Pi-NIC: Indoor sensing using synchronized off-the-shelf wireless network interface cards and raspberry Pis

This paper presents an indoor joint communication and sensing system that consists of synchronized off-the-shelf wireless network interface cards (NIC) and Raspberry Pis. There exists a significant body of research that uses the channel state information (CSI) reported by wireless network interface cards for sensing, but only the amplitude and phase difference of the CSI between receiver antennas are processed. The raw phase of the CSI is contaminated by the carrier frequency offset, packet detection delay and other hardware imperfections, so it is too noisy to use. Our work introduces the raw phase of CSI into sensing by synchronizing the transmitter and receiver clocks to remove carrier frequency offset and using a new method to remove packet detection delay. We validate our design in a real-world scenario to detect breathing and walking and demonstrate that the raw phase of the CSI offers an evident improvement in Wi-Fi CSI-based sensing. Additionally, we are the first to use the Raspberry Pi and ATH9k wireless network interface card together for CSI data collection, which is cheap, portable and versatile.