Browse Prior Art Database

Echo Suppressor Using a Correlation Detector

IP.com Disclosure Number: IPCOM000051417D
Original Publication Date: 1981-Jan-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 3 page(s) / 48K

Publishing Venue

IBM

Related People

West, LE: AUTHOR

Abstract

Full duplex line communication involves simultaneous transmission and reception over the same line. Therefore, the architecture must provide a mechanism to ensure that the transmitted signal is not fed back into the receiving section of same end of the line.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 53% of the total text.

Page 1 of 3

Echo Suppressor Using a Correlation Detector

Full duplex line communication involves simultaneous transmission and reception over the same line. Therefore, the architecture must provide a mechanism to ensure that the transmitted signal is not fed back into the receiving section of same end of the line.

The method shown in Fig. 1 supplies a cancelling signal to the input of the differential operational amplifier 1. If the cancelling signal is of the right magnitude, the transmitted signal T will be cancelled before reaching the detector 2 input. As shown in Fig. 1, the input signal to the detector is alpha-T-GT+R. Then alpha-T-GT+R = (alpha -G)T+R T signal is cancelled when G=alpha. If we knew alpha, we could set G=alpha and T signal would be cancelled. However, note that alpha = Z(L) over 600+Z(L) wher is a function of the telephone line; therefore, we have limited control over it. (Assume Z(L) is real at the present time.) The approach being proposed is to detect the presence of the T signal at the input to the receiver-detector with an echo correlation detector. The nulling controls will use the output of the echo correlation detector to adjust G such that the T signal will be nulled.

A positive signal from the echo correlation detector will indicate that the signal GT is insufficient to cancel the T signal; therefore, G must be increased. A negative signal from the echo detector would indicate that the GT signal is too large; therefore, G must be reduced.

Fig. 2 shows a functional diagram of how the echo correlation detector could be implemented. Note that when signal A and signal B are the same level, signal X is at +10 volts, and when signal A and signal B are not the same, signal X is at -10 volts. The zero crossing detector squares the incoming signals such that their outputs are either high or low.

To better understand the operation of the echo correlation detector, consider the following cases. In Case A, signal A and signal B are in phase. Assume that signal A is the...