Research On Some Localization Problems Of Wireless Sensor Networks

Advances in micro-electro-mechanical-system have triggered an enormous interest in wireless sensor networks(WSNs),which consists of a large number of simple and inexpensive sensor device equipped with wireless communication interface.WSNs have been proposed for various applications including environment monitoring,disaster relief,surveillance and target tracking,so on and so forth.In these applications,sensed data is always meaningless without relating to its physical location.Furthmore,some middle ware services such as location aided routing need location information.So,it is very important to gain location of sensor node automatically.Because of the importance of localization,many localization procedures have been proposed in this field recently.All of these localization schemes are based on different assumptions,such as node desity,special hardware etc.They all have one or several shortcomings listed as below:special hardware devices are needed, non-distributed,poor scalability and high computation and communication complexity.Considering all these shortcomings,we first study localization problem for wireless sensor networks carefully,then we propose voronoi diagram based localization scheme VBLS and a collaborative localization scheme from connectivity (CLFC) for wireless sensor networks.Finally,we develop a prototype localization system for wireless sensor networks.The main research contents of this paper are listed as follows:First of all,we introduce a distributed,accurate and reliable Voronoi diagrams based localization scheme(VBLS),which makes use of received signal strength indicator(RSSI) from anchors.First,VBLS sorts received signal strength indicator in descending order.Then,we use unit disk graph to calculate the Voronoi area of anchors in turn.Finally,the overlapping region of different anchors' Voronoi area is identified as the possible region where sensor resides in.We compare our work via simulation with two other range-free localization schemes(W-Centroid and Centroid) to show the efficiency of VBLS.For random anchor placement,VBLS outperforms centroid scheme and W-centroid scheme significantly,estimation error decreases by 18%and 13%,respectively.For uniform anchor placement,VBLS gets a gain of 7% decrease and 2%increase of estimation error,respectively. Then,we present a collaborative localization scheme from connectivity(called CLFC) for wireless sensor networks.In this scheme,the connectivity information is used to improve the accuracy of position estimation.Relative positions between sensors are corrected to satisfy the constraints of connectivity.The scheme is composed by two phases:initial setup phase and collaborative refinement phase.In initial setup phase,DV-Hop is run once to get a coarse location estimation of each unlocalized sensor.In collaborative refinement phase,a refinement algorithm is run iteratively to improve the accuracy of position estimation.We compare our work via simulation with two classical localization schemes:DV-Hop and AFL.The results show the efficiency of our localization scheme.When compared with DV-Hop, estimation error of CLFC is reduced by 14%and 20%for random beacon deployment and fixed beacon deployment respectively.Furthermore,the proposed method CLFC is much better than the traditional mass-spring optimization based scheme AFL(Anchor Free Localization Scheme) in terms of convergence rate.This results in significant saving in message complexity and computation complexity.Finally,we design and implement a prototype localization system for wireless sensor network.First,we realize CLFC algorithm on MicaZ motes.The experiment results show that the use of connectivity information of unlocalized sensors can reduce location estimation error by 4%and 8%for fixed topology and random topology respectively.During the test of CLFC,we discover the irrigurity of RSSI information.After exploring the irrigurity carefully,we find that RSSI information not only depends on euclidean distance between sensor nodes,but it also depends on angle between sensor nodes.In order to reduce the effect of anisotropy on location accuracy,we design an interpolation-based localization scheme and implement it on MicaZ motes.Then,we test this localization scheme and show its efficiency.