Research On Weak Satellite Signal Acquisition Technology

As people’s curiosity about the universe and national attention to space resources, global satellite navigation business is booming. In the process of development and exploration, the researchers constantly solve the problems and discover the new things. In recent years, companies, universities and research institutions are keen to problems of weak satellite signals acquisition. In this thesis,the problem of the weak satellite signal acquisition under low SNR is analyzed and discussed.First, this thesis describes the typical navigation system- GPS(Global Positioning System) and its structure and development. It introduces the current research institutions’ condition about the weak satellite signal acquisition under low SNR. And this thesis introduces common algorithms for weak signals acquisition.Secondly, this thesis is to analyze the channel characteristics of weak signals. Then, it analyzes the traditional methods of acquisition: serial acquisition, parallel frequency acquisition, and parallel code acquisition. Then it compares the complexity of those algorithms and acquisition time. Also, it analyzes the capture effect of traditional method under different SNR. In low SNR, the effect of the traditional acquisition algorithm is not very satisfactory.Furthermore, the thesis describes the accumulation of weak signal technology acquisition methods: coherent integration, differential coherent integration and non-coherent integration. Then, this thesis analyzes the performance gain between the three. Coherent integration can significantly improve the gain of the system, but it will cause bit transition. Non-coherent integration can solve the problem of data bit transition, but it will cause square loss. While the differential coherent solves the both problems.Then,this thesis analyzes the matched filter,and simulates its effects of white Gaussian noise channel. Then, it introduces the basic concepts of PMF-FFT algorithm and analyzes the relevant performance characteristics. In order to improve the processing gain of PMF-FFT algorithm, adding window method is proposed. In this thesis, we add the window in the front part of the PMF section and FFT section, which improves the detection probability and reduces the leakage alarm probability.Finally, this thesis introduces the weak signal acquisition with auxiliary information in aided navigation system. The auxiliary information can help us calculate the satellite Doppler frequency shift. Through the estimation of Doppler frequency shift, we can reduce the search scope and the acquisition time. This thesis also analyzes weak signal acquisition with inertial navigation system,which reduces acquisition time and improves the accuracy of the capture.