| Recent advances in the technology of wireless electronic devices have made possible to build ad-hoc Wireless Sensor Networks (WSNs) using inexpensive nodes consisting of low power processors, a modest amount of memory and simple wireless transceivers. Over the last years, many novel applications have been envisaged for distributed WSNs in the area of monitoring, communication and control. One of the key enabling and indispensable services in WSNs is localization (i.e., positioning), given that the availability of nodes' location may represent the fundamental support for various protocols (e.g., routing) and applications (e.g., habitat monitoring). Furthermore, WSNs are now being increasingly used for real-time applications having stringent Quality-of-Service (QoS) requirements, such as timeliness and reliability. Towards this end, Zigbee/IEEE 802.15.4 and the Cluster-Tree model are considered among the most promising candidates. Building from (i) our proposed Enhanced Steepest Descent (ESD) algorithm to solve positioning of nodes in a fully distributed fashion, (ii) the mechanism to evaluate at run-time the site-specific parameters for the correct operation of the ESD (i.e., RSSI-based ranging) and (iii) the recent availability of Zigbee/IEEE 802.15.4 implementations over TinyOS, the main output of this paper is to outline how a positioning service can be fully integrated into a communication protocol stack. |
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