| BeiDou Navigation Satellite System(BDS)was independently built by China.Real-time precise positioning service system based on BDS has a great significance for national economy and defense security.The most important factor to realize the high-precision positioning is the precision of real-time satellites orbit and clock.The ultra-rapid predicted orbit is regarded as space datum when we calculate the real-time satellite clock,which determines the precision of satellite clock and also has great influence on the PPP ambiguity resolution.Currently,BDS is still a regional satellite navigation system whose satellite constellations not only contains medium Earth orbits(MEO)but also geostationary Earth orbits(GEO)and inclined geosynchronous orbits(IGSO)whose real-time orbit accuracy is different from each other.At present,few scholars have studied the effect of BDS satellite orbit error on real-time satellite clock error estimation,real-time precise positioning and PPP un-difference ambiguity resolution,which is the main research content in this article.Nowadays,real-time PPP has been widely used in areas such as seismic monitoring,tsunami warning and GNSS meteorology.It is inevitable that the communication is interrupted for a few minutes or even hours.When differential signal is interrupted,it has a great significance to maintain high-precision positioning for a long time.In addition,the common means of wireless communication is unable to keep smooth connection between users and clients in mountainousm area,jungle,desert,earthquake disaster region,sea far from the coast and so on.BDS has a short message communication function and users are not restricted by the communication network and location which realize the high-precision positioning in above areas.The research target of this article is to realize the real-time precision service system based on BDS.Meanwhile,the precision maintenance technolodge of PPP for a long time when differential signal interruptted is studied and the high precision positioning based on the low frequency and low bandwidth of BDS short message is researched.Our main contributions and researches of this article are as follows:1.The influence of BDS ultra-rapid predicted orbit error on the real-time satellite clock error estimation is studied detailly and systematically.The effect of satellites orbit radial error on satellite clock estimation and users positioning is not subject to the distribution and range of tracking station network while satellites orbit tangential error is related closely to those.Because of the large BDS ultra-rapid predicted orbit error,it is impossible to absorb all the orbit error by estimating satellite clock error with wide-area and sparse stations,which would have great significance on users positioning.So it is the determinate factor to realize the real-time precise positioning service system.Based on the actual measured GNSS data from Global tracking network,China regional tracking network and Guangdong CORS,we proved the conclusion above.The experiment results illustrate that under the condiction of BDS ultra-rapid predicted orbits precision,satellites clock error with regional and dense tracking network have the great ability to absorb the tangential orbit error.Even if BDS navigation ephemeris orbits were used and GEO satellites kept,the cm-level high-precision posintiong can achieve.2.The influence of BDS ultra-rapid predicted orbit error on BDS FCB estimation and un-differenced ambiguity resolution is studied detailly and systematically.With Guangdong CORS network GNSS data,the effect of BDS satellites orbit error on the FCB estimation,ub-differenced ambiguity fixed rate and PPP float and fixed solution is studied by using BDS/GPS final precise orbits,ultra-rapid orbits and Broadcast ephemeris orbit,respectively.The experiment results illustrate that although satellites clock error with regional and dense network absorb most of BDS tangential orbit error,the rest error could still influence the PPP un-differenced ambiguity resolution to some extent.As the increase of orbit error,the consistency of BDS/GPS satellite FCBs,the narrow-lane ambiguity fixed rate and PPP float and fixed solution become worse to some extent.Meanwhile,it can realize PPP un-differenced ambiguity resolution even if we used BDS navigation ephemeris orbits.3.In ereas such as earthquake monitoring,tsunami warning and GNSS meteorology and so on,it is common that differential signal interrupt for a few minutes or even hours.Under this condition,we often switch to broadcast ephemeris orbit mode when the positioning accuracy will decrease to meter level.Thus,forecasting real-time satellite clock error received with sliding window is proposed and we can maintain decimeter positioning for at least 3 hours.Meanwhile,for BLOCK IIF satellies,whose prediction model is not clear,it is suggested that the quadratic polynomial with additional periodic term should be adopt.4.The communication mode of real-time positioning service system mainly includes mobile communication network,radio beacon and communications satellites,etc.Under the special environment,these communication ways are vulnerable which will affect the differential data transmission.The difference data communication based on BDS short message is proposed in this paper which can realize the continuous high precision positioning in the scenario above and realize the effective combination of RDSS and RNSS.Based on the BDS short message function,we made the differential signal encoding format and application method,overcomed low frequency data transmission and low bandwidth constraints and solved the high-precision positioning problem to by using BDS short message function.Meanwhile,we verified positioning effect based on BDS short message communication. |
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