Combining Frequency and Spatial Diversities to Calibrate Ranging over WLAN

Channel state information (CSI) is now popular in many emerging applications over WLAN, such as gesture recognition, indoor localization, line-of-sight (LOS) identification and ranging. Traditional power-based ranging approaches usually utilize received signal strength indicator (RSSI) because of its low cost and wide applicability. However, the coarse-grained RSSI is sensitive to the multipath effect and performs poorly in the non-line-of-sight (NLOS) situation. Compared with RSSI, CSI is a finer-grained value, and it depicts the amplitude and phase of each frequency-domain subcarrier in an OFDM channel. Besides, MIMO technology leveraged in 802.11 infrastructures extends the spatial diversity of WiFi signals and guarantees reliable communications. To obtain more stable and precise distance of direct path (DDP) between the transmitter and the receiver, we employ both the frequency diversity and spatial diversity of CSI and propose a new ranging system over WLAN. We consider multiple influence factors when implementing the system on commodity WiFi devices, and we evaluate its performance in diverse indoor environments. The results demonstrate that our system outperforms the baselines in all the pre-set scenarios, especially under the conditions of NLOS and dynamic multipaths.