Research On Key Problems Of Single Frequency GPS Precise Point Positioning

As a kind of high precision single point positioning technology,precise point positioning only one receiver observation,combined with the precise satellite ephemeris and clock error file downloaded from the official website of IGS,using pseudo range observation data in solution and carrier phase observations,so as to obtain the receiver in the earth coordinate system in precise coordinates sit the calculation results,the accuracy can reach centimeter level.Among them,the type of observation value received by the receiver,precise point positioning can be divided into single and dual frequency.Because SPPP can only use single frequency observation data,so in the observation equation,ionospheric correction and data processing with dual frequency precise point positioning is different,these are of single frequency precise point positioning technology is the key of this paper focuses.Based on the above problems,the main work of this paper is as follows:(1)introduced the single frequency precise point positioning principle and research status at home and abroad,including the combination method establishment,observation observation equation and IGS product information,all kinds of error sources and in-depth study of the single frequency precise point positioning needs to be considered,and detailed method to eliminate all kinds of error sources,weaken and the corresponding formula.(2)the impact of ionospheric delay has the greatest impact on the single frequency,this paper introduces the general situation,effects of ionosphere ionosphere on GPS signal propagation,and the commonly used ionospheric processing methods,including Klobuchar model,grid ionospheric model,ionospheric tomography(CIT).And then introduces the TWIM model,and the experimental results proved that the single frequency PPP advantages,precision is greatly improved compared with the Klobuchar model;finally the experimental analysis of effects of different ionospheric products on the static single frequency precise point positioning and draw the conclusion that all stations use different ionospheric products solution the error value is only in the mm level.(3)with the help of the precise ephemeris and clock error data of IGS,the convergence of single frequency precise point positioning is studied,and a new scheme is proposed to improve the convergence speed of single frequency precise point positioning.On the basis of the traditional height angle weighting method,the initial weights with different pseudo distance and phase observations are given,and then the robust estimation method is used to estimate the parameters.Compared with the least square method,it is shown that the two will converge to the same accuracy for a long time,but the robust estimation is better than the least squares.After theconvergence of the two methods in the same short period,the success rate and accuracy of the robust estimation method are higher.The results of several estimation methods are analyzed and compared when the observation value is abnormal.The Kalman filter is a very effective parameter estimation method,which is more stable and faster than the least square method when the errors are corrected and the observed values are not gross errors.But when the observations contain gross errors,such as coordinates,differential clock parameters standard Kalman filter has large deviation,the robust Kalman filter can effectively inhibit the effect of observations in the abnormal data,and the improved robust estimation scheme to improve the positioning results at the same time to avoid the subsequent epoch phase error the problem of increasing.