北斗三号系统中轨道地球卫星伪距多路径误差分析和改正

Analysis and correction of BDS-3 MEO satellites pseudorange multipath error

2018—2019年,北斗三号系统陆续发射十几颗中轨道卫星,逐步完成全球组网。北斗三号系统卫星同时播发平稳过渡信号B1I、B3I和新体制信号B1C、B2a。实际数据分析表明,中轨道地球卫星民用B1C和B1I频点包含明显的伪距多路径误差,并且由于中轨道地球卫星的轨道特性,这种现象在卫星低高度角,即出入境时十分显著。利用多路径半天球图(Multipath Hemispherical Map, MHM)与伪距噪声和多路径校正法(Code Noise and Multipath Correction, CNMC)两种算法对伪距多路径误差进行改正。MHM算法对伪距多路径误差的改正并不明显;CNMC算法在高度角大于30°时可以将B1C频点伪距多路径误差从0.11 m降低至0.03 m,将B1I频点伪距多路径误差从0.074 m降低至0.024 m,从而使中轨道卫星的多路径误差降低60%以上。

From 2018 to 2019,the BDS-3(BeiDou navigation satellite system phaseⅢ)has successively launched more than a dozen MEO(medium earth orbit)satellites,gradually completing global networking.The BDS-3 satellites simultaneously broadcast smooth transition signals B1 I,B3 I and new signals B1 C,B2 a.The analysis of actual data shows that the civil B1 C frequency and B1 I frequency of MEO satellites contains obvious pseudorange multipath errors.Due to the orbital characteristics of MEO satellites,this phenomenon is very significant at low altitude angles of satellites.Two algorithms of MHM(multipath hemispherical map)and CNMC(code noise and multipath correction)were used to correct the pseudorange multipath error.The correction of the pseudorange multipath error by the MHM algorithm was not obvious.The CNMC algorithm can reduce the B1 C frequency multipath error from 0.11 m to 0.03 m and reduce the B1 I frequency multipath error from 0.074 m to 0.024 m when the altitude angle is greater than 30 degrees.The multipath error of the MEO satellite is reduced by about 60%.