Research on calibration-free fingerprinting positioning techniques based on terrestrial magnetism databases for indoor environments

Location-based services (LBSs) in such indoor places as museums, airport terminals, and train stations are becoming more and more popular among smartphone users. Hence, the research on indoor positioning technologies is increasing. Indoor positioning technologies using Wi-Fi or Bluetooth wireless signals have some problems that cannot be overcome, for example, inconsistent data caused by human body shadowing effects. Positioning accuracy and stability still need to be improved to provide higher quality LBS applications. Smartphones have built-in geomagnetic and acceleration sensors, and the Earth's magnetic field is not affected by human body shadowing effects, so it increases the appeal of using geomagnetism to enable indoor positioning with smartphones. This article proposed approaches in light of calibration-free fingerprinting positioning techniques with terrestrial magnetism databases for indoor environments. For the differences in measurements yielded by various mobile phone (MP) models and brands, adjustments can be made using the ratio of the total intensity of the magnetic field and its horizontal component to correct the discrepancies. Finally, with the arrangement of four landmarks, the average error distance of the research results in the experimental environment is 3.59 m. The average accuracy of the k-nearest neighbour (k-NN) mobile phones is 71.3%.