GPS民用广播星历中ISC参数精度分析及其对导航定位的影响

2005年起发射的GPS Block IIR-M卫星在L2频率上新增了L2C民用信号,2010年起发射的Block IIF卫星新增了L5频率及L5I、L5Q两种民用信号。为此,GPS民用广播星历在原有时间群延迟(TGD)参数的基础上,新增了ISC_(C/A)、ISC_(L2C)、ISC_(L5I)及ISC_(L5Q)4种ISC(inter-signal correction)参数,以服务GPS实时导航定位用户。本文给出了ISC参数在GPS单/双频定位中的改正方法、利用不同机构提供的后处理差分码偏差(DCB)产品评估了ISC参数的实际精度、研究了ISC参数对GPS民用导航定位精度的影响。在明确TGD、ISC和DCB 3类参数之间区别与联系的基础上,本文研究表明:GPS广播的ISC_(C/A)参数精度可达0.2ns,TGD、ISCL2C及ISCL5Q参数精度可达0.5ns;以2014年连续11d全球12个MGEX(multi-GNSS experiment)站为例,经由ISC参数改正后,GPS L2C单频标准单点定位(SPP)的位置解精度提高了30.6%,L1C/A+L2C双频SPP的位置解精度提高了12.2%,该精度与L1P(Y)+L2P(Y)消电离层组合SPP的位置解精度相当。

Accuracy Evaluation of GPS Broadcast Inter-signal Correction (ISC) Parameters and Their Impacts on GPS Standard Positioning

With the introducing of GPS (Global Positioning System)Block IIR-M satellites in 2005,a new civil signal (L2C)was transmitted on L2 frequency,and two new signals (L5I and L5Q)on a new frequency (L5)were also introduced as standard signals with Block IIF satellites beginning in 2010.In addition to the timing group delay (TGD)parameter contained in the legacy navigation (LNAV)message,four additional inter-signal correction (ISC)parameters are introduced in the new civil navigation (CNAV)message to provide corrections for L1C/A,L2C and L5 signals with respect to L1P(Y)signal.In this study,the ISC correction models are first developed for GPS single-and dual-frequency navigation users.Thereafter ISCs are validated with the differential code bias (DCB)products of different organizations,and several standard point positioning (SPP)schemes are also carried out to analyze the impact of ISCs on GPS standard positioning.The results indicate that the precision of broadcast ISCC/A is about 0.2 ns,and those of TGD,ISCL2C and ISCL5Q are about 0.5 ns.The positioning accuracy of the SPP solution based on GPS L2C signals applying ISC corrections improves 30.6% and that based on L1C/A and L2C ionosphere-free combination improves 12.2%at 12 multi-GNSS experiment (MGEX)stations during day of year (DOY)300—310 in 2014,compared to the solutions without the consideration of ISCs.For GPS dual-frequency users,the broadcast ISCs enable a level of accuracy that is competitive with ionosphere-free combination of the present L1P(Y)and L2P(Y)signals.