VSAPIT Localization Algorithm For Wireless Sensor Networks

Wireless Sensor Network(Wireless Sensor Networks,WSN) is a multi-hop and distributed network system which deploys a large number of micro sensor nodes and communicate with other nodes by wireless mode.The system’s purpose is to help perceive,collect and process the monitored information in network coverage area,and send these information to the observer.Therefore, how to obtain the position information of sensor nodes is a key problem in wireless sensor networks.According to whether it is necessary to measure real distance between nodes,the existing algorithms are divided into based on range localization algorithm and range free localization algorithm.The localization algorithms which based on range can get higher localization accuracy,but need more external hardware devices,and bring higher cost of network;the range free localization algorithms rely on network connectivity to complete localization,without other hardware devices,has the advantages of low cost and low power consumption,but the localization accuracy is often not satisfaction.In view of the utility scale in wireless sensor network, the cost and energy consumption is very important,so the localization method without ranging has attracted the attention of many scholars.As one of the classical APIT localization algorithm in range free algorithm have attracted more researchers’ attention.In this paper, we take a deep study of the principle of APIT localization algorithm,take detail and deeply analyze about the source of low localization coverage rate and high localization error in APIT,points out the influence of APIT localization error in external objective factors and internal subjective factors.The external objective factors deterimined by the network settings, node deployment and so on, it is difficult to avoid.The internal subjective factors deterimined by the principle of localization algorithm,it can be improved and reduce the localization error.To sum up,begin from the subjective factors which affect the low error and low coverage rate in APIT localization algorithm,such as anchor node proportion and communication radius,in order to improve the localization coverage rate and reduce the localization error,we put forward an improved APIT localization algorithm,we present a localization algorithm based on Voronoi chart and sequence matching which named VSAPIT localization algorithm.VSAPIT localization algorithm based on APIT algorithm put forward threepoints of improvement:Improved point one:The result of APIT localization algorithm depend on the network connectivity deeply,when the system has few anchor nodes will produce very large localization errors,the localization coverage rate is low at the same time,to solve the above problems we present Voronoi chart,calculate the coordinate of intersection as virtual anchor nodes,and broadcast the information with real anchor nodes in a jump.Improved point two:When APIT localization algorithm take PIT test,there will produce two kinds of errors named Out-To-In and In-To-Out,we present the method based on direction search,search the best direction through the geometric relationship,can instead the process of the simulation of node motion,reduce the occurrence rate of the event that unknown nodes can’t judge without neighbor nodes in low connectivity network,decrease the probability about the occurrence of In-To-Out error and Out-To-In error extremely.Improved point three:APIT localization algorithm take grid scanning method to calculate the centroid of overlapping area as unknown nodes’ coordinate directly,which will bring large localization error, we present divide the overlapping area into several small areas,unknown nodes establish the sequence rank about the anchor nodes in one hop,each area also establish the sequence rank about these anchor nodes,then match the sequence rank,regard the highest similarity areas’ centroid as the estimated coordinate.In this paper,we take MATLAB R2012 b to simulate APIT localization algorithm and VSAPIT localization algorithm, the simulation result shows that the average localization error and localization coverage rate of VSAPIT algorithm was significantly better than APIT algorithm,the algorithm has fast convergence rate and stable performance,it is a promising algorithm.