Efficient implementation of arbitrary-length cosine-modulated filter banks

Cosine-modulated filter banks (CMFB's), which can be designed and implemented efficiently, have been investigated extensively in recent years. In this paper, the fast implementation of CMFB's is revisited. Two classes of paraunitary CMFB's with arbitrary lengths are considered. One is the conventional M-channel arbitrary-length CMFB, and the other is a class of 2M-channel arbitrary-length CMFB's with linear phase, which is defined in this paper and can be considered to be an extension of the existing ones to arbitrary length. By further reorganization of the polyphase component matrices and using the linear-phase property of a prototype filter, we obtain more efficient implementation structures for the CMFB's, in which we use 2x2 lossless matrices instead of 2 x 1 ones. In the traditional implementation, M and IM two-channel lossless lattices are required for the M-channel CMFB's and the 2Mchannel linear-phase CMFB's, respectively. In the new implementation, the numbers of two-channel lossless lattices are reduced by a factor of two.