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Top1. Introduction
Wireless sensor network (WSN) is a wireless network that consists of low-priced, less energy tiny nodes called sensors along with a central server called base station. The sensor nodes examine the event and send the event information to the Base station via multi-hop communication (Liu, Nayak, & Stojmenovic, 2010). In location-based applications, location information of sensor node that has detected the event is also significant along with event information. Thus, Localization, a way to find the location of a sensor node, is a very important problem.
With respect to the hardware required for computing the coordinates of the node, the localization algorithms can be divided into two categories: range-based and range-free (He, Huang, Blum, Stankovic, & Abdelzaher, 2003). Range-based need expensive equipments to find distance estimates or angle estimates between nodes (Kunz & Tatham, 2012). Range-free algorithms derive location information using approximate distance estimates between nodes (Panwar & Kumar, 2012; Niculescu & Nath, 2003;
Zhang, Ji, & Shan, 2012). These algorithms estimate the location by using approximate distances from anchor nodes (Song & Tam, 2015). Here a sensor node which knows its location is called anchor node and sensor node which does not know its location is called non-anchor node (Alrajeh, Bashir, & Shams, 2013; Nagpal, Shrobe, & Bachrach, 2003; Bahl & Padmanabhan, 2000). Due to hardware limitations, range-free algorithms like DV-Hop (Niculescu & Nath, 2003) achieve cost effectiveness but have low localization accuracy (Tomic & Mezei, 2016). The anchor nodes play an important role in deciding the location of non-anchor nodes in range-free algorithms. In these range-free algorithms, normally all the anchors in the network are required to determine the location of the non-anchor node. But rather than considering all anchor nodes, if only a few near anchors are considered then it is easier to locate a node with better precision. Thus it is more significant to study the influence of near anchors on DV-Hop based algorithms to improve their localization accuracy.
In this paper, most of the known DV-Hop based algorithms are surveyed and the effect of the closest anchors is explored. Improvement gained by considering only a few near anchors instead of all the anchors for finding the location of non-anchor nodes in their last phase has been evaluated. These improved algorithms have been compared with original algorithms to analyze the impact of the closest anchors on the localization error. It is observed that the closest anchors have a significant impact in reducing localization error of all these algorithms.