Research On Adaptive Filter Theory And Its Applications In Echo Cancellation

Adaptive filtering has been widely used in many applications, such as speech signal processing, echo cancellation, channel equalization, system identification, line enhancement, adaptive beamformer and biomedical signal processing, etc. Echo cancellation is of major importance in MODEM, long distance telephone, hands-free telephone and teleconference. However, a major difficulty encountered in applications like acoustic echo cancellation is the requirement for very long adaptive filters (N>1000). The implementation of such long adaptive filters requires heavy computational resources. The dissertation is focused on the research of reducing the computational complexity of large adaptive filters and their applications in echo cancellation.Fast affme projection algorithm may possess NLMS like complexity while having a better convergence rate for colored input signals. In order to reduce the computational complexity of fast affine projection algorithm, two simplified algorithms are presented. The convergence performance of the simplified algorithms is comparable to that of affine projection algorithm even with less computational complexity. The prefilter in the simplified algorithms can be implemented by Leaky LMS or noisy LMS. In acoustic echo cancellation, the computational complexity is still too large even for algorithms with O(N) complexity. Block processing is an effective approach to further reduce the computational complexity. A block exact fast affine projection algorithm and a block exact simplified affine projection algorithm are proposed in the dissertation. The block exact affine projection algorithm is an exact equivalent of the original affine projection algorithm. Thus, it performs identically with affine projection algorithm and at the same time, offers a considerable saving in complexity. The block exact algorithm allows the use of small block length, thus making the effect of processing delay negligible. In order to improve the subject quality of echo cancellation, a perceptually weighted echo canceller is also...