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In this paper, we propose the cluster-based hierarchical time synchronization protocol (CHTS) for wireless sensor networks (WSN). To couple the network with real world tightly, we provide a network-wide time synchronization through the introduction of abstractions for cluster and hierarchy. Generally the error of time synchronization has the tendency of(More)
In this paper, we present DGS, a driving guidance system based on wireless sensor networks (WSN) which guides a driver to drive a car in safety. The system consists of two sub-systems: SMS (speed measurement sub-system) and WPS (weather information providing sub-system). SMS measures the speed of a car and captures the image of the speeding car using a(More)
With low-power consumption, small code and data size, evolvability as design criteria, we develop an evolvable operating system (EOS) for wireless sensor network applications. The EOS provides memory space efficient thread management, collaborative thread communication model and network stack. It also supports power management of microcontroller and radio(More)
A sinkhole is occurring in urban area all over the world frequently, in fact, it is a roadside subsidence in geological terminology, which can harm property and safety of government and many people. To detect the roadside subsidence earlier, we monitor the aged or damaged underground infrastructures, report the sensed the values to analyzing system, and(More)
We consider a problem of retrieving the extreme value among sensed data under deadline constraints in wireless sensor networks with potential applications to alarm systems. The sensed data is mapped to a score which we adopt as a unified measure of the relative urgency of the data. The objective is to retrieve the data with the maximum score. We propose(More)
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