Simultaneous transmission of speech and data over an analog channel

The present invention relates to a technique for transmitting an entire analog speech signal and a modulated data signal over a transmission channel such as a common analog telephone speech channel. The present technique multiplexes the entire modulated data signal within the normal analog speech signal frequency band where the speech is present and its signal power density characteristic is at a low level. Separation of the speech and data signals at the receiver is effected by recovering the modulation carrier frequency and demodulating the received signal to recover the data signal. The data signal is then remodulated with the recovered carrier and is convolved with an arbitrary channel impulse response in an adaptive filter whose output signal is subtracted from the received composite data and speech signal to generate the recovered speech signal. To improve the recovered speech signal, a least mean square algorithm is used to update the arbitrary channel impulse response output signal of the adaptive filter.