Reduced Complexity Comb-filters for Decimation and Interpolation in Mobile Communications Terminals

In mobile communications systems complexity and efficiency are issues of paramount importance. Therefore when implementing integer factor sample-rate conversion, comb-filters especially cascaded-integratorcomb (CIC) filters are a good choice of realizing linearphase filters with low complexity. However, neither the direct implementation of comb-filters as transversal filters nor their implementation as CIC-filters are minimal realizations. Since both, decimators and interpolators are time-variant systems the minimal realization is certainly time-variant either. Based on an equivalent blockprocessing structure of the original system such timevariant realizations can be found. In the case of combfilters this results in halving the number of registers at the cost of multipliers though.