Local loop test arrangement in an echo canceller based full dupl

Details Local loop test arrangement in an echo canceller based full dupl Local loop test arrangement in an echo canceller based full dupl

1985-12-30

1989-04-25

Ng, Jin F.

Telephonic communications

Diagnostic testing, malfunction indication, or electrical...

Of hybrid or echo suppressor or canceller

375 10, 379410, H04B 1700, H04B 323

Patent

active

048254592

ABSTRACT:
In accordance with the present invention, local loop testing in an echo canceller based modem is provided in a manner in which proper operation of both the receiver and echo canceller can be assessed simultaneously. Specifically, the modem includes means for generating data and interfering symbol sequences and for applying the interfering sequence to both the echo canceller and the modem transmitter, while applying the data sequence only to either the transmitter or the echo canceller. During closed loop testing, the modem connection to the transmission line is opened, and a portion of the output of the modem transmitter is applied to the modem receiver via a leakage path through the hybrid. The received symbol is subtracted from the echo canceller output, resulting in application to the receiver of only a version of the data symbol sequence. Advanced knowledge of the characteristics of the data symbol sequence allows proper receiver operation to be verified.

REFERENCES:
patent: 4464545 (1984-08-01), Werner
patent: 4547633 (1985-10-01), Szechenyi
patent: 4549049 (1985-10-01), Guidoux
patent: 4594479 (1986-06-01), Farrow et al.

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