Energy Constraints of Localization Techniques in Wireless Sensor Networks (WSN): A Survey <s> Distance Vector Hop (DV-Hop) <s> Sensor localization has become an essential requirement for realistic applications over wireless sensor networks (WSN). Radio propagation irregularity and the stringent constraint on hardware cost, however, make localization in WSN very challenging. Range-free localizations are more appealing than range-based ones, since they do not depend on received signal strength to estimate distance and thus need simple and cheap hardware only. In this paper, we propose a ring-overlapping, range-free approach using the Ring Overlapping based on Comparison of Received Signal Strength Indicator (ROCRSSI). Simulation results have verified the high estimation accuracy achieved with ROCRSSI. <s> BIB001 </s> Energy Constraints of Localization Techniques in Wireless Sensor Networks (WSN): A Survey <s> Distance Vector Hop (DV-Hop) <s> In this paper, we perform thorough performance evaluation on two novel range-free localization methods, approximate point in triangle (APIT) [T. He et al. (2003)] and ring overlapping based on comparison of received signal strength indicator (ROCRSSI) [C. Liu et al. (2004)]. We disclose the inherent "undetermined node" problem of APIT, and investigate the system configurations that directly influence the performance of both methods, including anchor deployment strategies, which are ignored by most existing papers. We also illustrate the relationship between these configurations and the achievable estimation accuracy. <s> BIB002 </s> Energy Constraints of Localization Techniques in Wireless Sensor Networks (WSN): A Survey <s> Distance Vector Hop (DV-Hop) <s> Wireless sensor network (WSN) are more and more widely used in many different scenarios. The localization information is an important criterion for the capability of WSN. Nowadays, there are many localization algorithms. DV-hop is a classical Range-free localization algorithm, by which unknown nodes can obtain anchors' information within designated hops, and estimate the distances from themselves to anchors. Unknown nodes then use the information to localize themselves. But the estimative distances may incur large error, and will jeopardize the localization precision. In order to solve the problem, we propose a selective anchor node localization algorithm (SANLA) for wireless sensor networks in this paper, and it can make unknown nodes choose three anchors which are the most accurate to execute trilateration. The experiment results illustrate that our algorithm is valid and effective. <s> BIB003 </s> Energy Constraints of Localization Techniques in Wireless Sensor Networks (WSN): A Survey <s> Distance Vector Hop (DV-Hop) <s> Aiming at the positioning problem of wireless sensor network node location, an improved DV-hop positioning algorithm is proposed in this paper, together with its basic principle and realization issues. The proposed method can improve location accuracy without increasing hardware cost for sensor node. Simulation results show that it has good positioning accuracy and coverage. The influences of anchor nodes on the DV-hop algorithm are also explored in the paper. <s> BIB004
DV-Hop localization is a distributed, hop-to-hop positioning algorithm. Anchor nodes generate packets including their position information and a flag which is initialized as one to figure the number of hops away from them. These packets are broadcasted into WSN. When they are transmitted by the intermediate nodes, the hop number is increased by one. In this way, any node can determine the hop number from it to a certain anchor node. Similarly the anchor nodes can compute their hops to other anchors as well. The average distance for each hop can be computed by a simple formula and then will be broadcasted. When an unknown node receives it, the receiver will estimate its distance to the anchor node. The location can be figured out by trilateration BIB003 [33] [34] BIB004 , after an unknown node obtains three or more estimated values from anchor nodes. Position of anchor nodes also has a major effect on the localization accuracy BIB003 in the implementation of this technique. Most proposals using this technique assume a network where all nodes are in clear line of sight with each other, but in real applications nodes may have obstacles between them making the signal go round these obstacles which might not give clear indication of the actual hop count distance between an anchor node and an unknown node. To solve the problem BIB003 proposed a selective anchor node localization algorithm (SANLA). It is also evident that the number of anchor nodes does not necessarily increase the precision of the localization technique when using hop count. This technique involves internode communication and depends on anchor nodes. It has high accuracy in clear lineof-sight to the anchor nodes, but localization can be erroneous when there is no line-of-sight to anchors. It does not require any extra hardware. achieving higher estimation accuracy with lower communication overhead. However, in BIB001 , only a rough comparison on the performance of APIT and ROCRSSI is provided. In BIB002 a more detailed simulation results is presented to demonstrate that ROCRSSI effectively alleviates the "undetermined node problem and outperforms APIT in terms of achievable estimation accuracy and energy efficiency. Furthermore, system configurations that directly affect the performance of ROCRSSI are investigated thoroughly, and the achievable estimation accuracy under different system configurations is presented as guidelines of deciding system parameters when using ROCRSSI for sensor localization. If all directional antennas are used in a consistent environment, an isotropic radio attenuation model can be assumed and ROCRSSI can get the best estimation accuracy. Although ROCRSSI depends on the consistency of radio transmission in a wide range of directions, the estimated location errors by ROCRSSI are generally small even under circumstances with very irregular radio propagation BIB001 . This technique has a better accuracy compared to APIT and has low localization error in both line-of-sight and Non line-ofsight. This technique depends on RF signal strength and the configuration of its antennas which adds to the power consumption of the nodes in the network. 