Research On Short Multipath Mitigation Method In The Urban Environment

With the research and development of more than 30 years,Global Navigation Satellite System(GNSS)affects the the military and civil fields deeply.Due to the impact of high-rise buildings in the urban environment,the multipath effect is one of the most important error source in GNSS measurement,the multipath effect seriously affects the positioning precision and positioning performance.This thesis focuses on the application of Kalman filter algorithm in the suppression of multipath error,and research on short multipath mitigation method in the urban environment.This thesis built spherical positioning model according to the pseudo range positioning principle,and theoretically analyzed the spherical positioning error model caused by pseudo range residuals showing"sustained deviation" and "vibration" two distribution types,comes a conclusion that the positioning error is also showing same distribution,the height of the positioning error is higher than the horizontal positioning error and verified by the simulation of satellite signal simulator,the simulation results also show that the height of the positioning error is about three times of the horizontal of the positioning error.To improve the height positioning accuracy,this thesis propose a height constrained adaptive Kaman filtering(HCAKF),height constrained model is established for better height estimation in GNSS positioning and based on the fact that vehicle will not change sharply in the height direction.Then,height constrained model is used to constrain the search space for estimating state vector in the AKF,and finally find the optimal value in the search space by using the principle of minimum mean square error(MMSE).In order to verify the multipath rejection ability of the HCAKF algorithm,the simulation tests are carried out under the condition of static open sky and linear motion scene.the simulation results show that the height of the positioning error of HCAKF is almost zero,horizontal positioning error of HCAKF reduced by 25.36%comparing EKF,13.05%comparing AKF,average positioning error of HCAKF reduced by 44.37%comparing EKF,39.86%comparing AKF in static open sky scene.The height of the positioning error of HCAKF reduced by 67.12%comparing EKF,47.63%comparing AKF,average positioning error of HCAKF reduced by 63.50%comparing EKF,35.65%comparing AKF in linear motion scene.In order to compare the performance of subject localization algorithm and similar products on the market,GPS/BD2 dual-mode receiver verification platform is established based on the same signal source.Based on the dual mode receiver verification platform,the multipath mitigation performance of the HCAKF algorithm is tested.The test results show that,the height of the positioning error of HCAKF is almost zero,horizontal positioning error of HCAKF reduced by 48.44%comparing reference module;average positioning error of HCAKF reduced by 53.71%comparing reference module in static short multipath environment.The height of positioning error of HCAKF reduced by 69.24%comparing reference module;average positioning error of HCAKF reduced by 50.32%comparing reference module in urban complex dynamic environment.