Motion Sensing without Sensors: Information Harvesting from Signal Strength Measurements

This letter shows how physical phenomena affecting radio communication can be exploited to turn any wireless network into a wireless sensor network for motion detection without any actual sensing hardware. Motion of individuals or objects in the network area produces shadowing and multipath fading effects altering the received signal strength. The ability to measure signal strength, which wireless terminals normally have, is sufficient to enable motion detection. This idea is particularly suitable for 802.11-based networks, but its simplicity and the lightweight nature of its possible implementations also allow its use as a virtually free add-on feature for lower-end wireless sensor networks. Introduction: In the wireless realm, the term fading refers to deviations of the received signal strength (RSS) from its expected value [1]. Localized fluctuations are due to small-scale fading (a.k.a. multipath fading), whereas stronger variations of the signal are brought about by shadowing