Telephonic communications – Subscriber line or transmission line interface – Network interface device
Patent
1985-11-27
1988-11-01
Ng, Jin F.
Telephonic communications
Subscriber line or transmission line interface
Network interface device
370 321, 379345, H04B 323
Patent
active
047825251
ABSTRACT:
A two-wire transmission path repeater includes, between two hybrid circuits coupled to the path, an echo canceller and an amplifier for each direction of transmission, each echo canceller including a transversal filter and a subtracting circuit. The power ratio between signals before and after the subtracting circuit of each echo canceller is used to distinguish between simplex and duplex signals. If the power ratio exceeds a given value, which is dependent upon the input signal power, for only one transmission direction then a simplex signal in the opposite direction is determined, the gain of the amplifier for the one transmission direction is reduced, and adaptation of the transversal filter coefficients for the opposite direction is prevented. If the power ratio for both directions falls below the given value then a duplex signal is determined, the gain of both amplifiers is increased and adaptation of the coefficients of both transfer filters is continued for a short period, then the gain of both amplifiers is reduced and adaptation prevented, thereby facilitating stable operation of the repeater.
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Translation of Japanese publication 57-42242, Mar. 9, 1982, translation made Sep. 1987.
Dupuis Gilles
Millar Douglas J.
Sylvain Dany
Haley R. John
Ng Jin F.
Northern Telecom Limited
Vaas Randall S.
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