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An integrated hardware and software system for a scalable wireless sensor network ͑WSN͒ is designed and developed for structural health monitoring. An accelerometer sensor node is designed, developed, and calibrated to meet the requirements for structural vibration monitoring and modal identification. The nodes have four channels of accelerometers in two directions and a microcontroller for processing and wireless communication in a multihop network. Software components have been implemented within the TinyOS operating system to provide a flexible software platform and scalable performance for structural health monitoring applications. These components include a protocol for reliable command dissemination through the network and data collection, and improvements to software components for data pipelining, jitter control, and high-frequency sampling. The prototype WSN was deployed on a long-span bridge with 64 nodes. The data acquired from the testbed were used to examine the scalability of the network and the data quality. Robust and scalable performance was demonstrated even with a large number of hops required for communication. The results showed that the WSN provides spatially dense and accurate ambient vibration data for identifying vibration modes of a bridge.

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Many applications in Wireless Sensor Networks, including structure monitoring, require collecting all data without loss from nodes. End-to-end retransmission, which is used in the Internet for reliable transport, becomes very inefficient in Wireless Sensor Networks, since wireless communication, and constrained resources pose new challenges. We look at factors affecting reliability, and search for efficient combinations of the possible options. Information redundancy like retransmission, and erasure codes, can be used. Route fix, which tries alternative next hop after some failures, also reduces packet loss. We implemented and evaluated these options on a real testbed of Berkeley Mica2Dot motes. Our experimental results show that each option overcomes different kinds of failures. Link-level retransmission is efficient but limited in achieving reliability. Erasure code enables very high reliability by tolerating packet losses. Route fix responds to link failures quickly. Previous work had found it difficult to increase reliability past a certain threshold. We show that the right combination of primitives can yield more than 99% reliability with low overhead, providing a viable alternative to end-to-end retransmission over multiple hops.

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Designing a new sensor board is costly, especially for a production in a small quantity. By modularizing common functionalities, a large portion of the sensor board can be reused. In this work, we propose an Extension Board, a sensor board which is modularized into 3 parts. Power module, and MCU and RF module are shared, and only sensing module is redesigned for each sensor board. Diverse sensing modules are produced. The process was simple and inexpensive.

A main challenge with developing applications for wireless embedded systems is the lack of visibility and control during execution of an application. In this paper, we present a tool suite called Marionette that provides the ability to call functions and to read or write variables on pre-compiled, embedded programs at run-time, without requiring the programmer to add any special code to the application. This rich interface facilitates interactive development and debugging at minimal cost to the node.