Novel approach to GPS/SINS integration for IMU alignment

Strapdown inertial navigation system (SINS) requires an initialization process that establishes the relationship between the body frame and the local geographic reference. This process, called alignment, is generally used to estimate the initial attitude angles. This is possible because an accurate determination of the inertial measurement unit (IMU) motion is available based on the measurement obtained from global position system (GPS). But the update frequency of GPS is much lower than SINS. Due to the non-synchronous data streams from GPS and SINS, the initial attitude angles may not be computed accurately enough. In addition, the estimated initial attitude angles may have relatively large uncertainties that can affect the accuracy of other navigation parameters. This paper presents an effective approach of matching the velocities which are provided by GPS and SINS. In this approach, a digital high-pass filter, which implements a pre-filtering scheme of the measured signal, is used to filter the Schuler cycle of discrete velocity difference between the SINS and GPS. Simulation results show that this approach improves the accuracy greatly and makes the convergence time satisfy the required accuracy.