Research On BDS/GPS Baseline Network Processing Method And Its Software Development

Global navigation satellite systems(GNSS)such as GPS are continuously providing stable and reliable positioning,navigation and timing services.At present,China's Beidou Satellite Navigation System(BDS)also has the ability to serve positioning,navigation,and timing in the Asia Pacific region.Under the condition of simultaneous observation of multi-navigation satellite systems,how to achieve unified modelling of multi-mode GNSS observation data from continuous reference station networks and complete fusion of baseline network adjustments has become a hot topic in current research.This paper analyzes the theory of static relative positioning and various errors,and explains the main contents of the baseline solution such as cycle slip detection and fixed ambiguity.Combined with the characteristics of BDS satellites in China,a multi-system single baseline solution stochastic model was established.An independent baseline optimization plan was designed,a random model of baseline network adjustment was established,a baseline network adjustment model with additional constraint information was improved and constructed,a baseline network adjustment software was written,and two provincial CORS networks were developed.Differential data processing experiments verify the performance of the algorithm model and software.The main research content is as follows:1.The stochastic model of single baseline solution was studied in depth and the optimal weight ratio relationship of multimodal GNSS observation data was deduced.Using the observed data quality factors and satellite elevation angles,a stochastic model of the baseline solution was established.Taking into account the inverse relationship between the observed noise level and the weight,the consistent matching of the weights between the different navigation satellite systems and the navigation satellites of the same system is achieved.2.For the constraint adjustment requirement of the baseline network solution,an independent baseline optimization scheme was designed and implemented.The Kruskal algorithm was introduced into the independent baseline selection.For the Kruskal algorithm's applicability to independent baseline selection,the algorithm was optimized and improved.The improved Kruskal algorithm was applied to the CORS reference station network in Zhejiang and Hebei,and compared with the traditional adjacent shortest edge scheme.3.The baseline network adjustment model was improved,a random model of baseline network adjustment,and an additional constraint model for starting points were designed,which ensured the free baseline setting and accuracy matching adjustment.Through the error of the posterior unit weights and the covariance matrix of the baseline solution results,the synchronization loop covariance matrix is obtained.To establish the virtual observation equation for the coordinates of the starting point,add the constraint of the starting precision information,and establish an additional constraint model.The free setting of the starting reference is achieved,and the initial accuracy of the starting point is adjusted,which improves the adaptability of the baseline network adjustment.4.A baseline network adjustment software was written.The software has a single baseline solution,independent baseline networking,baseline random model generation,three-dimensional unconstrained adjustment,three-dimensional constraint adjustment and other functions to provide the station precise coordinates,the baseline length,baseline RMS value,PDOP value and other results Can complete single point positioning,multiple single baseline solution,independent baseline selection and network adjustment and other tasks.5.Baseline data processing experiments were conducted to verify the relevant models and software.The CORS data of Zhejiang,Hebei and other provinces were processed successively,and the data of BDS,GPS and BDS/GPS combined observation stations were solved.The accuracy of the baseline network adjustment software was verified,and the variations of the accuracy under different observation periods,baseline lengths,and navigation system conditions were explored.The results show that most of the CORS stations in China can use this software to solve the network adjustment.After the two systems are integrated,the plane accuracy of the solution is better than 2cm,and the elevation accuracy is better than 3cm.