Enhancing the performance of indoor localization using multiple steady tags

Indoor localization based on signal strength fingerprinting has received significant attention from the community. This method is attractive because it does not require complex hardware beyond off-the-shelf radio transceivers. However, its main limitation is the inaccuracy caused by the variability of the signal strength. When applied to the localization of people, the signal variability can be attributed to three main sources: environmental dynamics (movement of people or objects), movement of transceiver (changes in the position and/or orientation of the transceivers) and body effects (distortion of the wireless signal due to body absorption). Our work focuses on the impact of the last two sources and provides two important contributions. First, we present an analysis to quantify the effects of antenna disorientation and transceiver misplacement. For the RFID system used in our work, these effects can decrease the localization accuracy by up to 50%. Motivated by these results, we identify parts of the human body where tags are less affected by unintentional movements and describe how multiple transceivers can be used to overcome the absorption effects of the human body. We validate our findings through an extensive set of measurements gathered in a home environment. Our tests indicate that by following a set of simple guidelines, we can increase the localization accuracy (the percentage of correct location estimations) by a factor of four (from 20% to 88%), and reduce the maximum localization error (from 7 to 4 m).