The aim of the new generation of Global Geodetic Observing System is a millimeter-level accuracy in positioning, with a crucial role to be played by Global Navigation Satellites Systems (GNSS) in the Precise Point Positioning (PPP) mode. This is of course because GNSS constellations and receivers provide an efficient stand-alone technique with a homogeneous performance over large areas (positions, navigation and meteorology) when used in conjunction with the PPP mode, with also an ever-increasing data flow and different satellite line-of-sights. The requirement of accuracies reaching the millimeter or sub-millimeter implies a knowledge at this level of each line in the GNSS-PPP error budget, including, but not restricted to: clock biases, troposphere and ionosphere delays, multipath and ground deformations. In this review study, we consider this millimeter-/submillimeter level GNSS-PPP error budget, and possible mitigations and improvements in the frame of the existing global constellations: GPS, Galileo, GLONASS and BDS, in view of augmented constellations and/or Low Earth Orbit constellations, which will be available in the near future. We also pay a special attention to systematic biases that can/could exist between constellations.

新一代全球大地观测系统的目标是毫米级精度的定位，其中全球导航卫星系统（GNSS）在精密单点定位（PPP）模式中发挥着至关重要的作用。这当然是因为 GNSS 星座和接收器提供了一种高效的独立技术，当与 PPP 模式结合使用时，在大范围（位置、导航和气象）上具有均匀的性能，并且数据流不断增加，并且不同的卫星视线。达到毫米或亚毫米精度的要求意味着了解 GNSS-PPP 误差预算中每条线的这一水平，包括但不限于：时钟偏差、对流层和电离层延迟、多路径和地面变形。在本综述研究中，我们考虑了毫米/亚毫米级 GNSS-PPP 误差预算，以及现有全球星座框架内可能的缓解和改进：GPS、伽利略、GLONASS 和 BDS，考虑到增强星座和/或低卫星星座地球轨道星座，将在不久的将来推出。我们还特别关注星座之间可能存在的系统偏差。