Research Of Nodes Positioning Based On Range-free Technology For Wireless Sensor Networks

Wireless sensor networks have great prospect in the applications of military affairs, circumstance observation, disaster relief operation, dangerous area domination, etc. One of the key qualifications for these applications is localization of the targets needed monitoring and the network node. And some routing scheme, information of network coverage, load balance, topology control, all of which depend on the location information of the nodes in networks. All these indicate that localization is a fundamental and critical issue for the application, operation and management of wireless sensor networks. The study for self-positioning of wireless sensor networks possesses great significance in the theory and practice, and it will become an important part in the research area.The wireless sensor network positioning system contains self-positioning and tracking outside targets, and the later always depends on the former. In this thesis Two-Phase positioning algorithm is researched and the main works are deployed as follows:(1) The framework of wireless sensor networks, its characteristics, application and researching situations at home and abroad are summarized. Some key technologies and principle of nodes positioning are also analyzed.(2) The mechanism of Dv-Hop algorithm is analyzed and a comparison with another algorithm based on hop mechanism is also presented in the simulation section.(3) The principle of TERRAIN(triangulation via extended range and redundant association of intermediate nodes) is presented. On the condition of nodes connectivity, it uses RSSI(Received Signal Strength Indicator) technology or its one hop neighbor information to get extended range to compute the coordination of nodes when the target node acquires at least three anchors information, but the experiment data shows the TERRAIN algorithm directly suffers from an unacceptable high tendency to exponentially intensify error levels. (4) The Two-Phase positioning algorithm adopted in the thesis is improved. And the math regression method applied in the Two-Phase algorithm is used to compute the one hop range measurement before flooding. At start phase, the Hop-TERRAIN algorithm broadcasts this one hop range information and estimates the coarse value of the nodes in the network. In the Refinement phase, it uses the weighted LMS to triangulate new positions of nodes in the network.(5) At last, different algorithms under different number of anchors are simulated on the MATLAB platform. The simulation results indicate that the improved algorithm has a better feasibility and practicability. In the last section, it concludes the thesis and prospects the future work of positioning scheme in wireless sensor networks.