Research On The Model Of Precise Point Positioning Based On BDS-2/BDS-3 Joint

In June 2020,the successful launch of the last satellite announced the completion of the constellation deployment of BDS-3.Compared with BDS-2,BDS-3 has more frequencies and more satellites.However,some new BDS-3 satellites are still in the testing stage.In addition,BDS-2 will still provide navigation services in the next 10 years,Therefore,it is an important topic to consider the BDS-2/BDS-3 combination in order to improve the PPP positioning performance of the whole Beidou system.In this paper,the following research is carried out around this topic:(1)In view of the existing Bei Dou code bias modeling,each satellite is fitted based on the elevation angle alone,which does not make full use of the similarity between satellites.In this paper,a code bias processing model is proposed,which considers the MP combination correlation between satellites and solves the satellites jointly.In order to improve the fitting accuracy,the regularization method is used in the preprocessing.The single frequency PPP experiment shows that the positioning accuracy can be greatly improved by using the proposed correction model,especially in the U direction.(2)In order to verify whether the BDS-2/BDS-3 joint dual frequency PPP should distinguish the two generations of Beidou system,the PPP function model considering the inter system deviation(ISB)parameter is derived.Based on this model,the characteristics of ISB are analyzed.The results show that the ISB can be approximately constant in one day,and the variation amplitude is less than 2ns.In addition,the same type of receivers show similar time-varying characteristics.The variation trend of ISB calculated by using the precision products of the two analysis centers is the same,and the difference between them is approximately constant.Then,the PPP positioning performance under the estimation and non estimation ISB strategies is compared through experiments,and the results show that there is no obvious difference between the two strategies.Then,by comparing the observed residual,ambiguity and ionospheric delay parameters under the two processing strategies,the influence mechanism of ISB on positioning is explained from the perspective of parameter estimation.(3)For BDS triple-frequency cycle-slip detection,three detection quantities are constructed according to two code-phase combinations and one geometric-free phase combination.According to the requirements of weakening ionosphere influence,the optimal combination coefficients of BDS-2 B1I/B3I/B2 I and BDS-3 B1I/B3I/B1C(or B1I/B3I/B1C)are obtained.The experimental results show that the proposed method can detect the cycle jumps in any size of BDS-2/BDS-3 satellite.(4)Although BDS-2 and BDS-3 contain multi-frequency signals,there are only two common frequencies,B1I/B3 I,which makes it difficult to build a joint triple frequency PPP model.Based on the BDS-2 triple frequency PPP model,the BDS-2/BDS-3 joint triple frequency PPP mathematical model with B1C/B2 a new signal is derived.(5)Through experiments,the positioning errors of single BDS-2,single BDS-3and BDS-2/BDS-3 joint triple frequency PPP are compared.The results show that the positioning performance of BDS-2/BDS-3 joint strategy is better than the former two.At the same time,the PPP positioning performance of five models is compared under BDS-2/BDS-3 joint strategy.The experimental results show that the positioning performance of trip-frequency positioning mode is better than that of dual frequency positioning mode,but the improvement ability is limited.