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Determining the positions of nodes is essential in many applications and geographic routing protocols of Wireless Sensor Networks. Since localization is a fundamental component of sensor networks, the cost for localization itself should be minimized. In this paper, we focus on developing a localization algorithm which provides both low-cost and accuracy. Considering these requirements, we propose a novel range-free localization technique, called HCRL, which uses only the ratios of anchor-to-node hop-counts. HCRL satisfies low-cost with a single flooding from a small number of anchor nodes, and subdivides one-hop into several sub-hops by transmission power control to improve localization accuracy. Unlike previous work, we have conducted real experiments, which were made possible by using an external antenna with an omni-directional radiation pattern. The experimental results show that the performance of HCRL is superior to the conventional DV-Hop scheme with a small transmission overhead.

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Discovering the location of the mobile nodes carried by people is important issue for many sensor applications. Several localization techniques have been proposed, but human mobility patterns and collaboration between mobile nodes have been seldom considered. In this paper, we propose a mobile node localization system based on collaboration and route information that characterizes human mobility. To validate the feasibility of our approach, the proposed system is implemented and experiments are conducted on real routes and to evaluate various scenarios, simulation experiment was also conducted.

An ultrasound tracking system is an inexpensive and accurate technique for indoor object tracking. In this paper, we describe an IEEE 802.15.4-based active tracking system that tracks multiple mobile objects effectively. We analyze the problems of the active tracking system with multiple objects and propose an adaptive beaconing algorithm as the solution. In our algorithm, mobile nodes overhear the beacon messages of other mobile nodes and adaptively adjust their beaconing periods to avoid a simultaneous ultrasound pulse. We implemented the tracking system in a real environment and measured the performance of the system. The experimental results show that our algorithm successfully works with multiple mobile nodes and improves performance on the success rate.