Application and Performance Analysis of Subband Adaptive IIR Filters for Narrowband Signal Estimation

Adaptive IIR (infinite impulse response) filters have not been studied as extensively as the more common adaptive FIR (finite impulse response) filters based on the tapped delay line (TDL) structure.The main reason is likely that, during coefficient adaptation, significant stability loss can lead to divergence, rendering the system unstable and preventing any stability guarantee.Consequently, their use is reported to be limited to specific applications.Nevertheless, IIR filters have long been recognized as highly efficient in certain domains, as they enable desired signal processing by adjusting only a small number of coefficients.Meanwhile, subband adaptive algorithms-which divide the input signal's frequency range and employ adaptive models tailored to specific spectral bands-have been introduced in adaptive filtering.However, most research in this area has focused on TDL-type filters.Therefore, this study investigates the characteristics of adaptive IIR filters in sub-bands and how they differ in operation from conventional adaptive IIR filters that do not employ sub-band processing.Through this process, we intend to present and analyze several examples of adaptive signal processing where the sub-band approach offers advantages.Experimental results showed that the subband adaptive filter achieved an enhancement gain of 2-3 dB.