Localization Methods In Wireless Sensor Networks

In wireless sensor networks, the location of the nodes and monitored events is of critical importance to their monitoring activities. Accurate localizaion of nodes is not only the premise of monitoring events or targets, but also the foundation of network applications such as reporting network topology, improving the efficiency of routing, reporting the deployment of network coverage or quality and providing network name space. Location detection is complicated in sensor networks which are characterized by limited resources. No localization schemes can be used for all kinds of sensor networks. Existing positioning methods are only suite for a particular nodal hardware or network environment. Designing special positioning methods for specific nodes and working environments is very important for the practicability of sensor network technology.Most existing positioning systems assume secure and truthful environments and ignore security issues in the process of positioning. However sensor networks often work in open and unattended environments and are vulnerable to suffer from internal attacks as well as the external ones. Attacks against positioning system are often pointed and vary with different localization methods and processes. The invalid or wrong positioning results caused by attackers will bring incalculable losses to sensor network applications, especially to those with an important mission (for example, battlefield surveillance). Therefore, it's essential to design a secure positioning system for WSN working in hostile environments.The major work and new ideas of this dissertation are as follows:Firstly, it focuses on analyzing and comparing existing location algorithms and then a segmented localization scheme is proposed for location system using asynchronous distributed wireless sensor networks. This scheme segments the localization process according to the source speed. At the beginning of each segment, synchronous localization is performed to get a good estimation of source location and asynchronous localization is started after that. Segmented localization scheme, relaxing the assumption of source motion speed, solves the problem that ordinary asynchronous localizations cannot work well with slowly moving source.Secondly, it analyzes attacks against location system and various secure methods. Also, a new range-free secure localization scheme, called SAPIT, is presented. SAPIT utilizes anchor ID authentication and APIT test results safe aggregation. It solves the problem that APIT is easily attacked by compromised nodes, without any extra hardware. Simulation results indicates that SAPIT can resist jamming, wormhole, false anchors and InToOut attacks.At last, it provides a hardware platform and SAPIT is implemented in this platform.