CNMC与Hatch滤波方法比较及其在北斗相对定位中的精度分析

Comparison between CNMC and hatch filter & its precision analysis for BDS precise relative positioning

相位平滑伪据算法可以有效抑制多路径效应对伪距的影响,且不存在模糊度固定问题,在GNSS数据处理领域得到广泛研究和应用.本文对Hatch滤波和CNMC(Code Noise and Multipath Correction)相位平滑伪距方法的数学模型进行了系统分析和比较,证明了经过CNMC方法平滑后的单频伪距进行无电离层组合与双频Hatch滤波等价.在假定只存在随机误差和各种观测量互不相关的条件下,推导了CNMC方法平滑伪距的精度表达式,得出双频Hatch滤波在初始化的时段内观测噪声大于CNMC方法,经过十余分钟的收敛,其观测噪声逐渐好于CNMC方法.针对北斗导航系统伪距所受多路径影响幅度大,且低频部分比重大的特点,通过对实测北斗短基线相对定位的OMC(Observation Minus Computation)分析,得出相位平滑伪距虽然能大大减弱原始伪距随机误差方法,但不能改善系统误差,其中CNMC方法与原始伪距的系统误差相当,双频Hatch滤波反而增大了系统误差,进一步对该基线的相位平滑伪距进行相对定位试验,得出采用CNMC方法的平滑伪距,三维位置误差精度得到改善,从0.797 m提高至0.541 m,双频Hatch降低了定位精度,位置误差达到1.160 m.

Phase smoothing Pseudorange can effectively suppress the multipath effect on pseudorange, and there is no ambiguity problem, which has been widely studied and applied in the field of GNSS data processing. This paper made a systematic analysis and comparison of mathematical models for Hatch filter and CNMC phase smoothing pseudorange method. The ionsphere free combination of single frequency pseudorange through CNMC algorithm is proved equivalence with dual frequency hatch filter. On the assumption that there exists only random errors and the various measurements are independent, the accuracy expression of the CNMC method for smoothing pseudorange is deduced. Dual band hatch filter in the initialization period observation noise is bigger than CNMC smoothed pseudorange, but after a bit more than ten minutes, observation noise gradually gets better than CNMC smoothed pseudorange. BDS navigation system is qualified with serious and low-frequency characteristic for multipath errors through the comparison of OMC of double difference observation for real BDS short baseline, the conclusion that the phase smoothing pseudorange algorithm can greatly weaken the random error of original pseudorange, however, can＇t improve the system error is drawn. The system error of pseudorange smoothed by CNMC is at the save level with the original pseudorange, but the system error of pseudorange smoothed by double frequency hatch filter is increased. At last, relative positioning is carried through using the different kinds of phase smoothed pseudorange of that short baseline. The positioning results show that the positioning precision is improved from 0.797 m to 0.541 m using pseudorange smoothed by CNMC and the positioning precision is decreased to 1.160 m using pseudorange smoothed by hatch filter.