Delay-Synchronous Wideband Channel Sounding Using Off-The-Shelf Multi-Antenna WiFi Devices

It has been shown that WiFi devices enable sensing of environments and targets through their channel state information. However, the same devices have not been used for delay-synchronous channel sounding due to challenges related to the stability of synchronization and lack of reference power levels. Due to factors such as uncertainty in symbol reception timing, impulse responses are discontinuous across acquisitions. The present paper addresses the challenges to perform delay-synchronous channel sounding using off-the-shelf multiple-antenna IEEE 802.11ax WiFi devices, referred to as SoundiFi. Stable delay synchronization and power level reference are realized by remoting the antennas with coaxial cables and devoting one of the antennas as a reference channel, with which the gain and delay of other simultaneous channels are defined. Indoor experiments confirmed that the impulse response becomes continuous across successive acquisitions and provide the absolute delay. The impulse response has a noise level at -115 dB, indicating the maximum path gain value that can be measured with the devices. The impulse response also revealed the existence of long-delayed multipaths up to 132 m propagation distance in a reverberant 30-m-long corridor.