Offset FFT and its implementation on the TMS320C25 processor

Abstract

The paper outlines the concept of a frequency offset fast Fourier transform (FFT) algorithm called OFFT (offset FFT), and explains its relevance to realtime digital communication systems. Like the conventional FFT, the OFFT can simulate a bank of matched filters; this together with the frequency offset makes OFFT particularly suitable for detecting M-ary frequency shift keyed (MFSK) signals. The implementation using a TMS320C25 digital signal processor of a 128-point complex-input OFFT for MFSK signals is discussed, with particular emphasis upon those aspects of the design affected by the offset.