WiSensor: Passive Sensor Data Transmission by Way of Ambient Wi-Fi Channels

Recent developments in wireless sensor networks have empowered low-power, intelligent sensor nodes to be distributed over a large area. However, wireless sensor nodes that actively emit electromagnetic waves for energy-hungry communication are limited by the volumes and capacities of batteries, requiring periodic maintenance in widespread applications. To solve this problem, we propose a passive wireless sensor platform, WiSensor, which makes wireless sensor nodes take use of ambient Wi-Fi waves instead of actively emitting electromagnetic waves to transmit sensor data. By affecting the Wi-Fi channels through backscattering, the sensor node modulates the sensor data onto the Wi-Fi channels established by a Wi-Fi transmitting node and a Wi-Fi receiving node. The receiving node acts as the sensor receiver and the sensor data are extracted from the Wi-Fi channel state information. We define the signal-to-noise ratio at the sensor data receiver and analyze the WiSensor performance dependencies, providing guidance for the system design and implementation. A prototype of WiSensor is established, in which sensor data can be transmitted at 200 bps with a bit error rate of 0.01% while the sensor node is placed as far as 5 m from the Wi-Fi transmitting node and 2 m from the Wi-Fi receiving node at 2.37-
$\mu \text{W}$
power consumption for the wireless connection. WiSensor is a novel and general wireless sensor platform that embeds the utilization of Wi-Fi channels to practical sensing tasks without the need for wireless sensor nodes to follow Wi-Fi protocols, empowering ubiquitous commodity Wi-Fi devices in our daily life with general sensor connectivity. We believe WiSensor demonstrates promising potential in the field of next-generation smart homes and other applications that urgently require ultralow-power sensor data transmission.