PURPOSE: To carry out echo cancellation accurately by storing the turn-around component of a transmitted signal waveform and by subtracting it from a received signal.
CONSTITUTION: To remove the turn-around component of a transmitted signal of a digital information transmission to the reception side, the component that the transmitted signal used for the transmission of transmitted digital information from transmitter circuit 1 has turned around to receiver circuit 4 via hybrid circuit 2 is stored in echo memory 71 by switching change-over switch 43. Then, the turn- around component of a transmitted signal equivalent to digital information transmitted to receiver circuit 4 is read out from the turn-around component of the transmission signal stored in memory 71 to receiver circuit 4 via read change-over switch 72 and then supplied to subtracter 9. Subtracter 9 subtracts the turn-aroud component read out from the signal received by receiver circuit 4 to attain echo cancellation accurately.
FUJII KENSAKU
TERAUCHI MASAHARU
TAKAMI TOSHIHARU
NIPPON TELEGRAPH & TELEPHONE