Backscatter-based Localization With A Single Access Point

With the development of wireless communication technologies,location-based services have profoundly affected our daily lives.Different from the outdoor environment,the received satellite signal is poor in the indoor environment which has complicated multipath condition.It is challenging to achieve high-precision localization.At present,common indoor localization technologies often require the assistance of multiple access points(APs),such as localization technology based on Received Signal Strength Indication(RSSI).Localization technologies with single access point often require the assistance of custom firmware or other sensors,limiting the usage scenario.In some indoor localization scenarios,there is often only one access point available and cannot localize target based on multiple access points.Therefore,it is of great significance to design a localization scheme based on a single access point.In recent years,backscatter communication technology has developed rapidly.This technology uses environmental radio frequency signals to provide energy for scattering communication without the need for additional battery power.Commercial Wi-Fi devices can receive and decode backscattered signals.This thesis designs a single access point localization scheme based on backscatter technology.We deploy backscatter tags around the access point and use the backscatter tags to actively change the signal multipath propagation between target and AP.Firstly,this thesis designs a backscatter signal decoding scheme and proposes a phase deviation cancellation algorithm to extract accurate backscatter Channel State Information(CSI).Secondly,this thesis uses the characteristic that the number of Wi-Fi signal subcarriers is much larger than the number of multipaths and designs the Time of Flight(To F)estimation algorithm based on the Multiple Signal Classification Algorithm(MUSIC).Finally,in order to solve the To F estimation error caused by the hardware of commercial equipment,this thesis uses the feature that the To F estimation error is equal on each path at the same time and designs a localization algorithm based on relative To F.Based on the above scheme,this thesis implements it on commercial Wi-Fi devices and tests the system performance in a real indoor environment.The experimental results show that the localization system can achieve a median accuracy of 0.87 meters in a multipath-rich indoor environment,which has certain practical value.