Observability Analysis of Non-Holonomic Constraints for Land-Vehicle Navigation Systems

Over the past decades, the integration of a MEMS-based (Micro-Electro Mechanical Systems) Inertial Measuring Unit (IMU) with a GNSS receiver-chip has become commonly used navigation techniques by virtue of their advantages such as small sized, light weight, with low power consumption, and have extremely low cost. To provide accurate and reliable positioning solutions with a low-cost GNSS/MEMS INS system, it is valuable to introduce specific auxiliary information that can improve the navigation performance without adding extra hardware costs. The auxiliary information is especially useful during GNSS outage periods or when the vehicle is moving with low dynamics (e.g. no change of attitude and accelerations) which lead to the poor observability of the GNSS/INS navigation system. For LVN applications, Non-Holonomic Constraints (NHC) is one of the most common types of auxiliary information. This paper focuses on studying the contributions of the NHC from the perspective of observability, which provides a deeper insight and shows how the NHC improves the navigation solutions. Considering several typical vehicle dynamics, it is also clear to see the effects of the NHC to the inertial navigation under different situations. Both theoretical analysis and simulation tests have shown that the contributions of the NHC to the estimation of a certain state depend on both the current vehicle dynamic and the relative error magnitude of this state compared to the coupled state under the current vehicle dynamic; both the accelerating and turning motions can enhance the contributions of the NHC to the estimation of both the yaw and the pitch, and such contributions will be stronger with a higher vehicle speed; the NHC has significant effects on controlling the roll in all motion status. Furthermore, the effects of the NHC on the estimation of the biases of both gyroscopes and accelerometers are also analyzed. The outcomes of this paper show that the proposed observability analysis is beneficial to the utilization of NHC or other priori information in low-cost navigation systems.