B. Vo et al., A PENALTY APPROACH TO ITERATIVE ALGORITHMS FOR ENVELOPE CONSTRAINED FILTER DESIGN, IEEE transactions on signal processing, 45(7), 1997, pp. 1869-1873
The discrete-time envelope-constrained (EC) filtering problem can be f
ormulated as a quadratic programming (QP) problem with affine inequali
ty constraints, This QP problem is approximated by an unconstrained mi
nimization problem with two parameters, Descent direction-based algori
thms are applied to solve the unconstrained problem iteratively. It is
shown that these algorithms converge.