Sliding discrete Fourier transform based frequency-locked loop for adaptive carrier tracking of bi-phase signals

For bi-phase signals, an adaptive carrier tracking method based on sliding discrete Fourier transform (SDFT) frequency-locked loop (FLL) is proposed. Magnitude and phase spectra of closed-loop SDFT filter provide almost flat response around the centre frequency. However, the small magnitude and phase errors observed at the SDFT in-phase and quadrature components are corrected by adaptive sampling frequency control. The carrier frequency is estimated by computing the frequency error. Hence, the input frequency variation due to Doppler shift could be estimated for the bi-phase signal. Experimental investigations with digital implementation demonstrate the suitability of the FLL for bi-phase signals.