Frequency-Domain LOS Identification Compliant with Normalized CSI Values

Line-of-sight (LOS) identification methods based on WiFi devices have used time series of channel state information (CSI) instead of the frequency domain of CSI owing to limited bandwidth. However, the use of IEEE 802.11ac/ax devices allows one to obtain CSI with a wider bandwidth. In this paper, a LOS identification method using the frequency domain of CSI for WiFi devices is proposed. The proposed method focuses on the number of valleys observed in the shape of the frequency series of CSI amplitude and exploits the fact that the number is greater in LOS environments than in non-line-of-sight (NLOS) environments. Because the proposed method utilizes the shape of CSI, it performs well for normalized CSI obtained using typical CSI capture tools for IEEE 802.11ac/ax. The proposed method is experimentally evaluated in a real environment. The experimental results show that the proposed LOS identification method achieves an accuracy of 95%.