中文摘要：

现阶段北斗卫星导航系统（BeiDou navigation satellite system,BDS）的同步地球轨道（geostationary orbits,GEO）卫星、中倾斜地球同步轨道（inclined geo-synchronous orbits,IGSO）卫星和中圆地球轨道（medium earth orbit,MEO）卫星均存在伪距偏差,该伪距偏差的存在对精密定位的研究及其应用产生了较大的影响。根据北斗IGSO和MEO卫星的伪距偏差与高度角和频率相关的误差特性,本文分析了测站数目及分布,以及观测时长对建模的影响,选择18个测站2015年全年的数据作为MEO卫星的建模数据,其中可以连续观测到全弧段IGSO卫星的4个测站用于IGSO卫星的建模,采用加权分段线性拟合联合抗差估计的方法建立了北斗卫星伪距偏差改正模型。模型改正后,北斗IGSO和MEO卫星的伪距偏差得到明显的削弱,相比于传统的伪距偏差改正模型,精密单点定位（precise point positioning,PPP）的定位精度和收敛时间均得到提升。

英文摘要：

Thecode-phase divergences,which are absent for GPS,GLONASS,and Galileo,are commonlyfound in BDS geostationary （GEO）,Inclined Geo Synchronous Orbit （IGSO） and Medium Earth Orbit （MEO） satellites.Several precise applications that use code observations are severely affected by these code biases; therefore,it is necessary to correct biases in BDS code observations.Since the BeiDou satellite-induced code bias is confirmed to be orbit type-,frequency-,and elevation-dependent,an improved code bias correction model for IGSO and MEO satellites based on a large amount of the data was developed.To obtain the best fitting results,we analyzed the effect of the number and distribution of stations and observation time on model estimation,and also considered the different influence of multipath at different elevations.A robust estimation method controlled the observation quality.A dataset from 18 stations during one year period in 2015 was employed to estimate the correction model for MEO satellites and four stations for IGSO satellite.To validate the improved correction model,the effect of the code bias on precise point positioning （PPP） before and after correction is analyzed and compared.Results show that systematic variations were eliminated more clearly after applying the improved correction model as compared to the traditional model.After correction,the positioning accuracy of PPP solution was improved and the convergence time decreasedshowing a better performance than results using thetraditional model as proposed by Wanninger and Beer.