IMU-based enhancement of GPS attitude determination

Abstract: GPS carrier-phase measurements from two GPS antennas can be used to calculate the heading of the baseline that can be drawn between the two antennas. An integer ambiguity problem has to be solved, and the system is called GPS attitude determination (GPSAD). This way of calculating the heading is cheaper than the traditional ways to do it, but it requires GPS reception. This thesis investigates how and if an inertial measurement unit (IMU) can support the GPS-based system, and divides the question into four problems: heading estimate during GPS outages, reducing the ambiguity search space, cycle slip detection and multipath mitigation. A relatively cheap IMU was used, and an extended Kalman filter (EKF) was implemented to continue to supply heading estimates during GPS outages with a drift less than 1/min in the studied case. When the GPS reception is good enough after an outage, the EKF supplies the GPSAD with an interval of the heading estimate to reduce the ambiguity search space. It has been investigated how to detect and deal with cycle slips, and the conclusion is that an IMU can help with detecting the slips, although nothing has been implemented. Multipath is still an issue, but some approaches to reduce the effect are suggested. The overall performance of the system is greatly increased with the help of an IMU. Performance increasing work can still be done, especially for the cooperation between the GPSAD and the EKF.