Research On Node Localization Technology For Wireless Sensor Networks

Wireless Sensor Networks(WSNs)have widely applied in military and other fields due to the characteristics of random delivery and self-organization.Node localization is the foundation of WSNs' applications.The locations of the nodes affect practicality,accuracy and effectiveness of WSNs and the node localization algorithm has been widely studied in recent years.In WSNs,the minimum hop count between nodes and the average hop distance which are applied to estimate the distances between nodes result in the localization accuracy of hop count based algorithm is not high.The relationship between hop count and nodes' neighbors,the unequal distance of hop ring boundary and the distribution information of neighbors are analyzed.This thesis builds different mathematical models of distances between unknown nodes and anchors and proposes different localization algorithms.Meanwhile,node localization algorithms for static WSNs with holes and mobile WSNs with holes are analyzed and studied.The main content and innovation can be summarized as follows.(1)A novel approach termed MDS-HE algorithm is proposed to solve the problem that integer hop counts can not be able to accurately describe the distances between nodes.The distances between nodes are computed by the areas of the intersection regions of hop ring and node's one hop neighbor set.The integer hop counts can be transformed into real number hop counts.The real number hop count matrix is applied for the MDS method and the EKF algorithm is applied to accurately refine the locations of unknown nodes.Simulation and experimental results show that the performance of the MDS-HE algorithm outperforms the DV-Hop algorithm and the MDS-MAP algorihtm.A novel approach termed HCED algorithm is proposed to solve the problem that the distance of hop ring boundary is inequality.Unknown node selects the nearest anchor as the reference node.The expectation of the distance between the anchor and the reference node is computed according to the hop count between the reference node and the anchor.The expectation of the distance is applied to compute the distance between the anchor and the unknown node.The locations of unknown nodes are calculated via using maximum likelihood estimation method.Simulation results demonstrate that the localization accuracy of HCED algorithm is higher than IDV-Hop algorithm and DV-RND algorithm.(2)Node localization can be seen as a problem of regression analysis.The limitations of the number of anchors namely the small training samples in WSNs result in low localization accuracy.The KELM-HQ algorithm is proposed based on KELM.It employs the real number hop counts between anchors and unknown nodes and the locations of anchors as the training samples.The real number hop counts between unknown nodes are employed as the test inputs.The locations of the unknown nodes are computed by the trained KELM.Simulation results verify the effectiveness of the localization algorithm under small training samples.Node localization can be thought of as a problem of distance estimation based on different mathematical models.The distance estimation between nodes can be seen as a constrained optimization problem.The proposed NDB algorithm obtains the constrained relationship between anchors and unknown nodes applying the hop count information between anchors and unknown nodes and the information of the unknown node's neighbors' distribution.The bat algorithm is applied for fast solving constrained optimization problems and accurately computing the distances between anchors and nodes.The node locations can be computed via using maximum likelihood estimation algorithm.Simulation results show that the NDB algorithm has better localization accuracy than state-of-the-art localization methods.(3)In static WSNs with holes,the existence of holes will generate deviation from the shortest path to the actual distance between nodes.The HMDS algorithm is proposed to solve the problem that the information of distance estimation is not accurate as the existence of holes.The HMDS algorithm explores the virtual points by heuristic method and constructs geometric relationship to optimize the distances between nodes.The locations of unknown nodes are computed by MDS algorithm.Simulation results demonstrate that the HMDS algorithm is suitable for kinds of topologies with holes and the localization accuracy outperforms state-of-the-art methods.MDS-MN algorithm is proposed for mobile WSNs with holes.The virtual nodes which are produced by node mobility can restore the irregular network which contains holes so as to reduce the error of the distances between nodes.The locations of nodes can be better computed according to the selection rule of anchors.Simulation and experimental results verify the localization effectiveness of the MDS-MN algorithm.In the end,main results are summarized in this thesis and the possible extensions for future work are discussed.