Data over voice using time-warping technique

Simultaneous transmission of a digitally modulated signal and a voice signal known as data over voice (DOV) is discussed. In particular a minimum shift keying (MSK) modulation format is considered. A new method is used which is based on a time-warping technique, where having the instantaneous phase (frequency) of the MSK signal, the MSK signal is transformed into a harmonic one with known frequency, while the voice signal, which is broadband, is transformed into another broadband signal. Consequently, after performing the time-warping, it is possible to separate the transformed MSK signal and the transformed voice signal by using a fixed coefficient second order constrained notch filter. The instantaneous phase of the MSK signal, needed for time-warping, is synthesized by using the output of the MSK receiver. It is shown that if the peak value of the voice signal is below the amplitude of the MSK signal, then the performance of the MSK receiver is only midly influenced by the voice signal, and the reconstructed voice signal has high intelligibility.