Research Of Hot Start Strategies Of Dual-frequency BDS Receivers

With the improvement of BeiDou Navigation Satellite System(BDS), which is researched and developed by our country, and the publication of Interface Control Documents(ICD), which includes the signal information of B1 and B2 signal, the dual-frequency BDS receivers are widely used due to the high precision. Hot start strategies are the most common methods of the BDS receivers. With the development of technology, users put more speed and precision demands on the hot start of the BDS receivers. However, the dual-frequency BDS receivers have double search coverage in acquisition step, leading to the time consumption increasement of normal hot start strategies. The information delay has a negative impact on the performance of dual-frequency receivers. To decrease the time consumption of the hot start as well as maintain high position accuracy, the hot start strategies are extensively studied in this thesis.Two improvement strategies are implemented due to the hot start procedure of the dual-frequency BDS receivers. Due to the abvious errors of estimated satellite positions in the satellite signal launch time prediction method, a novel strategy is given to reduce the positioning error generated by satellite position errors. The new strategy modifies the satellite positions by more accurate estimated transfer time, which reduces the ionosphere delivering delay error as well. Meanwhile, a B1 assist B2 acquisition strategy is implemented in the hot start of BDS receivers, which uses the relationship between the two frequency points of one satellite and rearranges the acquisition channels to further reduce the Time to First Fix(TTFF).A novel local code padding method is proposed for the acquisition of BDS signal with D1 navigation message to remove the influence of bit sign transitions. The impacts of bit sign transition are analysed and transition occurring in the middle position is proved not the worst circumstance, which is different from the previous researches. To mitigate the peak splitting impairments and increase the correlation gain, the local code padding method is proposed in this thesis. The main idea of the proposed method is building two new local codes by splicing and zere-padding to deal with the different bit sign transition circumstances of the incoming signal, and the corresponding detector is designed as well. The effectiveness of the proposed method has been evaluated by acquiring real BDS signal and assessed with Monte Carlo simulations using B1 I signal with D1 navigation message.Finally, the proposed strategies in this thesis are implemented on the BDS dual-frequecy development platform, which is based on EP2S90F1020 and TMS320C6713. The experience results demonstrate that the proposed hot start methods can decrease TTFF, and have better accuracy of the first few position points, which lays a foundation for further theoretical research as well as engineering implementation.