Distributed Localization Algorithms for Wireless Sensor Networks: From Design Methodology to Experimental Validation 1 Distributed Localization Algorithms for Wireless Sensor Networks: From Design Methodology to Experimental Validation

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 ofmemory, and simplewireless transceivers. Over the last years, many novel applications have been envisaged for distributed WSNs in the area of monitoring, communication, and control. Sensing and controlling the environment by using many embedded devices forming a WSN often require the measured physical parameters to be associated with the position of the sensing device. As a consequence, one of the key enabling and indispensable services in WSNs is localization (i.e., positioning). Moreover, the design of various components of the protocol stack (e.g., routing and Medium Access Control, MAC, algorithms) might take advantage of nodes’ location, thus resulting in WSNs with improved performance. However, typical protocol design methodologies have shown significant limitations when applied to the field of embedded systems, like WSNs. As a matter of fact, the layered nature of typical design approaches limits their practical usefulness for the design of WSNs, where any vertical information (like, e.g., the actual node’s position) should be efficiently shared in such resource constrained devices. Among the proposed solutions to address this problem, we believe that the Platform–Based Design (PBD) approach Sangiovanni-Vincentelli (2002), which is a relatively new methodology for the design of embedded systems, is a very promising paradigm for the efficient design of WSNs. 1 In particular, the PBD methodology allows to define a standard set of services and interface primitives (called Sensor Network Services Platform or SNSP) that can bemade available to an application programmer independently from implementation issues on any (wireless) sensor network platform. In the depicted context, the present contribution reports our recent research advances along two main directions. Firstly, we exploit the PBD methodology for the efficient design of ad– hoc WSNs with localization capabilities. In particular, the PBD paradigm is used to derive a fully distributed positioning algorithm, and a general protocol architecture for WSNs. Secondly, we validate the suitability of a practical implementation of the proposed solutions onto commercially available WSN platforms, and analyze their achievable performance in realistic propagation environments. More specifically, the contributions of the present research work are as follows: 1) we will define a PBD–inspired Location Service (LS) along with its parameters and service primitives, which collects and provides network–wide information about the nodes’ spatial position, 2) we will introduce a novel iterative positioning algorithm, which is called Enhanced Steepest Descent – ESD Tennina et al. (n.d.), and will show, by using computer–based simulations, that it can outperform other well–known distributed localization algorithms in terms of estimation accuracy and numerical complexity, 3) we will analyze the implementation issues related on mapping the ESD algorithm onto the CrossBow’s MICAz sensor node platform, and investigate, via experimental activities, the effect of network topology and ranging errors on the performance of the proposed distributed localization algorithm, and 4) we will test the performance of the ESD algorithm during an extensive campaign of measurements conducted by using the Texas Instruments (TI)/Chipcon CC2431’s hardware location–finder engine in a realistic and dynamic indoor propagation environment. We will show that the ESD algorithm can be efficiently used to improve the localization accuracy provided by the CC2431’s location–finder engine. Moreover, as a byproduct of this latter experimental activity, we will show that the need of site–specific parameters for the correct operation of the CC2431’s location–finder engine may severely reduce the localization accuracy of the system in dynamic environments, as well as propose and validate a simple solution to counteract this problem.