Research On Acquisition And Code Tracking Technology Of Weak GNSS Signal

With the increasing diversification of Global Navigation Satellite System (GNSS) application scenarios, the technology of GNSS signal receiving in weak signal environment is attracting more and more attention. Due to propagation obstacles in such environment, the received signal usually suffers heavy power attenuation multipath effects and cross-correlation interference, which is a big challenge for the research on technology of weak GNSS signal receiving. This thesis focuses on exploring improved algorithms for acquisition and code tracking of weak GNSS signal.In order to improve acquisition sensitivity for GNSS receivers, this thesis proposed a novel detection algorithm based on peak position finding. Aiming at multipath resistance, an averaging filter based algorithm named AFPDI was designed here, which is capable of implementing anti-multipath in acquisition. On the other hand, this thesis also demonstrated the improved MEDLL and RLS algorithm, according to the existing algorithm. That makes code tracking loop more robust in multipath scenarios. The main chapters in this thesis are organized as follows:(1).In order to establish theoretical basis for following chapters, this thesis described the general expression and base-band signal processing for GNSS signal. It also discussed the signal characteristic in weak signal environment and did further analysis on weak and multipath signal channel.(2).Based on acquisition processing for weak signal, this thesis analyzed and discussed critical algorithms in acquisition, including pre-detection SNR improving algorithms, detection algorithms and anti-multipath algorithms. Especially, it proposed a new detection algorithm based on peak position finding, which is possessed of lower detection SNR. Besides, AFPDI was also designed to make acquisition algorithm more robust in multipath scenarios. (3).Concerning code tracking technology for weak GNSS signal, this thesis demonstrated the math model for classical code tracking loop and analyzed thermal noise variance for loop performance. That is helpful to find the way to improve tracking sensitivity. To obtain better performance in anti-multipath, this thesis proposed two improved MEDLL and RLS algorithms based on the existing algorithm. Also, it employed simulations to compare performance of these different algorithms.(4).An implement scheme of weak GNSS signal receiver was described. According to this scheme, this thesis gave the results of FPGA test and satellite test for acquisition system. In addition, it simply introduced the modernization plan for GNSS, discussed BOC signal and future GPS signal and shared the prospect of future development and challenge in GNSS application.