Use of magnetic quasi static field (QSF) updates for pedestrian navigation

This paper assesses a novel method of using a quasi-static magnetic field to provide updates to the navigation (i.e. attitude) filter. The method is able to make use of magnetometer measurements in a perturbed magnetic field, under the condition that the field´s magnitude remains constant for short periods of time. The fact that magnetometer measurements can still be used in perturbed environments makes this update significant in terms of incorporating the magnetometer measurements into a navigation solution. The QSF process requires a detection algorithm to first identify quasi-static fields and second to perform the update. Thus this paper applies the QSF algorithm in a navigation filter to assess its performance in GNSS degraded or denied environments. Data sets are used to assess QSF updates. These range from open athletic fields to deep indoors where GPS signals are denied. The environments vary in terms of soft iron effects. The data was collected with high grade miniature MEMS IMUs, a high sensitivity GPS receiver and a low cost magnetometer. An accurate reference solution is derived from a tactical grade IMU. For the backpack mounted IMU the application of QSF updates yielded a 56 % heading error improvement when used as a heading reference system. For a corresponding ankle mounted system the application of QSF updates yielded a 56 % improvement in the position error (RMS) when used as a pedestrian navigation system. The maximum error over a 45 minute GPS outage decreased from 208 m to 128 m. The updates do not significantly decrease the estimated gyro error state variances, indicating that it is more suited for gyros and magnetometers with a lower performance than those used herein.