一种改进的精密单点定位模型

针对现有精密单点定位（PPP）模型收敛慢的问题，提出了一种改进的PPP定位模型。采用码相位半合组合观测值以及几何无关组合观测值分别降低码伪距观测噪声和轨道误差的影响，该模型不仅具有较小的观测噪声，还降低了轨道误差影响。实验结果表明，引入新的组合观测值后明显改善了PPP的解算性能。当观测时长为0.5 h时，采用所提模型的收敛率较标准非组合（un-combined model，UC）模型、UofC（university of calgary model）模型和标准非差无电离层组合（un-difference ionosphere free combined model，UD）模型分别提高了37.6%、4.2%和235.9%，且收敛速度有明显提高；在定位精度方面，新模型与UofC模型较为一致，但明显优于UC和UD模型；采用新模型估计的天顶对流层延迟与UC模型较为一致，且高于UofC和UD模型。

A Modified Model for GPS Precise Point Positioning

According to the problem of slow convergence using existing PPP models, a modified PPP model was proposed. With this new model, a code-phase ionospheric-free combination is used to lower the code observation noise level, and a code-phase geometry-free combination is used to mitigate orbit errors. The new PPP model composed by the new combinations not only has a lower measurement noise, but also can reduce the impact of orbit error. Results show that the performance of PPP solution is improved by introducing the new combinations. For the 0.5 h duration observation data sets, the convergence percentage by using MUC model is increased by 37.6%, 4.2% and 235.9% compared with the Un-Combined (UC) model, UofC model and Un-Difference ionosphere-free combined (UD) model, respectively. Moreover, the positioning accuracies of the modified PPP model agree with those of the UofC model, which are better than those of the UC and UD models. The accuracy of zenith tropospheric delay agrees with those of the UC model, and these are better than those of the UofC and UD models.