Method of detecting pilot tones in a noisy signal

This invention relates to detecting a pilot tone in an optical fiber. In the method described in the invention, computational complexity is reduced significantly by almost completely removing the need to carry out multipli-cations. To calculate certain spectral components of DFT (Discrete Fourier Transform) only a few multiplications are required. The idea is that for de-tecting one pilot tone, it is adequate to calculate one spectral component of DFT if a specific ratio can be chosen between the pilot tone frequency and the sample rate of the receiver.