Study On Method Of Mitigating GPS Multi-path Error

Multipath error is closely related to the observation environments,it characterized as a space-time environment effect,and it's difficult to eliminate it through building accurate mathematical model.Moreover,the multipath error has no spatial correlation at both ends of the baseline,we can't eliminate it through using the differential technology.By a large number of scholar's research,the long delay multipath error is greatly weakened,but the remnant of short delay multipath error is still one of the main error sources in GPS high accuracy positioning.Aiming at these problems,this paper select the multipath error in carrier phase measurement as the research object,study the multipath error using Kalman filter and particle filter,discuss the new technology and method for mitigating multipath error in GPS positioning.The main research contents and train of thought as follows:(1)Multipath error analysis for carrier phase difference model.According to the GPS carrier phase observation equation,establish the carrier phase double difference observation model,and study the residual error in the model.The results show that the satellite clock error and the receiver clock error are eliminated in the double difference model,and the troposphere,ionosphere delay and ephemeris error which has spatial correlation is greatly weakened,the residual items mainly include multipath error and observation noise.(2)Research on multipath error characteristics.According to the multipath error generation mechanism,the multipath error function model of single and multiple reflection signals is studied deeply,and the temporal and spatial environmental effects,generation types,influence amplitude,frequency characteristics and daily repetition characteristics of multipath error are analyzed in detail.(3)Research on multipath error estimation based on Kalman filter.According to the time-varying characteristic of multipath error between generators,the multipath error state space model is established by using multipath error size,rate of change and acceleration as state variables.Estimate the multipath error from the coordinate residual sequence of the double difference fixed solution using standard Kalman filter.Since the multipath error is correlated between the epochs,the process noise is also correlated between the epochs.The standard Kalman filter assumes that the process noise and the observed noise are uncorrelated Gaussian white noise,therefore,it is difficult to ensure its estimate accuracy when using the standard Kalman filter.Based on the theory of colored noise Kalman filter,this paper studied the multipath error estimation method which process noise is colored noise.(4)Research on multipath error estimation based on particle filter.Considering the particle filter is not limited to the system observation noise and process noise,it is widely used in non-Gaussian and nonlinear system state estimation.Based on the multipath error state space model,estimate the multipath error from the coordinate residual sequence of the double difference fixed solution using particle filter.In this paper,we use the resampling algorithm to study the multipath error estimation method based on resampling particle filter because of the problem of weight degradation and effective sample depletion in the process of particle filtering.(5)Multipath error correction.Estimate the multipath error from the coordinate residual sequence of the first day from the monitoring station by using the above-mentioned multipath error estimation method,and according to the daily repetition characteristics of multipath error,correcting the coordinate sequence of the subsequent days,thereby mitigating the effects of multipath errors.