基于多观测量组合的北斗系统伪距方差自适应估计方法
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摘要
北斗卫星导航系统是我国自主研发的卫星导航系统,具有地球静止轨道、倾斜地球同步轨道及中圆轨道三种卫星的混合星座,同时播发B1、B2和B3三个频点观测值,传统确定观测值向量权矩阵的方法已无法满足北斗卫星导航系统定位的需求,需要探索研究确定北斗卫星导航系统观测值向量方差-协方差矩阵的新方法,以合理使用北斗卫星导航系统观测量,提高系统服务性能。为此,提出了一种基于伪距和相位线性组合的北斗卫星导航系统伪距方差实时自适应估计方法:首先,基于北斗卫星导航系统载波相位和伪距观测值,利用观测值线性组合,构造伪距方差统计量模型;其次,充分考虑北斗卫星导航系统卫星星座特点和多路径影响,引入渐消因子,分别统计伪距均值和方差;最后,基于伪距方差统计值,构造观测值向量权矩阵。新方法克服了传统确定方差-协方差矩阵方法的局限性,能够较真实地反映北斗卫星导航系统伪距观测值向量的随机特性,可有效提高伪距单点定位精度和载波相位模糊度固定效率。北斗卫星导航系统用户机实测数据计算结果表明,基于伪距方差自适应估计的北斗卫星导航系统单点定位精度可提高约3m,模糊度成功固定时间缩短至18个历元。
BeiDou navigation satellite system(BDS),which is developed independently in China,has the hybrid constellation of medium earth orbits(GEO),inclined geo-synchronous orbits(IGSO)and medium earth orbits(MEO)satellites,and it broadcasts three kinds of navigation message through B1,B2and B3,so traditional methods to calculate the weight matrix of observations have been unable to meet the needs of BDS positioning.In order to utilize BDS observations reasonably and improve performance of system service,a new method needs to be studied for fixing variance-covariance matrix of observations.Therefore,a real-time adaptive estimation method of pseudorange variance is proposed in this paper based on linear combination of code and phase(LCCP).First of all,based on carrier phase and pseudorange observations of BDS,a statistic model of pseudorange variance is constructed using linear combination of observations.Secondly,considering the effect of satellite constellation and multipath of BDS,the fading factor is introduced for calculating mean and variance of pseudorange.Finally,based on statistic values of pseudorange variance,the weighting matrix of observation vector is determined.The new method overcomes the limitation of traditional means in determining the variance-covariance matrix,and it can well reflect the random characteristics of pseudorange vector for BDS.It can effectively improve the positioning accuracy and the efficiency of fixing ambiguity for pseudorange and carrier phase respectively.In practical test with BeiDou receivers,the accuracy of point positioning can improve 3meters based on adaptive estimation method of pseudorange variance,and time of fixing ambiguity is 18 epochs shorter than identity matrix.
BeiDou navigation satellite system(BDS),which is developed independently in China,has the hybrid constellation of medium earth orbits(GEO),inclined geo-synchronous orbits(IGSO)and medium earth orbits(MEO)satellites,and it broadcasts three kinds of navigation message through B1,B2and B3,so traditional methods to calculate the weight matrix of observations have been unable to meet the needs of BDS positioning.In order to utilize BDS observations reasonably and improve performance of system service,a new method needs to be studied for fixing variance-covariance matrix of observations.Therefore,a real-time adaptive estimation method of pseudorange variance is proposed in this paper based on linear combination of code and phase(LCCP).First of all,based on carrier phase and pseudorange observations of BDS,a statistic model of pseudorange variance is constructed using linear combination of observations.Secondly,considering the effect of satellite constellation and multipath of BDS,the fading factor is introduced for calculating mean and variance of pseudorange.Finally,based on statistic values of pseudorange variance,the weighting matrix of observation vector is determined.The new method overcomes the limitation of traditional means in determining the variance-covariance matrix,and it can well reflect the random characteristics of pseudorange vector for BDS.It can effectively improve the positioning accuracy and the efficiency of fixing ambiguity for pseudorange and carrier phase respectively.In practical test with BeiDou receivers,the accuracy of point positioning can improve 3meters based on adaptive estimation method of pseudorange variance,and time of fixing ambiguity is 18 epochs shorter than identity matrix.
引文
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[2]HAN S,RIZOS C.Improving the Computational Efficiency of the Ambiguity Function Algorithm[J].Journal of Geodesy,1996,70:330-341.
[3]TEUINSSEN P J G.An Analytical Study of Ambiguity Decorrelation Using Dual Frequency Code and Carrier Phase[J].Journal of Geodesy,1996,70:515-528.
[4]魏子卿,葛茂荣.GPS相对定位的数学模型[M].北京:测绘出版社,1998:33-62.
[5]HOFMANN-WELLLENHOF B,LICHTENEGGER H,COLLIONS J.GPS Theory and Practice[M].2nd ed.Wien,Austria:Springer-Verlag,1993.
[6]何海波.高精度GPS动态测量及质量控制[D].郑州:信息工程大学测绘学院,2002.
[7]张锋.基于区域参考站网络的VRS动态定位算法研究与实现[D].郑州:信息工程大学测绘学院,2010.
[8]HAN S,RIZOS C.Comparing GPS Ambiguity Resolution Techniques[J].GPS World,1997(October):54-56.
[9]JIN X X.Theory of Carrier Adjusted DGPS Positioning Approach and Some Experimental Results[D].Delft,The Netherlands:Delft University of Technology,1996.