WS-WiFi: Wired Synchronization for CSI Extraction on COTS-WiFi-Transceivers

WiFi channel state information (CSI) is a key enabler of precise radio sensing applications for commercially available off-the-shelf hardware. By utilizing colocated WiFi devices, this article aims to perform Angle-of-Arrival (AoA) estimation as one instance of radio sensing. However, unsynchronized local oscillators (LOs) in a WiFi network can cause carrier frequency offsets and sampling frequency offsets, which can lead to imperfect CSI. To this end, we propose a wired LO clocking scheme to eliminate residual impairments on regular WiFi transceivers. By utilizing a common oscillator, we transform a standard WiFi setup to a frequency-aligned transceiver architecture across several colocated devices. Building upon the proposed scheme, we present a detailed investigation of hardware-related impairments and environmental conditions. In particular, we are the first to investigate the temperature-dependent behavior of the CSI phase across multiple devices. We validate the performance in a lab setup as well as in a real-world application assembly, namely, a nine-antenna uniform circular array for AoA estimation. Furthermore, we show that with only a single received packet and minor hardware adjustments, we are able to obtain the AoA of a WiFi transmitter with a mean absolute error of 1.5 degrees in line-of-sight conditions and 19.9 degrees in strong multipath living room conditions.