论精密单点定位整周模糊度解算的不同策略

精密单点定位（PPP）一般基于非差GPS观测值，其中相位观测所含的初始相位偏差（Initial Phase Biases, IPBs）与整周模糊度不可分离，故各类PPP估值均为模糊度浮点解。目前，借助区域或全球GPS网分离卫星IPBs，改正PPP相位观测值，可实现PPP整周模糊度解算，进而提高各类估值精度，显著缩短收敛时间。常用算法包括：分解卫星钟差（分解钟差法）和非整相位偏差（非整偏差法）估计方法。本文从GPS原始观测值入手，推导了卫星IPBs估计的满秩函数模型，以此为基础对两种算法的特点及实施进行了对比分析。研究表明：分解钟差法是一种观测信息的最优利用，且与传统的卫星钟差估计方法具有较优的一致性，但未利用卫星IPBs较为稳定的有利约束；非整偏差法对组合观测值之间的相关性未加考虑，进而是一种次优估计，其实时性实施较差，且较依赖于高精度的码观测值。文中的新模型可有效克服上述两种算法的不足，便于施加部分参数的合理时变性约束，以提高卫星IPBs估计的可靠性。

On the Different Strategies for Integer Ambiguity Resolution in Precise Point Positioning

The un-differenced GPS observations are usually adopted by precise point positioning (PPP), of which the initial phase biases (IPBs) underlying the phase observables are inseparable with the integer ambiguities, leading to ambiguity-float PPP-based solutions. Currently, the satellite IPBs as retrieved from regional or global GPS networks can be used for correcting PPP user’s phase observable and restoring the integer nature of the ambiguities. After successful ambiguity resolution, improving accuracy and convergence behavior of PPP-based solutions can be expected. The commonly used methods for estimating satellite IPBs include estimation of decoupled satellite clock or fractional phase biases. Starting from the original GPS observations, the full-rank mathematical model for satellite IPBs estimation is derived and used for comparatively analysis of the characteristics and implementation of both methods. It is concluded from the analysis that full utilization of information from GPS observations can be expected for the former method, and the process of generating decoupled satellite clocks is consistent with the standard satellite clocks estimation, but doesn’t make good use of the stable temporal behaviors of satellite IPBs. In contrast, the latter method doesn’t fully account for the stochastic correlations between the linear combinations of GPS observations, which would lead to a sub-optimal satellite IPBs, besides, the real-time implementation of this method is more troublesome than the former, and the GPS code observations of high-accuracy are always required. The strategy presented in this paper can avoid the shortcomings in both methods, and reasonable constraints due to the stability of several unknowns can be easily imposed upon during parameter estimation to generate more reliable satellite IPBs.