The Research Of Improved APIT Node Localization Algorithm Based On Cosine Theorem In Wireless Sensor Networks

In the recent years, with the rapid development of sensor technology, embeddedtechnology, wireless networks and distributed information processing technology,wireless sensor networks (WSN) become a hot research topic in the web of things,and gains lots of attention, and it has a good application prospect. As one of the mostimportant technologies in wireless sensor network, node localization technology is thepremise and basis to many other technologies and applications in WSN, and theresearch of node localization technology has important significance.Now there are many node localization algorithms, the most commonclassification method of node localization algorithms which according to whether thealgorithm need additional hardware to measure the physical distance between sensornodes, classify the algorithms into two categories: Range-based localization algorithmand Range-free localization algorithm. Range-based algorithm could achieve higherlocalization accuracy, but it cost more on hardware devices. Range-free algorithmdoes not require additional devices, it just need sensor nodes to communicate eachothers to positioning the unknown nodes. Range-free algorithm has lower cost, andcould fit the demand in many applications.The work of this paper is to study APIT algorithm, which is a typical algorithmin Range-free localization algorithm. Based on heterogeneous networks, APITalgorithm is widely used for its low cost and high localization accuracy. However,APIT algorithm has its shortages. It is prone to generate Out-To-In and In-To-Outerror when it executes the Point-In-Triangulation test, and its localization coverage islow. To fit these problems, this paper propose CT-PIT algorithm. In CT-PIT algorithm,it uses a new Point-In-Triangulation test method based on Cosine Theorem to solveOut-To-In and In-To-Out error. And in the last positioning step, CT-PIT algorithmclassifies unknown nodes into two categories according to whether the unknown nodeis covered by any triangle which composed of beacon nodes, and uses differentmethods to positioning different kinds of unknown nodes. At the last of the paper, theexperiments result shows that CT-PIT algorithm improved the localization accuracyand localization coverage visibly.