System and method for performing echo cancellation in a communications

Abstract

A system and method for performing echo cancellation in a communications network including a bi-directional two-wire communication line, and a four-wire communication line having a transmit path and a receive path. The system includes a filter coupled to the receive path for reducing the echo component. The filter uses a number of filter coefficients and selectively employs either a full LMS coefficient calculation technique to compute the filter coefficients during a first period of time to achieve quick convergence, or a sign-sign LMS coefficient calculation technique to compute the filter coefficients during a second period of time to achieve improved stability and convergence. The filter uses a power estimation of the transmit path signal to direct the filter as to which coefficient calculation technique to use. The filter controller also includes a counter for determining an amount of time passed since the establishment of a connection, and this information is also used to determine the coefficient calculation technique. The filter generates an echo estimate signal which it subtracts from the received signal to generate an echo canceled signal, also known as an error signal. The filter uses three different step sizes when computing the filter coefficients to selectively achieve quick convergence or greater echo cancellation accuracy.