Heading accuracy improvement of MEMS IMU/DGPS integrated navigation system for land vehicle

Many researches indicated that in land vehicle-based MEMS IMU/DGPS integrated navigation system, the vehicle heading is unobservable and its error can grow significantly fast with time, if the vehicle moves with only slow changes in attitude and acceleration, e.g. the vehicle moving along a straight road at almost constant velocity. In this paper, a new heading measurement is derived from the DGPS positions and this new measurement can improve the heading accuracy of MEMS IMU/DGPS integrated navigation system for land vehicle. However, the DGPS-derived heading will have a significant deviation from the true heading value while the vehicle makes a turn. Thus a sequential Kalman filter is proposed to process the DGPS position and heading measurements in a sequential order with MEM IMU measurements. This ensures the DGPS position measurements still can be used in the KF even if the DGPS heading measurements are unusable due to large deviation to the truth. To ensure the quality of the DGPS heading measurements, an innovation detection method is used to detect and reject the singular DGPS heading measurement from the sequential Kalman filter. A field test was conducted to test the effect of this new heading measurement on improving land vehicle heading accuracy. The test results showed that this new type of measurement can significantly reduce the heading error of MEMS IMU/DGPS integrated navigation solution from about 5 deg to less than 1 deg. Test results also showed that the innovation detection method can effectively control the quality of DGPS heading measurement. Without this control, the singular heading measurement would lead to a heading error as large as 100 deg. In summary, the introduction of DGPS-derived new heading measurement and the innovation detection method investigated in this paper can significantly improve the accuracy and reliability of the heading parameter in land vehicle MEMS IMU/DGPS integrated navigation system.