Modeling of Ambiguity Fixed Multi-GNSS PPP Tightly Coupled with INS

In urban environment, GNSS signal is interrupted by trees, bridges, and tunnels, which makes Precise point positioning (PPP) need to be reinitialized, and results in PPP-AR (ambiguity resolution) is easily affected. In this paper, we propose a model of multi-GNSS PPP-AR tightly coupled with inertial navigation system (INS) from three aspects: the estimation method of fractional bias (FCB) product at server end, the model of observation update and system update, and the method of ambiguity resolution at user end. The 248 global MGEX stations are selected as the server end to calculate FCB products. Three different grades of INS (Aviation, Tactical, MEMS) are selected to analyze the re-fixing time and the corresponding ambiguity of multi-GNSS PPP/INS under different GNSS outages. The marine experiment is carried out to further verify the conclusion. The experiment results show that, under the GNSS outage of 1 s, the re-fixing time of PPP/MEMS INS can be shortened from 174 s to 41 s; for tactical grade INS, the re-fixing time can be shortened from 174 s to 21 s; for aviation grade INS, the re-fixing time can be shortened from 173 s to 2 s. The precise position information provided by INS can constrain the ambiguity and the multi-GNSS with ambiguity resolution can enlarge the candidate subsets of ambiguity, which significantly shortens the re-fixing time of PPP/INS, and further expands the application of PPP in complex environment.