Multichannel Acoustic Echo Canceller Based on Fast Affine Projection Algorithm

The task of the identification of the multichannel linear system with long channel impulse responses is considered in this paper. The multichannel acoustic echo cancellation in the closed rooms is an example of this task. Dependently on the room size, its decoration and the signal sampling frequency value the duration of the identified impulse responses may take a few thousand samples. To solve this task a multichannel adaptive filter with the corresponding large number of weights is required. The implementation of such filters is a difficult task as the arithmetic complexity of the adaptive filters depends on the number of the filter weights. Due to this reason the effective time-domain Recursive Least Squares (RLS) adaptive filters even in their fast (computationally efficient) forms are rarely used in the acoustic echo cancellers. The computationally simple but less effective time-domain Least Means Squares (LMS) or the Normalized LMS (NLMS) adaptive filters are usually used for this purpose. However, such filters have a number of well-known drawbacks. The slow convergence is one of them when the correlated or nonstationary signals are processed. Speech is an example of such signals. The frequency-domain LMS/NLMS adaptive filters de-correlate the signals. These filters have a smaller computational complexity comparing to their time-domain prototypes. However, as the signals are processed using the blocks of the samples, the frequency-domain adaptive filters introduce the output signal delay and demonstrate a slower convergence because their weights are updated only once per block. This decreases the tracking ability of the frequency-domain adaptive filters. The ability is an important feature of the adaptive filters in the acoustic echo cancellation task because the acoustic medium is usually a not time-invariant one. The usage of the Fast Affine Projection (FAP) adaptive filter is the tradeoff between the acoustic echo canceller efficiency and its complexity. Such adaptive filter is widely used in the single-channel acoustic echo cancellers. This paper considers the adaptive filter application in the multichannel echo cancellers. The computational procedure of a multichannel FAP adaptive filter is presented and an example of the two-channel echo canceller is considered in this paper. The simulation demonstrates about the same steady-state performance of the FAP adaptive filter as that of the time-domain RLS adaptive filter or the time/frequency domain NLMS adaptive filter. However the convergence of the FAP adaptive filter comparing to the NLMS one is a few times faster. Because of this feature the FAP adaptive filter can efficiently track the changes in the processed signal statistics and/or the changes in the acoustic medium.