一种FLL辅助PLL的GNSS接收机矢量跟踪环路

GNSS receiver vector tracking loop with FLL⁃assisted PLL

全球导航卫星系统(GNSS)接收机的设计主要包括捕获、跟踪、解算三个环节,其中,跟踪环节中载波频率和码频率的稳定性直接影响着导航定位性能。为改善动态环境中载波频率和码频率的波动性,提高定位精度,提出一种频率锁定环路(FLL)辅助相位锁定环路(PLL)的GNSS矢量跟踪环路结构。在载波环中,采用二阶FLL辅助三阶PLL的跟踪方法,通过预测载波相位、载波频率、载波频率率,更新载波相位值并反馈到载波NCO,实现载波稳定跟踪;在码环中,将解算环节获取的伪距信息反馈到跟踪环节,实时更新各跟踪通道的码频率,实现码环稳定跟踪。实验结果表明,相较于传统的标量跟踪方法,所提出的FLL辅助PLL的矢量跟踪方法能够在动态环境下输出较小的载波频率和码频率误差,且具有更高的定位精度。相较于其他的环路改进算法,该方法融合了载波改进技术与矢量跟踪技术,且利用真实卫星数据验证了所提方法的定位效果。

The design of the receiver in the global navigation satellite system(GNSS)mainly consists of three steps of acquisition,tracking and solution.The stability of the carrier frequency and code frequency in the step of tracking affects the navigation and positioning performance directly.Therefore,a GNSS vector tracking(VT)loop structure with frequency⁃locked loop(FLL)assisted phase⁃locked loop(PLL)is designed to improve the fluctuation of the carrier frequency and code frequency in dynamic environment and improve the positioning accuracy of GNSS.In the carrier loop,a tracking method of second⁃order FLL assisted third⁃order PLL is used to achieve the stable carrier tracking by predicting the carrier phase,carrier frequency and change rate of carrier frequency,updating the value of carrier phase,and feeding them back to the carrier numerical control oscillator(NCO).In the code loop,the pseudo⁃range information obtained at the step of solution is fed back to the step of tracking,and the code frequency of each tracking channel is updated in real time,so as to realize stable tracking of the code loop.The experimental results show that,in comparison with the traditional scalar tracking methods,the proposed vector tracking method based on FLL⁃assisted PLL can output smaller carrier frequency and code frequency error in a dynamic environment and has higher positioning accuracy.In comparison with the other loop improvement algorithms,the carrier improvement technology and the vector tracking technology are fused into this method.Its positioning effect has been verified by real satellite data.