Research And Software Implementation Of Multi-mode GNSS Baseline Solution Method

With the continuous development and improvement of GPS,GLONASS,BDS and Galileo global four satellite navigation systems,especially the smooth deployment of China's Beidou-3 satellite navigation system,multi-mode GNSS data processing methods and applications have gradually become the field of satellite navigation hot spot.A large number of studies have shown that the comprehensive utilization of multiple GNSS signals can effectively improve the stability and reliability of positioning,especially in areas where satellite signals such as mountains,cities,and canyons are heavily occluded.Therefore,the multi-mode GNSS relative positioning theory and baseline solution are studied.The combination of software development has important and practical value.The main content and results of this article:(1)The basic model of multimode GNSS positioning and error correction.Compare and analyze the time system and coordinate system of GNSS and realize the time and space unification of the four systems.The function model stochastic model of multi-mode fusion is introduced in detail.The joint algorithm of height angle SNR and stochastic model and the method of post-difference estimation based on stochastic model are studied.The measured data show that the method can significantly improve the positioning accuracy,although the average number of iterations Increased by 1.5 times,but implementation complexity is within acceptable limits.(2)Construction of multi-mode GNSS double-difference baseline solution model.The method of constructing the double difference observation of single difference-double difference and reference station-reference star and its inadequacies are analyzed,and compared with the global search method,the experimental data is obtained:under the same data,the reference station-reference star The number of double difference observations obtained is the benchmark.The number of double difference observations obtained by single difference double difference method is only 95.6%of the reference station-reference star,and the number of double difference observations obtained by the global search method is 99.94%of the reference station-reference star.Combined with the availability of epochs,the overall optimality of the global search method is obtained.The ill-posedness of the baseline solution model and its influence on the ambiguity are studied.The estrangement of the model is significantly reduced by introducing the pseudorange observation equation,and the convergence speed of the ambiguity is accelerated.The baseline solution model for short baseline and medium-long baseline is studied.The experimental results show that the positioning accuracy of multi-mode GNSS is higher than that of single system.The positioning accuracy of short-baseline four-system positioning is 27.5%higher than that of single GPS in ENU direction,28.1%,34.0%,the positioning accuracy of the medium and long baseline four system positioning relative to the single GPS in the ENU direction increased by 51.2%,47.8%,35.1%(3)Study on the influencing factors of multi-mode GNSS double-difference baseline solution.There are many factors affecting the accuracy of baseline calculation.In addition to various factors such as error influencing factors and ambiguity resolution,this paper mainly discusses the influence of starting point coordinate precision on baseline solution.GNSS network adjustment is based on coordinate mode and based on The mode selection of the baseline model introduces the impact of the extra long baseline of the IGS station data addition on the baseline solution.Finally,it is concluded that the initial coordinate error has no effect on the baseline solution within 3m,the influence is millimeter on the 3?10m,the centimeter on the 40m,and the reliability is lost when the error is 100m;the IGS is introduced The extra long baseline added by the station has an effect on the baseline solution.When the known point is distributed in the case of A.,the maximum value of the influence value is 5.7 mm,and the average value is between 1.2 and 2.1 mm.The maximum value of the influence value reaches 9.4mm,and the average value is between 3.0 and 5.3mm.The difference is obvious.Therefore,it is necessary to consider the influence of the data of the IGS station on the high-precision baseline solution;compare the two cases of A and B,from the influence In terms of the maximum value and the average value,the difference in the B scheme is significantly different from that in the scheme A.At this time,the influence of the different distribution of the known points on the baseline solution should also be considered(4)Multi-mode GNSS baseline solution software design and development.Based on the theory and algorithm results of this paper,a multi-mode GNSS baseline solving software(goGNSS)is developed based on Matlab.The zero-baseline comparison is used to analyze the positioning performance of pseudo-single point and pseudo-range double difference in six different combination modes.At the same time,the correctness of multi-mode GNSS function model and stochastic model established in this paper is verified.Secondly,short baseline and medium length are used.Baseline data was compared with the baseline calculations of commercial software and GAMIT software.The results show that the resolution of the software is comparable to that of commercial software.The baseline solution vector is in three directions and the baseline solution vector of GAMIT.The mutual difference is less than 1cm to verify the correctness of the software writing..