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Real-Time Relative Positioning with WSN

Aranha, ; Rocha, R.

Real-Time Relative Positioning with WSN, Proc International Conf. on Sensor Technologies and Applications, Cap Esterel, France, Vol. 1, pp. 10 - 16, August, 2008.

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The continuous development of wireless and MEMS technology gave rise to a new type of networks composed of tiny nodes interconnected wirelessly – the Wireless Sensor Networks (WSN). Comprising usually a high number of nodes, which have the mission of collecting information and forward it to a central node, these networks have a spontaneous nature being self-organized in an Ad-Hoc fashion.
This paper addresses a scenario where a WSN is used to implement a real-time positioning system. Its goal is to obtain relative coordinates of objects (the WSN nodes) in which the nodes are generally moving relatively to each other. To accomplish this, the distance among nodes is measured and its relative position is computed allowing the representation of their spatial distribution.
The test platform uses Crossbow’s motes to which special ultrasound (US) boards have been adapted. The US is thus the process used to measure distances in this system. Some of the issues addressed by this work are: precise time-synchronization between nodes, distance measurement procedure, positioning algorithms and its implementation on the TinyOS, Operating System used in the Crossbow’s motes. Tests have shown that object positioning could be obtained with errors below 2% and using a computing time of about 1s per network node, on average.