Acoustic Echo Cancellation Technology

With the rapid development of communication techniques, digital signal processing and VLSI techniques, people demand higher and higher speech quality in communication. However, it is not always easy to implement acoustic equipments for communication system with satisfactory speech quality. The most important requirement is to protect against howling and echo, due to acoustic feedback from loudspeaker to microphone, and to ensure a sufficient listening level. So acoustic echo cancellation (AEC) technique has become a hot issue of competition in the famous communication company all over the world.This paper is focused on the AEC in communication system, e.g. videoconference system. Acoustic echo cancellation is normally achieved by means of an acoustic echo canceller, which, in its simplest form, consists of an adaptive filter which estimates the echo signal and subtracts this estimate from the microphone signal.This paper is organized as follows:The background knowledge about AEC such as acoustic echo mechanism, principle of AEC and basic components of AEC is introduced in Chapter 1.In Chapter 2, many kinds of adaptive filter algorithms are discussed. This section analyzes the Least Mean Squares (LMS), Normalized LMS (NLMS) and Recursive Least Squares (RLS) algorithms, and evaluates their performance as acoustic echo canceller.In order to further reduce the computation complexity and improve the convergence behavior, many sorts of subband filter algorithms are depicted in Chapter 3. Finally, associated with NLMS algorithm, the suband NLMS (SNLMS) algorithm is proposed.In Chapter 4, various implementation issues associated with an acoustic echo cancellation system, such as double-talk detection, finite precision effects, nonlinear processing and howling detection and control are discussed.Finally, experiment results are given to demonstrate the performance of the proposed AEC algorithm, where ERLE and rate of convergence are the main indexes.