GNSS Global PPP System Technology: Bottleneck and Development Direction

The basic navigation and positioning service and precise single-point positioning service of contemporary global navigation satellite systems (GNSS) and its augmented systems mainly serve people and machines that are supervised or operated by people. Its system architecture and signal framework have undergone nearly 40 years of application and performance continuous improvement, and have encountered the bottleneck of the contradiction between accuracy and real-time performance that cannot be reconciled. It is urgent to research at the level of system architecture and signal framework to seek breakthroughs, and solve the contradiction between dm/cm-level positioning accuracy and second-level real-time performance from the system design source so that GNSS can step into the next generation, serve the machine independently, and provide real-time and accurate space-time information support for the intelligent era and society of “No Man, intelligence and IoT”. The paper first summarizes that the contemporary GNSS system adopts “sub-meter-level broadcast ephemeris + m/cm-level code pseudorange measurement signal” to realize instantaneous meter-level positioning, and further adopts “cm-level precision ephemeris enhancement + cm/mm-level carrier pseudorange measurement signal”. After 10 to 40 min of initialization and convergence, cm-level positioning is realized. Secondly, the current status of the space-time reference establishment, maintenance and synchronization system architecture, the current status of civil space signal framework, and the current status of civilian message structure are analyzed one by one, and the bottleneck of the contradiction between accuracy and real-time is summarized and analyzed. Then, it is proposed to use a new generation of code-based precision point positioning system (NextGen-Code-PPP) to realize instantaneous dm-level positioning, which is “cm-level broadcast ephemeris + cm-level code pseudorange measurement signal”, and further use “cm/mm-level carrier pseudorange measurement” to realize instantaneous cm-level positioning system-level solutions. Finally, the space-time reference system architecture and signal frame sources, such as the space “net” ground “net” space-time reference, unambiguous instantaneous cm-scale space meta signals, high-power fast message signals of UHF/VHF and other new frequency bands are analyzed, and a feasible conclusion is given.