Study On The Theory And Method In Integrated Navigation Of Multi-constellation GNSS/INS

With the rapid development of BDS along with the advancement of both GPS and GLONASS in the context of modernization capability.Capacity and reliability of positioning will be greatly improved by a multi-constellation fusion approach.However,satellite signals are frequently blocked or even lose lock in complex dynamic environment,where the effectiveness of positioning cannot be guaranteed.INS is not affected by external environment and can obtain high-accuracy pose parameters in short time.The integrated navigation technology of GNSS/INS can obtain continuous,reliable and high-accuracy navigation information,and it has been widely applied in military and civilian fields.Based on GNSS positioning algorithm,the integrated navigation algorithm of GNSS/INS is further studied in this dissertation,which includes the positioning model of multi-constellation GNSS,ambiguity fixing of multi-constellation GNSS,the filtering model of GNSS/INS integrated navigation,smoothing model of GNSS/INS integrated navigation,data processing method of GNSS/INS integrated navigation in data gaps,and INS aided model.The main research contents and contributions are as follows,(1)The fixed performance of ambiguity is affected by the accuracy of observations for dynamic positioning.In order to fix the ambiguity fast and reliably,a step-by-step and stepwise fixed strategy of ambiguity is proposed.In order to improve the fixed performance of wide-lane ambiguities,these wide-lane ambiguities are divided into primary ambiguity group and secondary ambiguity group based on signal-to-ratio.In order to improve the fixed efficiency of ambiguity,the primary ambiguity group is divided into different levels in a(4,1,1…,1)pattern based on signal-to-ratio.Based on the improved guidance algorithm and LAMBDA algorithm,the different levels' ambiguities of primary ambiguity group and secondary ambiguity group are resolved successively.When the wide-lane ambiguities are accurately fixed,the base ambiguities can be fixed by the constraint of fixed wide-lane ambiguities.These experiments showed that the success rate of ambiguity fixing is 100%,99.82%,and 99.52% for the multi-constellation data of static short-baseline,dynamic short-baseline and dynamic medium-short baseline respectively,and the accuracy of GNSS positioning based on this method can achieve centimeter level.(2)The filtering algorithm of GNSS/INS integrated navigation takes some time to converge to the desired accuracy,and INS is used alone for a long time because of satellite unlock in dynamic environment.In order to meet the requirement of high-accuracy users,both RTSS smoothing and TFS smoothing algorithms are researched.These experiments showed that these smoothing algorithms can effectively improve the accuracy of parameters for forward and backward filter algorithm,the performance of RTSS smoothing and TFS smoothing is basically the same and the further smoothing performance is not obvious by the smoothing method based on RTSS smoothing and TFS smoothing.(3)It is inevitable to encounter data gaps caused by short-term hardware failure in engineering data collection.In order to improve the data availability,a combined AR model based on forward prediction and backward prediction is used to forecast the INS data where a data gap occurs.In order to enhance the accuracy of filter parameters and to effectively avoid the parameters of data normal period affected by the parameters of data gaps,a piecewise RTSS smoothing is used.These experiments showed that this proposed method can obtain more accurate and reliable navigation parameters than these of commercial software to provide relatively accurate geographic reference for mobile mapping system.(4)The performance of single-frequency and single-epoch ambiguity fixing is affected by the accuracy of GNSS observations that is easily disturbed by the external environment for the dynamic positioning.In order to effectively improve the performance of ambiguity fixing,the partial ambiguity based on INS aided is researched.The high-accuracy prior information predicted by INS can enhance the intensity of variance matrix for ambiguity and improve the accuracy of floating resolution of ambiguity.The partial ambiguity fixing based on satellite elevation angle and the posteriori residual can reduce the influence of low-accuracy observations,and improve the performance of ambiguity fixing for the blocked environment.The experiment showed that this method can effectively improve the success rate of ambiguity fixing for the blocked environment.(5)Aiming at the problem that the performance of cycle-slip detection for single-frequency GNSS signal is easily affected by low-accuracy observations,an INS aided method based on double difference between stations and epochs for cycle-slip detection and repair is proposed.The mean square error of unit weight calculated by equation of cycle-slip detection is used to detect cycle slip initially,avoiding the cycle-slip detection for each epoch and each satellite.The intensity of cycle-slip detection equation can be effectively enhanced based on the short-term and high-accuracy position information predicted by INS.These experiments showed that the cycle slip can be detected and repaired based on the INS aided method,the cycle slip can still be detected and repaired when the number of satellites is little and the performance of cycle-slip detection will not be affected by the duration of outage when the satellites are enough.