Nonuniformly offset polyphase synthesis of a bandpass signal from complex-envelope samples

Abstract

In this paper we consider the synthesis of a bandpass signal from complex-envelope samples using a polyphase conversion structure based on periodically nonuniform output samples. This approach provides the flexibility to independently choose the sampling rate and carrier frequency, overcoming the restrictions of reconstruction from uniformly spaced output samples. Key to the design of such a system is a particular equivalent filter with a piecewise-constant impulse response that determines both the actual implementation filters and system performance. The transition times of this impulse response are found to be periodically nonuniform, leading to a characterization of the corresponding frequency response. An example design using a previously unavailable carrier frequency is presented which requires fewer filter taps than the alternative, a higher-rate uniform system.