A localization scheme for wireless sensor networks is proposed and its performances are investigated in this paper. The proposed scheme is an anchor-free scheme, in which no geometrical information of sensor nodes is required for their localization. Thus, only local interaction among sensor nodes is used to estimate their locations. This scheme employs the link quality indicator and hop count between sensor nodes for location estimation. A weighted averaging and Kalman filtering schemes are incorporated in order to reduce the effects of the measurement errors in the obtained values of the link quality indicator. We performed experiments by implementing the proposed scheme on ZigBee sensor modules. The results of our experiments indicate that estimation could be successfully performed for networks comprising four sensor nodes. 1. Introduction A wireless sensor network (WSN) is a network that consists of many sensor nodes. Each sensor node has sensing devices, a processor, and a battery. Communications among sensor nodes are typically conducted via radio frequency (RF) signals. Localization is a process of estimating the location of each sensor node in a WSN. It has potential applications such as environmental monitoring, human and object tracking, and human interfacing. Several approaches based on communication between sensor nodes have been proposed to achieve localization in WSNs [1–5]; many of these approaches involve the use of anchor nodes to implement localization. Anchor nodes are sensor nodes whose location coordinates are set either manually or by using a global positioning system (GPS). The use of anchor nodes facilitates localization; however, this technique has an inherent drawback in that localization cannot be achieved if some of the anchor nodes accidentally break down, even if the remaining nodes continue to function. In addition, GPS-based configuration of anchor nodes is ineffective in indoor environments where RF signals from satellites cannot reach. Hence, investigating localization schemes without anchor nodes, that is, anchor-free localizations, becomes important, for the abovementioned applications and also for supporting the functionalities of anchor-based localization schemes. Several researches concerning anchor-free localization schemes have been proposed [6–9]; however, many of the proposed schemes are evaluated only by computer simulations and there are only a few investigations for anchor-free localization with experiments in the real world [10]. We have previously proposed an anchor-free localization scheme and implemented
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