A CONSTRAINED TRANSFORM DOMAIN ADAPTIVE IIR FILTER STRUCTURE FOR ACTIVE NOISE-CONTROL

An active noise controller utilizing a transform domain recursive LMS (RLMS) infinite impulse response (IIR) filter is presented in this pap er, The new filter, termed the TRLMS adaptive filter, mitigates the fi lter instability problems that often exist with controllers based on d irect form IIR filters by directly constraining the adaptation of the filter's frequency response, A filtered-U adaptive algorithm for the T RLMS filter structure is derived. Two different implementations of the constrained TRLMS filter are discussed, The first represents the adap tive filter in terms of its transform domain weights, They are directl y adapted by the filtered-U TRLMS adaptive algorithm, The second imple mentation represents the filter in terms of its original time domain w eights, These are updated by the filtered-U RLMS algorithm and subsequ ently projected onto an adaptation subspace at each iteration, Extensi ons of these algorithms that enforce soft constraints on the filter re sponse are also presented, The stability of the constrained TRLMS adap tive filter is investigated utilizing two different transformations.