Research On BDS/GNSS Multi-reference Multimode Multi-frequency Positioning Technology

Single reference station differential positioning technology is based on the assumption of the fractional observation error with spatial correlation,however the operating distance of the technology is limited.In order to achieve a larger range of precision positioning,it is necessary to conduct research on multi-reference station differential positioning technology.At present,the research of multi-reference station differential positioning technology is mainly focused on single system research.There are many problems with this technology,such as fewer available satellites in the network of reference stations and the decline in user positioning accuracy when the satellite signals can be seriously blocked under the urban or canyon environment.Therefore,the key to promoting the application of multi-reference station differential positioning technology in the field of high-precision navigation and positioning services is to improve the performance of multi-reference station differential positioning.Aiming at improving the positioning performance and providing the theoretical basis in the application of high precision navigation and positioning services for multi-reference station differential positioning technology,we research the ambiguity resolution between reference stations,error correction number generation,virtual observation value generation,BDS/GNSS combined positioning technology,etc.The main research contents of this thesis are as follows:1.Since the ambiguity resolution method between reference stations with ionosphericfree combination takes a long time,it cannot meet the real-time positioning requirements.Therefore,we study the ambiguity resolution method between reference stations based on M-W combination.This method uses M-W combination to resolve ambiguity of wide lanes,and then uses single epoch data to calculate the ambiguity between reference stations.The experimental results show that,the ambiguity resolution method between reference stations based on M-W combination has better ambiguity fixation rate and positioning accuracy than the ionospheric-free combination.2.Considering the importance of error correction numbers to positioning accuracy,this paper studies the main error sources,which affect the positioning accuracy.Combining the multi-reference station positioning mathematical model,a new error vector expression form is constructed,and this expression includes the error of related to the ionosphere and the error of irrelevant to the ionosphere.Using the error correction vector to obtain the generated model of error correction on the master reference station and the virtual reference station.Considering that the accuracy of the error correction number model will directly affect the user station positioning accuracy,the effects of three different the generated model of error correction currently used on the positioning accuracy are studied and analyzed.The experimental results show that the error correction number generated by the linear combination method is the most accurate for the multi-reference station positioning proposed in this paper.3.Proposes a virtual observation generation method based on the deviation of the master station.After the error correction is generated,a virtual observation value including the deviation of the master station is generated using the double difference observation equation betweent the master station and the virtual reference station.The network of reference stations with different baseline lengths is used to locate user stations.The experimental results show that high-precision positioning of multi-reference stations with medium and long baselines can be achieved in this method.4.The thesis proposes the BDS/GNSS combined positioning technology for the situation that there are few available satellites due to the distance between the reference station networks and the satellite signals can be seriously blocked.This method improves the redundancy of the observation equation and improves the positioning performance in complex environments.We takes BDS/GPS as the research object,and builds a BDS/GPS tight combination observation model based on the differences between BDS and GPS systems.The GPS satellite was selected as the reference satellite,and the stability of the ISB was used to eliminate the impact on the tight combined positioning,which eventually increased the redundancy of the observation equations and improved the positioning accuracy.The experiment simulates an environment with few satellites by increasing the satellite cutoff altitude angle.Experimental results show that tight combination has higher positioning accuracy than single GPS system,single BDS system,and traditional BDS/GPS combination.