Research On Vector Based Tracking Algorithms For BDS Signals

Study of global satellite navigation systems are widely carried out, China's Beidou satellite navigation system (BDS) is rapidly formed and begin to expand services from the regional to global gradually. Receivers as clients of the system,remain a research focus in the area as the performance requirements of aviation, aerospace, military and other fields of application. Vector based tracking is the key technology to improve receiver's performance in continuous positioning and in complex application environment. Besides,it is also the key technology of a deep GNSS/INS integrated navigation system. Based on the Beidou satellite system,the paper researchs on vector tracking algorithm, presents a distributed coherent VDFLL tracking algorithm for Beidou signal and gives the performance results and analysis.The main research contents of this paper are as follows:(1) This paper introduces and studies the structure and characteristics of Beidou signal.Traditional Beidou signal processing method based on software receiver is introduces,including signal acquisition,signal tracking and navigation solution. This paper focuses on the traditional scalar tracking (Scalar Tracking Loop,STL) of BeiDou signal. The carrier phase lock loop, frequency lock loop and the delay lock loop are studied in detail. Traditional BeiDou signal tracking and navigation solutions will be the initialization information of the vector based tracking loop.(2) Vector based tracking algorithms for Beidou signal are discussed in detail. This paper illustrates the difference between the scalar tracking loop (STL) and the vector tracing loop(VTL). Results show that vector tracing loop has obvious advantages in the signal block,weak signal and high dynamic environment. On this basis, the system modeling method and parameters determination of vector tracking loop are researched. Two modeling methods including location model and pseudo-range model are proofed, which can both implement the vector tracking loop for BeiDou signal. Besides,there are three main filter structures for vector tracking loop, including the centralized vector tracing loop, the distributed coherence vector tracking loop and the incoherent vector tracking loop. This paper gives detail analysis of these filter structures.The advantages and disadvantages of the three structures are summarized and compared.(3) This paper presents the design of distributed coherence VDFLL (Vector Delay Frequency Lock Loop) tracking algorithm for Beidou signal. The measurement model of the pre-filter for each channel is derived. The states and state model of the pre-filter are selected and designed. Then, this paper shows the pre-filter's tracking results and performance. In the navigation filter design, a second order position model is used for the system modeling and measurement model. Due to the impact of signal quality, the noise measurement matrixs of pre-filters and navigation filter are determined by the carrier to noise ratio estimation of system. The additional noise channel method (ANCM) for the carrier to noise ratio estimation is introduced. Then, system can adjust the filter's parameter according to signal quality, which in order to achieve an optimal loop tracking state. Finally, the scalar processing method is proposed in order to optimize filter processing in measurement updates. On the basis of the technique, an effective fault detection and isolation of the vector tracking loop is designed.The scalar processing method for optimizing updates can reduce the computational burden and be able to take full advantage of designing the measuring residual RAIM algorithms for measurement of detected fault detection and isolation.(4) To test and verify the distributed coherence VDFLL tracking algorithm, experiments and performance test are carried out, including static scene test, bridging the instantaneous disappearance of satellite test, fault detection and isolation of measurements and dynamic scene test. Results show that compared with the traditional scalar tracking algorithm, the distributed coherence VDFLL tracking algorithm can improve the positioning accuracy by 49.46% in the horizontal direction and 30.65% vertical direction under static conditions and 29.05% in the horizontal direction and 46.32% vertical direction under dynamic conditions.Meanwhile, velocity measurement accuracy is improved by by 30.30% in the horizontal direction and 23.68% vertical direction under static conditions and 2.10% in the horizontal direction and 15.27% vertical direction under dynamic conditions respectively. In addition,the distributed coherence VDFLL tracking algorithm has capacity to bridge instantaneous disappearance of satellite and achieve tracking again rapidly, while traditional scalar tracking lost lock when signal recover. Final, the measuring residual detection algorithm implement fault detection and isolation of the measurement. The measuring residual detection algorithm can effectively avoid the pollution problem, which caused by some channel's abnormal noise or error.With the rapid development of Beidou satellite navigation system, this study of vector tracking algorithm for Beidou signal provides some references on improving the performance of Beidou navigation receivers, and localization of BDS/INS deep navigation technology.