Simultaneous Transmission of Speech and Data Using Code-Breaking Techniques
Robert JC Steele, D. Vitello · Bell System Technical Journal · 1981
A system whereby speech is used as a data carrier is proposed. The speech, sampled at 8 kHz, is divided into blocks of N samples, and provided the correlation coefficient and mean square value of the samples exceed system thresholds, data is allowed to be transmitted. If the data is a logical 0, the samples are sent without modification; however, if a logical 1 is present, frequency inversion scrambling of the samples occurs. The receiver performs the inverse process to recover both the speech and data. Data rates of 700 b/s were achieved without data errors or speech distortion via an ideal channel. The effects of additive background and channel noise were investigated, and the system was shown to operate at 126 b/s with no data errors when the additive noise was as high as 10 dB below the mean square value of the speech signal.