Implementation of Linear-Phase FIR Nearly Perfect Reconstruction Cosine-Modulated Filterbanks Utilizing the Coefficient Symmetry

The analysis and synthesis parts of a cosine-modulated M-channel filterbank (FB) contain two sections, a modulation block and a prototype filter implemented in a polyphase structure. Although, in many cases, a linear-phase prototype filter is used, the coefficient symmetry of this filter is not utilized when using the existing polyphase structure. In this paper, a method is proposed for implementing a linear-phase prototype filter building a nearly perfect reconstruction cosine-modulated FB in such a way that it enables one to partially utilize the coefficient symmetry, thereby reducing the number of required multiplications in the implementation. The proposed method can be applied for implementing FBs with an arbitrary filter order and number of channels. Moreover, it is shown that, in all cases under consideration, the cosine-modulation part of the FB can be implemented by using a fast discrete cosine transform. The efficiency of the proposed implementation is evaluated by means of examples.