TABLE OF CONTENTS In this section an example modification of the Subband adaptive polyphase FFT echo cancellation system [79] is presented in which the standard FIR filter banks are replaced with the polyphase IIR structure. It is demonstrated that such an alternative approach results in a much more computationally efficient implementation combined with more accurate channel detection and improvement in the adaptation speed.
Adaptive signal processing applications such as adaptive equalization or adaptive wideband active noise and echo cancellation involve filters with hundreds of taps required for accurate representation of the channel impulse response. The computational burden associated with such long adaptive filters and their implementation complexity is very high. In addition adaptive filters with many taps may also suffer from long convergence time, especially when the reference signal has a large dynamic range. It is well known that subband adaptive techniques are well suited for high-order adaptive FIR filters, with a reduction in the number of calculations by approximately the number of subbands, whereby both the number of filter coefficients and the weight update rate can be decimated in each subband. Additionally faster convergence is possible as the spectral dynamic range can be greatly reduced in each subband [79] and [80]. A number of subband techniques have been developed in the past that uses a set of bandpass filters; block transforms [81] or hybrids [82], which introduce path delays dependent on the complexity of subband filters employed. The architecture proposed in [79] avoids...
