An indoor magnetic field matching positioning solution based on consumer-grade IMU for smartphone

Abstract

Magnetic field matching positioning (MFMP) has become one of the mainstream indoor positioning methods for mass application. However, the problem of the large workload of magnetic field mapping and the instability of the magnetometer bias remains to be solved. This paper designs an indoor MFMP scheme based on consumer-grade Inertial Measurement Units (IMUs). In the magnetic field mapping stage, the high-precision poses of the smartphone obtained by combining a foot-mounted IMU, a smartphone built-in IMU, and a few control points in the building are employed to generate a magnetic field grid map with high efficiency. In the real-time positioning stage, the relative trajectory generated by pedestrian dead reckoning (PDR) is used to improve the position discrimination of the magnetic field feature by adding spatial profile; and the differential magnetic field strength in the sensor frame (instead of in the reference frame) is used to achieve matching positioning that is immune to the magnetometer bias. The consistency of the magnetic field maps built using different smartphones show that the proposed magnetic mapping scheme achieves an average efficiency of 37 m2 /min and is not affected by the mapping trajectory and walking speed. The real-time positioning results using multiple smartphones show that the proposed MFMP algorithm is barely affected by the magnetometer bias, and can achieve an average RMS value of ±0.83 meters in a typical office scenario.