Device-free localization using redundant 2.4 GHz radio signal strength readings

Radio-based device-free localization (DFL) for indoor environments are based on signal anomalies due to obstacles on the line-of-sight (LOS) between previously applied reference nodes. They take use of radio signal strength (RSS) attenuation (radio tomographic imaging, RTI) or variations caused by shadowing and small-scale fading effects. An advanced methodology using redundant RSS information for each pair of reference nodes is proposed. The method uses a moving RSS variance estimator and antenna diversity with four uncorrelated 2.4 GHz radio channels to predict the user´s position. With the redundant RSS values the accuracy of user detection is increased by more than 50 % while the number of false positives is reduced to zero. Tracking results in a hallway test bed illustrate the behavior and improvements of the applied redundant sensor technique.