Iteratively reweighted design of oversampling complex-modulated filter-banks for high output-signal quality

This paper addresses the improvement of the signal-to-disturbance ratio of the output-signal of an oversampling, complex-modulated subband-coder filter-bank pair with extensive subband-signal amplification. The undesired non-linear disturbance is induced by the sample rate conversion within the filter-bank pair and it is hard to predict in dependence of the signal amplification. This has not been considered in most current design methods, leading to high prototype filter lengths in order to obtain desired signal-to-disturbance ratios. In this paper, we propose a formulation for the design of a filterbank which is based on the definition of the signal-to-disturbance ratio. The algorithm iteratively optimises the coefficients of the prototype filters of the analysis and synthesis filter-banks using iteratively adapted weighting factors. We show that all iteration steps represent quadratic constrained optimization problems, and propose an efficient implementation. A numerical example shows that the signal-to-disturbance ratio of the output-signal is highly improved compared to that of standard designs.