BDS-2导航电文的TGD参数精度及其对用户导航定位精度的影响

TGD Parameter Accuracy of BDS-2 Navigation Message and Its Influence on User Navigation and Positioning Accuracy

北斗二号(Bei Dou Navigation Satellite System-2,BDS-2)卫星播发以B3频点为基准的卫星钟差参数,并播发B1和B2频点相对于B3频点的群延迟(time group delay,TGD)参数。以差分码偏差(differential code bias,DCB)参数为基准,计算BDS-2群延迟参数的精度。在计算过程中,发现在2017年年积日202 d以前,各颗卫星TGD1参数精度较差,与DCB1参数互差在2~4 ns之间,TGD2与DCB2的互差约为0.5 ns。在2017年年积日202―203 d处,所有卫星群延迟参数均发生明显跳变,该跳变主要是因参与群延迟解算的北斗系统的接收机不再采用抗多径算法所致。跳变后,群延迟参数与MGEX(Multi-GNSS Experiment)公布的差分码偏差参数的差值小于0.5 ns,与GPS卫星播发的群延迟参数精度接近。进一步利用实测数据计算了群延迟参数改正精度对用户导航定位精度的影响。结果表明,使用跳变前的群延迟参数,单频定位精度为2.078 m,双频定位N方向精度为1.451 m,E方向精度为1.648 m,U方向精度为3.467 m;使用跳变后的群延迟参数,单频定位精度为1.968 m,双频定位N方向精度为1.361 m,E方向精度为0.998 m,U方向精度为2.789 m,在双频定位的N,E,U方向,双频定位精度分别提升6.2%,39.4%,19.5%。

Parameters of the satellite clock errors, whose foundational frequency are under B3, and the group delay parameters(T GD) whose frequency are under B1 and B2, are all broadcasted by BD-2 satellite. According to references, the largest deviation between the T GD parameter of BD-2 satellite and the DCB parameter published by MGEX is 5 billi-seconds, which is the main factor that will affect the allocation of the timing accuracy for BD-2 customers. This paper firstly evaluates the accuracy of the T GD parameters of the BD-2 by taking the DCB parameter as the reference, whose results show that before the day202 of the year 2017, the T GD1 parameters of each satellite show a poor accuracy, whose mutual deviation between the DCB1 parameter is between 2 ns and 4 ns, and the mutual deviation between T GD2 parameters and DCB2 parameters is around 0.5 ns. Between the days 202 and 203 of the year 2017, T GD parameters of all satellites show a sudden and obvious jumping change, which is resulted from the adjustment of solution strategy of T GD parameters. After the jump, the parameter deviation between the T GD parameters and the DCB parameters published by MGEX will be lower than 0.5 ns, which is comparable to the accuracy of the T GD parameters broadcasted by GPS satellite. Then, this paper further evaluates the effect of the revised accuracy of the T GD parameters on the accuracy of the GPS of customers. According to the result, before the DOY 202, the accuracy for sonic frequency positioning is 2.078 m, and for dual band positioning of direction N is 1.451 m, for direction E is 1.648 m, and for direction U is 3.467 m;while after the DOY 203, the accuracy for sonic frequency positioning is 1.968 m, and for dual band positioning of direction N is1.361 m, of direction E is 0.998 m, and of direction U is 2.789 m, in which the accuracy of the dual band positioning of direction N, E and U are respectively enhanced up to 6.2%,39.4% and 19.5%.