Research On Indoor Distance Measuring Technology Based On Channel State Information

The increase in demand for location-based services has made location-aware technology under indoor conditions a hot topic at home and abroad.As the most important part of indoor location sensing technology,indoor distance measuring technology has great significance in combination with the widely deployed wireless local area network.In recent years,Channel State Information(CSI)in wireless local area networks has gradually become the major research target of indoor distance measuring technology with its fine-grained advantages.Since the error model existing in the CSI phase is too complicated,the current technology cannot completely eliminate the phase error of the CSI collected in the commercial network card.Existing CSI phase-based distance measuring techniques mainly use frequency hopping approach to avoid phase errors existing in CSI,and need to use multiple WiFi access points or multiple WiFi channels.For single access point and single channel indoor scenario,this thesis studies the indoor distance measuring technology based on WLAN channel state information.The main research contents of this thesis are as follows:Firstly,this thesis studies the theoretical model of CSI phase in WiFi signal,and demonstrates that carrier phase and the linear relationship between subcarrier phase are related to Time of Flight(ToF).Thesis deeply analyzes various errors in CSI phase and the causes of each error.This thesis proposes a corresponding elimination method for various phase errors existing in the CSI phase and build a test system based on software radio platform which can achieve accurate CSI measurements by using clock synchronization in universal software radio peripherals.Secondly,for the integer ambiguity problem in WiFi carrier phase,this thesis analyzes the problems of the existing integer ambiguity solving algorithm which based on frequency hopping.Under the premise of CSI phase measurement with slight error,a method of solving the integer ambiguity based on the carrier phase and the linear relationship between subcarrier phase is proposed under the single access point condition and single-channel condition and the accurate estimation of ToF realized.On the basis of extracting the accurate ToF,The principle and architecture of the distance measuring system in this thesis are presented.Finally,the proposed scheme is verified.The performance and noise of the carrier phase and subcarrier phase slope are measured by the software defined radio platform to verify the feasibility of the distance measuring system.On the premise that the carrier phase and subcarrier phase slope performance meet the requirements,the distance measuring scheme is verified.The results show that the distance measuring accuracy can reach the decimeter level and realize the high precision indoor distance measuring demand.