Location information acquisition is crucial for many wireless sensor network (WSN) applications. While existing localization approaches mainly focus on 2D plane, the emerging 3D localization brings WSNs closer to reality with much enhanced accuracy. Two types of 3D localization algorithms are mainly used in localization application: the range-based localization and the rangefree localization. The range-based localization algorithm has strict requirements on hardware and therefore is costly to implement in practice. The range-free localization algorithm reduces the hardware cost but at the expense of low localization accuracy. On addressing the shortage of both algorithms, in this paper, we develop a novel hybrid localization scheme, which utilizes the range-based attribute RSSI and the range-free attribute hopsize, to achieve accurate yet low-cost 3D localization. As anchor node deployment strategy plays an important role in improving the localization accuracy, an anchor node configuration scheme is also developed in this work by utilizing the MIS (maximal independent set) of a network. With proper anchor node configuration and propagation model selection, using simulations, we show that our proposed algorithm improves the localization accuracy by 38.9% compared with 3D DV-HOP and 52.7% compared with 3D centroid. Recently, there has been growing interest in localization protocols that utilize the network topology characteristic [15] . CATL [12] splits the whole rugged network into several subsections and then carries out the localization in each subnetwork. It optimized the anchor node configuration to improve 2 International Journal of Distributed Sensor Networks localization accuracy. Considering the node deployment strategy [16] , the 3D range-free techniques always have strict network connectivity requirements, making them unsuitable for the large scale sensor networks. In this paper, we propose a hybrid localization approach to overcome the shortage of range-free and range-based algorithms, by combining RSSI value and hop distance for 3D WSN localization, henceforth referred to as 3D-RDH algorithm. Our proposal utilizes the range-free technique by blending the RSS information under a proper selected model. As RSS data can be easily collected with current off-theshelf equipment, it is the basis of many popular techniques for inferring the relative positions of the nodes in a WSN, whereas DV-HOP uses the network connectivity information to estimate unknown node location, especially considering the connectivity of 3D sensor network much higher than the 2D case. Inspired by the idea of virtual backbone [17] of a wireless sensor network, we place anchor nodes in the network based on maximum independent set (MIS) of the network to further improve the localization accuracy. Experimental results show that our proposal can achieve much higher localization accuracy compared with existing proposals. Towards the accurate localization, a key is to identify the hybrid approach of localization and extract a graph of the network for anchor node configuration during deployment, which is, however, often impractical to achieve in reality. This is attributed to many fundamental engineering challenges as follows. Firstly, there is a lack of understanding of selecting proper localization techniques. Secondly, there are available schemes from the computer graphics community to find an independent set. They target high connectivity and low cost. The network is discrete and a sensor node can only obtain local information via message exchanges. A low communication complexity scheme to identify a MIS is necessarily required considering the limited resource of each sensor node. Lastly, since an independent set is discrete and arbitrary, it is not easy to clearly specify which nodes in a MIS can be selected as the anchor nodes. In this paper, we address the aforementioned challenges in one framework. Our key contributions can be summarized in three key points.
Zhang et al. put forward a hybrid localization approach REF to overcome the weakness of range-free and range-based algorithms by combining RSSI value and hop distance for 3D WSN localization.
A Hybrid Localization Approach in 3D Wireless Sensor Network
International Journal of Distributed Sensor Networks
Computer Science