@Article{cmc.2020.07297,
AUTHOR = {Zengshan Tian, Weiqin Yang, Yue Jin, Liangbo Xie, Zhengwen Huang},
TITLE = {MFPL: Multi-Frequency Phase Difference Combination Based Device-Free Localization},
JOURNAL = {Computers, Materials \& Continua},
VOLUME = {62},
YEAR = {2020},
NUMBER = {2},
PAGES = {861--876},
URL = {http://www.techscience.com/cmc/v62n2/38281},
ISSN = {1546-2226},
ABSTRACT = {With the popularity of indoor wireless network, device-free indoor 
localization has attracted more and more attention. Unlike device-based localization
where the target is required to carry an active transmitter, their frequent signal scanning 
consumes a large amount of energy, which is inconvenient for devices with limited 
energy. In this work, we propose the MFPL, device-free localization (DFL) system 
based on WiFi distance measurement. First, we combine multi-subcarrier characteristic 
of Channel State Information (CSI) with classical Fresnel reflection model to get the 
linear relationship between the change of the length of reflection path and the 
subcarrier phase difference. Then we calculate the Fresnel phase difference between 
subcarrier pairs with different spacing from CSI amplitude time series. Finally, we get 
the change of the length of the reflection path caused by target moving to achieve 
distance measurement and localization. Using a combination of subcarriers with 
different spacing to achieve distance measurement effectively broadens the maximum 
unambiguous distance of the system. To solve the complex non-linear problem of the 
intersection of two elliptic equations, we introduce Newton's method to transform the 
non-linear problem into a linear one. The effectiveness of our approach is verified 
using commodity WiFi infrastructures. The experimental results show our method 
achieves a median error of 0.87 m in actual indoor environment.},
DOI = {10.32604/cmc.2020.07297}
}