围绕BeiDou/GPS三频PPP 固定解模型、方法及其关键技术深入开展研究。建立三频PPP观测模型和随机模型；利用北斗和GPS星座中GEO、MEO和IGSO三类卫星的不同特点，构建自适应的电离层时空约束模型，提高不同频率上的频间偏差和相同频率不同观测值类型上的码偏差的估计精度；针对当前北斗卫星轨道和钟差精度不如GPS，PCO和PCV模型还不完善等不利因素，研究三频相位小数偏差分离和估计方法，并精确建模；优化构造弱电离层、低噪声、长波长的组合相位，实现三频PPP非差整数模糊度快速确定；利用统计理论和方法，在码偏差和频间偏差估计、相位小数偏差估计和模糊度确定等环节，进行有效的质量控制，提高三频PPP 固定解的可靠性和成功率。项目研究对丰富PPP定位的理论和方法，推动我国BeiDou实时精密定位技术的发展具有重要意义。研究条件成熟，有望解决PPP初始化时间较长这一技术瓶颈并取得创新成果。

The objective of this project is to investigate the method and key technology of three-frequency precise point positioning (PPP) ambiguity resolution based on BeiDou/GPS data set. First, we will develop the functional and stochastic models for three-frequency PPP fixed solution. The inter-frequency biases between observation on same frequency and intra-frequency biases (IFB) between observations on the different frequencies will be estimated by constraining the spatial and temporal ionosphere variation which can be characterized by each of IGSO, GEO and MEO satellites of Beidou and GPS. We will find a way to separate fractional part of the uncalibarated phase delay from the real-value phase ambiguities based on the real three-frequency pseudo range and carrier phase observations and IFBs estimated from a network with sparse stations then to model their spatial and temporal variations. We also develop optimal combination of carrier phase and pseudo-range to find less ionosphere delay residual, low observation noise and long wavelength ones which can be applied to reduce the three-frequency undifferenced ambiguity searching space them shorten the initialization time of PPP. Finally, we will investigate the quality control method for IFB estimation, ambiguity resolution to ensure the validity and reliability of PPP ambiguity resolution by using the statistical theory. This study is significant for enriching the fundamental theory and method of PPP and promoting the development of high accuracy positioning technology with China BeiDou system. The basis for this study is substantial. It is expected to solve the PPP critical problem which requires a long initialization time under the condition that only dual-frequency observations are used. Innovative achievements are expected.