Position Algorithm Of Multi-constellation GNSS Single-frequency Real Time Inter-system Mixed Double Difference

With the construction,improvement and modernization of global navigation satellite system,GNSS is developing towards the direction of multi-system compatibility.Multi-GNSS combined positioning makes full use of the observations of different satellite system to improve the availability,reliability and accuracy of navigation and positioning,which is an important development trend of GNSS.MultiGNSS inter-system mixed double difference combination positioning not only takes into account the intra-system double difference,but also the inter-system double difference,further enhancing the compatibility of GNSS,and improving the navigation and positioning performance of GNSS in the complex environment.Considering that most GNSS users currently use single-frequency GNSS receivers,stable and reliable multi-system single-frequency high-precision positioning algorithm has become an urgent demand in the consumer market.This thesis focuses on the positioning algorithm of multi-GNSS single-frequency real-time inter-system mixed double difference,studies the mathematical model and the key algorithms,discusses the IFB/DISB estimation algorithms and its stability,analyses the inter-system mixed double difference combination positioning performance.The main research contents and results of this thesis are summarized as follows:1.The mathematical model of inter-system mixed double difference combination positioning is derived in detail,and the intra-system classical double difference function model of multi-GNSS,the inter-system mixed double difference function model of multi-GNSS with estimated IFB/DISB and fixed IFB/DISB,as well as their stochastic models are discussed.2.We propose a position variation calculation algorithm suitable for multi-system single-frequency inter-system mixed double difference model.Based on the double difference model between stations and between epochs,the algorithm uses correlation analysis to accurately detect the cycle slip in single-frequency observations,and then calculates the reliable position variation between epochs.The algorithm does not need multi-frequency observations and does not have inter-satellite difference.3.The step by step fixed IFB algorithm is improved by introducing geometric distance term,which enhances the stability of the algorithm and expands the application range of the algorithm.The validity and reliability of the improved algorithm are verified by the zero/short baseline experiments.The experiments show that the improved algorithm is basically consistent with the IFB of the zero/short baseline estimated by the particle filter algorithm,and the improved algorithm is simpler to implement and more efficient than the particle filter algorithm.4.We study the algorithm model of parameter renormalization to estimate the fractional part of carrier phase DISB in the same frequency and different frequency inter-system mixed double difference,and theoretically analyse the influence of the integer part of carrier phase DISB in inter-system mixed double difference with different frequency on the positioning result.The comparison between parameter renormalization algorithm and particle filter algorithm shows that the estimation results of the two algorithms are basically the same,with the maximum difference of about 0.05 cycle,but the parameter renormalization algorithm has higher computational efficiency and better applicability.5.We analyse the long-term stability and restart stability of IFB/DISB by zero/short baseline experiment.The results show that IFB/DISB is stable for a long time,IFB and pseudo-range DISB are not affected by the receiver restart,but carrier phase DISB contains the receiver relative initial phase bias,which may change after the receiver restart,as to whether the change is related to the receiver type.6.We implement the multi-GNSS real-time inter-system mixed double difference combination positioning algorithm,and analyse the performance of inter-system mixed double difference algorithm by static/dynamic experimental data of different receiver types.Experimental results show that carrier phase DISB of GPS L1/Galieo E1 with overlapping frequencies is generally zero in baselines of the same receiver type,and may or may not be zero in baselines of different receiver types.However,for the carrier phase DISB of GPS L1/GLONASS L1 and GPS L1/BDS B1 with different frequencies,the baselines of the same receiver type or different receiver types may not be zero.In addition,experimental results show that the inter-system mixed double difference with fixed IFB/DISB compared with the intra-system classical double difference can improve the float positioning accuracy and the ambiguity fixed rate,especially when the number of observation satellite is small and the satellite geometry is poor,the promotion effect is remarkable,float accuracy and ambiguity fixed rate can be improved by 10% ~ 30%.