Patent ID: 6226380
Filing Date: 2001-05-01
Classification: H04B,H04M

Abstract:
A method of detecting double talk (DT) and echo path change (EPC) conditions in an echo canceller comprising an adaptive filter for being communicatively coupled between a receive path and a transmit path at a network node of a communication system and means for distinguishing between DT and EPC conditions, comprising the steps of:generating an echo return loss enhancement (ERLE) signal from signals at the echo canceller using the relationship: ##EQU6##wherein:E[ ] is a statistical expectation operator;d(n) is a perceived near-end signal which is the sum of a near-end generated signal s(n) and an echo signal u(n); ande(n) is an output signal to be transmitted from the echo canceller to the network link;and comparing it to a first threshold level;generating a signal corresponding to the energy level of a signal x(n) which is the incoming reference signal for the echo canceller and comparing it to a second threshold level;generating a predetermined signal to an orthogonality monitor if the energy level of the ERLE signal is below the value of the first threshold level and the energy level of the x(n) signal is above the value of the second threshold level, the predetermined signal indicating that a DT or EPC condition has been detected;the orthogonality monitor generating an EPC acknowlegement signal in response to the predetermined signal if the absolute value of cross-correlation between signals e(n) and y(n) is greater than the product of a predetermined EPC threshold level (T.sub.EPC) and an average amplitude estimate of e(n)y(n), in accordance with the relationship:.vertline.R.sub.ey (n).vertline.>T.sub.EPC.multidot.A.sub.ey (n)wherein:y(n) is the echo estimate signal generated by the adaptive filter of the echo canceller; andthe orthogonality monitor generating a DT acknowledgement signal if the absolute value of cross-correlation between signals e(n) and y(n) is equal or less than the product of T.sub.EPC and A.sub.ey (n).