The Research And Implementation Of PN-Code Capture In The Low-SNR Enviornment

Spread Spectrum communication has been widely used in the Satellite positioning system because of the advantages of low probability of intercepting, a high immunity to interference, hiding the usefulinformation and multiple-access communication ability. The GPS, the GLONASS and the BD system of the Chinese all use the Spread Spectrum system for communication.The author bear the related research work in the process of the thesis writing. The main content of research is the capture Technology of the Direct Sequence Spread Spectrum. According to research of the Theoretical Analysis and the realization of the program, the author proposes the best Design. The article divided into two parts, one of them is Theoretical Analysis and the other is the Analysis to achieve. The Theoretical Analysis include the establishing of the completed PN-Code capture systems and the analysis of the key technology in the system. In the processing of the research, the author specialy analysis the performance and the methods in the low-SNR environment. The result of the simulation results indicate that changing the capture method can effectively improve the capture Performance.In the parts of the analysis to achieve, the author first introduce the hardware development platform. And then based on the results of the theoretical analysis, the author design the capture system from the two aspects: overall and branches. This paper constructs the every module, and analysis the relationship between the data at different module. At last simulate the result of capture module at the FPGA simulation soft Modelsim.The article reference the previous research result, innovate in the article many times, include determining the threshold using data inputed and twice FFT integration and so on. First of them can make system both adapte the capture adjudge powerful and the weak signal. Second of them can improve the capture gain and not add the Frequency slot. These innovation not only summarize and upgrade the result of the capture existing, and also laid a good foundation for the futher rearch at the field.