An adaptive multiple echo canceller for slowly time-varying echo paths

An adaptive structure that cancels multiple echos with slowly time-varying echo path characteristics is presented. The structure consists of two echo path models. One is a primary long-length transversal filter initially used to estimate the echo path in the startup period. The other is a reduced-size filter consisting of several short-length filters used to inherit the significant coefficients of the primary filter after the predetermined conditions are simultaneously satisfied and to function as the echo canceller thereafter. In addition, a monitor/control circuit is used to estimate the time locations of individual dispersive regions from the primary filter and to monitor the short filters to make sure that each one can cover its own dispersive region. With the delays determined, the short filter structure can update the echo path accurately since the number of tap coefficients has been dramatically reduced, increasing the convergence speed. The results of computer simulations utilizing white noise input and speech input are presented