BDS接收机星间载波相位偏差

摘要

BDS(BeiDou satellite navigation System,北斗卫星导航系统)的MEO/IGSO (Medium Earth Orbit/Inclined Geosynchronous Satellite Orbit,中圆地球轨道/倾斜地球同步轨道)卫星在D1导航电文上调制了NH(Neumann-Hoffman,奈曼-霍夫曼)二次编码,而在GEO(Geostationary Earth Orbit,地球静止轨道)卫星上未使用.利用北斗MEO/IGSO和GEO卫星进行差分定位时,采用不同NH码符号映射规则的接收机之间会出现半周载波相位偏差的问题,严重影响RTK (Real-Time Kinematic,实时动态差分)应用.通过分析半周载波相位偏差的形成机理,从单差、双差、三差应用角度分别研究了半周载波相位偏差的影响.分析结果表明,接收机NH码符号映射规则与卫星不一致时,接收机直接用乘法器对NH码解调将存在反相,也即引入了半周载波相位偏差;在满足特定条件下,单差和双差应用时会存在半周载波相位偏差的问题;三差应用时不存在半周载波相位偏差的问题.最后,提出了需在北斗接口控制文件中明确卫星NH码调制或映射规则的修订建议.%The D1 NAV messages broadcasted by the Medium Earth Orbit/Inclined Geosynchronous Satellite Orbit (MEO/IGSO) satellites of BeiDou satellite navigation System (BDS) are modulated by a Neumann-Hoffman (NH) secondary code,while the D2 NAV messages broadcasted by the Geostationary Earth Orbit (GEO) satellites do not.In the case of differential positioning between BDS MEO/IGSO and GEO satellites,half-cycle carrier phase bias may be induced between receivers that take different NH sign conventions,which results in a failure when performing Real-Time Kinematic (RTK) positioning.Formation mechanism of the half-cycle carrier phase bias is analyzed,and its impact on single,double,and triple difference is discussed.Theoretical analysis shows that the NH sign convention difference between BDS satellites and receivers brings a phase opposition,i.e.,half a cycle phase bias,after the NH code being demodulated by using multiplication in receivers;only under several specified conditions,halfcycle carrier phase bias presents in single difference and/or double difference model.There is no half-cycle carrier phase bias problem in triple difference model.Finally,it is proposed that the NH code modulation rule or sign convention needs to be explicitly indicated in the revised Interface Control Document (ICD) of BDS.