Research On GNSS Weak Signal Acquisition Algorithm

In the strong noise environment,the Global Navigation Satellite System(GNSS)signal received by the navigation receiver is very weak.How to improve the sensitivity of receiver and ensure the reliability of positioning service in the case of weak signal is the focus and hotspot of current research.The thesis takes the weak signal as the research object and focuses on the acquisition algorithm.Firstly,this thesis models the GNSS IF signal,analyzes the principles of several traditional acquisition algorithms,and discusses the causes of signal attenuation.After that,the common methods of integration and overcoming bit jump are explained.The purpose of these methods is to prolong the signal accumulation time and realize the acquisition of weak signals.Then the weak periodic signal detection method based on stochastic resonance is studied.By adjusting the parameters of the nonlinear system,the system,noise and signal can cooperate,and the output signal-to-noise ratio of the system can be enhanced.Then,an improved algorithm combining partial matched filtering and fast Fourier transform(PMF-FFT)is proposed.The scallop loss of the algorithm can be effectively suppressed by zeroing.Dividing the data into blocks and using the difference to detect the position where the symbol reversal of the signal occurs can greatly increase the integration time.The thesis mainly simulates the acquisition sensitivity of the improved algorithm.The experimental results show that the acquisition can be realized under low signal-to-noise ratio through zero filling and differential detection,and the sensitivity of the improved algorithm is also better than that of the previous algorithm.Finally,a weak signal acquisition algorithm based on stochastic resonance is proposed,the algorithm flow is analyzed,and the principle of the main part is explained.The code phase signal can be obtained by multiplying the signal and the local PN code delay,and then the signal is preprocessed to capture the Doppler frequency through the output of stochastic resonance.Simulation results show that compared with direct FFT operation,stochastic resonance has at least 2d B acquisition gain.By estimating data bits and using frequency compensation,the computational complexity and acquisition accuracy can be balanced,and the acquisition sensitivity of code phase can be further improved.