Latest Progress and Challenges in Multi-frequency and Multi-global Navigation Satellite System Precise Point Positioning Ambiguity Resolution Technology

The development of multi-frequency Global Navigation Satellite System (GNSS) signals and multi-GNSS constellations and precise positioning sensors has significantly improved positioning performance. As a representative of highly precise positioning technology, precise point positioning ambiguity resolution (PPP AR) technology has also made significant progress. In this paper, the latest progress and challenges of multi-frequency and multi-GNSS PPP AR technology are comprehensively discussed. According to the time development sequence of multi-frequency and multi-GNSS PPP AR, we present the development of multi-GNSS dualfrequency PPP AR, multi-frequency single-system PPP AR, and multi-frequency and multiGNSS PPP AR in turn and explain the problems with key technologies that needed to be solved in the process of realizing multi-frequency and multi-GNSS PPP AR, such as mathematical models, ambiguity resolution algorithms, and inter-system and inter-frequency biases. Further research challenges of PPP AR popularization and application are also summarized.