Method for estimation of distance between objects and its application for finding lost objects

In this paper, we propose a method to estimate the distance between objects attached with radio-frequency identification (RFID) tags that are used for finding lost objects. Many systems for finding lost objects adopt real-time location systems (RTLSs) using received signal strength indication (RSSI). The fundamental structure of a general method for an RTLS using RSSI involves the creation of a number of reference nodes whose locations are known in advance. Crowded objects often form a group; hence, it is very helpful to find some object members of the group in a certain place so as to find the lost object belonging to the group. However, an RTLS is not required to know the objects located in a certain place or to estimate the distance between these objects. Hence, we propose a method to estimate the distance between objects rather than the individual object locations without using a method to obtain location-dependant information.