基于码载偏离度的改进自适应Hatch滤波算法

针对单频地基增强系统（GBAS）中载波相位平滑伪距精度易受电离层延时和伪距测量噪声影响的问题，分析卫星信号码载偏离度对Hatch滤波器平滑精度影响，提出一种基于码载偏离度的自适应Hatch滤波算法。根据伪距和载波相位观测值计算码减载波，建立其1阶线 性模型；在此基础上采用最小二乘法估计电离层延时变化率，由此分离得到伪距测量噪声；建立平滑后伪距误差均方根与电离层延时变化率、伪距测量噪声标准差以及Hatch滤波器平滑时间三者之间的函数模型，并根据该函数表达式计算得到滤波器最优平滑时间。利用GBAS原理样机进行了验证实验，结果表明：自适应Hatch滤波算法能够根据实时计算得到的电离层延时变化率和伪距测量噪声标准差确定滤波器最优平滑时间，且在机载差分定位中采用自适应Hatch滤波算法平滑伪距后其位置精度相比传统固定平滑时间算法最大提高了53.19%，验证了所提算法的有效性。

Improved Adaptive Hatch Filter Algorithm Based on Code-carrier Divergence

The smoothing accuracy of carrier-phase smoothing pseudorange in single-frequency ground-based augmentation system (GBAS) is easily affected by the ionospheric delay and pseudorange measurement noises. The influence of code-carrier divergence of satellite signal on the smoothing accuracy of Hatch filter is analyzed, and an improved adaptive Hatch filter algorithm based on code-carrier divergence is proposed. The code-minus-carrier is computed using pseudorange and carrier-phase measurements, and its first-order linear model is established. The ionospheric delay rate is estimated by using the least square method. Given the estimated ionospheric delay rate, the pseudorange measurement noise can be separated. A function model between the root mean square of smoothed pseudorange and the ionospheric delay rate, the standard deviation of pseudorange measurement noise and the smoothing time of Hatch filter is established, from which the optimal smoothing time of Hatch filter can be calculated. The verification experiments were carried out by using GBAS prototype. The experimental results show that the adaptive Hatch filter is able to calculate the optimal smoothing time of filter based on the real-time ionospheric delay rate and the standard deviation of pseudorange measurement noise. Compared with the traditional fixed smoothing time algorithm, the maximum position accuracy of airborne differential positioning is improved by 53.19 percent by using the adaptive Hatch filter algorithm, which verifies the effectiveness of the proposed algorithm.