Transposed FIR filter structure with time-varying coefficients for digital data resampling

A new time-domain derivation is presented for interpolation and decimation by a fractional factor U/D. Though it is well known that such a filter can be implemented using a direct-form I, FIR filter with time-varying coefficients, a novel time-varying alternative, using a transposed filter structure, is described. Time-varying filters are especially important for implementation on a digital signal processor. The new time-varying structure has the advantage of reduced buffer memory for downscaling, or increased parallelism for high-speed upscaling, compared to the conventional time-varying structure.