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-integrator-comb (CIC) filters-are a good choice of realizing linear-phase 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 also. Based on an equivalent block-processing structure of the original system such time-variant realizations can be found. In the case of comb-filters this results in halving the number of registers though at the cost of multipliers