The Study Of BDS Data Preprocessing And Optimization Of Observation Model Of Relative Positioning

Chinese BeiDou navigation satellite system(BDS)is different from GPS,GLONASS and Galileo,BDS is the first satellite navigation system combined by mixed constellation and is able to transmit triple frequency data.Due to the special constellation and signal structure of BDS,the error characteristic of the observation data is different from other navigation systems.So the data processing method of other navigation systems may not be perfectly suitable for BDS.This paper focuses on data processing technology of BDS relative positioning.The main work and achievements of this paper are summarized as follows:(1)This paper proposes a method which uses modified MW combination and ionospheric combination to detect cycle slips.The MW combination is easy to be affected by multipath error,when using the MW combination to detect cycle slips,the occurrence of fake cycle slip is frequent.Based on the time correlation of multipath error,this paper proposed a method to filter the multipath of MW combination by Kalman Filter.This paper uses the modified MW combination and ionospheric combination to detect and repair cycle slips,and a group of data is used to validate the efficiency of the method,the method is used on different satellites and under different observe intervals.The result has shown that when using the traditional method and the interval is 10 s,fake cycle slips will occur.However,the modified method is able to detect all kinds of cycle slips under the interval of 15 s,and even when the interval is 30 s,the modified method is still applicable to GEO satellite.(2)This paper takes research on the choose of reference satellite.The observation quality of the reference satellite should be the best.For GPS,the bigger the elevation angle of a satellite,the better the observation quality.However,BDS is combined of different constellation,the elevation angle can't be the only index of the observation quality,this paper analysis the observation quality of different constellation and proposes 4 optional method to choose reference satellite.At last,3 groups of data is used to validate the efficiency of the 4 methods,the results are compared to show which method is the optimal one.The result shows that under observation environment of the data groups,there is not obvious different between the 4 methods.(3)this paper studies the ratio of pseudorange and carrier phase observation.Commonly the ratio is set 100,but in reality,the ratio is relevant to the receiver type and observation environment.This paper uses a method to evaluate the variance of the observation and calculate the accurate ratio.Then the ratio is applied to the elevation angle model to weight the different observations.Three groups of data is used to validate the efficiency of the method.The result has shown that,under data group A,the ambiguity fix rate is uplifted from 11.2% to 22.5%,under data group B,the ambiguity fix rate is uplifted from 48.96% to 82% and under data group C,the ambiguity fix rate is uplifted from 53.4% to 58.4%.