AnchLP: An Anchor-Based Localization Protocol for Wireless Sensor Networks Ash Mohammad Abbas, Hamzah Ali Abdulrahman Qasem Department of Computer Engineering Aligarh Muslim University, Aligarh - 202002, India am.abbas.ce@amu.ac.in, hamzahinda@yahoo.co.in Abstract—Devising a protocol for localization in a wireless sensor network is a formidable task. In this paper, we present a localization protocol for a wireless sensor network. In our protocol, a sensor computes its location using the locations of either anchors or sensors whose locations are already computed, and their distance estimates. Our protocol is distributed and does not need the availability of the topological information of the whole network at a centralized sensor before starting the computation. Our protocol is asynchronous as it does not need the clocks of sensors to be synchronized. Each sensor relies on its local clock. Our protocol is scalable and can be applied to a network irrespective of its size. We evaluate the performance of the proposed protocol by carrying out simulations. We study the effect of the number of anchors and the transmission range of sensors on the localizability and the error of localization. Further, we provide an expression for computing the probability that a sensor is localized in a sensor network. Index Terms—Localization, anchors, wireless sensor networks. I. I NTRODUCTION A Wireless Sensor Network (WSN) is a collection of sensor devices that are connected with one another using wireless links. The sensor devices are often used to gather information about some specific parameters, which can then be sent to a centralized station for further processing. There can be several applications of a sensor network such as health monitoring, environmental monitoring, controlling forest fires, monitoring the movement of wild animals, tracking an object, and detect- ing infiltration across the line of control (LoC). In some applications of a WSN, it is required to locate the sensors sending particular data. For example, if the tem- perature in the vicinity of a particular sensor is suddenly increasing, it is required to know its location so as to take corrective measures. An alternative can be that all sensors possess Geographic Positioning System (GPS) devices. How- ever, sensor nodes are spread in significantly large quantities, therefore, it does not seem to be a cost-effective solution. As a result, we need a scheme other than GPS to locate the sensors. There are many characteristics of a WSN that distinguish it from other types of networks. Firstly, the computational and communication capabilities of sensors are very small, and therefore, a protocol or scheme should not require exces- sive computational and communication overhead. Secondly, sensors are mostly operated through built-in batteries whose powers are often limited. The depletion of the battery power may result in failure of a sensor and the associated links to other sensors. Further, the information about the whole sensor network is not available at a centralized sensor. The partial information about the topology of the sensor network requires the localization protocol or scheme to be distributed. These characteristics make the localization a challenging task in a WSN. Many researchers have proposed localization schemes for wireless sensor networks from different perspectives. Local- ization using a WSN may find applications in games such as a cricket location support system [1] and in child care such as a smart kindergarten [2]. Schemes for outdoor localization are proposed in [3] and [4]. A centroid-based localization scheme is proposed in [5]. A scheme called RADAR for finding and keeping track of the locations of users is proposed in [6]. In [7], an organization of a global coordinate system using local information obtained from an ad hoc WSN is described. Schemes that do not measure distances for locating a sensor are often called range-free schemes. Range-free schemes for a WSN are proposed in [8], [9]. The performance of range- free schemes for computing locations of sensors in a wireless sensor network is evaluated in [10]. A survey of schemes for finding locations of sensors in WSNs is presented in [11]. An anchor-based scheme for locating a sensor in irreg- ular areas is proposed in [12]. A localization scheme for an anisotropic network is proposed in [13]. A method for computing the locations of sensors in a network with concave areas is proposed in [14]. Schemes for finding locations of objects in an Under-Water Sensor Network (UWSN) are proposed in [15] and [16]. A method for finding locations of sensors in a WSN using Angle- of-Arrival (AoA) is proposed in [17]. A positioning system called Ad hoc Positioning System (APS) that uses AoA is proposed in [18]. A GPS-free localization using directional antennas with dual wireless radios is proposed in [19]. There are schemes based on Monte-Carlo Localization (MCL) [20] including Sequential Monte-Carlo Localization (SMCL) [21], Monte-Carlo Sensor Localization (MSL*) [22], Weighted Monte-Carlo Localization (WMCL) [23]. All these schemes are range-free. A version of MCL that is range- based is proposed in [24]. A localization scheme based on Semi-Definite Programming (SDP) for a WSN with noisy environment is proposed in [25]. A localization scheme based on Multi-Dimensional Scaling (MDS) is proposed in [26]. A quantitative comparison of localization schemes for WSNs is presented in [27]. 2122 978-1-4799-3080-7/14/$31.00 c 2014 IEEE