Method and apparatus for adaptive receiver squelch echo control

Details Method and apparatus for adaptive receiver squelch echo control Method and apparatus for adaptive receiver squelch echo control

1984-05-31

1987-09-15

Olms, Douglas W.

Multiplex communications

Wide area network

Packet switching

379 97, 379407, H04J 1500, H04L 514, H04B 320

Patent

active

046944508

ABSTRACT:
After receipt of the answerback tone in a conventional handshaking procedure, the originate modem is connected to the communication line, sends a short echo control training (ECT) sequence to the answer modem, and starts a timer. Upon receipt of the ECT.sub.o sequence, the answer modem sends its own ECT.sub.a sequence to the originate modem and starts its own timer. Upon receiving the ECT.sub.a sequence, the originate modem measures the round trip propagation delay (T.sub.RTPD) and transmits a second ECT.sub.o sequence. The time of receipt of this sequence at the answer modem is used by the answer modem to determine T.sub.RTPD. Either modem may now start data transmission. Because of the measurements made, the receiver at the transmitting modem is aware that the echo from its transmission will be delayed by T.sub.RTPD. Accordingly, it will open an "echo monitor window" in a time interval around T.sub.RTPD during which time frame any received energy is assumed to be an echo. If an echo is detected in such time interval, the receiver will be squelched until energy is no longer detected. Moreover, knowledge of T.sub.RTPD also permits the modem to select an optimum length training sequence because the quality of the communication line depends on its length.

REFERENCES:
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patent: 4029912 (1977-06-01), Geigel et al.
patent: 4064378 (1977-12-01), Kitayama et al.
patent: 4394767 (1983-07-01), Shum
patent: 4481622 (1984-11-01), Cheng et al.

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