多模GNSS并存与发展的局面已初步形成，兼容与融合互用已成为卫星导航领域的前沿热点课题。本项目重点研究基于实测多模数据的GPS/GLONASS/北斗三系统融合精密定轨定位理论与方法，解决高精度时空基准统一的问题，并应用于多系统融合精密导航定位。项目具体研究多模GNSS时空基准转换与统一方法；突破多模系统误差消除方法，建立基于随机过程的多模信号延迟估计方法；建立基于赫尔墨特方差分量估计的多模观测值随机模型；实现统一时空基准下的融合精密定轨，三系统融合定轨精度分别达到3cm、5cm和20dm级；并在融合轨道与钟差产品的基础上实现mm级融合静态精密单点定位与cm级融合动态定位。项目研究的融合精密定轨是融合精密导航定位的基础，将促进我国北斗系统在全球范围内的推广与应用；而融合精密单点定位又可提高GPS、GLONASS、北斗单一系统的导航定位性能；该研究既具有重要的科学意义，又具有显著的实用价值。

Coexistence and development of four kinds of global satellite navigation system (GPS/GLONASS/Beidou/Galileo、Multi-GNSS) have initially taken shape, combined processing of Multi-GNSS have been listed as the key issue for study by many GNSS institutes all over the world, so as to realize the compatibility and integrated applications of GNSS. This subject aims at the theory and method of GPS/GLONASS/Beidou combined precise orbit determination and precise point positioning. Key issues for this project are as follows: transformation and unification of time-space datum; remove system errors from Multi-GNSS observations, using stochastic process for the Inter-System Bias estimation; determine stochastic model for Multi-GNSS observation using Helmert variance component estimation; realize GPS/GLONASS/Beidou combined orbit determination, the precision of GPS、GLONASS and Beidou orbit reach up to 3cm、5cm and 20dm respectively; based on the combined products, realize the combined precise point positioning（PPP）, and the precision of the static PPP and kinematic PPP will reach up to mm and cm respectively. This project would provide the orbit products of Beidou in the GPS or GLONASS time-space datum, which will facilitate the worldwide popularization and application of Beidou. In addition, positioning with Multi-GNSS will improve the performance of navigation and positioning then the single GPS、GLONASS or Beidou.The study have important scientific significances and research values.