Inertial Aided High Dynamic GNSS Baseband Signal Tracking Technology

As Bei Dou Satellite Navigation System has been successfully established and servicing in Asian,it is one of the four main Global Satellite Navigation Systems. The demand of aerospace and aviation navigation is of increasingly urgent nowadays, so the high dynamic application research of Bei Dou Navigation System is important. On the application of high dynamic aircraft, based on the inertial aided baseband tracking loop in GNSS/INS tightly integrated navigation system, this thesis studies on the velocity aided, acceleration aided, jerk aided PLL structure and aiding method. The aided PLL steady error and transient error are also analyzed to insure the high dynamic satellite signal tracking.The main work and innovative points of this thesis include the following aspects:1. The baseband tracking loop expression is studied and a carrier/code unite tracking filter is designed. Altering the traditional discrete tracking loop to the more explicit tracking loop expression based on state vectors, which represents the code phase, carrier phase, carrier Doppler frequency and Doppler frequency rate separately. On the basis, a carrier/code unite tracking loop is proposed,in which the carrier tracking and code tracking can be achieved simultaneously. Use the Bei Dou B3 satellite middle-frequency data to test and verify. Compared to independent tracking loops,the proposed 3-order PLL and 1-order DLL carrier/code unite tracking loop improves the static tracking precision of 27%. It is able to track the high dynamic signal of 40 g with precision of 0.033 cycles(12°, 1?), while the same order independent tracking loop’s performance decreases and loses lock, unable to estimate the Doppler frequency and frequency rate.2. The PLL’s transient response is analyzed. Introduce classic control theory analysis methods including the high order system transient indicators analysis method, nonlinear Phase-Plane method or equivalent Ordinary Difference Equation method to calculate PLL pull-in time and transient phase error limit. When PLL steady state error and transient error are within their thresholds, PLL can track stably. The analysis and experiment results show that the LOS acceleration step is the may cause of three-order PLL losing lock.3. The aided PLL structure and stability are studied. We propose the velocity aided and acceleration aided direct filtering method and error filtering method. The aided direct filtering method and error filtering method each has advantages: the former method’s transient response process is more rapid, and the transient performance is better; the latter method can avoid the affect of aiding information bias. Correspondingly, the steady state error and transient state error of above aiding methods are calculated, their thresholds for steady tracking are also given. For velocity aided PLL, the error transferring mechanism is studied, and the error enlarge coefficient is deduced. Analysis results indicate that, the velocity aided direct filtering method has a smaller error enlarge coefficient than velocity aided error filtering method. In GNSS/INS tightly integration system, the inertial aiding information update rate is lower than baseband tracking loop update rate, which induces aiding information time delay. The delayed information aided PLL tracking performance is researched. The experiment results indicate that, with delayed aiding information, the tracking phase bias will be enlarged by direct filtered PLL, and the tracking phase noise will be enlarged by error filtered PLL. However, the effect on acceleration aided PLL is more less than velocity aided PLL.4. Based on the high dynamic satellite radio frequency signal with maximum acceleration of 50 g, maximum jerk of 5g/s in ECEF reference and synchronized INS data, the position and velocity accuracy of GNSS/INS tightly integration system prototype is tested. The unaided system is not able to track the above high dynamic satellite signal while the acceleration aided system can track stably. Under horizontal circling motion situation, the three-dimensional position accuracy is 0.24m(RMS), velocity accuracy is 0.06m/s(RMS); Under straight back and forth motion situation, the three-dimensional position accuracy is 0.39m(RMS), velocity accuracy is 0.44m/s(RMS);5. To solve the problem of high jerk satellite signal tracking, an adaptive KFPLL and jerk aided KFPLL are proposed. The adaptive KFPLL is able to adjust its state error covariance prameter according to carrier phase error, which improves the non-aided PLL performance when tracking high jerk satellite signal. Besides, the jerk aided KFPLL adjust the state error covariance prameter according to aiding jerk information obtained based on nonlinear tracking differentiator. If acceleration aiding method is adopted, the aiding information bias will induce phase bias by direct filtered PLL, and LOS dynamic variation will induce long time trasient process by error filtered PLL, while these problems can be solved by jerk aided KFPLL. Validation is achieved through high dynamic Bei Dou B3 signal collected by GNSS simulator, and the results indicate that the proposed jerk aided KFPLL can track the satellite signal with 10g/s LOS jerk.