Research On Beidou Navigation Signal Capturing Algorithm And Design Of Beidou Timing Service System

With constant improvement of the Beidou Navigation Satellite System, Beidou navigation services have already covered most areas of Asia. The number of Beidou terminal users continues to increase. The service environment has become more complicated. So the performance of the receivers has to be improved. Recently, the performance of receiving weak signal is considered to be a key indicator of satellite navigation system, which is directly related to the continuity, accuracy, availability and integrity of navigation system. For GPS receivers and Beidou II civilian receivers, many domestic research institutions have accumulated a lot of experience and have achieved major breakthrough in weak signal reception technologies. But there is still a big gap compared to international standards. Therefore, the issue of weak signal reception of Beidou II satellites stays open to be resolved. Since the sensitivity is an indicator of the receiving weak signal, it has been highly valued.The first step in the base band signal processing is the capture process, so the performance of the capture algorithm directly relates to the sensitivity of the receiver. Thus improvement of the algorithm performance is an eternal pursuit. Before studying the capture algorithm, there is a need of IF signal to prove the acquisition performance of the algorithm. Therefore, this paper analyzes the structure of Beidou B1 I satellite signal first, and then analyzes the IF signal model. Then the paper introduces the methods and procession of generating the IF signal. Finally, the simulation results under different signal to noise ratio are obtained and compared.The navigation receiver processes satellite signal in two parts: RF part and base band part. The capture of the baseband signal is first to be carried out. This paper introduces the principle of signal capturing before studying signal capture algorithm. Based on the principle, serial acquisition algorithm and parallel code phase acquisition algorithm are analyzed. Then the performances of these two algorithms are compared and analyzed. The simulation results show that the two algorithms have the same performance, but parallel code phase acquisition algorithm is better than the serial algorithm in capturing time. After that high sensitivity capturing algorithms in weak signal condition are analyzed. The ways to improve the sensitivity include: coherent integration,non-coherent integration and differential coherent integration. Due to the D1 data being secondary coded by NH code, coherent integration and differential coherence integration cannot be directly used, only non-coherent integration can be used. Thus a full bit algorithm is proposed in this paper. The non-coherent integration algorithm and the full bit algorithm are compared by simulation. The results show that the full bit algorithm can reach the same performance while using less data bits than non-coherent integration algorithm. But the full bit algorithm is more time consuming and requires further optimization.Beidou timing services assume to be promising in the civilian. Aiming at this problem, we designed a timing hardware system based on Beidou navigation information. This system uses Beidou timing service to distribute precision time to the LAN terminal. Timing service system is designed based on architecture as FPGA + MCU + Beidou navigation module + Wi-Fi module. FPGA has a strong capability of processing parallel data and can receive real-time information from navigation module. Then the real time is displayed on the LED dot matrix. In WLAN network timing service aspect, NTP protocol is used to maintain the consistence which is implemented on both of the MCU and Wi-Fi module. The principle and implementation methods of each module are introduced in detail. Finally, the results of the system operation have been shown.