Filter design via inner-outer factorization: Comments on "Optimal deconvolution filter design based on orthogonal principle"

This paper is written with two purposes in mind. First, it points out some mistakes made in the paper \Optimal deconvolution lter design based on orthogonal principle", recently published in this journal. Secondly, in order to sort out the reason for those mistakes, the relations between inner{ outer factorization, spectral factorization, whitening lters and Diophantine equations in MMSE lter design are stressed. It is emphasized that computation of an inner matrix corresponds to performing a spectral factorization and the inverse of the outer matrix is a whitening lter. Furthermore, nd-ing the causal part of an expression is the same as solving a Diophantine equation.