Design of FIR Filter Banks for a 24-Channel Transmultiplexer

The design of a bank of FIR bandpass filters for channel filtering and sample rate alteration in a 24-channel transmultiplexer is considered. It is shown that such a filter bank can be realized by the combination of a weighting network and a discrete cosine transform. A minimum phase design is suggested for the low-pass prototype filter in order to solve the long absolute delay problem inherent in linear phase filters. Two approaches to the design of long minimum phase filters are disclosed; one employs frequency sampling design techniques, and the other makes use of the properties of the complex cepstrum of a minimum phase sequence. Filter specifications for the low-pass prototype are discussed and a design example is included. The hardware realization of the filter bank using a multiplier-accumulator as the arithmetic element is also discussed.