Echo Cancellation In Long Distance Telephone Circuits Using VSS-APA

Applied Electronics

In telephone circuits, Acoustic Echo Cancellation (AEC) provides one of the best solutions to the control of acoustic echoes generated by hands-free audio terminals. In this type of application, an adaptive filter identifies the acoustic echo path between the terminal’s loudspeaker and microphone, i.e., the room impulse response. The filter output, which provides an electronic replica of the acoustic echo, is subtracted from the microphone signal to cancel the echo. Nevertheless, there are several specific and challenging problems associated with AEC applications. Hence, the residual echo caused by the part of the system that cannot be modeled acts like an additional noise and disturbs the overall performance. Second, the background noise that corrupts the microphone signal can be strong and highly non stationary. In my project, the Variable Step-Size Affine Projection Algorithm (APA) and some of its versions were found to be very attractive choices for AEC applications. The main advantage of this family of algorithms over the well known Normalized Least-Mean-Square (NLMS) algorithm consists of a superior convergence rate, especially for speech signals. This algorithm does not require any a priori information about the acoustic environment, so that it is easy to control in practice. The simulation results indicate the good performance of the proposed algorithm as compared to other members of the APA family.

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