Research On The High-Sensitivity Acquisition Technology For BD B1I Signal

With the expansion of human activities, the Global Navigation Satellite System is more and more applied to indoor positioning, field survey, earthquake and fire rescue, geographical topographic survey etc.. In these complex environments, the satellite signal is weakened because of many factors such as multipath reflection, obstacle sheltering, broad-band interference and so on, which make the ordinary receiver can't capture the weak signals for navigation and positioning. So the application of GNSS is limited. High sensitivity navigation satellite signal acquisition is the technology which studies the navigation satellite signal capture in weak signal environment.BDS-2 is a global navigation satellite system which is constructed and run by our country independently. By 2012, BDS has entered into commercial stage formally. Now there are 19 satellites on orbit. It has provided navigation service in Asia-Pacific Region. With the continuous development of the BDS, the Beidou navigation and positioning terminal has a very broad market prospects. Therefore, the research on high sensitivity Beidou satellite signal acquisition technology is a very challenging and prospective research topic.Firstly, in this thesis, the structure and characteristics of the BDS-2 signal are analyzed, which include the signal's structure, the generation and properties of the C A code, the Doppler effect and the intermediate frequency signal model. The simulation program of the intermediate frequency signal is designed and realized, and the production flow of the intermediate frequency signal is introduced in detail. Then the acquisition principle of navigation satellite signal and two basic acquisition methods in time domain and frequency domain separately are introduced.Then, high sensitivity signal acquisition technology accumulates the local replication signal and received satellite signal correlation results. According to the different accumulation way, it is divided into three methods: coherent integration method, non-coherent integration method and differential coherent integration method. In this thesis, these three algorithms are introduced in detail, and the simulation analysis is carried out. The simulation results proved that d ue to the high bit rate of BD signal, coherent integration time is limited to 1ms, and differential coherent integration method is not applicable. Then two kinds of weak BD signal acquisition methods are analyzed, that are the non-coherent integration method and the full bit algorithm. In the light of the high computation quantity of high sensitivity acquisition algorithm and long time running, an optimization method was put forward. When doing the correlation operation of a ranging code period, this optimization method can reduce half of the inverse Fourier transform operations and half of the multiplication operations.Finally, a method for weak B1 I signal acquisition is designed, namely the improved half bit-characteristic sequence method. The feasibility of the algorithm is verified by experiments, and the anti- interference ability of NH20 sub sequence with different length is analyzed in detail. The algorithm is carried out by using the simulated intermediate frequency signal, and the experiment results are compared with the non-coherent integration method and the full bit algorithm. It proved that the proposed method performed better than the non-coherent integration method and the full bit algorithm. Then, the proposed algorithm is used to capture real BD signal which is collected by a satellite intermediate signal collection system. And the experiment captured weak BD signal successfully.