Coding and modulation for simultaneous voice and data transmission

Simultaneous voice and data (SVD) transmission over voiceband channels is an important step in realizing personal communication systems. Two of the techniques that have been proposed are (1) digital SVD (DSVD) where compressed speech is multiplexed with data, and (2) analog SVD (ASVD) where analog speech is superimposed on the data signal constellation. We evaluate the performance of an ASVD scheme. Data is transmitted as a PAM or a QAM signal with optional error protection and speech is superimposed on this constellation. We consider a number of techniques for decoding data as well as for recovering speech from the received signal. We also consider schemes which perform linear prediction at the transmitter and transmit the prediction residual instead of the speech. Informal listening tests reveal that excellent speech quality at data rates of up to 8000 bps can be achieved with acceptably low bit-error-rates