北斗二号中AS信号多径抑制方法及性能分析

Multipath Mitigation Methods for BeiDou-2 AS Signals and Performance Analysis

针对北斗二号系统中AS(Authorized Service,授权服务)采用的BPSK(10)、BOC(14,2)、BOC(15,2.5)信号,研究如何抑制多径效应对AS信号跟踪的影响,提高定位精度。对3种信号的自相关特性及功率谱密度进行比对,并在对基于码跟踪环的EML(Early Minus Late,早减迟)和HRC(High Resolution Correlator,高精度相关器)技术进行分析的基础上,将这2种技术用于北斗二号AS信号的多径抑制。仿真表明:EML和HRC均适用于北斗二号AS信号,采用EML时,对BOC(14,2)、BOC(15,2.5)的多径抑制性能优于对BPSK(10)的;采用HRC时,对BPSK(10)的多径抑制性能优于对BOC(14,2)、BOC(15,2.5)的;对于BPSK(10),HRC较EML在误差包络面积上多径抑制性能提高约89.7%;对于BOC(14,2)、BOC(15,2.5),HRC和EML多径抑制性能相当,而EML的计算量相对较小因而整体性能更优;通过减小相关器间隔和增大带宽,可提高多径抑制性能,对BPSK(10)的效果比对BOC(14,2)、BOC(15,2.5)的更为明显。

BPSK （10）, BOC （14, 2） and BOC （15, 2.5） signals of BeiDou-2 AS （Authorized Service） are studied to find ways to mitigate the impact of multipath on tracking of AS signals and enhance the positioning accuracy of BeiDou-2 system. The auto-correlation characteristics and power spectrum density of the three types of signals are compared. EML （Early Minus Late） and HRC （High Resolution Correlator） methods based on code tracking loop are analyzed. The technologies are used to mitigate the impact of multipath on BeiDou-2 AS signals. Simulation shows that both EML and HRC are applicable to BeiDou-2 AS signals. The performance of multipath mitigation for BOC （14, 2） and BOC （15, 2.5） is getter than that for BPSK （10） with EML while the performance of multipath mitigation for BPSK （10） is better than that for BOC （14, 2） and BOC （15, 2.5） with HRC. The performance of multipath mitigation with HRC is increased by about 89.7% over EML for BPSK （10） while it is almost the same for BOC （14, 2） and BOC （15, 2.5）. However, EML is generally more practical since its calculation overhead is smaller. Its performance of multipath mitigation can be enhanced by decreasing the intervals of correlators and in- creasing bandwidth. This is particularly true for BPSK （10） in comparison with BOC （14, 2） and BOC （15, 2.5）.