Hansel: Distributed Localization in Passive Wireless Environments

This work presents a distributed routing protocol to help mobile users locate items in passive wireless environments. In these environments, a mobile user can detect items that are in its proximity, but items can not communicate directly with each other. For example, an area where passive RFID tags are embedded in the environment and mobile users are provided with RFID readers. The localization protocol is based on the following idea: while searching for a specific node, mobile users populate the memory of the nodes they encounter with information about the nodes they have already seen; later, this information is used to guide other users. The contribution of our work is to demonstrate the feasibility of the proposed protocol, in particular, we provide: (a) a lower bound for the required memory space (in the nodes) to store routing information, (b) a proof that disseminate-while-search routing is loop-free and (c) an study on the extent of user mobility required to disseminate the routing information. A proof-of-concept of the proposed protocol was implemented in a small test-bed of MicaZ motes resembling a passive environment.