Carrier tracking loop for high-dynamic spread spectrum signals aided by estimation of Doppler rate

To reach a compromise between efficient dynamic performance and high tracking accuracy of carrier tracking loop in high-dynamic circumstance which results in large Doppler frequency and Doppler rate, a tracking loop structure aided by the estimation of Doppler rate is proposed in this paper. First, the instant self-correlation function is used for a process of dimension-reduction of the received signal. Second, the high resolution estimation of Doppler rate is achieved by making use of the phase difference of segmental discrete Fourier transform (DFT). Finally, the estimation of Doppler rate as a control variable of numerical controlled oscillator (NCO) is added in the traditional tracking loop to reduce the dynamic stress and to improve the tracking accuracy. Tracking performance of this loop is simulated under typical high-dynamic conditions, the RMS of Doppler frequency error tracked is only 3.46Hz with carrier to noise power ratio (C/N₀) 33dB-Hz. Compared to the general methods of 2nd FLL assisting 3rd PLL and linear Kalman filter in 3rd PLL, the performance is improved obviously under low C/N₀.