ECHO CANCELLATION IN TWO-WIRE TRANSMISSION PATH REPEATERS

摘要

ECHO CANCELLATION IN TWO-WIRE TRANSMISSION PATH REPEATERSAbstract of the DisclosureA two-wire transmission path repeater includes, between twohybrid circuits coupled to the path, an echo canceller and anamplifier for each direction of transmission, each echo cancellerincluding a transversal filter and a subtracting circuit. The powerratio between signals before and after the subtracting circuit ofeach echo canceller is used to distinguish between simplex andduplex signals. If the power ratio exceeds a given value, which isdependent upon the input signal power, for only one transmissiondirection then a simplex signal in the opposite direction isdetermined, the gain of the amplifier for the one transmissiondirection is reduced, and adaptation of the transversal filtercoefficients for the opposite direction is prevented. If the powerratio for both directions falls below the given value then a duplexsignal is determined, the gain of both amplifiers is increased andadaptation of the coefficients of both transfer filters is continuedfor a short period, then the gain of both amplifiers is reduced andadaptation prevented, thereby facilitating stable operation of therepeater.