BDS PPP/INS Tight Coupling Method Based on Non-Holonomic Constraint and Zero Velocity Update

According to the problem that the positioning error increased with the increase of navigation time in the environment of complete lack of satellite signals such as viaduct and tunnel, the precise point positioning (PPP) / inertial navigation system (INS) tight coupled continuous positioning with non-holonomic constraint (NHC) and zero velocity update (ZUPT) in BeiDou navigation satellite system (BDS) was proposed. Firstly, the ionospheric composite model was analyzed from the aspects of observation equation, parameter estimation, fuzziness, degree of freedom and noise. The BDS PPP dynamic positioning model of ionospheric composite was established, and the errors that affect the positioning accuracy and convergence rate were analyzed. According to the motion characteristics of land vehicles, a scheme of velocity NHC was proposed to limit the accumulation of system positioning error with time, and ZUPT was used to increase the navigation accuracy of the integrated system when the vehicle was in the static state at the traffic light. The experimental results showed that the horizontal positioning accuracy of converged BDS PPP was better than 5 cm, the vertical positioning accuracy was better than 10 cm, and the dynamic positioning results are different from the high-precision real-time kinematic (RTK) / INS integrated navigation results by centimeters. The positioning accuracy of the system could be effectively improved by the BDS PPP/INS tight coupling method of NHC+ZUPT. Compared with the PPP/INS tight coupled positioning results without any constraints, the accuracy of the method in the three directions of East, North, and Up was increased by 0.08 m, 0.02 m and 0.01 m respectively.