Research On Passive Moving Target Localization Algorithm In WiFi Environment

The intensive indoor activities and the increasing demand for indoor Internet surfing have already promoted the development of indoor wireless network.Thanks to the natural advantages of mature deployment of indoor wireless network,the indoor localization technology based on Wi Fi has important research value.Aiming at the problem that traditional multi-link localization technology needs to deploy too many devices,and considering the fact that the localization accuracy is low due to the poor estimability of some parameters in the case of a single link.This thesis studies the localization technology based on Wi Fi Channel State Information(CSI),and attempts to realize the localization of the moving target by using only two links to jointly measure the Angle of Arrival(Ao A)and Fresnel reflection distance of the target.The specific research contents of this thesis are as follows:First of all,this thesis studies the frequency diversity characteristics of CSI in the frequency domain,and through the theoretical analysis of the Fresnel phase difference between the subcarrier pairs,the linear relationship between the Fresnel phase difference and the target's Fresnel reflection distance is established,and the measurement of the Fresnel reflection distance is realized.The simulation results of algorithm prove its effectiveness,and the actual measurement results in the real environment show that the frequency diversity of CSI can be used to measure the Fresnel reflection distance of the moving target,and the target localization based on dual-link distance measurement can be realized.Then,based on the research of Fresnel reflection distance localization algorithm,in order to solve the problem of large localization error of the current algorithm when the target moves in some directions,the channel parameter estimation algorithm of passive target is studied,hoping to achieve a more general localization algorithm design with the help of channel parameters.The research issues include: the feasibility analysis of the Doppler frequency offset estimation of the moving target based on the Multiple Signal Classification(MUSIC)algorithm,establishment of super-resolution estimation model by combining Doppler and Ao A,channel parameter estimation using two-dimensional spatial smoothing MUSIC algorithm based on phase offsets compensation and strong interference suppression,and use the extended Viterbi algorithm to match the parameters associated with the moving target from the channel parameter set.Next,the Doppler-corrected Fresnel reflection distance combined with Ao A estimation is used to achieve high-precision localization of the target.Finally,the experimental platform is built and the algorithm is tested and verified in real test environment.The experimental results show that the dual-link localization algorithm designed in this thesis achieves a reflection distance estimation error of 1.0 meters,an Ao A estimation error of 12 degrees,and a localization error of 1.74 meters with 67% confidence,therefore,the algorithm meets the localization needs of indoor scenes.