Properties and applications of some periodically varying digital signal processors

A situation often encountered in a communication system, in which a digital interpolation filter is followed by a sinusoidal modulator, is considered. A mathematical model of the system is developed and some useful properties derived. These properties lead to an equivalent realisation of the interpolation filter and the subsequent commutation of the filter with the modulator. Applications to digital SSB generator designs are described, and it is shown that these properties explain why the complexity of the designs can be reduced.