Single-Input-Multiple-Output Wi-Fi Radar for Vital Signal Sensing and Device Tracking

Multiple Input Multiple Output (MIMO) radar systems enhance detection and anti-interference capabilities by increasing the number of antennas compared to traditional radar systems. Despite significant research into Wi-Fi sensing in recent years, constructing Wi-Fi MIMO radar remains challenging due to half-duplex RF hardware and limited access to low-level multi-antenna signals in commercial Wi-Fi chips. This paper presents a SIMO Wi-Fi radar with one Tx and two Rx antennas, based on the open-source Wi-Fi SDR platform, openwifi, which has implemented the full 802.11 stack. The hardware includes an FPGA and an AD9361 RF front-end. Directional antennas are used to reduce Tx-Rx interference in full-duplex mode. This Wi-Fi MIMO radar system brings dual capabilities: sensing the passive target that is not transmitting any signals and the normal Wi-Fi device that transmits signals for data traffic. In this paper, the dual capabilities are demonstrated in two cases: vital signal sensing for humans and Angle of Arrival (AoA) tracking of another device. More specifically, millimeter-level movement detection is achieved by processing phase information from the Channel State Information (CSI) of the two Rx antennas.