Sensorless Sensing in Wireless Networks: Implementation and Measurements

Multipath fading and shadowing are usually regarded as negative phenomena hindering proper radio communication. Adopting a completely different stance, this paper illustrates that such phenomena enable information harvesting from received signal strength leading to a number of original applications requiring no conventional sensing hardware. The radio itself, provided that it can measure the strength of the incoming signal, is the only sensor we use; with this sensor-less sensing approach, any wireless network becomes a sensor network. We show that motion of the nodes in the network or motion of bodies external to the network leaves a characteristic footprint on signal strength patterns, which may be exploited for motion detection. We illustrate a technique to extract an estimate of velocity from signal strength, and we leverage on the spatial memory properties of wireless links to present a method for spatial configuration recognition.