Research On Network RTK Technology Based On Multi-mode And Multi-frequency GNSS

Fast ambiguity resolution of CORS is the premise and key of to realize network RTK,and it is also a technical difficulty.Ambiguity resolution based on dual-frequency observation requires a relatively long observation time,such as more than ten minutes or even twenty minutes.The emergence of new multi-frequency GNSS constellation and civil signals makes it possible to solve the ambiguity of single epochs on CORS side.Accurate and reliable ambiguity resolution in a single epoch can improve the performance of Network RTK and avoid cycle slips.In this paper,the multi-mode and multi-frequency ambiguity solution method is studied to further improve the fixed efficiency of ambiguity and enhance the accuracy and reliability of Network RTK.In addition,as a supplement to network RTK technology,a time baseline positioning method based on single station observation is proposed for long time precise positioning and navigation applications in remote areas where wireless communication is not available.1.The theory of GNSS linear combination observation and the characteristics of combination observation are studied.The characteristics of extra wide lane and wide lane of GPS,Galileo and Bei Dou systems are analyzed and discussed.According to the combination wavelength,ionospheric amplification coefficient and noise amplification coefficient,the multi frequency optimal linear combination is given.2.The algorithm for extracting the multipath effect and observation noise of pseudorange and carrier phase is derived.According to the experiment,the multipath effect and observation noise of pseudorange and carrier phase are two orders of magnitude higher than those of carrier phase;3.A new single epoch ambiguity resolution method is designed for a small CORS network whose distance between reference stations is about 50 km,which includes three steps: extra wide lane,wide lane and narrow lane.But in the last step,a new difference scheme is proposed,that is,a difference is formed between adjacent satellites of the same GNSS with approximate tropospheric mapping function to reduce and ignore the troposphere error effect on ambiguity solution of narrow lanes.Numerical experiments based on 49 km and 35 km baselines show that the success rate of ambiguity resolution in a single epoch can reach more than 90%;4.In view of the fact that the distance between reference stations is longer,such as about100 km,a new single epoch ambiguity resolution method based on tight combination is designed by making full use of the common L1 / 1575.42 and L5 / 1176.45 signals on GPS,Galileo and beidou-3 systems,including five steps: extra wide lane,wide lane,wide lanes between GNSS systems,a subset of narrow lane and other narrow lanes.The experimental results show that for the 104 km baseline,the success rate is only about 50%,while for the 35 km baseline,the success rate is about 98%;5.A real-time precise relative positioning method based on time baseline is proposed for remote mapping and navigation applications without traditional wireless communication and network RTK.The experimental results show that the performance of GPS / Galileo / Bei Dou combination is the best,which can meet the needs of long-term navigation and positioning.