such a communication system is that it relies on the robust transmission of
binary information in the form of audio signal.
  This work presents a novel Data over Voice (DoV) technique based on codebooks
of short harmonic waveforms. The technique provides a sufficiently fast and
reliable data rate over cellular networks and many VoIP applications. The new
method relies on general principles of Linear Predictive Coding for voice
compression (LPC voice coding) and is more versatile compared to solutions
trained on exact channel models. The technique gives by design a high control
over the desired rate of transmission and provides robustness to channel
distortion. In addition, an efficient codebook design approach inspired by
quaternary error correcting codes is proposed.
  The usability of the proposed DoV technique for secure voice communication
over cellular networks and VoIP has been successfully validated by empirical
experiments. The paper details the system parameters, putting a special
emphasis on system's security and technical challenges.
