GNSS授时原理及其精度分析

GPS timing and timing accuracy analysis

GPS授时在石油勘探中已获得广泛地应用,但在山区以及树林等地区,可视GPS数量减少,以致授时困难。GNSS相比单一的GPS,有更多的可视卫星,在接收信号困难地区可以增加可视卫星数量,使授时变得相对容易。本文针对GNSS授时,阐述其授时原理,给出了零基线法计算伪距精度的方法,并根据原理分析影响授时精度的各种因素,计算了主要因素对授时影响的大小。GNSS授时精度主要受卫星轨道径向精度、卫星钟差和伪距测量精度三方面的影响。相对于双频GNSS接收机,GPS与Galileo授时精度最高,实验数据中总体小于5ns,BDS二代在卫星轨道径向和伪距精度比GPS略差,但BDS二代卫星钟差太大,导致授时精度在30ns左右,GLONASS授时精度小于30ns。单频GNSS接收机的授时精度会在双频接收机授时精度的基础上降低50ns左右。

GPS timing has been widely used in petroleum exploration,but in some difficult areas such as the mountains and the woods,it is difficult for timing because of the fewer visible GPS satellites.GNSS has much more satellites than GPS and the more visible satellites can be got,so GNSS timing is easier than GPS timing at the difficult areas.Here,for GNSS timing,we have expounded the timing theory and provided the method how to get the pseudo-range accuracy by zero baseline.Based on the theory of timing,the various factors that affecting the timing accuracy have been considered and analyzed and the main factors have been done quantitative analysis.GNSS timing accuracy is mainly affected by the satellite orbits radial accuracy,the satellite clock error and pseudo-range measurement accuracy.As for dual frequency GNSS receiver,the timing accuracy of GPS and Galileo is the best,less than5 ns in the experiments.The timing accuracy of BDS is lower,less than 30 ns,because the clock error of BDS is too large although the pseudo-range accuracy is just a little lower than GPS.The timing accuracy of GLONASS is less than 30 ns.The timing accuracy of single frequency GNSS receiver will be 50 ns less than dual-frequency receiver.