Research On Vector Tracking Based Ultra-tightly Integrated Navigation For High Dynamic Vehicles

Nowadays, many countries pay more attention on aerospace domain and moreand more high dynamic vehicles are designed and developed. To improve theperformances of high dynamic vehicles and enhance their survival capability, it isurgent to develop a navigation system which can achieve stable, continuous and highaccurate navigation. In this context, the navigation technology for high dynamicvehicles gets more attention from many countries.The different navigation systems all have their own advantages and drawbacks,any independent navigation system cannot meet all navigation requirements of highdynamic vehicles. Therefore, the navigation system which can integrate severaldifferent navigation sensors is becoming the navigation selection of high dynamicvehicles. Among the three integrated GNSS/INS navigation modes, the looselyintegrated and tightly integrated modes are both dependent on the performances ofGNSS receivers. The standard receivers can’t uaually work in the complicated andharsh environments, thus it is also difficult to achieve the loosely or tightly integratedGNSS/INS navigation in harsh environments. To face this issue, the ultra-tightlyintegrated GNSS/INS navigation system is developed. This system can significantlyimprove the navigation performances of the integrated navigation system in the highdynamic, weak signal and interfered environments by replacing scalar tracking withvector tracking and coupling INS with tracking loops. Hence, the ultra-tightlyintegrated mode is very suitable for high dynamic vehicles.Funded by the Shanghai Aerospace Administration in2009and2011, theresearch of the vector tracking based ultra-tightly integrated GNSS/INS navigationtechnology for high dynamic vehicles is done in this paper. In the research of thispaper, the initial alignment of INS, the GNSS signal acquisition aided by IMU, vectortracking, stable navigation in high dynamics and integrity monitoring arecomprehensively investigated. These researches build the theory base for theapplications of the ultra-tightly integrated GNSS/INS navigation system on highdynamic vehicles. The primary research contributions are summarized as followings:1. Collecting and summarizing all related literatures and previous works about the navigation technology of high dynamic vehicles and the integrated navigationtechnology. With these collections and the project background, the research contentsof ultra-tightly integrated GNSS/INS navigation system for high dynamic vehicles arechosen and determined.2. The scheme of the transfer alignment on dynamic base is proposed based onthe features of high dynamic vehicles. To achieve the proposed transfer alignment, theerror models of the transfer alignment is built and the alignment filter is designed.Moreover, the information delay of the transfer process is also discussed and analyzed.Furthermore, based on the observability analysis of the transfer alignment, thealignment filter is simplified and a filter with fewer dimensions is designed to achievea simplified transfer alignment and reduce alignment time. Finally, a simulationplatform of the transfer alignment is built for simulation experiments. Theperformances of the ordinary transfer alignment and the simplified transfer alignmentare compared and evaluated according to the results of simulation experiments.3. Investigating the acquisition performance indexes of the GNSS signalacquisition aided by IMU and stating the reasons of the acquisition performanceimprovement brought by IMU aiding. After the principle of IMU aided estimation ofthe Doppler frequency shift is introduced, the accuracies of the Doppler shiftestimation with IMU aiding and without IMU aiding are compared and themathematic relationship between the IMU quality and the accuracy of the Dopplershift estimation is derived to analyze the effect of the IMU quality on the Dopplershift estimation. Furthermore, the generation and collection platform of the navigationdata is built, the experiments of the acquisition aided by different grade IMUs isperformed with the data generated by the experiment platform to compare theacquisition time and capability of the acquisitions aided by different grade IMUs.4. The principle and type of the vector tracking based ultra-tightly integratednavigation system is introduced. The models of the tracking loop errors are built andthe essence of the tracking performance improvement brought by ultra-tightintegration is disclosed according to the analysis of the error sources and errordistributions. Moreover, the mathematic relationship between the IMU quality and thetracking loop errors of the ultra-tightly integrated navigation system is derived. Forhigh dynamic vehicles, the scheme and filter of the ultra-tightly integrated navigationis designed and a software defined ultra-tightly integrated navigation system isdeveloped by myself. The semi-physical experiment platform is built and theperformance evaluation experiments of the ultra-tightly integrated navigation system for high dynamic vehicles are performed on this platform.5. To face the drawbacks of the receiver autonomous integrity monitoring andintegrated navigation system integrity monitoring method, a new integrity methodwhich has no constrain on the number of visible satellites is proposed based on theultra-tightly integrated navigation system. Furthermore, the differential technology isbrought to the integrity monitoring of the ultra-tightly integrated navigation systemand the error identification method of the ultra-tightly integrated navigation systemwith the differential assistance is proposed.The novelties of this paper are listed as followings;1. Different with previous researches which usually use the observabilityanalysis on the system performance analysis, the observability analysis is applied onthe transfer alignment on dynamic base to simplify the alignment filter in this paper.By eliminating the unobservable state, the simplified filter with fewer dimensions isdesigned to achieve the rapid transfer alignment. The simplified transfer alignmentcan reduce computation burden and enhance alignment efficiency with acceptablealignment accuracy. It is more suitable for high dynamic vehicles.2. The mathematic relationship between the IMU quality and the estimationaccuracy of the Doppler frequency shift is derived in details to analyze the influenceof the IMU quality on the performance of the IMU aided acquisition. By comparingthe experiment results of the acquisitions aided by different grade IMUs, thereasonableness and correctness of the derivation and analysis are proved.3. The error models of the tracking loops in the standard receiver and theultra-tightly integrated navigation system are built, respectively. Based on thesemodels, the tracking loop errors and error distributions are compared by simulationsto disclose the essence of the tracking performance improvement brought by theultra-tight integration. According to these error models, the mathematic relationshipbetween the IMU quality and the tracking loop errors are further derived and provedby simulation experiments.4. A new integrity method is proposed based on the ultra-tightly integratednavigation system. This method can not only detect and exclude the faulty of theultra-tightly integrated navigation system, but also has no constrain on the number ofvisible satellites. Referring the principle of the differential positioning, the differentialtechnology is brought to the integrity monitoring of the ultra-tightly integratednavigation system and the error identification of the ultra-tightly integrated navigationsystem with the differential assistance is proposed.