Research On GNSS Triple-frequency Ambiguity Resolution Methods For Multi-system

Nowadays,the Global Navigation Satellite System(GNSS)have entered the era of multi-system and multi-frequency,mainly including the GPS system of the United States,the GLONASS system of Russia,the Galileo system of the European Union and the BDS system of China,etc.The navigation,timing and other functions used by global users depend on these systems.The emergence of triple-frequency signals makes it possible to use the linear combination of multi-frequency observations to improve the success rate of ambiguity resolution.Based on the above background,this topic focuses on the key technology in GNSS high-precision positioning,namely GNSS carrier phase ambiguity resolution technology.In this paper,the working principle,development history,service performance and other basic conditions of GNSS were introduced.The time and space benchmarks of multi-system GNSS are introduced,which are divided into time system and coordinate system.The basic types of observations in the observation model,and the mathematical model are deduced in detail,which are divided into functional model and random model.The three types of error sources are introduced in detail.Then,the definitions of the triple-frequency observations of carrier phase in weeks and meters are given,the basic parameter formulas after the combination are derived,and the three types of errors of the combined observations from the original observations are analyzed.The selection scheme of the optimal combination coefficient under different conditions are given.By introducing the geometry-free TCAR single epoch solution algorithm,the steps of fixing the ambiguity step by step are derived,and a TCAR algorithm that takes into account the quality control of the observation value is proposed.The single epoch baseline solution is greatly improved through the four-point optimization strategy.Based on the RTKLIB open source platform,the code implementation and measured data verification experiment have been completed.The performance of the algorithm in an open environment with a short baseline is analyzed by the difference between the solution result and the high-precision coordinate.A multi-epoch baseline solution algorithm with geometric TCAR constraints is proposed,which combines the observation equations of ultra-wide lanes and wide lanes with the original dual-frequency observation equations,the fixed solution of the triple-frequency ambiguity is used as the constraint of the floating solution by combinated the original observation to perform the adjustment calculation.Through short/medium-long baseline experiments,the success rate of fixed ambiguity and the accuracy of coordinate resolution are analyzed.The results show that this improvement improves the algorithm's resolution performance and expands the scope of application of the algorithm.