The Research on Frequency Estimation Algorithm Based on Q-N Method

In the capture method of direct sequence spread spectrum signal, after the pseudo-code phase alignment, the residual Doppler frequency offset needs to be further estimated. For the signal with low frequency resolution, a large number of sampling points are needed for FFT spectrum analysis. Therefore, a frequency estimation based on Quinn algorithm and Newton iteration method is adopted. The algorithm firstly estimates the frequency offset by FFT spectrum analysis using a small number of phase-aligned signals, and then further optimizes the initial value of the frequency offset by the Quinn algorithm. Finally, the Newton iteration method is used to continuously estimate the frequency offset to the real value. This method not only reduces a large amount of FFT resources, but also has a fast convergence speed and high estimation precision. Through theoretical analysis and experimental simulation, the Q-N method reduces frequency estimation error by 90% at SNR=5dB compared to traditional FFT methods. There are great advantages in frequency offset estimation algorithm with low frequency resolution.