Noise performance of two frequency-error detectors derived from maximum likelihood estimation methods

Frequency tracking loops are used in digital links to control the carrier frequency of the received signals. A basic component in these loops is the frequency difference detector. This paper concentrates on two detectors that have previously been derived from maximum likelihood estimation criteria. Noise spectra of the detector outputs are computed and the results are used to assess the performance of frequency control loops operating in the tracking mode. Computer simulations are used to validate the theory. The detector implementation in digital form is also addressed and design criteria are provided that lead to structures with a limited computing complexity. Comparisons are made with other frequency detection schemes available in literature