| 摘要 |
Various methods and apparatuses are provided for performing a radix-M FFT (Fast Fourier Transform) upon N time domain samples to produce N/S frequency domain samples for detecting tones of dithers impressed on channels of a WDM (wavelength Division Multiplexed) optical signal. Successive tones have a tone frequency spacing, .DELTA.f ta, and a sampling frequency, f S, is chosen so that f s = N.DELTA.f ta/S. S is a spacing given by S = M w with w being an integer. The radix-M FFT is performed in k = log M(N) stages and within the stages a reduced number of radix-M computations, when compared to the number of radix-M computations of a conventional radix-M FFT, are performed on data points associated with the N time domain samples. This is possible because successive frequency domain samples of the N/S frequency domain samples differ by .DELTA.f ta = S.DELTA. f where .DELTA.f is a frequency bandwidth.
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