JOINT ADAPTIVE ECHO CANCELLATION AND CHANNEL EQUALIZATION FOR DATA-TRANSMISSION

This paper deals with the coupling of an echo canceller and a channel equalizer which are adaptive filters usually involved in the receiver for high speed, full-duplex data transmission over two-wire lines. The coupling consists of a joint optimization of the two filters so that the same error at the output of the whole receiver is used to update both of them. Two types of structures are considered whether echo cancellation is made before equalization or after it. A comprehensive analysis is made both of the optimal performances and of the least mean square updating algorithm behavior, and is presented with a unified formalism describing a unique adaptive system. Finally, it is shown that when compared to the usual decoupled structure, coupling the two filters represents an improvement for the residual echo that is worth the signal-to-noise ratio (SNR) at the input of the equalizer. For an identical residual echo, the coupling reduces the bit length of the echo canceller taps by 1 2log2 SNR. © 1990.