Method and apparatus for improved control and time sharing of an echo

Abstract

An improved echo canceller control method utilizes two adaptive level detectors for controlling or inhibiting the updating of coefficients in the echo canceller. Updating is permitted only when an actual received signal is present and no transmit signal as measured by the adaptive level detector exists. During periods when no transmit or receive signals are present, update is inhibited and the adaptive level detector establishes a noise reference level. When transmission activity is present but no receive activity is present, inhibiting of the echo canceller updating allows the adaptive level detector to seek and establish the background noise reference level and avoids the disruption of the echo canceller coefficients that would occur from double talk if a receive signal were suddenly to become present. When actual double talk, i.e., both receive and transmit activities are present occurs, updating is also inhibited for the same reason. Since channel activity is typically present only 30-40% of the time in either transmit or receive mode, the echo canceller will spend the remaining 70-60% of its time inhibited and can be shared with other channels which do have the appropriate activity for updating separate echo canceller coefficients. If the coefficients are separately stored in association with each channel as is the case in this invention, the echo canceller coefficients are loaded whenever updating is to take place for a given channel.