II. SATISFACTION OF REQUIREMENTS
We applied several technologies to the system in order to satisfy the requirements which are described in Section 1. For Requirement (1), we use the Android terminals, to which we can install application freely without dependence of manufacturers or carriers. Therefore, we are able to implement and get functions smoothly. For Requirements (2) and (3), we adopt the Autonomous Clustering technique. It is necessary to compose groups autonomously, because the system must deal with various mobilities of children. Thus, we apply the Autonomous Clustering technique to smooth collection of children information. We have Bluetooth communication between the Android terminals. Compared with wireless LAN, it can mitigate the radio wave interferences because of its radio’s limited power. Additionally, Bluetooth FHSS also helps mitigation of the interference caused by tags in the Mesh Networks and other radio waves. For Requirement (4), we construct the Mesh Network consisting of tags with wireless LAN. The cost of maintaining the system is cheaper than that of the Hiroshima City Tracking System which uses the mobile cell phone network. We implement the ad hoc routing protocol which maintains multi-path routes to tags. For Requirement (5), we apply the Secret Sharing Scheme for their secure end-to-end communication in the Mesh Network. Encrypted and distributed information is delivered to the server through multipaths. Therefore, it is secure against suspicious individuals.