Investigation Of WSN Location Technology Based On Range-Based Approach

Many applications of Wireless Sensor Networks (WSN) require knowing the position of the nodes or relative position among them. The location accuracy of range-based approach is relatively higher than range-free algorithm, so this thesis focuses on the study of range-based localization algorithm and its application in sensor networks. Among major of range-based localization algorithms, TDOA and RSSI algorithms are discussed and analyzed in detail in the chapter three and chapter four respectively.First of all, the research status of wireless location techniques and positioning systems for WSN are summarized based on the study of a lot of related literatures. In this thesis, the criterion of performance evaluation and algorithms, the taxonomy for wireless sensor networks localization systems are described, the principles and characteristics of recent representative localization approaches are discussed and presented.Secondly, we presented a novel EKF-based positioning scheme using TDOA for sensor networks. Our scheme which is based on time measurement requires no global time synchronization in the wireless sensor networks and minimal extra hardware in sensor construction. We firstly utilize the TDOA measurements to locate target sensor node, and then make use of the estimated values which is educed from the algorithm as observed values for Extended Kalman filtering and estimation, then we analyze the results of simulation based on three anchor sensors. It is shown that the location accuracy of the algorithm mentioned in this thesis is close to the CRLB (Cramer-Rao lower bound).Thirdly, an efficient robust location algorithm is proposed based on the mean received signal strength (RSS) measurement. Our positioning scheme doesn't need sensor node make radio transmission constantly but only listen to three beacon signals passively. This efficiently reduces sensor energy cost and also improves the use of RF channels. As data processing is performed by the PC rather than sensor devices in our scheme, we can employ more sophisticated algorithms to improve location performance. As shown in the simulation results, it can be stated that the approach is effective and obviously has good location accuracy than conventional RSSI algorithm.Finally, we implemente our EKF-based RSS localization scheme to verify its computational efficiency and estimation accuracy in a real environment. Experiments in a large indoor meeting room show that the location accuracy is approximately 1.56m in the office LOS environment. The feasibility of our algorithm is validated on the hardware platformt, it can be stated that this approach is effective and obviously can satisfy location request in some special indoor sensor networks...