The Research And Implementation Of The Acquisition Technique In BeiDou Navigation Receiver

With China’s BeiDou2nd Generation Satellite Navigation System putting into use, it is urge to develop user device which support BeiDou2nd Generation System. Secondary code modulation techniques have been introduced into BeiDou2nd Generation System, it helps improving cross-correlation performance, but it also challenge the signal acquisition algorithm. The NH codes modulated on B1signal which has possible bit sign reversal every lmillisecond restricts the coherent integration time down to1ms. This, in turn, significantly affects the acquisition performance. To solve this problem, Fixed-length coherent integration traverse/non-traverse algorithm based on parallel code phase searching is proposed in this paper, it can perform a long time coherent integration acquisition on B1signal and greatly improve the acquisition sensitivity. After the coarse acquisition, the doppler frequency estimation achieved can’t meet the demand of the tracking loop, so a fine frequency acquisition module is needed, this paper proposed a carrier frequency estimation algorithm based on interpolated DFT, it can improve the frequency estimation accuracy.Firstly, in this paper, we made analysis of B1signal’s structure, the Fixed-length coherent integration traverse algorithm based on parallel code phase search is then proposed, and simulation is perform and the result show that this algorithm functions successfully, when the coherent integration length is4ms, the acquisition sensitivity can achieve37dB· Hz. Then this paper proposes Fixed-length coherent integration non-traverse algorithm based on parallel code phase search in order to reduce the computing load at the cost of sacrificing the acquisition performance simultaneously. Then simulations under different search times have been performed.The frequency estimation accuracy achieved after the coarse acquisition can not meet the demand of tracking loop. In order to improve the frequency estimation accuracy, a carrier frequency estimation algorithm based on interpolated DFT is proposed, the simulation result shows that this algorithm can successfully improve the estimation accuracy in low SNR circumstance.B1signal generated from thesignal generator is used to test the performance of frequency estimation algorithm, the result show that this algorithm is effective.At last, Fixed-length coherent integration traverse/non-traverse algorithm based on parallel code phase search is implemented on FPGA platform, real B1signal of three different scenes has been used for test, and the test result shows that the implementation is correct.