Application of frequency-domain polyphase filtering to quadrature sampling
Andrew K. Halberstadt · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 1995
A new method for developing in-phase and quandrature samples of a band limited real signal is presented and compared with other methods. The proposed method improves the computational efficiency of a frequency-domain implementation of the required filtering by taking advantage of mirror-image symmetry between the filters on the in-phase and quandrature channels. This technique makes it possible to filteer both the in-phase and quadrature channels at once using one standard FFT for complex-valued input and one standard IFFT for complex-valued output without adding computational overhead. The proposed method is more computationally efficient than techniques using commonly available FFT routines for real-valued input. Specialized FFT routines derived specifically for real- valued input can achieve greater computational efficiency than the proposed method, but these routines are not as commonly available as the standard FFT routines used in the proposed method. For systems where the effective channel filter is short in length or has special structure, there are other implementations of the channel filters which are more efficient than the proposed method.