Design of signal-adapted FIR paraunitary filter banks

We study the design of signal–adapted FIR paraunitary filter banks, using energy compaction as the adaptation criterion. We present some important properties that globally optimal solutions to this optimization problem satisfy. In particular, we show that the optimal filters in the first channel of the filter bank are spectral factors of the solution to a linear semi–infinite programming (SIP) problem. The remaining filters are related to the first through a matrix eigenvector decomposition. We discuss uniqueness and sensitivity issues. The SIP problem is solved using a discretization method and a standard simplex agorithm. We also show how regularity constraints may be incorporated into the design problem so as to obtain globally optimal (in the energy compaction sense) filter banks with specified regularity. We also consider a problem in which the polyphase matrix implementation of the filter bank is constrained to be DCT–based. Such constraints may also be incorporated into our optimization algorithm, so we are able to obtain globally optimal filter banks subject to regularity and/or computational complexity constraints. Numerous experiments are presented to illustrate the main features that distinguish adapted and nonadapted filters, as well as the effects of the various constraints. The conjecture that energy compaction and coding gain optimization are equivalent design criteria, is shown not to hold for FIR filter banks. ∗Work partly presented at ICASSP’95 and ICASSP’96. †Part of this work was performed while P. Moulin was at Bellcore, Morristown, NJ. ‡Corresponding Author: tel (217) 244-8366, fax (217) 244-8371, Email: [email protected]