Multi-sensor Fusion For Real-time Attitude Determination Utilizing Global Navigation Satellite System

Low-cost direction determination for civil ship has long been an issue of great interest in navigation. Satellite compass, or GNSS compass, an equipment to indicate direction using GNSS technologies and provide realtime heading information for other devices (AIS, VDR and ARPA), becomes a major alternative for the traditional electronic-/magnetic-gyrocompass because of its non-accumulation error, little influence of earth magnetic and low cost.The key to the direction determination by GNSS carrier phase measurements lies in the algorithms of solving integer ambiguity and attitude/heading. What is described in this thesis is based on the results collected during the extended research of which is a 863 project named'High precision integrated navigation technology under long endurance and high dynamic conditions'(No. 2006AA705320) and other related projects. The major topic is integration of GNSS and various sensors for attitude determination and special emphasis has been put on the theoretical analysis and experimental verifications of single-baseline satellite compass, which is prepared for preliminary report before production.The major contributions and roadmap of the thesis are summarized as follows:(1) Collection and summary of all the related literature and previous work. With this information, and taking into account the hardware limits, I specify the specifications of the GNSS compass to be researched and propose how to implement a low-cost attitude determination system.(2) The attitude determination is done using differential attitude equations developed in a local level frame. A detailed derivation and analysis of ADOP formula is given. The multipath is considered the primary error source and simulation and experiments show the feasibility of mitigating multipath using piecewise difference.(3) Considering the jam cases, the low-cost three-axis magnetometer and sigle-baseline GNSS attitude determination were ingerated. For the influence of earth magnetic field, error compensation algorithms were investigated deep. The test platform was built and theory simulations and experiments were carried out.(4) For the strict situation, double-antenna GNSS attitude determination and low-cost INS integated technology were investigated. The mutually supporting of the two systems is important for the whole system and the measurement equation and unscented kalman filter (UKF) were built up.(5) Based on all the above mentioned, a hardware and software prototype is worked out for improving the performance through diverse experiments, static or dynamic. Results have been given and grouped by different scenarios and conditions.The key technology and innovativeness of the thesis are summarized as follows:(1) The GNSS integrated attitude determination system has been developed. Based on the research of differenc attitude equation of local level fram (LLF), the error problems of GNSS attitude determination were investigated deep. The attitude dilution of precision (ADOP) of sigle-difference attitude equation was analysed and derived and some useful deduction could be used in the algorithm implementation. The multipath error is the main error source of carrier phase attitude determination. The theory model of multipath was given and the tests in simple and complicated enviroments have been carrier out.(2) The GNSS attitude determination equations and magnetmeter linearization equation have been built up and filted by EKF. The attitude/heading precision and continuity become better. The heading output of magnetmeter could be used for constraint condition of integer searching range and the calculation load was reduced greatly.(3) Based on single baseline, the deep integration structure of GNSS attitude determination and INS have been built up and filted by unscented kalman filter (UKF). The attitude output of INS could be used for constraint condition of integer searching range and the calculation load was reduced greatly. The mutually supporting of the two systems is important for the whole system.The research conclusions of the thesis are summarized as follows:(1) The integation of difference attitude equation and ambiguity function method (AFM) has improved the real-time and reliability of integer ambiguity resolution. A number of experiments demonstrate that this improved approach significantly outperforms the traditional ones in terms of the computation load. Compared with the traditional approach, the efficiency of the improved one is faster than the traditional one on average, with equivalent performance in reliability and accuracy.(2) In open environment, the standard deviations and means of multipath error have little change. And in complicated environment, the influence of multipath has the same result and could be removed easily under the same test conditon. Considering the ADOP, some processes should be taken into accout in some special positons.(3) Low-cost three-axis magnetometer and GNSS integation improves the continuity, reliability and precision and could be implemented in simple way. The cost of the whole system is not more expensive than only GNSS attitude determination.(4) The initial attitude output of INS could be used for constraint condition of integer searching range and the calculation load was reduced greatly. The mutually supporting of the two systems provides the better performance. The cost of the whole system increases great and the high precision and good reliability coule be obtained, especially in some advanced application. Finally, different costs have different performance figures depended upon the user's requirements and choice.