Hybrid subband/frequency-domain adaptive systems

For many years now, subband and frequency-domain adaptive filtering techniq ues have been proposed for the identification of high-order FIR systems. Cl assical LMS-based algorithms are less attractive as their computational loa d is higher and their convergence behaviour for coloured inputs is worse. S ubband processing has many desirable properties. However, when used to impl ement adaptive filters, various effects (such as residual errors and slow c onvergence due to aliasing) occur and reduce performance. On the other hand , it is known that frequency-domain adaptive filters do not suffer from the se problems despite being (nearly) equivalent to subband adaptive filters, be it with "poor" filter banks (modulated sine frequency responses). In thi s paper the operation of the frequency-domain techniques are unravelled and explained in the "subband jargon" and among other things it will be shown how aliasing is compensated for in the frequency-domain approach. This pape r aims at generalising frequency-domain aliasing-compensation techniques to subband adaptive systems. Further, some design criteria for subband adapti ve systems are formulated. Three realisation conditions and an alternative adaptation scheme will be proposed. Standard subband adaptive filters canno t fulfil all conditions, whereas for frequency-domain-based algorithms the design criteria are met. (C) 2001 Elsevier Science B.V. All rights reserved .