The Research Of MIMU Assisted GNSS Attitude Determination Technology

Attitude determination technology is required strongly in automatic control and intelligent control of ground and aquatic low-speed vehicles. Expensive and vulnerable to the interference of the environment are shortcomings of the existing attitude determination system, which greatly limit the application of the attitude determination technology in these vehicles. In this paper, the attitude determination technology based on MIMU assisted GNSS is researched. It is the design to study the high precision, low cost, strong anti-jamming attitude determination system so as to meet the requirement of practical applications.In this paper, the MIMU and GNSS attitude determination system are integrated on the basis of GPS attitude determination, and the MIMU is used to assist the GNSS. The method of MIMU assisted GNSS attitude determination is deeply studied in theoretical based on the research platform of software receiver. A kind of MIMU assisted GPS ultra-tight integrated attitude determination method is proposed. The MIMU and GPS are integrated in multi-levels, the receiver tracking loops are assisted by accelerometer, and the integer ambiguity search is assisted by gyroscope, data fusion is used in two attitude angles to get the optimal attitude estimation. For the ultra-tight integrated system has the problems of different data update frequency, non-linear relationship, computational burden and instability. The ultra-tight integrated attitude determination algorithm based on FEKF is proposed. The tracking loop filters are taken as sub-filters, and the error of loop and acceleration assisted are estimated by them. The results of sub-filters are fused by the primary filter to reduce the computational complexity and improve the reliability of the filter. The MIMU assisted GNSS loop tracking algorithm based on EKF is used to reduce the dependence between the assisted loop and the precision of MIMU. The sub-filters work independently, to reduce the correlation between the measurement noises. The EKF carrier phase measurement algorithm can improve accuracy and stability.MIMU assisted GNSS tracking loop can improve tracking accuracy, but it will increase the loop settling time, resulting in the tracking error correlation with time. The time delay filter loop tracking algorithm is proposed in this paper. The MIMU assisted GNSS tracking loop based on time delay filter is designed. The time delay filter is used in the loop, and the signal is pre-filtering by it. The simulation results show that the algorithm can effectively reduce the transition time of the loop, and the time correlation of the tracking error. The evaluation of adaptability is affected by the noise in AFM. To solve this problem, the adaptive design method for fitness function based on carrier phase measurement is presented in this paper. The error in the AFM search process is derivated, and the error model is established. The filtering fitness function is constructed based on carrier phase measurement noises according to the low-pass filter theory. This function changes the adaptability evaluation of the search candidates with the change of the carrier phase measurement noises, to adapt the observation noises. The experiment results show that this method can reduce the sensitivity of the fitness function to the observation noises, and enhance the efficiency of ambiguity solver. According to the characteristics of ultra-tight integrated attitude, the auxiliary function of attitude information and carrier phase measurement accuracy promotion on ambiguity resolution is derived.The experiment system of MIMU/GPS ultra-tight integrated attitude determination is built. The static experiment and boat-loading experiment are done. These algorithms in this paper are calculated off-line with experiment data. The results of experiment prove that these algorithms proposed in this paper are superior and feasible in attitude measurement applications.