| With the rapid operation of BDS,the development of Galileo,GPS and GLONASS,the Global Navigation Satellite System(GNSS)has been applied to various fields.GNSS is susceptible to various observation errors in practical applications.Usually,satellite related error,receiver related error,ionosphere and troposphere error can been eliminated by doubledifference methods between inter-station or the inter-satelalite.However,multipath error's randomness and complexity which depends on the surroundings of receivers' antennae and the geometric characteristics of reflection.The conventional difference method cannot effectively mitigate it.In addition,it is difficult to correct it with a universal prior model.This paper analyzes the multipath error extraction and calibration method for the observation domain research by analyzing the generation and characteristics of the multipath error.Based on these,in view of the different application scenarios,three function models and random models oriented to the observation domain are proposed to mitigate multipath errors and make a comprehensive evaluation of their positioning performance.The main work and contributions are listed as follows:(1)Analyzed the generation and characteristics of multipath errors,and compared the extraction methods of double-difference,single-difference,and non-difference methods.In addition,a multipath error based on normalized C/N0 calibration method is proposed.The double-difference model needs to select a reference satellite that is consistent with the model in the application process,while the single-difference model can avoid this problem and is suitable for the establishment of multipath maps.Non-difference multipath error extraction method is mainly used to extract code multipath,and is suitable for the correction model established by using multipath time repeatability.The mothod performs different calibration methods for different types of satellites.For GPS and BDS IGSO&MEO,the relationship between normalized C/N0 and elevation can be considered to establish a calibration fitting function.However,for BDS GEO,The Mean and STD of the C/N0 of each satellite should be calibrated.(2)For short-baseline code differential positioning in complex environments,a refined random model based on single-frequency normalized C/N0 is proposed,and the consistency check method is used to further mitigate multipath errors on code differential positioning and improve positioning accuracy.The experimental results show that the positioning accuracy of the refined random model is better than the conventional equal-weight model and the elevation model,and the positioning accuracy is improved by 7.1%-33.3% in the 3D direction.In addition,the positioning accuracy increased by 12.4%-19.5% after adding the consistency check method.two experiments have significant improvement in the U direction,which indicates that the multipath error has a greater impact on the U direction of the positioning result.The model has significant improvement in the epochs with large positioning errors or even peaks.(3)For medium baseline RTK solution,a medium-baseline RTK positioning method considering code multipath is proposed,and the wide-lane(WL)solution model for code multipath correction and the ionospheric-free narrow-lane(IF-L1)model are established.The experiment results of repeatability analysis show that there is a high degree of cross-correlation between the two cycles of low-frequency multipath.The positioning experiment results show that the low-frequency multipath correction model can reduce the RMS value of the MW combined sequence.After applying the multipath correction model established in the previous cycle,the current cycle of single BDS,GPS+BDS WL and IF-L1 positioning can be fast convergence,and the positioning accuracy has been improved in the pre-convergence stage and the overall stage,the improvement ratio is about 13%-48%.Moreover,the accuracy is basically unchanged after convergence.In addition,the positioning accuracy of GPS+BDS WL and IFL1 are better than single BDS,and the improvement ratio is about 41%-71%.The positioning accuracy is close to the decimeter level before convergence.After the WL positioning solution converges,the single BDS can reach within 8cm,and the GPS+BDS can reach within 5cm;after the IF-L1 positioning solution converges,the single BDS can reach within 4.5cm,GPS+BDS can reach within 2.5cm.(4)For the calculation of deformation monitoring carrier solution,a multi-resolution and multipath spatial map correction method based on single-difference filtering is proposed,and it is actually applied to bridge deformation monitoring.The actual measurement results show that the maps established on each day have strong correlation,and the average value of the ambiguity checking Ratio after multipath correction is increased by about 2 times,and the average value of the ambiguity fixation success rate is more than 99%.At the same time,the improvement effect of carrier residual value is 10%-40%,and the best grid resolution is0.2°×0.2°×1°.On the basis of algorithm research,a real-time monitoring software for bridge deformation based on this multipath suppression method is developed to solve the problem that traditional detection technology cannot continuously measure for a long time and is easily restricted by the observation environment.Provide basis and guidance for management decision-making.The actual operation results show that the high-resolution multipath spatial map based on single-difference filtering can effectively correct the multipath errors experienced by the receiver in the bridge monitoring environment. |
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