Method and apparatus for echo removal in a communication system

Abstract

A signal processor for, e.g., a telephonic communication system interconnecting a near location and at least one far location includes an echo canceller for suppressing the re-transmission of received signals. The operation of the echo canceller is controlled according to whether the near location is transmitting or receiving, and whether the far location is transmitting or receiving. The signal processor includes means for detecting doubletalk, and for controlling the echo canceller in response to the detection of doubletalk, such that doubletalk is permitted. In one method of operation, a delay is applied to the inputs to the echo canceller from the near and far ends, such that each of these signals is used for determining the operating state of the echo canceller before being used to operate an adaptive filter of the echo canceller. In another method of operation, doubletalk detection is carried out, in part, by evaluating the performance of an auxiliary adaptive filter. In another method of operation, the doubletalk detection is carried out, in part, by evaluating a pair of statistics that respectively indicate whether the near-end input to the echo canceller contains more energy than an expected echo generated from the far-end input, and whether an echo is being effectively removed. According to such method, a doubletalk state is declared only is these statistics satisfy predetermined conditions.