| Global navigation satellite system(GNSS)-based attitude determination has been widely applied in terrestrial,sea,air and space navigation fields because of long-term stability,low cost,and high accuracy,simultaneously.With the rapid development of the diversity of safety-critical navigation applications,the accuracy and reliability of GNSS attitude determination are increasingly stricter.Since the high-precision attitude determination depends on precise carrier phase measurements,the correct integer ambiguity resolution is a key factor affecting GNSS high-precision attitude determination.Therefore,considering the multiple antennas configuration feature of multi-baseline attitude determination system,this paper focuses on the multi-baseline attitude determination algorithm,the ambiguity resolution and validation method,and the integrity monitoring method are developed to satisfy the high accuracy and reliability requirements of navigational users.The main research work of this paper is organized as follows:(1)The observation error propagation law of GNSS high precision attitude measurement in different differential modes is analyzed.The double difference observation model of GNSS attitude measurement is constructed.It is concluded that incorrect ambiguity resolution and abnormal observation error are the two primary risk sources of attitude measurement.To solve the issue of missing observation in carrier phase difference between multiple antennas,the polynomial interpolation method is studied to realize the time synchronization of observation.The test results show that the carrier phase observation accuracy obtained by the polynomial interpolation method can meet the high-precision attitude determination accuracy and continuity requirements.(2)Two problems in the traditional GNSS multi-baseline attitude determination methods are analyzed.Firstly,the baseline vector and attitude parameter are estimated as two separate processes,and the correlation between the multi-baseline ambiguities and the attitude parameters is disregarded.The attitude estimation model strength is relatively weak.Secondly,the redundant measurements for multi-baseline are not fully utilized,which inevitably leads to the loss of the accuracy and reliability of ambiguity and attitude resolution.Therefore,a multi-baseline attitude determination method is proposed to solve the ambiguity and attitude simultaneously.This method constructs the attitude-ambiguity linear function model based on the measurement domain,maximizes the observation redundancy of attitude determination,and considers the correlation of unknown parameters.In addition,in order to solve the multidimensional ambiguity vector for multi-baseline attitude determination,the partial ambiguity resolution method based on minimum success rate requirement criterion is proposed to enhance the accuracy and reliability of attitude determination.Compared with the traditional position domain-based attitude determination method,the proposed method can effectively improve the accuracy of the attitude determination and achieve the best balance between accuracy and reliability performance by strictly controlling the probabilities of false alarm and missed detection of attitude determination.(3)The traditional unconstrained ambiguity resolution method ignores the prior baseline configuration information,which leads to the suboptimal solution of fixed ambiguity for multi-baseline attitude determination.Thus,the ambiguity resolution and validation methods with multi-baseline constraints are proposed.The proposed method incorporates multiple constraint information into the ambiguity objective function and constraints search space to improve the performance of multi-baseline ambiguity resolution.On this basis,using the prior baseline length information,the ambiguity validation method based on attitude parameters is derived to ensure the reliability of the fixed ambiguity and attitude solution.The effectiveness of the proposed method is validated by experiments of single-frequency and dual-frequency observation data respectively.The results show that the proposed method can effectively improve the ambiguity fixing success rate and the attitude determination accuracy when compared with the unconstrained and single constrained ambiguity resolution methods.In particular,when the single-frequency observation does not have sufficient strength of the model,the improvement is more obvious for the performance of the ambiguity fixed and attitude solution.(4)The key factors of GNSS attitude determination mainly include ambiguity resolution and the observation noise.Since the standalone ambiguity validation method is difficult to guarantee the reliability of attitude solution,an integrity monitoring method in the attitude domain is proposed.The proposed method constructs the complete set and subset detection statistics using multi-baseline observation residuals.It derives the attitude protection level of multi-fault assumption based on the worst protection level principle.Regarding to the absent of attitude alarm limit,the navigation performance parameters required for attitude determination integrity monitoring are derived equivalently.The attitude integrity monitoring alarm limit is obtained to meet the integrity risk and continuity risk requirements simultaneously.The simulation and experiments results show that the proposed integrity monitoring method can monitor the ambiguity fault and the excessive measurement noise and improve the attitude accuracy and reliability,when compared with the ratio test method in the ambiguity domain. |
