The Study On The GPS Based Real-Time Attitude Determination Technique And Multipath Effects

With the rapid development of the carrier phase differencing technique and digital signal processing hardware, it is possible to implement real-time processing of GPS based attitude determination system. In this dissertation,the theory and realiztion of GPS based attitude determination technique are studied, multipath effects on GPS observables and carrier phase multipath mitigation are also analyzed.Integer ambiguity resolution is the key problem of GPS based real-time attitude determination system which use double differencing carrier phase observables. Z-tranformation augmented FASF algorithm proposed in the dissertation can reduce the search space of integer ambiguity effectively, improve the effiency and real-time processing ability of integer ambiguity resolution; It is essential to analyse the reliability of integer ambiguity after it was fixed, the ratio test algorithm proposed in the dissertation can reduce the time to fix new integer ambiguity after wrong fixes are detected; To reduce further the number of epochs required for ambiguity resolution, that the baseline length constraint information which acts as observables is used to do kalman filtering to speed up ambiguity resolution is proposed. Furthermore, it is insure that the carrier pahse measurement data does not have cycle slips in GPS based attitude determination system, using phase rate prediction algorithm and baseline length constraint information algorithm, the cycle slips can be detected and corrected successfully, which markedly reduce the initialization numbers of attitude determination system.Most of error sources can be eliminated by double differencing due to the short antenna seperations within GPS based attitude determination system, multipath is the dominant error source. By way of analysis about the typical GPS receiver tracking loops, the mathematical models of code multipath error and carrier phase multipath error are proposed in the dissertation; By way of analysis about geometrical model of multipah signal, the mathematical model of differential path delay is proposed in the dissertation; Based on the above analysis, a improved carrier phase multipath mitigation algorithm using closely-spaced multiple antennas array is proposed, the result of computer simulation proves that the algorithm is feasible.The attitude parameters are often estimated using direct computation method. The relationship between the accuracy of attitude parameters and baseline length as wellas relative dilution of precision are derived. The impact of the stand-alone position on accuracy of relative position is also analyzed. The high precision GPS based real-time attitude determination system scheme using twin Novatel OEM4 sensors is proposed, the prototype of twin antennas real-time attitude determination system is also implemented using universal digital signal processor or PC/104 in-board computer. It is shown that output rate of 10Hz as well as yaw accuracy about 0.02 degrees and pitch accuracy about 0.1 degrees for the estimated attitude parameters has been achieved through a lot of experiments.