Experimental Derivation of Channel Correlation Functions Using the ESP32-CSI-TooL

Accurate evaluation of the Channel State Information (CSI) is crucial for performance optimization in wireless communications. Recently, the channel probing techniques that rely on the embedded tools of wireless communication devices have gained an increasing attention. One of such techniques is the cheap and easy-to-implement ESP32-CSI-Tool. This paper elaborates the use of the ESP32-CSI-Tool for an experimental derivation of correlation functions of the wireless channel. We present the empirical channel autocorrelation and frequency correlation functions, as well as the channel cross-correlation function to check for the symmetry of the CSIs derived with the ESP32-CSI-Tool at the both link ends. The experimental scenarios involved both stationary and mobile cases. According to the experimental data obtained a mobility of any of the nodes reduced the channel coherence time from 4.6 seconds to 1.5 seconds, and the coherence bandwidth from 8.8 MHz to 4.1 MHz compared to the stationary case. Our results proved that the ESP32-CSI-Tool might be a powerful solution for determining the channel correlation functions provided that the main technical issue of the probe packets loss is addressed.