We describe the architecture of iPOS (short for iPAQ Positioning System), a fault-tolerant and adaptive self-positioning system with quality-of-service guarantees for resource-limited mobile devices. The architecture is based on a novel sensor modelling technique in combination with a probabilistic data-fusion engine, which is capable of efficiently combining the location information obtained from an arbitrary number of location sensors. As proof of concept, we present a prototypical

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... ion and discuss an experimental evaluation of the iPOS system.