The Research On Technologies Of Multi-GNSS Tight Combination Precision Positioning

With the further improvement and modernization of GPS,BDS,Galileo and GLONASS,satellite navigation and positioning technology has entered a new era of multi-frequency and multi-system.Combining multiple GNSS systems for integration positioning can significantly increase the number of visual satellites,improve the spatial geometry of satellites,and improve the accuracy and reliability of positioning,especially in areas where satellite signal reception is difficult.Therefore,how to make full use of multi-GNSS system resources to achieve multi-system integration positioning processing,and further improve the positioning accuracy and reliability is the current research hotspot in the field of GNSS.Relative positioning is a classical positioning mode for high precision positioning,and the key step of the positioning mode is to fix the double-difference ambiguity.In multi-system GNSS relative positioning,two kinds of double-difference ambiguities can be formed: intra-system double-difference ambiguity and inter-system double-difference ambiguity.Due to the deviation between different GNSS systems and the possible inconsistency of signal frequencies between different systems,the ambiguity of double-difference between systems is generally difficult to fix.Therefore,in the current relative positioning,only the ambiguity of double difference in the system is fixed,that is,the multi-system loose combination positioning.However,the loose combination positioning can not make full use of satellite resources,and it is difficult to locate with high accuracy and reliability under the harsh observation environment and the small number of observation satellites in a single GNSS system.For this reason,this paper focuses on the characteristics of phase deviation between different GNSS systems at the receiver,proposes corresponding estimation and correction methods,breaks through the key techniques of fixed double-difference ambiguity between different GNSS systems,and realizes multi-system GNSS tight combination precision positioning.Improve the accuracy and reliability of positioning in complex environments.The main work and research contents of this paper include:(1)The basic theory and method of GNSS relative positioning are systematically studied.The similarities and differences of the positioning models based on zero-difference and double-difference modes are compared and analyzed.The estimation and processing methods of parameters in different positioning models under different baseline lengths are given.(2)An estimation method of inter-system phase bias(ISPB)based on zero-difference mode is proposed.Firstly,the single-difference ambiguity between stations is fixed,and then the ISPB value is determined based on the receiver phase fractional deviation(RUPD)of different GNSS systems.This method can not only estimate the phase deviation of the same frequency signals between different GNSS systems,but also estimate the phase deviation of different frequency signals between different GNSS systems.The experimental results show that the ISPB obtained by this method is consistent with the existing research results,which proves the effectiveness of this method.(3)The stability of ISPB at receiver is analyzed systematically.Through the experimental analysis of more than 20 baseline GPS and Galileo data with the length of 0-2000 km,the results show that for the same frequency signal GPS L1 and Galileo E1,the ISPB between the same receiver types is almost zero and can be neglected,while the ISPB between different receivers is not zero.The average STD of ISPB in 14 days is only 0.003 weeks,which shows that the ISPB has good stability.However,the ISPB of L1/L2 and E1/E5 a signals with dual-frequency non-ionospheric combination observation values is not zero regardless of the type of receiver.The average STD of ISPB in 31-day wide lane is only 0.03 weeks,and that of ISPB in narrow lane is only 0.05 weeks,which shows that the ISPB has good stability.However,it is also found that ISPB may jump when the ambiguity arc is interrupted and hardware or software upgrades occur.(4)The multi-system GNSS tight combination precision relative positioning considering ISPB is realized,and the positioning effect of the method in complex environment is analyzed.The experimental results show that the tight combined positioning method can effectively improve the accuracy and reliability of positioning.With the increase of the height angle,the lifting effect is more obvious.When the cutoff height angle is set to 25 degrees,the tight combined precision positioning method can achieve the accuracy in E.The three directions of N and U were increased from 3.2cm,1.2cm,and 2.8cm to 0.3cm,0.3cm,and 2.2cm,respectively,and the increase rates were 90.6%,75.0%,and 21.4%,respectively.When the cutoff height angle is greater than 35 degrees,the loose combination ambiguity is difficult to fix,and the tight combined plane and elevation positioning accuracy can still be better than 2cm and 5cm respectively.Even when only 4 GPS and 2?4 Galileo satellites are observed,the positioning accuracy of the tight combination can be better than 3cm and 5cm in the horizontal and elevation directions,respectively.