Pedestrian Tracking by Acoustic Doppler Effects

Localization is the foundation of location-based services and has received considerable attention recently. Pedestrian dead-reckoning (PDR) systems are widely used to infer user positions. However, a main problem is that the errors may easily accumulate during multiple integrations. In this research, we exploit the frequency shift of a wave caused by relative movement, i.e., the Doppler effect, of feet to infer user movement for locating user's location. Specifically, when the two feet of a person move, the relative movements exhibit self-Doppler effect. This observation allows us to implement a PDR system by mounting two speakers and one microphone on shoes. The advantage is that the displacement can be inferred by integration once, as opposed to twice for accelerometers. To investigate the performance of our system, we evaluate its capability in measuring step event, step length, and step direction. Field trial results are presented, which show that our approach performs very well in step detection with 99.6% accuracy and step length estimation with error $\approx 0.0073$ m. However, its direction estimation is still not accurate enough and, thus, needs the help of other sensors.