Research On Fast Aequisition Method Of High Dynamic DS-SS Signals

With the development of science and technology, the application and service of the high-speed aircraft, such as airplane and satellite, gradually deepen, which have wide application prospects in both military and civil fields. Because of the anti-interference and security requirements in signal transmission, spread spectrum technology has been widely used. But in the high dynamic environment, the changing speed and trajectory lead to large Doppler frequency shift and frequency change rate. Meanwhile, the multipath effect and noise interference make pseudo code generate phase delay. These effects increase the difficulty of high dynamic signal’s real-time acquisition. But the traditional algorithm’s ability is limited, so the research on fast acquisition of high dynamic spread spectrum signals has important significance.This paper mainly studies the spread spectrum signal acquisition algorithm. Traditional algorithm’s acquisition time is affected by the pseudo code length or the Doppler frequency offset range, so it cann’t be used to real-time application. This paper proposes the delay self-correlation frequency offset estimation algorithm and the circular correlation code phase estimation algorithm. It divides traditional two-dimensional search into the separate estimation of Doppler frequency offset and frequency change rate as well as pseudo-code phase.In the estimation of Doppler frequency offset and frequency change rate, Matching Fourier Transform algorithm uses different basis function to match signal and noise. It has strong anti interference ability and high estimation precision, but the operation is too huge for direct calculation. In order to reduce the operation, the delay self-correlation frequency offset estimation algorithm is proposed. Algorithm removals the effect of PN code through delay multiplication, then estimate frequency change rate and Doppler frequency offset through FFT. The calculation is greatly reduced and the accuracy is improved. But the delay multiplication reduces SNR. The influence mechanism is analysed and the improvement algorithm is given to enhance SNR. The improved algorithm can capture effectively even when the received signal’s SNR is-15 d B without any noise reduction method.In the estimation of pseudo code phase, FFT parallel acquisition is combined into the algorithm. After compensation of Doppler frequency shift and frequency change rate, the new application of the pseudo code estimation algorithm is more effective. It only needs one time of PN code acquisition without frequency search and the calculation is greatly reduced. Then the algorithm for low SNR is improved, and the influence of PN code acquisition performance by coherent accumulation as well as acquisition precision of Doppler frequency offset and frequency change rate is analyzed.The acquisition time of the proposed algorithm is influenced little by pseudo code length and Doppler frequency offset range. Compared to traditional algorithm, the capture time and the amount of calculation are greatly reduced and it has high acquisition precision in a certain SNR range.Therefor, it’s applicable to the fast acquisition for high dynamic spread spectrum signal.