Line disconnection detection circuit for echo-cancelling transce

Details Line disconnection detection circuit for echo-cancelling transce Line disconnection detection circuit for echo-cancelling transce

1994-07-28

1995-10-24

Chin, Stephen

Telephonic communications

Diagnostic testing, malfunction indication, or electrical...

Of hybrid or echo suppressor or canceller

379406, 379410, 379411, 379345, H04M 124, H04M 300, H04M 100

Patent

active

054616611

ABSTRACT:
A circuit for comparing transmitted and received data frames containing appropriate stuff symbols to detect when a channel is disconnected. Transmit data symbols consisting of frames of user data, each with a constant number of symbols, are separated by a sequence of symbols known as the frame pattern. At the end of each data frame, just before the next frame pattern, a small number of stuff symbols are added into the frame. The stuff symbols injected in the transmit signal are chosen to be identical to the last scrambled data symbol in the frame of user data. Stuff symbols in a recovered receive signal are chosen to look identical to data symbols which were scrambled at the remote transceiver. A frame-by-frame comparison between the transmit stuff symbols and the next received stuff symbols is carried out on a continual basis. When the two sets of symbols are equal in each frame for a number of consecutive frames N, then the circuit indicates that only the transmit signal is being received and channel disconnection is detected.

REFERENCES:
patent: 4564934 (1986-01-01), Macci
patent: 4896318 (1990-01-01), Kokubo et al.
patent: 5014263 (1991-05-01), Vairavan
patent: 5062102 (1991-10-01), Taguchi
patent: 5157653 (1992-10-01), Genter
patent: 5237495 (1994-07-01), Shenoi
patent: 5283784 (1994-02-01), Genter
patent: 5315585 (1994-05-01), Iizuka
patent: 5319636 (1994-06-01), Long

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