Tdoa Algorithm In The Nlos Environment

In cellular environments, under the influence of some factors, such as multi-path propagation, noise, interference, and channel frequency characteristics, especially the non-line-sight propagation, mobile location accuracy is not very well. To improve the mobile location accuracy, the TDOA location techniques under NLOS environments has been studied, and a location system based on WCDMA is analyzed and discussed.At first, the model of TDOA location algorithm is presented and the impact of NLOS error to TDOA location algorithms is analyzed, and a Kalman filtering tracking location algorithm for NLOS condition is proposed. In this algorithm, a new decision mechanism is employed to get the NLOS information and weight the measured value, and then this information is used to reconstruct the weighted measured value. The position of the MS is estimated and located by Kalman filtering tracking location algorithm. Simulation results show that it decreases the affect of the NLOS error effectively, and increases the accuracy and robustness.The Kalman filtering tracking location algorithm for NLOS condition can't be used, if the position of the MS suddenly changed. So a TDOA location based on immune algorithm is investigated. In this algorithm, several location algorithms are used to locate the position of the MS, then use immune algorithm to deal with the data and obtain the final position of the MS. Simulation results show that this algorithm not only resolve the problem of the Kalman filtering tracking location algorithm, but also reduced the NLOS error, and its' location performance is better than that of the weighted and reconstructed Kalman filter tracking location algorithm.Finally, the basic location method, network architecture, and location procedure of WCDMA network mobile location are analyzed, and several advices about the development of location server are presented.