Wireless sensor nodes can act as distributed detectors for recognizing activities online, with the final goal of assisting the users in their working environment. We propose an activity recognition architecture based on fuzzy logic, through which multiple nodes collaborate to produce a reliable recognition result from unreliable sensor data. As an extension to the normal fuzzy inference, we incorporate temporal order knowledge of the sequences of operations involved in the activities. The performance evaluation is based on experimental data from a car assembly trial. The average recognition accuracy is 93.53\%. We also present early experiences with implementing the recognition system on sensor nodes. The results show that the algorithms can run online, with execution times less than 40ms for the whole recognition chain and memory overhead in the order of 1.5kB RAM.
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