Research On The High Dynamic Tracking Technology Of GNSS/INS Deep Integration

With the development of long range, high dynamic and high precision guided weapons, research on the applications of global navigation satellite system (GNSS) in high dynamic environments brings increasing attentions. The high dynamics of the receiver will bring serious impact on the stability of GNSS signal tracking, which leads to the failure of precise positioning. In order to support the long range precision navigation for weapon delivery, the GNSS receiver's high dynamic performance should be improved. Most of the precision guided weapons has been equipted with GNSS/INS compound guidence system and the integration of GNSS and INS can overcome the shortcomings of the individual systems, as they have significant complementary characteristics. The conventional loose and tight integration of GNSS and INS can improve the system navigation performance, but neither of them has a supporting role in GNSS signal tracking in high dynamics. In GNSS/INS deep integration, the impact of the dynamics on the tracking loops can be mitigated by INS aiding, which can improve the performance of the loop. So GNSS/INS deep integration is the most effective way to solve the problems of the signal tracking and precise positioning of GNSS in high dynamics.In western developed countries, the high dynamic GNSS/INS deep integration has been widely used in all kinds of precision guided weapons, and the integrated guidance system with GNSS carrier phase measurement capability has been successfully developed; however, it has been restricted on export the relevant technology to China. On the other hand, domestic studies of the deep integration remain at simulation stage. Most of the studies are mainly based on qualitative analysis, which lacks theoretical methods to guide system design and test solutions to evalute system performance. The limitations above seriously restrict the development and high dynamic applications of the domestic deep integration technology.To meet the requirements of long-range precision guided weapon, this thesis describes an in-depth study on the signal tracking technology of scalar-based GNSS/INS deep integration system in high dynamics. The error propagation models of the INS aided carrier tracking loop are established to make the quantitative analysis of the tracking errors caused by INS error sources. And the optimization designs of the deep integration system are achieved based on the guidance of theory analysis. Besides, the carrier phase tracking accuracy and navigation performance are comprehensively evaluated by high dynamic simulations and real tests. The primary contributions and roadmap of this research can be summarized as the following aspects.1. Quantitative analysis of the tracking error are made by developing the INS error propagation models of deep integration system. Under the assumption of high dynamic uniform acceleration linear motion (100g), it establishes the connections between all INS error sources and carrier phase tracking errors by the INS error dynamic equations and the INS aided PLL model. Then it quantitatively analyzes the effects of the INS error sources on tracking performance, when the receiver moves along the north, east and vertical directions with large accelerations. The analysis shows that:the major error sources, which affect the carrier phase tracking accuracy in high dynamics, are the initial attitude errors, accelerometer scale factors, gyro noise and g-sensitivity errors. The initial attitude errors are usually combined with the receiver acceleration to influence tracking loop performance, which can easily cause the failure of signal tracking. Besides, the main error factors vary with the receiver motion direction and the relative position of receiver and satellites.2. The INS error propagation models of GNSS/INS deep integration in high dynamics are verified by the simulation tests of typical high dynamic scenes. Simulations of the horizontal and the vertical uniform acceleration linear motion (100g) are accomplished by GNSS/IMU simulator, and the simulation data are processed by the deep integration system software. Then the carrier phase tracking error outputs are compared with the quantitative analysis results. The simulation test results are consistent with the quantitative analysis results, which verifies the INS error propagation models are correct and reasonable.3. The deep integration system design is optimized based on the analysis results of the error model.(a) A frequency-step compensation method is developed to eliminate the effect of the integrated navigation updates and the tracking performances of the loops are more robust after the optimization.(b) An acceleration extrapolation algorithm for the INS aiding information is designed to solve the problems caused by the limited IMU data sampling frequency. And the proposed algorithm can effectively reduce the influence of the sampling interval when the acceleration or jerk of the receiver is constant.(c) The relationship between carrier phase tracking error and loop bandwidth is analyzed based on the INS error propagation analysis results. And it shows that the bandwidth of MEMS INS aided 2nd-order PLL should be larger than 17Hz within 100g maneuvers, and the bandwidth can be reduced to 5Hz if the PLL is aided by tactical INS.(d) The selection of inertial sensors of deep integration system in high dynamics is guided based the results of the INS error propagation analysis. And it suggested that if the heading error of the INS is less than 1 degree, the GNSS/INS deep integration system can keep tracking the satellites signals stably with 100g maneuvers under the conditions of 45dB-Hz CNo,20Hz bandwidth and 1 ms coherent integration time.4. The performance of the optimized deep integration system is fully evaluated by simulation and real tests, respectively.(a) Simulations of linear (100g, 100g/s) and circular (50g) motion scenes are accomplished by GNSS/IMU signal simulator, and the performance of carrier phase tracking and system navigation accuracy are analyzed either with or without INS aiding. Simulation test results indicate that the INS aided 2nd-order PLL can keep carrier phase tracking stably and output precise navigation solutions, while the ordinary PLLs cannot track the satellite signals in high dynamics; the MEMS INS can be used to aid the carrier phase tracking in the GNSS/TNS deep integration in high dynamics.(b) A high-speed rotating platform is developed and the real tests of circular motion with more than 5g acceleration and 30g/s jerk is carried out. The performance of carrier phase tracking and system navigation aided by MEMS INS are analyzed and the results show that the GNSS/MEMS INS deep integration system can not only keep the carrier phase tracking stably, but also improve the tracking accuracy of carrier phase by reducing the loop bandwidth and extending the coherent integration time. Furthermore, the deeply coupled system can output integrated navigation results with high accuracy, while the integrated navigation results of oridinary loosely coupled system are diverged as the receiver cannot provide continuous measurement without INS aiding. The results also prove that the deep integration system designed in the thesis can be used in real high dynamic environments.In summary, this thesis describes a thorough study on the signal tracking technology of the GNSS/INS deep integration system with scalar tracking loop in high dynamics. The INS error propagation models in high dynamics are developed and the effect of the INS error sources on the tracking performance is analyzed quantitatively. Besides, the system design is optimized and the system performance are evaluated by the comprehensive simulation and real tests.The proposed error models, optimization designs in the thesis can be further applied to the research on the engineering realization of the GNSS/INS deep integration system for high dynamic applications.