GNSS/MEMS IMU ultra-tightly integrated navigation system based on dual-loop NCO control method and cascaded channel filters

A coherent scheme of federated architecture for the ultra-tight integration of global navigation satellite system (GNSS) and MEMS (micro-electro-mechanical system) inertial measurement unit (IMU) is presented. Inside the receiver baseband, both the controls for code numerically controlled oscillator (NCO) and carrier NCO are designed. They are each composed of two parts, one part is derived from the navigation solutions of outer loop, and the other part is given on the basis of the channel pre-filter outputs from inner loop. Each tacking channel has two filters of cascaded structure, one is the traditional pre-filter which is used to achieve GNSS signal tracking errors, and the second one is an extractor which is constructed to extract navigation solution derivation errors from the designed NCO controls and the signal tracking errors. For the ultra-tight integration navigation filter, the receiver clock residual error model after compensating the receiver clock drift is derived in detail. Finally, semi-physical simulation environment of the proposed ultra-tight integration scheme is built and closed-loop experiment under high dynamics scenario is put forward. The simulation results show that the proposed integration scheme can stably and robustly track the GNSS signals, and can achieve accurate navigation solutions even in harsh cases.