TOA Ranging Based Indoor Positioning Methods Using Wi-Fi Network

With the rapid development of mobile Internet technology and the accelerating process of urbanization,the demand for location based services,especially for the indoor mobile location based services,is showing explosive growth trend.Since people's requirements for location accuracy is increasingly getting high,indoor positioning technology with high precision has become the research hotspot in the field of wireless positioning and even the field of wireless communications.Based on the deep research on the current indoor positioning scheme and related technical characteristics,this paper chooses the Wi-Fi network which has advantages of good universality,convenient communication and excellent applications as the carrier for the indoor positioning solution.For the purpose of improving the accuracy as well as reducing the system's complexity under the indoor environment with complex Wi-Fi network,research on the key technologies based on the TOA positioning mechanism is carried out,which includes time delay parameter estimation,the selection of access points and location resolving methods.The main work is as follows.1.In order to solve the problem that existing time delay estimation algorithm has either low accuracy or high computational complexity under multipath propagation condition,a hierarchical time delay estimation algorithm combined Leading-edge Detection based Cross-Correlation and Phase Difference Fit(LDCC-PDF)is proposed according to the feature of the Wi-Fi signal.Simulation results show that high accuracy can be achieved by the algorithm with lower computational complexity,and it also has a better adaptability in multi-path environment.2.Aiming at the problem that the access points with poor quality of wireless transmission have great impacts on the positioning accuracy under the complex Wi-Fi network and changing indoor environment,an access points selection method with the Received Signal Strength(RSS)based step-by-step screening and Point in Triangle(PIT)detection based combination is proposed,which is considered from the point of view that reducing the parameter measurement error and optimizing the access point geometric layout.The simulation results proved that reasonable access points selection not only reduces the computation complexity of the original positioning algorithm,but also improves the positioning performance.3.Aiming at the problem that the traditional TOA localization algorithm has a poor performance in NLOS environment and the complexity of existing NLOS error recognition and suppression algorithm is very high,a hierarchical positioning algorithm based on weighting processing is proposed.Based on the coarse positioning result of LLOP algorithm,two weighting methods are adopted: weighting based on the geometric layout and weighting based on convex combination optimization.The former one is simple and easy to implement so that it can be used in the better transmission environment.The latter method has higher complexity but better performance and can be applied into the NLOS transmission environment.The simulation results show that both of them can get good positioning performance in corresponding conditions.4.A prototype of the indoor positioning system based on Wi-Fi network is given according to the fat client based system architecture,including the overall positioning process and the software design framework of both client terminal and positioning server.Finally,a test using the real measurement data is carried out in a real office environment to verify the effectiveness and feasibility of the proposed algorithm and system architecture.