SINS/GNSS Integrated Navigation Based on Invariant Error Models in Inertial Frame

The invariant error model in the inertial frame is investigated for Strapdown Inertial Navigation System (SINS)/Global Navigation Satellite System (GNSS) integrated navigation, which is no longer limited by small misalignment angle and linear approximation error like traditional SINS/GNSS integrated model, so initial alignment and integrated navigation could be combined into one stage, and the navigation solution is more accurate and faster. At first, the matrix Lie group-based navigation state is defined in an inertial frame and proved to satisfy group affine without introducing an auxiliary velocity like the Lie group state defined in other frames. Then both the left and right invariant error state models are derived in inertial frames respectively corresponding to the group affine model. On this basis, the left and right invariant measurement models for SINS/GNSS are also derived respectively. Finally, the simulation and a boat-mounted field test are conducted to evaluate the actual performance of the investigated models. The results show that the proposed left invariant error model performs better for SINS/GNSS than the right invariant error model and also outperforms other existing SINS/GNSS integration models. Especially, compared with the current advanced invariant error model defined in the earth frame, the model we investigated is more concise, efficient, and accurate.