Abstract:
The rapid growth of technology in recent decades has changed the whole dimension of communications. Today people are more interested in hands-free communication. In such a situation, the use of a regular loudspeaker and a high-gain microphone, in place of a telephone receiver, might seem more appropriate. This would allow more than one person to participate in a conversation at the same time. Another advantage is that it would allow the person to have both hands free and to move freely in the room. However, the presence of a large acoustic coupling between the loudspeaker and microphone would produce a loud echo that would make conversation difficult. Furthermore, the acoustic system could become unstable, which would produce a loud howling sound to occur.
The solution to these problems is the elimination of the echo with an echo suppression or echo cancellation algorithm. Echo suppressor offers a simple but effective method to counter the echo problem. However, it possesses a main disadvantage as it supports only half-duplex communication. Half-duplex communication permits either calling or called person to speak at a time. This drawback lead to the development of echo cancellers. An important aspect of echo cancellers is that full-duplex communication can be maintained, which allows both speakers to talk at the same time.
Acoustic echo cancellation (AEC) provides one of the best solutions to control the acoustic echoes generated by the hands-free audio terminals. In this type of application, an adaptive filter provides an estimate of the echo. The primary requirement of an adaptive filter algorithm is to provide a high convergence rate and low misalignment. The performance of an adaptive filter algorithm is mainly dependent on the step-size, parameter. When a fixed step-size is used, trade off has to be maintained on either high convergence rate or low misalignment, while both cannot be achieved simultaneously. To solve this problem a variable step-size parameter can be used, which keeps updating according to the system statistics.
This work mainly involves the detailed study of a variable-step size affine projection algorithm and its application to AEC. The performance of this algorithm is evaluated under various scenarios such as single-talk and double-talk.
