Infra-free Indoor Positioning Using only Smartphone Sensors

Though a variety of indoor positioning systems have been proposed for a GPS-denied environment, most of them depend on dedicated devices which must be installed in a building. The preparation of this infrastructure usually entails considerable cost, which prevents the spread of indoor positioning technology. On the other hand, smartphones are already widespread and their low cost sensors are promising as rich data sources that can be used for indoor navigation. Several studies have demonstrated the possibility of smartphone-based infrastructure-free positioning. However, this navigation is not yet practical because of the accumulative error of inertial sensors and the communication range measurement error. We propose a solution to reduce the accumulative error of pedestrian dead reckoning carried out with only the low cost sensors and WiFi in smartphones by realizing cooperative positioning among multiple pedestrians. Our proposed method introduces linkage structures to simplify trajectories of pedestrians; these structures work as a constraint to reduce the number of variables to be estimated. Since this constraint makes positioning problems solvable with a small number of observations, our proposed method screened WiFi data by the signal strength and selected only strong signals for use in positioning. Our testing results showed that the positioning accuracy improved as the number of participants in the cooperative positioning operation increased. The positioning uncertainty was a few meters, comparable to GPS, when the density of participants is high enough.