Smooth orthogonal signal extensions for paraunitary tree-structured filter banks

This work is concerned with subband processing of finite length signals using tree-structured filter banks. In many applications the subband transform is required to be orthogonal. For this purpose, the filter bank must be paraunitary, and the signal borders must be processed via either orthogonal boundary filters or via orthogonal signal extension methods. Periodization is an orthogonal extension technique, but introduces undesired artificial discontinuities or spurious high frequencies in the transform vector. Boundary filter design techniques do not solve this problem either. The solution we provide is a new algorithm for the generation of alternative orthogonal signal extensions which do not introduce spurious high frequencies in the subband signals. Some experimental results illustrate the effectiveness of the proposed design method in comparison to other existing techniques.