Research On Key Technologies Of GNSS Real-Time Precise Positioning Based On Multi-Antenna With A Receiver

In the field of GNSS deformation monitoring,the conventional receivers are usually used for precise relative positioning,which can obtain the high-precision position coordinates of the measuring station in real time.However,with the increase in the number of monitoring points,a large number of GNSS receiver equipment is needed,resulting in an increase in the cost of the monitoring system.The emergence of multi-antenna with a receiver solves the problem of high cost of high-precision GNSS receiver,enabling a receiver to connect multiple antennas and ensuring the integrity and reliability of signals.The cost of the whole monitoring system will be significantly reduced without affecting the accuracy of the monitoring system.The multi-antenna technology has been widely used in dam monitoring,landslide monitoring,bridge monitoring and other deformation monitoring fields.However,there are still some problems in precise relative positioning with multi-antenna with a receiver.When the GNSS multi-antenna switch(GMAS)switches from one antenna to the next antenna,the interruption of continuous phase observation will generate frequent cycle slips,leading to the re-initialization of ambiguity parameters and the reduction of data utilization.In addition,the multi-GNSS positioning usually adopts the loose combining model,which has low positioning accuracy and reliability in complex environments such as areas with severe satellites and poor observation quality.According to the above requirements and problems,this paper study the key technical problems of precision positioning based on multi-antenna system,including real-time cycle slip detection and repairing,GNSS DISB estimation and tight combining positioning.This paper put forward the corresponding algorithm model with innovation,in consideration of the shortcomings of the existing models,to solve problems in practical application.This paper's main work and conclusions are as follows:(1)Studying and analyzing the commonly used GNSS precise positioning model,including zero-difference model,single difference between stations,single difference between satellites,single difference between epoch and double difference model,systematically comb the meaning and characteristics of various parameters,then introduce the common error sources in positioning,and derive the commonly used GNSS double-frequency linear combination of observations.The basic methods and strategies of parameter estimation are described.The least square estimation method and Kalman filter algorithm are studied respectively.The ambiguity fixing and checking are studied in depth,which lays a foundation for the follow-up research.(2)While the cycle slips will frequently occur as the GMAS switches from one antenna to the next antenna.In this contribution,a new real-time cycle slip detecting and repairing model was put forward and a large number of experimental data show that the feasibility of the algorithm,including the short baseline and medium baseline observation data added simulated cycle slips.The results show that for the short baseline,adopt single system or multi-GNSS can successfully fixed wide lane cycle slip value,and larger data gap has little effect on fixing rate.For medium baselines,the fixing rate of wide lane cycle slips can be significantly improved by using multiple systems,and the larger data gap has a greater impact on the fixing approach,and the data gap or interval should be less than 30 s.Then,the influence of real-time positioning with and without cycle slip and repair was studied by using the short baseline observation data collected by multi-antenna system.The results show that the algorithm can achieve the instantaneous re-initialization of ambiguities and increased the availability of observation data,which can realize the purpose of obtaining highprecision real-time positioning solutions using multi-antenna system.(3)In order to improve the performance of positioning in complicated environment,such as the satellites are severely blocked and poor satellite observation quality,the method to estimate the DISB was put forward.The characteristic of ISCB and ISPB are studied,and then process data with tight combining method.This paper compares and analyzes the effect of tight combining on the improvement of positioning accuracy compared with traditional double difference in complicated environment.The results show that the ISCB and ISPB values on two frequencies of the same type of receivers are close to 0,while the ISCB and ISPB values on two frequencies of different types of receivers are generally not equal to 0,and their absolute values are generally greater than the ISCB and ISPB of the same type of receivers.The ISCB and ISPB values of GLONASS-GPS may change periodically,and the reason may be related to the linear correlation between the rate of change of IFB and ISB,which requires further research.In general,the ISCB and ISPB values on the second frequency are more stable than those on the first frequency.Compared with GLONASS G1-GPS L1 and BDS B1-GPS L1,ISCB and ISPB value of Galileo E1-GPS L1 are more stable.For multi-antenna system,the switching process of the antenna has little effect on the ISCB and ISPB values.For the multi-antenna system,although the receiver types corresponding to the three antennas are the same,their ISCB and ISPB values may be different and need to be estimated respectively.After correcting DISB parameters,the improvement effect of tight combining positioning on positioning accuracy in complicated environment is studied compared with traditional double difference.On the basis of existing experiments,the blocking environment was simulated by setting the size of cut-off angle of satellites in each time period.In the tight combining positioning,the research results show that: in the occlusion environment,with the decrease of the number of satellites,the positioning accuracy of the compact combination positioning in the E direction is significantly improved compared with the traditional double difference.When the cut-off angle of the satellite is set to 45°,the positioning accuracy is improved by 79.1% in the E direction.The positioning accuracy of multi-antenna system has been improved to some extent.