Three coupling modes of satellite-inertial integrated navigation system

There are three main coupling modes of satellite-inertial navigation system: loose coupling, tight coupling and deep coupling. In the loose coupling mode, the GNSS/RTK positioning results and the IMU raw data are fused to solve the carrier's orientation and motion information respectively. In the tight coupling mode, the GNSS receiver outputs the original sampling data of pseudorange and Doppler shift, which are subtracted from the predicted values ​​of the INS system to obtain the measurement residuals of pseudorange and Doppler shift as the observations of the data fusion filter. In the deep coupling mode, the INS unit assists the GNSS receiver, improving the dynamic performance of the receiver, especially in a strong RF interference environment.