The performance of suppressed carrier tracking loops in the presence of frequency detuning

Abstract

The extraction of a coherent reference for purposes of demodulating double-sideband suppressed carrier (DSB-SC) signals can be accomplished using either a squaring loop or a Costas loop. By means of the Fokker-Planck equation, this paper establishes the tracking performance of these two circuits in the presence of frequency detuning, and then applies the results in evaluating the performance of coherent demodulators of digital (coded or uncoded) data. The results are sufficiently general to assess the effects of a broad class of prefiltering characteristics on tracking performance, as well as the effects due to various loop filter mechanizations. An expression for the moments of the time to first loss of synchronization is also given.